Assimilation efficiency of prey in the Hawaiian monk seal (Monachus schauinslandi)

Assimilation efficiency, digestive efficiency, metabolizable energy, and ni trogen retention in three captive adult male Hawaiian monk seals (Monachus schauinslandi) were measured with the indigestible marker chromic oxide for four experimental diets: a control diet of herring (Clupea harengus) and t hree test diets consisting of flagtail (Kuhlia sandvicensis), squid (Loligo sp.), and lobster (Panulirus marginatus), each of which was used in combin ation with herring. The addition of all three test prey to herring decrease d the digestibility of gross energy by a mean of 3.58 +/- 3.89%. Assimilati on efficiency of gross energy was 96.1 +/- 4.0% for herring, 73.8 +/- 6.8% for flagtail, and 94.1 +/- 5.7% for squid, but could not be determined for lobster. Digestive efficiency and metabolizable energy of the diets examine d were high (4602.2 +/- 247.1 and 4062.5 +/- 178.4 kcal/d, respectively; 1 kcal = 4.18 kJ) and were positively correlated with the amount of gross ene rgy ingested. Nitrogen retention was highest for the squid-herring diet (33 .2 +/- 1.2 g.d(-1)) followed by the lobster-herring diet (11.5 +/- 3.3 g.d( -1)), the flagtail-herring diet (6.0 +/- 0.0 g.d(-1)), and the herring (con trol) diet (-5.7 +/- 1.6 g.d(-1)). This study indicates that prey which are both higher in protein and lower in fat than herring provide greater metab olizable energy for productive functions in Hawaiian monk seals.