ICES Journal of Marine Science - Advance Access

Sublethal effects of catch-and-release fishing: measuring capture stress, fish impairment, and predation risk using a condition index

Campbell, M. D., Patino, R., Tolan, J., Strauss, R., Diamond, S. L. — Sun, 15 Nov 2009 23:36:03 PST

Campbell, M. D., Patino, R., Tolan, J., Strauss, R., and Diamond, S. L. 2010. Sublethal effects of catch-and-release fishing: measuring capture stress, fish impairment, and predation risk using a condition index. – ICES Journal of Marine Science, 67: 000–000.

The sublethal effects of simulated capture of red snapper (Lutjanus campechanus) were analysed using physiological responses, condition indexing, and performance variables. Simulated catch-and-release fishing included combinations of depth of capture and thermocline exposure reflective of environmental conditions experienced in the Gulf of Mexico. Frequency of occurrence of barotrauma and lack of reflex response exhibited considerable individual variation. When combined into a single condition or impairment index, individual variation was reduced, and impairment showed significant increases as depth increased and with the addition of thermocline exposure. Performance variables, such as burst swimming speed (BSS) and simulated predator approach distance (AD), were also significantly different by depth. BSSs and predator ADs decreased with increasing depth, were lowest immediately after release, and were affected for up to 15 min, with longer recovery times required as depth increased. The impairment score developed was positively correlated with cortisol concentration and negatively correlated with both BSS and simulated predator AD. The impairment index proved to be an efficient method to estimate the overall impairment of red snapper in the laboratory simulations of capture and shows promise for use in field conditions, to estimate release mortality and vulnerability to predation.

Immediate maximum economic yield; a realistic fisheries economic reference point

Lleonart, J., Merino, G. — Fri, 13 Nov 2009 05:31:32 PST

Lleonart, J., and Merino, G. 2010. Immediate maximum economic yield; a realistic fisheries economic reference point. – ICES Journal of Marine Science, 67: 000–000.

Unregulated or poorly managed fisheries tend towards overexploitation, but fisheries rent does not completely dissipate when immediate rent maximization is sought. The principle of immediate economic rent maximization is the basis of the derivation of a classic model and has led to the definition of a relationship in a catch-and-effort diagram termed the dynamic immediate maximum economic yield (DIMEY) curve. For any initial biomass, if the economic rent in the immediate fishing season is maximized, then the fishing effort and catch strategy that follows will be located on the DIMEY curve. The DIMEY curve is not only used for dynamic simulation but also used to identify a new reference point, the immediate maximum economic yield (IMEY), which is proposed as more realistic than the classic open-access solution for unregulated fisheries. IMEY is proposed as an asymptotic outcome for unregulated or poorly managed fisheries when short-term economic objectives drive fleet activities. IMEY properties are described and compared with traditional fisheries reference points in the yield-and-effort diagram. Theoretical conclusions are compared with empirical evidence provided by the red shrimp fishery off Blanes, Spain (NW Mediterranean). Observed catch-and-effort records are plotted and were positively correlated with the DIMEY curve and IMEY.

Remote sensing of underwater vegetation using single-beam acoustics

Fri, 13 Nov 2009 05:31:31 PST

Quintino, V., Freitas, R., Mamede, R., Ricardo, F., Rodrigues, A. M., Mota, J., Pérez-Ruzafa, Á., and Marcos, C. 2010. Remote sensing of underwater vegetation using single-beam acoustics. – ICES Journal of Marine Science, 67: 000–000.

A single-beam, acoustic, ground-discrimination system (QTC VIEW, Series V) was used to study the distribution of underwater macrophytes in a shallow-water coastal system, employing frequencies of 50 and 200 kHz. The study was conducted in Mar Menor, SE Spain, where the expansion of Caulerpa prolifera has contributed to the silting up of the superficial sediments. A direct relationship was identified between algal biomass and sediment-fines content. Acoustic information on sediment grain size and data on algal biomass were obtained in muddy and sandy sediments, including vegetated and non-vegetated seabed. Non-vegetated muddy areas were created by diving and handpicking the algae. The multivariate acoustic data were analysed under the null hypotheses that there were no acoustic differences between bare seabeds with contrasting superficial sediment types or among low, medium, and high algal-biomass areas, having in mind that grain size can act as a confounding factor. Both null hypotheses were rejected, and the results showed that 200 kHz was better than 50 kHz in distinguishing cover levels of algal biomass. The relationship between the 200-kHz acoustic data and algal biomass suggests utility in modelling the latter using the former.

The analysis of echotrace obtained by a split-beam echosounder to observe the tilt-angle dependence of fish target strength in situ

Furusawa, M., Amakasu, K. — Fri, 13 Nov 2009 05:31:30 PST

Furusawa, M., and Amakusu, K. 2010. The analysis of echotrace obtained by a split-beam echosounder to observe the tilt-angle dependence of fish target strength in situ. – ICES Journal of Marine Science, 67: 000–000.

A method of echotrace analysis (ETA), proposed by Furusawa and Miyanohana in 1988 utilizes successive echodata from an individual fish to obtain the target-strength (TS) pattern as a function of fish tilt angle and behaviour. The method can be applied to data from an echosounder with any beam configuration, single-, dual-, and split-beam. However, the method has not been applied rigorously to split-beam sounder data, which provide most comprehensive and accurate information. The aim of this work is to establish an accurate and practical ETA method for split-beam echosounder data. Although the basic theory had already been developed, some theoretical and practical enhancement was needed; smoothing of an echotrack by linear and quadratic regressions, correction for transducer motion, and comparison of an observed TS pattern with a prolate-spheroid theoretical model. The analysis starts from careful selection of a single echotrace on an echogram and ends with a composite display of results including a three-dimensional fish track and a TS pattern as a function of the tilt angle of the fish. The method was applied to typical echotrace examples, and utility and practicality were confirmed. A means of increasing the number of applicable echotraces is discussed.

Horizontal and vertical movements of swordfish in the Southeast Pacific

Abascal, F. J., Mejuto, J., Quintans, M., Ramos-Cartelle, A. — Wed, 11 Nov 2009 02:01:59 PST

Abascal, F. J., Mejuto, J., Quintans, M., and Ramos-Cartelle, A. 2010. Horizontal and vertical movements of swordfish in the Southeast Pacific. – ICES Journal of Marine Science, 67: 000–000.

In all, 21 swordfish (Xiphias gladius) were tagged with pop-up archival satellite tags in the Southeast Pacific. Despite problems of premature release, the information obtained provided insight into the horizontal and vertical behaviour of the species in the area. A consistent migratory pattern was observed, fish moving northwest by autumn and presumably returning south by early spring. Swordfish typically forage in deep water during the day and stay in the mixed layer at night, although this behaviour is occasionally modified. The maximum depth recorded was 1136 m, and dives deeper than 900 m were found in five of the six tags analysed. There was a significant positive relationship between average depth by night and visible moon fraction.

Probabilistic-based genetic assignment model: assignments to subcontinent of origin of the West Greenland Atlantic salmon harvest

Sheehan, T. F., Legault, C. M., King, T. L., Spidle, A. P. — Wed, 11 Nov 2009 02:01:58 PST

Sheehan, T. F., Legault, C. M., King, T. L., and Spidle, A. P. 2010. Probabilistic-based genetic assignment model: assignments to subcontinent of origin of the West Greenland Atlantic salmon harvest. – ICES Journal of Marine Science, 67: 000–000.

