Uruguay (orcas) ~ Bioblogia.net

7 de septiembre de 2004

Uruguay (orcas)

In Uruguay, WDCS is funding this new project, headed by Veronica Iriarte, to study the occurrence, behaviour, and feeding habits of orcas in the waters surrounding Isla de Lobos, Punta del Este.Orcas are considered opportunistic feeders, and have the most diverse feeding habits of all toothed whales. However, some orca populations have become specialised in different foraging strategies based on the food source available to them. In British Columbia (Canada) and Washington State (USA) at least two different orca populations have been described - residents and transients. The two populations share the same area but don't associate with one another, and have differences in their genetics, morphology and feeding habits (which leads to differences in behaviour and social organisation). Residents prey on fish, while transients prey primarily on marine mammals.In Antarctic waters, two orca populations with different feeding habits, morphology and ecology have also been described. Currently, however, all orcas are considered one species, the world over. The specialisation of sympatric populations in foraging techniques is unusual for mammals and vertebrates in general. The system used by orcas can provide important information about the consequences of reproductive isolation on populations and, to discover more, new studies on orca populations in different parts of the world are necessary.Prey species of orcas inhabiting the southwestern Atlantic include fish, rays, octopus and squid, birds, and marine mammals (including pinnipeds - seals and sea lions - and other cetacean species). Orca predation from longlines used for catching large pelagic species (such as tuna) has also been observed in Brazil and Uruguay causing losses to the industrial fisheries. As a result of this, the orcas are often shot at and, as orca population have a slow growth rate, this threat, even occasional, could limit population growth rate further. The orcas of South America are also threatened by accidental capture in fish gillnets and, until a few years ago, orcas were live-captured in Argentina to supply the captivity industry.During this new study, Veronica aims to:1) Determine whether the presence of orcas in the coastal waters of the study area is seasonal or year round.2) Determine whether the orca populations present prey upon the pinnipeds (Arctocephalus australis and Otaria flavescens) that inhabit the island. 3) Photo-identifiy individuals. This will allow Veronica to determine movement patterns and association patterns between individuals. Knowledge of these patterns can then be used for estimating population parameters.4) Integrate the resulting information with what is known about other orcas off South America (Argentina and Brazil).Working together with Brazilian and Argentine researchers (such as the WDCS-Argentina team), a detailed study and comparison of photo-identified individuals in Argentina, Brazil and Uruguay can be achieved. This will be fundamental for obtaining important data on orca presence in the region, contributing to the knowledge of the geographic variation of the species.The knowledge of the presence and feeding habits of the species in Uruguayan waters will be extremely important for developing the understanding of orca interactions with industrial fisheries, analysing the responsibility of orcas in the decreasing of fish catches, and establishing non-lethal methods for diminishing and preventing losses.2003 UpdateSighting surveys began on January 2, 2003. So far we have the results from 4 of the surveys (3/1/03 - 21/1/03; 20/2/03 - 1/4/03; 17/403 - 29/4/03; 30/5/03 - 11/6/03). A following survey was to be conducted from June 25 to September 3, 2003.So far during the four surveys, orcas have only been recorded in the fourth survey (30/5/03 - 11/6/03). Depending on results form the fifth (June to Sept) survey, it may be that like in Argentinian and Brazilian waters, the species are seasonally present in Uruguayan waters (but in the winter not summer). Future activities planned for this field project are continued sighting surveys form the Lighthouse, to liaise with Miguel Iniguez and WDCS Argentina, plus zodiac surveys for photoidentification.
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