ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on April 23, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(6):899-905; doi:10.1093/icesjms/fsn067
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Effects of hook size and barbless hooks on hooking injury, catch per unit effort, and fish size in a mixed-species recreational fishery in the western Mediterranean Sea
1 Instituto Mediterráneo de Estudios Avanzados, IMEDEA (CSIC–UIB), C/ Miquel Marqués 21, 07190 Esporles, Illes Balears, Spain
2 Laboratori de Biologia Marina, Departament de Biologia, Universitat de les Illes Balears, Edif. Guillem Colom. Crta., Valldemossa Km 7.5, 07122 Palma de Mallorca, Illes Balears, Spain
3 Direcció General de Pesca, Govern de les Illes Balears, C/ Foners 10, 07006 Palma de Mallorca, Illes Balears, Spain
Correspondence to J. Alós: tel/fax: +34 971 610829; e-mail: pep.alos{at}uib.es.
Alós, J., Palmer, M., Grau, A. M., and Deudero, S. 2008. Effects of hook size and barbless hooks on hooking injury, catch per unit effort, and fish size in a mixed-species recreational fishery in the western Mediterranean Sea. – ICES Journal of Marine Science, 65: 899–905.The effects of hook size (small vs. large) and type (conventional vs. barbless) on hooking injury, catch per unit effort (cpue), and fish size in a mixed-species recreational fishery in the Balearic Islands (western Mediterranean) are evaluated. Hook size was the most important predictor of deep-hooking, which is reduced by the use of large hooks. The size of fish captured was another predictor of deep-hooking incidence, because large fish tended to be caught in deep-hooking locations. Deep-hooking was highly correlated with the presence of bleeding, and unhooking time was reduced by the use of large hooks and barbless hooks, although differences were small. To determine the effects of different hook treatments on cpue and species composition, a mixed-effect linear model was used as a univariate procedure, and redundancy analysis was used as a multivariate analysis. Results showed a drastic decrease in cpue with barbless hooks. In contrast, large hooks reduced the incidence of hooking injuries, with a small reduction in catch rate. Moreover, large hooks were associated with a larger mean size of fish caught than small hooks. Hence, control of hook size, along with other traditional management measures that involve the release of fish, is presented as a management option for sustainable development of recreational fisheries in the western Mediterranean Sea.
Keywords: barbless hook, cpue, deep-hooking, hook size, management, recreational fisheries
Received 6 December 2007; accepted 28 March 2008; advance access publication 23 April 2008.
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Introduction |
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Size-limit regulations, daily bag limits, and the promotion of catch-and-release fishing have become increasingly important tools for recreational fisheries management. However, the utility of such voluntary and mandatory practices (e.g. undersized fish) as management tools requires sufficient survival rates and successful reproduction among released fish to be effective (Cooke and Suski, 2004, 2005; Bartholomew and Bohnsack, 2005; Cooke et al., 2005, 2006; Arlinghaus et al., 2007).
Bartholomew and Bohnsack (2005) reviewed the factors influencing mortality of fish caught and released, and concluded that deep-hooking was the most significant. Fish hooked in sensitive areas such as the stomach, oesophagus, and gills suffered greater mortality than those hooked in non-critical locations (Ayvazian et al., 2002; Aalbers et al., 2004; Bartholomew and Bohnsack, 2005; Broadhurst et al., 2005; St John and Syers, 2005; Butcher et al., 2006; Cooke et al., 2006).
Few studies have examined the relationship between hook size and the probability of deep-hooking in recreational fisheries, but the results of those studies do suggest that the probability of deep-hooking is related to hook size (Carbines, 1999; Cooke et al., 2005; Grixti et al., 2007). Many selectivity studies on longline fisheries report better catch rates for small hooks than for large hooks (Erzini et al., 1996, 1998, 1999). Conversely, the effects of hook size on the size range of captured fish are unclear. Size selectivity by larger hooks was clearly demonstrated for some fisheries (Cortez-Zaragoza et al., 1989; Otway and Craig, 1993), but in other cases, catch size distributions seemed to be nearly independent of hook size (Erzini et al., 1996, 1998, 1999; Halliday, 2002; Stergiou and Erzini, 2002; Cooke et al., 2005). The relationship between mouth size and body length is likely the most important factor affecting hook size selectivity (Erzini et al., 1998; Karpouzi and Stergiou, 2003).
