Spring, Summer, and Fall Censuses of the Pinnipeds on San Nicolas Island, California

Abstract

Between May 11, 1949, and April 24, 1950, through the kindness and cooperation of the United States Navy, I was able to make six visits to San Nicolas, the outermost of the islands off the coast of southern California. One of the purposes of these visits was to take censuses of the pinnipeds, and the results of these counts are presented here. All of the species of seals and sea lions known to come ashore regularly in California occur on San Nicolas. The gregarious nature of the seals and sea lions and the marked localization of their hauling grounds made it possible to make a careful on-the-spot count of all the animals hauled out on the island. The location of the hauling grounds was a relatively simple matter. The major ones were known to the naval personnel on the island. On two different occasions it was possible to examine the entire coast of the island from the air. As a final check the whole coast line was visited either by jeep or on foot. The censuses were taken by observation with naked eye, binoculars, or telescope. All possible areas within each hauling ground were examined and this occasionally required crawling directly through the rookeries. To avoid frightening the animals into the water, however, most of the counts were made from distances of 100 to 400 feet. The number of individuals reported represents a minimal number for the island because it was not possible to determine the number of animals at sea while the censuses were being taken. The results of the six censuses are summarized in Table 1 and the situation with regard to each of the species found is discussed briefly below. Because of bad weather and limitations on time, on one of the trips it was not possible to take a complete census of the Zalophus, and on three of the trips it was not possible to take a complete census of the Phoca. I am indebted to the officers and men of the Naval Air Missile Test Center, Point Mugu, California, for their co-operation and assistance, and to William G. Reeder, William R. Dawson, Herbert Caswell, and Yost Amrein for help in taking the censuses.