Exploited Fish Stocks Research Articles

Population Structure, Age and Growth of Sardine (Sardina pilchardus, Walbaum, 1792) in an Upwelling Environment

Information on the biological parameters of exploited fish stocks facilitates the objective assessment and management of these living resources. The sardine (Sardina pilchardus) is considered as overexploited in northwest Africa. It is a key species of the Canaries current large marine ecosystem (CCLME) of the Atlantic Ocean due to its socioeconomic importance, as well as being a key intermediary species in marine food web. A massive decline in caught fish for Senegal over half a century is also reported (61,648 t in 1994 to 7486 t in 2017). Here, we analyzed the age and growth parameters of sardines in the Exclusive Economic Zone of northern Senegal. Maximum body size was 31 cm total length (TL). A growth performance index (φ′) and a growth rate coefficient (K) of 2.65 and 0.85, respectively, were determined, with this being the first record for this country. Sardines had higher asymptotic length (L∞, 30.5 cm TL) and age (6 years) in northern Senegal compared with Morocco (Atlantic Ocean) and the Mediterranean Sea. The asymptotic length found in Northern Senegal was also higher than in other part of the CCLME and Mediterranean Sea. This difference might be attributed to differences in the pelagic habitat, environmental factors, and/or fishing pressure. This study provides new insights towards establishing management measures, especially in data-poor fisheries and should act as an advocacy to increase sub-regional collaborations.

Move and you're dead: commercial trawl fisheries select for fish that don't move far

Abstract Recent research on harvest-induced evolution of behaviour in (especially aquatic) animals has focused on the shy-bold axis, but foraging and dispersal behaviour have received little attention. Here, we consider the selective effect of systematically localised trawl harvesting from a wild population of mobile animals that vary phenotypically in their range of movement (resulting in a continuum between wide-ranging and sedentary behaviours). We use a spatially explicit individual-based model of an empirically-based demersal fish population and trawl fishing in a realistic seascape. We test whether a sustained spatially concentrated pattern of fishing can select for or against wide-ranging vs. more sedentary behaviour as the fish perform biased random foraging in a seascape of spatially varying resource quality, leading to an approximation of the ideal free distribution. The simulation predicted a strong micro-evolutionary shift towards more sedentary behaviour as wide-ranging animals flow into a population sink caused by concentrated fishing. The shift towards short-rangers increased with fishing intensity and spatial precision with which fishing activity matches fish abundance; it decreased with habitat spatial complexity (fragmentation of suitable habitat). Most cases led to the effective extinction of the trait values at the upper end of the ranging continuum, indicating important implications for the management of exploited fish stocks.

Dispersal and seasonal movements of Pacific halibut (Hippoglossus stenolepis) in the eastern Bering Sea and Aleutian Islands, as inferred from satellite-transmitting archival tags

BackgroundUnderstanding connectivity is critical to the management of exploited fish stocks, but migratory dynamics of Pacific halibut (Hippoglossus stenolepis) in the Bering Sea and Aleutian Islands region are not well-understood. In the current study, 145 Pacific halibut ≥ 82 cm fork length were tagged with Pop-up Archival Transmitting (PAT) tags to evaluate interannual dispersal, seasonal migration, and depth-specific habitat use.ResultsEndpoint locations obtained after 1 year at liberty (n = 79), fishery recoveries after 2–3 years at liberty (n = 5), and at-liberty geopositions based on light data (n = 5313 estimates from 109 fish) indicated geographically distinct movement patterns: Pacific halibut tagged in the Western and Central Aleutian Islands remained within the island groups in which the fish had been tagged; fish in the eastern Bering Sea remained in that ocean basin, moving among International Pacific Halibut Commission (IPHC) regulatory areas and into Russian waters; those tagged south of Unimak Pass in IPHC Regulatory Area 4A displayed the greatest amount of emigration, dispersing eastward both seasonally and interannually to as far south as Washington State. Analysis of daily maximum depth and temperature data from 113 individuals demonstrated group-level variation in summer temperatures experienced by the fish and in the timing, duration, and synchrony of movement to deep-water wintering grounds.ConclusionsDepth-specific habitat use was suggestive of regionally explicit migratory contingents, while interannual dispersal patterns were consistent with the existence of multiple functional spawning units. The results may guide future research to examine cross-basin connectivity in the Northern Bering Sea and provide inputs for numerical modelling of individual movements, larval advection, and recruitment analyses.

