Abstract
The successful recruitment of Northeast Arctic (NEA) cod is thought to depend on sufficient and suitable prey for the newly hatched larvae, in particular the nauplii stages of the lipid-rich calanoid copepod species Calanus finmarchicus. The role of spatial and temporal variations in prey availability in combination with temperature and other factors in influencing growth and survival of cod larvae is, however, incompletely understood. By combining an individual based model for NEA cod larvae at the Norwegian coast with a high-resolution ocean model and a nutrient-phytoplankton-zooplankton-detritus model providing 18 years of daily environmental conditions and prey availability we assessed larval growth and survival until they settle in their feeding habitat in the Barents Sea in early fall. We find on average a two-week delay from the peak timing of first-feeding cod larvae to the peak in prey availability. In warm years, more larvae experience food limitation than in normal years. The positive effects of high temperature on growth, survival and ultimately recruitment are nonetheless larger than the negative effects of food limitation. Food limitation mainly affects larvae spawned in southern areas or late in the spawning season as these larvae experience the highest temperatures and have the highest energy requirements. Our findings highlight the spatial and temporal differences in mechanisms that regulate growth and survival of early life stages of NEA cod and suggest that spatially resolved data may be essential for understanding match-mismatch dynamics.
Highlights
Variability in the number of individuals in adult fish populations results mainly from the loss of individuals through natural and fishing mortality, and recruitment of individuals through the reproduction process (Payne et al, 2009)
We believe that due to a constant Norwegian Coastal current (NCC), low ambient temperatures result in a prolonged drift period until 30 days after spawning and a longer distance traveled from the SS
The results presented here shed light on the processes and mechanisms that affect larval growth, distribution and survival from Northeast Arctic (NEA) cod egg and larval stages until arrival of juveniles in their nursery grounds in the Barents Sea and through the first winter by considering previously established empiricalbased size-dependent survival prospects
Summary
Variability in the number of individuals in adult fish populations results mainly from the loss of individuals through natural and fishing mortality, and recruitment of individuals through the reproduction process (Payne et al, 2009). The “Match-mismatch” hypothesis explains the year-class survival variability through phenology and extends the critical period from the first-feeding stage until after metamorphosis (Cushing, 1969, 1990). This hypothesis highlights mechanisms that connect the temporal overlap between prey and predators as a key for the survival of the predators, assuming spatial overlap is present. The three above mentioned hypotheses account for many underlying processes of various spatial and temporal resolutions that affect survival of the early life stages of fish, including starvation, transport to and from favorable habitats, and metabolic rates due to varying ambient conditions. The relative importance of these processes to recruitment varies in space and time (Gallego et al, 2012; Hare, 2014)
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