Fulton's condition factor: Is it a valid measure of sea lice impact on juvenile salmon?

Condition factor formulas have been developed and are used to assist in assessing the state of fish health. Fulton's condition factor has been used to measure anthropogenic impacts on fish, such as oil spills, and has provided results that, at times, are contentious. Recently, it has been used to suggest that infestation rates of sea lice Lepeophtheirus salmonis currently reported for juvenile pink salmon Oncorhynchus gorbuscha and chum salmon O. keta in the Broughton archipelago, British Columbia, may have no impact on fish health. Here, we show that Fulton's condition factor values will remain high in salmon fry lethally infected with sea lice until shortly before death. Furthermore, we report that as condition factor values declined, the affected fish exhibited high predator risk behavior. We conclude that Fulton's condition factor does not provide a reliable indicator of the impact of sea lice infestations on juvenile pink and chum salmon.