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Catch rates and sizes of hingebeak shrimp Rhynchocinetes uritai Kubo, 1942 were studied with two types of traps: bait traps that were exposed for 1-2 days and unbaited "refuge traps" exposed for 2-4 weeks. Shrimp were collected twice a month from June 2010 to May 2012 on rocky substrata in Oura Bay, Shimoda, Japan. Overall the numbers of shrimp caught did not differ between the two trap types, but when adjusted for soak times, the bait traps had substantially higher catch rates than the refuge traps. Addition of light to the bait traps had no significant effect on catch rates. However, shrimp in the baited traps were significantly larger than those in the refuge traps. The results show that size distribution can be greatly affected by trap type. Consequently, using two types of traps simultaneously increases not only the catch efficiency but also ensures that all sizes of the reproductively mature shrimp population are sampled in adequate numbers, which is especially important in protandric hermaphrodites. [ABSTRACT FROM AUTHOR]

This Comment was prompted by the substantial difference in weir catch estimates in the Gulf between (i) those reported by Al-Abdulrazzak and Pauly (2014. Managing fisheries from space: Google Earth improves estimates of distant fish catches. ICES Journal of Marine Science, 71(3), 450–454), who used Google Earth to count weir numbers, and (ii) those available from official national statistics provided by two major weir fishing countries (Bahrain and Iran). Satellite imageries, including Google Earth, are powerful tools for collecting data on visible structures when verified with adequate ground validation. However, an extension of their contribution to improving overall catch estimates is rather limited without having solid information on daily catch, which will substantially differ according to time and area, and fishing season lengths. It was noted that Al-Abdulrazzak and Pauly (2013) introduced positive biases through their interpretation of Google Earth images and data treatment. They included several assumptions, such as removing the impact of poor visibility, correcting grids of low resolutions, estimating number of unseen weirs, and applying daily catch rates higher than referenced observed values. The overall extent of such potential positive bias could be more than six times that which we considered reasonable. This Comment also corrects misconceptions about “FAO catch data”, discusses other available national data, and introduces the existence of the Regional Commission for Fisheries (RECOFI), a mechanism for fisheries management in the Gulf region, and its recent activities to collect more complete catch and effort data separated by gear. [ABSTRACT FROM PUBLISHER]

Recreational fishing effort greatly fluctuates in space and time. Therefore, one of the most relevant conceptual issues when managing recreational fishing is to understand the primary complexities associated with anglers' preferences in selecting site and day, and the way that these choices affect the catch. However, two practical pitfalls (data acquisition and statistical issues) are hampering progress towards the understanding of this problem. In this study, we propose several strategic improvements and apply them to the recreational squid fishery in Palma Bay (Balearic Islands). The spatial scenario (20 km width) was surveyed 63 times (visual censuses) during two years. For each of the 173 grid cells (1 km2) into which Palma Bay was divided, the fishing effort (number of recreational boats targeting squid) was recorded. In addition, a number of variables intended to summarize any potential driver of anglers' choices were also recorded. The principal drivers of squid recreational fishing in Palma Bay appeared to be expected harvest and distance to the nearest port, but the effect of these variables was clearly modulated by sea conditions. The fine-scale estimates of effort (daily predictions for each 1 km2 cell) provided here represent the first step towards understanding angler preferences, estimating total catches, and selecting the best management options for avoiding conflicts between stakeholders, thus ensuring resource sustainability. [ABSTRACT FROM PUBLISHER]

