1017 Abstract.-The humpback whale Population size of humpback whale, tMcgaptera nocaeangliae) is a cosmo- pohtanspecieswhosestocksweredras- Megaptera novaeangliae, tiincgalplryacdteiccreesasperidorbytoco1n9i6m7e.rcTihae!Nwohratlh- in waters off the Pacific coast of Mexico Pacific populationwas estimated tobe between 15.000 and 20.000 animals before the practice ofwhaling. At the Jorge Urban R. timeofthecommencement ofitsinter- Departamento de Biologia Marina national protection in 1967,thispopu- Universidad Autonoma de Baia California Sur lation may have been reducedtofewer Ap Post 19-B than 1000individuals.ThePacificcoast La Paz, BC-S. 23081 Mexico ofMexico and the RevillagigedoArchi- E-mail lurbana'calafiauabcsmx pelagoconstituteoneofthemainbreed- ingandcalvingareas forNorthPacific humpbackwhales.Theobjectiveofthis Carlos Alvarez F. paper is to present an estimation of Mario Salinas Z. abundanceofhumpbackwhalesinthis Laboratorio de Mamiferos Marines region based on photographic identifi- Universidad Nacional Autonoma de Mexico cationofindividualanimals.Estimates ofpopulationsizewereobtainedbyus- AMpe,xiPcoos,tD70F-50742510 Mexico ingmarkandrecapturemodelsforboth closedandopenpopulations,witheach year representing a capture occasion. Jeff Jacobsen Atotalof1184 humpbackwhaleswere PO Box 4492 identified in Mexican waters between Areata, California 95521 1986 and 1993. The best estimates of population size forthe Mexican stocks were those provided by the modified Kenneth C. Balcomb III Jolly-Sebermethod: 1813OS^rCI:918- Center for Whale Research 2505)forthecoastalstockin 1992,and 1359 Smugglers Cove Road 914 (95'y CI: 590-1193) for the Revil- Fnday Harbor, Washington 98250 lagigedostock in 1991. Armando Jaramillo L. Departamento de Biologia Marina Universidad Autonoma de Baia California Sur Ap. Post 19-B La Paz, B.C.S- 23081 Mexico Paloma Ladron de Guevara P. Anelio Aguayo L. Laboratorio de Mamiferos Marines Universidad Nacional Autonoma de Mexico Ap Post 70-572, Mexico, DP 04510 Mexico Humpback whales, Megaptera no- south as southern California. Dur- vaeangliae, make seasonal migra- ing the winter breeding season, tions between low-latitude winter- these whales congregate in three ing areas used for mating and calv- geographically isolated tropical ar- ingandhigh-latitudefeedingareas. eas: the Ryukyuan, Bonin, and The general distribution offeeding Mariana IslandssouthofJapan; the areas in the North Pacific covers islands of the Hawaiian Archi- coastalwatersinthewesternNorth pelago: and the Pacific coast of Pacific from northern Japan Mexicoand theRevillagigedoArchi- throughout the Bering Sea and in pelago (Rice, 1974; Johnson and Manuscript accepted 15January 1999. Fish. Bull. 97:1017-1024(1999)'. the eastern North Pacific as far Wolman, 1984). 1018 Fishery Bulletin 97(4), 1999 Humpbackwhales havebeenhsted asendangered sinceseverereductionofallstocksworldwidebycom- Table 1 mercialexploitation(Rice, 1974; Gambel, 1976). The Matches(abovethediagonal)and interchange index' ibe- numberofthesewhaleswereestimatedtobebetween lowthediagonal)amongthethreemainwinteringaggi-ega- 15,000 and 20,000 animals before whaling depleted tions in the Mexican Pacific. Sample size in parentheses. them duringthe first halfofthe 20th century; atthe Baja Mainland Revilla- timeofitsinternational protection in 1967this popu- California coastof gigedo lation may have been reduced to fewer than 1000 Peninsula Mexico Archipelago individuals(Rice, 1974, 1978). However, thereliabil- (471) (383) (4501 ityTohfetheexsteenftigoufretsheisruenckonvoerwyn.in the North Pacific BMaajianlCaanlidfocronaisatPofenMienxsiucloa 0—.38 64— 22—03 population over the last 25 years is debatable. Esti- RevillagigedoAj-chipelago 0.12 0.18 mates ofabundance with mark and recapture tech- niques based upon photo-identification data have ' TIhnidsexinodfeixnqtuearncthiafnyget.hedegreeofinterchangeamongtwosamples beenmade fordifferentareasofthis ocean,butthere (amongregions)thataccountedforsamplesize: has been much debate regarding the reliability of Indexofinterchange=(m^.^Kn,xnjV x 1000, suchestimates!Darlingetal., 1983;Bakeretal., 1986; DarlingandMorowitz, 1986;BakerandHerman, 1987; where/!n.,y ==wwhhaalleessiiddeennttiiffiieedd(incaspatmurpelde)2i;nasnadmple 1; Alvarezetal., 1990;Calambokidisetal., 1990;Cerchio, ni.,=capturedwhalesfromsample1recapturedinsample2, c1i9e9n8t;eCvaildaemnbcoektiodiassseetssal.w^h).etThheerreaissicguniiTfeinctalnyt icnhsaufnfgie- (seeBakeretal. 