Seasonal shift in the effects of predators on juvenile Atlantic salmon (Salmo salar) energetics

Abstract

Predator effects on prey populations are determined by the number of prey consumed and effects on the traits of surviving prey. Yet, effects of predators on prey traits are rarely evaluated in field studies. We measured the effects of predators on energetic traits (consumption and growth rates) of juvenile Atlantic salmon (Salmo salar) in a large-scale field study. Salmon fry were released at 18 sites that encompassed a wide range in abundance of predatory slimy sculpin (Cottus cognatus). We sampled salmon after 21 and 140 days to measure salmon growth and estimate consumption using a mass-balance model of methylmercury accumulation. Salmon population density was reduced fivefold at sites with abundant sculpin. Over the early season, salmon consumed less where sculpin were abundant, suggesting that reduced foraging under predation risk contributed to predator-caused mortality. In contrast, over the late season, salmon grew more where sculpin were abundant, suggesting that compensatory growth at reduced salmon population density moderated predator-caused mortality. Predator effects on prey energetics can drive variation in survival and growth, with important consequences for population dynamics.

Interactions between parental traits, environmental harshness and growth rate in determining telomere length in wild juvenile salmon

“…It is possible that the difference in growth rate between the streams was also partially due to the difference in predator density, as an increased predator density may result in reduced foraging (Ward et al . ). Fry density had a negative effect on fry growth rate in both streams, as would be expected because density‐dependent growth is well established in fish (for salmonid example see Jenkins et al .…”

Low but significant genetic differentiation underlies biologically meaningful phenotypic divergence in a large Atlantic salmon population

“…Temporal or microspatial variation in the environment, food availability and predation may maintain growth variation among populations (Amundsen & Gabler ; Jonsson & Jonsson ; Ward et al . ; Reid et al . ).…”

“…Erkinaro & Niemel€ a 1995). Temporal or microspatial variation in the environment, food availability and predation may maintain growth variation among populations (Amundsen & Gabler 2008;Jonsson & Jonsson 2011;Ward et al 2011;Reid et al 2012). On the other hand, P ST -F ST analysis indicated that, in general, divergence between freshwater traits (other than third-year fresh water growth, Growth FW3 ; Fig.…”

Low but significant genetic differentiation underlies biologically meaningful phenotypic divergence in a large Atlantic salmon population

“…Erkinaro & Niemelä 1995). Temporal or microspatial variation in the environment, food availability and predation may maintain growth variation among populations (Amundsen & Gabler 2008; Ward et al 2011; Reid et al 2012; Jonsson & Jonsson 2011). On the other hand, P ST - F ST analysis indicated that, in general, divergence between freshwater traits (other than third year fresh water growth, Growth FW3 ; Figure 6) generally did not deviate from neutral expectations and therefore variation between the sub-populations may be explained by neutral processes alone.…”