Natural mortality in exploited fish stocks: annual variation estimated with data from trawl surveys

Abstract Natural mortality (M) is difficult to measure directly in exploited fish stocks. Therefore, in stock assessments, M has usually been assumed to be constant for age classes of fishable size. However, M is likely to vary annually due to temporal changes in food availability, predation, fish size at age, and other biological and environmental factors. We suggest that M of fish at age and year is the sum of length-related mortality and condition-related mortality (M = ML + MC). We propose that MC is directly proportional to PKH, the percentage of fish in the stock with condition factor (K) and liver condition (H) below critical values. This relationship is used to demonstrate likely patterns in annual variation in MC for ages 2–9+ in Icelandic cod (Gadus morhua) based on fish measurements in groundfish surveys in spring and autumn. There were annual fluctuations and temporal trends observed in MC for different age classes attributable to variation in food availability. The described method is suitable for age-structured stock assessments of cod and other fish stocks. Our results indicate that basic stock assessments may be improved by including estimates of variable MC.

Mesoscale assessment of sedentary coastal fish density using vertical underwater cameras

Accurate and precise monitoring of the absolute density (i.e., number of fish per area or volume unit) of exploited fish stocks would be strongly advisable for deriving stock status and for designing proper management plans. Moreover, monitoring should be achieved at relevant (i.e., sufficiently large) temporal and spatial scales. This objective is particularly challenging for data-poor fisheries, as is often the case for recreational fisheries. Therefore, the feasibility of underwater video monitoring (vertical unbaited cameras) for estimating, as a proof of concept, the absolute density (and its ecological drivers) of a coastal sedentary fish species is demonstrated. The absolute density of a small serranid (Serranus scriba) targeted by recreational fishing was estimated along the southern coast of Mallorca Island (nearly 100 km). The median fish density ranged between 111 ind/km2 (Es Molinar) and 14,110 ind/km2 (Cabrera). Absolute density was correlated with fishing exposure, habitat, and depth. Site specific, seemingly long-term, effects of fishing exposure were negatively correlated with fish density, but short-term effects (assessed by the interaction between fishing exposure and before/after the season when recreational fishing occurred in the study area) were not detected. We suggest that the short-term effects of fishing may remain undetected because highly exploited sites could contain fish that are already not vulnerable to recreational fishing gear, irrespective of the short-term fishing pressure exerted. Such a process may explain some hyper-depletion patterns and should preclude the use of fisheries-dependent data for monitoring fish density. The results reported here indicate that monitoring fish abundance with vertical unbaited cameras at large spatial and temporal scales can be a reliable alternative for many species.

Long-term increase in growth of an estuarine predator, mulloway Argyrosomus japonicus, predicted to continue under future warming scenarios

Understanding the effects of climate change on fish biology and ecology is crucial for effective management of fisheries resources. Estuaries are warming at a faster rate than nearby oceans in south-eastern Australia, yet there is little understanding of how this may impact the growth of estuarine fish. We examined long-term changes and drivers of growth in an ecologically and economically important estuarine fish in this region, the mulloway Argyrosomus japonicus, using a growth chronology spanning 39 yr (1980-2018). The chronology was developed using 3112 otoliths collected over 12° of latitude. Mixed effects models identified a long-term increase in the growth rate of A. japonicus spanning nearly 3 decades in south-eastern Australia and a positive growth response to temperature. Temperature during the months of November-February best explained this growth response, likely representing a specific growing season for the species. However, there also remained some variation in growth not explained by increasing temperature over the period. We also found evidence of faster growth in individuals sampled at both younger and older ages, potentially caused by selectivity mechanisms. Regional climate forecasts predict that, based upon the observed response to temperature, the mean annual growth rate of A. japonicus in south-eastern Australia may increase by up to 8.9% by 2099. These results add to the growing body of literature demonstrating positive growth responses by marine species in warming environments and highlight the value of understanding the drivers of long-term growth variation in exploited fish stocks in order to predict future productivity under a range of environmental and fisheries management scenarios.

