The life history and ecology of the gray whale (Eschrichtius robustus)

Abstract

SUBFOSSIL FINDSFic. 1. Distribution of the gray whale.A few gray whales spend the summer in the migration area, especially along the coast of Washington and Oregon.by investigators using small boats or aircraft in attempts to implant telemetering and tracking devices or drug darts may deleteriously affect reproduction (Schevill et al., 1967;American Society of Mammalogists, 1967).Another threat to the survival of the gray whale is increasing industrial development and boat and ship traffic in the remaining calving lagoons (Marx, 1966).The species has long since been driven from San Diego Bay.The gray whale is clearly an important species from the standpoint of basic scientific interest, esthetic appeal, and economic significance.If commercial exploitation is resumed it should be limited to the sustainable yield so that the scientific and esthetic values of the population may be preserved.A wise management program must be based on a sound knowledge of the biology of the species.small, lean, right whales (Allen, 1916; Eschricht and Reinhardt, 1866).As the identity of Dudley's scrag whale can never be unequivocally determined, we agree with Cederlund (1939) and Schevill (1952) that Lilljeborg's specific name should be used for the Atlantic gray whales.The question of the taxonomic relationship of the Pacific and Atlantic gray whale stocks has been investigated by van Deinse and Junge (1937) and Cederlund (1939), who compared the subfossil skeletal material from the Atlantic with skeletons and published data and photographs of Pacific gray whales.These authors found no consistent differences between the Atlantic and Pacific specimens and concluded that these populations were conspecific.CoasTaL STATIONS.-Duringthe southward migration in 1967-68, 1968-69, and 1969-70, coastal lookout stations were established to count migrating whales.One was on Point Loma at San Diego, California (32°40' N lat.), 130 meters above sea level (Rice, 1961) and is the site where previous counts were made (Gilmore, 1960a(Gilmore, , 1960b;;Rice, 1961).This station was manned for 52 days (27 December to 16 February) in 1967-68 and for 57 days (20 December to 14 February) in 1968-69.The second station was 2 km.§ Yankee Point, Monterey Co., California (36°29' N lat.), 23 meters above sea level and about 100 meters back from the shoreline.This was near the site where a partial count of migrating gray whales was made in 1966-67 (Adams, 1968).We manned this station for 49 days (18 December to 4 February) in 1967-68, 60 days (10 December to 7 February) in 1968-69, and 64 days (8 December to 9 February) in 1969-70.Observations were made continuously from 0700 to 1700 hours (essentially sunrise to sunset) each day.At each station, two observers each worked a 5-hour shift; morning and afternoon shifts were alternated between the two observers.The number of whales, time of passage, estimated distance from shore, and direction of travel were recorded for each group sighted.Wind direction and force, cloud cover, precipitation, and fog were logged throughout the day.VEssELS.-Between 25 January and 9 February 1968, we ran a series of transect cruises between Point Loma and a position west of Tanner and Cortez Banks.A similar transect was run off Yankee Point on 18 January 1968.While the vessel was underway, a constant watch for gray whales and other marine mammals was maintained on the bridge.All whales sighted were approached closely enough to ensure positive identification and the number of whales in each pod, the direction of travel, and the position and time of sighting recorded.Observations on gray whales also were made during many cruises conducted for marking rorquals (Balaenopteridae) and sperm whales (Physeter catodon).The area covered included the waters along the coast from Point Reyes, California (38° N lat.), south to Isla Clarion off Colima, Mexico (18° N lat.).The cruises, totaling 15 months, were made mostly between December and April from 1962 to 1969.The calving grounds in Laguna Ojo de Liebre, Laguna Guerrero Negro, Laguna San Ignacio, and Bahia Magdalena, Baja California, were briefly visited.Gray whales were sighted on 304 occasions, and a total of 1045 individuals was recorded.AIRCRAFT.-On 25 and 26 March 1969, an aerial survey was made in both directions along the entire coast beween San Francisco, California (38° N lat.), and Cape Flattery, Washington (48° N lat.).Two aircraft (a Cessna 177 and a Cessna 185) were used, each with two observers in addition to the pilot.The flight path was 0.3 to 2.0 kilometers offshore at an average altitude of 230 meters and air speed of 200 kilometers per hour.When pods of whales were sighted they were often circled at a lower altitude.Data were recorded on a tape recorder.Sighting conditions were optimum, with calm seas and clear skies, throughout the period of the survey.On whale marking cruises in 1965, 1966, 1967, and 1969, we traveled north during late February, March, and early April, b