The role of the environment at the local and large-scale levels on the abundance of gray whales (Eschrichtius robustus) in Baja California

Abstract

The Ojo de Liebre Lagoon is the largest wintering and calving area on the Baja California Peninsula for the north Pacific stock of gray whales (Eschrictius robustus), where up to 2721 individuals have been counted in a single season (January-April). This study describes the effects of spatial (zones), temporal (months), and environmental factors at the local (temperature and chlorophyll-a) and large-scale levels (Pacific Decadal Oscillation, PDO) on the abundance of gray whales in this lagoon using generalized additive models. Results suggest that larger populations are expected at temperatures below 15 °C and Chl-a values above 1 mg m−3 during the neutral (0−1) and positive (>1) phases of the PDO, in February and March, and around the mouth of the lagoon (zone 6). Findings highlight the importance of environmental variability on the abundance of this species at the local and large-scale levels. According to our models, the abundance of the gray whales that arrive in the Ojo de Liebre Lagoon is affected by local and large-scale environmental variability. The latter factor was evaluated by an index that integrated atmospheric and oceanic variations in the northeast and tropical Pacific Ocean. In spatial terms, the physical characteristics inside the lagoon may be the main factors that impact the distribution of whales. Management and conservation measures can use these results to improve strategies, considering the variability of the population in both local and long-term perspectives.