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Stock–recruitment relationships (SRRs) may vary over time due to ecological and anthropogenic impacts, challenging traditional approaches of calculating maximum sustainable yield (MSY)-based reference points that assume constant population traits. We compare seven methods to calculate MSY, F MSY and B MSY by modelling constant, stochastic (uncorrelated), and autocorrelated SRRs using simulations and two case studies [Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) on the Grand Bank off Newfoundland, Canada]. Results indicated that the method used to model SRRs strongly affected the temporal pattern of recruitment projection, and the variations generated by autocorrelated SRRs were more similar to observed patterns. When the population productivity had low-frequency and large-magnitude variations, stochastic SRRs generated greater MSY and F MSY estimates than constant or autocorrelated SRRs, while no consistent pattern of B MSY was detected. In the case studies, stochastic and autocorrelated SRRs produced asymmetric relationships between fishing mortality and yield, with higher risk of overfishing by going beyond F MSY. Overall, our results suggest that caution should be taken when calculating MSY-based reference points in highly dynamic ecosystems, and correctly accounting for non-stationary population dynamics could, therefore, lead to more sustainable fisheries. [ABSTRACT FROM AUTHOR]

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Growth and condition in fishes have been taken as indicating levels of energy available for survival and reproduction, major components of a population's productivity. After a rapid collapse in population size, northern (NAFO Division 2J3KL) cod (Gadus morhua) remained at a very low level of abundance for 20 years. We investigated the potential for poor growth and condition to have played a role in the collapse and lack of recovery of northern cod. Juveniles and adult males and females all showed similar patterns. Perceptions about the importance of growth and condition to population status depended on the metrics and area examined. When the northern cod population was declining, the northern areas of the population clearly had reduced growth and condition, while these metrics improved in the south. Results were equivocal as to the potential role of growth and condition in the continued low abundance of northern cod and, to some extent, depended on the nature of the metric being examined. Indices of condition, which included lipid storage in the form of liver weight, were generally lower in the north while the stock remained at a low level. Metrics associated with longer-term protein storage returned to precollapse levels quickly following the period of collapse. An index of food availability was more closely related to growth and condition than was temperature. These results point to the need both for studies of growth and condition in a population to have a comprehensive time-series of data covering the entire range of the population and the need for a better understanding of the causes and implications of changes in different metrics of condition. [ABSTRACT FROM AUTHOR]

Compensatory responses are important because they increase spawning stock biomass (SSB) growth rates in depleted fish populations. We analyze recruits per spawner (R/SSB) and spawners per recruit (SSB/R) data from six well-studied depleted, or depleted and recovering, Northwest Atlantic groundfish stocks for evidence of compensatory responses. All stocks had periods of high R/SSB at low SSB; however, R/SSB showed considerable variability, and significant compensatory responses were only found in two stocks. For compensation in SSB/R, relationships were significant for three of the stocks. We examined the potential impact of compensation in R/SSB and SSB/R on SSB growth rate and concluded that SSB/R could have a greater potential impact on enhancing SSB growth rate in depleted stocks. Overall, cod (Gadus morhua) populations showed greater compensation than flatfish, mainly due to the lower potential in flatfish to increase SSB/R. This suggests that cod are more resilient to overfishing than are flatfish. Estimates of population growth rate at low stock size, which ignore compensation in SSB/R, will underestimate maximum SSB growth rates. Compensation in both R/SSB and SSB/R should both be considered when evaluating stock productivity, sustainable harvest levels, and biological reference points. [ABSTRACT FROM AUTHOR]

The relationship between stock size and recruitment is an essential element in the understanding of the productivity of a population. However, predicting the number of recruits produced by a population has proven to be a difficult challenge. This may in part be a result of poor estimation of reproductive potential (RP). We determined if including increased information on reproductive biology in indices of RP results in better predictions of recruitment. We investigated some of the conditions that lead to better (or worse) recruitment prediction when more biologically complex indices of RP are used. Data from four populations in the Northwest Atlantic were examined: southern Grand Bank (NAFO Division 3NO) cod (), Flemish Cap (NAFO Division 3M) cod, Newfoundland (NAFO Division 3LNO) American plaice (), and Greenland halibut () (NAFO Subarea 2 + Division 3KLMNO). Stock-recruit models paired with complex indices of RP gave a better estimate of recruitment in slightly more than half of the tests conducted. When there were larger trends in the reproductive biology (maturity at age, sex ratio and egg production), more complex indices of RP were more likely to provide a better estimate of recruitment. [ABSTRACT FROM AUTHOR]

