No abstract

The first standardised summer aerial survey of dugongs within Shark Bay in Western Australia, and the fourth in a series of surveys of this area, was undertaken during February 2002. This survey returned a population estimate of 11 021 ± 1357 (s.e.), a result similar to the first two winter surveys in 1989 and 1994 but considerably lower than the 1999 survey. Distribution was markedly different in this survey compared with all previous surveys, which were conducted during winter, confirming that dugongs within Shark Bay undertake a seasonal migration driven by changes in sea surface temperature. In addition to this distribution pattern it was identified that 24% of the population during summer occurred within an area known as Henri Freycinet Harbour. That is, while dugongs have been reported in this south-western region of the bay previously in summer, this is the first time that the substantial size (2629 ± 780, s.e.) of the summer dugong population has been quantified. Differences in the population estimate between the 1999 survey and this survey may be explained through large-scale movement patterns of dugongs between Shark Bay and Ningaloo Reef and Exmouth Gulf to the north, patterns that should be considered in the management of dugongs for the entire region.

The Australian sea lion is a listed threatened species under Australian Commonwealth legislation, based on limited population size and the likelihood of further declines in population abundance. Incidental mortality of this species in the west coast rock lobster fishery was identified as a key threat to the distinct sub-population of about 700 ind. on the west coast of Australia. Reports of incidental mortalities in this fishery from a variety of fishery-dependent sources suggested that a minimum of 4 to 5 mortalities occur every fishing season. All reported captures were in shallow waters (< 20 m) and within 30 km of a breeding colony. Foraging ranges of vulnerable-sized animals were confirmed by use of satellite-linked transmitters and time-depth recorders. Mitigation of this incidental mortality was effected by means of modifying the lobster pots with a sea lion exclusion device within the area of known interaction. The mandatory implementation of this programme resulted in a very high compliance rate (95%) in the first season and was achieved through active consultation and involvement of the industry, and of fishery and wildlife managers.KEY WORDS: Australian sea lion · Western rock lobster fishery · Neophoca cinerea · Mitigation of bycatch · Commercial fishing · Sea lion exclusion Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESS Contribution to the Theme Section 'Fisheries bycatch problems and solutions'

New Zealand fur seals have been increasing in abundance across Australia over the past 20 years, with annual population growth rates of 10–15%. Recent changes in distribution in Western Australia suggested that the population was increasing and expanding in range beyond the known historical distribution. We aimed to determine the growth rate of individual colonies and the overall population across Western Australia and identify new breeding and haulout sites. We used the direct count technique to estimate New Zealand fur seal pup production at 17 breeding sites. We estimated pup production to be 3518 in the 2010/11 austral summer, producing a resultant population estimate of ~17 200 New Zealand fur seals in Western Australia. This represented an exponential growth rate over the past 12 years of ~1% per annum, a significant reduction from the estimated rate of 10% per annum between 1989 and 1999. There were clusters of colonies that showed large annual declines of 6–7% in pup production over the past 12 years and at other colonies maximal rates of increase of pup production were 6–9% per annum. Three new breeding colonies were discovered. It appears that the New Zealand fur seal population is nearing its carrying capacity in Western Australia.