ISSN 1441-8487 FISHERY ASSESSMENT REPORT TASMANIAN ABALONE FISHERY 2005 Compiled by David Tarbath, Craig Mundy and Malcolm Haddon May 2006 National Library of Australia Cataloguing-in-Publication Entry: Tarbath, David Bruce, 1955- Fishery assessment report: Tasmanian abalone fishery. Bibliography. Includes index. ISBN 0 7246 4770 8. 1. Abalones - Tasmania. I. Tarbath, D. B. (David Bruce), 1955- . II. Tasmanian Aquaculture and Fisheries Institute. Marine Research Laboratories. (Series: Technical report series (Tasmanian Aquaculture and Fisheries Institute)). 338.37243209946 This report was compiled by D. Tarbath, C. Mundy and M. Haddon, TAFI Marine Research Laboratories, PO BOX 252-49, Hobart, TAS 7001, Australia. E-mail: [email protected]. Ph. (03) 6227 7277, Fax (03) 6227 8035 Published by the Marine Research Laboratories, Tasmanian Aquaculture and Fisheries Institute, University of Tasmania 2006. Abalone Fishery Assessment: 2005 Abalone Fishery Assessment: 2005 Executive summary Like previous assessments, the 2005 Abalone Fishery Assessment was based primarily on commercial catch and effort statistics and size-composition data from the Tasmanian fisheries for blacklip abalone (Haliotis rubra) and greenlip abalone (H. laevigata). Commercial catch and effort data were supplied by the Tasmanian Department of Primary Industry, Water and Environment (DPIWE). These data were obtained from catch dockets provided by licensed divers. Catch rates were derived from the catch- effort data and annual variation in catch rate was interpreted as an approximate relative index of abalone abundance. The commercial catch sampling size-composition data were mostly collected by TAFI research staff, but some data were obtained directly from divers. Changes in median size of commercial catch samples were used in addition to any trends in catch and catch rates to assist in understanding the status of different stocks. Since 2000, the Tasmanian blacklip abalone fishery has been sub-divided into geographical management zones, which in 2005 included the Eastern, Western, Northern and Bass Strait Zones. The purpose of zoning is to provide a mechanism for managing the distribution of effort and to protect the more accessible areas from high fishing pressure and consequent over-exploitation. Each of these zones and the greenlip abalone fishery are individually managed, with separate total allowable catch (TAC), legal minimum size(s) and in some cases, include annual catch limits (catch caps) in smaller regions of the zones. In 2005, the combined TAC for Tasmania was 2502.5 tonnes. The use of catch and effort data to monitor trends in abundance of abalone is widely regarded as unreliable by fisheries researchers, and has been associated with the collapse of many abalone fisheries. There are several factors that adversely affect the relationship between catch rates and abalone abundance: the gregarious behaviour of abalone; the serial depletion of local populations making up each stock; and changes in fishing efficiency by divers. However, provided that the effect of these factors on abundance is understood and compensated for where possible, catch rates in Tasmania appear to provide a reliable index of abundance. There is a high degree of confidence in the use of catch rates to monitor the Tasmanian fishery, particularly throughout the south east part of the Eastern Zone, and other parts of the fishery where effort is consistently applied. Less confidence in the use of catch rates to describe abundance occurs where there is evidence of a recent increase in effective effort potentially affecting catch rates, or the relative effort is low in proportion to the size of abalone populations and is applied at irregular intervals (e.g. most of the Western Zone). Catch rates are not considered reliable in the greenlip fishery, the King Island blacklip fishery and the Bass Strait Zone, hence the assessment is correspondingly less certain in these areas. It is apparent that recovery of Eastern Zone stocks has continued in 2005 following earlier signs of recovery during the previous year. The Eastern Zone has operated in both 2004 and 2005 with the TAC set at 770t, which is a relatively low level of catch compared to earlier years. This has resulted in several of the most depleted areas TAFI Fishery Assessment Report Page i Abalone Fishery Assessment: 2005 receiving less fishing pressure, and other areas of higher abundance have been fished at only moderate levels. This reduction appears to have promoted recovery in all four fishing regions. At the Actaeons, there were good indications that recovery had started. At Bruny Island, most areas continued to exhibit the indications of recovery observed in 2004. In Storm Bay, where signs of recovery were first observed in 2003 and which has received proportionally the greatest levels of fishing pressure, the performance of the fishery has continued to improve. On the East Coast there were continuing signs of recovery. All