A Large-Scale Study of Diet and Morphology of Black Perch ( Embiotoca jacksoni): Comparing Stomach Content and Stable Isotope Analyses

Abstract

A species’ diet is central to shaping both its life history and the dynamics of its populations. I measured diet and morphology of Black Perch (Embiotoca jacksoni) within eight different populations located throughout the Southern California Bight. Diet was assessed using three different methods including stable isotope analysis (SIA), stomach content analysis (SCA), and electivity (E), an index that accounts for differences in prey availability. My goals were 1) to evaluate the degree to which diets varied among populations, and 2) to assess the agreement of SIA and SCA by comparing estimated diets in three focal populations where I also analyzed isotopes of prey.

The results revealed considerable among-population variation in morphology, including traits such as eye size (among-population component of variance (APCV) = 27%) and gape (APCV = 24%). However, there were no obvious patterns such as island versus mainland morphotypes, or spatial similarity in morphology. The APCV in diet was substantial (42% for SIA, 37% for SCA) and significant among population variation in electivity (18% of total) suggested that fish in different populations preferred different sets of prey. There was modest agreement between diet reconstructed from stable isotope signatures, and diet inferred from stomach contents. Stable isotope mixing models indicated that decapods and polychaetes may be more common or important prey than stomach contents suggest. These results indicate that diets of Black Perch populations may be more variable than previously thought; that populations vary with respect to prey preference; and that SCA can be augmented with SIA to provide more accurate estimate diets within wild populations.