Guiana dolphins (Sotalia guianensis) displaying beach hunting behavior in the Cananéia Estuary, Brazil: social context and conservation issues

Abstracts

To elaborate a fuller description of the beach hunting behavior displayed by Guiana dolphins (Sotalia guianensis) in the Cananéia Estuary (CE) (25ºS, 48ºW), a photo-identification study was conducted from May 2000 to July 2003. Three land platforms were chosen at the main entrance of the above-mentioned estuary, where scientists enjoy a unique opportunity to observe dolphins at greater proximity, undisturbed. Observations were opportunistic and unevenly distributed in time and space. To enhance the identification efforts, an 80-pound crossbow was used to collect skin samples in order to determine the sex of the eight individuals thus monitored. In 67 days of surveys, rendering approximately 80h of direct observations, 4,102 photographs were taken, of which 1,098 (26.8%) were considered useful for identification purposes. A total of 103 groups were reported (3.7 ± 2.6 individuals), ranging from solitary dolphins to 15 individuals. Female-calf pairs were observed in 92.4% of all the groups investigated. On the first occasion, a calving interval was observed for the species in the CE: approximately 3 years and 9 months. Of the 40 individuals identified at least once, eleven used the sloping beaches regularly: females KN #s 10, 30, 255, 268 and 279; males KN #s 86 and 257; and four individuals of unknown sex. The characteristics of the associations among beach hunters were evaluated by the analyses of association indices. A total of 83 possible associations between dyads were analyzed using the half-weight index and two selective criteria (5+ and 8+ sightings/individual). Mean association indices varied from 0.12 to 0.16, evidencing weak bonds among beach hunters. Most regular beach hunters were females, showing that the beach hunting behavior should probably be considered more typically female. Beach hunting in the CE might be considered another example of cultural transmission in cetacean societies.

Cetacea; Sotalia guianensis; Guiana dolphin; Behavior; Beach hunting

Com o intuito de detalhar o comportamento de procura e captura de alimento em praias (“beach hunting”) exibido por botos-cinza (Sotalia guianensis) no Estuário de Cananéia (EC) (25ºS, 48ºW), um estudo baseado na aplicação da técnica de foto-identificação foi conduzido de maio de 2000 a julho de 2003. Três plataformas de observação a foram escolhidas na principal entrada do mencionado estuário, onde os pesquisadores encontram uma oportunidade ímpar de observar os botos a uma pequena distância sem incomodá-los. As observações foram oportunísticas e desigualmente distribuídas ao longo do tempo e do espaço. Adicionadas às observações de identificação individual, uma balestra de 80lbs de pressão foi utilizada para coletar amostras de pele de oito indivíduos monitorados com vistas à determinação do sexo. Em 67 dias de investigação, que renderam aproximadamente 80h de observações diretas dos botos, 4.102 fotografias foram tomadas, das quais 1.098 (26,8%) foram consideradas úteis para o propósito de identificação individual. Um total de 103 grupos foi observado (3,7 ± 2,6 indivíduos), variando entre botos solitários e 15 indivíduos. Pares de fêmeas e filhotes foram observados em 92,4% dos grupos investigados. Apresenta-se a primeira notificação de intervalo de nascimento de um filhote para o EC: aproximadamente 3 anos e 9 meses. De 40 indivíduos identificados ao menos uma vez, onze usaram regularmente as praias: fêmeas KN #s 10, 30, 255, 268 e 279; machos KN #s 86 e 257; e quatro indivíduos de sexo desconhecido. As características das associações entre os indivíduos monitorados foram avaliadas através das análises de índices de associação. Um total de 83 associações possíveis entre pares de botos foi analisado utilizando o índice de peso médio e dois critérios de seleção (5+ e 8+ avistamentos/indivíduo). A média dos índices de associação variou entre 0,12 e 0,16 evidenciando laços fracos entre os indivíduos monitorados, cuja maioria foi composta por fêmeas, evidenciando-se que o comportamento de uso de águas rasas próxima às plataformas monitoradas para alimentação parece ser direcionado às fêmeas. Este fato evidencia que o comportamento de procura e captura de alimento em praias (“beach hunting”) do EC poderia ser considerado como outro exemplo de transmissão de cultura em sociedades de cetáceos.

Cetacea; Sotalia guianensis; Boto-cinza; Comportamento; Forrageamento

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Publication Dates

• Publication in this collection
  06 Aug 2010
• Date of issue
  June 2010

History

• Accepted
  09 Feb 2010
• Reviewed
  14 Dec 2009
• Received
  27 July 2009