Inferring movement patterns of a coral reef fish using oxygen and carbon isotopes in otolith carbonate

Ratios of oxygen and carbon isotopes (δ18O and δ13C) in otolith carbonate provide information on stock separation and migration of fish populations inhabiting isotopically different environments. δ18O and δ13C were analysed from Lethrinus miniatus (Forster 1801) otoliths to elucidate the probability of broad-scale movement in the Great Barrier Reef. Otolith core and edge portions were compared between and within individuals from the same cohort (n = 120) to determine whether isotopically different environments were inhabited by juveniles and adults from different latitudes. A comparison between individuals revealed that δ18O and δ13C increased with latitude and were generally higher in edge than in core portions. Similarly, within most individual otoliths, δ18O and δ13C were higher in edge than in core portions. For some individuals, however, there was no difference in δ18O between core and edge portions, potentially signifying self-recruitment to the area or occupation of areas of similar chemistry. The majority of individuals from 19 to 22°S and almost half of individuals from 18°S displayed juvenile δ18O signatures characteristic of a warmer environment, suggesting movement to cooler environments or potential southerly migration of early life stages to adult habitat. In contrast, almost half of adult individuals in the most northern latitude (18°S) appeared to originate from cooler environments, suggesting movement to warmer environments or potential northward migration with ontogeny. These results infer that movement of L. miniatus individuals occurred across different isotopic environments with life stage and was related to latitude. Isotope ratios provided insight into movement patterns of L. miniatus at scales that will be important for delineating management units for this commercially important species