Vitamin D content in Alaskan Arctic zooplankton, fishes, and marine mammals

We postulated that dietary ingestion of vitamin D may be used by some Alaskan Arctic marine mammal species in addition to, or instead of, cutaneous production to meet nutritional requirements. Zooplankton ( n =5) sampled near Kaktovik, Alaska, contained no measurable vitamin D 2 or D 3 , but did contain provitamin D (7‐dehydrocholesterol), the cutaneous precursor for previtamin D 3 in mammals. Fillets and livers from five fish species were sampled near Barrow, Alaska, and evaluated for vitamin D 3 content (no vitamin D 2 was detected). Differences in vitamin D 3 content appeared significant ( P ≤0.10) among fish livers (Kruskal‐Wallis [H test]=8.25, df =4, P =0.08) and among fish fillets (H=7.80, df =4, P =0.01). We also found significant differences in several pairwise comparisons (Mann‐Whitney U‐test) of vitamin D 3 levels in fillets and livers. Blubber from six species of marine mammals had no detectable vitamin D 2 . The H test results for blubber vitamin D 3 concentration were highly significant: 28.12, df =5, P <0.001. There were also significant differences in vitamin D 3 content from blubber in pairwise comparisons of primarily invertebrate feeders (bowhead whale ( Balaena mysticetus ) [mean=4.20 SD±1.10 ng/g], and Pacific walrus ( Odobenus rosmarus divergens ) [5.43±2.82 ng/g]) vs. primarily piscivorous feeders (ringed seal ( Phoca hispida ) [746.57±493.00 ng/g] and beluga whale ( Delphinapterus leucas ) [426.00±174.92 ng/g]) and a semiaquatic terrestrial carnivore (polar bear ( Ursus maritimus ) [406.17±311.70 ng/g]). The bearded seal ( Erignathus barbatus ) had intermediate blubber vitamin D 3 concentration (156.83±139.25 ng/g), which may reflect an intermediate‐type feeding strategy or an artifact of the small sample size. Zoo Biol 23:33–43, 2004. © 2004 Wiley‐Liss, Inc.