Humpback whales in Banderas Bay, Mexico: relative abundance and temporal patterns between 2004 and 2017

Banderas Bay, Mexico is an important breeding and transit area for the North Pacific humpback whale (Megaptera novaeangliae) population. In this paper we estimated relative abundance (RA = number of whales/hours of navigation) as a proxy to assess population temporary patterns in the area. We analyzed data from 14 breeding seasons (2004-2017), collected between December and March each winter. A total of 8,013 whales were observed in 1,394.6 navigation hours. Average seasonal RA was 5.7 whales per hour with a maximum of 7.5 (2013) and a minimum of 4.0 (2016). Sea surface temperature (SST) averaged 25.1°C and remained within the range considered optimal for humpback whale reproduction areas. SST showed no significant correlation with RA (r = 0.183). Inter-seasonal RA values suggested an increase throughout the study period, although the increase was not statistically significant (R = 0.32; R2 = 0.10; t = 1.15, p > 0.05). Intra-seasonal analyses showed that RA in December and January were significantly higher (U = 150, p < 0.05) than in February and March; this pattern was consistent throughout the seasons of study. These results represent a shift in the intra-seasonal abundance peak relative to previous studies when most whales were observed between January and February. It is important to recognize changes in population parameters of humpback whales in breeding areas to improve management practices. This study also highlights the potential of opportunistic platforms, such as whale watching tour boats, as viable sources of quality information, particularly in contexts when funding is limited.