A multistock Atlantic salmon (Salmo salar) fishery operates off the coast of West Greenland and harvests fish of North American and European origin. Annual landings peaked in 1971 at 2700 t, but declined to 22 t in 2003. Biological data are collected to characterize the catch and its stock composition. Multilocus genotypes, generated via microsatellite DNA analysis, are used to derive statistics on continent of origin and less accurate finer-scale assignments. We developed a probabilistic-based genetic assignment (PGA) model to estimate the contribution of salmon from individual North American rivers in the 2000–2003 West Greenland catch. Uncertainty associated with finer-scale assignments is addressed by incorporating estimated misclassification rates and by reporting results as distributions generated via Monte Carlo resampling. US-origin fish represented ~1% (by number) of the salmon harvested at West Greenland during the years 2000–2003. The resulting loss of spawners to this stock complex was approximately half the estimated adult returns in 2001, but was below 4% in the other 3 years. This is the first attempt to partition the US component of the West Greenland mixed-stock fishery to its finer parts. The approach can be used to identify the effects of fishing on individual stocks within any multistock complex where genetic samples of known origin are available.

Total stock size and cannibalism regulate recruitment in cod (Gadus morhua) on the Faroe Plateau

Steingrund, P., Mouritsen, R., Reinert, J., Gaard, E., Hatun, H. — Mon, 09 Nov 2009 05:03:01 PST

Steingrund, P., Mouritsen, R., Reinert, J., Gaard, E., and Hátún, H. 2010. Total stock size and cannibalism regulate recruitment in cod (Gadus morhua) on the Faroe Plateau. – ICES Journal of Marine Science, 67: 000–000.

Year-class strength of fish is often considered to be determined at the pelagic larval stage, but we show that year-class strength of cod on the Faroe Plateau seems to be determined later, at the 1- or 2-group stage. Adult cod (C), measured in terms of the catch per unit effort (cpue) of small longliners, move into nearshore nursery areas of juvenile cod when in poor condition and probably displace 1-year-old cod to deeper water, where they are cannibalized. In addition, the recruitment of 2-year-old cod, at least up to a certain level, is positively related to the total biomass (B) of older cod on the Faroe Plateau, which are present at about the same time as the recruitment event. This feature, which seems to be a new observation in terms of the recruitment dynamics of cod, is possibly related to enhanced foraging or a reduced predation risk. The recruitment of 2-year-old cod during the years 1984–2006 is described by aB/C + d (r² = 0.87), where a and d are fitted constants. The implications for stock assessment and management are discussed.

The predation of farmed salmon by South American sea lions (Otaria flavescens) in southern Chile

Vilata, J., Oliva, D., Sepulveda, M. — Fri, 06 Nov 2009 04:06:14 PST

Vilata, J., Oliva, D., and Sepúlveda, M. 2009. The predation of farmed salmon by South American sea lions (Otaria flavescens) in southern Chile. – ICES Journal of Marine Science, 67: 000–000.

The South American sea lion Otaria flavescens is abundant off southern Chile. Because Chilean salmon farming has experienced an explosive growth in the past two decades, interactions between O. flavescens and this industry have increased. Fieldwork, including in situ behavioural observations, was carried out at three salmon farms off southern Chile from May to July 2008. The aim was to analyse possible patterns in the interactions and to evaluate whether they were influenced by the endogenous circa-rhythms of the species, prey size, tidal flux, and the use of an acoustic harassment device (AHD). The results showed that the attacks by O. flavescens followed seasonal patterns, with salmon predated more in autumn and winter, and daily patterns, with more interactions at night. In addition, attacks were more frequent on larger salmon, suggesting the existence of a prey-size preference. More sea lions were sighted at the ebb and flow tide peaks, when currents are stronger, suggesting that currents linked to tidal flux might facilitate the access of the sea lions to the farmed salmon. Although the use of AHDs appeared positive at one site, there is a strong suspicion that their efficacy may be site-specific.

Comparing methods for building trophic spectra of ecological data

Libralato, S., Solidoro, C. — Thu, 05 Nov 2009 00:23:09 PST

Libralato, S., and Solidoro, C. 2010. Comparing methods for building trophic spectra of ecological data. – ICES Journal of Marine Science, 67: 000–000.

The distribution of biomass, production, and catches over trophic levels (TLs) of the foodweb has been shown theoretically and empirically to provide powerful insights into ecosystem functioning and the effects of fishing. One approach for building trophic spectra of ecological data is based on smoothing original data and assuming zeroes when no values are available for a TL (smoothing-based method). An alternative method is proposed, based on the distribution of ecological data according to density functions (dispersion-based method), and a systematic review of the different alternatives is presented. Six different methods for building trophic spectra, i.e. the smoothing-based and five alternative forms for dispersion-based (using normal, lognormal, and Weibull distributions, also including shifted lognormal and Weibull with zero at TL 2), were applied to ecological properties (i.e. production, biomass, and catches) derived for 24 foodweb models to test their relative performance. The smoothing-based method suffers from the lack of consistency with original data and from unrealistic emergent properties, such as transfer efficiency. The analysis demonstrates the advantages of the dispersion-based method for overcoming these issues and shows, using transfer efficiencies estimated from the models (flow-based estimates) as a reference, that the normal density distribution function performs better.

Fishing simulation experiments for predicting the effects of purse-seine capture on sardine (Sardina pilchardus)

Wed, 04 Nov 2009 00:42:36 PST

Marçalo, A., Marques, T. A., Araújo, J., Pousão-Ferreira, P., Erzini, K., and Stratoudakis, Y. 2010. Fishing simulation experiments for predicting the effects of purse-seine capture on sardine (Sardina pilchardus). – ICES Journal of Marine Science, 67: 000–000.

To study the impact of purse-seine fishing on deliberately released sardine, two laboratory experiments were performed to explore the effect of net confinement for 10, 20, 40, and 60 min at 18 and 23°C. A third experiment considered two levels of fish density while confined for 20 and 40 min at 16°C. Analysis of cortisol and haematocrit demonstrated that stress immediately after simulated fishing was milder than in commercial fishing and did not correlate with observed delayed mortality. Scale loss was related to the probability of dying (mean values of 16.3 and 2% for dead fish and survivors, respectively), and fin erosion was a long-term stress response observed in both dead and surviving fish. Time of confinement was an important stressor, with survival rates decreasing significantly with increasing periods in the net, and temperature having an additional negative effect. Density effects were less conclusive, but there was some indication that survival correlated with biological condition (heavier fish were more likely to survive). It seems that delayed mortality after release can be substantial, although death is not certain and appropriately modified fishing operations and favourable environmental conditions may enhance the probability of sardine survival.

Marine reserves and the evolutionary effects of fishing on size at maturation

Miethe, T., Dytham, C., Dieckmann, U., Pitchford, J. W. — Tue, 03 Nov 2009 06:05:36 PST

Miethe, T., Dytham, C., Dieckmann, U., and Pitchford, J. W. 2010. Marine reserves and the evolutionary effects of fishing on size at maturation. – ICES Journal of Marine Science, 67: 000–000.

