Length-weight relations and growth rates of dominant fishes of the Salton Sea: implications for predation by fish-eating birds

The Salton Sea is the largest lake in California. Inflows are primarily from agricultural runoff, which render it eutrophic and able to support extensive fisheries. The lake and its surrounding wetlands are critical links for the Pacific Flyway, providing refuge and food for an extensive and diverse avifauna. We document fish size distributions, body shapes and growth rates and consider how they determine availability of fish to birds. Tilapia (Oreochromis mossambicus x O. urolepis hornorum) is the most important resource for fish-eating birds. Tilapia grow fast to a size that is readily handled by large birds and are the most abundant fish in the lake. Bairdiella (Bairdiella icistia) grow to a smaller size over a longer period. Corvina (Cynoscion xanthulus), sargo (Anisotremus davidsoni), and shad (Dorosoma cepedianum) are less important for fish-eating birds because they quickly grow to sizes outside bird handling capabilities (corvina) or are not readily catchable and currently of low abundance (shad and sargo). Shape, in particular girth, determines the weight of the largest individual fish that a bird can handle; a slender 1,000 g corvina, for example, being more easily ingested than a deeper-bodied 1,000 g tilapia. Shape, however, is of secondary importance to growth rate in determining importance of a fish species in a bird's diet. Predation by corvina on tilapia and other smaller species may have historically played a large role in determining availability of fish to fish-eating birds.