Fisheries management agencies and fishing industry representatives depend on reliable estimates of fish biomass and mortality for the determination of sustainable catch levels. Lack of data or misreporting may be reasons for unreliable stock assessment, which, in turn, may result in advice that does not reflect the availability of fisheries resources. It has been suggested that the mixed pelagic trawl fisheries in the Baltic represent a case of biased estimates of fish biomass and mortality resulting from misreporting. Here, we estimate the degree of misreporting in the Swedish pelagic fishery (1996–2009) and propose an approach for reconstructing historical catches based on commercial effort data. The analysis suggests that total catches have been underestimated during part of our study period and that systematic misreporting of species composition has taken place over the whole study period. The analysis also suggests that there is overcapacity in the fishery and that such economic incentive could explain the general patterns of misreporting. Applying our method for fisheries with suspected misreporting could significantly improve assessment accuracy, reduce uncertainty and thereby allow for a better link between catches and resource levels. [ABSTRACT FROM PUBLISHER]

Fish aggregating devices (FADs) are deployed to aggregate fish over a limited area to improve fish catch. Fish enhancing devices (FEDs), which are FADs deployed in no-fishing areas, are fast gaining popularity as a fisheries management tool in the western Pacific. Yet, the impacts of utilizing FADs and FEDs are not yet well understood. In this work, we used a mean-field model to assess the effects of utilizing FADs and FEDs on stock biomass and catch. Our results indicate that using FADs enhances catch per boat when total fishing pressure is low, but can exacerbate fishery collapse when fishing effort is high. On the other hand, a FED-based system can increase the resistance of the fishery to collapse. A FED-based fishery may thus serve as pelagic marine protected areas and/or refugia. In a quota-based system, where fishing time is tied to catch quota, a phase transition occurs: both catch and biomass abruptly shift to low levels without warning. Deploying FADs to act as FEDs in a high quota fishery can prevent this phase transition resulting to a stabilizing effect. [ABSTRACT FROM PUBLISHER]

Torniainen, J., Vuorinen, P. J., Jones, R. I., Keinänen, M., Palm, S., Vuori, K. A. M., and Kiljunen, M. 2014. Migratory connectivity of two Baltic Sea salmon populations: retrospective analysis using stable isotopes of scales. – ICES Journal of Marine Science, 71: 336–344.Migratory connectivity refers to the extent to which individuals of a migratory population behave in unison, and has significant consequences for the ecology, evolution and conservation of migratory animals. We made a retrospective assessment of the migratory connectivity of River Simojoki and River Kymijoki populations of Atlantic salmon Salmo salar L. by using stable isotope analysis of archived scales to identify the final feeding areas used before ascending rivers for spawning. We also tested differences in migratory connectivity between wild and hatchery-reared salmon and compared Carlin-tag recoveries with salmon scale stable isotope analysis as methods for studying salmon migrations. Stable isotope (δ13C, δ15N) values from the last growth region of scales from salmon caught ascending their natal rivers were compared via discriminant analysis with those from scales of salmon caught in different Baltic Sea areas during 1989–2011. Most River Simojoki salmon had likely fed in the Baltic Proper (mean ± SD for ascending fish probability 0.59 ± 0.32) with secondary likely feeding areas in the Bothnian Sea (0.21 ± 0.26) and the Gulf of Finland (0.20 ± 0.27). Most River Kymijoki salmon had likely fed in the Gulf of Finland (0.71 ± 0.42) with the Baltic Proper (0.29 ± 0.41) a secondary feeding area. The results did not indicate the Bothnian Sea to be an important feeding area. The two salmon populations showed weak migratory connectivity and rather fixed areal preference throughout the record irrespective of wild or stocked origin. Although the results from the scale stable isotope analyses were broadly consistent with previously reported Carlin-tag recoveries, we argue that the stable isotope approach offers several important advantages in the study of salmon migratory behaviour. [ABSTRACT FROM PUBLISHER]