Size-selective fishing may induce rapid evolutionary changes in life-history traits such as size at maturation. A major concern is that these changes will reduce population biomass and detrimentally affect yield and recruitment. Although marine reserves have been proposed as a tool for fisheries management, their evolutionary implications have as yet attracted little scrutiny. A simple model is used to investigate whether marine reserves can be expected to mitigate the evolutionary impacts of fishing on maturation size. The adaptive dynamics of size at maturation are analysed based on a stage-structured population model including size-selective fishing and marine reserves with different retention rates. As has been shown before, imposing greater fishing mortality on the largest individuals promotes an evolutionary change towards smaller maturation size. In the model, protecting part of a fish stock using a marine reserve can prevent such fisheries-induced evolution, and this protection critically depends on the type and extent of movement between the reserve and the fished area. Specifically, although the frequent movement of large adults increases catches of large adult fish outside a marine reserve, it also reduces the reserve's effectiveness in preventing fisheries-induced evolution. In contrast, when there is exchange between protected and fished areas through juvenile export alone, a marine reserve can effectively prevent evolution towards smaller maturation size, but does so at the expense of reducing the yield of large adult fish. Differences in the movement behaviour of successive life stages need to be considered for marine reserves, to help make fisheries more sustainable evolutionarily.

The biological impact of overflowing sands around a marine aggregate extraction site: Dieppe (eastern English Channel)

Desprez, M., Pearce, B., Le Bot, S. — Tue, 03 Nov 2009 06:05:35 PST

Desprez, M., Pearce, B., and Le Bot, S. 2010. The biological impact of overflowing sands around a marine aggregate extraction site: Dieppe (eastern English Channel). – ICES Journal of Marine Science, 67: 000–000.

The study investigates the physical impact of sediment deposition associated with aggregate dredging at a site off Dieppe, and the consequences for benthic fauna. Sampling stations were sited across potential zones of impact classified as high, moderate, and low deposition, depending on their proximity to dredging activities and their position relative to the net sediment transport route. Samples were also taken west of the dredge site outside the zone of likely impact (no deposition). A strong gradient was observed from the sediments dominated by fine sands in the high and moderate deposition zones, through to coarse sands and gravels in the low and no deposition zones. The benthic fauna sampled from the deposits of fine sand in the high and moderate deposition zones were sparse compared with the coarser deposits sampled from the low and no deposition zones. There was a strong correspondence between the distribution of different sediment fractions and the associated benthic fauna, with a weighted Spearman rank correlation of 0.638, higher than reported in related studies. This suggests that in deposition areas such as this, biological interactions play a less important role in shaping communities than the changes in the physical environment, which may have a greater impact on the biological communities.

Epifauna associated with an introduced crab in the Barents Sea: a 5-year study

Dvoretsky, A. G., Dvoretsky, V. G. — Thu, 29 Oct 2009 07:47:00 PDT

Dvoretsky, A. G., and Dvoretsky, V. G. 2010. Epifauna associated with an introduced crab in the Barents Sea: a 5-year study. – ICES Journal of Marine Science, 67: 000–000.

Species composition, prevalence, intensity, and spatial distribution of macro-invertebrates colonizing the invasive red king crab (Paralithodes camtschaticus) in a typical bay of the Barents Sea, Dalnezelenetskaya Bay (depths 5–40 m), and adjacent deeper water (120–180 m) were examined in the summers of 2004–2008. In all, 43 associated species were found on the crabs. The most common epibionts were Mytilus edulis (Bivalvia), Obelia spp. (Hydrozoa), and Circeis armoricana (Polychaeta). Symbiotic species included Ischyrocerus commensalis and Ischyrocerus anguipes (Amphipoda), Harmothoe imbricata (Polychaeta), and Johanssonia arctica (Hirudinea). There were no significant differences in the prevalence of infestation between male and female crabs. The prevalence of most of the common species was greater in crabs with old shells than in crabs with new shells. Infestation levels of J. arctica were higher in deeper than in shallow water, and M. edulis was less abundant in deep water. All species found on the crabs appear to be native to the Barents Sea. However, I. commensalis amphipods were not found at the site examined before the introduction of the red king crab, indicating that their distribution may have changed after association with this host species. Introduced hosts may well influence the distribution of rare native species.

Measurements of acoustic scattering from zooplankton and oceanic microstructure using a broadband echosounder

Lavery, A. C., Chu, D., Moum, J. N. — Thu, 29 Oct 2009 07:46:59 PDT

Lavery, A. C., Chu, D., and Moum, J. N. 2010. Measurements of acoustic scattering from zooplankton and oceanic microstructure using a broadband echosounder. – ICES Journal of Marine Science, 67: 000–000.

In principle, measurements of high-frequency acoustic scattering from oceanic microstructure and zooplankton across a broad range of frequencies can reduce the ambiguities typically associated with the interpretation of acoustic scattering at a single frequency or a limited number of discrete narrowband frequencies. With this motivation, a high-frequency broadband scattering system has been developed for investigating zooplankton and microstructure, involving custom modifications of a commercially available system, with almost complete acoustic coverage spanning the frequency range 150–600 kHz. This frequency range spans the Rayleigh-to-geometric scattering transition for some zooplankton, as well as the diffusive roll-off in the spectrum for scattering from turbulent temperature microstructure. The system has been used to measure scattering from zooplankton and microstructure in regions of non-linear internal waves. The broadband capabilities of the system provide a continuous frequency response of the scattering over a wide frequency band, and improved range resolution and signal-to-noise ratios through pulse-compression signal-processing techniques. System specifications and calibration procedures are outlined and the system performance is assessed. The results point to the utility of high-frequency broadband scattering techniques in the detection, classification, and under certain circumstances, quantification of zooplankton and microstructure.

Individual quotas, fishing effort allocation, and over-quota discarding in mixed fisheries

Poos, J. J., Bogaards, J. A., Quirijns, F. J., Gillis, D. M., Rijnsdorp, A. D. — Thu, 29 Oct 2009 07:46:58 PDT

Poos, J. J., Bogaards, J. A., Quirijns, F. J., Gillis, D. M., and Rijnsdorp, A. D. 2010. Individual quotas, fishing effort allocation, and over-quota discarding in mixed fisheries. – ICES Journal of Marine Science, 67: 000–000.

Many fisheries are managed by total allowable catches (TACs) and a substantial part by individual quotas. Such output management has not been successful in mixed fisheries when fishers continue to fish while discarding marketable fish. We analyse the effects of individual quotas on spatial and temporal effort allocation and over-quota discarding in a multispecies fishery. Using a spatially explicit dynamic-state variable model, the optimal fishing strategy of fishers constrained by annual individual quotas, facing uncertainty in catch rates, is studied. Individual fishers will move away from areas with high catches of the restricted quota species and, depending on the cost of fishing, will stop fishing in certain periods of the year. Individual vessels will discard marketable fish, but only after their individual quota for the species under consideration has been reached. These results are in line with observations on effort allocation and discarding of marketable fish, both over-quota discarding and highgrading, by the Dutch beam-trawl fleet. The models we present can be used to predict the outcomes of management and are therefore a useful tool for fisheries scientists and managers.

Structure and spatio-temporal dynamics of artisanal fisheries around a Mediterranean marine protected area

Forcada, A., Valle, C., Sanchez-Lizaso, J. L., Bayle-Sempere, J. T., Corsi, F. — Mon, 26 Oct 2009 06:16:28 PDT

Forcada, A., Valle, C., Sánchez-Lizaso, J. L., Bayle-Sempere, J. T., and Corsi, F. 2010. Structure and spatio-temporal dynamics of artisanal fisheries around a Mediterranean marine protected area. – ICES Journal of Marine Science, 67: 000–000.

