Salmon fry predation by seabirds near an Alaskan hatchery

Scheel, David; Kr, Hough

doi:10.3354/meps150035

Cited by 22 publications

(19 citation statements)

References 20 publications

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“…In 1995, field counts of seabirds and observations of feeding rates for plunge‐diving seabirds were also obtained during salmon fry releases from WHN Hatchery between April and June. The mortality of salmon due to seabird predation was estimated from these field observations and energetic models (Scheel and Hough, 1997).…”

Section: Methodsmentioning

confidence: 99%

Ecological processes influencing mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska

Willette

Cooney²,

Patrick

et al. 2001

Fisheries Oceanography

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Our collaborative work focused on understanding the system of mechanisms influencing the mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska. Coordinated field studies, data analysis and numerical modelling projects were used to identify and explain the mechanisms and their roles in juvenile mortality. In particular, project studies addressed the identification of major fish and bird predators consuming juvenile salmon and the evaluation of three hypotheses linking these losses to (i) alternative prey for predators (prey‐switching hypothesis); (ii) salmon foraging behaviour (refuge‐dispersion hypothesis); and (iii) salmon size and growth (size‐refuge hypothesis). Two facultative planktivorous fishes, Pacific herring (Clupea pallasi) and walleye pollock (Theragra chalcogramma), probably consumed the most juvenile pink salmon each year, although other gadids were also important. Our prey‐switching hypothesis was supported by data indicating that herring and pollock switched to alternative nekton prey, including juvenile salmon, when the biomass of large copepods declined below about 0.2 g m−3. Model simulations were consistent with these findings, but simulations suggested that a June pteropod bloom also sheltered juvenile salmon from predation. Our refuge‐dispersion hypothesis was supported by data indicating a five‐fold increase in predation losses of juvenile salmon when salmon dispersed from nearshore habitats as the biomass of large copepods declined. Our size‐refuge hypothesis was supported by data indicating that size‐ and growth‐dependent vulnerabilities of salmon to predators were a function of predator and prey sizes and the timing of predation events. Our model simulations offered support for the efficacy of representing ecological processes affecting juvenile fishes as systems of coupled evolution equations representing both spatial distribution and physiological status. Simulations wherein model dimensionality was limited through construction of composite trophic groups reproduced the dominant patterns in salmon survival data. In our study, these composite trophic groups were six key zooplankton taxonomic groups, two categories of adult pelagic fishes, and from six to 12 groups for tagged hatchery‐reared juvenile salmon. Model simulations also suggested the importance of salmon density and predator size as important factors modifying the predation process.

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Section: Methodsmentioning

confidence: 99%

Ecological processes influencing mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska

Willette

Cooney²,

Patrick

et al. 2001

Fisheries Oceanography

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“…Within the marine environment, aerial surveys have historically centred on apex predators, such as pinnipeds (Bengtson et al 1990, Thompson et al 2001) cetaceans (Sonntag et al 1999, Forcada et al 2004 and sea birds (Scheel & Hough 1997, Gilchrist & Mallory 2005. The underlying similarity of these species is their residence at the surface, or periodic requirement to return there to breathe.…”

Section: Introductionmentioning

confidence: 99%

Developing a simple, rapid method for identifying and monitoring jellyfish aggregations from the air

Houghton

Doyle²,

Davenport³

et al. 2006

Mar. Ecol. Prog. Ser.

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Within the marine environment, aerial surveys have historically centred on apex predators, such as pinnipeds, cetaceans and sea birds. However, it is becoming increasingly apparent that the utility of this technique may also extend to subsurface species such as pre-spawning fish stocks and aggregations of jellyfish that occur close to the surface. In light of this, we tested the utility of aerial surveys to provide baseline data for 3 poorly understood scyphozoan jellyfish found throughout British and Irish waters: Rhizostoma octopus, Cyanea capillata and Chrysaora hysoscella. Our principal objectives were to develop a simple sampling protocol to identify and quantify surface aggregations, assess their consistency in space and time, and consider the overall applicability of this technique to the study of gelatinous zooplankton. This approach provided a general understanding of range and relative abundance for each target species, with greatest suitability to the study of R. octopus. For this species it was possible to identify and monitor extensive, temporally consistent and previously undocumented aggregations throughout the Irish Sea, an area spanning thousands of square kilometres. This finding has pronounced implications for ecologists and fisheries managers alike and, moreover, draws attention to the broad utility of aerial surveys for the study of gelatinous aggregations beyond the range of conventional ship-based techniques. KEY WORDS: Aerial surveys · Gelatinous zooplankton · Jellyfish blooms · Scyphozoan · Rhizostoma octopus · Irish SeaResale or republication not permitted without written consent of the publisher

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“…Both competition and predation are thought to influence early marine mortality of juvenile salmon via density-dependent processes (Beamish and Mahnken 2001). High densities of hatchery salmon can lead to trophic competition (Fresh 1997;Ruggerone and Nielsen 2009) and to selective predation by predators attracted to unusually high fish concentrations (Scheel and Hough 1997). Therefore, as production of hatchery salmonids around the Pacific Rim and knowledge of density-dependent processes have increased, so have local and international concerns about salmon interactions and carrying capacity Zaporozhets and Zaporozhets 2004;Fukuwaka et al 2007).…”

mentioning

confidence: 99%

Lack of trophic competition among wild and hatchery juvenile chum salmon during early marine residence in Taku Inlet, Southeast Alaska

et al. 2011

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Early marine trophic interactions of wild and hatchery chum salmon (Oncorhynchus keta) were examined as a potential cause for the decline in harvests of adult wild chum salmon in Taku Inlet, Southeast Alaska. In 2004 and 2005, outmigrating juvenile chum salmon were sampled in nearshore habitats of the inlet (spring) and in epipelagic habitat at Icy Strait (summer) as they approached the Gulf of Alaska. Fish were frozen for energy density determination or preserved for diet analyses, and hatchery stocks were identified from the presence of thermal marks on otoliths. We compared feeding intensity, diets, energy density, and size relationships of wild and hatchery stocks (n=3123) across locations and weeks. Only hatchery fish feeding intensity was negatively correlated with fish abundance. In both years, hatchery chum salmon were initially larger and had greater energy density than wild fish, but lost condition in early weeks after release as they adapted to feeding on wild prey assemblages. Diets differed between the stocks at all inlet locations, but did not differ for hatchery salmon between littoral and neritic habitats in the outer inlet, where the stocks overlapped most. Both diets and energy density converged by late June. Therefore, if density-dependent interactions affect wild chum salmon, these effects must be very rapid because survivors in Icy Strait showed few differences. Our study also demonstrates that hatchery release strategies used near Taku Inlet successfully promote early spatial segregation and prey partitioning, which reduce the probability of competition between wild and hatchery chum salmon stocks.

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Salmon fry predation by seabirds near an Alaskan hatchery

Cited by 22 publications

References 20 publications

Ecological processes influencing mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska

Ecological processes influencing mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska

Developing a simple, rapid method for identifying and monitoring jellyfish aggregations from the air

Lack of trophic competition among wild and hatchery juvenile chum salmon during early marine residence in Taku Inlet, Southeast Alaska

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