Smith, A. D. M., Smith D. C., Haddon, M., Knuckey, I., Sainsbury, K. J., and Sloan, S. 2014. Implementing harvest strategies in Australia: 5 years on. – ICES Journal of Marine Science, 71: 195–203.Australian Commonwealth fisheries are managed using a formal harvest strategy policy (HSP) introduced by the federal government in 2007. At the State level, a number of commercial fisheries are also managed under formal harvest strategies, but no overarching policy currently exists to guide their consistent implementation across jurisdictions. There have been 5 years of experience with implementation of the Commonwealth policy across the highly diverse array of commercial fisheries found in Australia. The HSP has an explicit target of maximum economic yield, and an explicit limit set at half the biomass that would support maximum sustainable yield. The policy also specifies an acceptable level of risk associated with falling below the limit reference point. We discuss the experience gained from implementing the HSP in Australia, including a number of challenges faced, and attempt to summarize the benefits and costs of implementing harvest strategies. Our view is that, overall, the benefits clearly outweigh the costs. [ABSTRACT FROM PUBLISHER]

Vinther, M., and Eero, M. 2013. Quantifying relative fishing impact on fish populations based on spatio-temporal overlap of fishing effort and stock density. – ICES Journal of Marine Science, 70: 618–627.Evaluations of the effects of management measures on fish populations are usually based on the analyses of population dynamics and estimates of fishing mortality from stock assessments. However, this approach may not be applicable in all cases, in particular for data-limited stocks, which may suffer from uncertain catch information and consequently lack reliable estimates of fishing mortality. In this study we develop an approach to obtain proxies for changes in fishing mortality based on effort information and predicted stock distribution. Cod in the Kattegat is used as an example. We use GAM analyses to predict local cod densities and combine this with spatio-temporal data of fishing effort based on VMS (Vessel Monitoring System). To quantify local fishing impact on the stock, retention probability of the gears is taken into account. The results indicate a substantial decline in the impact of the Danish demersal trawl fleet on cod in the Kattegat in recent years, due to a combination of closed areas, introduction of selective gears and changes in overall effort. [ABSTRACT FROM PUBLISHER]

Fernández-Boán, M., Freire, J., Parma, A. M., Fernández, L., and Orensanz, J. M. 2013. Monitoring the fishing process in the sea urchin diving fishery of Galicia – ICES Journal of Marine Science, 70: 604–617.The assessment and management of small-scale benthic fisheries requires attention to the spatial structure of stocks and patterns of effort allocation. Spatial information helps in the interpretation of fisheries data, and is required for designing spatially explicit management strategies, often prescribed in the case of benthic fisheries. Monitoring of boats with GPS, combined with port interviews, was evaluated as an approach to investigate the spatial pattern of fishing intensity and catch per unit of effort (CPUE) in the sea urchin (Paracentrotus lividus) diving fishery from Galicia, Spain. Fishing opportunities (FOs), relatively small regions of high fishing intensity, were identified and mapped at a fine scale. New FOs were first visited at an approximately constant rate. Concentration analysis shows that effort intensity was not uniformly distributed within FOs. CPUE did not exhibit a significant trend throughout the season, either at the scale of the aggregated fishery or within individual FOs. Catch per area and area covered per unit of diving time were inversely related, indicating that fishers stay longer in high-density patches. While abundance is the primary driver of effort allocation, other factors contributing to suitability were identified. Based on these results, we discuss realistic options for the monitoring of this and comparable fisheries. [ABSTRACT FROM PUBLISHER]

Benoît, H. P., Plante, S., Kroiz, M., and Hurlbut, T. 2013. A comparative analysis of marine fish species susceptibilities to discard mortality: effects of environmental factors, individual traits, and phylogeny. – ICES Journal of Marine Science, 70:99–113.Determining the sustainability of fishing mortality for discards requires information on discard amounts as well as capture and release mortality rates. Formal estimates of these rates are costly and only available for a limited number of species and fisheries. In their absence, proxies for discard mortality could inform risk assessments of fishing mortality sustainability for discarded species. Here, time-to-mortality (TM) was assessed for 48 marine fish species exposed to air following capture during an annual multi-species bottom-trawl survey. Species-specific estimates of TM were related qualitatively to more formal estimates of discard mortality from commercial fisheries, confirming the use of TM as a proxy. The effects on TM of species and individual traits, phylogenetic similarity (proxy for traits not explicitly included in the analysis) and environmental factors related to capture were also assessed. Much of the observed individual variability was explained by intraspecific and interspecific positive relationships between body size and TM. Sedentary species and those lacking a gas bladder or deciduous scales had greater TM. Effects of phylogeny and capture depth and temperature were also found. This study demonstrates how reliable proxies of discard mortality rate can be readily obtained in the field or estimated from relevant covariates. [ABSTRACT FROM PUBLISHER]

