ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on November 30, 2008
ICES Journal of Marine Science: Journal du Conseil 2009 66(2):237-247; doi:10.1093/icesjms/fsn195
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Demographic and morphological responses to prey depletion in a crested tern (Sterna bergii) population: can fish mortality events highlight performance indicators for fisheries management?
1 South Australian Research and Development Institute, Aquatic Sciences, 2 Hamra Avenue, West Beach, PO Box 120, Henley Beach, South Australia 5022, Australia
2 School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
3 303 Payneham Road, Royston Park, South Australia 5070, Australia
4 17 Ashmore Avenue, Pymble, New South Wales 2073, Australia
Correspondence to L. J. McLeay: tel: +61 08 8207 5439; fax: +61 08 8207 5406; e-mail: mcleay.lachie{at}saugov.sa.gov.au.
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 <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.
Keywords: crested tern, demography, ecosystem-based management, indicator, morphology, prey availability, sardine, seabird, Sterna bergii, survival
Received 20 May 2008; accepted 26 October 2008; advance access publication 30 November 2008.