Marine protected areas (MPAs) have been proposed and established throughout the world, but few studies have adequately assessed the spatial adaptations of fishers to the limitations imposed by their placement. The main objectives of this work were to identify and describe the characteristics of the artisanal fisheries around Tabarca Marine Reserve (western Mediterranean Sea) and to define their activity in space and time. Data were collected through questionnaires to fishers and onboard sampling. The artisanal fisheries were complex owing to the multispecific nature of the landings, the variety of gears involved, and their marked seasonality. All boats of the three harbours around the MPA were assessed, for a total of 32 boats. The fishers exploit 18 fishing grounds with eight gear types, for a total of 17 métiers. Mullus trammelnet, Sepia trammelnet, and sparid longline are the most frequently used métiers. The main factors determining the spatial distribution of the fishing effort are proximity to home harbour, habitat heterogeneity, and closeness to the MPA. Total fishing effort appeared slightly concentrated around the MPA, but each métier showed different patterns of effort distribution. Although the sparid gillnet and the sparid longline concentrated along MPA boundaries, the Sepia trammelnet and the Mullus trammelnet did not.

South American sea lion and spiny dogfish predation on artisanal catches of southern hake in fjords of Chilean Patagonia

de la Torriente, A., Quinones, R. A., Miranda-Urbina, D. A., Echevarria, F. — Fri, 16 Oct 2009 03:37:54 PDT

de la Torriente, A., Quiñones, R. A., Miranda-Urbina, D. A., and Echevarría, F. 2010. South American sea lion and spiny dogfish predation on artisanal catches of southern hake in fjords of Chilean Patagonia. – ICES Journal of Marine Science, 67: 000–000.

The South American sea lion (Otaria flavescens) is a pinniped known to interact with fisheries, potentially damaging gear and lowering catches. Predation by O. flavescens and spiny dogfish (Squalus acanthias) on artisanal southern hake (Merluccius australis) catches in fjords of Chilean Patagonia is estimated and compared. Observations were made in the Gulf of Ancud and Comau Fjord in southern Chile from October 2005 to September 2006. Losses of southern hake catches to O. flavescens predation were 1.6% of the total catch of the species, and to spiny dogfish predation were slightly higher, at 3.3%. The predation of both species on southern hake catches varied throughout the year, but was lower in summer. Both predators showed a preference for adult southern hake over juveniles. There was no significant relationship between predation on southern hake catches by the sea lion and the availability of adult and juvenile southern hake on longlines (AHCL). However, there was a significant relationship (p < 0.05) between AHCL and spiny dogfish predation. Most O. flavescens interaction events (81.4%) were during longline retrieval. Our results showed minimal interactions between O. flavescens and the artisanal southern hake fishery in the area, so with the present abundance of O. flavescens, there is no justification for reducing the sea lion population by hunting.

What controls the spatial distribution of the North Sea plaice spawning population? Confronting ecological hypotheses through a model selection framework

Loots, C., Vaz, S., Planque, B., Koubbi, P. — Sat, 10 Oct 2009 04:32:56 PDT

Loots, C., Vaz, S., Planque, B., and Koubbi, P. 2010. What controls the spatial distribution of the North Sea plaice spawning population? Confronting ecological hypotheses through a model selection framework. – ICES Journal of Marine Science, 67: 000–000.

The spatial dynamics of spawning fish are crucial because they influence the survival rates of eggs and larvae and ultimately impact the reproductive success of populations. The factors that control these dynamics are complex and potentially many, and they interact. A model-selection-based approach was developed to confront various hypotheses of control of the spatial distribution of spawning population of North Sea plaice (Pleuronectes platessa). For each hypothesis or combination thereof, statistical models were constructed. These were then ranked and selected based on their ability to adjust and predict observed spatial distributions. The North Sea plaice population seems to have developed strong attachment to specific spawning sites, where geographic location and population memory are important controlling factors. Temporal changes in spatial distribution patterns appear to be influenced primarily by population size and demography. Variations in hydrographic conditions such as temperature and salinity do not appear to control interannual fluctuations in spatial distribution. This means that, for reproduction, applying conventional habitat models may falsely attribute major controlling effects to environmental conditions. It is concluded that a multiple-hypothesis approach is essential to understanding and predicting the present and future distribution of the North Sea plaice population during its spawning season.

Cod, haddock, saithe, herring, and capelin in the Barents Sea and adjacent waters: a review of the biological value of the area

Olsen, E., Aanes, S., Mehl, S., Holst, J. C., Aglen, A., Gjosaeter, H. — Fri, 09 Oct 2009 04:16:17 PDT

Olsen, E., Aanes, S., Mehl, S., Holst, J. C., Aglen, A., and Gjøsæter, H. 2010. Cod, haddock, saithe, herring, and capelin in the Barents Sea and adjacent waters: a review of the biological value of the area. – ICES Journal of Marine Science, 67: 000–000.

Cod, haddock, saithe, herring, and capelin are the most important fish species in the Barents Sea and adjacent waters. Ecosystem-based management requires species-specific knowledge of the biological value and vulnerability throughout their life history and distributional range. For each of the five species and four annual quarters, the spawning (egg) areas, nursery areas for larvae and juveniles, and feeding grounds for adults are described and mapped. Areas of eggs (spawning) and larvae were the most important because these are the life stages when fish are most vulnerable to anthropogenic impact. The greatest overlap of spawning areas was from Røstbanken in the south to the Varanger Peninsula in the northeast, and overlap of larval distribution was more extensive.

Co-management: an alternative to enforcement?

van Hoof, L. — Sun, 04 Oct 2009 22:51:06 PDT

van Hoof, L. 2010. Co-management: an alternative to enforcement? – ICES Journal of Marine Science, 67: 000–000.

The decline in fish stocks worldwide has often been attributed to problems inherent with resources being treated as common property. Government is usually called upon to define and implement solutions, but the issues society face today cannot be dealt with by the classical, state-centred system of the industrial society. In this article, the Dutch case of fisheries management is used to demonstrate how a government-orientated solution, such as the recently inaugurated EU Community Fisheries Control Agency, and a governance-type solution, such as co-management, relate to each other and whether a partnership between government and the market, such as co-management, can serve as an alternative to direct government enforcement. Although the Dutch case is not a true-bred form of co-management, but rather a case of co-enforcement, it can be used to service a theoretical assessment of the possibilities of co-enforcement at a European scale.

An investigation of the spawning behaviour of the chokka squid Loligo reynaudii and the potential effects of temperature using acoustic telemetry

Downey, N. J., Roberts, M. J., Baird, D. — Sat, 03 Oct 2009 00:33:53 PDT

Downey, N. J., Roberts, M. J., and Baird, D. 2009. An investigation of the spawning behaviour of the chokka squid Loligo reynaudii and the potential effects of temperature using acoustic telemetry. – ICES Journal of Marine Science, 67: 000–000.

