Comparison of the offshore distribution of southbound migrating gray whales from aerial survey data collected off Granite Canyon, California, 1979-96
Kim E. W. Shelden, Jeffrey L. Laake
Abstract
Aerial surveys provide an assessment of the offshore distribution of gray whales and an estimate of the proportion of whales that migrate beyond the visual range of shore-based observers. Six surveys were conducted concurrent with shore-based surveys during 1979, 1980, 1988, 1993, 1994 and 1996. Annual differences were tested for in the distribution of whales within an area 3 n.miles north and south of Granite Canyon, and it was found that the distributions within 3 n.miles of the shore differed by year but the shifts in the distribution were minor ( < 0.3 n.miles). The inshore ( < 2.25 n.miles) and offshore ( > 2.25 n.miles) distribution of gray whale pods did not differ significantly between survey years. An average of 4.76% (SE = 0.85%) of the whale pods were observed beyond 2.25 n.miles and only 1.28% (SE = 0.07%) beyond 3 n.miles.