1018 



Fishery Bulletin 97(4), 1999 



Humpback whales have been hsted as endangered 

 since severe reduction of all stocks worldwide by com- 

 mercial exploitation (Rice, 1974; Gambel, 1976). The 

 number of these whales were estimated to be between 

 15,000 and 20,000 animals before whaling depleted 

 them during the first half of the 20th century; at the 

 time of its international protection in 1967 this popu- 

 lation may have been reduced to fewer than 1000 

 individuals (Rice, 1974, 1978). However, the reliabil- 

 ity of these figures is unknown. 



The extent of the recovery in the North Pacific 

 population over the last 25 years is debatable. Esti- 

 mates of abundance with mark and recapture tech- 

 niques based upon photo-identification data have 

 been made for different areas of this ocean, but there 

 has been much debate regarding the reliability of 

 such estimates! Darling etal., 1983; Baker etal., 1986; 

 Darling and Morowitz, 1986; Baker and Herman, 1987; 

 Alvarez et al., 1990; Calambokidis et al., 1990; Cerchio, 

 1998; Calambokidis et al.^). There is cuiTently insuffi- 

 cient evidence to assess whether a significant change 

 in abundance has occurred since whaling ceased. 



Three main wintering aggregations of humpback 

 whales are recognized off the Pacific coast of Mexico: 

 the Baja California Peninsula; the mainland coast 

 of Mexico (including, Isabel Island, Tres Marias Is- 

 lands, and the mainland coast); and the Revillagigedo 

 Archipelago (including Socorro, San Benedicto, Roca 

 Partida, and Clarion Islands) (Rice, 1979; Urban y 

 Aguayo, 1987). 



The comparison of photo-identified humpback 

 whales in these wintering gi-ounds showed that there 

 was a greater affinity between whales off Baja Cali- 

 fornia and those off the mainland coast of Mexico 

 than those off either Baja California or the main- 

 land coast and those off the Revillagigedo Archipelago 

 (Urban et al., 1989; Ladron de Guevara et al., 1993; 

 Jaramillo, 1995) (Table 1). From these results, two 

 different population units of humpback whales dur- 

 ing winter in Mexican waters were previously pro- 

 posed: the coastal Stock (including Baja California 

 and mainland coast of Mexico), and the Revillagigedo 

 stock (Alvarez et al., 1990; Urban et al.^) (Fig. 1). 



' Calambokidis, J., G. H. Steiger, .J. Straley. T. J. Quinn II, L. M. 

 Herman, S. Cerchio, D. Salden, M. Yagamuchi, F. Sato, J. Urban 

 R., J. K. Jacobsen, O. von Ziegesar, K. C. Balcomb, C. M. 

 Gabriele, M. E. Dahlheim, N. Higashi, S. Uchida, J. K. B. Ford, 

 Y. Miyamura, P. Ladron de Guevara P., S. A. Mizroch, L. 

 Shlender, K. Ra.smussen. 1977. Abundance and population 

 structure of humpback whales in the North Pacific ba.sin. 

 Final Kep. to Southwest Fisheries'Science Center, Natl. Mar 

 Fish. Serv., NOAA, La JoUa, CA, 72 p. 



2 Urban R., J., J. C. Salinas V., A. Guillen G., and E. Vazquez M 

 1997. La ballcna jorobada Mcgciptera novcwanfiluw en al Penin- 

 sula de Baja California Sur. Mexico. Final Report to the Bio- 

 diversity National Commission (CONABIOi. Contract Il():3.'>, 41 p. 



Table 1 



Matches (above the diagonal) and interchange index' i be- 

 low the diagonal) among the three main wintering aggi-ega- 

 tions in the Mexican Pacific. Sample size in parentheses. 



Baja Mainland Revilla- 

 California coast of gigedo 

 Peninsula Mexico Archipelago 



(471) (383) (4501 



Baja California Peninsula — 64 20 



Mainland coast of Mexico 0.38 — 23 



Revillagigedo Aj-chipelago 0.12 0.18 — 



' Index of interchange. 

 This index quantify the degree of interchange among two samples 

 (among regions) that accounted for sample size: 



Index of interchange = (m^.^Kn, x njV x 1000, 



where/!, = whales identified (captured) in sample 1; 

 n.y = whales identified in sample 2; and 

 ni.,= captured whales from sample 1 recaptured in sample 2, 



(see Baker et al. 1985; Cerchio et al , 19981 



This division of winter aggregations is also supported 

 by mitochondrial DNA lineage analyses (Medrano- 

 Gonzalez et al., 1994, 1995a, 1995b); however, be- 

 cause the waters off California, Oregon and Wash- 

 ington are the primary feeding destination of the 

 whales observed in Baja California and the main- 

 land coast, the migratory destination of the whales 

 seen around the Revillagigedo Islands is still un- 

 known (Urban et al. 1987; Urban et al.'^). 



Previous estimates of humpback whale abundance 

 in Mexican waters are the following: 500-600 for 

 Socorro Is. (Campos, 1987); 200-400 for Isabel Is. 

 (Alvarez, 1987); 600-700 for the mainland coast 

 (Alvarez et al., 1990); and 1200-1700 for all the Mexi- 

 can Pacific (Urban et al., 1989). However, it is recog- 

 nized that these estimates were based on limited data 

 and on assumptions that generally were not tested. 



In our study we present an analysis of photographic 

 data obtained during the winter breeding and calv- 

 ing seasons from 1983 to 1993 in the different as- 

 sembly areas of the Mexican Pacific. We use this 

 analysis to calculate reliable independent estimates 

 of abundance of humpback whales for the coastal and 

 the Revillagigedo stocks. 



' Urban R., J., A. Jaramillo L., A. Aguayo L., Paloma Ladron de 

 Guevara P., M. Salinas Z., C. Alvarez F., L. Medrann G., J. 

 Jacobsen, K. C. Balcomb, D. E. Claridge, J. Calambokidis, G. 

 H. Steiger, J. M. Straley, O von Ziegesar, S. Mizroch, .M. 

 Dahlheim, J. M. Waite, J. D. Darling, and C. S. Baker. 

 19xx. Migratory destination of the Mexican Pacific humpback 

 whales. Universidad Autdnoma de Baja California Sur, Ap. 

 Post. 19-B, La Paz, Baja California Sur, Mexico. 