With respect to hook type, barbless hooks represent a good way of reducing unhooking time, stress, and hooking injury in fresh-water fisheries (Gjernes et al., 1993; Diggles and Ernst, 1997; Schill and Scarpella, 1997; Cooke et al., 2001). Meka (2004) described the same trends, but also demonstrated that barbless hooks reduce the catch efficiency for Oncorhynchus mykiss. Other studies have not detected substantial differences in mortality and hooking injury between barbed and barbless hooks, but have detected a reduction in catch per unit effort (cpue; DuBois and Dubielzig, 2004). With respect to marine recreational fisheries, among Lutjanus carponotatus and Epinephelus quoyanus (Diggles and Ernst, 1997), and Pomatomus saltatrix (Ayvazian et al., 2002), the unhooking time, a good predictor of mortality rate (Broadhurst et al., 2005), is reduced when barbless hooks are used (Diggles and Ernst, 1997). Schaeffer and Hoffman (2002) examined variations in unhooking time, hooking injury, and cpue produced by barbed and barbless hooks in different species in a nearshore marine sportfishery in the Gulf of Mexico near St Petersburg, FL (USA). Mean unhooking time was significantly shorter with barbless hooks, but the cpue differed between hook types, so the authors concluded that barbless hooks provided only a slight benefit at the expense of reduced capture rates.
The purpose of our study was to compare the relative importance of the effects of hook size (small vs. large hooks) and hook type (barbed vs. barbless hooks) on deep-hooking probability, the presence of blood, and unhooking time (as a surrogate for hooking mortality) in a recreational fishery in the Balearic Islands (western Mediterranean). Boat-angling makes up >60% of the total effort in this fishery, which is characterized by mixed-species catches. In all, 54 species are targeted by anglers, and a light-tackle fishery captures many small fish (see Morales-Nin et al., 2005, for detail about the fishery). In addition, for a new gear to be acceptable to anglers, it is important that catch rates and fish sizes are better or at least similar to those taken by existing conventional gear. Because of this, we investigated the effects of hook size and type on cpue and fish size.
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Material and methods |
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Field site and experimental procedures
Experimental boat-angling was conducted at Palma Bay, southern Mallorca (western Mediterranean) in July 2007. The area traditionally supports a large number of recreational anglers. In total, 16 sites with similar bottom characteristics (seagrass beds dominated by Posidonia oceanica, with depths between 6.6 and 12.1 m) were selected randomly.
Four hook treatments were used in the experimental trials: barbed hooks of sizes 12 and 8 (HAYABUSA model chn1060) and barbless hooks of sizes 12 and 8 (TEKLON model B6071; i.e. four hook treatments: barbed #12, barbed #8, barbless #12, and barbless #8). The dimensions of the hooks were measured and are shown in Figure 1. For the experimental angling sessions, four anglers with similar levels of experience were selected. The experimental gear was composed of three hooks of the same type and size mounted on a 5.9-lb main leader with three 15-cm side leaders and a terminal weight of 100 g. The gear was placed on a 10-lb main nylon leader reel (0.25 mm). All hooks were baited with pieces of marine worm (Paranereis acrata) covering the whole hook surface.
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For each site, one hook treatment was assigned to each angler (i.e. Angler 1-barbed #12, Angler 2-barbed #8, Angler 3-barbless #12, and Angler 4-barbless #8), and a 30-min angling session was completed by each angler at the same time (i.e. four angling sessions per site). Whenever sites were changed, the anglers changed hook treatments, so that the different hook treatments were used the same number of times by each angler. Time lost by moving between sites, changing the experimental gear, and anchoring the boat was not included in the 30-min sessions. With this design, each angler completed four 30-min sessions with the same hook treatment. The total number of 30-min sessions over the two trips was 64.
Global Positioning System positions of the sites, and depth, hook treatment per angler, and time were recorded for each of the 16 sessions. One researcher was assigned to each angler to evaluate deep-hooking locations, presence of bleeding, and unhooking times (s). Deep-hooking locations were categorized as being shallow hooked (when fish suffered injury to lips or jaws) or deep-hooked (when the injury was to gills, oesophagus, or stomach). The presence of blood was coded as presence or absence for each fish caught. Species were identified, and the total length (TL) was measured to the nearest millimetre. All fish caught were released.
