Use of stable isotopes to assess king and Spanish mackerel groups

Abstract

The number of stocks of king (Scomberomorus cavalla) and Spanish mackerel (S. maculatus) that exist in the Gulf of Mexico is unknown. Presently, both species are each treated as two stocks, an Atlantic migratory group and a Gulf of Mexico migratory group. There is evidence for existence of two stocks of these species within the Gulf of Mexico, but boundaries for the stocks are uncertain. Previous genetic and tag and recovery research suggest the Gulf of Mexico is comprised of two stocks of each species. King and Spanish mackerel were collected at ten sites in the Gulf of Mexico and along the southeast coast of the United States. Stable nitrogen (81,5N) and carbon (613C) isotope measurements were conducted on collagen extracted from the dorsal fin spines. Dorsal fin spines were divided into sections in order to determine isotopic trends and isotopic ranges within the spine. Stable nitrogen isotope results suggest that at least two groups of king mackerel exist within the Gulf of Mexico. The northwestern Gulf of Mexico king mackerel were significantly different, in nitrogen, from the Florida and Mexican king mackerel. Limited sample collection of Spanish mackerel made it difficult to differentiate isotopically distinct groups for this species.