8 research outputs found
Factors contributing to inter- and intra-annual variation in condition of cod Gadus morhua in the Barents Sea
Reconstructing the stock-recruit relationship for Northeast Arctic cod using a bioenergetic index of reproductive potential
Systematic bias in estimates of reproductive potential of an Atlantic cod (Gadus morhua) stock: implications for stock–recruit theory and management
Stock–recruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume
that the proportion of SSB composed of females and the relative fecundity (number of eggs produced per unit mass)
are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production
(TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period.
The proportion of females (FSB/SSB) varied between 24% and 68%, and the variation was systematic with length such
that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock
(TEP/SSB) varied between 115 and 355 eggs·g–1 and was significantly, positively correlated with mean length of
spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size
(overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference
between SSB and FSB in the assessment of stock status; however, in recent years (1980–2001) TEP fell below
the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB
as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status
Systematic bias in estimates of reproductive potential of an Atlantic cod ( Gadus morhua
Deriving condition indices from standard fisheries databases and evaluating their sensitivity to variation in stored energy reserves
The effects of oil spills on marine fish: Implications of spatial variation in natural mortality
The effects of oil spills on marine biological systems are of great concern, especially in regions with high biological production of harvested resources such as in the Northeastern Atlantic. The scientific studies of the impact of oil spills on fish stocks tend to ignore that spatial patterns of natural mortality may influence the magnitude of the impact over time. Here, we first illustrate how spatial variation in natural mortality may affect the population impact by considering a thought experiment. Second, we consider an empirically based example of Northeast Arctic cod to extend the concept to a realistic setting. Finally, we present a scenario-based investigation of how the degree of spatial variation in natural mortality affects the impact over a gradient of oil spill sizes. Including the effects of spatial variations in natural mortality tends to widen the impact distribution, hence increasing the probability of both high and low impact events