fishery performance measures indicated that Eastern Zone stocks were being fished sustainably. There continues to be concern for Western Zone stock levels, which are believed to be declining after being fished at historically high levels of catch since 2000 when zonal TACs were introduced. In the 2004 assessment, there was concern that divers were selectively fishing for smaller abalone, and thus only taking the TAC from a fraction of the fishable biomass with the potential to deplete this size class. This practise is clearly unsustainable. More recent information, obtained from divers' responses to a detailed questionnaire, revealed that the extent of this practise has become very limited, and most divers now take all abalone of legal size. Nevertheless, nearly all questionnaire respondents (20 of 28) who fished in the Western Zone expressed concern at the level of stock depletion. The most problematic regions in the Western Zone were the South Coast and the North West. Catch rates in most parts of the South Coast have declined continuously since 2000, and have now been below the suggested mean threshold levels of 100 kg/hr for two years. There were consistent indications that the median size of abalone in this region's 2005 catch was getting smaller, implying increasing fishing mortality. The 2005 catch in Block 12 on the South Coast was among the highest recorded. These all indicated that continued fishing on the South Coast at the prevailing high levels was likely to be unsustainable. In the North West, catch rates have shown little response to greatly reduced levels of catch in recent years, suggesting that stock levels should be considered low. During the 1980's, the North West supplied much greater annual catches, and we are unable to explain the region's apparent decline in productivity since this time. Stock levels in the remainder of the Western Zone were indeterminate but were believed to be falling. In the Central West region, for the past three years the Block 7 catch has greatly exceeded its long term average, and in 2005 was the highest recorded for this block. While catch rates in Block 7 were stable at moderate levels suggestive of sustainable fishing, some divers have moved elsewhere and reported that populations were being depleted. In the South West, the Block 11 catch has also been high, but here catch rates have fallen in most areas since the inception of the Western Zone in 2000, indicative of on-going depletion. Previous experience in other blocks suggests that the risk is increasing that current levels of fishing in the Western Zone are becoming unsustainable. The irregular spatial and temporal nature of fishing in the Western Zone causes catch rates to be a poor predictor of abundance and stock levels are likely to be declining at faster rates than catch-rate trends indicate. TAFI Fishery Assessment Report Page ii Abalone Fishery Assessment: 2005 The Northern Zone has been primarily dependent on the North West and King Island for most of its catch, and there were significant problems with stock levels in both regions. King Island blacklip populations on shallower reefs have been extensively depleted, while deeper water populations that were reported abundant are difficult to access with standard air supplies. Current levels of catch are not high in a historical context, and while serial depletion has occurred, a transfer of effort to the deeper reef/water populations may enable recovery in shallower water while maintaining catch levels. However, the majority of the blacklip catch has been taken by visiting mothership-based divers who have used standard air supplies and any future redistribution of effort and catch to deeper waters will be dependent upon the willingness and ability of the these divers to work in deeper water. The 280t Northern Zone TAC was partly based on the understanding that North West blacklip catches during the 1980's were mostly sustainable, and that a TAC derived from a smaller fraction of those catches would be sustainable. It is of concern that the region's stocks now appear to be either fully exploited, or at risk of overfishing at much lower levels of catch than those used to estimate the TAC. Stock levels may be recovering in the south of Block 5, but have yet to recover from intensive fishing in the north. The Block 5 100t catch cap is no longer effective as a means of preserving sustainability. Other parts of the region, particularly Block 48, which in the 1980's were productive, also no longer appear capable of supporting former levels of catch. There is little opportunity for increased levels of catch in this region and any transfer of catch from King Island would be unsustainable. Catches from the North East and the Furneaux Group have never reached the size of those from either King Island or the North West, because the amount of productive reef is small, abalone sizes and growth rates are less than in the west, and the remoteness of both regions has deterred many buyers.