Effects of Fishing on the Population of Speckled PavonCichla temensisin the Middle Negro River (Amazonas State, Brazil): A Decrease in the Size of the Trophy Fish?

AbstractFishing acts selectively on exploited fish stocks, catching larger individuals and altering age and size structure. Thus, the objective of this study was to evaluate the impacts of a multi‐use fishery in regards to the size truncation of populations of Speckled PavonCichla temensis. Data collection was carried out in the middle Negro River region, where the two modalities of recreational and commercial fishing occur with greater intensity. Questionnaires were administered to fishers in order to collect information on fishing. Individual fish were captured by recreational fishers in different rivers, were measured and weighed, and were released back into their environments. Weight (g) and TL (mm) data were used to assess the size structure at different fishing intensities. Asymmetry measurements were performed, and kurtosis of the distribution curve of the population was assessed. Linear models were also performed for both fisheries. The analysis of length distribution, asymmetry, and kurtosis showed a trend toward a decrease in the mean length of Speckled Pavon in line with the increase in fishing intensity. In linear models, the average distance (km) between fishing grounds and the fleet headquarters showed a positive relationship only for recreational fishing, which indicates that with an increasing distance from the municipality, the possibility of catching larger individuals increases and, consequently, the fishing yield also increases. The number of fishers presented a negative relationship, indicating a decrease in mean size and mean yield with increasing numbers of fishers in both modalities. The model predicted that low exploitation would cause a decline in the abundance of trophy fish. The results suggest that the Speckled Pavon population of this region exhibits signs of high exploitation and that fisheries management measures should be implemented to ensure the sustainability of stocks and fisheries that have high socioeconomic importance in the region.

Local, Seasonal, and Yearly Condition of Juvenile Greenland Halibut Revealed by the Le Cren Condition Index

AbstractAn understanding of biological characteristics, such as growth patterns, condition, and energy reserves, is important for better understanding the environmental constraints exerted on fish populations. This is especially true for exploited fish stocks in the current context of climate change. Using biological data collected from 2006 to 2009 during bottom trawl research surveys by Fisheries and Oceans Canada in the estuary and Gulf of St. Lawrence (EGSL) as well as data from 2000 to 2018 in the northwest Atlantic, we sought to improve our knowledge on the seasonal condition of Greenland Halibut Reinhardtius hippoglossoides juveniles and to better understand the divergence in some life history traits between juveniles captured in these two regions. We validated the use of the Le Cren condition index and evaluated its relationship with energetic status in juvenile (20–32‐cm TL) Greenland Halibut. In the EGSL, juvenile condition was higher in winter and spring compared to summer and fall. Such variations may result from this species’ pelagic predation activity and prey availability. Juveniles captured in the EGSL during 2016–2017 were larger but had a lower condition index than those captured in the northwest Atlantic, but we found no indication of earlier sexual maturation in the EGSL that could explain the sex ratio differences we observed in catches from these two areas.

