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Determining how resilient a stock-recruitment relationship is to environmental variation is crucial for fisheries management. Steepness is a key factor characterizing the resilience of a fish stock and, hence, for establishing management reference points. This study estimates the distribution of steepness for Pacific saury using a simulation approach based on evolutionary ecology and reproductive biology, and how it changes in response to environmental change. The median estimated steepness is 0.82 (80% probable range 0.59, 0.93) based on the best available biological information, which suggests that Pacific saury can produce a relatively high proportion of unfished recruitment when depleted to 20% of unfished spawning biomass. Elasticity analysis indicates that steepness for Pacific saury is most sensitive to the survival rate of early life stages, mean body weight, growth, and length-at-maturity. Environmental change could substantially impact steepness, with unfavorable conditions related to survival rates, length-at-maturity, mean body weight, and growth potentially leading to a reduction in resilience. Understanding these impacts is crucial for the assessment and management of Pacific saury. Our numerical simulation approach provides an analytical tool applicable for calculating the steepness distribution in other small pelagic fish influenced by increases in sea surface temperature due to global warming. [ABSTRACT FROM AUTHOR]

Impacts of biological uncertainties on estimates of stock–recruitment relationships (SRRs) in elasmobranchs such as lamniform sharks were evaluated using a numerical approach based on an age-structured model considering reproductive ecology in elasmobranchs. The values of steepness were estimated using several combinations of life history parameters for North Pacific shortfin mako to elucidate whether the numerical approach could identify reasonable values for fundamental life history parameters as well as steepness. The results of the numerical approach indicated that the mean values of steepness and their 95% confidence intervals were highly sensitive to combinations of values for growth rate, maturity ogive, longevity, reproductive cycle, and natural mortality rate. Meanwhile, the most plausible combinations of the biological parameters and values of steepness were identified based on the numerical approach with biological knowledge. The mean values and their standard deviation (SD) for steepness with the Beverton-Holt-SRR model were 0.353 (SD =0.057) and 0.273 (SD =0.046) for 2- and 3-year reproductive cycles, respectively. The numerical approach therefore has high potential to become an important tool for estimating SRR in elasmobranchs such as lamniform sharks, and the application of this approach to other elasmobranchs could greatly contribute to improvements in stock assessment and management. [ABSTRACT FROM AUTHOR]

The English Channel cuttlefish (Sepia officinalis) is the most abundant cephalopod resource in the Northeast Atlantic and one of the three most valuable resources for English Channel fishers. Depletion methods and age-structured models have been used to assess the stock, though they have shown limitations related to the model assumptions and data demand. A two-stage biomass model is, therefore, proposed here using, as input data, four abundance indices derived from survey and commercial trawl data collected by Ifremer and Cefas. The model suggests great interannual variability in abundance during the 17 years of the period considered and a decreasing trend in recent years. Model results suggest that recruitment strength is independent of spawning–stock biomass, but appears to be influenced by environmental conditions such as sea surface temperature at the start of the life cycle. Trends in exploitation rate do not reveal evidence of overexploitation. Reference points are proposed and suggestions for management of the sustainable utilization of cuttlefish in the English Channel are advanced. [ABSTRACT FROM AUTHOR]

Tjelmeland, S., and Røttingen, I. 2009. Objectives and harvest control rules in the management of the fishery of Norwegian spring-spawning herring. – ICES Journal of Marine Science, 66: 1793–1799.The main element in the management of the Norwegian spring-spawning herring, as implemented by the coastal states, is to conduct the fishery based on a maximum fishing mortality (F) of 0.125. As the appropriateness of this rule (given the stated objectives) has not yet been tested thoroughly, we set out to do this by long-term simulations, in which we applied a range of alternative stock–recruitment relationships. These different relationships are estimated from historical replicates of the stock, as calculated by the herring-stock assessment model SeaStar. During prognostic simulations, a recruitment model is selected probabilistically for each historical replicate based on Akaike weights. We evaluate whether the management objectives are met by applying the present harvest control rule. Results are given for the current assessment option of natural mortality (M = 0.5) in the oldest aggregated age group and for the assessment option used in 2005 and earlier (M = 0.15). These show that perceptions of the long-term yield differ considerably and that the current management is somewhat on the conservative side from the perspective of maximum sustainable yield. [ABSTRACT FROM PUBLISHER]

