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Abstract How has parasitism changed for Alaskan salmon over the past several decades? Parasitological assessments of salmon are inconsistent across time, and though parasite data are sometimes noted when processing fillets for the market, those data are not retained for more than a few years. The landscape of parasite risk is changing for salmon, and long‐term data are needed to quantify this change. Parasitic nematodes of the family Anisakidae (anisakids) use salmonid fishes as intermediate or paratenic hosts in life cycles that terminate in marine mammal definitive hosts. Alaskan marine mammals have been protected since the 1970s, and as populations recover, the density of definitive hosts in this region has increased. To assess whether the anisakid burden has changed in salmonids over time, we used a novel data source: salmon that were caught, canned, and thermally processed for human consumption in Alaska, USA. We examined canned fillets of chum (Oncorhynchus keta,n = 42), coho (Oncorhynchus kisutch,n = 22), pink (Oncorhynchus gorbuscha,n = 62), and sockeye salmon (Oncorhynchus nerka,n = 52) processed between 1979 and 2019. We dissected each fillet and quantified the number of worms per gram of salmon tissue. Anisakid burden increased over time in chum and pink salmon, but there was no change in sockeye or coho salmon. This difference may be due to differences in the prey preferences of each species, or to differences in the parasite species detected across hosts. Canned fish serve as a window into the past, providing information that would otherwise be lost, including information on changes over time in the parasite burden of commercially, culturally, and ecologically important fish species.
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Juvenile Chum Salmon and Pink Salmon use of submerged vegetative habitats and the influence of an apex predator
ABSTRACT ObjectiveApex-predator-initiated trophic cascades occur in many nearshore marine habitats that simultaneously serve as critical habitat and food sources for commercially and ecologically important species, including juvenile Pacific salmon Oncorhynchus spp. Yet the potential relationships among apex predators (e.g., sea otters Enhydra lutris), submerged aquatic vegetation, and juvenile salmonids are not well understood. In Southeast Alaska, we investigated (1) juvenile salmonid abundance in eelgrass Zostera marina meadows and understory kelp beds and (2) potential drivers of juvenile Chum Salmon Oncorhynchus keta and Pink Salmon O. gorbuscha abundance in eelgrass meadows. MethodsWe analyzed historic (1998–2007) beach seine surveys to compare juvenile salmonid abundance in nearshore habitats. We then employed the same survey (2017, 2019) in eelgrass to quantify juvenile salmonid abundance alongside the influence of sea otter density (number/km2), distance from anadromous stream (km), seasonality, sediment categorization, and aboveground eelgrass biomass (g/m2). ResultsWe found greater abundance of Chum Salmon in understory kelp compared with eelgrass, whereas Pink Salmon abundance was similar between habitats. In eelgrass, Chum Salmon abundance peaked in June and was positively associated with sea otter density. Pink Salmon abundance varied seasonally, peaking in May. We found increased Pink Salmon abundance with increasing sea otter density and distance from anadromous stream and decreased abundance with increased eelgrass biomass. ConclusionGrowth and survival while juvenile salmonids are out-migrating from streams and relying on nearshore vegetated habitats can determine if they recruit to fisheries as adults. Here, we highlight the use of multiple habitats, eelgrass and understory kelp, indicating that both should be explored as critical nursery habitat. We present evidence of indirect effects of sea otters influencing the abundance of juvenile salmonids, with potential further implications as sea otter populations expand. Apex predators, quality of vegetated habitats, and their structuring roles in the nearshore are critical for informing adaptive coastal fisheries management.
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- Award ID(s):
- 2022190
- PAR ID:
- 10581988
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Marine and Coastal Fisheries
- Volume:
- 17
- Issue:
- 2
- ISSN:
- 1942-5120
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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