Cox, M. J., Watkins, J. L., Reid, K., and Brierley, A. S. 2011. Spatial and temporal variability in the structure of aggregations of Antarctic krill (Euphausia superba) around South Georgia, 1997–1999. – ICES Journal of Marine Science, 68: .Antarctic krill are important in the South Georgia (54°S 35°W) marine ecosystem. They form aggregations that vary widely in packing density (<1 to 1000 s of individuals m−3), length (tens to thousands of metres), and height (tens of metres). Acoustic surveys are often used to estimate krill biomass and provide data that give insight into aggregation structure. Using dual-frequency (38 and 120 kHz) acoustic data collected during six surveys conducted around South Georgia during the 1997, 1998, and 1999 austral summers, we isolated 2990 aggregations by applying the Shoal Analysis and Patch Estimation System algorithm in Echoview and a krill-length-dependent acoustic identifier (ΔSv120–38). Multivariate cluster (partition) analysis was applied to metrics from each of the aggregations, resulting in three aggregation types with an overall proportional split of 0.28:0.28:0.44. Types 1 and 3 had low mean densities (<2 g m−3), whereas Type 2 had a mean density of 94 g m−3. Intersurvey differences were found between the effort-corrected numbers of aggregation types (p = 2.5e−6), and between on- and off-continental shelf areas (p = 1.5e−7), with a greater number of Type 2 aggregations being found on-shelf. The findings suggest intersurvey variation in krill catchability, with krill being more likely to be caught on-shelf. [ABSTRACT FROM PUBLISHER]

Bahamon, N., Sardà, F., and Aguzzi, J. 2009. Fuzzy diel patterns in catchability of deep-water species on the continental margin. – ICES Journal of Marine Science, 66: 2211–2218.Exploited deep-water fish communities on continental margins are poorly understood in terms of variations in species composition and abundance by depth and season as a response to diel changes in light intensity and length of photoperiod. Innovative fuzzy clustering and traditional agglomerative hierarchical clustering methods were applied to data from bottom trawls collected continuously for 4 d in October and June, on the shelf (100–110 m) and upper slope (400–430 m). Fuzzy clustering was more effective than hierarchical clustering at characterizing diel variations in catches from the upper slope because the species assemblage did not show a distinct day and night structure. On the shelf, the species assemblages shifted abruptly between a diurnal and a nocturnal structure at sunset and sunrise, and the two clustering methods yielded similar results. Endobenthic decapods with marked crepuscular-nocturnal emergence from the substratum were mostly responsible for this pattern. No clearly discernible diel pattern was found with the dampening of light intensity with depth, weakening the behavioural response of endobenthos to the day–night cycle. The results indicated that the regulatory effect of the light cycle on diel activity rhythms weakens with depth. [ABSTRACT FROM PUBLISHER]

Mullers, R. H. E., Navarro, R. A., Crawford, R. J. M., and Underhill, L. G. 2009. The importance of lipid-rich fish prey for Cape gannet chick growth: are fishery discards an alternative? – ICES Journal of Marine Science, 66: 2244–2252.A recent decline in population numbers of Cape gannets (Morus capensis) breeding off the west coast of South Africa coincided with decreased availability of lipid-rich fish prey: anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax). Seabirds can use fishery discards as an alternative, but the quality of this food in the Benguela ecosystem is lower than that of their natural prey species. We consider whether chick growth and survival during chick rearing co-vary with the periods of high and low availability of their lipid-rich prey species and whether fishery discards would be an alternative. The proportion of anchovy and sardine in the diet was between 66 and 84% in the years 1986–1988, but just 16–35% from 2004 to 2006. Months with large proportions of anchovy and sardine in the diet were associated with faster chick growth. No association between the proportion of fishery discards in the diet and chick growth was found. The patterns are consistent with the notion that a distributional shift of anchovy and sardine decreased their contribution to the diet of Cape gannets and slowed chick growth along with lessening chick survival at the breeding colony. The reduced survival may partially explain the decline in numbers of Cape gannets breeding in the southern Benguela. [ABSTRACT FROM PUBLISHER]

