Jack Silverside

Atherinopsis californiensis

The jack silverside, better known to Californian anglers as the jacksmelt, is the largest of the West Coast silversides and the only member of its genus. It reaches about 49 cm and occasionally 55 cm, far outgrowing the topsmelt it is routinely confused with; a yellow blotch on the gill cover behind the eye and the heavier body are the easiest ways to tell the two apart underwater. The body is bright silver with a grey wash over the back. Its range runs down the Pacific coast from Yaquina Bay in Oregon to Bahia Magdalena in Baja California Sur, and it is at home in bays and estuaries as readily as on the open coast, tolerating a wide swing in salinity. Divers meet it in the top few metres over sand and along kelp edges, where daytime schools hang in the sunlit water and scatter in a sheet of mirrors when approached; it is rarely found below about 29 m. Spawning happens inshore on the bottom, the eggs bound to one another and to weed by sticky filaments in the egg case, while newly hatched larvae drift at the very surface grazing phytoplankton. It is netted commercially for food, and its sheer abundance makes it an important forage fish for seabirds, sea lions and larger predatory fish.