Research Technical Report

Marine Mammal and Seabird Abundance and Distribution Around the Davidson Seamount, July 2010

Newton, K.M., and A. DeVogelaere (August 2013)

MBNMS Technical Report, 28pp.

EXECUTIVE SUMMARY

The Davidson Seamount, located 129 km southwest of Monterey, California, was incorporated into the Monterey Bay National Marine Sanctuary on November 20, 2008 and is the first seamount within the National Marine Sanctuary system. The Sanctuary conducted a ship-based survey of the waters above and around the Davidson Seamount during July 2010. The three-day survey onboard the NOAA Ship McArthur II was the first dedicated at-sea survey of the Seamount to record marine mammal and seabird observations. Overall, 8 transect lines were surveyed for a total of 605 km of "on-effort" observations. Seventeen species of seabirds and 6 marine mammal species were observed. Cook's Petrel (Pterodroma cookii) was the most abundant seabird observed (8.4 birds km-2), followed by Leach's Storm-Petrel (Oceanodroma leucorhoa; 5.6 birds km-2). Including off effort sightings, the greatest number on Cook's Petrel ever recorded in California waters were observed. The seabird assemblage to the northwest of the seamount was distinctly different than that to the southeast with the northwest region characterized by more pelagic species such as Cook's Petrels and Leach's Storm-Petrel while the southeast region was characterized by more coastal species such as shearwaters, phalaropes, gulls, and alcids. Of a total of 200 marine mammal sightings, fin whales (Balaenoptera physalus) were the most commonly encountered marine mammal (51% of sightings), comprising 94% of whales sighted. In addition, fishes and other ancillary sightings were recorded. This survey in combination with aerial surveys along the same transect lines will serve as a baseline for future studies of the Davidson Seamount.