Spawning aggregations of chokka squid are influenced by environmental conditions. Acoustic telemetry was used to monitor the behaviour of spawning squid in relation to environmental variability. During the November squid-fishery closed seasons of 2003–2006, hexagonal VR2 receiver arrays were moored on and around active spawning aggregations in Kromme Bay, South Africa. In all, 45 squid were tagged (V9P-6L-S256 transmitters) and released within these arrays. Three presence–absence behaviours were identified: (i) arrival on the spawning site at dawn and departure after dusk, (ii) continuous presence for a number of days, and (iii) presence interrupted by frequent but short periods of absence. Movement between spawning sites was both diurnal and nocturnal. Squid presence at the monitored sites increased after dawn and decreased towards and after dusk. Occasionally, a core aggregation of squid remained on the spawning sites at night. Temperature data at the sites indicated occasional upwelling, and although the role of temperature in the spawning process is not well understood, data suggest that it is linked to the continuation and or interruption of spawning after an aggregation has formed. The initial formation of spawning aggregations appears to be triggered by upwelling events.

Evaluating management strategies to implement the recovery plan for Iberian hake (Merluccius merluccius); the impact of censored catch information

Jardim, E., Cervino, S., Azevedo, M. — Sat, 03 Oct 2009 00:33:52 PDT

Jardim, E., Cerviño, S., and Azevedo, M. 2010. Evaluating management strategies to implement the recovery plan for Iberian hake (Merluccius merluccius); the impact of censored catch information. – ICES Journal of Marine Science, 67: 000–000.

Iberian hake assessment revealed an increase in fishing mortality (F) despite enforcement of a recovery plan. Recent landings exceeded the total allowable catch and discarding rates were high. Alternative management strategies based on F control were evaluated with respect to the probability of recovering spawning-stock biomass (SSB), expected profits, and robustness to uncertainty on catch information and stock dynamics. Results showed that the use of censored catch data, i.e. excluding the Gulf of Cádiz or discards, may lead to inappropriate conclusions. Reducing fishing mortality was necessary for SSB to recover. An F_max strategy with discard reduction showed the highest probability of rebuilding SSB and led the fishery to sustainable exploitation, with an expected %SPR of 30–40% in 2025, mean individual weight in the landings of 450 g in 2015, and yield increasing by >20%. Because of uncertainty in the estimates of maximum sustainable yield, management strategies based on F_MSY were least robust, but all strategies were robust to alternative stock–recruit models.

Towards a precautionary approach to managing Canada's commercial harp seal hunt

Leaper, R., Lavigne, D. M., Corkeron, P., Johnston, D. W. — Fri, 25 Sep 2009 08:31:54 PDT

Leaper, R., Lavigne, D. M., Corkeron, P., and Johnston, D. W. 2010. Towards a precautionary approach to managing Canada's commercial harp seal hunt. – ICES Journal of Marine Science, 67: 000–000.

The Canadian government's approach to the management of its commercial harp seal hunt is compared with other precautionary approaches developed for setting anthropogenic removal limits for marine mammal populations. For Canada's harp seal hunt, the current management strategy has not been fully specified or tested, and its robustness to changes in biological parameters, uncertainty in input data and environmental variability, remains unknown. As such, the management approach cannot be considered precautionary and there is a substantial, but not quantified, probability that it will not meet its objectives. There is an urgent need for a fully specified and rigorously tested management procedure, and steps towards this are suggested that should reduce the risks associated with the current approach.

Stable isotope analysis of marine feeding signatures of Atlantic salmon in the North Atlantic

Dempson, J. B., Braithwaite, V. A., Doherty, D., Power, M. — Fri, 25 Sep 2009 08:31:53 PDT

Dempson, J. B., Braithwaite, V. A., Doherty, D., and Power, M. 2010. Stable isotope analysis of marine feeding signatures of Atlantic salmon in the North Atlantic. – ICES Journal of Marine Science, 67: 000–000.

Differences in the marine feeding of three geographically distinct populations of Atlantic salmon (Salmo salar) in the North Atlantic (Conne River, Newfoundland; Koksoak River, Ungava Bay, Québec; River Erne, northwest Ireland) were examined using analyses of stable isotopes of carbon and nitrogen (¹³C and ¹⁵N) and contrasted with isotope signatures obtained from a sample of salmon of unknown origin captured in the Labrador Sea. Although the overall range of ¹³C and ¹⁵N values (¹³C: X from –22.42 to –19.37; ¹⁵N: X from 10.70 to 13.38) was similar to that reported by others, significant differences were found among populations and between different sea-age life-history groups. Reported differences in marine feeding between populations from the Northeast and Northwest Atlantic corroborated the stable isotope results. A surrogate measure of lipid content, the C:N ratio, was also compared among 1-sea-winter salmon. The highest levels were associated with the Koksoak River, suggesting that Subarctic populations may require higher energy reserves to contend with their longer migrations and more-severe environmental conditions.

Capture efficiency and size selectivity of hydraulic clam dredges used in fishing for ocean quahogs (Arctica islandica): simultaneous estimation in the SELECT model

Wed, 23 Sep 2009 07:07:31 PDT

Thorarinsdóttir, G. G., Jacobson, L., Ragnarsson, S. Á., Garcia, E. G., and Gunnarsson, K. 2010. Capture efficiency and size selectivity of hydraulic clam dredges used in fishing for ocean quahogs (Arctica islandica): simultaneous estimation in the SELECT model. – ICES Journal of Marine Science, 67: 000–000.

Estimates of capture efficiency and size selectivity for commercial dredges are important in estimating stock biomass and setting catch limits for the ocean quahog off Iceland and the United States. Ocean quahogs are long-lived, slow-growing, and sensitive to overharvest resulting from poor estimates of capture efficiency and stock biomass. Capture efficiency and size selectivity were estimated simultaneously in mixed-effect SELECT models using diver and commercial dredge experiment data from the shallow-water habitats off Iceland. Estimated capture efficiency for the commercial dredge E = 92% (CV = 8%) was high for large [107.5 mm shell length (SL)] ocean quahogs. Size selectivity followed an ascending logistic curve, with L₅₀ = 70.5 mm SL (CV 4%), a selectivity range of 17.6 mm SL, and substantial variability among experimental dredge tows. Estimated capture efficiency was higher than that for ocean quahogs in US waters, possibly because of the deep habitats off the United States or uncertainty about dredge position during US depletion experiments. Scaling maximum selectivity from the SELECT model to one reduces correlations between size-selectivity and capture-efficiency parameters and may enhance the utility of selectivity estimates in stock assessment modelling. Our experimental and modelling approach may be useful for studies with other non-mobile benthic species.

Elevations of lobster fishery groundlines in relation to their potential to entangle endangered North Atlantic right whales in the Bay of Fundy, Canada

Brillant, S. W., Trippel, E. A. — Wed, 23 Sep 2009 07:07:30 PDT

Brillant, S. W., and Trippel, E. A. 2010. Elevations of lobster fishery groundlines in relation to their potential to entangle endangered North Atlantic right whales in the Bay of Fundy, Canada. – ICES Journal of Marine Science, 67: 000–000.

Fishing gear is known to be a threat to North Atlantic right whales (Eubalaena glacialis), and groundlines used in the American lobster (Homarus americanus) trap fishery are hypothesized to be an integral component of entanglements that may, in some incidents, lead to mortality. This research measured the elevations above the seabed of 17 regular groundlines on commercially active lobster gear in the Bay of Fundy and evaluated several factors governing rope elevation profiles. Mean elevation was 1.6 m (s.d. = 0.9, n = 5968, range = 0.0–7.0 m). The hypothesis that groundline elevations were ≤1.0 m (predicted height of taut groundlines) was rejected (Fisher's C = 66.9, p < 0.01), as was the hypothesis that elevations were >3.0 m (approximate body height of a right whale; Fisher's C = 129.5, p < 0.01). The proportion of groundline elevations ≤1.0 m was 0.32, and that <3.0 m was 0.92. Groundline elevations were negatively related to tidal current velocity at the time of setting (p < 0.001, r² = 0.33) and were closer to the seabed in deep than in shallow water (p < 0.05, r² = 0.07). It is suggested that groundlines in the Bay of Fundy may not constitute a large part of the risk associated with the entanglement of right whales, because most lines remained below the elevation hypothesized to be a threat (3 m). We also identified factors within the control of fishers setting trawls that minimize groundline elevations.

