Predation: Compensation and Context Dependence

Ward, Darren M.; Hvidsten, Nils Arne

doi:10.1002/9781444327755.ch8

Cited by 23 publications

(42 citation statements)

References 82 publications

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“…This is noteworthy, as swimming closer to the surface may represent yet another trade-off for the sea trout, i.e. between parasite avoidance and predation risk, due to increased exposure to preda tory birds (Ward & Hvidsten 2011). We expected, but did not find, a treatment effect.…”

Section: Infestation Swimming Depth and Distance To The River Outletmentioning

confidence: 57%

Effects of salmon lice infection on the behaviour of sea trout in the marine phase

Gjelland¹,

Serra‐Llinares²,

Hedger³

et al. 2014

Aquacult. Environ. Interact.

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Salmon lice Lepeophtheirus salmonis Krøyer may affect survival and growth of anadromous salmonids through physiological stress and/or behavioural changes. Using acoustic telemetry tracking, we investigated the behaviour of 30 infected sea trout Salmo trutta throughout the summer in a fjord with very high salmon lice infection pressure. Most of the tracked sea trout adopted a movement pattern expected to suppress salmon lice infestation, as they showed a strong preference for fresh or brackish water, spending most of the time close to a river outlet or even migrating into the river. Highly infested sea trout preferred shallower depths, associated with lower salinity. The fish lost to predation stayed further away from the river outlet than nonpredated fish, and were likely subjected to a stronger infection pressure. Half of the tracked group were treated with a salmon lice prophylaxis, emamectin benzoate. The effect of treatment on infestation was monitored in a separate group held in a sea cage and found to be moderate; the mortality in this group was associated with infestation by motile lice stages. In contrast, treatment was not found to have an effect on tracked fish behaviour. It is likely that some physiological and behavioural responses to high salmon lice infection pressure may be present even after a prophylaxis treatment, in particular when the treatment is given after exposure to salmon lice infection. We conclude that increased salmon lice infection pressure associated with altered salmon farming practice may have the potential to influence the marine behaviour and growth of sea trout.

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Section: Infestation Swimming Depth and Distance To The River Outletmentioning

confidence: 57%

Effects of salmon lice infection on the behaviour of sea trout in the marine phase

Gjelland¹,

Serra‐Llinares²,

Hedger³

et al. 2014

Aquacult. Environ. Interact.

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“…Atlantic salmon are vulnerable to predatory birds, mammals, and fish (Ward and Hvidsten, 2011). This is generally not considered an anthropogenic factor, but is included to the extent that predation is influenced by human activities.…”

Section: Predationmentioning

confidence: 99%

“…This is generally not considered an anthropogenic factor, but is included to the extent that predation is influenced by human activities. Human activities may increase the number of predators (Ward and Hvidsten, 2011) and the vulnerability of salmon to predation. Overexploitation or habitat changes may reduce salmon abundance to the point that salmon become disproportionately vulnerable to predators (Ward et al, 2008).…”

Section: Predationmentioning

confidence: 99%

“…There is little data available to assess how and to what extent predation affect salmon populations, but there is little doubt that predation influences behaviour, recruitment, and population dynamics of salmon (Ward and Hvidsten, 2011). In Norway, there are likely few Atlantic salmon populations impacted by predation influenced by human activity.…”

Section: Predationmentioning

confidence: 99%

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The major threats to Atlantic salmon in Norway

Forseth

Barlaup

Finstad

et al. 2017

ICES Journal of Marine Science

221

186

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Atlantic salmon (Salmo salar) is an economically and culturally important species. Norway has more than 400 watercourses with Atlantic salmon and supports a large proportion of the world's wild Atlantic salmon. Atlantic salmon are structured into numerous genetically differentiated populations, and are therefore managed at the population level. Long-distance migrations between freshwater and ocean habitats expose Atlantic salmon to multiple threats, and a number of anthropogenic factors have contributed to the decline of Atlantic salmon during the last decades. Knowledge on the relative importance of the different anthropogenic factors is vital for prioritizing management measures. We developed a semi-quantitative 2D classification system to rank the different anthropogenic factors and used this to assess the major threats to Norwegian Atlantic salmon. Escaped farmed salmon and salmon lice from fish farms were identified as expanding population threats, with escaped farmed salmon being the largest current threat. These two factors affect populations to the extent that they may be critically endangered or lost, with a large likelihood of causing further reductions and losses in the future. The introduced parasite Gyrodactylus salaris, freshwater acidification, hydropower regulation and other habitat alterations were identified as stabilized population threats, which have contributed to populations becoming critically endangered or lost, but with a low likelihood of causing further loss. Other impacts were identified as less influential, either as stabilized or expanding factors that cause loss in terms of number of returning adults, but not to the extent that populations become threatened. Management based on population specific reference points (conservation limits) has reduced exploitation in Norway, and overexploitation was therefore no longer regarded an important impact factor. The classification system may be used as a template for ranking of anthropogenic impact factors in other countries and as a support for national and international conservation efforts.

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“…While the peak vulnerability of newly-emerging or newly-stocked Atlantic salmon fry to fish predators only lasts a few days, (Henderson and Letcher 2003, Ward et al 2008a), the effects of predators on salmon traits may persist through the growing season (Ward and Hvidsten 2010). High early predation losses could suppress mean growth over the season if early predation mortality is biased towards inherently active foragers.…”

Section: Introductionmentioning

confidence: 99%

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

Ward

Nislow

Folt

2011

Can. J. Fish. Aquat. Sci.

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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.

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Predation: Compensation and Context Dependence

Cited by 23 publications

References 82 publications

Effects of salmon lice infection on the behaviour of sea trout in the marine phase

Effects of salmon lice infection on the behaviour of sea trout in the marine phase

The major threats to Atlantic salmon in Norway

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

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