ICES Journal of Marine Science - Advance Access

Sensitivity of predicted cohort size and catches to errors in estimates of fishing mortality in the terminal year

Horbowy, J. — 2008-07-19

Horbowy, J. 2008. Sensitivity of predicted cohort size and catches to errors in estimates of fishing mortality in the terminal year. – ICES Journal of Marine Science, 65.

Formulae for the sensitivity of projected cohort size and catches to errors (bias) in estimates of fishing mortality in the terminal year were developed. Assessment models allowing for random errors in the observed catches as well as models in which catches are treated as exact were considered. The formulae were applied to a Gulf of Riga (Baltic Sea) herring assessment to show how well they estimated prediction errors and to evaluate the effect of assessment errors on predictions. The errors propagate quickly with time, and the higher the fishing mortality, the bigger the projection error. The errors in predicted catches are somewhat lower than the errors in predicted cohort sizes. The formulae developed show that with moderate error in estimated fishing mortality (20%), the errors in predicted cohort size can reach 100%, and the errors in predicted catches may be 50% for fishing mortality estimated at 1.0 in the terminal year and the status quo prediction. As the Gulf of Riga herring case demonstrates, the overall error in predicted stock size and catches may be lower when terminal fishing mortality is underestimated at some ages and overestimated at others (cancelling effect).

The use of meiofauna diversity as an indicator of pollution in harbours

Moreno, M., Vezzulli, L., Marin, V., Laconi, P., Albertelli, G., Fabiano, M. — 2008-07-18

Moreno, M., Vezzulli, L., Marin, V., Laconi, P., Albertelli, G., and Fabiano, M. 2009. The use of meiofauna diversity as an indicator of pollution in harbours. – ICES Journal of Marine Science, 65.

We assessed several meiofaunal indices in sediments of three Mediterranean harbours differing in environmental contamination to evaluate their usefulness as indicators of pollution and to identify those that best described environmental quality. In general, indicators based on meiofaunal taxa demonstrated a significant correlation with the concentration of contaminants, especially the polycyclic aromatic hydrocarbons (PAHs). Nematode genus-based indicators correlated with contaminant concentrations at similar levels of significance, suggesting that a high taxonomic resolution does not improve the information content of meiofauna diversity indicators for assessing the environmental quality in these harbours. Notably, environmental variables that affect meiofaunal and nematode assemblages (e.g. water depth, grain size, and food sources) demonstrated a low spatial and temporal variability in the harbours investigated and did not represent important confounding factors. We conclude that the application of meiofaunal and nematode indices can be a useful tool for assessing the environmental quality of harbour ecosystems.

Three initial OSPAR tests of ecological coherence: heuristics in a data-limited situation

Ardron, J. A. — 2008-07-17

Ardron, J. A. 2009. Three initial OSPAR tests of ecological coherence: heuristics in a data-limited situation. – ICES Journal of Marine Science, 65.

As marine protected area (MPA) networks become established worldwide, it will be necessary to track the progress made in meeting the networks’ underlying ecological goals. The 12 coastal European nations of the OSPAR Convention have agreed to establish an "ecologically coherent" network of MPAs within the waters of the Northeast Atlantic by 2010. However, the meaning of ecological coherence has not been explicitly defined, and it has not been explained how it can be assessed. OSPAR’s work on this topic over the past 4 years is summarized here. As the 2010 deadline approaches, the urgency to assess ecological coherence increases. Proper scientific assessment is hampered by the current lack of detailed ecological data, and policy-makers are concerned that collecting data for indicators will tax already limited resources. Unconventional approaches that can make do with what little information is available are being developed, and three initial spatial tests are presented here. A personal perspective of lessons learnt is provided.

Biological features of the Lophius piscatorius catch in Scottish waters

Laurenson, C. H., Dobby, H., McLay, H. A., Leslie, B. — 2008-07-02

Laurenson, C. H., Dobby, H., McLay, H. A., and Leslie, B. 2008. Biological features of the Lophius piscatorius catch in Scottish waters. – ICES Journal of Marine Science, 65.

Here, data on 50 265 Lophius piscatorius sampled between 1998 and 2006 on board commercial fishing vessels during observer trips and chartered surveys at Shetland, west of Scotland, and Rockall are analysed. In each area, length differed significantly with depth (p < 0.001), there was an increase in modal size with increasing depth down to 450 m, and large fish dominated hauls in deeper water. The sex ratio of all data combined was 0.88 females:1 male, but it varied by area, depth, and season, with males greatly outnumbering females in deep water west of Scotland during the first quarter of the year. The proportion at length that were female differed significantly with depth, and the highest proportions of mature fish were in deep water at Rockall and west of Scotland. L_50% maturities, for all data combined, were 102.4 cm for females and 58.3 cm for males.

