The diet and digestive physiology of the Hawaiian monk seal, Monachus schauinsland

The intent of this research was to gain a better understanding of the feeding ecology of the Hawaiian monk seal (Monachus schauinslandi ) through prey identification and digestive physiology studies because little work has been performed on these aspects of feeding ecology to date.;The total intestine length to standard body length ratio is 8.3:1 +/- 1.4 (n = 12), which is significantly smaller than harbor seal and Northern elephant seal ratios, but was not different from other phocids.;Diet of the Hawaiian monk seal was determined from 940 fecal and regurgitate samples collected from the Northwestern Hawaiian Islands (NWHI) between 1991 and 1994. Seals consumed teleosts (78.6%), cephalopods (15.7%) and crustaceans (5.7%). A significant difference was seen in the diet among the years 1991--1994, among the NWHIs, and among juvenile, subadult, adult female and adult male seals.;Proximate nutrient, mineral, amino acid and fatty acid composition were determined for the more common prey of the Hawaiian monk seal. Gross energies ranged from 4.0 +/- 0.01 kcal/g (Labridae) to 6.0 kcal/g (moray eel). Total amino acid concentrations were similar to those required by other organisms. Fatty acid concentrations varied among species (range = 1.2--16.5%); however, teleosts had higher total fatty acids than non-teleosts.;Initial defecation time (IDT) and rate of passage of digesta were determined using three captive adult male seals. The IDT ranged from 9.5 to 19 h and the rate of passage was approximately 39 h. Both measurements were longer than that reported for other pinnipeds.;Assimilation efficiency, digestive efficiency, metabolizable energy, and nitrogen retention were measured using three adult male seals fed four diets: herring (control), flagtail (Kuhliidae), squid, and lobster. Assimilation efficiency of gross energy was highest for herring, then squid, and flagtail. Digestive efficiency and metabolizable energy were positively correlated with the amount of energy ingested. Nitrogen retention ranged from 33.19 +/- 1.18 g*d-1 (flagtail/herring) to -5.69 +/- 1.58 g*d-1 (herring). These studies indicate the Hawaiian monk seal is an opportunistic forager that eats and digests high energy prey; therefore, starvation of juveniles may be due to a reduced availability of prey.