Posted by: editor. | February 28, 2010

Important Research: sea lice and salmon population dynamics

Sea lice and salmon population dynamics: effects of exposure time for migratory fish

by Martin Krkošek, Alexandra Morton, John P. Volpe and Mark A. Lewis

Published by Royal Society Biology, April 2009 – full text at:

http://rspb.royalsocietypublishing.org/content/276/1668/2819.full.pdf+html?sid=c0a135fd-99fd-4112-b5da-cdb69525d23c

Abstract:       The ecological impact of parasite transmission from fish farms is probably mediated by the migration of wild fishes, which determines the period of exposure to parasites. For Pacific salmon and the parasitic sea louse, Lepeophtheirus salmonis, analysis of the exposure period may resolve conflicting observations of epizootic mortality in field studies and parasite rejection in experiments. This is because exposure periods can differ by 2–3 orders of magnitude, ranging from months in the field to hours in experiments. We developed a mathematical model of salmon–louse population dynamics, parametrized by a study that monitored naturally infected juvenile salmon held in ocean enclosures. Analysis of replicated trials indicates that lice suffer high mortality, particularly during pre-adult stages. The model suggests louse populations rapidly decline following brief exposure of juvenile salmon, similar to laboratory study designs and data. However, when the exposure period lasts for several weeks, as occurs when juvenile salmon migrate past salmon farms, the model predicts that lice accumulate to abundances that can elevate salmon mortality and depress salmon populations. The duration of parasite exposure is probably critical to salmon–louse population dynamics, and should therefore be accommodated in coastal planning and management where fish farms are situated on wild fish migration routes.

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