Harbor seal-pebble sacks-SST

In the northeast Pacific Ocean, the harbor seal exhibits its southernmost distribution in waters off the Baja California Peninsula, which includes nine islands and archipelagos and some sites on the coast. A decrease in abundance at the coastal colonies was reported for 2016, when pebble extraction at some of those beaches increased. The present study analyzed seal counts in aerial photographs taken in 2016, 2018, 2019, and 2022, evaluating them as a function of both the sea surface temperature (SST) obtained from from the US National Oceanic and Atmospheric Administration (NOAA) climate data record, as taken from its polar-orbiting satellite (ftp.oceans.ncei.noaa.gov/pub/data.nodc/pathfinder/Version5.3/L3C) for the 50 km around each colony and the occurrence of pebble extraction. We found a consistent decrease in the number of seals over time for all colonies off the Baja California Peninsula in the southern California Current Large Marine Ecosystem, coinciding with an increase in SST that could indicate lower habitat suitability. However, the decline of seal numbers on the Todos Santos, San Jeronimo, San Benito, Natividad, and San Roque islands was slower, possibly because these are more productive sites. Additionally, the disappearance of many seal colonies on the coast could result from disturbances caused by pebble extraction. We used aerial photographs to count sacks containing pebbles. The present study provides evidence of the effect of ocean warming trends and disturbance on harbor seal distribution and abundance.