Demographic and morphological responses to prey depletion in a crested tern (Sterna bergii) population: can fish mortality events highlight performance indicators for fisheries management?

Abstract

<jats:title>Abstract</jats:title><jats:p>McLeay, L. J., Page, B., Goldsworthy, S. D., Ward, T. M., Paton, D. C., Waterman, M., and Murray, M. D. 2009. Demographic and morphological responses to prey depletion in a crested tern (Sterna bergii) population: can fish mortality events highlight performance indicators for fisheries management? – ICES Journal of Marine Science, 66: 237–247. Disease-related mortality events in 1995 and 1998, which killed ∼70% of adult sardine (Sardinops sagax) biomass, provided an opportunity to assess whether crested tern (Sterna bergii) populations were affected by decreased prey abundance. We investigated the diet, age structure, and morphology of a population of crested terns to determine whether survival and growth were reduced for cohorts reared in years immediately following sardine mortality events. The diet of chicks and adults differed significantly. Australian anchovy (Engraulis australis) and sardine were the dominant prey in the diets of chicks, constituting an average of 36.3 and 14.6% of individual prey items, respectively. Degens leatherjacket (Thamnoconus degeni) dominated the prey of adult terns, an average of 51.9% of individual prey items. Age-specific information collected from banded adults indicated that the cohort reared after the first sardine mortality event in 1995 exhibited significantly lower rates of recruitment to the breeding colony than as predicted by life-table analyses, suggesting that survival was reduced in response to the absence of sardine. Females from cohorts reared &lt;1 year after the end of each sardine mortality event (in 1996 and 1999) were smaller than other age classes, suggesting that chick growth was reduced during periods of low sardine abundance. Future data on diet and on the survival and growth of crested tern chicks could provide performance indicators for management of sardine populations and aid in the development of conservation strategies for the populations of crested tern.</jats:p>