Stage-specific biomass overcompensation by juveniles in response to increased adult mortality in a wild fish population

To test the hypothesis that fish in schools forage more successfully than individual fish, an analysis was made of the stomach contents of barracouta (Thyrsites atun), a facultatively schooling species of fish, in a wild fish population. Schooling (n = 29) and non-schooling (n = 86) barracouta were captured during a side-scan sonar survey of pelagic fish off the coast of Otago, New Zealand. The proportion of fish with empty stomachs was lower and the mean wet mass of gut contents was higher in barracouta from schools. The increased feeding success of fish in schools was due to increased consumption of krill, Nyctiphanes australis. In regions where the density of krill in net tows was high (>1000 individuals km-1 tow length) or moderate (100–1000 individuals km-1), the mean wet mass of krill in the stomachs of schooling barracouta was 2–4 times higher than in the stomachs of non-schooling barracouta. Few schools of barracouta were observed in areas with low densities of krill (<100 individuals km-1). Schooling by barracouta seems to be a feeding strategy to exploit surface swarms of krill.

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Heritability estimation via molecular pedigree reconstruction in a wild fish population reveals substantial evolutionary potential for sea age at maturity, but not size within age classes

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2018-0123 ◽

2019 ◽

Vol 76 (5) ◽

pp. 790-805 ◽

Cited By ~ 3

Author(s):

Thomas E. Reed ◽

Paulo Prodöhl ◽

Caroline Bradley ◽

John Gilbey ◽

Philip McGinnity ◽

...

Keyword(s):

Body Size ◽

Fish Population ◽

Wild Fish ◽

Phenotypic Traits ◽

Evolutionary Potential ◽

Heritable Variation ◽

Heritability Estimation ◽

Scottish Population ◽

Rapid Changes ◽

Genetic Contributions

While evolutionary responses require heritable variation, estimates of heritability (h2) from wild fish populations remain rare. A 20-year molecular pedigree for a wild Scottish population of Atlantic salmon (Salmo salar) was used to investigate genetic contributions to (co)variation in two important, correlated, phenotypic traits: “sea age” (number of winters spent at sea prior to spawning) and size-at-maturity (body length just prior to spawning). Sea age was strongly heritable (h2 = 0.51) and size exhibited moderate heritability (h2 = 0.27). A very strong genetic correlation (rG = 0.96) between these traits implied the same functional loci must underpin variation in each. Indeed, body size within sea ages had much lower heritability that did not differ significantly from zero. Thus, within wild S. salar populations, temporal changes in sea age composition could reflect evolutionary responses, whereas rapid changes of body size within sea ages are more likely due to phenotypic plasticity. These inheritance patterns will influence the scope of evolutionary responses to factors such as harvest or climate change and, hence, have management implications for salmonid populations comprising a mix of sea ages.

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