Data analysis
Analysis was carried out in two ways: (i) testing the effects of hook type on cpue and fish size, and (ii) discerning the variables affecting hooking injury (deep-hooking, unhooking time, and presence of blood). For the first analysis, univariate and multivariate analyses were performed.
For univariate analyses, a mixed-effect linear model was used to analyse the relationships between hook type and size (explanatory variables) and mean fish length and cpue (total catches pooled). In both cases, hook size (small vs. large) and type (barbed vs. barbless) were considered to be fixed categorical factors, and angler and site were considered to be random factors. The effects of fixed factors were tested and eventually included in the final model, following a forward step-by-step sequence until maximum explanatory power was reached, the Akaike's Information Criterion (AIC). The AIC is (log) likelihood plus a term that penalizes for the number of model parameters. Therefore, the AIC has been used to achieve model simplification, i.e. to select the combination of variables with the best fit, but with the minimum number of parameters (Crawley, 2005). Residual distributions were examined for normality by visually inspecting residual histograms and normal quantile–quantile plots. Adequate transformation (log-transformed) was applied in some cases where normality assumptions were violated. Homoscedasticity was examined using box plots and fitted residuals.
In contrast to the univariate analyses, multivariate analyses focused on the ability of multivariate methods to test the existence of a relationship between the main faunistic gradients and hook size and type (Legendre and Gallagher, 2001). Specifically, we used redundancy analysis (RDA). Those species with a frequency of occurrence <10% were considered occasional or rare and were not considered in the multivariate analysis. The ratio between variability (inertia in multivariate terminology) explained by the model and residual inertia was used to test the model’s significance using Monte Carlo permutation methods. The strategy adopted here for model building was model-based for the variables of no direct interest (i.e. site and angler were considered as covariables, and their effects were kept statistically constant before testing for size and hook-type effects). Selection of the best subset of explanatory variables was made following a step-by-step forward addition procedure (AIC-based), and significance tests for partial effects (i.e. partial RDAs) of the variable were added at each model-building step.
The second group of analyses focused on identifying the set of variables affecting hooking injury. Logistic regression was utilized to fit the data, with the maximum estimated likelihood of describing the relationships between deep-hooking and four putative explanatory variables: hook size (size 12 vs. 8), hook type (barbed vs. barbless), TL, and angler (Grixti et al., 2007). Step-forward selection with the AIC was employed to determine the minimal adequate model using only the main effects. The same procedure was applied for all species pooled and for the three most common species caught in the experiment (i.e. a total of four models). To examine the effects of unhooking time, we developed a mixed-effects linear model, as in the first group of analyses. With respect to bleeding, contingency tables using 
2 were applied to test for associations between different hooking locations and the presence/absence of blood.
Model building and ordination analyses (principal components analyses, PCA, and RDA) were completed using the basic statistical package and the libraries lmer4 (Crawley, 2005) and Vegan (Oksanen, 2005) in R (Version 2.0.1, http://www.r-project.org/). Multivariate analyses results were visualized using CANOCO 4.5 software. An 
-value of 0.05 was chosen as the critical level for rejection of the null hypotheses for all analyses.
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Results |
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Univariate statistical analysis of cpue between hook sizes and types
In all, 1047 fish of 15 different species were captured (Table 1). The mixed-effects model of the cpue univariate log-transformed indicated that hook type (ANOVA;
2 = 22.274; p < 0.001) and hook size (ANOVA; 2 = 27.150; p < 0.001) were highly significant. Barbed hooks caught seven fish per angler per 30 min and nine fish per angler per 30 min more than barbless hooks of sizes 12 and 8, respectively (Table 2). With respect to hook size, results showed that size 12 hooks caught more fish per angler per 30 min than size 8 hooks (Table 2). The interactions between the two factors were not significant (ANOVA; 2 = 1.394; p = 0.238).
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Mean size of fish caught
The sizes of fish captured by the different hook treatments are listed in Table 1. The mixed-effects model detected significant effects on mean fish size caught between the two hook sizes (ANOVA;
2 = 9.163; p < 0.001). In general, large hooks tended to catch larger fish than small ones. The use of barbless hooks had no significant effect on the average size of fish caught (ANOVA; 2 = 0.065; p < 0.799). Results of average fish size (when all fish were pooled) for each combination of hook size and type are listed in Table 2.
