Recruitment Of Atlantic Cod Research Articles

Spatial synchronicity in recruitment of Atlantic cod (Gadus morhua) stocks off Newfoundland and Labrador and the Flemish Cap

Spatial synchronicity in recruitment was examined for Atlantic cod (Gadus morhua) in the Newfoundland and southern Labrador (NL) and Flemish Cap regions. Recruitment was estimated using a cohort strength model for survey indices of abundance at pre-exploitation ages, and spatio-temporal covariation in recruitment was then examined. Patterns of recruitment synchrony were generally consistent with management boundaries. However, there were some exceptions that suggest structure at the sub-stock level and mixing across adjacent stock boundaries. In particular, we observed weak correlations between the eastern and western 3Ps RV (Research Survey) recruitment indices. We also observed strong correlations between the eastern 3Ps RV and the fall and spring 3NO RV recruitment indices, as well as fairly strong correlations between the southern 3L, central 3KL, and 3Ps sentinel GN and LT recruitment indices. Correlations between the summer 3M RV recruitment indices and all other survey recruitment indices included in our analysis were generally very weak, as was expected. We demonstrate that survey recruitment indices can be used to identify either areas of potential sub-stock structure or mixing or areas where recruitment drivers may be operating across or differentially within stock management boundaries. Hence, our results should improve the design of future stock structure research, and provide useful new information for fisheries management.

Maternal age effects on Atlantic cod recruitment and implications for future population trajectories

Abstract Exploited fish populations frequently exhibit truncated age-structure. To address a basic question in fisheries science and conservation biology—how does age truncation affect population dynamics and productivity?—we explored the effect of age-structure on recruitment dynamics of ten stocks of Atlantic cod (Gadus morhua). Based on six alternative stock–recruitment relationships, we compared models that included and excluded maternal age-structure effects on recruitment. In all ten stocks, a recruitment model that included a maternal age-dependent effect was preferred over the standard Ricker model and in seven of the ten stocks, the preferred statistical model included a positive effect of either maternal age or mass on recruitment. Simulations comparing standard and maternal age dependent recruitment two decades into the future suggest that the inclusion of maternal age in recruitment models has little effect on projected biomasses. However, this similarity in biomass trajectory masked an increased sensitivity of populations with maternal age-dependent recruitment to stock age-structure. In particular, simulations with maternal age-dependent recruitment responded strongly to changes in fishing mortality on the oldest age classes, while simulations using standard recruitment models did not. Populations with maternal age-dependent recruitment can exhibit increased biomass catch even if fishing mortality on older individuals was reduced. Overall, simulations suggested that the influence of maternal age on population dynamics are more nuanced than suggested by previous research and indicate that careful consideration of the effects of age-structure on populations may lead to substantially different fisheries management reference points—particularly with respect to age-specific fishing mortality—than classical models. While these results suggest a link between maternal age and population productivity, future research requires the incorporation of biologically reasonable and empirically defensible mechanisms to clarify the effect of age on population dynamics.

Episodic downwelling predicts recruitment of Atlantic cod, Greenland cod and white hake to Newfoundland coastal waters

Episodic downwelling predicts recruitment of Atlantic cod, Greenland cod and white hake to Newfoundland coastal waters

Erratum: Effect of the North Atlantic Oscillation on recruitment of Atlantic cod (Gadus morhua)

Erratum: Effect of the North Atlantic Oscillation on recruitment of Atlantic cod (<i>Gadus morhua</i>)

Effect of the North Atlantic Oscillation on recruitment of Atlantic cod (Gadus morhua)

We examine the effect of introducing an environmental factor — the North Atlantic Oscillation (NAO) index — into a stock–recruit relationship fitted to 13 North Atlantic cod (Gadus morhua) stocks and discuss the implications for management. The NAO has a significant effect on recruitment of four of the stocks (positive effect on recruitment in the North Sea, Baltic Sea, and Irish Sea; negative effect on recruitment at Iceland), and the pattern of positive and negative effects on all stocks is consistent with the geographic influence of the NAO on environmental variables. Observed variability in the NAO should be taken into account in interpreting the causes of past changes in cod stocks. The NAO index for the previous winter is available by April and thus may provide an early indication of the likely range of cod recruitment in the current year. In areas, such as the North Sea, where the effect is strong, medium- and long-term assessments of recruitment and yield of the cod stocks should consider likely future states of the NAO. The NAO can be used to represent environmental variability in stock projections and thereby provide a better basis for the estimation of risk.

Variation in Growth and Recruitment of Atlantic Cod (Gadus morhua) off Greenland During the Second Half of the Twentieth Century

The variation in length-at-ages 4 to 5 years for Atlantic cod (Gadus morhua) off Greenland was analysed based on a time series of samples taken from commercial catches comprising 190 000 individual age determinations. Multiple linear regressions revealed significant declines in size for age groups 4 and 5 since the mid-1950s, by 10 and 5 cm, respectively. Growth models accounting for temperature, fishing mortality and stock abundance effects were constructed. Positive temperature and negative fishing mortality effects were found to dominate the variation in length-at-age. The analyses did not indicate a negative effect of stock density on cod growth. During the period 1956–89, the number of recruits at age 3 years was significantly correlated with the spawning stock biomass and June water temperature on top of Fyllas Bank (West Greenland). Both factors positively affected the number of offspring and explained 51% of the observed variation in recruitment.

Temperature and the recruitment of Atlantic cod (Gadus morhua)

Variability in the recruitment of fish has been attributed to either changes in the environment or variations in the size of reproductive stocks. Disentangling the effects of environment and stock has proven to be problematic and has resulted in recurrent controversy between studies supporting either hypothesis. In the present study, we examine the relationship between interannual changes in temperature and variation in recruitment for nine Atlantic cod (Gadus morhua) stocks in the North Atlantic. We show that for individual stocks, the relationship often appears weak and statistically not significant. On the other hand, by combining in a single metaanalysis the results from individual stocks, we demonstrate that recruitment of Atlantic cod is linked to interannual fluctuations in temperature in such a way that for stocks located in warm water the relationship is negative, for stocks located in cold water the relationship is positive, and there is no relationship for stocks located in the middle of the temperature range.

Salinity and Recruitment of Atlantic Cod (Gadus morhua) in the Newfoundland Region

Recruitment predictions for Atlantic cod (Gadus morhua) in the North Atlantic, based upon a previously published regression with salinity, are found to be well correlated with recent recruitment estimates from both virtual population analysis and those derived from research surveys. The addition of spawning stock biomass in the regression significantly increased the percentage of the variance accounted for in the recruitment time series. A similar relationship between recruitment and salinity was found for two nearby stocks (southern Grand Banks and St. Pierre Bank). Oceanographic and food chain mechanisms that might be responsible for a link between salinity and recruitment are discussed.