Project Summary
Knowledge of the mechanisms by which neonatal mammals acquire the tools necessary to become competent predators is crucial to our understanding of how physiological processes influence behavioral strategies. While such questions can be addressed in many species, the study of how pinniped neonates become marine predators offers several unique and significant advantages. All pinniped neonates are essentially terrestrial at birth, yet most true seals (the phocids) are foraging independently by the time they are six months of age. Therefore, pinniped neonates, unlike most terrestrial mammals, must quickly develop the physiological and behavioral skills to become efficient predators in an ecosystem where oxygen is spatially and temporally separate from their food resources. Previous research reveals that this transition is accompanied by dramatic changes in the size of body oxygen stores and the ability to regulate metabolic and heart rate patterns. It is also clear that the rate at which these changes occur varies among species with different developmental strategies.
Hooded seals are one of the most precocial mammals. They have the shorted nursing period of all the pinnipeds (4 days) and one of the earliest onsets of independent foraging (~4 weeks). In addition, pups are born with adult pelage and larger subcutaneous fat stores than most other phocid neonates. In combination, these findings suggest that hooded seal pups may show a more rapid maturation of the physiological processes related to diving than do pups of species with longer dependent periods. Early development of body oxygen reserves and metabolic control may be especially critical for young hooded seals because of their foraging ecology. Hooded seal adults make foraging dives that are remarkably long and deep for their body size, and apparently rely upon large body oxygen reserves and lowered diving metabolic rates to do so. Most juveniles studied so far attempt to mimic adult foraging patterns as soon as possible, and it is likely that young hooded seals will do so as well. However, because of their smaller size, it is unlikely that juveniles can forage efficiently at these depths.
This study will quantitatively study the development of diving capacity in hooded seal pups in order to understand how juveniles have adapted to their short dependent period and possible deep-water foraging strategies. By measuring the oxygen stores in the blood, muscle, and lungs of 10 newborn pups, 10 weaned pups, and 10 adults, we will test whether juvenile hooded seals are limited in their dive duration relative to adults as a result of smaller mass specific oxygen stores and higher metabolic rates. These values will then be integrated with measures of resting metabolic and heart rate patterns so that the aerobic diving capacity of each age class can be calculated. We will then determine whether the foraging behavior of weaned pups is constrained by their physiological capacity by monitoring their diving behavior through their first year of life using satellite-linked dive recorders, and relating observed behavioral patterns to their measured aerobic capacity. The impact that physiological status has on diving and foraging patterns will be determined, and juvenile behaviors will be contrasted with those of adults in order to determine if young hooded seals exploit similar habitats and resources, or if their smaller size obligates them to utilize a separate ecological niche. Finally, through comparison with data from other phocid species, we will assess whether hooded seals develop physiologically at a more rapid rate than is seen in related species with longer dependent periods. As hooded seals are one of the most precocial pinniped species, this research should provide insight on the maximum rate at which physiological and behavioral processes can develop.