Recruitment Forecasting Research Articles

Recruitment forecasting using indices of young-of-the-year Pacific herring (Clupea pallasi) abundance in the Strait of Georgia (BC)

Abstract Schweigert, J. F., Hay, D. E., Therriault, T. W., Thompson, M., and Haegele, C. W. 2009. Recruitment forecasting using indices of young-of-the-year Pacific herring (Clupea pallasi) abundance in the Strait of Georgia (BC). – ICES Journal of Marine Science, 66: 1681–1687. Within the Strait of Georgia (BC, Canada), recruitment of Pacific herring (Clupea pallasi) to the spawning stock at age 3 can be highly variable, and this component may compose a major portion of the spawning-stock biomass. Therefore, a reliable method of forecasting recruitment strength would be useful for determining total allowable catches for the fishery. We developed an empirical approach to forecasting recruitment from young-of-the-year (YOY) surveys using purse-seine sampling in late September and evaluate its predictive capability for estimating the relative size of a year class before it enters the fishery. For each year, we compared YOY catches-by-weight with the number of age-3 recruits derived from subsequent catch-at-age analyses. The relationship is positive but not statistically significant because of considerable annual variation in the estimates. However, it is worth noting that in years when YOY herring were least abundant, the resulting cohort also was low. Consequently, although the relationship may not be sufficiently precise for accurate recruitment forecasting, it can be used by fishery management for the qualitative evaluation of the likelihood of strong or weak returns in future seasons when setting quotas for the fishery.

Uncertainties in population dynamics and outcomes of regulations in sockeye salmon (Oncorhynchus nerka) fisheries: implications for management

Fisheries managers usually have multiple options available but are often unclear on how to choose among them owing to uncertainties in biological and management components of fisheries systems. We evaluated the performance of current and possible future assessment and management practices for sockeye salmon ( Oncorhynchus nerka ) in British Columbia and Alaska by using a computer model that included major biological and management components and their associated uncertainties (interannual variability in recruitment, age-at-maturity, and sex ratio, as well as uncertainty in observations of spawner abundances, forecasts of recruitment, and outcomes from implementing management regulations). One option for management practices that we evaluated was designed to make the forecasting model more realistic by accounting for long-term trends in age-at-maturity. A second option was designed to reduce deviations between management targets and actual or “realized” harvest levels. We found that compared with practices that ignore those sources of uncertainty, the second option produced annual catches that were higher, on average, and less variable over time while maintaining recruitment above critical conservation levels. Contrary to our expectations, the first modification did not result in comparable benefits. Our results demonstrate the value of using simulation models to evaluate potential modifications to Pacific salmon management practices.

Recruitment prediction for Pacific herring ( Clupea pallasi) on the west coast of Vancouver Island, Canada

The accurate prediction of recruitment to the fishery is a very important tool within the management structure of any fish stock being exploited. In the case of the Pacific herring, Clupea pallasi, fishery in Canada, a forecast of the abundance of each herring stock is particularly important for formulating an annual catch quota. The sustainable management of the fishery and the resource is based in part on accurate recruitment forecasting because Pacific herring are short-lived and so the recruitment contributes a significant part of the total spawning run targeted by the fishery each year. Several factors are believed be important in determining the success of recruitment besides spawners biomass. Since herrings are “r” strategists, conditions related to the egg, the planktonic, or even the juvenile stage might determine the future level of recruitment. Recently a formula that defines conditions for a semi-quantitative level of recruitment forecast was elaborated using genetic algorithms and current study attempts to improve on this model. Using salinity in two quarterly periods during the planktonic and pre-recruit stages, temperature and spawning biomass for the west coast of Vancouver Island stock, classification rules that define recruitment in 3 different levels (low, medium and high) were developed with a genetic algorithm, setting low and high boundaries for each condition. A 75% success in classifying recruitment was obtained. The model was shown to be particularly effective at predicting when the recruitment would be low, which could be important from the perspective of the Precautionary Approach and the sustainable management of this stock.

