SRL IPA: assessing the feasibility of spatial management in the South Australian Northern Zone Rock Lobster (Jasus edwardsii) fishery
SARDI Food Safety and Innovation
The primary needs in relation to this work are: 1. To assess the level of stock abundance in regions outside the main fishery areas, in deep water and the far west regions of the fishery. 2. To assess the economic feasibility of fishing in these areas. 3. To assess the biological characteristics of lobsters taken in deep water and the far west, including maturity of females and length frequency. 4. To assess the survival and condition of lobsters taken, in processing and transport.
1. Attain estimates of lobster abundance in deep water and far west areas of the Northern Zone Rock Lobster Fishery
2. Estimate size-of-maturity and length frequencies of these populations
3. Estimate survival rates of these lobsters held in wells on-board, corfs, and processing plants
4. Evaluate the economics of fishing outlying areas within the Northern Zone Rock Lobster Fishery
The Northern Zone rock lobster fishery of South Australia is extensive covering an area of approximately 207,000 km2. As a result, number of spatial management options are currently being considered which focus on the far-west and deep-water regions of the fishery. Currently, levels of commercial exploitation in both these areas are low compared to eastern and inshore areas. For example, in the 2011/12 fishing season only 12 t (4%) of the 307 t total catch came from the far-west, while just 29 t (9%) came from >90 m depth.
Despite low levels of total catch, catch rates (kg of legal lobster/potlift) in both regions are high compared to eastern and inshore areas. In the far-west at least, this is influenced by a larger mean lobster size compared to eastern regions, presumable due to faster growth rates. While higher, catch rates trends from 1970-2011 in both far-west and deep-water regions are comparable to other regions in the fishery. In particular, catch rates in both areas declined simultaneously with eastern regions from 1999 to 2008 suggesting that the abundance of lobsters in the far-west and deep-water is driven by common recruitment patterns to the rest of the zone.
The far-west region is close to the western limit of Jasus edwardsii distribution within Australia with pre-recruit (undersized) abundances in this area the lowest in the zone suggesting that the region is recruitment limited. The size of maturity in far-west regions is substantially higher than the minimum legal size which again reflects faster growth rates. This is offset somewhat by the fact that few lobsters close to legal size are found within the commercial catch. However, if exploitation rates are increased in far-west regions, given that size limits are set in part to protect immature females, higher size limits may need to be considered under a spatial management regime. Alternatively, a male only fishery may be considered during specific months in line with management rules for J. edwardsii fisheries in Victoria and Tasmania. Data to estimate size of maturity in deep-water sites are limited in South Australia.
Keywords: rock lobster, Jasus edwardsii, spatial management, bio-economic, fleet dynamics, stock assessment