Pollution fingerprints in eels as models for the chemical status of rivers

Belpaire, C., Goemans, G., Geeraerts, C., Quataert, P., Parmentier, K. — 2008-06-30

Belpaire, C., Goemans, G., Geeraerts, C., Quataert, P., and Parmentier, K. 2008. Pollution fingerprints in eels as models for the chemical status of rivers. – ICES Journal of Marine Science, 65.

The 2006 EU Water Framework Directive (WFD) proposed the monitoring of a selection of priority substances in the aquatic phase, including lipophilic substances. However, there are strong arguments for measuring lipophilic substances in biota. Yellow eel is a good candidate because it is widespread, sedentary, and accumulates many lipophilic substances in its muscle tissue. Several authors have described the indicative value of measured concentrations, yet few studies have investigated to what extent the spectrum of contaminants present characterizes the local environmental pollution pressure. To evaluate the value of the pollution profile of an eel as a fingerprint of the chemical status of the local environment, two datasets were selected from the Flemish Eel Pollutant Network database. The pollution profiles in individual eels along a river (even at distances <5 km) proved to be significantly different. Analysis of pooled contaminant data from multiple sites and sampling years within rivers allows characterization of river-specific chemical pressures. These results highlight the usefulness of eels as bio-indicators for monitoring pollution with lipophilic chemicals, such as polychlorinated biphenyls and organochlorine pesticides, in rivers. As such, eels may be used effectively within the monitoring programme for a selection of priority substances referred to in the WFD.

The optimized interpolation of fish positions and speeds in an array of fixed acoustic receivers

Hedger, R. D., Martin, F., Dodson, J. J., Hatin, D., Caron, F., Whoriskey, F. G. — 2008-06-30

Hedger, R. D., Martin, F., Dodson, J, J., Hatin, D., Caron, F., and Whoriskey, F. G. 2008. The optimized interpolation of fish positions and speeds in an array of fixed acoustic receivers. – ICES Journal of Marine Science 65.

The principal method for interpolating the positions and speeds of tagged fish within an array of fixed acoustic receivers is the weighted-mean method, which uses a box-kernel estimator, one of the simplest smoothing options available. This study aimed to determine the relative error of alternative, non-parametric regression methods for estimating these parameters. It was achieved by predicting the positions and speeds of three paths made through a dense array of fixed acoustic receivers within a coastal embayment (Gaspé Bay, Québec, Canada) by a boat with a GPS trailing an ultrasonic transmitter. Transmitter positions and speeds were estimated from the receiver data using kernel estimators, with box and normal kernels and the kernel size determined arbitrarily, and by several non-parametric methods, i.e. a kernel estimator, a smoothing spline, and local polynomial regression, with the kernel size or smoothing span determined by cross-validation. Prediction error of the kernel estimator was highly dependent upon kernel size, and a normal kernel produced less error than the box kernel. Of the methods using cross-validation, local polynomial regression produced least error, suggesting it as the optimal method for interpolation. Prediction error was also strongly dependent on array density. The local polynomial regression method was used to determine the movement patterns of a sample of tagged Atlantic salmon (Salmo salar) smolt and kelt, and American eel (Anguilla rostrata). Analysis of the estimates from local polynomial regression suggested that this was a suitable method for monitoring patterns of fish movement.

Back to the future: using landscape ecology to understand changing patterns of land use in Canada, and its effects on the sustainability of coastal ecosystems

Mercer Clarke, C. S. L., Roff, J. C., Bard, S. M. — 2008-06-30

Mercer Clarke, C. S. L., Roff, J. C., and Bard, S. M. 2008. Back to the future: using landscape ecology to understand changing patterns of land use in Canada, and its effects on the sustainability of coastal ecosystems. – ICES Journal of Marine Science, 65: 000–000.

In Canada, concerns are mounting that the coastal environments may be more affected by human activities than is evidenced by current monitoring and assessment of environmental quality. Holistically orientated approaches to coastal management have concluded that indicators of coastal sustainability must include a wider array of factors that go beyond marine ecosystem health to include the health and well-being of coastal terrestrial environments and human communities. Research is needed to bridge the disciplinary and jurisdictional barriers that hamper better understanding of the relationships between terrestrial and marine ecosystems, and to help recognize the role of humans as both a contributing and an affected species in the coastal ecotone. Our examination of past and current knowledge of conditions along the Atlantic shore of Nova Scotia led us to challenge the predominant view that all is well along Canadian coasts. Using an interdisciplinary approach derived from landscape ecology, we examined international, national, and local efforts to assess management indicators against factors that gauge their relevance to marine- and land-development planning and management. We propose a new context for indicators, one that challenges scientists to provide decision-makers with information that can be used to drive social change, avoiding or mitigating human activities and sustaining coastal ecosystems.