Multivariate statistical analysis of cpue
The final multivariate analysis included eight species: Diplodus annularis (Dip.ann), Coris julis (Cor.jul), Serranus scriba (Ser.scr), Boops boops (Boo.boo), Spondyliosoma cantharus (Spo.can), Trachurus mediterraneus (Tra.med), Oblada melanura (Obl.mel), and Diplodus vulgaris (Dip.vul). Variance partitioning showed that the most important variable affecting species composition was site (50.9%). Differences attributable to hook type, angler, and hook size accounted for 6.1%, 5.9%, and 4.8% of the total variability in species composition, respectively, but up to 32.2% of the variability was unexplained by the above variables. Figures 2 and 3 show the two first axes resulting from RDA procedures to test the effects of hook type and size on species composition. First, barbed hooks seemed to promote increased capture of most species, except S. cantharus (Figure 2). The most abundant species, such as D. annularis, C. julis, and S. scriba, were prone to capture more frequently with barbed hooks. The percentage of faunistic variability explained by hook type (6.1%) was significantly different from zero (the probability after 5000 random permutations was 0.0004). Hook size also had a significant effect on species composition per sample (variance explained 4.8%; probability after 5000 random permutations, 0.0008). In this case, D. annularis and C. julis were the species most frequently caught using small hooks, whereas S. cantharus, D. vulgaris, and S. scriba were caught most frequently using large hooks (Figure 3).
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Hooking injury
Hook size had a large effect on the incidence of deep-hooking location (Table 3). The percentages of deep-hooking in fish pooled between hook treatments are listed in Table 2. TL was another significant predictor of deep-hooking (Table 3). Therefore, the probability of deep-hooking significantly increases with increasing fish size. Species-specific logistic regressions were also carried out for the three most common species caught. For D. annularis and C. julis, hook size was the most important predictor of deep-hooking, and TL was the second most important explanatory variable (Table 3). In contrast, for S. scriba, TL was the only significant predictor of deep-hooking. Interactions between explanatory variables included in each model were not significant and were not included in the final model.
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The presence of bleeding was related to hooking locations on fish (
2 = 735.067; p < 0.001). A large proportion of the total fish caught by deep-hooking bled as a consequence of the hook injury (90.4%). With respect to unhooking time, the mixed-effects model found significant effects of hook size (ANOVA; 2 = 19.118; p < 0.001) and type (ANOVA; 2 = 8.138; p < 0.01; Table 2). |
Discussion |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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The number and species composition of fish caught in fisheries can be influenced by a number of variables, hook size and design being two important factors (Erzini et al., 1998). In our case, site was the most important cause of variability in abundance and species composition. Noticeable small-scale spatial heterogeneity in the fish species composition associated with P. oceanica beds or meadows, attributable to local meadow characteristics and habitat structure, has been reported in the western Mediterranean (Moranta et al., 2006). With respect to variables of interest, our results demonstrated a significant increase in cpue using small hooks. Similar results were obtained for some hook and line fisheries (Otway and Craig, 1993; Erzini et al., 1996, 1998, 1999; Halliday, 2002). In our case, however, the increase in cpue was mainly related to catches of C. julis and D. annularis. In contrast, species such as D. vulgaris, S. cantharus, and S. scriba (i.e. those most sought by local anglers) were captured more frequently with large hooks.
Barbless hooks reportedly reduce handling time, but, in some cases, catch efficiency is also reduced (Meka, 2004). Other studies have not revealed quantitative differences in catch rates between barbed and barbless hooks (e.g. DuBois and Dubielzig, 2004). In marine recreational fisheries, however, Schaeffer and Hoffman (2002) reported that anglers landed 20% more fish with barbed hooks. In our study, the use of barbless hooks resulted in a significant decrease in cpue, and the RDA revealed that only catches of S. cantharus increased with barbless hooks.
