Abstract: Satellite tags were deployed on 47 humpback whales (Megaptera novaeangliae) in Panama and Ecuador between 2009 and 2015 to monitor both short- and long-distance movements within the breeding season. Ultimately, data from 37 animals (23 mothers with a calf and 14 unsexed adults) were included in the assessment. Transmissions were filtered and behavior states defined using a Bayesian state-space model. Mean tag longevity was 14.2 d (SD = 12.43; range: 1 to 70 d), and longevity was significantly longer in mothers (53%) than in unsexed individuals (t test = 2.43, p = 0.02). Based on the extent of their movements, two different habitat use patterns were recognized and referred to as short range (SR) and long range (LR). SR movements were associated mainly with slow, area-restricted movements (ARM) and short periods of fast, directed movement (FDM). LR movements were related mainly to FDM and, in some cases, with short ARM periods. We found significant differences in the proportion of time spent in each behavioral mode and in swim speed between mothers and unsexed individuals (p < 0.01, in all cases). Mothers displaying SR movements stayed in relatively small areas with back and forth movements up to 350 km along the coast; the 95% home range (kernel density) was estimated to be 61,105 km2 in whales from Panama and 26,331 km2 in whales from Ecuador. In mothers displaying LR movements, distribution range was seven times greater in Panama and up to 2.5 times greater in Ecuador. Since tag longevity was not significantly different between SR and LR movements in females (t test = 0.063, p > 0.05), a shift from the nursing to migration phase is a plausible explanation for this increased range. Information from unsexed animals is inconclusive because of the short tracking periods. Mothers were distributed closer to shore than other tagged unsexed individuals, but both types of whales swam into deeper waters mainly during migration. Our results confirm maternal-biased stratification in this population along the entire breeding range. These findings have important implications for coastal management, including reduction of risk posed by human activities such as bycatch, ship strikes, and whale watching.
Key Words: satellite tracking, breeding grounds, habitat use, spatial-state switching model, Southeast Pacific, population structure, Panama, Ecuador, humpback whale, Megaptera novaeangliae
Document Type: Research Article
DOI: https://doi.org/10.1578/AM.43.2.2017.139
Page Numbers: 139-155

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