Journal
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 281, Issue 1776, Pages -Publisher
ROYAL SOC
DOI: 10.1098/rspb.2013.2913
Keywords
parasite; predation; functional response; salmon; sea lice; model
Categories
Funding
- Alberta Ingenuity Graduate Scholarship
- Vanier Scholarship
- Mathematics of Information Technology and Complex Systems internship
- Watershed Watch Salmon Society
- ESSA Technologies Ltd.
- Save our Salmon Society
- NSERC
- Canada Research Chair
- Killam Research Fellowship
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The impact of parasites on hosts is invariably negative when considered in isolation, but may be complex and unexpected in nature. For example, if parasites make hosts less desirable to predators then gains from reduced predation may offset direct costs of being parasitized. We explore these ideas in the context of sea louse infestations on salmon. In Pacific Canada, sea lice can spread from farmed salmon to migrating juvenile wild salmon. Low numbers of sea lice can cause mortality of juvenile pink and chum salmon. For pink salmon, this has resulted in reduced productivity of river populations exposed to salmon farming. However, for chum salmon, we did not find an effect of sea louse infestations on productivity, despite high statistical power. Motivated by this unexpected result, we used a mathematical model to show how a parasite-induced shift in predation pressure from chum salmon to pink salmon could offset negative direct impacts of sea lice on chum salmon. This shift in predation is proposed to occur because predators show an innate preference for pink salmon prey. This preference may be more easily expressed when sea lice compromise juvenile salmon hosts, making them easier to catch. Our results indicate how the ecological context of host-parasite interactions may dampen, or even reverse, the expected impact of parasites on host populations.
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