EXPLANATORY FACTORS FOR VARIATION IN HARBOR SEAL HEART RATE DURING PERIODS OF RESTING J. photo by S. Karpovich
1,* Skinner ,
S.
2 Karpovich ,
M.
2 Keogh ,
J.
3 Mondragon ,
and G.
3 Blundell
All authors are affiliated with the Alaska Department of Fish and Game at the following locations: 1.) 525 W. 67th Avenue., Anchorage; 2.) 1300 College Rd., Fairbanks; 3.) 1255 W. 8th St., Juneau. *E-mail:
[email protected]
Background. Previous research has shown a relationship between marine mammal heart rate and expenditure of metabolic energy; however, this relationship is complicated since heart rate is influenced by many factors including animal size, activity, and environment. Additionally, heart rate during haulouts may reflect the delayed repayment of costs from past activity such as exercise or diving. The goal of this project was to study the influence of previous activity and present conditions on the heart rate of hauled-out, resting harbor seals Phoca vitulina in Southeast Alaska.
Table 1.
What We Did • Captured 11 male and 11 female adult and subadult harbor seals in Tracy and Endicott fjords of Southeast Alaska during spring and summer, 2008-2010
Predictor variable abbreviations (Abbr.) and descriptions. Duration of heart recovery (response variable) was modeled using combinations of predictor variable main effects, quadratic terms, and selected interactions using linear mixed effects models.
Abbr. SEX
Description Seal sex
• Deployed data loggers to measure heart rate, diving, and resting behavior for up to 100 days
MASS VTD
vertical diving rate; total diving -1 distance divided by time (m∙s )
• Estimated rested heart rate for each seal (Fig. 1)
DUR
Previous time in water (s, sqrt)
TIME
Hour of day
WEEK
Week of year
TEMP
Mean temperature (◦C)
LIGHT
Mean light level
• Defined rest periods as haulouts >1 hour with no water entries >5 mins • Defined duration of heart rate recovery as the resting time required for heart rate to drop below rested heart rate (Fig. 2).
• Determined which variables (Table 1) best predicted duration of heart rate recovery using linear mixed effects models and model averaging
diving
surfaced
Fig. 1.
All 5-minute maximum heart rate readings for seal 09TE014. Shown are estimated bradycardic (diving, red) and tachycardic (surfaced, green) heart rate distributions. Rested heart rate (blue dashed line) was defined as the lower 5% tail of the estimated tachycardic heart rate distribution.
Seal body mass (kg)
Table 2. Model estimates. Shown are model averaged parameter estimates (βj), unconditional standard errors (s.e.), and significances (‘*’ = p
