Census of Gray Whale Abundance in San Ignacio Lagoon: A Follow-Up Study inResponse to Low Whale Counts Recorded during an Acoustic Playback Study of Noise-Effects on Gray Whales

摘要

Surveys done in 1984 as part of a study to determine the effects of noise on graywhales (Eschrichtius robustus) that calve and breed in San Ignacio Lagoon, Mexico sighted substantially fewer whales than had been sighted in the lagoon from 1978 through 1982. Two additional surveys, the results of which are described in the paper, were done in 1985 to determine whether a population decline had occurred and was continuing in the lagoon. A review of human activities in the lagoon from 1978 through 1985, which could have influenced the relative abundance of whales is also reported. The second series of surveys in 1985 was done in mid-March, when in previous years the maximum number of cows and calves had gathered prior to beginning the north migration. Regression analysis of the high counts in 1978, 1979, 1980, 1981, 1982, and 1985 indicate that, during this seven year period, the maximum number of whales present in San Ignacio Lagoon increased an average of 4.5% per year. The study results suggest that (1) the noise-effect studies conducted in 1984 caused both single whales and cow-calf pairs to abandon or avoid San Ignacio Lagoon; and (2) most if not all of the whales returned to and used this lagoon in 1985 as they had in 1978-82.