Effectiveness of a feedback management procedure based on controlling the size of marine protected areas through catch per unit effort

Kai, M., Shirakihara, K. — 2008-06-27

Kai, M., and Shirakihara, K. 2008. Effectiveness of a feedback management procedure based on controlling the size of marine protected areas through catch per unit effort. – ICES Journal of Marine Science, 65.

The effectiveness of a feedback management procedure using marine protected areas (MPAs) was investigated. This procedure does not control fishing effort, but it does increase the size of the MPA when the catch per unit effort (cpue) is below a predetermined target level and reduces the size when the cpue is above this level. Stability analyses of the approach, which consisted of a population dynamics model and a model to control MPA size, suggest that this procedure can lead to recovery of a depleted population and sustain that population at a predetermined target level, even when there is hyperstability (a non-linear relationship between population size and cpue). An alternative procedure using fishing effort instead of MPA size may also function well, although both procedures may need a long time for a depleted population to approach the target level. Performance of both procedures was examined using numerical simulations focused on system dynamics in the short term after management implementation. The procedure using MPA size was more effective at preventing population collapse. Simulations suggest that if this procedure starts from a desirable level of initial MPA size, it has advantages over the alternative procedure through creating speedier population recovery and a higher level of short-term catch.

The distribution of chondrichthyans along the northern coast of Norway

Williams, T., Helle, K., Aschan, M. — 2008-06-27

Williams, T., Helle, K., and Aschan, M. 2008. The distribution of chondrichthyans along the northern coast of Norway. – ICES Journal of Marine Science, 65.

The relationship between temperature, latitude, and depth and the distribution and relative abundance of chondrichthyans along the northern coast of Norway was examined based on catches made in scientific trawls north of 62°N from 1992 to 2005. It appears that Chimaera monstrosa, Etmopterus spinax, Squalus acanthias, and Galeus melastomus were more abundant in the south, and Amblyraja radiata more common in the north. Between 1992 and 2005, the distribution and relative abundance did not appear to change significantly, although average water temperatures rose during the period. Current fishing levels do not appear to be impacting the populations of the more common species, but the status of species rarely found in the survey catches is unclear.

Biodiversity of North Sea fish: why do the politicians care but marine scientists appear oblivious to this issue?

Greenstreet, S. P. R. — 2008-06-27

Greenstreet, S. P. R. 2008. Biodiversity of North Sea fish: why do the politicians care but marine scientists appear oblivious to this issue? – ICES Journal of Marine Science, 65.

Political drivers underpinning the development of an Ecosystem Approach to Marine Management (EAMM) focus on conserving and restoring biodiversity. However, the Element of Ecological Quality for Fish Communities that emerged from the 2002 Bergen North Sea Ministerial Conference relates to "Changes in the proportion of large fish and hence the average weight and average maximum length of the fish community". How did this apparent change in direction arise? Responding to advice requests from OSPAR, ICES established seven criteria for identifying "state" indicators capable of supporting indicator-based management. Application of these criteria underlined the merits of indicators of fish size, whereas diversity indices performed poorly against four of the criteria. These difficulties are examined here. Far from being oblivious to the issue of biodiversity, marine scientists recognized that they were not in a position to recommend Ecological Quality Objectives (EcoQOs) for fish biodiversity that would have relied on the use of biodiversity indicators. The use of indicators of size structure, for which the theoretical foundation was better developed, allowed the continued development of an EAMM in the short term. However, if the issue of biodiversity is to be addressed in the longer term, then shortcomings associated with the use of biodiversity indicators need to be addressed.

An operational monitoring system to provide indicators of CO2-related variables in the ocean

2008-06-26

Hardman-Mountford, N. J., Moore, G., Bakker, D. C. E., Watson, A. J., Schuster, U., Barciela, R., Hines, A., Moncoiffé, G., Brown, J., Dye, S., Blackford, J., Somerfield, P. J., Holt, J., Hydes, D. J., and Aiken, J. 2008. An operational monitoring system to provide indicators of CO₂-related variables in the ocean. – ICES Journal of Marine Science, 65.

Demand by governments and scientists is increasing for indicators of CO₂-related variables for the ocean. We describe a recent project, CARBON-OPS, during which a "supply chain" was developed for automated measurement of pCO₂ in the surface of the ocean, data processing, and its use in providing information for research and policy development. Data are gathered by new pCO₂ measurement systems on five UK research ships in the Southern Ocean, Atlantic Ocean, and northwestern European shelf seas. These send data in near-real-time, via satellite communication systems, to the British Oceanographic Data Centre, where they are automatically processed, quality controlled, and archived. The data are then delivered to the UK Met Office and others for use in testing predictions from operational ocean models. These models will generate indicator products and assist government through the Marine Climate Change Impact Partnership, a partnership of scientists, government, its agencies, and NGOs, by providing information on ocean CO₂ uptake, changes in ocean pH, and potential impacts on global climate and marine ecosystems.

