Ling (Genypterus blacodes) catches are an increasing component of the South East Fishery. There is increasing pressure to raise the trawl sector TAC for ling and there has been a substantial increase in catch by the non-trawl sector, particularly line, which is currently unregulated. Despite the increasing importance ofling in the SEP, population parameters were poorly understood.

 

Ageing studies were carried out by the Central Ageing Facility to provide a comparison of the current age composition of catches by different sectors and enable a refinement of growth and estimation of mortality rates. The age composition of current and historical trawl catches were compared as a preliminary basis for an evaluation of the impacts of fishing on the population. A workshop, through the SEFSAG process, was convened to undertake a stock assessment ofling using the ageing data, catch statistics and other relevant biological information.

 

The greatest catches of ling are taken in Eastern Sectors A and B, with lesser amounts taken off the west coast of Tasmania and in western Bass Strait. Catch rate data for the period 1986 to 1994 were relatively stable in all areas. However, there were marked differences in the seasonality of catches between areas.

 

Unlike the previous Australian growth study which indicated differences with New Zealand, revised growth curves were consistent with New Zealand studies; and ageing methods and interpretation were identical. The maximum age in Australian samples was 28 years but catches were dominated by 3 to 6 year olds except for catches from the west coast of Tasmania and longline catches which had relatively more old fish. There was a marked decline in the proportion of older fish in recent samples from Eden and Ulladulla and an associated increase in total mortality compared to data from the mid to late 1980s. Results from all years suggested that natural mortality was higher for ages 3-10 (approx 0.3) than for older fish (approx 0.1).

 

Considerable progress was made at the ling workshop. Results indicated that recent mortality rates in the eastern sector of the fishery were high. However, these were not consistent with catch rate data and were considered most likely due to unrepresentative sampling. Comprehensive age and size information if collected during 1995/96 will clarify this. In addition, the proposed 1995/96 age/length data together with the results of the workshop will enable the estimation of current and virgin biomass.