Reproductive hyperallometry and managing the world’s fisheries

Marine fisheries are an essential component of global food security, but many are close to their limits and some are overfished. The models that guide the management of these fisheries almost always assume reproduction is proportional to mass (isometry), when fecundity generally increases disproportionately to mass (hyperallometry). Judged against several management reference points, we show that assuming isometry overestimates the replenishment potential of exploited fish stocks by 22% (range: 2% to 78%) for 32 of the world's largest fisheries, risking systematic overharvesting. We calculate that target catches based on assumptions of isometry are more than double those based on assumptions of hyperallometry for most species, such that common reference points are set twice as high as they should be to maintain the target level of replenishment. We also show that hyperallometric reproduction provides opportunities for increasing the efficacy of tools that are underused in standard fisheries management, such as protected areas or harvest slot limits. Adopting management strategies that conserve large, hyperfecund fish may, in some instances, result in higher yields relative to traditional approaches. We recommend that future assessment of reference points and quotas include reproductive hyperallometry unless there is clear evidence that it does not occur in that species.

Length-Based Assessment of Fish Stocks in a Data-Poor, Jointly Exploited (China and Vietnam) Fishing Ground, Northern South China Sea

The Beibu Gulf is one of the most important fishing grounds in the South China Sea (SCS), and the fisheries resources in this area are exploited by both China and Vietnam. In recent decades, some indications of overfishing have appeared, including declining catch rates, frequently changing catch composition, and shrinking body sizes in main commercial fish species. Due to limited data availability, only a small subset of exploited fish stocks in this area has been assessed. Here, we applied two length-based methods, electronic length frequency analysis (ELEFAN) and length-based Bayesian biomass estimation (LBB), to stock assessment of nine exploited fish species in the Beibu Gulf. There were total 53, 652 length records of 30 target stocks used in this study during the survey period from 1960 to 2015. The results showed that the two length-based methods presented different ability in estimating exploitation rate (E), and the estimated E ranged from 0.34 to 0.87 using ELEFAN method while ranged from 0.26 to 0.86 using LBB method. The prior information from ELEFAN method was effective for LBB method, as there were significant differences in 66.7% of the 30 target stocks in estimated Linf, and 93.3% in estimated B/BMSY, using LBB method with and without prior information. The estimated Lc/Lc_opt and B/BMSY of LBB method suggest a pressing situation for the fisheries in the Beibu Gulf, as 86.7% of the 30 target stocks had been suffering from growth overfishing (Lc/Lc_opt < 1), and 83.3% had been overexploited or fully exploited (B/BMSY ≤ 1.2). In addition, we suggest using both ELEFAN and LBB methods to fit length-frequency data of data-poor fish stocks because they are complementary in estimating management reference points. We also emphasize collaboration mechanism should be established by China and Vietnam for the sustainability and recovery of fishery resources in the Beibu Gulf.

Achieving sustainable and climate‐resilient fisheries requires marine ecosystem forecasts to include fish condition

AbstractMarine ecosystem forecasting is an important innovation in fisheries science with considerable value for industry and management, providing new data‐driven means of predicting the distribution and availability of commercially exploited fish stocks over a range of timescales, including near‐real‐time and seasonal. Marine ecosystem forecasting is rapidly advancing as a field, yet tools produced for fisheries to date focus primarily on predicting species distributions. The next generation of marine ecosystem forecasting products could be enhanced by also incorporating predictions of biological characteristics of fish caught, such as body condition and epidemiological status, thereby expanding the utility of these methods beyond predicting distribution alone. Improving the biological dimensions of marine ecosystem forecasting could allow for optimization of efficiencies in wild‐capture fisheries by minimizing discarding and waste and maximizing the value of landed fish. These advancements are of direct benefit to industry and management, address several of the United Nations Sustainable Development Goals pertaining to fisheries sustainability and have the potential to support the maintenance of global food and micronutrient security under rapidly changing environmental conditions. Here, we describe the current state of the art in marine ecosystem forecasting; review the physical‐biological linkages that underlie variability in the body condition of commercially valuable fish and shellfish with particular reference to marine climate change; and outline key considerations for the next generation of marine ecosystem forecasting tools for wild‐capture fisheries.

