Résumé
Recent increases in emergent infectious diseases have raised concerns
about the population stability of some marine species. The complexity and
expense of studying diseases in marine systems often dictate that
conservation and management decisions are made without quantitative data
on population-level impacts of disease. Mark-recapture is a powerful,
underutilized, tool for calculating impacts of disease on population size
and structure, even in the absence of etiological information. We applied
logistic regression models to mark-recapture data to obtain estimates of
disease-associated mortality rates in three commercially-important marine
species: snow crab (Chionoecetes opilio) in Newfoundland, Canada, that
experience sporadic epizootics of bitter crab disease; striped bass
(Morone saxatilis) in the Chesapeake Bay, USA, that experience chronic
dermal and visceral mycobacteriosis; and American lobster (Homarus
americanus) in the Southern New England stock, that experience chronic
epizootic shell disease. All three diseases decreased survival of diseased
hosts. Survival of diseased adult male crabs was 1% (0.003 – 0.022, 95%
CI) that of uninfected crabs indicating nearly complete mortality of
infected crabs in this life stage. Survival of moderately and severely
diseased striped bass (which comprised 15% and 11% of the population,
respectively) was 84% (70 – 100%, 95% CI), and 54% (42- 68%, 95% CI) and
that of healthy striped bass. The disease-adjusted yearly natural
mortality rate for striped bass was 0.29, nearly double the previously
accepted value, which did not include disease. Survival of moderately and
severely diseased lobsters was 30% (15 – 60%, 95% CI) that of healthy
lobsters and survival of mildly diseased lobsters was 45% (27 – 75%, 95%
CI) that of healthy lobsters. High disease mortality in ovigerous females
may explain the poor recruitment and rapid declines observed in this
population. Stock assessments should account for disease-related mortality
when resource management options are evaluated.