, ~ F~i"ÍAS "' 0 .ct dI 2aJL .. , SC/54/H11 .! Population estimate for humpback whales from Abrolhos Jb.nk, Brazil wintering ground in the southwestem Atlantic Ocean . ANA C. FREITAS*, PAUL G. KINAS**, CRISTIANE C. A. MARTINS* , MÁRCIA H. ENGEL* * Projeto Baleia Jubartellnstituto Baleia Jubarte, Praia do Kitongo sln°- Caravelas. Bohia - Brazil- 45,900-000 ** Fundação Universidade Federal do Rio Grande, Departamento de Matemálica, Rio Grande, RS. Brazil, 96200-970 Contact e-mail: veleirocoronado@ypl.com.br ABSTRACT We present abundance estimate of tbe ftactioo of tbe humpback whaIe popuIation wintering offBraziI which "visits" tbe sorveyed area in tbe Abrolhos Bank and displays fluk&exposing behaviour. The study is based on photo-identification data collected between 1996 and 2000. Chapman-corrected Petersen estimates for ali pairs of data result in estimates fi-om1389 individuais up to 3971 witb average coefficient ofvariation ofO.21. A mire elaborate cIosed popuIation muItiple-«capture maximum likelihood estimate is 2393 witb 95% profile-likelihood confidence interval CI: [1924; 3060]. Assuming a changing population witb constant intrinsic growth rate over tbe study period, tbe maximum likelihood estimate of populatioo size for year 2000 is 3811 witb CI:[2195; 5542J. The anaIysis aIso estimates an annual growth rate of 31% in tbe surveyed area. Because tbe popuIation which winter in tbe Abrolhos Bank is some (unknown) ftaction ofwhales wintering offBrazil, it is unclear at this time how to interpret tbe estimated growth rate. KEYWORDS: ABUNDANCE ESTIMATE; HUMPBACK WHALE; PHOTO-IDENTIFICATION; BRAZIL; sourn ATLANTIC OCEAN INTRODUCTION The tec1miqueofbuilding a cataIog of photo-identified whaIes and to use tbis infonnation in sequentiaI statisticaI mark-recapture models has heen a usefuI tool in tbe study of cetacean popuIations over tbe Iast 20 years, particuIarly for humpbacks, (perkins et ai., 1984; Darling and Morowitz, 1986; Baker and Herman, 1981; Katona andBeard, 1990; Smitb et aL, 1999). Altbough tbe numher ofhumpback whaIes tbat have heen individually identified in tbe SoutbOOlHemisphere is substantiaI - more tban 2000 - on1ya few studies have attempted to use tbe information to estimate abundanee by capture-recapture models (Baker, 1995). Knowledge about tbe total population size of breeding stock 'A' tbat corresponds tbe humpback whales wintering offtbe Brazilian Coast is lacking (Zerbini et aL, 2001). Also, information about stock A's population growth rates is unknown (Johnston et al., 200 I). Estimates of tbese parameters will contribute for tbe study started by tbe Scientific Conunittee of tbe IWC in 2000, which evaluate tbe humpback whaIes' breeding stocks in tbe SoutbOOlHemisphere. The humpback whale popuIation tbat concentrates on tbe breeding ground of Abrolhos Bank, off tbe southernmost coast ofBahia state -Brazil, has beeo studied since 1988, but popuIation estimates based on tbe photo-identification of individual a8imals started onIy in 1995. A photographic cataIog of982 individually identified whaIes assembled over I r years of surveys in tbe area, provides tbe most complete records of sightiogs ofhumpback whaIes offtbe Brazilian coast. Preliminary assessment oftbe population abundance for 19% using intra-annual resightiogs in a contiouous time nm-parametric closed populatioo models (Betblem, 1998)resuIted in a confidence interval [231, 1519J. Ao empiricaI-Bayes approach applied to intra-annual resightiogs in 1995resu1tedin a 90"10a-edibility imervaI [1319; 1881] (Kinas and Betblem, 1998). Ia tbe Abrolhos Bank tbe distribotim of tbis popuIation has aIso heen studied in relation to batbymetry, proximity to land and water turbidity (Martins et al., 2001 ; Freitas et 01.,in review). Recent aeriaI surveys in tbe whole , ~;;;í