Population biology of monkfish Lophius americanus

Richards, R. A., Nitschke, P. C., Sosebee, K. A. — 2008-06-26

Richards, R. A., Nitschke, P. C., and Sosebee, K. A. 2008. Population biology of monkfish Lophius americanus. – ICES Journal of Marine Science, 65.

This paper provides an overview of the biology of monkfish in US waters of the Northwest Atlantic Ocean using data from resource surveys spanning the period 1948–2007. Monkfish exhibited seasonal onshore–offshore shifts in distribution, migrated out of the southern Mid-Atlantic Bight (MAB) in mid-spring, and re-appeared there in autumn. Sex ratios at length for fish 40–65-cm long were skewed towards males in the southern MAB, but approximated unity elsewhere, suggesting that a portion of the population resides outside sampled areas. Growth was linear at 9.9 cm year^–1 and did not differ by region or sex. Maximum observed size was 138 cm for females and 85 cm for males. Length at 50% maturity for males was 35.6 cm (4.1 years old) in the north and 37.9 cm (4.3 years old) in the south; for females 38.8 cm (4.6 years old) in the north and 43.8 cm (4.9 years old) in the south. Ripe females were found in shallow (<50 m) and deep (>200 m) water in the south, and in shallow water (<50 m) in the north.

Integrating commercial and research surveys to estimate the harvestable biomass, and establish a quota, for an "unexploited" abalone population

Mayfield, S., McGarvey, R., Carlson, I. J., Dixon, C. — 2008-06-26

Mayfield, S., McGarvey, R., Carlson, I. J., and Dixon, C. 2008. Integrating commercial and research surveys to estimate the harvestable biomass, and establish a quota, for an "unexploited" abalone population. – ICES Journal of Marine Science, 65.

A key challenge facing many fisheries managers is the absence of information on the level of harvestable biomass. We describe an integrated, two-stage survey approach that was used to measure the spatial distribution and harvestable biomass of a largely unexploited metapopulation of greenlip abalone (Haliotis laevigata) over a large area of northwestern Spencer Gulf, South Australia. In stage 1, commercial fishers conducted systematic surveys to identify subareas with abalone at harvestable densities. Cpue measures from these surveys were used to map and stratify a bounded survey subregion, within which leaded-line, research-diver surveys measured absolute density and harvestable biomass (stage 2). Decision tables, showing minimum biomass at various probabilities vs. harvest fraction, were developed to provide a risk-assessment framework for quota setting. Within two years, our approach allowed, first, the mapping of the broad-scale, spatial distribution and abundance of greenlip abalone in an area of 1143 km², second, the estimation of harvestable biomass in a smaller (16.9 km²) area, and finally, the allocation by State fishery managers of an additional quota inside a newly defined management subzone. The collaborative approach we describe for providing estimates of absolute biomass over large spatial scales affords multiple advantages for the assessment and management of invertebrate dive fisheries.

Changes in spawning-stock structure and recruitment pattern of red mullet, Mullus barbatus, after a trawl ban in the Gulf of Castellammare (central Mediterranean Sea)

2008-06-23

Fiorentino, F., Badalamenti, F., D’Anna, G., Garofalo, G., Gianguzza, P., Gristina, M., Pipitone, C., Rizzo, P., and Fortibuoni, T. 2008. Changes in spawning-stock structure and recruitment pattern of red mullet, Mullus barbatus, after a trawl ban in the Gulf of Castellammare (central Mediterranean Sea). – ICES Journal of Marine Science, 65.

The increase in biomass of red mullet, Mullus barbatus, in the Gulf of Castellammare (northwestern Sicily, central Mediterranean) after a 14-year trawl ban, prompted us to compare the spawning-stock structure and the recruitment pattern before and after the closure. Datasets obtained from three experimental trawl surveys were available before the ban (April and September 1985; April–May 1986) and four post-ban (September and November 2004; March and May 2005). Spawning-stock biomass increased significantly after the ban. Moreover, females at depths >50 m in the post-ban period were larger than those collected before the ban at the same depth. The recruitment pattern of the population also changed. Notably, recruit numbers increased and recruitment occurs over a broader period. The increase in biomass after the trawl ban seems to be the result of a combination of different processes, mainly associated with the lowering of fishing mortality. A positive trend in sea surface temperature in the area may have played a role too.

The Lophius budegassa component of monkfish catches in Scottish waters

Laurenson, C. H., Dobby, H., McLay, H. A. — 2008-06-19

Laurenson, C. H., Dobby, H., and McLay, H. A. 2008. The Lophius budegassa component of monkfish catches in Scottish waters. – ICES Journal of Marine Science, 65.