MacCall, A. D. 2009. Depletion-corrected average catch: a simple formula for estimating sustainable yields in data-poor situations. – ICES Journal of Marine Science, 66: 2267–2271.The depletion-corrected average catch (DCAC) formula is an extension of the potential-yield formula, and it provides useful estimates of sustainable yield for data-poor fisheries on long-lived species. Over an extended period (e.g. a decade or more), the catch is divided into a sustainable yield component and an unsustainable “windfall” component associated with a one-time reduction in stock biomass. The size of the windfall is expressed as being equivalent to a number of years of sustainable production, in the form of a “windfall ratio”. The DCAC is calculated as the sum of catches divided by the sum of the number of years in the catch series and this windfall ratio. Input information includes the sum of catches and associated number of years, the relative reduction in biomass during that period, the natural mortality rate (M, which should be <0.2 year−1), and the assumed ratio of FMSY to M. These input values are expected to be approximate, and based on the estimates of their imprecision, the uncertainty can be integrated by Monte Carlo exploration of DCAC values. [ABSTRACT FROM PUBLISHER]

MacNeil, M. A., Carlson, J. K., and Beerkircher, L. R. 2009. Shark depredation rates in pelagic longline fisheries: a case study from the Northwest Atlantic. – ICES Journal of Marine Science, 66: 708–719. A suite of modelling approaches was employed to analyse shark depredation rates from the US Atlantic pelagic longline fishery. As depredation events are relatively rare, there are a large number of zeroes in pelagic longline data and conventional generalized linear models (GLMs) may be ineffective as tools for statistical inference. GLMs (Poisson and negative binomial), two-part (delta-lognormal and truncated negative binomial, T-NB), and mixture models (zero-inflated Poisson, ZIP, and zero-inflated negative binomial, ZINB) were used to understand the factors that contributed most to the occurrence of depredation events that included a small proportion of whale damage. Of the six distribution forms used, only the ZIP and T-NB models performed adequately in describing depredation data, and the T-NB and ZINB models outperformed the ZIP models in bootstrap cross-validation estimates of prediction error. Candidate T-NB and ZINB model results showed that encounter probabilities were more strongly related to large-scale covariates (space, season) and that depredation counts were correlated with small-scale characteristics of the fishery (temperature, catch composition). Moreover, there was little evidence of historical trends in depredation rates. The results show that the factors contributing to most depredation events are those already controlled by ships' captains and, beyond novel technologies to repel sharks, there may be little more to do to reduce depredation loss in the fishery within current economic and operational constraints. [ABSTRACT FROM PUBLISHER]

Cutter, G. R. Jr and Demer, D. A. 2007. Accounting for scattering directivity and fish behaviour in multibeam-echosounder surveys. – ICES Journal of Marine Science, 64. Multibeam echosounders can improve the efficiency and the precision of acoustic-survey estimates by providing greater sampling volumes than single-beam echosounders. For a multibeam echosounder, the target strength of fish can vary with its pitch, roll, and yaw. Here, normalized, acoustic backscatter patterns from fish schools are modelled by beam-incidence angle,0–180°, considering the scattering-directivity patterns of each fish. Variation of pitch angle causes a decrease in the mean and an increase in the variance of the backscatter in the vertical beam, but has no effect on the backscatter in the outer beams. Conversely, variation of the yaw causes a decrease in the mean and an increase in the variance of the backscatter in only the outer beams. Because the fish-scattering model predicts different backscatter at dorsal- vs. lateral-incidence angles, backscatter did vary with roll angle. In the hypothetical case of fish avoiding a vessel, the backscatter decreases strongly the outer beams. The results of the model were compared with multibeam measurements of fish schools. In general, the measured mean backscatter vs. beam-incidence angle was nearly uniform. The methods described here provide an approach to accounting for scattering directivity and fish behaviour in multibeam-echosounder surveys. [ABSTRACT FROM PUBLISHER]

