Title of Project
ENERGY DENSITIES OF FORAGE FISH FROM THE MESOPELAGIC ZONE OF THE NORTH PACIFIC OCEAN AND ITS IMPLICATIONS FOR A HIGH-LEVEL MARINE PREDATOR, THE NORTHERN ELEPHANT SEAL (MIROUNGA ANGUSTIROSTRIS)
Division
Physical and Biological Sciences
Course or Program
Marine Biology
Description / Abstract
The Costa Lab has been at the forefront of applying tracking technology to study the foraging behavior of mesopelagic predators. These tools provided unprecedented insight into the foraging migrations of northern elephant seals (Mirounga angustirostris), revealing routine dives to 517 m (1,696 ft) with some dives exceeding one mile (1,761 m, 5,778 ft). While the behavior of these animals is well documented, the ecological factors that drive these amazing migrations remains unclear. To better understand the energetic benefit associated with these migrations we used bomb calorimetry to conduct a caloric cost-benefit analysis of potential prey species. Prey were collected from the mesopelagic zone via mid-water trawls that spatially and temporally correlated with elephant seal foraging activity in the North Pacific Ocean. Preliminary data from 11 species has thus far showed that the Northern pearleye (Benthalbella dentata), found from 98 to 3,4000 m, with the highest energy density output of 10,787 kJ kg -1 compared to the average energy density of 7, 119 kJ kg -1. Such a prey library has only been completed in one other Phocid, the Weddell seal (Leptonychotes weddellii), and marks one of the first steps towards understanding the diet and bioenergetics of foraging in the deep-diving, far-ranging elephant seals at the Año Nuevo State Reserve in California. While prey selection may be driven by the high caloric value of mesopelagic organisms, this remains to be tested via further analysis of the energy content of additional prey species.
