Temporal variation in Steller sea lion diet at a seasonal haul-out in southeast Alaska

Abstract

Pinniped diet may vary spatially and temporally and can be influenced by prey availability. Several prey species of Steller sea lions are densely aggregated during the nonbreeding season of sea lions and may be seasonally important because sea lion energetic requirements increase during winter and spring. To assess temporal variation in Steller sea lion diet at Benjamin Island in Lynn Canal, Southeast Alaska, we collected scat samples (n = 787) each February, April, October, and December from 2001 to 2004. Scat samples were not collected during summer because few sea lions were present at Benjamin Island during that season. Pacific herring (frequency of occurrence [FO] = 90.0%) and walleye pollock (FO = 87.5%) were the two most common prey species in sea lion scat samples, followed by skate, Pacific salmon, Pacific cod, capelin, cephalopods, north ern lampfish, sculpins, arrowtooth flounder, eulachon, and Pacific hake. The FO of herring, pollock, skates, Pacific cod, and cephalopods did not differ significantly between seasons; however, the FO of capelin, Pacific salmon, northern lampfish, sculpins, arrowtooth flounder, eulachon, and Pacific hake differed between seasons. Sea lion diet diversity increased in spring and corresponded to the spawning season of several forage fish species. Exploiting salmon in fall, herring during winter, and eulachon, capelin, and northern lampfish in spring likely helps sea lions meet the increased energetic demands that occur during winter and spring.