Friedland, K. D., Miller, M. J., and Knights, B. 2007. Oceanic changes in the Sargasso Sea and declines in recruitment of the European eel. – ICES Journal of Marine Science, 64: 519–530. Anguillid eel recruitment in the North Atlantic has declined in recent decades, raising concerns that climatic changes in the Sargasso Sea may be influencing oceanic reproduction and larval survival. There is a significant negative correlation between the North Atlantic Oscillation and long-term variations in catches of glass eel stages of the European eel Anguilla anguilla recorded by the fishery independent Den Oever recruitment index (DOI) in the Netherlands, lagged by one year. Ocean-atmospheric changes in the Sargasso Sea may affect the location of spawning areas by silver eels and the survival of leptocephali during the key period when they are transported towards the Gulf Stream. A northward shift in a key isotherm (22.5°C), defining the northern boundary of the spawning area, a declining trend in winds and transport conditions in larval transport areas, and a shallowing of the mixed layer depth could affect primary productivity in areas where leptocephali feed. The relationships between these ocean parameters and the DOI suggest that these changing ocean conditions could be contributing to declining recruitment of the European eel and probably also of the American eel (A. rostrata), but anthropogenic factors during their continental life stage must also be considered. [ABSTRACT FROM PUBLISHER]

Karlson, A. M. L., Almqvist, G., Skóra, K. E., and Appelberg, M. 2007. Indications of competition between non-indigenous round goby and native flounder in the Baltic Sea. – ICES Journal of Marine Science, 64: 479–486. The Ponto-Caspian round goby (Neogobius melanostomus) was introduced to the Gulf of Gdańsk, southern Baltic Sea, in the late 1980s, and it has now become the dominant demersal fish species in shallow water. This study aimed to assess diet preferences and the degree of diet overlap between the round goby and the native flounder (Platichthys flesus). Results from time-series of stomach contents and stable isotope analyses of wild-caught fish, together with prey preference experiments carried out in the laboratory, showed that the two species consumed similar species and sizes of prey. The similarities in diet suggest potential for food competition. Catch data showed both reverse depth distributions of round goby and flounder when round gobies were abundant and that the abundances of the two species were negatively correlated. The diet overlap between small flounders and round gobies was greatest when goby abundance was least, suggesting that abundance of round gobies may restrict flounder habitat utilization and, therefore, also food availability to the latter. Therefore, round gobies may have a negative influence on the commercially important flounder. [ABSTRACT FROM PUBLISHER]

Mills, C. M., Townsend, S. E., Jennings, S., Eastwood, P. D., and Houghton, C. A. 2007. Estimating high resolution trawl fishing effort from satellite-based vessel monitoring system data. – ICES Journal of Marine Science, 64: 248–255. High resolution estimates of trawling effort are needed to underpin studies of trawling impacts on species, habitats, and ecosystem processes, and to monitor responses to area closure and other management actions. Satellite-based vessel monitoring systems (VMS) were designed for fishery control and enforcement, but they provide potentially valuable source information on spatial and temporal patterns of trawling activity at multiple scales. Based on an analysis of VMS data for UK beam trawlers in the North Sea, a method is described for identifying trawling activity and estimating fishing intensity based on the minimum and maximum potential spatial extent of trawling effort from VMS data. The optimal method for identifying trawling and steaming behaviour combined speed and directionality rules and correctly identified trawling and steaming in 99% and 95% of cases, respectively. Using speed- and directionality-filtered VMS data, trawling effort can be reported as area impacted per unit time per unit area at a range of grid scales from 1 km to 100 km (10 000 km2). Trawling effort is accurately represented at a grid cell resolution of 3 km or less. [ABSTRACT FROM PUBLISHER]

