School Shark Galeorhinus galeus

Southern Australian biological stock

Assessments since 1991 have consistently estimated that the School Shark biological stock is less than 20 per cent of the unfished biomass. As such, School Shark is subject to a rebuilding strategy. Recent analyses of catch data have not indicated any targeting of School Shark in the Southern and Eastern Scalefish and Shark Fishery – Shark Gillnet and Shark Hook Sectors. Therefore, all catch can be considered to be incidental. School Shark are predominantly taken as incidental catch in fisheries targeting Gummy Shark.

The most recent full stock assessment for school shark was published in 2009³. In 2012, the 2009 assessment was rerun with additional catch data for the years 2009 to 2012⁴. The updated model allows the rate of maximum sustainable yield (MSY:B_MSY) to be estimated within the model, rather than being fixed at an assumed value (as was the case in the 2006 assessment). This resulted in a higher rate of maximum sustainable yield (4.4 per cent) than the 2006 assessment (3.5 per cent).

Concern remains about the ability of the stock assessment to reliably estimate the state of the stock. The assessment incorporates a number of fishery-dependent (catch-and-effort) and fishery-independent (survey) data series. However, given the low total allowable catches in recent years (potentially affecting quota availability, and the accurate reporting of catch and discards), the reported avoidance behaviour of fishers, and recent introduction of spatial closures predominantly off South Australia that prohibit the use of gillnets, the catch-per-unit-effort index may have become less reliable as an index of abundance in recent years⁵.

The biological stock is still considered to be below the Commonwealth Harvest Strategy Policy⁶ limit reference point (20 per cent of unfished biomass; B₂₀) and as such is considered to be recruitment overfished⁷. Under a zero catch scenario, the stock was projected to rebuild to B₂₀ within 23 years. However, even the setting of a total allowable catch that would allow rebuilding within 32 years (125 tonnes [t]) would severely constrain the Commonwealth Gummy Shark fishery. Catch scenarios up to 250 t were projected to allow recovery of the stock within three generation times (66 years), but catches of 275 t could not be sustained⁴. Total landed catch (that is, excluding discards) across all jurisdictions was 210 t in 2013.

Industry members have reported signs of increasing availability of School Shark, and that School Shark are becoming harder to avoid⁵. This is supported by preliminary survey work currently being conducted by the Institute for Marine and Antarctic Studies in pupping areas adjacent to Tasmania. The results are consistent with the 2009 stock assessment³, which suggested that adult biomass levels have stabilised or begun recovering. The results are also consistent with the 2012 stock assessment model results, which predict that rebuilding is likely to be occurring and that catches of 250 t or less would allow rebuilding, provided that gear selectivity and spatial and temporal distribution of catches remain similar to those in 2011. However, there is uncertainty around the rebuilding projections, resulting from uncertainty in assumptions relating to gear selectivity, and spatial and temporal distribution of catches in the 2012 assessment. It is therefore uncertain whether the total School Shark mortality (state and Commonwealth catches plus discards) is restricted to a level that will allow rebuilding. The above evidence indicates that it is uncertain whether the current level of fishing pressure is adequately controlled to allow the stock to recover from its recruitment overfished state⁷. Measurable improvements in biomass are yet to be detected.

On the basis of the evidence provided above, the biological stock is classified as an overfished stock.