Report of the 2007 Gray Whale Studies at Laguna San Ignacio B.C.S. Mexico
Steven L. Swartz1, Jorge Urbán R.2, Alejandro Gómez-Gallardo U., Sergio González C., Benjamín Troyo V. and Mauricio Nájera C.
1 Cetacean Research Associates, 14700 Springfield Road, Darnestown, Maryland 20874 USA
2 Programa de Investigación de Mamíferos Marinos, Departamento de Biología Marina. Universidad Autónoma de Baja California Sur Ap.Post 19-B. La Paz, B.C.S. 23081 MEXICO
Abstract
Laguna San Ignacio se localiza en la costa occidental de la península de Baja California en México y es una de las cuatro principales lagunas de reproducción de la población oriental de ballena gris del Pacífico Norte (Eschrichtius robustus). Los primeros resultados de la temporada de invierno 2007 fueron presentados e incluyen: estimaciones de abundancia, densidad y distribución de las ballenas dentro de la laguna, estudios de fotoidentificación, y observaciones de ballenas flacas. Se llevaron a cabo doce censos completos en la LSI desde el 5 de febrero hasta el 30 de marzo. These boat surveys followed a standard survey transect and methodology to determine minimum whale abundance and distribution, and to allow comparisons with historical surveys conducted during the periods of peak whale abundance in February between 1978 to 2006. The maximum count of adult whales was 217 on 22 February (197 “single” whales and 20 cows with calves). The highest count of single whales was 197 and occurred on 22 February, and the highest cow-calf pairs count was 37 on 17 February. The high count of adult whales was 46% less than the highest recorded count of 407 adult whales on 14 February 1982, and occurred later in the season than 10 of the previous February highest count surveys suggesting a continuing decline in the number of whales utilizing this lagoon and a delay and shortening of the winter occupation of the lagoon by whales. Counts of female calf pairs also demonstrated declines from 137 pairs counted on 14 February 1982 to 37 pairs on 17 February 2007, or a decline of 73%. These findings could reflect the overall decline in the eastern North Pacific population and/or a differential use of the San Ignacio lagoon compared to other breeding lagoons and coastal areas during the winter. The distribution of whales within the lagoon at the time of the maximum adult whale count was: 63% in the lower zone nearest the entrance, 30% in the middle zone and 7% in the upper zone furthest from the entrance. This represents a change in the utilization of the lagoon since the highest historical count in 1982 when 50% of the whale utilized the lower zone, 16% used the middle zone, and 34% utilized the upper zone. This change in distribution is largely the result of fewer females with calves observed in the lagoon at the peak of the season. From 615 photo-identified whales, 453 were single whales, 137 cows with calves, and 25 undetermined; there were 200 recaptured whales, 111 of cows with calves and only 80 of solitary whales. The longest period between re-captures was 37 days from a cow with calve. A calving interval of 2.48 + SD 0.607 years was estimated for females during the period 1996 to 2000 from photographic identification data, and suggests that females are reproducing less frequently than in the past. Of those 615 individual whales photographed, 12.35% showed evidence of the “skinny whale” syndrome.