There has been a fishery for the great scallop, Pecten maximus, around the Isle of Man, since 1937. Research up to the end of the 1980s suggested that these scallop stocks were in continuous decline. The fishery is now largely dependent on the strength of each recruiting year-class, placing it at considerable risk from recruitment failure. This study utilised data on the spat settlement, age structure, abundance and commercial catch rates of scallops, collected between 1975 and 2001, to examine recent population dynamics and the potential for predicting future catch rates. Spat settlement was generally low, but there were two exceptionally strong year-classes. Surveys of the stock revealed high exploitation rates during each fishing season (November to May inclusive) with variable recovery due to recruitment by the following October. In 1997/1998, scallop catch rates reached a 20-year high on several grounds and have generally remained high since. The strong spat settlements in 1989 and particularly 1994 were largely responsible for recent rises in catch rates, although the maintenance of high catch rates between 1999 and 2001 has occurred despite poor spat settlement between 1995 and 2000. Within stock surveys, the density of 2-year-old scallops was generally an accurate predictor of the density of 3- and 4-year-old scallops, 1–2 years later. The nature and strength of these relationships varied considerably between fishing grounds due to spatial variation in both scallop biology and patterns of exploitation. Results from fishery independent surveys did not always correlate well with commercial catch rates, however, suggesting the need for an expansion of the survey on some grounds. Overall, our study indicated that current levels of exploitation appear to be sustainable in the Isle of Man scallop fishery. Our results also demonstrated that monitoring of both spat settlement and the abundance of juveniles has considerable potential for predicting future catch rates of commercial sized scallops. [Copyright &y& Elsevier]

In longline fisheries, decreasing the catch of undersized fish and minimizing the rate of gut-hooking over all sizes will reduce incidental mortality, and improve the landed value of the commercial catch. In this study, standard Tainawa 16R longline hooks were simultaneously fished for snapper (Pagrus auratus) with the same hook pattern modified by the addition of 20-mm and 40-mm wire appendages. The experimental design also included three bait types. Gut-hooking rates were markedly lower on modified hooks relative to normal hooks. Normal hooks gut-hooked 17% and 30% (pooled across baits) of snapper caught in January and June, respectively, whereas 20-mm modified hooks gut-hooked 7% and 12%, and 40-mm hooks gut-hooked only 2% in both seasons. Overall catch rates were significantly lower on modified hooks, however most of the loss of catch comprised undersized fish and “deads” (unsuitable for export). There was no significant reduction in the weight of export-quality snapper landed using modified hooks. Modified hooks reduced both the catch rate and gut-hooking rate of undersized snapper. If it is assumed that all gut-hooked discards are likely to die, the estimated annual reduction in discard mortality at the stock level would be 78% if 20-mm hook modifications are used, and 96% if 40-mm modifications are used. These estimates are consistent for scenarios where minimum legal size is set at both 25 cm and 27 cm, however they are based on the assumption that observed catch and mortality rates are representative of the commercial fishery. [ABSTRACT FROM PUBLISHER]

A comparison of catch rates of demersal fish during beam trawl and otter trawl surveys carried out in the period 1990–1995 and 1906–1909 indicates lower abundance in recent years for the total assemblage as well as for individual groups. There appear to have been shifts in the community associated with reduced diversity and evenness indices. Length-frequency distributions of roundfish and flatfish show a shift towards smaller-sized fish. [ABSTRACT FROM PUBLISHER]