To date, research efforts on Lophius species in waters around Scotland (ICES Divisions IVa, VIa, and VIb) have focused almost exclusively on Lophius piscatorius. Here, the characteristics and distribution of the Lophius budegassa component of the catch are described using data collected by observers during commercial fishing trips and scientific surveys on chartered commercial fishing vessels between 1998 and 2006. At Rockall Bank (VIb), L. budegassa were rare, just 0.1% of the catch of Lophius spp., whereas west of Scotland (VIa) and around the Shetland Islands (IVa), they made up 18 and 2% of catches, respectively, with greatest prevalence towards the shelf edge. Fish length ranged from 16 to 89 cm with a modal length at 40 cm. Greater proportions of large individuals were recorded around the Shetland Islands than in other parts of the study area. Overall, the sex ratio was 1:1, and lengths at 50% maturity were estimated to be 70.4 cm for females and 49.4 cm for males.

Megafauna community structure and trophic relationships at the recently discovered Concepcion Methane Seep Area, Chile, ~36{degrees}S

Sellanes, J., Quiroga, E., Neira, C. — 2008-06-19

Sellanes, J., Quiroga, E., and Neira, C. 2008. Megafauna community structure and trophic relationships at the recently discovered Concepción Methane Seep Area, Chile, ~36°S. – ICES Journal of Marine Science, 65.

The fauna, community composition, and trophic support of the newly discovered Concepción Methane Seep Area (CMSA) are compared with those at a nearby non-seep control. The assemblage of chemosymbiotic bivalves is defined by eight species, including the families Lucinidae, Thyasiridae, Solemyidae, and Vesicomyidae. Seep polychaetes are represented by Lamellibrachia sp. and two commensal species of the vesicomyid Calyptogena gallardoi. Although taxonomic analysis is still under way, most of the chemosymbiotic species seem to be endemics. The CMSA is a hotspot for non-seep benthic megafauna too; 101 taxa were present, but most of them are colonists or vagrants (i.e. not endemics of methane seeps). Isotope analysis supported the belief that non-symbiont-bearing species utilize photosynthetically fixed carbon, because they were isotopically distinct from the chemosymbiotic bivalve species present. It is our opinion that, at this site, which underlies one of the most productive coastal upwelling regions of the world, spatial heterogeneity and the availability of hard substratum, generated by the presence of authigenic carbonate crusts, are more important factors in attracting non-seep fauna than the availability of locally produced chemosynthetic food.

Cross-front variations in adult abundance and recruitment of Patagonian scallop (Zygochlamys patagonica) at the SW Atlantic Shelf Break Front

2008-06-18

Mauna, A. C., Franco, B. C., Baldoni, A., Acha, E. M., Lasta, M. L., and Iribarne, O. O. 2008. Cross-front variations in adult abundance and recruitment of Patagonian scallop (Zygochlamys patagonica) at the SW Atlantic Shelf Break Front. – ICES Journal of Marine Science, 65.

We studied cross-front variations in adult abundance and recruitment of Patagonian scallop (Zygochlamys patagonica) and their relationship with the Shelf Break Front and satellite-derived chlorophyll a in the Southwest Atlantic between 38°S and 39°30'S. Integrated data from commercial fleets (CF, 1996–2005), research cruises (RC, 1998–2005), sea surface temperature (SST; 1985–1997), and satellite-derived chlorophyll a (CSAT; 1998–2004) were included in the analysis. One-way ANOVA was used to assess differences in recruitment and scallop abundance in a cross-front direction. The abundance of scallops was greatest (RC > 200 kg h^–1) closer to the onshore side of the front or beneath it, and the East–West extension of scallop beds (~40 km) matched the seasonal zonal displacement of the front (~37 km). The highest CSAT gradients were west of or matched the position of the front. The annual mean position of the front correlated with the spatial variability in recruitment within areas where the species recruited successfully (RC > 2000 h^–1). The spatial variability in adult abundance and recruitment of scallops is strongly related to the spatial variability in the position of the front and with the high CSAT concentrations associated with it.

Buoyancy and vertical distribution of Norwegian coastal cod (Gadus morhua) eggs from different areas along the coast

Stenevik, E. K., Sundby, S., Agnalt, A. L. — 2008-06-17

Stenevik, E. K., Sundby, S., and Agnalt, A. L. 2008. Buoyancy and vertical distribution of Norwegian coastal cod (Gadus morhua) eggs from different areas along the coast. – ICES Journal of Marine Science, 65.

