Seasonal abundances of the harbor seal (Phoca vitulina richardsi Gray 1864), at Punta Banda Estuary (B.C., Mexico)

Abstract

In order to know the present abundance and seasonal variability of the seals (Phoca vitulina richardsi Gray, 1864) hauling at the inner northwest portion of Punta Banda Estuary (Baja California, Mexico), 40 counts were carried out between November 1988 and August 1990. The average abundance during the study period was 52 individuals, although a significant seasonal variability was noted. The largest mean abundance occurred in spring (X = 69; n = 12; range = 31-110) and it was the best season to assess the number of seals that use the estuary. The lowest abundance was recorded in summer (X = 28; n = 5; range = 2-72) while in autumn the number of seals was lower than in winter and spring (X = 31; n = 8; range = 18-48). The maximum seal counts were noted in winter, although their average abundance was lower than in spring (X = 58; n = 15; range = 18-151) since the herd increased by the occasional presence of pups and juveniles. No relationship was found between the abundance of seals and the sea level. The seasonal variation in the size of the herd was associated with its breeding season which occurs late in winter and with herd movements to other near haul-out sites.