1985;Cerchioetal , 19981 in abundance has occurred since whalingceased. Three main wintering aggregations ofhumpback whales arerecognizedoffthe Pacific coastofMexico: Thisdivision ofwinteraggregationsisalsosupported the Baja California Peninsula; the mainland coast by mitochondrial DNA lineage analyses (Medrano- ofMexico (including, Isabel Island, Tres Marias Is- Gonzalez et al., 1994, 1995a, 1995b); however, be- lands,andthemainlandcoast);andtheRevillagigedo cause the waters off California, Oregon and Wash- Archipelago(includingSocorro, San Benedicto, Roca ington are the primary feeding destination of the Partida, and Clarion Islands) (Rice, 1979; Urban y whales observed in Baja California and the main- Aguayo, 1987). land coast, the migratory destination ofthe whales The comparison of photo-identified humpback seen around the Revillagigedo Islands is still un- whales in these winteringgi-ounds showedthatthere known (Urban et al. 1987; Urban et al.'^). was a greater affinity between whales offBaja Cali- Previousestimatesofhumpbackwhale abundance fornia and those off the mainland coast of Mexico in Mexican waters are the following: 500-600 for than those off either Baja California or the main- Socorro Is. (Campos, 1987); 200-400 for Isabel Is. landcoastandthoseofftheRevillagigedoArchipelago (Alvarez, 1987); 600-700 for the mainland coast (Urban et al., 1989; Ladron de Guevara et al., 1993; (Alvarezetal., 1990); and 1200-1700forall theMexi- Jaramillo, 1995) (Table 1). From these results, two can Pacific (Urban et al., 1989). However, it is recog- different population units ofhumpback whales dur- nizedthattheseestimateswerebasedonlimiteddata ing winter in Mexican waters were previously pro- and on assumptions that generally were not tested. posed: the coastal Stock (including Baja California In ourstudy wepresentan analysisofphotographic andmainlandcoastofMexico), andthe Revillagigedo data obtained during the winter breeding and calv- stock (Alvarez et al., 1990; Urban et al.^) (Fig. 1). 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 ' Calambokidis,J.,G. H. Steiger,.J. Straley.T.J. Quinn II, L. M. ofabundanceofhumpback whales forthecoastal and HR.e,rmJ.anK,.SJ.aCceorbcsheion,,DO..SavlodnenZ,iMeg.eYsaarg,amKu.chCi.,FB.aSlactoom,bJ,.UCr.baMn. the Revillagigedo stocks. 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 ' Urban R., J.,A. Jaramillo L.,A.Aguayo L., Paloma Ladron de sFtinraulctKuerpe.otfohSuomupthbwaecskt wFihsahleersieisn'StciheencNeorCtehntePra,ciNfaitcl.baM.sainr. JGauceovbasrean,P.K,.MC.. BSaallicnoamsb,Z.D,.CE..ACllvaarriedzgeF,.,J.L.CaMleamdbroaknindiGs.,,GJ.. Fish. Serv., NOAA, LaJoUa, CA, 72 p. H. Steiger, J. M. Straley, O von Ziegesar, S. Mizroch, .M. 2 Urban R., J., J. C. Salinas V.,A. Guillen G., and E. Vazquez M Dahlheim, J. M. Waite, J. D. Darling, and C. S. Baker. 1997. LaballcnajorobadaMcgciptera novcwanfiluwenalPenin- 19xx. MigratorydestinationoftheMexican Pacifichumpback sula de Baja California Sur. Mexico. Final Report to the Bio- whales. Universidad Autdnoma de Baja California Sur, Ap. diversityNationalCommission (CONABIOi.ContractIl():3.'>,41 p. Post. 19-B, La Paz, Baja California Sur, Mexico. Urban R. et al.: Megapteranovaeangliae in waters off the Pacific coast of Mexico 1019 24° BajaCalifornia Peninsula -20° Revillagigedo Stock • SanBenedictoIs. o Soconx)Is. Clari6nIs. 115° 110° 105" _] _J _J Figure 1 Studyarea showing, by shading, thedistributionoftheRevillagigedoandcoastalstocks. Materials and methods On the basis offocus, angle, and light conditions, all fluke photographs werejudged to be either good, Individual identification fair, or of poor quality; only photos in the first two categories were included in this study. Within these Humpbackwhales were individually identified from qualitylevels, thewhales showedatleast50%ofeach photographs taken by different institutions from flukeatasufficientlyverticalangletoallowtheshape approximately December to March, along the main- ofthe trailing edge to be distinguished. Calves were land coast of Mexico (1983-92), from mid-January excluded from the analysis owing to their tendency to March in Baja CaUfornia (1987-93), and at the toshowchangesinpigmentationpatternsduringthe Revillagigedo