Kyle Kolda presents 'Adaptive Capacity and Diving Constraints of Northern Fur Seals', Feb. 19

Kyle Kolda, a master's candidate in biology, will present 'Adaptive Capacity and Diving Constraints of Northern Fur Seals (Callorhinnus ursinus)' on Feb. 19.

Abstract

The population of northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska, has declined for several decades, with nutritional stress identified as a likely contributing factor. Concurrently, environmental change in the Bering Sea has altered access to walleye pollock (Gadus chalcogrammus), a primary prey species for lactating females. Because these seals are central-place foragers constrained by the need to provision pups on land, their ability to adjust to changing prey fields depends on both behavioral flexibility and physiological diving capacity. Diving performance is partially constrained by the aerobic dive limit (ADL), which is the dive duration associated with the buildup of lactic acid. Exceeding this limit can occur but is energetically costly and reduces foraging efficiency due to extended surface recovery times. This study used constraint line analysis on time-depth data from 52 lactating females (2010, 2014, and 2016) to evaluate how closely lactating northern fur seals dives to this limit and if there is evidence of behavioral adaptations in response to changing ocean conditions in the Bering Sea. Performance envelopes were generated to model the minimally required surface recovery time for a set of successive dives with boundaries representing aerobic and anaerobic diving. Two metrics were then derived: (1) aerobic foraging effort, and (2) median dive duration expressed as a percentage of the upper limit, indicating how closely individuals operated to the calculated ADL (cADL). We found that northern fur seals rarely exceeded their cADL, and most dives occurred well within aerobic limits. Therefore, anaerobic constraint lines could not be delimited, indicating limited use of anaerobic metabolism during foraging. Both aerobic foraging effort and proximity to the upper limit varied among years, with significantly lower aerobic effort observed in 2014 and 2016 than in 2010, while dive depths and foraging trip durations remained consistent. A generalized additive mixed model (GAMM) revealed significant effects of year, dive depth, and ordinal date on aerobic effort, with effort peaking between 10 and 20 meters, depths corresponding to the vertical distribution of juvenile walleye pollock. Changing ocean conditions during the study period did not push seals closer to their physiological limits. Instead, individuals adjusted foraging behavior within their aerobic boundaries, demonstrating behavioral flexibility that may buffer against moderate environmental change. These findings establish a physiological and behavioral baseline for the species, providing valuable context for assessing how continued environmental change in the Bering Sea may affect the resilience of northern fur seals.

Event details

Event location - CPISB 120 and Zoom
Event date - Feb. 19, 2026
Event start time - 11:30 a.m.
Event end time - 12:30 p.m.

Zoom link