Researching Reef Fish Life Histories with NOAA & DAR

What does Life History Mean? Species can be described by a wide range of traits, including behavioral patterns (e.g., diurnal activity, schooling size, preferred temperature in water column); morphological body types (e.g., maximum body size, body shape, mouth position); ecological influences (e.g., diet, spawning strategy, depth of occurrence, life span); and biogeographical limitations (e.g., geographic range extension, species distribution). Life history research seeks to understand different subsets of these traits better and inform more sustainable fishery management practices. For example, fish population health is reliant on reproductive adults, which tend to be the oldest and largest fish–the types of fish most likely to be targeted during fishing. By collecting data from these older fish, researchers can determine the lifespan of fish in the population or when in a season new generations are spawned, which informs more accurate stock assessment models.

How do we get that information? Otoliths, small calcium carbonate structures in a fish’s inner ear, are powerful tools for understanding fish life history. Much like tree rings, otoliths form annual growth layers that reveal a fish’s age, growth rate, and even movements across different ocean environments. Since otoliths are thin bones, they are quite fragile. To count their rings, the otolith is encased in epoxy, then the block is cut in half to show the cross-section of the rings. Maggie Chen, an undergraduate student in PICCH, has been using otoliths to study the life history of Gindai (Pristipomoides zonatus) in Hawaiʻi and the Mariana Islands.