There are significant genetic differences in coastal cod (Gadus morhua) along the Norwegian coast, and in order to maintain these differences, there must be mechanisms that ensure local retention of eggs and larvae in the spawning areas. The buoyancy of eggs from four different areas along the Norwegian coast was measured using a density gradient column, and the results from modelling experiments showed that in three of the groups (Tysfjord, Helgeland, and Øygarden), the buoyancy in combination with local hydrography would place the eggs in subsurface waters where retention is greater than in surface waters.

Dispersal of Munida gregaria (Decapoda: Galatheidae) larvae in Patagonian channels of southern Chile

Leon, R., Castro, L. R., Caceres, M. — 2008-06-16

León, R., Castro, L. R., and Cáceres, M. 2008. Dispersal of Munida gregaria (Decapoda: Galatheidae) larvae in Patagonian channels of southern Chile. – ICES Journal of Marine Science, 65.

The dispersal of Munida gregaria larvae in Chilean Patagonian channels was assessed in spring 2002 and 2003, and winter 2003. In winter 2003, zoea I was the most abundant stage in all channels and there were no larval stages older than zoea IV. In spring 2002 and 2003, there were six larval stages in all channels, and the greater abundance of older larvae suggested that reproduction takes place in winter and larval development in spring. Further, analysis of spatial distribution by stage revealed that early zoeae moved seawards. Generalized Additive Models analyses showed that most larval stages were temperature-dependent, and that the salinity range of the youngest zoea was wider than that of older larvae and post-larvae, coinciding with an ontogenetic distribution change from estuary to shelf. Residual flows determined with an acoustic Doppler current profiler revealed two layers of opposite flow: the shallowest layer moved seawards and the deeper layer onshore. The surface layer was wider in spring than in winter because of seasonal increase in fresh-water input. The dispersal pattern of M. gregaria consisted of an inner channel larval release in winter, followed by an along-channel larval drift and subsequent export to the shelf in spring. The mechanism by which juveniles return to the channels seemed to be associated with the onshore subsurface flow.

Wax-ester mobilization by female Calanus finmarchicus (Gunnerus) during spring ascendance and advection to the Faroe Shelf

Madsen, M. L., Gaard, E., Hansen, B. W. — 2008-06-10

Madsen, M. L., Gaard, E., and Hansen, B. W. 2008. Wax-ester mobilization by female Calanus finmarchicus (Gunnerus) during spring ascendance and advection to the Faroe Shelf. – ICES Journal of Marine Science, 65.

Time of ascendance and initiation of reproduction in Calanus finmarchicus is closely correlated with the phytoplankton spring bloom. However, significant egg production can take place before the bloom, fuelled by mobilizing stored wax-ester lipids. Calanus finmarchicus from stations on the Faroe Shelf were compared with specimens collected off the shelf. Biological parameters such as gut contents, egg production, developmental stage, and lipid content were determined and correlated with phytoplankton concentration and spatial distribution along two transects in late April 2003 across the shelf northeast and southwest of the Faroe Islands. Grazing by C. finmarchicus on phytoplankton was significantly lower northeast of the Faroe plateau. However, the egg production was generally high for a pre-bloom situation, with significantly higher rates of egg production on the shelf than off it, along both transects. Wax-ester content of female C. finmarchicus was significantly higher and more variable at off-shelf stations than on the shelf (<2 µg female^–1). From this, we suggest that off-shelf C. finmarchicus had recently emerged from overwintering depths, in contrast to individuals from stations on the shelf, which had been in the upper water masses for some time. Females (from off-shelf stations) most likely supported the initial egg production from their wax-ester reserves.

Application of dynamic factor analysis in the assessment of Iberian anglerfish stocks

2008-06-05

Azevedo, M., Duarte, R., Cardador, F., Sousa, P., Fariña, C., Sampedro, P., Landa, J., and Costas, G. 2008. Application of dynamic factor analysis in the assessment of Iberian anglerfish stocks. – ICES Journal of Marine Science, 65.

Dynamic factor analysis (DFA) was applied to six time-series of catch per unit effort data of the Iberian (ICES Divisions VIIIc and IXa) white anglerfish (Lophius piscatorius) and black anglerfish (L. budegassa). Results showed that grouping the abundance indices reflected the fleet's area of exploitation and fish size selection. Two common trends (CTs) were extracted for each species, capturing the main signal of abundance over time. The white anglerfish was assessed using these CTs as input to the biomass dynamic model currently used in the ICES assessment, to investigate whether the approach would reduce the uncertainty in parameter estimates and related quantities. Using the CTs, bias estimates are lower. The current perception of an overexploited stock is unchanged, but a much lower intrinsic rate of biomass increase was estimated, indicating that the biomass recovery might be much slower. A lower maximum sustainable yield, ~3600 t, was obtained, and this is more consistent with the historical landings trajectory. The application of DFA to stock assessment of anglerfish, presented here for the first time, can be extended to age-based assessments.