Density-dependent distribution of Atlantic cod (Gadus morhua) into deep waters on the Faroe Plateau

Steingrund, P., Ofstad, L. H. — Wed, 23 Sep 2009 07:07:29 PDT

Steingrund, P., and Ofstad, L. H. 2010. Density-dependent distribution of Atlantic cod (Gadus morhua) into deep waters on the Faroe Plateau. – ICES Journal of Marine Science, 67: 000–000.

The natural production of cod on the Faroe Plateau depends on the spatial overlap between cod and their prey. However, cod tend to be distributed shallower than the bulk of their prey fish, such as Norway pout and blue whiting. We used commercial and survey catch per unit effort (cpue) data to investigate the distribution of cod in the deep water (150–400 m) on the Faroe Plateau. Cod often move to deep water when they are 4 or 5 years old. The extent of this habitat shift was positively correlated with the total biomass of 3- or 4-year-old cod on the Faroe Plateau, whereas prey densities in the shallow and deep areas, respectively, seemed to have much less influence. Hence, year classes that were a year older than strong year classes were distributed deeper than normal, and vice versa. The cpue in deep water for all ages pooled was strongly correlated with the age 3–6 biomass of cod on the entire Faroe Plateau. These findings are discussed in relation to food utilization and management.

The eastern Baltic cod fishery: a fleet-based management strategy evaluation framework to assess the cod recovery plan of 2008

Bastardie, F., Nielsen, J. R., Kraus, G. — Wed, 16 Sep 2009 01:40:04 PDT

Bastardie, F., Nielsen, J. R., and Kraus, G. 2010. The eastern Baltic cod fishery: a fleet-based management strategy evaluation framework to assess the cod recovery plan of 2008. – ICES Journal of Marine Science, 67: 000–000.

A management strategy evaluation framework was developed for the international Baltic cod fishery to evaluate the performance and robustness of the 2008 multi-annual management plan for the eastern stock. The spatially explicit management evaluation covered two cod recruitment regimes and various fleet adaptation scenarios. The tested management options included total allowable catch control, direct effort control, and closed areas and seasons. The modelled fleet responded to management by misreporting, improving catching power, adapting capacity, and reallocating fishing effort. The model was calibrated with spatially and temporally disaggregated landings and effort data from five countries covering 83% of the total cod catches. The simulations revealed that the management plan is robust and likely to rebuild the stock in the medium term even under low recruitment. Direct effort reduction limited underreporting of catches, but the overall effect was impaired by the increased catching power or spatio-temporal effort reallocation. Closures had a positive effect, protecting part of the population from being caught, but the effect was impaired if there was seasonal effort reallocation. Over the entire 15-year simulation period, all fleets could realize variable but positive profits under all scenarios tested, owing to stock recovery.

Analytical reference points for age-structured models: application to data-poor fisheries

Brooks, E. N., Powers, J. E., Cortes, E. — Wed, 16 Sep 2009 04:37:45 PDT

Brooks, E. N., Powers, J. E., and Cortés, E. 2010. Analytical reference points for age-structured models: application to data-poor fisheries. – ICES Journal of Marine Science, 67: 000–000.

Analytical solutions for biological reference points are derived in terms of maximum lifetime reproductive rate. This rate can be calculated directly from biological parameters of maturity, fecundity, and natural mortality or a distribution for this rate can be derived from appropriate metadata. Minimal data needs and assumptions for determining stock status are discussed. The derivations lead to a re-parameterization of the common stock–recruit relationships, Beverton–Holt and Ricker, in terms of spawning potential ratio. Often, parameters in stock–recruit relationships are restricted by tight prior distributions or are fixed based on a hypothesized level of stock resilience. Fixing those parameters is equivalent to specifying the biological reference points. An ability to directly calculate reference points from biological data, or a meta-analysis, without need of a full assessment model or fisheries data, makes the method an attractive option for data-poor fisheries. The derivations reveal an explicit link between the biological characteristics of a species and appropriate management. Predicted stock status for a suite of shark species was compared with recent stock assessment results, and the method successfully identified whether each stock was overfished.

Stalked barnacle (Pollicipes pollicipes) harvesting in the Berlengas Nature Reserve, Portugal: temporal variation and validation of logbook data

Jacinto, D., Cruz, T., Silva, T., Castro, J. J. — Tue, 15 Sep 2009 00:28:19 PDT

Jacinto, D., Cruz, T., Silva, T., and Castro, J. J. 2010. Stalked barnacle (Pollicipes pollicipes) harvesting in the Berlengas Nature Reserve, Portugal: temporal variation and validation of logbook data. – ICES Journal of Marine Science, 67: 000–000.

Stalked barnacle (Pollicipes pollicipes) exploitation at the Berlengas Nature Reserve, Portugal, by professional harvesters has been subject to specific regulation since 2000. The only available information on barnacle exploitation there comes from catch reports (logbooks) provided by the harvesters. We evaluated the quality of the logbook information, described the temporal patterns of P. pollicipes fishing effort from 2000 to 2006 based on the logbook data, and modelled the daily fishing effort in relation to variability in oceanographic conditions. Results suggest different levels of reliability for the information contained in the logbooks: (i) information on the date of harvest seems to be reliable because 83% of the observed harvest dates were also declared; (ii) information on the quantity harvested shows a large discrepancy (mean = 31.8%) between declared and observed amounts, but we believe it can be used to analyse temporal patterns of exploitation, because there was no systematic bias (under- and overreporting was to the same extent). The total quantity of barnacles harvested between 2000 and 2006 (~16 t year^–1) was closely related to the effort applied. Daily harvesting effort was considered a function of two predictive variables (significant wave height and tidal range) and of their interaction. Neither the harvesting activity nor the resource itself seems to be at risk of collapse if such levels of pressure are maintained, but efforts should be made to increase surveillance and monitoring within the marine protected area.

Exploring spatial non-stationarity of fisheries survey data using geographically weighted regression (GWR): an example from the Northwest Atlantic

Windle, M. J. S., Rose, G. A., Devillers, R., Fortin, M.-J. — Fri, 04 Sep 2009 06:54:34 PDT

Windle, M. J. S., Rose, G. A., Devillers, R., and Fortin, M-J. 2010. Exploring spatial non-stationarity of fisheries survey data using geographically weighted regression (GWR): an example from the Northwest Atlantic. – ICES Journal of Marine Science, 67: 000–000.