Scrabbling around for understanding of natural mortality

The authors have collaborated for the past 40 years on a sequence of initiatives for a range of fisheries and marine ecosystems projects. These had natural mortality (M) as a common thread and have helped increase understanding of this elusive parameter. Here, we provide a reprise as well as an extension of our earlier results. Taken together, these help to develop an understanding of M of exploited fish stocks, particularly those of the North Sea. Firstly, a reprisal is given of the key findings about M due to predation by important fish stocks of the North Sea. Estimates were first produced by the ICES Multispecies Working Group using multispecies virtual population analysis (MSVPA) in combination with extensive stomach content data - collected for all four quarters and around the whole North Sea during 1981. Results from this initiative demonstrate that predation mortality (M2) represents a large portion of M for many North Sea fish species, but varies markedly both by age and by year, thus refuting the then widely adopted hypothesis that M was constant. Moreover, these variations were sufficiently large to overturn single species predictions of sustainable yield. M2 results from the 1980′s also indicated that mortality levels were related to prey size and species. The paper then reprises results from studies made by the private working group (PWG) that the authors formed to continue their collaboration. These focused first on size spectra of fish communities both by data analysis and by developing a simple trait-based model (cartoon) of the North Sea - the charmingly simple model (CSM). This modelling led to further questions about the basis of the coexistence of fish species in an ecosystem given that egg production scales approximately with asymptotic weight. This led to a plausible hypothesis that differential natural mortality rates are required that increase with the von Bertalanffy parameters of curvature K and asymptotic length L∞, but decrease with fish length. Data from the literature supported this hypothesis, which was further refined into canonical form: M=K(L∞/L)1.5. However, this hypothesis is also questioned because this form might not be compatible with the predicted and observable fact that size-spectra slopes become more negative with increased general levels of fishing. Clearly, changes in size spectra should cause changes in M2. Results of new modelling work are presented where the CSM is modified to include differential natural mortality rates by K and L∞. The results suggest that M responds both to general levels of fishing and the slope of the ensuing size spectrum. This suggests that a more general expression for predation mortality would be M2=α(F)K(L∞χ)(Lβ(F)), where χ is likely to be close to the 1.5 value used in the canonical form. The work thus provides a likely form for M2 but by no means a universally applicable formula. It remains a hypothesis needing to be tested and perhaps calibrated against data from the sea. Such calibrations might indeed point toward a universal formula for M2.

Assessments of 16 Exploited Fish Stocks in Chinese Waters Using the CMSY and BSM Methods

Sixteen marine fish species (populations) exploited by Chinese fisheries were assessed, using published time series of catch and the CMSY and BSM methods. Given the catch times series as inputs, some ancillary information and reasonable constraints, carrying capacity, maximum sustainable yield, and likely time series of biomass and exploitation rate were estimated. The results show that one (7%) of the assessed species was severely depleted, four species (27%) were fully/overfished, six (40%) were outside of safe biological limits, one species (7%) was recovering and three species (20%) were in a healthy state at the end year of their assessment. However, one species, Pacific sardine (Sardinops sagax), could not be assessed using CMSY, as the exceedingly large fluctuations of its biomass were mainly environmentally driven. These results correspond with previous knowledge on the status of fish populations along the coast of China, where overfishing is rampant. Based on these assessments, some of the benefits that would result from a reduction of the excessive fishing effort are outlined.

European small pelagic fish distribution under global change scenarios

AbstractThe spectre of increasing impacts on exploited fish stocks in consequence of warmer climate conditions has become a major concern over the last decades. It is now imperative to improve the way we project the effects of future climate warming on fisheries. While estimating future climate‐induced changes in fish distribution is an important contribution to sustainable resource management, the impacts on European small pelagic fish—representing over 50% of the landings in the Mediterranean and Black Sea between 2000 and 2013—are yet largely understudied. Here, we investigated potential changes in the spatial distribution of seven of the most harvested small pelagic fish species in Europe under several climate change scenarios over the 21st century. For each species, we considered eight Species Distribution Models (SDMs), five General Circulation Models (GCMs) and three emission scenarios (the IPCC Representative Concentration Pathways; RCPs). Under all scenarios, our results revealed that the environmental suitability for most of the seven species may strongly decrease in the Mediterranean and western North Sea while increasing in the Black and Baltic Seas. This potential northward range expansion of species is supported by a strong convergence among projections and a low variability between RCPs. Under the most pessimistic scenario (RCP8.5), climate‐related local extinctions were expected in the south‐eastern Mediterranean basin. Our results highlight that a multi‐SDM, multi‐GCM, multi‐RCP approach is needed to produce more robust ecological scenarios of changes in exploited fish stocks in order to better anticipate the economic and social consequences of global climate change.