The exploitation history of North Sea plaice is reconstructed from the late 1800s to 1993 using data on catch per unit of effort, total international landings, size and age composition of landings, and growth rate. Available data indicate that fishing mortality was already high in the 1890s (Fu=0.4) and increased to a record high in the late 1920s and early 1930s (F=0.8). After World War II, fishing mortality was reduced, but from the 1960s onwards it increased steadily to a level of F=0.6 in the early 1990s. Indices of catch per unit of effort during the last quarter of the 19th century are concurrent with the expansion of the fisheries. Stock biomass was at a low level in the 1930s but increased between the 1960s and 1980s owing to increased recruitment and improved growth. Landings were fairly stable around 55 000 t until the mid-1950s when they increased almost threefold to a record level of 170 000 t in 1989. The causes of these changes are discussed. It is suggested that changes in both growth rate and exploitation rate in young fish have been important. [ABSTRACT FROM PUBLISHER]

The species and size selectivity of long-lines using small hooks were studied off the south coast of Portugal using “Mustad” brand round bent, flatted sea hooks (Quality 2316 DT) numbers 15, 13, and 11 baited with razor shell clam (Ensis siliqua). Hook numbers 13 and 11 are 49 and 109% larger respectively than number 15 hooks in terms of overall size (maximum width × maximum length). A total of 39 900 hooks were fished in 45 sets and 35 species of fish and cephalopods were caught. As a group, 13 species of sea breams (Sparidae) dominated the catch by numbers (58%) and weight (73%). Six species of sea breams, along with the greater weever fish (Trachinus draco) accounted for 81% of the total catch by weight, with the common or white sea bream (Diplodus sargus) being the most important (29%). Catch size distributions by hook size were, in general, highly overlapped for all species and hook size had little apparent effect on minimum size at capture. All hooks caught a wide range of sizes per species, but the catch rate (number of fish per 100 hooks) was significantly lower for the largest hook. Except for the black sea bream (Spondyliosoma cantharus), capture of illegally sized or immature fish was minimal. Small increases in average size with hook size were evident for four species: Diplodus sargus, D. vulgaris, Lithognathus mormyrus and Serranus cabrilla. No differences in size selectivity were detected for Boops boops, D. annularis, Spondyliosoma cantharus and Trachinus draco. A skew-normal model adequately described differences in size selectivity in five of six species. [ABSTRACT FROM PUBLISHER]

Choosing a location for fishing is the major short-run decision made by the skipper of a fishing vessel. Because the spatial density of fish is not uniform everywhere, where a skipper decides to fish largely determines the size and value of his catch. For that to be a rational decision, the skipper must consider not only the catches he is likely to make at different locations but also the costs incurred in fishing at those locations. As a consequence the catch rates and the catch per unit effort observed in a fishery depend not just on fish stock abundance but also on economic factors such as wage rates and fish and fuel prices. This paper develops some simple theoretical models for examining a fisherman's selection of fishing location. The spatial distribution of the fish stock is reduced to a single dimension, distance from port, and it is assumed that fish density increases linearly with distance from port and that the relative densities remain constant regardless of the absolute level offish stock abundance. If a skipper operates his vessel further from port, he gains access to greater densities offish and higher instantaneous catch rates but uses more fuel and time for travel. A skipper can maximize his share of the fishing profits by operating his vessel at a particular distance from port. The skipper operates within constraints which determine the form of the revenue and cost functions. Two models are considered. In the first, the duration of a fishing trip is constrained by the size of the fish hold or by some other limit to the amount of fish that can be landed; each fishing trip continues until the hold is filled. In this case catch and revenue per trip are constant but the fishing costs vary non-linearly with distance from port. Here the catch per unit effort (c.p.u.e., catch per trip divided by time spent fishing per trip) is a non-linear function of the total biomass of the fish stock but the c.p.u.e. is independent of the price offish. In the second model, there is a time constraint; to fill the hold would take too much time. In this case each trip is of a fixed duration and catch and revenue per trip are quadratic functions of distance from port and operating costs vary linearly. Here c.p.u.e. is a linear function offish stock biomass and a non-linear function offish price. [ABSTRACT FROM PUBLISHER]