Seasonal patterns and diets of wild fish assemblages associated with Mediterranean coastal fish farms

2008-06-05

Fernandez-Jover, D., Sanchez-Jerez, P., Bayle-Sempere, J. T., Valle, C., and Dempster, T. 2008. Seasonal patterns and diets of wild fish assemblages associated with Mediterranean coastal fish farms. – ICES Journal of Marine Science, 65.

Fish are attracted to floating structures, including coastal cage fish farms, sometimes in dense aggregations. To understand better the influence of aquaculture on wild fish stocks, we carried out seasonal visual censuses around three southwestern Mediterranean farms over 2 years to assess the temporal patterns of the aggregated fish assemblage. In addition, we analysed the diet of the five most abundant species. Aggregations around all farms were large throughout the year, although species composition and abundance differed among farms and seasons. Fish farms are attractive habitats for certain species of wild fish in specific seasons. Adult fish of reproductive size dominated the assemblages, and stomach content analysis revealed that 66–89% of fish of the five most abundant taxa had consumed food pellets lost from the cages. We estimated that wild fish consume up to 10% of the pellets used at farms, indicating that food is a key attractant. Regional monitoring of farm-associated wild fish assemblages could aid management of the interaction of aquaculture and wild fish resources, because changes in feeding behaviour may have consequences for fish populations and local fisheries.

Spatial probability modelling of eelgrass (Zostera marina) distribution on the west coast of Norway

2008-06-04

Bekkby, T., Rinde, E., Erikstad, L., Bakkestuen, V., Longva, O., Christensen, O., Isæus, M., and Isachsen, P. E. 2008. Spatial probability modelling of eelgrass (Zostera marina) distribution on the west coast of Norway. – ICES Journal of Marine Science, 65.

Based on modelled and measured geophysical variables and presence/absence data of eelgrass Zostera marina, we developed a spatial predictive probability model for Z. marina. Our analyses confirm previous reports and show that the probability of finding Z. marina is at its highest in shallow, gently sloping, and sheltered areas. We integrated the empirical knowledge from field samples in GIS and developed a model-based map of the probability of finding Z. marina using the model-selection approach Akaike Information Criterion (AIC) and the spatial probability modelling extension GRASP in S-Plus. Spatial predictive probability models contribute to a better understanding of the factors and processes structuring the distribution of marine habitats. Additionally, such models provide a useful tool for management and research, because they are quantitative and defined objectively, extrapolate knowledge from sampled to unsurveyed areas, and result in a probability map that is easy to understand and disseminate to stakeholders.

The relation between concentrations of ovarian trace elements and the body size of Atlantic cod Gadus morhua

Bang, A., Gronkjaer, P., Lorenzen, B. — 2008-06-03

Bang, A., Grønkjær, P., and Lorenzen, B. 2008. The relation between concentrations of ovarian trace elements and the body size of Atlantic cod Gadus morhua. – ICES Journal of Marine Science, 65.

Trace metals in the ovaries of fish are transferred from the female via the yolk to the offspring, which makes the early life stages susceptible to deleterious effects of potentially toxic elements contained in the ovaries. Here, the concentrations of 13 elements from the ovaries of 133 ripe female North Sea cod Gadus morhua weighing 0.2–18 kg were correlated with female size, accounting for differences in maturity and condition. Most elements were negatively correlated with the size variables weight, length and, especially, ovarian dry weight. Further, they were negatively correlated with maturity and condition. Many of the trace elements showed true size-dependence, but the correlations were generally weak. A linear discriminant analysis separated "small" and "large" fish at a length of 85 cm based on concentrations of Co, Mn, Se, and Zn, and correctly assigned 78 of 102 small fish and 23 of 31 large fish to their respective size category. This corresponds to an overall classification success of 75.9%. The results suggest that embryos and early larvae from small females are exposed to higher levels of potentially harmful metals. If the differences in trace element concentration influence survival success, this will add to the negative effects of size distribution truncation and declines in size-at-maturity experienced by many populations of cod.

The use of sagittal otoliths in discriminating stocks of common dolphinfish (Coryphaena hippurus) off northeastern Brazil using multishape descriptors

Duarte-Neto, P., Lessa, R., Stosic, B., Morize, E. — 2008-06-03

Duarte-Neto, P., Lessa, R., Stosic, B., and Morize, E. 2008. The use of sagittal otoliths in discriminating stocks of common dolphinfish (Coryphaena hippurus) off northeastern Brazil using multishape descriptors. – ICES Journal of Marine Science, 65.

