Development of Diving by Harbor Seal Pups in Two Regions of Alaska: Use of the Water Column

Abstract

Satellite-linked dive recorders were attached to 53 harbor seal pups in Prince William Sound (PWS) and at Tugidak Island, Alaska, during 1997-1999. We used generalized additive models and bootstrap techniques to describe pup diving behavior during their first year of life. Pups increased their ability to dive during the first 3-6 mo, as indicated by increases in proportion of time in the water (time wet) and maximum dive depth achieved by a pup each day (max-depth) values. Time wet and/or max-depth later decreased, suggesting a seasonal component to diving behavior. Monthly time wet varied from an overall minimum of 0.68 at tagging in July to a maximum of 0.89 in November. Pups spent half of their time wet swimming in water <25 m deep, the shallowest 30% of the available water column. They spent only 5% of their time swimming in the deepest 30% of the available water column, at depths >60-70 m. This strongly suggests they were not feeding on or near bottom during their first year. Average maxdepths and deepest actual dives were similar for PWS and Tugidak pups. PWS pups dove deeper sooner and spent less time wet than Tugidak pups during the first few months after tagging, probably as a result of regional bathymetric differences. Diving behavior and body condition suggest that food availability was not 1 Current address: 73-

Postrelease dive ability in rehabilitated harbor seals

“…However, rerunning our analyses with variations in these parameters had no affect on our general conclusions. We also note that Frost et al (2006), reported a maximum “wet time” between 86% and 88% for juvenile harbor seals, a figure in accord with the PD 90 values in this study.…”

Diving Related Changes in the Blood Oxygen Stores of Rehabilitating Harbor Seal Pups (Phoca vitulina)

“…This suggests that as pups age, those that perform more HID generally also have higher Hct, Hb, MCH and MCV values. Unlike previous studies, which indicate that depth drives dive duration, hypoxia [ 1 , 15 , 62 , 63 ] and subsequently the production of more, large RBC, [ 20 , 58 ] this study indicates that hematological parameters may be driven by frequent periods of extended apnea without an increase in depth. Since these parameters were not significantly affected by maximum dive duration or mean dive duration in the models, it can be inferred that the frequency of long-duration dives as opposed to depth, may drive this process in captivity.…”

“…A similar trend was observed in wild harbor seal pups, [ 1 , 15 , 25 ] though wild pups were recorded to dive deeper and for longer periods of time at a younger age (8 min, age 1 week: [ 61 ]; approximately 9 minutes, age under 12 days:[ 25 ]; 8.5 min, age under 25 days: [ 1 ]; 3.6 min, under 25 days: [ 15 ]) than the captive pups in this study (maximum 13.6 min at 89 days, maximum under 25 days: 2.68 min). Harbor seal pup dive durations may be dependent on available depth in the water column [ 1 , 15 , 62 , 63 ] and pup motivation [ 63 ]. This study suggests that although the pool depth may affect the rate of development of these skills, it does not impede pups from performing long duration dives.…”

Ontogeny of Movements and Foraging Ranges in the Australian Sea Lion

“…Otariids have longer dependency periods and, therefore, increased opportunities for maternal transfer of knowledge. Although some researchers have assumed mothers and their dependent young dive and forage together (Pitcher and Calkins 1981, Loughlin et al 2003, Frost et al 2006) and others have assumed they do not (Atkinson 1997, Trillmich and Weissing 2006), no prior studies have directly investigated otariid mother‐pup associations at sea. The Australian sea lion, Neophoca cinerea , demonstrates one of the longest lactation periods in pinnipeds (17.6 mo: Higgins and Gass 1993), and pups begin diving before they are weaned (Fowler et al 2006).…”