Inter-Research > MEPS > v666 > p217-229  
Marine Ecology Progress Series

via Mailchimp

MEPS 666:217-229 (2021)  -  DOI:

Maternal foraging trip duration as a population-level index of foraging and reproductive success for the northern fur seal

Greg B. Merrill1,2,*, J. Ward Testa3, Jennifer M. Burns4,2

1Duke University Marine Laboratory, Duke University, Beaufort, NC 28516, USA
2Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99507, USA
3National Marine Mammal Laboratory, Alaska Fisheries Science Center/National Marine Fisheries Service/NOAA, Seattle, WA 98115, USA
4Present address: Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA
*Corresponding author:

ABSTRACT: The duration of maternal foraging trips has been regarded as an indicator of foraging conditions in many marine mammals, including northern fur seals Callorhinus ursinus (NFS). However, previous work has focused on individual variation, was conducted during limited portions of the lactation period, and/or reached conclusions based on relatively small sample sizes. Here, we build upon the substantial foundations of this previous work to establish maternal foraging trip duration (MFTD) as an index of foraging success at the rookery level. We found that a 1 d increase in rookery-averaged MFTD corresponded to a 6.52% reduction in the average mass of female pups. Furthermore, rookery-averaged MFTD increased by 0.34 d per 1°C increase in average ocean bottom temperature. The magnitude of variation observed in both MFTD and pup mass is likely too small to help explain the general decline in population size seen over recent decades. However, the correlation between rookery-averaged MFTD and pup mass highlights the potential power of the MFTD index to detect bottom-up effects on pup growth, a likely indicator of survival. Furthermore, when compared with concurrently conducted studies on prey distribution, availability, and quality, the relationship between MFTD and bottom temperature suggests a northward shift in distribution of NFS preferred prey, walleye pollock Gadus chalcogrammus, that is associated with an increase in trip duration across the study period. Thus, rookery-averaged MFTD is a promising metric for tracking broad environmental changes, such as northerly shifts in the Eastern Bering Sea cold pool.

KEY WORDS: Pup mass · Northern fur seal · Callorhinus ursinus · Walleye pollock · Gadus chalcogrammus · VHF telemetry · Bering Sea · Pribilof Islands

Full text in pdf format
Supplementary material

Cite this article as: Merrill GB, Testa JW, Burns JM (2021) Maternal foraging trip duration as a population-level index of foraging and reproductive success for the northern fur seal. Mar Ecol Prog Ser 666:217-229.

Export citation
RSS - Facebook - - linkedIn