Assimilation Efficiency of Northern Fur Seals Determined Using Dietary Manganese

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Abstract
We validated the use of dietary manganese (Mn2+) as an inert marker for estimating assimilation efficiency (AE%) of captive northern fur seals (Callorhinus ursinus) for possible applications to free-ranging marine mammals. Dietary Mn2+ derived AE% estimates were compared to estimates from Cr2O3 and 51Cr marker techniques. Assimilation efficiency measured using Mn2+ was 90.0 .+-. 1.2 (SE)% which was not significantly different from estimates using other marker techniques. Excess Mn2+ added to the diet was fully recovered in the feces, indicating that Mn2+ functioned as an unabsorbed marker. The Mn2+ technique might permit measurement of AE% in free-ranging marine mammals.