Spatiotemporal changes in demersal fish habitats suggest potential impacts of fishing pressure: A case study of yellow seabream Dentex hypselosomus in the East China Sea

We evaluated spatiotemporal dynamics of yellow seabream (YSB) in the East China Sea (ECS) from 1993 to 2018 with a delta-type approach using generalized additive models (delta-GAM). We used catch records from the Japanese bull-trawl fishery and otter-trawl surveys. The delta-GAMs incorporated several explanatory variables and predicted YSB habitats for each size category. The best models, based on the Bayesian information criterion, included all available explanatory variables: season, fishing method, temperature at 100-m depth, bottom depth and spatial and spatiotemporal effects. Temperature and bottom depth had different influences on the catch-per-unit-effort (CPUE) for each size category: there were positive effects for young fish across a wide range of temperatures and depths, whereas for adult fish the positive effects only appeared at colder temperatures and deep bottom depths. Habitat predictions showed high presence probabilities for young fish over a broader area than for adult fish through all periods. CPUEs declined for both sizes after the 2000s in the mid- to southern ECS (≤31∘N) but increased for adult fish in the north (≥31∘N). Previous studies reported that Chinese fisheries have drastically exploited fish stocks in the ECS after the 1980s and 1990s and the current fishing intensities in the mid- to southern ECS could indicate high levels, whereas Japanese vessels operated sparsely and only in the narrow area of northern region after the 2000s. These facts suggest that the different fishery exploitation rates in different locations could have significant influences on spatiotemporal patterns of YSB distributions in the ECS.

A connectivity portfolio effect stabilizes marine reserve performance.

Well-managed and enforced no-take marine reserves generate important larval subsidies to neighboring habitats and thereby contribute to the long-term sustainability of fisheries. However, larval dispersal patterns are variable, which leads to temporal fluctuations in the contribution of a single reserve to the replenishment of local populations. Identifying management strategies that mitigate the uncertainty in larval supply will help ensure the stability of recruitment dynamics and minimize the volatility in fishery catches. Here, we use genetic parentage analysis to show extreme variability in both the dispersal patterns and recruitment contribution of four individual marine reserves across six discrete recruitment cohorts for coral grouper (Plectropomus maculatus) on the Great Barrier Reef. Together, however, the asynchronous contributions from multiple reserves create temporal stability in recruitment via a connectivity portfolio effect. This dampening effect reduces the variability in larval supply from individual reserves by a factor of 1.8, which effectively halves the uncertainty in the recruitment contribution of individual reserves. Thus, not only does the network of four marine reserves generate valuable larval subsidies to neighboring habitats, the aggregate effect of individual reserves mitigates temporal fluctuations in dispersal patterns and the replenishment of local populations. Our results indicate that small networks of marine reserves yield previously unrecognized stabilizing benefits that ensure a consistent larval supply to replenish exploited fish stocks.

