Abstracts Biological Sciences

Effects of diet on growth and development of nesting seabirds

by Marc D. Romano

Recent declines in nesting success of some fish-eating seabirds in Alaska have been attributed to declines in availability of certain schooling forage fishes (e.g., capelin Mallotus villosus, Pacific sand lance Ammodytes hexapterus, and Pacific herring Clupea harengus pallasi). These fishes tend to have high lipid content compared with other species and, consequently, are assumed to have high nutritional value as food for young seabirds. I tested hypotheses that type of fish consumed by the nestling, and lipid:protein ratio of the diet constrain growth and development of piscivorous seabird nestlings. I raised seabird nestlings (Black-legged Kittiwakes, Rissa tridactyla and Tufted Puffins, Fratercula cirrhata) on controlled diets of either capelin, herring, or sand lance (high-lipid fish), or juvenile walleye pollock (Theragra chalcograma; a low-lipid fish). Seabird nestlings fed herring, sand lance, or capelin had higher growth rates (body mass and wing length) than nestlings fed equal biomass rations of pollock. Growth in body mass and wing length of kittiwake nestlings was not affected by lipid:protein ratio of the diet when on a high nutritional plane (i.e., high caloric intake), but growth was significantly affected by dietary lipid:protein ratio when on a low plane of nutrition. Growth in body mass and wing length of puffins was not significantly affected by the lipid:protein ratio of the diet. Diets with a higher lipid:protein ratio resulted in greater fat reserves in both seabird species, regardless of nutritional plane. Additionally, diets with a higher lipid:protein ratio resulted in higher apparent metabolizable energy coefficients. The increased growth rates, fat reserves, and energy utilization efficiencies of chicks fed high-lipid diets suggest that pre- and post-fledging survival are enhanced when parent seabirds have access to high-lipid forage fish.