On the prediction of short term changes in the recruitment of North Sea cod (<i>Gadus morhua</i>) using statistical temperature forecasts

Empirical evidence supports the hypothesis of a general relationship between sea temperature and recruitment of cod stocks across the North Atlantic, as well as between recruitment and the size of the spawning population. In the North Sea, cod year-class strength is inversely related to sea surface temperature during the first half of the year. This stock is currently at a low level, and the future trajectory of the stock biomass will be strongly influenced by recruitment levels. In the present study we investigate the possible use of observed and modelled sea surface temperature (SST) to increase the accuracy and/or time horizon of recruitment forecasts for this stock. We show that the statistical model developed for forecasting spring temperature has good skill (35% skill, with a standard error of 0.36°C) when predictions are made in late January. Within the frame of the current fish stock assessment working group we incorporate SST observations and January forecasts and simulate short-term recruitment projections. The resulting model accounts for a greater fraction of the variance in recruitment (42%) than that obtained without temperature (17%). In operational mode, the model allows forecasting 1.5 years in advance but the accuracy of predicted recruitment remains low. This example indicates that we have not yet reached a point where environmental information can be used with great benefit for the management of North Sea cod. However, a similar strategy may yield greater benefits if developed for other stocks for which environmental effects are better understood and/or account for a larger fraction of the variability in recruitment, for species with a shorter generation time and species for which recruitment forecast is critical to management (e.g. anchovy), and in areas where environmental prediction capabilities may be greater either in accuracy or in lead time.

Predation-mediated recruitment in the Georges Bank fish community

Understanding the mechanisms that control recruitment in marine fish populations is important for conservation and also for more efficient management through improved predictions of abundance. We examined the role of predation in regulating recruitment by applying multispecies virtual population analysis (MSVPA) to eight fish species on Georges Bank. Cod and silver hake were the most important predators and herring and silver hake were the most important prey species. Predation on cod and silver hake was compensatory, because cannibalism was the dominant source of predation for these species. Predation on herring and mackerel appeared to be slightly depensatory or density-independent. Predation on young fish also affected the relative cohort size at age 2. Therefore, predation should be considered when making medium- to long-term recruitment forecasts.

Forecasts of recruitment in South African anchovy from SARP field data using a simple deterministic expert system

A rule-based deterministic model is used to forecast recruitment of anchovy Engraulis capensis in the southern Benguela from field measurements of biological and environmental variables collected during two consecutive years. Field data were obtained on a monthly basis during the anchovy spawning season as part of the South African Sardine and Anchovy Recruitment Programme (SARP). A total of six indicator variables was considered for the analysis: distance offshore of the 16°C isotherm; southerly wind stress; anchovy egg abundance; incidence of oocyte atresia in adult females; an index of fish starvation; and oil : meal ratios obtained from commercial data (which were used as an index of fish condition). In the model, data for each variable were assessed against a threshold value. “Active” variables were assumed to contribute towards below-average recruitment by being either above or below their threshold values, as defiNed by the rules. The model was not based on the SARP field data, which were used to test the model. Predicted results from the expert system compared favourably with final estimates of recruitment strength for both 1994 and 1995 (years of below average recruitment), indicating that field measurements of biological and environmental variables may be used in a structured manner to obtain forecasts of anchovy recruitment to the fishery.

Relevance of cod (L.) predation for inter-cohort variability in mortality of juvenile Norwegian spring-spawning herring (L.)

Barros, P., Tirasin, E. M., and Toresen, R. 1998. Relevance of cod (Gadus morhua L.) predation for inter-cohort variability in mortality of juvenile Norwegian springspawning herring (Clupea harengus L.) ‐ ICES Journal of Marine Science, 55: 454‐466 Mortality of juvenile Norwegian spring-spawning herring growing up in the Barents Sea is characterized by a high inter-cohort variability. Variable predation pressure from the north-east Arctic cod stock has been proposed as an explanation, but it has been diYcult to test this hypothesis with actual field data. Data on the abundance of the main fish stocks in the Barents Sea ecosystem, collected by the Institute of Marine Research in Bergen during the period 1983‐1993, were analysed to test this hypothesis. Since capelin has been the major prey of cod during the period investigated, the relationship between herring juvenile mortality and the abundance of cod, capelin and herring was investigated. More than 90% of the inter-cohort variation in mortality of juvenile herring observed during this period was explained by a simple model using the ratio of capelin abundance to the abundance of juvenile cod as the explanatory variable. The relationship is strong enough to warrant using the simple model for improving the short-term forecasts of recruitment to the spawning stock of Norwegian spring-spawning herring. ? 1998 International Council for the Exploration of the Sea

Larval parameters determining preschooling juvenile production of Pacific saury (Cololabis saira) in the northwestern Pacific

