Predator avoidance during reproduction: diel movements by spawning sockeye salmon between stream and lake habitats.

Predator avoidance during reproduction: diel movements by spawning sockeye salmon between stream and lake habitats.

J Anim Ecol. 2014 Apr 5;

Authors: Bentley KT, Schindler DE, Cline TJ, Armstrong JB, Macias D, Ciepiela LR, Hilborn R

Abstract
1. Daily movements of mobile organisms between habitats in response to changing trade-offs between predation risk and foraging gains are well established; however, less in known about whether similar tactics are used during reproduction, a time period when many organisms are particularly vulnerable to predators. 2. We investigated the reproductive behaviour of adult sockeye salmon (Oncorhynchus nerka) and the activity of their principal predator, brown bears (Ursus arctos), on streams in southwestern Alaska. Specifically, we continuously monitored movements of salmon between lake habitat, where salmon are invulnerable to bears, and three small streams, where salmon spawn and are highly vulnerable to bears. We conducted our study across 2 years that offered a distinct contrast in bear activity and predation rates. 3. Diel movements by adult sockeye salmon between stream and lake habitat were observed in 51.3 ± 17.7% [mean ± SD] of individuals among years and sites. Fish that moved tended to hold in the lake for most of the day, and then migrated into spawning streams during the night coincident with when bear activity on streams tended to be lowest. Additionally, cyclic movements between lakes and spawning streams were concentrated earlier in the spawning season. 4. Individuals that exhibited diel movements had longer average reproductive life-spans than those who made only one directed movement into a stream. However, the relative effect was dependent on the timing of bear predation, which varied between years. When predation pressure primarily occurred early in the spawning run (i.e., during the height of the diel movements), movers lived 120 – 310% longer than non-movers. If predation pressure was concentrated later in the spawning run (i.e., when most movements had ceased), movers only lived 10-60% longer. 5. Our results suggest a dynamic trade-off in reproductive strategies of sockeye salmon; adults must be in the stream to reproduce, but must also avoid predation long enough to spawn. Given the inter-annual variation in the timing and intensity of predation pressure, the advantages of a particular movement strategy will likely vary among years. Regardless, movements by salmon allowed individuals to exploit fine-scale habitat heterogeneity during reproduction that appears to be a strategy to reduce predation risk on the spawning grounds. This article is protected by copyright. All rights reserved.

PMID: 24702169 [PubMed – as supplied by publisher]

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Riding the crimson tide: mobile terrestrial consumers track phenological variation in spawning of an anadromous fish.

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Riding the crimson tide: mobile terrestrial consumers track phenological variation in spawning of an anadromous fish.

Biol Lett. 2013;9(3):20130048

Authors: Schindler DE, Armstrong JB, Bentley KT, Jankowski K, Lisi PJ, Payne LX

Abstract
When resources are spatially and temporally variable, consumers can increase their foraging success by moving to track ephemeral feeding opportunities as these shift across the landscape; the best examples derive from herbivore-plant systems, where grazers migrate to capitalize on the seasonal waves of vegetation growth. We evaluated whether analogous processes occur in watersheds supporting spawning sockeye salmon (Oncorhynchus nerka), asking whether seasonal activities of predators and scavengers shift spatial distributions to capitalize on asynchronous spawning among populations of salmon. Both glaucous-winged gulls and coastal brown bears showed distinct shifts in their spatial distributions over the course of the summer, reflecting the shifting distribution of spawning sockeye salmon, which was associated with variation in water temperature among spawning sites. By tracking the spatial and temporal variation in the phenology of their principal prey, consumers substantially extended their foraging opportunity on a superabundant, yet locally ephemeral, resource. Ecosystem-based fishery management efforts that seek to balance trade-offs between fisheries and ecosystem processes supported by salmon should, therefore, assess the importance of life-history variation, particularly in phenological traits, for maintaining important ecosystem functions, such as providing marine-derived resources for terrestrial predators and scavengers.

PMID: 23554279 [PubMed – indexed for MEDLINE]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/pubmed/23554279?dopt=Abstract


Riding the crimson tide: mobile terrestrial consumers track phenological variation in spawning of an anadromous fish.

Riding the crimson tide: mobile terrestrial consumers track phenological variation in spawning of an anadromous fish.

Biol Lett. 2013;9(3):20130048

Authors: Schindler DE, Armstrong JB, Bentley KT, Jankowski K, Lisi PJ, Payne LX

Abstract
When resources are spatially and temporally variable, consumers can increase their foraging success by moving to track ephemeral feeding opportunities as these shift across the landscape; the best examples derive from herbivore-plant systems, where grazers migrate to capitalize on the seasonal waves of vegetation growth. We evaluated whether analogous processes occur in watersheds supporting spawning sockeye salmon (Oncorhynchus nerka), asking whether seasonal activities of predators and scavengers shift spatial distributions to capitalize on asynchronous spawning among populations of salmon. Both glaucous-winged gulls and coastal brown bears showed distinct shifts in their spatial distributions over the course of the summer, reflecting the shifting distribution of spawning sockeye salmon, which was associated with variation in water temperature among spawning sites. By tracking the spatial and temporal variation in the phenology of their principal prey, consumers substantially extended their foraging opportunity on a superabundant, yet locally ephemeral, resource. Ecosystem-based fishery management efforts that seek to balance trade-offs between fisheries and ecosystem processes supported by salmon should, therefore, assess the importance of life-history variation, particularly in phenological traits, for maintaining important ecosystem functions, such as providing marine-derived resources for terrestrial predators and scavengers.

PMID: 23554279 [PubMed – in process]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/pubmed/23554279?dopt=Abstract