Diet of the Hawaiian monk seal ( Monachus schauinslandi ) from the Northwestern Hawaiian islands during 1991 to 1994

Abstract

This study provides the first detailed description of the diet of the Hawaiian monk seal, Monachus schauinslandi. A total of 940 fecal and regurgitate samples were collected from the beaches of five islands in the Northwestern Hawaiian Islands (NWHI) between 1991 and 1994. Some samples were collected from known ages and sexes of seals. Prey were identified from all available hard parts and identified to the lowest possible taxa. Teleosts were the most represented prey (78.6%) followed by cephalopods (15.7%) and crustaceans (5.7%). Of the teleosts, 31 families were identified, 30 of which are prevalent reef-associated fishes. The most common families found were marine eels, Labridae, Holocentridae, Balistidae, and Scaridae. Of the cephalopods, 7 octopus species and 21 squid species were identified, representing coastal, benthic, and offshore-mesopelagic species. A significant difference was seen in both the teleost and cephalopod components of the diet of the Hawaiian monk seal among the years 1991 to 1994 among the islands in the NWHI chain, and among juvenile, subadult, adult female and adult male seals. Some overlap was seen between the diet of the Hawaiian monk seal and the commercial fisheries that currently exist in the NWHI. These findings indicate that Hawaiian monk seals are opportunistic predators that feed on a wide variety of available prey.