The impact of marine fish predation on Atlantic salmon smolts (Salmo salar) in the Tana estuary, North Norway, in the presence of an alternative prey, lesser sandeel (Ammodytes marinus)

Svenning, Martin‐A.; Borgstrøm, Reidar; Dehli, T.O.; Moen, Gro Kvelprud; Barrett, Robert T.; Pedersen, Torstein; Vader, Wim

doi:10.1016/j.fishres.2005.06.015

Cited by 26 publications

(13 citation statements)

References 24 publications

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“…When it is unidirectional, as there is some support for in the present study, it is known as apparent commensalism. Such a reduction in predation with an increase in alternative prey is common (Lester & Harmsen 2002, Heimpel et al 2003, Rickers & Scheu 2005, especially when the alternative prey species is preferred (Eubanks & Denno 2000, Svenning et al 2005, Tschanz et al 2007). The mechanism behind this reduction is generally either predator satiation, predator switching, or preference (Murdoch 1969, Holt & Lawton 1994, Tschanz et al 2007, and both the first and last processes seem to be in effect in this system.…”

Section: Discussionmentioning

confidence: 99%

Density-dependent indirect effects: apparent mutualism and apparent competition coexist in a two-prey system

Long¹,

Gamelin²,

Johnson³

et al. 2012

Mar. Ecol. Prog. Ser.

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A predator consuming multiple prey species usually causes indirect effects. Apparent mutualism results when multiple prey species reduce predation risk for each other by altering a predator's functional response. Short-term apparent competition occurs when multiple prey species increase predation risks for each other through the numerical response, i.e. increasing the predator's birth rate, or aggregative response, i.e. attracting a higher density of predators. Our objectives in this study were to determine the aggregative response and 2-prey functional response of a predator and to examine indirect effects over a range of prey densities. We used the clam Macoma balthica and juvenile blue crabs Callinectes sapidus as prey for adult blue crabs. In laboratory experiments, we determined the single-prey functional responses of the crabs to each prey species and the 2-prey functional response. We combined the 2-prey functional response with the known blue crab aggregative response to clams to estimate field predation rates. Our model predicts that at low prey densities, clams and juvenile blue crabs exhibit apparent mutualism, whereas at high clam densities, this relation switches to short-term apparent competition. These unexpected results highlight the need to incorporate multiple aspects of predation at multiple scales when considering indirect effects.KEY WORDS: Predator-prey interactions · Functional response · Indirect effects · Blue crab · Macoma balthicaResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 456: 139-148, 2012 increases the predator density (i.e. changes either the predator's numerical or aggregative response), thus increasing predation on the other species (Holt & Lawton 1994). This occurs either through increasing the predator population growth rate (Settle et al. 1996, Carvalheiro et al. 2008 or through a local increase in predator density due to predator movement (Holt & Kotler 1987, Brown & Mitchell 1989, Murakami & Nakano 2002. Study organismsThe blue crab Callinectes sapidus Rathbun, 1896, is an important benthic predator in Chesapeake Bay (Virnstein 1977). Large adult crabs are opportunistic omnivores, feeding primarily on bivalves (~50% of diet) and crustaceans (~30%) as well as fish and polychaetes (Hines et al. 1990). Blue crabs are cannibalistic, with adults feeding on juveniles (Hines & Ruiz 1995). Because cannibalism represents a major source of mortality for juvenile blue crabs, juveniles congregate in shallow waters (<1 m), where adults are less abundant (Hines & Ruiz 1995, and in structured habitats that provide a predation refuge (Everett & Ruiz 1993).Macoma balthica Linnaeus, 1758, is a small (shell length < 40 mm) tellinid clam that is the dominant biomass in unvegetated mud habitats within the mesohaline regions of Chesapeake Bay (Holland et al. 1977) and is a major source of food for blue crabs (Baird & Ulanowicz 1989). M. balthica avoids predation by burying deeply, up to 35 cm, in the sediment (Hines & Comtois 1985)...

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Section: Discussionmentioning

confidence: 99%

Density-dependent indirect effects: apparent mutualism and apparent competition coexist in a two-prey system

Long¹,

Gamelin²,

Johnson³

et al. 2012

Mar. Ecol. Prog. Ser.

