Spawning Origins and Ontogenetic Movements for Demersal Fishes: An Approach Using Eye-lens Stable Isotopes

The larval to postlarval period (the period between egg and juvenile) of many continental-shelf fish species lasts only a few weeks but has been shown to be critical to survival. During this period, individuals may travel long distances from spawning to juvenile habitats and are often difficult to locate. Fish eye lenses, which are constructed sequentially with minimal tissue turnover, record successive isotopic values for the entire lifespan. We present a widely applicable method of using the isotope values from the inner-most eye lens lamina (core: representing the larval to postlarval period) as a historical record of early life movement and location. By correlating the eye-lens core δ13C and δ15N values with juvenile capture location (i.e. settlement habitat) or with core size (i.e., growth during the first few weeks of life), we interpreted variability within the isotope values of a species as geographic origin and movement. We then evaluated the method using four northeastern Gulf of Mexico reef-fish species. Gag isotope values indicated movement inshore during the postlarval period. Red Grouper values suggested movement in both the inshore and alongshore directions. Black Seabass isotope values indicated a widely distributed early life with potential southward movement. Red Snapper isotope values suggested that larvae and postlarvae are widely distributed along the outer continental shelf, but do not move far from spawning origins in the eastern Gulf of Mexico. Bulk isotope values in fish eye lens cores can strengthen early life origin and movement data for many species of marine fishes, including those for which little early-life information exists.