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Edited by Leon P. Zann
Great Barrier Reef Marine Park Authority, Townsville Queensland
Ocean Rescue 2000 Program
Department of the Environment, Sport and Territories, Canberra, 1995
ISBN 0 642 17406 7
Parks and Wildlife Service
Department of Environment and Land Management
The entanglement of Australian fur seals in human debris in Tasmanian waters has been documented over four breeding seasons (1989-1993) both at Australian fur seal breeding colonies and on an opportunistic basis at haul-out sites in Bass Strait and southern Tasmania. The results to these surveys are summarised here and the methods of data collection and analysis are outlined in Pemberton et al. (1992).
A total of 136 Australian fur seals (Arctocephalus pusillus) and 1 New Zealand fur seal (A. forsteri) with neck collars were observed over the four year study period.
Polyethylene trawl nets accounted for 42% of neck collars, polypropylene straps (packaging straps) 29%, monofilament gill nets 15% and nylon rope 11%. Other incidental items included steel rings (n=2) and a rubber loop.
The high rate of entanglement of seals in packaging straps has continued despite the successful development by SAFCOL and the Department of Parks Wildlife and Heritage (Tasmania), of a bait box which does not require straps. Observations of the bait boxes being loaded onto fishing boats at Tasmanian ports suggests that whilst the strapless bait box was accepted by some sectors of the industry, they are not being used to a significant extent. It is also noteworthy that some of the straps (white and green) observed on the seals are rarely used by the Tasmanian fishing industry and probably originate from other nations fishing either in Australian waters or on the high seas west of Tasmania. The West Wind Drift will continue to bring flotsam and jetsam to Tasmanian waters as long as there is a source for this material west of Tasmania and therefore attempts to reduce the amount of debris have to be directed at both international and international levels.
Trawl nets continue to be the major source of entanglement materials for seals in Tasmanian waters. This form of entanglement is probably the most lethal as the typically large pieces of entangled netting is both resilient to wear and buoyant. The frequency of occurrence of trawl net entanglements has increased in southern waters and is now similar to that in Bass Strait. This increase was anticipated as the orange roughy fishery shifted from operating over soft bottom to fishing over rocky sea mounts off southern Tasmania. This resulted in an increase in the number of nets lost due to 'hook-ups' (Pemberton et al. 1992). This trend may change as a reduction in the quota of orange roughy to the south-east trawl fishery has been offset by an increase in the quota of blue grenadier. A major fishery occurs off western Tasmania and west and east of Bass Strait over the continental shelf.
The majority of entangled seals were juvenile and subadult animals (75%). Amongst adult animals, females (23% were entangled more often that males (2%). As suggested by Pemberton et al. (1992), this probably reflects the tendency for smaller animals to become entangled and the consequent mortality of these animals due to physical injury imposed by the increased restriction of neck collars as the animals grow. Some seals however do survive entanglement. A total of 15% of seals classified as 'entangled' had circular scars around their necks. The only neck collars which were observed to be fraying whilst on the seals were packaging straps. It is probable, therefore, that the majority of those seals that survive entanglement had this form of entanglement, although monofilament and rope neck collars have been found on breeding colonies suggesting that these do occasionally fall off.
The entanglement of fur seals is a management issue for both the conservation of the species and the alleviation of suffering by individual seals. The mean incidence of entanglement of Australian fur seals was 1.6+/-1% (n=22, range 0-3.4). This rate must be considered as an underestimate because of the probable mortality of seals entangled in debris which prevent the animals travelling to haul-out sites, and hence being observed. This incidence of entanglement is higher than that recorded to northern fur seals (Callorhinus ursinus) where entanglement was implicated in the decline of this species (Fowler 1987). The entanglement of Australian fur seals is therefore considered to be a threat to the status of the population and consequently a conservation problem. Also, because entanglement results in gross wounding to the seals and prolonged suffering over years, there is a moral responsibility by wildlife organisations to alleviate the suffering of individual seals.
Fowler, C.W. 1987, 'Marine debris and northern fur seals: a case study', Marine Pollution Bulletin, vol. 18, pp. 326-335.
Pemberton, D., Brothers, N., & Kirkwood, R. 1992, 'Entanglement of Australian fur seals in man-made debris in Tasmanian waters', Wildlife Research , vol. 19, pp. 151-9.