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“…At this time, post‐smolts in the Drammen River may still be in the continental shelf waters where the abundance of potential predators is higher than in oceanic areas. Numerous factors affect mortality during this time, however, especially in the presence of alternate abundant prey species that may reduce the predation pressure on Atlantic salmon (Svenning et al , 2005). Instead, the mortality effect may be more dominant later in the post‐smolt period.…”

Section: Discussionmentioning

confidence: 99%

Monthly indices of the post‐smolt growth of Atlantic salmon from the Drammen River, Norway

McCarthy

Friedland

Hansen

2008

Journal of Fish Biology

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Indices of the monthly post-smolt growth of three maturity groups of Atlantic salmon Salmo salar from the Drammen River in Norway were examined. Scale samples were collected from 1983 to 2003, providing a retrospective growth history for 2854 individuals. Overall post-smolt growth of all three maturity groups decreased throughout the study period. When the post-smolt year was segmented into 8 monthly indices, there was a significant decline in growth during the fourth and fifth month, typically months of maximum growth. The pre-fishery abundance of one and two seawinter fish from Norway also showed a decline throughout the study period and was positively correlated to the post-smolt growth of fish returning to the Drammen River. Freshwater growth was negatively correlated to the pre-fishery abundance, thus indicating that factors affecting postsmolt growth during the fourth and fifth months at sea may be responsible for declining return numbers in Norway.

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“…Esox lucius density in the estuary was high, and the longer residence time in the cold years may have reduced the overall sea survival owing to high predation. The occurrence of alternative prey may significantly influence the predation rate of smolts (Svenning et al , 2005), and anthropogenic factors affecting the occurrence of such prey species may indirectly affect the smolt predation rates. Fisheries and aquaculture may alter distribution, abundance and diversity of predators in the coastal and ocean environment, and these changes could potentially affect smolt survival.…”

Section: Anthropogenic Effects On Smolt and Post‐smolt Migration Behamentioning

confidence: 99%

A critical life stage of the Atlantic salmon Salmo salar: behaviour and survival during the smolt and initial post‐smolt migration

Thorstad

Whoriskey

Uglem

et al. 2012

Journal of Fish Biology

295

394

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The anadromous life cycle of Atlantic salmon Salmo salar involves long migrations to novel environments and challenging physiological transformations when moving between salt-free and salt-rich waters. In this article, (1) environmental factors affecting the migration behaviour and survival of smolts and post-smolts during the river, estuarine and early marine phases, (2) how behavioural patterns are linked to survival and (3) how anthropogenic factors affect migration and survival are synthesized and reviewed based on published literature. The timing of the smolt migration is important in determining marine survival. The timing varies among rivers, most likely as a consequence of local adaptations, to ensure sea entry during optimal periods. Smolts and post-smolts swim actively and fast during migration, but in areas with strong currents, their own movements may be overridden by current-induced transport. Progression rates during the early marine migration vary between 0.4 and 3.0 body lengths s(-1) relative to the ground. Reported mortality is 0.3-7.0% (median 2.3) km(-1) during downriver migration, 0.6-36% (median 6.0) km(-1) in estuaries and 0.3-3.4% (median 1.4) km(-1) in coastal areas. Estuaries and river mouths are the sites of the highest mortalities, with predation being a common cause. The mortality rates varied more among studies in estuaries than in rivers and marine areas, which probably reflects the huge variation among estuaries in their characteristics. Behaviour and survival during migration may also be affected by pollution, fish farming, sea lice Lepeophtheirus salmonis, hydropower development and other anthropogenic activities that may be directly lethal, delay migration or have indirect effects by inhibiting migration. Total mortality reported during early marine migration (up to 5-230 km from the river mouths) in the studies available to date varies between 8 and 71%. Hence, the early marine migration is a life stage with high mortalities, due to both natural and human influences. Factors affecting mortality during the smolt and post-smolt stages contribute to determine the abundance of spawner returns. With many S. salar populations in decline, increased mortality at these stages may considerably contribute to limit S. salar production, and the consequences of human-induced mortality at this stage may be severe. Development of management actions to increase survival and fitness at the smolt and post-smolt stages is crucial to re-establish or conserve wild populations.

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The impact of marine fish predation on Atlantic salmon smolts (Salmo salar) in the Tana estuary, North Norway, in the presence of an alternative prey, lesser sandeel (Ammodytes marinus)

Cited by 26 publications

References 24 publications

Density-dependent indirect effects: apparent mutualism and apparent competition coexist in a two-prey system

Density-dependent indirect effects: apparent mutualism and apparent competition coexist in a two-prey system

Monthly indices of the post‐smolt growth of Atlantic salmon from the Drammen River, Norway

A critical life stage of the Atlantic salmon Salmo salar: behaviour and survival during the smolt and initial post‐smolt migration

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