Changes in blue whale survival and abundance in the Gulf of California

Georgina Whittome*, John Calambokidis, Annie B. Douglas, Michael Fishbach, Richard Sears, Philip Steven Hammond

*Corresponding author for this work

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Understanding the drivers of population abundance and distribution is fundamental to ecology and key to informing conservation actions, particularly in endangered species like blue whales (Balaenoptera musculus). Historically, some Eastern North Pacific blue whales have aggregated in the Gulf of California (GoC) each winter. Using photo-identification data collected around Loreto Bay from 1984 to 2020, we analyzed 453 sightings histories using mark-recapture models. Estimated apparent survival (including permanent emigration) decreased from 0.991, 95% CI [0.977, 0.997] in 1985 to 0.889, 95% CI [0.807, 0.939] in 2019. The estimated number of whales using the study area declined from 96 whales, 95% CI [50, 254] in 2012 to 13 whales, 95% CIs [12, 23 and 12, 28] in 2018 and 2019. Abundance of the whole Eastern North Pacific population is slowly increasing, so our results likely reflect declining usage of the GoC. Linear models found a relationship between the number of whales in the GoC and the difference in sea surface temperature between the study area and the Costa Rica Dome wintering area, suggesting that environmental variation could explain variation in blue whale numbers in the GoC. These results highlight the importance of tracking population dynamics as changing environmental conditions affect the range and distribution of populations.
Original languageEnglish
Article numbere13132
Number of pages17
JournalMarine Mammal Science
VolumeEarly View
Early online date3 May 2024
Publication statusE-pub ahead of print - 3 May 2024


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