Salmon and sea lice in BC

British Columbia (BC) is Canada's leading aquaculture producer, and has seen rapid growth of Atlantic salmon (Salmo salar) farms over the past two decades (DFO 2009). The salmon farming industry provides jobs and economic income to a region that has experienced declines in other major industries (e.g., forestry and commercial fisheries). However, the expansion of the salmon farming industry has not been without issue. Concerns from the public and scientific communities have included the exchange of disease and parasites between farmed and wild Pacific salmon (Krkosek 2010). The effect of sea lice from salmon farms on wild salmon in particular has been hotly debated in the literature (e.g., Krkosek et al. 2007, Brooks & Jones 2008, Krkosek et al. 2008).

Sea lice (Lepeoptheirus salmonis) are a parasitic copepod that feed on the skin and blood of salmonids, causing mechanical damage (Pike & Wadsworth 1999), physiological stress, inflammatory responses (Jones et al. 2007), behavioural change (Krkosek et al. 2011a) and host mortality (Krkosek et al. 2009, Morton & Routledge 2005). Although sea lice are native to both Pacific and Atlantic salmon (Costello 2006), Pacific salmon (Oncorhynchus spp.) have evolved a lifecycle that reduces the transmission of lice to juvenile salmon in the absence of salmon farms. Adult Pacific salmon return from the ocean to their natal rivers, spawn, and then die. This life cycle leaves few hosts to sustain significant sea lice populations over the winter, clearing a path for juveniles that emerge and migrate to sea the following spring. However, salmon farms offer a novel host that can sustain and even amplify lice populations through the winter (Krkosek et al. 2010). Pink (O. gorbuscha) and chum (O. keta) salmon are particularly vulnerable to lice from farms because of their small size at ocean entry.

The impact of sea lice on wild juvenile salmon has been studied (e.g., Jones et al. 2007, Krkosek et al. 2011a), and the productivity of wild salmon populations has been found to decline with exposure to salmon farming locally (Krkosek et al. 2007, Krkosek et al. 2011b) and globally (Ford & Myers 2008). However, there remains debate about the population level effects of sea lice on wild salmon (e.g., Marty et al. 2010) and the biotic and management factors that mediate the effect of sea lice on wild salmon are not well understood (Krkosek 2010). My goals are to determine factors influencing the rates of growth and decline of sea lice on salmon farms, and how these dynamics influence the infection pressures on wild juvenile salmon. Using mathematical models, I aim to determine the effect of parasitism on salmon migrations, and ultimately on wild salmon population productivity.

References

K. Brooks and S. Jones. Perspectives on pink salmon and sea lice: scientific evidence fails to support the extinction hypothesis. Reviews in Fisheries Science, 16(4):403–412, 2008.

B. M. Connors, M. Krkosek, J. Ford, and L. M. Dill. Coho salmon productiv- ity in relation to salmon lice from infected prey and salmon farms. Journal of Ap- plied Ecology, 47(6):1372–1377, 2010. doi: 10.1111/j.1365-2664.2010.01889.x. URL http://dx.doi.org/10.1111/j.1365-2664.2010.01889.x.

M. Costello. Ecology of sea lice parasitic on farmed and wild fish. Trends in Parasitology, 22:475–483, 2006.

Fisheries and Oceans Canada. Socio-economic impact of aquaculture in Canada. A report by Gardner-Pinfold Consulting Economists Ltd., Fisheries and Aquacul- ture Management, Fisheries and Oceans Canada, Ottawa, Ontario, 2009. URL http://www.dfo-mpo.gc.ca/aquaculture/ref/aqua-es2009-eng.htm.

J. Ford and R. Myers. A global assessment of salmon aquaculture impacts on wild salmonids. PLoS Biol, 6(2):e33, 2008.

S. Jones, M. Fast, S. Johnson, and D. Groman. Differential rejection of salmon lice by pink and chum salmon: disease consequences and expression of proinflammatory genes. Diseases of aquatic organisms, 75(3):229, 2007.

M. Krkosek and R. Hilborn. Sea lice (Lepeoptheirus salmonis) infestations and the productivity of pink salmon (Oncorhynchus gorbuscha) in the Broughton Archipelago, British Columbia, Canada. Canadian Journal of Fisheries and Aquatic Sciences, 68(1):17–29, 2011. doi: 10.1139/F10-137. URL http://www.nrcresearchpress.com/doi/abs/10.1139/F10-137.

M. Krkosek, M. Lewis, and J. Volpe. Transmission dynamics of parasitic sea lice from farm to wild salmon. Proceedings of the Royal Society B, 272(1564):689–696, 2005.

M. Krkosek, M. Lewis, A. Morton, L. Frazer, and J. Volpe. Epizootics of wild fish induced by farm fish. Proceedings of the National Academy of Sciences, 103(42):15506–15510, 2006.

M. Krkosek, J. Ford, A. Morton, S. Lele, R. Myers, and M. Lewis. Declining wild salmon populations in relation to parasites from farm salmon. Science, 318(5857):1772, 2007.

M. Krkosek, B. Connors, H. Ford, S. Peacock, P. Mages, J. S. Ford, A. Morton, J. P. Volpe, R. Hilborn, L. Dill, and M. Lewis. Fish farms, parasites, and predators: implications for salmon population dynamics. Ecological Applications, 21(3):897–914, 2011a.

M. Krkosek, B. M. Connors, A. Morton, M. A. Lewis, L. M. Dill, and R. Hilborn. Effects of parasites from salmon farms on productivity of wild salmon. Proceedings of the Na- tional Academy of Sciences, 108(35):14700–14704, 2011b. doi: 10.1073/pnas.1101845108. URL http://www.pnas.org/content/early/2011/08/12/1101845108.abstract.

M. Krkosek. Sea lice and salmon in Pacific Canada: ecology and policy. Frontiers in Ecology and the Environment, 8(4):201–209, 2010. doi: 10.1890/080097. URL http://www.esajournals.org/doi/abs/10.1890/080097.

M. Krkosek, J. Ford, A. Morton, S. Lele, and M. Lewis. Sea lice and pink salmon declines: a response to Brooks and Jones (2008). Reviews in Fisheries Science, 16(4):413–420, 2008.

M. Krkosek, A. Morton, J. Volpe, and M. Lewis. Sea lice and salmon population dynamics: effects of exposure time for migratory fish. Proceedings of the Royal Society B, 276:2819–2828, 2009. doi: 10.1098/rspb.2009.0317. URL http://rspb.royalsocietypublishing.org/cgi/content/abstract/rspb.2009.0317v2.

M. Krkosek, A. Bateman, S. Proboscz, and C. Orr. Dynamics of outbreak and control of salmon lice on two salmon farms in the Broughton Archipelago, British Columbia. Aquaculture Environment Interactions, 1:137–146, December 2010. doi: 10.3354/aei00014.

G. D. Marty, S. M. Saksida, and T. J. Quinn. Relationship of farm salmon, sea lice, and wild salmon populations. Proceedings of the National Academy of Sciences, 107(49), 2010. URL http://www.pnas.org/content/early/2010/12/03/1009573108.abstract.

A. Morton and R. Routledge. Mortality rates for juvenile pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon infested with sea lice (Lepeoptheirus salmonis) in the Broughton Archipelago. Alaska Fishery Research Bulletin, 11(2):146–152, Jan 2005.

A. Pike and S. Wadsworth. Sealice on salmonids: Their biology and control. Advances in Parasitology, 44:233 – 337, 1999. doi: DOI: 10.1016/S0065-308X(08)60233-X. URL http://www.sciencedirect.com/science/article/pii/S0065308X0860233X.