Variation in maturity-at-age, sex ratio, and potential egg production (through changes in length at age) were examined for northern cod (NAFO Division 2J + 3KL), southern Grand Bank cod (3NO), and southern Newfoundland cod (3Ps). All showed significant interannual variability in each stock. Estimates of reproductive potential were produced by sequentially incorporating estimates of proportion mature at age, sex ratio at age, and potential egg production. The estimates of reproductive potential produced by each method were broadly similar, but there were important differences. This leads to differing perceptions of stock productivity, as measured by relative rate of recruitment of a stock and in the spawning stock produced per recruit. These differing perceptions can have a major impact on expectations for the recovery of depleted stocks and the sustainability of various levels of fishing. Efforts should be made to improve estimates of reproductive potential by further exploring the impacts of changes in the spawning characteristics of populations, and by collecting such basic information as fecundity data. [ABSTRACT FROM PUBLISHER]

Concomitant with declines in abundance, many commercially exploited marine fishes have undergone significant life history changes that are critically important as they impact population growth rate and, thus, recovery rate of depleted stocks. By examining data collected as part of offshore surveys conducted during 1971–2012, we evaluated whether there have been changes in growth rate and size at maturity for haddock on Grand Bank and St. Pierre Bank, two over-exploited stocks at the northern extremity of the species range in the western Atlantic Ocean. Contrary to expectation, we found no evidence for change in either growth or maturity since 1971. However, there were differences in life history characteristics between the two stocks, as well as between males and females. Although no difference in growth was observed between sexes, differences in maturation were evident with 50% of males maturing at ∼40 cm and 50% of females maturing at ∼48 cm. Haddock from Grand Bank were larger than haddock from St. Pierre Bank at ages 8 and 10 by 4.4% and 7.6%, respectively. We also found that haddock on Grand Bank matured at smaller sizes (length at which the probability of maturity was 50% was 38.2 cm for males and 46.3 cm for females) than those from St. Pierre Bank (42.1 cm for males and 49.9 cm for females). The haddock fishery off Newfoundland developed rapidly from 1945 but collapsed within less than two decades. Available information suggests that while fishery exploitation rates were undoubtedly high, haddock on Grand Bank and St. Pierre Bank may not have been exposed to sufficient multigenerational fishing pressure to generate decreases in growth and maturity timing as seen in other over-exploited stocks and appear to have maintained historic life history characteristics. [ABSTRACT FROM AUTHOR]

Reproductive life history parameters, such as size-specific fecundity, can contribute to our understanding of fish population dynamics. However, most of these parameters are difficult or time-consuming to obtain. Therefore, previously calculated parameters are often used in combination with more easily collected metrics of size. Significant temporal variation in fecundity is known to occur in many fish species, meaning that previous estimates may be unreliable when examining contemporary fish stocks. For southern Newfoundland haddock, the only published fecundity data were collected more than 50 years ago when this species supported a major fishery in the area. Here we present fecundity data collected during the 1960s immediately following stock collapse, as well as data from 2013 to 2014 (after 20 years of a fishing moratorium) and examine potential differences in egg production among the time periods. Contemporary estimates of haddock fecundity were more similar to estimates of fecundity immediately following stock collapse than estimates during the period of maximum exploitation. Additionally, comparison of haddock fecundity throughout the northwest Atlantic Ocean revealed contemporary estimates from southern Newfoundland to generally be higher than those from the Scotian Shelf for haddock at all lengths as well as greater than those from George's Bank until about 60 cm in total length. The ability of various fish characteristics (length, weight, age, and condition) to serve as metrics of haddock fecundity were investigated and found that while length was the best predictor of fecundity, explanatory power was relatively low (maximum R2 = 0.37), and there was little to no effect of fish condition on fecundity. Inter-annual variability in fecundity estimates, coupled with the lack of a suitable proxy for fecundity for Newfoundland haddock suggests that ongoing monitoring is required to accurately estimate reproductive potential. [ABSTRACT FROM AUTHOR]