TY - JOUR
T1 - Survival probabilities and movements of harbor seals in central California
AU - Manugian, Suzanne C.
AU - Greig, Denise
AU - Lee, Derek
AU - Becker, Benjamin H.
AU - Allen, Sarah
AU - Lowry, Mark S.
AU - Harvey, James T.
N1 - Funding Information:
Research was funded in part by The Marine Mammal Center (TMMC) in Sausalito and Moss Landing Marine Laboratories (MLML). Permits were obtained from the National Marine Fisheries Service (permit no. 555-1870-00) and San Jose State University (IACUC no. 931). We thank TMMC staff (Frances Gulland, Bill Van Bonn, Vanessa Fravel, Lauren Campbell, Erin Brodie, Matt Hoard) and volunteers for surgery-related efforts. We also thank members of the MLML Vertebrate Ecology Lab and volunteers (Stephanie Hughes, Liz McHuron, Deasy Lontoh, Tenaya Norris, Scott Hansen, Alex Olson, Sean Hayes, Greg Frankfurter, Patrick Flanagan) for help with seal captures and sample collection. Airplane pilots K. Harmon and B. Van Wagenen (Ecoscan Resources) graciously donated and aided in aerial tracking efforts. The National Park Service, Don Edwards National Wildlife Refuge, and the CDFW San Francisco Bay Study and the Interagency Ecological Program for the San Francisco Estuary provided logistical support. Additional funding was provided by the Student Packard Fund and the San Francisco State University travel fund. We thank reviewers Jason Baker and Jeff Laake for thoughtful critiques of the manuscript and helpful analysis recommendations.
Publisher Copyright:
© 2016 Society for Marine Mammalogy
PY - 2017/1/1
Y1 - 2017/1/1
N2 - Harbor seal numbers and population trajectories differ by location in central California. Within San Francisco Bay (SFB) counts have been relatively stable since the 1972 Marine Mammal Protection Act, but in coastal areas like Tomales Bay (TB), counts increased before stabilizing in the 1990s. Emigration, poor survival, and environmental effects have been hypothesized as contributors to differences between trajectories; however, basic demographic data were not available to evaluate these hypotheses. We monitored 32 radio-tagged adult females (SFB n = 17, TB n = 15) for 20 mo (2011–2013), and estimated survival, resight, and movement probabilities using mark-resight analyses and multistate mark-resight models. Annual survival probability for both sites was 0.90 (95% CI = 0.18–0.99). Six seals were observed moving between locations resulting in an estimated probability of 0.042 (95% CI = 0.023–0.076) per month equal movement between sites. Resight probability was less in SFB relative to TB, likely due to differential haul-out access, area surveyed, visibility, and resight effort. Because of wide confidence intervals and low precision of these first estimates of adult female harbor seal survival in California, this demographic must be further examined to dismiss its contribution to differing population trajectories. Using aerial survey data, we estimated 950 harbor seals in SFB (95% CI = 715–1,184) confirming numbers are still stable.
AB - Harbor seal numbers and population trajectories differ by location in central California. Within San Francisco Bay (SFB) counts have been relatively stable since the 1972 Marine Mammal Protection Act, but in coastal areas like Tomales Bay (TB), counts increased before stabilizing in the 1990s. Emigration, poor survival, and environmental effects have been hypothesized as contributors to differences between trajectories; however, basic demographic data were not available to evaluate these hypotheses. We monitored 32 radio-tagged adult females (SFB n = 17, TB n = 15) for 20 mo (2011–2013), and estimated survival, resight, and movement probabilities using mark-resight analyses and multistate mark-resight models. Annual survival probability for both sites was 0.90 (95% CI = 0.18–0.99). Six seals were observed moving between locations resulting in an estimated probability of 0.042 (95% CI = 0.023–0.076) per month equal movement between sites. Resight probability was less in SFB relative to TB, likely due to differential haul-out access, area surveyed, visibility, and resight effort. Because of wide confidence intervals and low precision of these first estimates of adult female harbor seal survival in California, this demographic must be further examined to dismiss its contribution to differing population trajectories. Using aerial survey data, we estimated 950 harbor seals in SFB (95% CI = 715–1,184) confirming numbers are still stable.
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U2 - 10.1111/mms.12350
DO - 10.1111/mms.12350
M3 - Article
AN - SCOPUS:84982307176
VL - 33
SP - 154
EP - 171
JO - Marine Mammal Science
JF - Marine Mammal Science
SN - 0824-0469
IS - 1
ER -