MARINE MAMMAL SCIENCE, 30(2): 763–781 (April 2014) © 2013 Society for Marine Mammalogy DOI: 10.1111/mms.12078 Analysis of growth and stable isotopes in teeth of male Australian fur seals reveals interannual variability in prey resources TRAVIS C. KNOX, 1 School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125, Australia; HILARY STUART-WILLIAMS, Research School of Biology, Australian National University, Canberra, Australian Capital Territory 0200, Australia; ROBERT M. WARNEKE, Blackwood Lodge, 1511 Mount Hicks Road, Yolla, Tasmania 7325, Australia; ANDREW J. HOSKINS and JOHN P. Y. ARNOULD, School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125, Australia. Abstract To detect and monitor long-term ecosystem responses to environmental variabil- ity, managers must utilize reliable and quantitative techniques to predict future eco- system responses. Canine teeth from 67 male Australian fur seals (aged 2–19 yr), collected at Seal Rocks, between 1967 and 1976, were measured for relative growth within the dentine growth layer groups (GLGs), as an index of body growth. Fluctua- tions in relative growth were apparent during 1956–1971, suggesting interannual variation in prey resources within Bass Strait. These were positively correlated with the Southern Oscillation Index and negatively with the Indian Ocean Subtropical Dipole, both on a 2 yr lag. The observed delay may reflect the time required for the nutrient cascade to filter through to the predominantly benthic prey of Australian fur seals. Stable isotope analysis (d 15 N/d 13 C) was also used to investigate whether fluctu- ations in growth were associated with differences in diet. Relative growth was found to be negatively correlated with d 15 N, suggesting years of greater resource availabil- ity may be associated with individuals consuming proportionally more prey biomass of lower isotopic value. This study demonstrates that fluctuations in the dentine GLGs of male Australian fur seals are related to environmental parameters, suggest- ing variation in body growth is mediated by changes in prey resources. Key words: Australian fur seal, tooth growth, dentine, stable isotope, environmental variability, pinniped. The global climate is currently warming at an unprecedented rate, which is having substantial impacts on habitat and ecosystem structures (Harley et al. 2006, Cleugh et al. 2011). Despite this accelerated warming, ecosystem managers already face inherent difficulties in monitoring long term ecological responses to ecosystem vari- ability, particularly within the marine environment. These difficulties within the marine environment often pertain to the complex and submerged nature of trophic 1 Corresponding author (e-mail: tckn@deakin.edu.au). 763