An integrated tagging and catch-curve model reveals high and seasonally-varying natural mortality for a fish population at low stock biomass

Rebuilding of exploited fish stocks at low biomass requires accurate mortality estimates. Weakfish (Cynoscion regalis) abundance is at historical lows caused by an increasing instantaneous total mortality (Z) in recent years, but uncertainty exists regarding the relative importance of instantaneous fishing mortality (F) and natural mortality (M) to Z. Data from a tag-return study and catch-curve of weakfish in North Carolina were analyzed jointly using a Bayesian statistical framework to estimate seasonal and annual mortality (i.e., F, M, and Z). We accounted for key auxiliary parameters in the tag-return portion of the model (i.e., tag-reporting rate and tag loss) through field studies and an experimental design, including use of high-reward tags and double tagging. Estimates of Z from the joint model were similar in magnitude to the weakfish stock assessment. From mid-2014 to 2017, we estimated a constant annual instantaneous mortality rate of 0.05 yr−1 (95 % credible interval [CrI]: 0.04, 0.07) for F and 2.33 yr−1 (CrI: 2.10, 2.6) for M. In the most recent stock assessment, estimates of M had an upper bound of 1.0; thus, our findings suggest that these estimates of M are biased low and F biased high. Our seasonal analyses showed that a large portion of mortality occurred from fall to spring, coinciding with weakfish migration and overwintering periods on the continental shelf. Through an integrated modeling approach, our study provides insights into the magnitude, timing, and sources of weakfish mortality, and enhances understanding of weakfish population dynamics to guide management strategies.

Improving the age reading of East Greenland Atlantic cod (Gadus morhua) by determining otolith growth zone timing and annuli widths

AbstractAccurate and consistent age readings are cornerstones of age‐based assessment and management of exploited fish stocks. Otoliths are the preferred structure for age determination, often performed by counting the number of completed 001 zones. Uncertainty regarding the identification of the first translucent zone and the timing of translucent zone formation can cause skewed age determination even in species with otherwise clearly defined annuli. This study addresses an inter‐institutional discrepancy in age readings of the East Greenland Atlantic cod Gadus morhua L. By analysing the opacity of the otolith margin of cod sampled monthly from February to December, it was shown that translucent zones are formed primarily during March–May. Size distributions of the dorsal–ventral and proximal–distal widths of the first three translucent zones are provided as guide to their identification. This study provides new knowledge that resolves the discrepancy in age reading of East Greenland Atlantic cod.

Assessments of 15 Exploited Fish Stocks in Chinese, South Korean and Japanese Waters Using the CMSY and BSM Methods

The status of fifteen marine fish and invertebrate populations exploited by Chinese, South Korean or Japanese fishing fleets were assessed, using two newly developed computer-intensive methods, CMSY and BSM. The results show that among these fifteen populations in question, 2 have collapsed, 3 are grossly over-fished and 9 are overfished. Also, we compared results of the CMSY and BSM methods, and it shows that, while the CPUE data for use with the BSM method lead to narrower confidence intervals and may modify the shape of the biomass trajectory, they do not lead to over- or underestimates of terminal B/BMSY values. These results, although still tentative because the methods used to generate them are relatively new, generally match what is known of the status and exploitation of the populations in question, which makes CMSY and BSM to be promising stock assessment approaches in data-sparse situations. Based on our results, a consistent signal is obtained, thus suggesting that a reduction in fishing pressure would be necessary to restore the abundance status of these fifteen populations.

Improving the interpretability of the effects of environmental factors on abundance of fish stocks

Adequately assess the environmental effects on commercially exploited fish stocks is one of the main challenges faced by stock managers in their attempt to achieve ecosystemic management. In this study, we have developed a methodology which allows simulate the evolution of abundance or biomass of a fish population and calculate two indexes (the significant effect of the environmental parameter –EF- and the relative weight index –RW-) that improve the interpretability of the environmental effects on abundance of fish stocks. This methodology is based on the assumption that under the premise of environmental invariability the variation in the abundance of a population is linearly dependent on its abundance in the past. These indexes have been integrated into a decision support system namely SFish SubClass 1.1, specifically designed to disaggregate the effects of different environmental factors on a commercially exploited fish population. We have applied our model to the fishery of Pagellus bogaraveo in a complex environmental area (Strait of Gibraltar). The results show that the developed methodology provides plausible simulations. Finally, the RW and EF indexes indicated that the most influential variables were salinity, sea temperature and salinity flux.