Abstract
We investigate how the reproductive strategy in a migratory marine fish may be influenced by spatial variations in mortality in early life stages. In particular, we examine how spawning time and location affect offspring survival and growth. A drift model for early life stages (eggs to age 1) of the Barents Sea cod (Gadus morhua) is combined with empirical estimates of spatial variation in mortality at two different life stages. We examine seasonal and interannual differences in survival and growth in offspring originating from two spawning grounds, with the central site requiring higher migration distance, and hence cost, than the northern site. When accounting for spatially explicit mortality fields, central and northern spawned offspring have about equal survival, as do early and late spawned offspring. Furthermore, central spawned offspring grow faster and are likely to reach a larger size compared with northern spawned offspring. Our results indicate that the fitness benefit of southward migration in the Barents Sea cod is not mainly due to higher early survival of offspring, but rather due to effects of offspring acquiring a larger size.
Highlights
Conditions experienced during early life stages may result in longlasting effects on individuals and may have important implications at the population level (Metcalfe and Monaghan 2001; Beckerman et al 2002; Vindenes and Langangen 2015)
We investigate offspring survival and growth based on two selected spawning grounds: Moskenesgrunnen outside the Lofoten archipelago and Breivikbotn in western Finnmark; see Fig. 1
When we account for the spatial variations in natural mortality in addition to the stage-specific mortality, the advantage of central spawning is almost fully compensated (Fig. 3, lower panel; survival in north on average 94% of survival in central area)
Summary
Conditions experienced during early life stages may result in longlasting effects on individuals and may have important implications at the population level (Metcalfe and Monaghan 2001; Beckerman et al 2002; Vindenes and Langangen 2015). Typically defined as nongenetic reproductive traits, are often considered to be adaptive responses to a heterogeneous environment and can be important in shaping the fitness of the offspring (Mousseau and Fox 1998). Theory on reproductive strategy suggests that there is often a trade-off between offspring fitness and parental cost, including maternal effects (Lack 1954). Maternal effects may affect the offspring through egg condition such as size, fat content, and buoyancy, and spawning location and time (Green 2008). The optimization of timing and location of spawning involves extensive parental migration For such migrations to be beneficial, the cost of the migration must be outweighed by payoff in, for example, increased survival and growth of the offspring
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