Fraser River sockeye salmon: data synthesis and cumulative impacts

wild salmonids, but it is highly lethal for farm salmon if they are not vaccinated. Parasitesinclude Parvicapsula (freshwater, marine), Ich (freshwater), PKX (found previously in kokanee;freshwater and marine) and sea lice. Not a lot of effort was devoted to sea lice because it isexpected to be dealt with in-depth in the fish farm paper. It is very controversial there is noinformation specific to sockeye salmon.Assessing impacts of chronic infections (e.g. parasites): Criteria for investigations includehaving adequate data on prevalence and abundance; infections that are easy to identify andevaluate and which persist; and temporal studies, which can be difficult to do with salmonids,since you need to look at what is happening over time.Parasite distribution issues include abundance vs. prevalence. Normal is not normal for parasites(negative binomial distribution) and having many animals with no or light infections, but fewwith heavy infections. A 1971 Crofton paper compares predicted and observed frequency of theparasite, based on data from lightly-infected animals, to provide parasite-associated mortality.Impacts of highly-virulent pathogens: Virulence is documented in lab studies and prevalenceneeds to be considered at various life stages. Environmental influences include temperature(most pathogens increase with temperature, as do hosts vectors, while temperature influences theimmune status of fish). Pollution and contaminants may also play a role. Organic eutrophicationcan increase intermediate hosts and opportunistic fungi and bacteria. Toxicants can impair fishimmune systems but may also kill invertebrate hosts. Land use practices are a key consideration,as temperature and organic loads influence prevalence and abundance of pathogens, directly andindirectly. Land use practices have also been strongly linked to these changes in other systems.Conclusions: Most research on disease has focused on hatchery fish and there is minimal dataon the marine phase. There have been few documented outbreaks for BC sockeye and limitedsurvey data do not point to increases. Many potential pathogens could cause wild mortality andKent agrees for the most part with the PSC’s potential list.Recommendations include more research, especially in the marine phase; continuedsurveillance of farmed fish; surveys and data collection so that established methods can beapplied; collaborative research with ecologists, oceanographers and epidemiologists toinvestigate links of prevalence and abundance with environmental factors and land use practices.DiscussionReynolds: How specific are these pathogens to specific species of salmon? And is it a good ideato restrict the scope to known cases involving sockeye?Kent: I don’t exclude any from the list. Where sockeye are less susceptible to disease, I wouldput it as a moderate risk assessment.Reynolds: Is that a good criterion to use? If studies show sea lice can infect other species ofsalmon, it might be useful to tackle it head-on, to take sea lice out of the picture.Kent: There are some studies, with pretty empirical data. Others just reported it in pinks. Itwould be good to separate whether the studies document that sockeye are not susceptible orwhether it was just not seen.Q: Will the fish farm study go ahead?42