The effect of hook size on mean length of fish caught is controversial. In hook and line fisheries, the length distribution of fish caught by different hook sizes can overlap considerably, with little or no significant difference in some cases (Erzini et al., 1996, 1998, 1999). Other studies have demonstrated size selectivity based on hook size (Cortez-Zaragoza et al., 1989; Otway and Craig, 1993). Other authors have reported a significant increase in fish size associated with an increase in hook size for Lepomis macrochirus and Acanthopagrus butcheri in recreational fisheries, but the differences were small in both cases (Cooke et al., 2005; Grixti et al., 2007). Similarly, our results demonstrated a small increase in mean length of fish caught by increasing the hook size. Such a small increase in length could be caused by two factors. First, this fishery targets fish populations with limited ranges of body size and little variation in mouth size. Second, as reported by Erzini et al. (1998), the apparent lack of selectivity obtained could result from the limited size range of hooks. In our case, hook sizes differed by a factor of just 0.14. Size selectivity would likely become evident only by increasing hook size substantially.
Deep-hooking has historically been considered to be the most significant factor influencing the mortality of fish following release (Ayvazian et al., 2002; Aalbers et al., 2004; Bartholomew and Bohnsack, 2005; Broadhurst et al., 2005; St John and Syers, 2005; Butcher et al., 2006; Cooke et al., 2006). In our case, larger hooks decreased the incidence of deep-hooking, not only after pooling all species, but also for two of the most common species. Reduction in deep-hooking helps to avoid bleeding, which probably increases hooking mortality. This effect has been observed in other marine fisheries (Carbines, 1999; Bacheler and Buckel, 2004; Cooke et al., 2005). For A. butcheri, Grixti et al. (2007) concluded that increased hook size diminishes the probability of deep-hooking by a factor of 6.6. Comparatively, our results show that only for S. scriba could hook size not be used as a predictor of deep-hooking. Serranus scriba has a larger mouth and mouth area, and a hook larger than those used in this study would be necessary to investigate any effect of hook size on capture (Karpouzi and Stergiou, 2003). Hooking location did not differ between barbed and barbless hooks, as found by other authors (Schaeffer and Hoffman, 2002; DuBois and Dubielzig, 2004). The reduction in unhooking time and, consequently, in stress on fish is the most significant factor in the effectiveness of barbless hooks (Gjernes et al., 1993; Diggles and Ernst, 1997; Schill and Scarpella, 1997; Cooke et al., 2001; Bartholomew and Bohnsack, 2005). Schaeffer and Hoffman (2002) reported a decrease of 16.1–6.1 s in unhooking time with barbed and barbless hooks, respectively. In our study, the unhooking time was significantly shorter with barbless hooks, but the differences were small (<2 s). Similar results were obtained by DuBois and Dubielzig (2004).
Size-limit regulations and daily bag limits have been used in the Balearic Islands as management tools for some years. Recently, voluntary catch-and-release and its promotion at local tournaments has become popular among anglers, based on the principle that fish caught and released aid the conservation of marine resources. The effectiveness of these regulations and measures requires high rates of survival of the fish released (Arlinghaus et al., 2007). Our study demonstrates that the use of large hooks results in reduced incidence of deep-hooking and a small decrease in catch rates. The results obtained strongly support the use of large hooks because (i) they reduce hooking injuries, (ii) they do not cause a decrease in cpue, and (iii) they provide benefits to local anglers through an increase in abundance of some preferred species and an increase in mean fish size. In contrast, the use of barbless hooks results in a small reduction in unhooking time (so it was assumed that the mortality rate could be improved), but at the cost of a dramatically reduced cpue. Hence, in our case, we conclude that, unlike with the effect of hook size, the use of barbless hooks does not provide any significant advantage from a conservation perspective. However, control of hook size, along with other traditional management measures that involve the release of fish, is suggested as a good management tool for the sustainable development of recreational fisheries in the western Mediterranean.
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Acknowledgements |
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We thank the Balearic Islands Association of Sea Anglers, especially the anglers involved in the experimental procedures: P. Alós, C. Vives, M. A. Simó, and J. Llanera. Thanks are extended to a number of researchers at IMEDEA and UIB for their assistance: M. Linde, E. Ceballos, D. March, M. Cabanellas, T. Box, and A. Beltran. We also thank G. Mateu-Vicens for providing assistance and valuable comments in improving the manuscript. The study was supported by the applied research project, "Practice of the catch-and-release in sport tournaments from Balearic Islands", funded by FOGAIBA (Department of Agriculture and Fisheries of the Balearic Government) and by the research project ROQUER (CTM2005-00283), funded by Ministerio de Educación y Ciencia of the Spanish Government. We also thank E. Anderson, J. Schaeffer, and T. Rapp for their helpful comments and advice on the submitted manuscript.
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