Archipelago (1986-92) (Table 2). first year oflife (Carlson et al., 1990). Selected pho- Although photo-identification data have been tographs were compared visually by at least three availableforthe coastal stocksince 1983 and forthe persons with experience in matching humpback Revillagigedo stock since 1985, efforts before 1986 whales flukes photographs from both Universidad were limited in time and space, and also lacked con- Nacional Autonoma de Mexico and Universidad tinuity. Beginning in 1986, surveys were conducted Autonoma de Baja California Sur. off Socorro Island for the Revillagigedo stock, and near San Jose del Cabo or the mainland coast (or Abundance estimation both) for the coastal stock. No data were obtained for either Revillagigedo or the mainland in 1993. Abundance estimates were obtained by using an The whales were identified individually through eight-year period for the coastal stock, from 1986 to photographs ofthe black andwhitepigmentation pat- 1993, and a seven-year period for the Revillagigedo ternsontheventral surfaceoftheirflukes(seeKatona stock, from 1986 to 1992. 3an5d-Wmhmitceahmeearda,s19e8q1ui).pPpheodtowgirtahph2s0w0e—r3e00obmtamineldenwsietsh. ingEsmtairmakteasndofrpeocpaupltautrieonmosdiezleswefroreboobtthaicnleodsebdyaunsd- Although the film used varied by region and season, open populations, witheachyearrepresentinga cap- most photographs were taken with black and white ture occasion. The time span ofthe study was seven Kodak Tmax 400 ISO pushed to 1600 ISO, ensuring years; consequently, although calves were not in- shutter speeds as high as 1/1000 ofa second. cluded in the analysis, it is inevitable that additions 1020 Fishery Bulletin 97(4), 1999 Urban R. et al.: Megapteranovaeangliae in waters off the Pacific coast of Mexico 1021 abundance was also estimated for the coastal stockby usingthe model thatonly allows relaxation of the requirement for constant capture probability in time (Darroch, 1958; model M^ in Otis et al., 1978). Model M,[, provides the estimator of population size for a situation where capture probabilities vary in time and amongindividuals. Model Mjprovidesthe estimate ofpopulation size when capture arethesameamongindividu- probabilities als but vary in time (Otis et al., 1978). Outputs from CAPTURE were used only as a"screeningtechnique," as suggested by MenkinsandAnderson(1988)toinvestigate departures from the assumption ofequal catchability. The test for population closure within CAPTURE was ignoi-ed because its poweris low (Otis et al., 1978). Open population estimation was done through the software program RECAP^ This program provides estimates ofparameters under the basicJolly-Seber model where all individualshaveequal capture prob- abilities and survivorship, but these were allowedto vary between sampling occasions. Also, it incorpo- rates a modification ofthe Jolly-Seber model (modi- fiedJ-S model) that constrains estimates to feasible values, stabilizingthem andprovidingmore reliable confidence intervals (Buckland, 1980). Open popu- lationestimates were alsoobtainedby usingthe soft- ware program JOLLY described by Pollock et al. (1990). Of particular interest is the goodness-of-fit tests performed for this program to investigate how well ourdata areexplainedbytheJolly-Sebermodel or any ofthe variants included in the program. The results obtained under such variants were also very useful because they allowed for the estimation of more precise parameters when either capture prob- abilitiesorsurvivorship (orboth)werekeptconstant. Even in the case when the more general Jolly-Seber model was chosen (model A), observation of survi- vorship estimates under model 2 (temporary trap response model) were useful to look for the amount oftransit within the areas occupied by each stock. Results and discussion Photo identification Atotal of 1184 humpback whales were identified in Mexican waters between 1986 and 1993. Ofthe to- 1022 Fishery Bulletin 97(4), 1999 Urban R et al : Megapteranovaeangliae in waters off tfie Pacific coast of Mexico 1023 Acknowledgments Cerchio, S. 1998. EstimatesofhumpbackwhaleabundanceoffKauai, We would like to thank JeffLaake for valuable ad- Hsaawmapilii,ng19t8h9etHoa1w9a9i3i:aenvaIlsulaatnidnsg bbiraeseedsinagssaocsisaetmebdlawgiet.h viceand fruitful discussions. 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