Sources of otolith barium and strontium in estuarine fish and the influence of salinity and temperature

Otoliths are commonly used to reconstruct migratory patterns and to determine stock structure of fish, owing to the chemical relations between water and otolith chemistry. Water is only 1 source of variation in otolith chemistry, and the contribution that diet plays to the chemical composition of otoliths under different environmental influences, including temperature and salinity, has been largely unexplored. To determine the percentage contributions from water and diet to otolith Ba and Sr, juvenile Acanthopagrus butcheri (Munro 1949) (Sparidae) were reared in 3 different salinities under 3 different water temperatures. For the first time, both rearing water and diet were enriched with stable isotopes of Ba (Ba-137 and Ba-136) and Sr (Sr-88 and Sr-86); thus enabling us to determine contributions of water versus diet to the otolith. Ambient water was the primary contributor to otolith Ba (between 62 and 84%) and Sr (between 59 and 84%). Water contributions to otolith Ba were not significantly affected by temperature or salinity. A significant interactive effect of temperature and salinity on water contributions to otolith Sr was detected, which was most evident at high temperatures where contributions from the water decreased with increasing salinity. This study supports water as the primary contributor of otolith chemistry and suggests that the contribution of water can be influenced by environmental factors such as temperature and salinity.