Analyses of fisheries data have traditionally been performed under the implicit assumption that ecological relationships do not vary within management areas (i.e. assuming spatially stationary processes). We question this assumption using a local modelling technique, geographically weighted regression (GWR), not previously used in fisheries analyses. Outputs of GWR are compared with those of global logistic regression and generalized additive models (GAMs) in predicting the distribution of northern cod off Newfoundland, Canada, based on environmental (temperature and distance from shore) and biological factors (snow crab and northern shrimp) from 2001. Results from the GWR models explained significantly more variability than the global logistic and GAM regressions, as shown by goodness-of-fit tests and a reduction in the spatial autocorrelation of model residuals. GWR results revealed spatial regions in the relationships between cod and explanatory variables and that the significance and direction of these relationships varied locally. A k-means cluster analysis based on GWR t-values was used to delineate distinct zones of species–environment relationships. The advantages and limitations of GWR are discussed in terms of potential application to fisheries ecology.

Age and growth of longtail tuna (Thunnus tonggol) in tropical and temperate waters of the central Indo-Pacific

Griffiths, S. P., Fry, G. C., Manson, F. J., Lou, D. C. — Sun, 30 Aug 2009 23:16:46 PDT

Griffiths, S. P., Fry, G. C., Manson, F. J., and Lou, D. C. 2010. Age and growth of longtail tuna (Thunnus tonggol) in tropical and temperate waters of the central Indo-Pacific. – ICES Journal of Marine Science, 67: 000–000.

Age and growth of longtail tuna (Thunnus tonggol) were assessed by examination of annual growth increments in sectioned sagittal otoliths from 461 fish (238–1250 mm fork length, L_F) sampled from tropical and temperate waters in the central Indo-Pacific between February 2003 and April 2005. Edge and microincrement analyses (presumed daily increments) suggest that longtail tuna deposit a single annual growth increment mainly between August and October. Age was, therefore, estimated for all fish by counting assumed annual growth increments. Ages ranged from 154 d to 18.7 years, with most fish being 3–9 years. Five growth models were fitted to length-at-age data, all of which indicated that the species is relatively slow-growing and long-lived. Recaptures of two tagged fish at liberty for 6.2 and 10.5 years support this notion. A bias-corrected form of Akaike's Information Criterion determined that the Schnute–Richards model provided the best fit to length-at-age data, with model parameter estimates (sexes combined) of L = 135.4 cm L_F, K = 22.3 year^–1, t₀ = 0.120 years, = 150.0, v = 0.019, and = 2.7 x 10^–8. There was no significant difference in growth between sexes. The results suggest that longtail tuna grow more slowly and live longer than other tuna species of similar size. Coupled with their restricted neritic distribution, longtail tuna may be vulnerable to overexploitation by fisheries, and caution needs to be exercised in managing the species until more reliable biological and catch data are collected to assess the status of the population.

Misleading the masses: detection of mislabelled and substituted frozen fish products in South Africa

von der Heyden, S., Barendse, J., Seebregts, A. J., Matthee, C. A. — Sun, 30 Aug 2009 23:16:45 PDT

von der Heyden, S., Barendse, J., Seebregts, A. J., and Matthee, C. A. 2010. Misleading the masses: detection of mislabelled and substituted frozen fish products in South Africa. – ICES Journal of Marine Science, 67: 000–000.

Mislabelling poses a threat to the sustainability of seafood supply chains and, when frequent, can significantly affect conservation efforts. Here we identify the most popular fish in the South African market through consumer and retailer surveys and data gathered by a sustainable seafood campaign. Of these species, we tested a number of widely available and generally high-market priced fish, utilizing mtDNA 16S rRNA sequencing. Tests of 178 samples revealed that about half of all fillets are mislabelled. Most problematic was kob, Argyrosomus spp., for which some 84% of fillets provided belonged to other species, including mackerel, croaker, and warehou. Phylogenetic analyses provided strong support that the fillets sold as barracuda and wahoo were probably king mackerel and that red snapper fillets included fillets of river snapper, Lutjanus argentimaculatus, which is a species prohibited for sale in South Africa. We also discovered substitution of yellowtail for dorado. From preliminary population genetic comparisons, some 30% of kingklip samples probably had their origin in New Zealand, rather than southern Africa. The research revealed a market conducive to mislabelling through poor consumer and retailer awareness, and highlighted the value of sustainable seafood campaigns to draw attention to this.

Why compare marine ecosystems?

Sun, 30 Aug 2009 23:16:44 PDT

Murawski, S. A., Steele, J. H., Taylor, P., Fogarty, M. J., Sissenwine, M. P., Ford, M., and Suchman, C. 2010. Why compare marine ecosystems? – ICES Journal of Marine Science, 67: 000–000.

Effective marine ecosystem-based management (EBM) requires understanding the key processes and relationships controlling the aspects of biodiversity, productivity, and resilience to perturbations. Unfortunately, the scales, complexity, and non-linear dynamics that characterize marine ecosystems often confound managing for these properties. Nevertheless, scientifically derived decision-support tools (DSTs) are needed to account for impacts resulting from a variety of simultaneous human activities. Three possible methodologies for revealing mechanisms necessary to develop DSTs for EBM are: (i) controlled experimentation, (ii) iterative programmes of observation and modelling ("learning by doing"), and (iii) comparative ecosystem analysis. We have seen that controlled experiments are limited in capturing the complexity necessary to develop models of marine ecosystem dynamics with sufficient realism at appropriate scales. Iterative programmes of observation, model building, and assessment are useful for specific ecosystem issues but rarely lead to generally transferable products. Comparative ecosystem analyses may be the most effective, building on the first two by inferring ecosystem processes based on comparisons and contrasts of ecosystem response to human-induced factors. We propose a hierarchical system of ecosystem comparisons to include within-ecosystem comparisons (utilizing temporal and spatial changes in relation to human activities), within-ecosystem-type comparisons (e.g. coral reefs, temperate continental shelves, upwelling areas), and cross-ecosystem-type comparisons (e.g. coral reefs vs. boreal, terrestrial vs. marine ecosystems). Such a hierarchical comparative approach should lead to better understanding of the processes controlling biodiversity, productivity, and the resilience of marine ecosystems. In turn, better understanding of these processes will lead to the development of increasingly general laws, hypotheses, functional forms, governing equations, and broad interpretations of ecosystem responses to human activities, ultimately improving DSTs in support of EBM.

Hierarchical analysis of a remote, Arctic, artisanal longline fishery

Dennard, S. T., MacNeil, M. A., Treble, M. A., Campana, S., Fisk, A. T. — Sat, 22 Aug 2009 04:19:45 PDT

Dennard, S. T., MacNeil, M. A., Treble, M. A., Campana, S., and Fisk, A. T. 2010. Hierarchical analysis of a remote, Arctic, artisanal longline fishery. – ICES Journal of Marine Science, 67: 000–000.

This is the first paper to explore trends in catch per unit effort (cpue) through time of a Greenland halibut Reinhardtius hippoglossoides stock targeted by an artisanal, winter fishery in Cumberland Sound on southern Baffin Island, Canada. We modelled cpue data from 1987 to 2003, looking at two questions: what factors have driven cpue trends, and is cpue an accurate index of a stock's abundance? In the context of limited data availability, we used generalized linear models (GLMs) and hierarchical models to assess important predictors of cpue. Hierarchical models with multiple fixed environmental effects contained fishing location or individual fisher as random effects. A month effect showed greatest catch rates during February and March; the monthly North Atlantic Oscillation index was positively associated with catch rates; and a change from decreasing to increasing cpue after 1996 was linked to reduced fishery participation following a large storm. The best Akaike's information criterion-ranked GLM identified a negative relationship of cpue with shark bycatch. Although data limitations precluded conventional stock assessment, our models implicated the environment and fisher behaviour as drivers of cpue trends. Additionally, using multiple hierarchical models to predict cpue provided a more informative analysis for understanding trends in cpue than a GLM alone.