The shape of sagittal otoliths from the dolphinfish (Coryphaena hippurus) was studied to test the hypothesis that two stocks exist off the northeast coast of Brazil. In all, 82 sagittal otoliths were collected from fish caught by the artisanal fleet in two coastal regions of northeastern Brazil in December 2003 and April/May 2004. Several shape descriptors were determined [area, perimeter, rectangularity, circularity, eccentricity, fractal dimension (FD), and Fourier coefficients (FCs)] to evaluate the degree of similarity in the otoliths between regions. A three-morphotype pattern was revealed through cluster and principal component analyses based on FCs of the 30th harmonics. Apparently, this pattern is not influenced by clinal factors. Despite the great variability between otolith shapes, separation of the samples from two regions was suggested using multivariate and univariate analyses of variance for all shape descriptors and using canonical discriminant analysis. The methods successfully classified 57.1 and 69.6% of otoliths from the Maranhão and Rio Grande do Norte regions, respectively. The FD was a powerful descriptor in discriminating the two stocks. Differences in the shapes of sagittal otoliths may be related to different growth rates of the species and lend credence to the belief that there are two stocks along the Brazilian coast.

Effort allocation and marine protected areas: is the North Sea Plaice Box a management compromise?

Kjaersgaard, J., Frost, H. — 2008-05-30

Kjærsgaard, J., and Frost, H. 2008. Effort allocation and marine protected areas: is the North Sea Plaice Box a management compromise? – ICES Journal of Marine Science, 65.

A complex bioeconomic model is used to study the economic and biological consequences of establishing a marine protected area (MPA). The model is a multispecies age-structured bioeconomic model that treats days at sea and number of vessels, for different fleets fishing inside and outside the protected area, as endogenous variables. A simulation applies an adaptive investment rule that determines fleet size from year to year, and an optimization procedure provides a benchmark for a profit-maximizing solution over time. In contrast to most conventional studies on MPAs, fishing within the protected area is possible. Moreover, the stock is not divided between inside and outside the protected area, although the abundance of different age classes in each area differs. Therefore, the economic and biological impacts of fishing inside or outside are different. The North Sea flatfish fishery is used as a case study, so the analysis is particularly relevant because North Sea flatfish regulation is currently under revision.

Characterization and classification of acoustically detected fish spatial distributions

Burgos, J. M., Horne, J. K. — 2008-05-27

Burgos, J. M., and Horne, J. K. 2008. Characterization and classification of acoustically detected fish spatial distributions. – ICES Journal of Marine Science, 65

High-resolution, two-dimensional measurements of aquatic-organism density are collected routinely during echo integration trawl surveys. School-detection algorithms are commonly used to describe and analyse spatial distributions of pelagic and semi-pelagic organisms observed in echograms. This approach is appropriate for species that form well-defined schools, but is limited when used for species that form demersal layers or diffuse pelagic shoals. As an alternative to metrics obtained from school-detection algorithms, we used landscape indices to quantify and characterize spatial heterogeneity in density distributions of walleye pollock (Theragra chalcogramma). Survey transects were divided into segments of equal length and echo integrated at a resolution of 20 m (horizontal) and 1 m (vertical). A series of 20 landscape metrics was calculated in each segment to measure occupancy, patchiness, size distribution of patches, distances among patches, acoustic density, and vertical location and dispersion. Factor analysis indicated that the metric set could be reduced to four factors: spatial occupancy, aggregation, packing density, and vertical distribution. Cluster analysis was used to develop a 12-category classification typology for distribution patterns. Visual inspection revealed that spatial patterns of segments assigned to each type were consistent, but that there was considerable overlap among types.

Spatial and temporal prediction of fin whale distribution in the northwestern Mediterranean Sea

Laran, S., Gannier, A. — 2008-05-20

Laran, S. and Gannier, A. 2008. Spatial and temporal prediction of fin whale distribution in the northwestern Mediterranean Sea. – ICES Journal of Marine Science, 65.

Understanding the distribution of the cetaceans is crucial to improving their conservation. Therefore, a prediction model of fin whale’s (Balaenoptera physalus) summer distribution was developed from data collected between May and August, in the Pelagos Mediterranean Marine Mammals Sanctuary. Explanatory variables were selected by multiple logistic regression, among several physiographic and oceanographic parameters. Depth, chlorophyll (Chl a) concentration, and sea surface temperature (SST) were selected for characterizing fin whale presence. Remote sensing imagery (Chl a and SST) was used at an 8-d resolution to capture short-term environmental variability. With the selection of a presence/absence threshold by the receiver operating characteristic curve, a correct classification of 70% (49% for presence, 85% for absence) was achieved for the initial dataset. Model reliability was also tested on an independent dataset, collected in the northwestern Basin; a correct classification of 71% (41% for presence prediction, 86% for absence prediction) was obtained. This study contributes to an understanding of where fin whales might concentrate to feed in summer. Weekly predictions of their distribution represent a valuable conservation tool in a marine protected area, for example to prevent collisions with ships.