AFSC/MML/CCEP: Stable carbon and nitrogen isotope values in segments of vibrissae of unrelated northern fur seal pups and adult females at San Miguel Island, California collected during September 2012.

Stable isotope analysis is a useful tool for studying foraging ecology of marine mammals and other consumers. Changing ratios of stable carbon (del13C) and nitrogen (del15N) isotopes in consumer tissues reflect foraging patterns over time and can be used to inform studies on historically vulnerable populations. Northern fur seals (Callorhinus ursinus) at San Miguel Island, California, have been severely impacted by climate events such as El Nino and remain susceptible to future disturbances, necessitating the need to further understand their foraging ecology. We analyzed sequential del13C and del15N values along single whiskers sampled from unrelated northern fur seal pups and post-parturient females at San Miguel Island, estimated whisker growth rates for pups and adult females, and reconstructed temporal stable isotope profiles for each whisker. The del13C and del15N values from pup whiskers increased over an estimated 93-day period, likely due to consumption of maternal milk. Concurrently, profiles were significantly correlated among pups, not correlated among adult females, and negatively correlated between the age classes. Our data suggest that isotopic differences between pup and adult female whiskers are not consistent throughout the nursing period. Adult female profiles likely reflect minimal foraging outside the Southern California Bight.

To examine if northern fur seal pups can be used as proxies for unrelated adult females when examining the assimilated diet of this species. To estimate vibrissae growth rates and temporally align the vibrissae isotope data. Compare stable isotope values from pups and unrelated adult females during an overlapping time period. Broadly categorize adult female northern fur seal foraging ecology in the California Current from Fall 2006 to Summer 2012.

Cite dataset as: Howard, Tanner J., Orr, Anthony J., Narel, Kimberly, Kurle, Carolyn M. 2021. Stable carbon and nitrogen isotope values in sequential segments of vibrissae of unrelated northern fur seal pups and adult females at San Miguel Island, California collected during September 2012 (NCEI Accession 0239459). [indicate subset used]. NOAA National Centers for Environmental Information. Unpublished Dataset. https://www.ncei.noaa.gov/archive/accession/0239459. Accessed [date].

Tables include ancillary information about individuals sampled for the study, isotopic information about segments of vibrissae submitted for analyses, and analytical data.

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San Miguel Island, California

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MS Excel

Ages for pups were based on a July birthdate.

The collection dates of vibrissae from adult females were 8–10 days earlier than the collection date of pup vibrissae, so we designated the stable isotope values assigned to 10, 23, 36, 49, 62, 75, 88, and 101 days prior to pup vibrissae collection as our values for statistical analysis.

We did not find trophic discrimination factor (TDF) values for NFS mother-pup paired vibrissae in the existing literature, so we referenced vibrissae TDF values from Australian sea lions (ASL; Neophoca cinerea) and Steller sea lions (SSL; Eumetopias jubatus) when assessing isotopic differences in our study.

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Mystacial vibrissae were plucked from five adult female northern fur seals (4-18 years old) and five pups (~3 month old) at San Miguel Island. Vibrissae were cleansed and each one was divided into 1 mm segments starting from proximal end toward the distal end. Segments were weighed and packaged for stable isotope analyses using a mass spectrometer at the Stable Isotope Laboratory at the University of California Santa Cruz. Resulting data were analyzed to address our study objectives.