Gray whale's body condition in Laguna San Ignacio, BCS, Mexico, during 2020 breeding season
Ronzon-Contreras, F., Martinez-Aguilar, S., Swartz, S.L., Huerta-Patino, R., Viloria-Gomora, L., and Urban R., J.
International Whaling Commission
The Eastern North Pacific (ENP) gray whale (Eschrichtius robustus) population feeds during the summer months in the Bering, Chukchi, and Beaufort seas. It migrates to winter breeding and calving grounds along the Pacific coast of Baja California, in Mexico. The assessment of gray whale body condition upon their arrival at the breeding grounds provides an indicator of the whales' "health and reproductive condition." It indirectly is an indicator of the health of the environment. Gray whales were photographed (n= 553) to evaluate body condition in Laguna San Ignacio (LSI) in Baja California Sur in 2020. Photographs were sorted into two reproductive-sex categories: Females with calves, and Single whales (males and females without a calf). The condition of each whale was scored as "good," "fair," or "poor," using a numerical method developed for the Western North Pacific (WNP) gray whales. In 2020 the proportion of females with calves in ???good condition??? was 70.4% (n=38); ???fair??? 24.1% (n=13) and "poor" 5.5% (n=3). The proportion of single whales with "good," "fair," and "poor" condition was 33.3%, 36.7%, and 30%, respectively. Compared to previous years, the proportion of single whales in "good" condition decreased during 2020. However, a similar decrease was not reflected in the percent of females with calves; this may be the result of a small sample of female-calf pairs photo-identified in 2020 (n=57), compared to the average (n= 226) pairs photo-identified each year from 2011 to 2017. The percent of single whales with "poor" body condition in 2020 is the highest observed in LSI in the last eleven years. We conclude that the body condition of all whales was probably similarly affected; however, comparison and correlation with environmental data from the feeding grounds (e.g., prey availability) is needed to understand the factors that contribute to the whale's body and reproductive condition.