Coherent trends in contiguous survey time-series of major ecological and commercial fish species in the Gulf of Maine ecosystem

Nye, J. A., Bundy, A., Shackell, N., Friedland, K. D., Link, J. S. — Tue, 18 Aug 2009 00:35:39 PDT

Nye, J. A., Bundy, A., Shackell, N., Friedland, K. D., and Link, J. S. 2010. Coherent trends in contiguous survey time-series of major ecological and commercial fish species in the Gulf of Maine ecosystem. – ICES Journal of Marine Science, 67: 000–000.

Fish are often delineated into distinct population or stock units that reflect human institutional borders more than ecological factors. In the Northwest Atlantic, there are many species in the broader Gulf of Maine area (GOMA), yet the area is surveyed and managed for the most part in the south by the United States and in the north by Canada. Biomass time-series of 19 representative fish species and total biomass from 7 different surveys conducted by the United States and Canada in the GOMA are compared. All species showed coherent trends in relative biomass across at least two survey time-series, and in many species a single trend could describe all time-series trends accurately. For instance, Canadian and the US time-series of Atlantic cod, Atlantic herring, haddock, thorny skate, and goosefish had comparable trends. Conversely, species such as longhorn sculpin and spiny dogfish showed differing survey time-series trends and asynchronous event timing, suggesting that their population dynamics differ spatially. Collectively, the results demonstrate the value of comparing time-series for common species from contiguous ecosystems and elucidate the relative importance of environmental and fishing factors on each species.

Variability in the density and sound-speed of coastal zooplankton and nekton

Forman, K. A., Warren, J. D. — Thu, 13 Aug 2009 01:08:05 PDT

Forman, K. A., and Warren, J. D. 2010. Variability in the density and sound-speed of coastal zooplankton and nekton. – ICES Journal of Marine Science, 67: 000–000.

Acoustic sampling techniques provide an advantage over traditional net-sampling by increasing scientist ability to survey a large area in a relatively short period, as well as providing higher-resolution data in the vertical and horizontal dimensions. To convert acoustic data into measures of biological organisms, physics-based scattering models are often used. Such models use several parameters to predict the amount of sound scattered by a fluid-like or weakly scattering animal. Two important input parameters are the density (g) and sound-speed (h) contrasts of the animal and the surrounding seawater. The density and sound-speed contrasts were measured for coastal zooplankton and nekton species including shrimps (Palaemonetes pugio and Crangon septemspinosa), fish (Fundulus majalis and Fundulus heteroclitus), and polychaetes (Nereis succinea and Glycera americana) along with multiple physiological and environmental variables. Factors such as animal size, feeding status, fecundity, gender, and maturity caused variations in g. The variations in g observed for these animals could lead to large differences (or uncertainties) in abundance estimates based on acoustic scattering models and field-collected backscatter data. It may be important to use a range of values for g and h in the acoustic scattering models used to convert acoustic data into estimates of the abundance of marine organisms.

Spatial segregation among fishing vessels in a multispecies fishery

Poos, J. J., Quirijns, F. J., Rijnsdorp, A. D. — Wed, 12 Aug 2009 02:15:26 PDT

Poos, J. J., Quirijns, F. J., and Rijnsdorp, A. D. 2010. Spatial segregation among fishing vessels in a multispecies fishery. – ICES Journal of Marine Science, 67: 000–000.

Individual decisions of fishers on where to fish in heterogeneous environments may shape the relation between fishing effort and fishing mortality. Fishers may be viewed as individual foragers, whose decisions are aimed at optimizing short-term gain, as in ideal free distribution (IFD) theory. Although IFD assumes all foragers to be equal, they are likely to differ in competitive abilities for different prey types or target species. Here, we present an IFD-like model of a fishing fleet consisting of two components with different competitive abilities for two target species, showing that spatial segregation can result from unequal interference competition, but also in the absence of interference competition. Differences in catch efficiency between vessels for target species in combination with differences in the spatial distribution of target species can result in spatial segregation among vessel groups. The theoretical results are used to interpret the observed spatial segregation of two components within the Dutch beam trawl fleet using observations from a vessel monitoring by satellite system. However, this study cannot pinpoint which of the processes included in the theoretical model is the prime cause of the segregation within the Dutch beam trawl fleet.

Growth of European hake (Merluccius merluccius) in the Gulf of Lions based on conventional tagging

Mellon-Duval, C., de Pontual, H., Metral, L., Quemener, L. — Wed, 12 Aug 2009 01:34:06 PDT

Mellon-Duval, C., de Pontual, H., Métral, L., and Quemener, L. 2010. Growth of European hake (Merluccius merluccius) in the Gulf of Lions based on conventional tagging. – ICES Journal of Marine Science, 67: 000–000.

Growth of European hake was estimated from the results of a conventional tagging study in the Gulf of Lions, the first tagging experiment to have been undertaken on the species in Mediterranean waters. In all, 4277 hake 15–40 cm long were tagged and released on the inshore fishing grounds during spring 2006. The overall recapture rate was 6.5% and times-at-liberty ranged from 1 to 717 d. Growth rate in hake varied with size and sex. The estimated growth parameter (von Bertalanffy k) was estimated as double previously published values based on size frequency distribution in the area. Compared with recent growth parameters derived from the tagging experiments in the Bay of Biscay, k was estimated to be slightly lower in the Gulf of Lions. With this faster growth, hake would mature earlier than previously thought: at age 2 for both sexes, instead of at age 3 or 4 as currently accepted for the Mediterranean. Growth rate by sex decreased to a similar level once fish had attained sexual maturity.

Swimbladder condition and target strength of myctophid fish in the temperate zone of the Northwest Pacific

Yasuma, H., Sawada, K., Takao, Y., Miyashita, K., Aoki, I. — Thu, 06 Aug 2009 06:44:01 PDT

Yasuma, H., Sawada, K., Takao, Y., Miyashita, K., and Aoki, I. 2010. Swimbladder condition and target strength of myctophid fish in the temperate zone of the Northwest Pacific. – ICES Journal of Marine Science, 67: 000–000.

We report theoretical values of the target strength (TS) of four myctophid fish (Ceratoscopelus warmingii, Myctophum asperum, Diaphus garmani, and Diaphus chrysorhynchus) based on morphometry of the swimbladder. None of the D. chrysorhynchus had an inflated swimbladder, but the other species had both inflated and non-inflated swimbladders, depending on body size. The relationships between swimbladder and body length showed that once gas production started, the swimbladders grew faster than the rest of the body (positive allometric growth). However, M. asperum showed regression of the swimbladder after positive allometric growth, so larger specimens had non-inflated swimbladders. Based on the measurements of swimbladder and body length, the theoretical TS values at 38 and 120 kHz were calculated using existing sound-scattering models. In fish with inflated swimbladders, TS values were relatively low (less than –67 dB, reduced TS_cm) at both frequencies. Regression slopes on TS–body length (log) plots were >20, suggesting that their scattering cross sections were not proportional to the square of the body length. In contrast, the TS values of M. asperum decreased with growth in large fish (60–80 mm long) through swimbladder regression. Scattering cross sections of fish without swimbladders were not proportional to the square of the body length over the whole size range.