Åström M., and Dekker W. 2007. When will the eel recover? A full life-cycle model. – ICES Journal of Marine Science, 64: 000–000: –.The European eel population has declined over the past decades in most of its distribution area, and the stock is outside safe biological limits. The EU has taken up the challenge to design a management system that ensures the escapement of 40% of spawning-stock biomass, relative to unexploited, unpolluted circumstances in unobstructed rivers. This ultimately aims to restore the spawning stock to a level at which glass eel production is not impaired, i.e. to restore to full historical glass eel recruitment. To explore the trajectory from the current depleted state to full recruitment recovery, we developed a simple model of stock dynamics, based on a simplified stock–recruitment relationship and the conventional dynamic pool assumptions. Recruitment trajectories under different future fishery regimes are explored, for the medium (one generation time) and long time-span (until full recruitment recovery). Reducing fisheries to zero, recovery is expected within ∼80 years, whereas under an ultimately sustainable fishing regime of just 10% of the current rate of fishing mortality, recovery may take more than 200 years. Moreover, management regimes, apparently leading to slight recovery of the stock in the coming 5–15 years, might still be unsustainable in the long run. [ABSTRACT FROM PUBLISHER]

Kimoto, A., Mouri, T., and Matsuishi, T. 2007. Modelling stock–recruitment relationships to examine stock management policies. – ICES Journal of Marine Science, 64: 870–877. Simulation studies are used widely for fish stock management. In such studies, forecasting future recruitment, which can vary greatly between years, has become an essential part of evaluating management strategies. We propose a new forecasting algorithm to predict recruitment for short- or medium-term stochastic projections, using a stock–recruitment relationship. We address cases in which the spawning stock has dropped below previously observed levels, or in which predicted recruitment is situated close to the maximum observed level. The relative prediction error of seven existing algorithms was compared with that of the new model using leave-one-out cross-validation for 61 data sets from ICES, the Japanese Fisheries Agency, and PICES. The new algorithm had the smallest prediction error for 49 of the data sets, but was slightly biased by the precautionary treatment of predictions of high recruitment. [ABSTRACT FROM AUTHOR]

To measure and predict the response of fish communities to exploitation, it is necessary to understand how the direct and indirect effects of fishing interact. Because fishing and predation are size-selective processes, the potential response can be explored with size-based models. We use a simulation approach to describe the relationship between size spectrum slope and overall fishing mortality and to try to understand how a linear spectrum might be maintained. The model uses 15 parameters to describe a 13-“species” fish community, where species are defined by their maximum body size and the general relationship between size and life-history characteristics. The simulations allow us to assess the role of changes in the strength and type of density dependence in controlling the response to fishing, and to investigate the trade-off between catches and stock status of the different species. The outputs showed that the linear slope of the size spectrum was a function of community exploitation rate. Density-dependent controls, specifically predation mortality and the extent of compensation in the stock-recruit relationship, were key mechanisms in maintaining a linear spectrum. A linear spectrum emerged independent of the rate of compensation in the stock-recruit relationship. When this rate was low, the effects of changes in fishing mortality on predator abundance dominated those on spawning-stock biomass, whereas the dominance was reversed when the compensation rate in the stock-recruit relationship was high. The approach allows us to explore the effects of different fishing mortality schedules on properties of the fish community, to assess how fishing affects species with different life histories in mixed fisheries, and to assess the effects of selectively fishing different size classes. The simulations indicate that the size classes to be included when developing and interpreting size-based metrics must be carefully considered in relation to the trophic structure and likely strength of predatory interactions in the community. Runs with different fishing mortality by size suggest that the dynamics of predation cannot compensate fully for changing rates and patterns of exploitation, implying that the effects of selectively fishing different size classes should be assessed on a case-by-case basis. [Copyright &y& Elsevier]

The relationship between spawning stock and recruitment in penaeid shrimp fisheries has been questioned because they exhibit unique characteristics with respect to population dynamics and fisheries. This study used meta-analyses to test the null hypothesis that recruitment is a series of random, independent events based on the penaeid shrimp stocks found in published sources. Both the derivative hypothesis test and Granger causality test rejected the null hypothesis. Thus, recruitment is related to spawner abundance. Shrimp populations should be managed so as to maintain sufficient spawning stock abundance to yield high recruitment. [ABSTRACT FROM PUBLISHER]