Oceanographic conditions and marine mammals: identifying a potential relationship in the coastal region of the Mexican Central Pacific

The oceanographic conditions that could influence richness and distribution of marine mammal species in the coastal area of the Mexican Central Pacific (MCP) were investigated throughout 2011. Marine mammals observations were obtained from two research platforms. CTD casts were deployed down to 100 m, water samples were taken monthly at six stations for determination of organic nutrients, and another 15 stations were sampled over a wider area only during the winter. Satellite images from MODIS-AQUA L2 were used to obtain sea surface temperature (SST) and chlorophyll-a (Chl-a) values, likewise altimetry data to identify mesoscale dynamic structures in the region. High salinity values (34.6), low concentrations of nitrates and nitrites (~3-4 µM), silicates (5-7 µM), Chl-a (~10 mg m^-3), and low SST (~23.5°C) were detected, as well as the presence of cyclonic gyres near the coast during the winter-spring period. This coincided with high marine mammal species richness in the area (from 5 to 9 species depending on spatial scale). The dominant species was Megaptera novaeangliae (0.092 sightings km^-1), which was distributed close to the coast in shallow waters. Low salinity (32.8) and Chl-a values (0.1 mg m^-3) were detected during the summer-fall period. High phosphate availability (2.5 µM), presence of anticyclonic gyres, and high SST (~31°C) were also found, coinciding with low species richness (3 species). The dominant species was Stenella attenuata (0.036 sightings km^-1); those individuals were found distributed near the Jalisco-Colima coast (0-3 nm) in shallow waters with high inorganic nutrient availability. The principal components analysis showed that bathymetry (99.6%) was the main parameter explaining data variance; this parameter could therefore potentially modulate ecological aspects of marine mammals.