Phylogeography of the Pacific Sardine, Sardinops sagax, in the Northeastern Pacific

The Pacific Sardine, (Sardinops sagax), is a small, coastal pelagic species in the family Clupeidae. Sardine are an ecologically important forage fish for many animals, including larger, economically and ecologically important fishes, and have historically supported an important commercial fishery. When the fishery declined in the 1940s, a massive effort in understanding population structure for the Pacific Sardine resulted in a wealth of literature. Initially, these studies agreed on a large panmictic population with high annual variation, but the general consensus has since been that there are multiple subpopulations of the Pacific Sardine along the West Coast of North America. However, there has been no molecular evidence that disparate groups exist within the Pacific Sardine in the Northeastern Pacific. Marine fishes often do not show deep population structure, and regional populations of Sardinops are subject to massive natural population fluctuations which often result in shallow gene lineages. Mitochondrial sequences are known for their rapid mutation rates as compared to nuclear gene sequences, thus are good indicators of population structure over evolutionary time scales. To test if population structure was apparent in Sardines, 434 individuals were examined ranging from Vancouver Island, British Columbia to Bahía Magdalena, Baja California, and a group from the Gulf of California. A 1062 bp fragment of the cytochrome b gene yielded extremely low but significant fixation rates for ɸST. Concordantly low fixation was observed for ɸCT, and was non-significant in all but one instance. These data support the null hypothesis of an absence of genetic structure in the Pacific Sardine.