Production of larvae in the hatching size-class of Pacific saury (Cololabis saira) was highest in autumn 1990-1994, implying that spawning activity was highest in this season. Growth and mortality rates were stable in the winter-spawned cohorts in Kuroshio waters (south of Honshu); variable rates were found in the autumn- and spring-spawned cohorts in the mixed water region to the northeast. Although no particular period of high mortality was detected through the larval and juvenile stages, overall percent survival through the larval and juvenile stages differed by an order of magnitude among seasons. Production of 40-mm preschooling juveniles was determined by larval production in the smallest size-class in the winter cohort, but by overall percent survival through the larval and juvenile stages in the spring and autumn cohorts. Over the last 44 yr, percentage of winter-spawned cohorts in commercial catches was stable, compared with large interannual variations of autumn- and spring-spawned cohorts. These observations were assumed to stem from stable juvenile production in winter and variable production in autumn and spring, suggesting the possibility of recruitment forecasts of seasonally spawned cohorts of saury based on preschooling juvenile production estimates in the northwestern Pacific.

Factors Affecting the Recruitment of Lake Whitefish in Two Areas of Northern Lake Michigan

Stock-recruitment and integrated recruitment models incorporating biotic and abiotic factors were developed for lake whitefish populations in northern Green Bay and the North Shore areas of Lake Michigan. Abundance and recruitment indices were calculated for the 1961-1985 year classes based on lake whitefish catch and effort data from the commercial fishery in each area. Previous research indicates that spawning stock abundance, winter ice cover, and spring temperatures are important in determining the egg and larval abundance and survival of lake whitefish. Therefore, spawning stock abundance, ice cover, winter wind velocity, and spring water and air temperature variables were used as model inputs in regression modeling. The biotic/abiotic recruitment model for northern Green Bay hindcasted lake whitefish recruitment as a function of spawning stock abundance and the number of days that ice cover exceeded 40% during egg incubation. This regression model (R 2 = 0.62) demonstrated improved hindcasting ability of historic recruitment when compared to the Beverton-Holt (R 2 = 0.37) or the Ricker (R 2 = 0.33) stock-recruitment models for the 1961-1985 cohorts. The biotic/abiotic recruitment model for the North Shore hindcasted lake whitefish recruitment as a function of average air temperature in May after larval emergence, the number of days that ice concentration exceeded 70% during egg incubation, and spawning stock abundance. The regression model (R 2 = 0.57) also demonstrated improved hindcasting ability of historical recruitment when compared with Beverton-Holt (R 2 = 0.09) or the Ricker (R 2 = 0.13) stock-recruitment models. Results of this study indicate that biotic/abiotic recruitment models were more successful in hindcasting recruitment than solely biologically based stock-recruitment relationships. Consideration of significant abiotic variables will be useful in the management of lake whitefish stocks in the Great Lakes by improving forecasts of recruitment.

Evaluating Forecasting Procedures for Predicting Pacific Herring (Clupea harengus pallasi) Recruitment in British Columbia

The ability of four forecasting methods to generate one-step-ahead forecasts of Pacific herring (Clupea harengus pillasi) recruitment is considered in this paper. Recruitment time series for five coastal stocks and various environmental time series are employed in the analyses. Information up to and including time t is employed to estimate the parameters of each model used to forecast recruitment in year t + 1. Parameter estimates are then updated after each time step with a total of seven one-step-ahead forecasts being generated by each model for each stock. The forecast errors are compared using the five criteria: (1) root mean squared error, (2) mean absolute deviation, (3) mean absolute percent error, (4) median absolute deviation, and (5) median absolute percent error. The results of the study indicate that time series models may provide better forecasts of recruitment for the Strait of Georgia/Johnstone Strait stocks than the other competing procedures. A Ricker stock–recruitment model that takes into account environmental data appears to produce marginally better forecasts for the Central Coast and Queen Charlotte Island stocks, while all models produced equally good/bad forecasts for the Prince Rupert district stocks.

Insights from the Markets for Limited Entry Permits in Alaska

Under Alaska's entry limitation program, transferable permits convey fishing rights. Information from permit markets is used to study several key issues regarding the behavior of fishermen and the effects of fishery management policy. I conclude that (1) expectations of future fishing incomes are the primary determinants of permit prices, (2) Alaska Department of Fish and Game forecasts of fish recruitment are capitalized in permit values, (3) a state program that provides low-interest loan money to some purchasers of permits has coincided with a significant increase in permit prices, (4) the "average memory" of fishermen in projecting future incomes is about 2.5 yr, and (5) it is possible to infer the rate at which the markets discount future fishing income flows.