Fish otoliths, or ear stones, are mm-sized structures located in the auditory canals of teleost fish and function as hearing, balance and postural control. The use of stable oxygen and carbon isotope ratios (18O/16O or d18O, and 13C/12C or d13C) in otoliths has received growing attention in recent years, particularly in examining the climate-related regime shifts in fisheries research. The principle is that otoliths are likely precipitated in oxygen isotopic equilibrium with the ambient seawater, and the isotopic fractionation of 18O/16O is temperature dependent. Carbon isotopes of otoliths have offsets from equilibrium, but may reflect metabolic sources and dietary shift as the fish grow. In this study, we report results of using archived otoliths of Pacific halibut (Hippoglossus stenolepis) to detect regime shifts in the northeast Pacific, and the migration paths of tagged Pacific halibut from the Bearing Sea to British Columbia of Canada.
Results/Conclusions
The d18O values of selected otoliths ranged from -1.5 to +2.8 ‰, whereas the d13C values of the same samples ranged from -3.3 to +0.9 ‰. Isotopic data from otoliths of tagged halibut suggested that the ocean conditions between the Bering Sea and the Gulf of Alaska were markedly different, but the boundaries between the Gulf of Alaska and British Columbia were not clear. Evaluation of the isotopic composition of mature halibut (ages 8-12) indicated that the 1977 regime shift was an event of warming; while the 1990 regime shift may reflect a temperature decrease of about 2 oC in bottom seawater. More regime shifts are being determined with the dataset. The connection between isotopic variations in otoliths and the regime shifts is thus potentially useful in assessing the population dynamics of Pacific halibut, and the decadal-scale (e.g., the last 20-30 years) ocean ecosystem changes.