THE SUSTAINABILITY OF THE INDIGENOUS DUGONG FISHERY IN TORRES STRAIT,AUSTRALIA PAPUA-NEW-GUINEA

The sustainability of the indigenous dugong (Dugong dugon) fishery in Torres Strait is evaluated on the basis of aerial survey estimates of the size of the regional dugong population in 1987 and 1991 and a surv ey of catches of dugongs taken by local communities between 1991 and 1 993. The estimate of the dugong population in the Torres Strait region in November-December 1991 was 24,225 (+/- SE 3,276) compared with the corresponding estimate of 13,319 (+/- SE 2,136) for November 1987. Th e difference between the two estimates cannot be explained by natural increase of the population or variations in the sighting conditions en countered during the two aerial surveys. We believe this difference is due to a major redistribution of dugongs within the survey region or migration into Tot-res Strait, probably from Irian Jaya (Indonesia). D ugongs are a major component of the traditional fishery in Torres Stra it. The biomass of dugongs landed between June 1991 and May 1993 was h igher than the weight of any other component of the traditional catch. The estimated annual dugong catch of 1226 (+/- SE 204) was higher tha n previous catch estimates. It is impossible to verify the sustainabil ity of this harvest without an understanding of the movements of the d ugong population, better absolute estimates of dugong population size, dugong catch statistics for Papua New Guinea and adjacent regions in Australia, and current estimates of life history parameters for dugong s in Torres Strait, all of which will be difficult to obtain. The mean estimate of the annual dugong catch in Torres Strait for 1991-1993, h owever, is approximately 5% of the mean estimate of the dugong populat ion size in 1991. This is too close to the estimated maximum rate of i ncrease of the dugong population to be sustainable if the estimate of dugong numbers is close to an absolute estimate or if there is substan tial emigration of dugongs from the area. Co-management arrangements m ust be developed between the government agencies responsible for the d ugong fishery and the Torres Strait Islanders in order to develop mana gement strategies that will provide for the Islander's traditional hun ting expectations and maintain dugong numbers.