Relação entre movimentos dos golfihos sousa chinensis, ciclos de marés e ictiofauna na baía sul da ilha da Inhaca

Abstract

ABSTRACT The movements of the Sousa chinensis dolphins and their relationship with the abundance of the ichthyofauna were studied in the southern bay of Inhaca Island from January to April 1999. The movements and the ichthyofauna were studied by phases of circadian and semi-lunar cycles from one fixed point located 3 meters high from the average level of the sea surface, in Ponta Ponduíne during 78 watch sessions in a total of 394 hours. On the route, 3 locations were chosen ( Ponta Ponduíne, Ponta Raza and Canal do Banco) to sample the ichthyofauna by siege and measure the Secchi depth, bottom and surface salinity and the bottom and surface temperature. During observations the rate of dolphin encounters was higher from 9 am to 10 am and from 3 pm to 6 pm, being low from 10 am to 3 pm. There were 21 occurrences of dolphins and group size ranged from 4.4 individuals at high tide, 5.4 individuals at ebb tide, 5.4 individuals at spring tide and 4.3 individuals at low tide. The dolphins moved mainly West-East during high tide and East-West during ebb tide but there was no association between the movement and slack and tide tides. The most prevalent behaviors were foraging and socialization. The Channel was the most preferred habitat used in relation to the Bank. The total weight and total number of ichthyofauna at the 3 sites at ebb and flood tides were not different, but at spring tide the weight was higher than at low tide. Diversity and evenness were highest in Ponta Raza and low in Ponta Ponduíne. The species Gerres acinaces was more frequent in all places but dominant in Ponta Raza and Ponta Ponduíne. The species Crenidens crenidens and Rabdosargus sarba were dominant in Canal do Banco. Secchi depth, bottom and surface salinity, and bottom and surface temperature did not have significant influences with the total weight (R2=0.04) and total number of individuals (R2=0.06) of the ichthyofauna. The movement of dolphins seems to have no relationship with the total weight and number of individuals of the ichthyofauna.