Decade of recovery for rock lobster stock off Tasmania’s east coast

Southern rock lobster stock off Tasmania’s east coast is recovering well thanks to management actions introduced in 2013 through the State Government’s East Coast Stock Rebuilding Strategy. These actions were based on IMAS stock modelling under different catch scenarios and included changes in commercial and recreational regulations.

“A statewide stock decline was observed in the 2007-2008 season, with the total allowable catch not being caught despite an increase in the fishing effort,” IMAS Crustacean Fisheries Team Leader, Dr Rafael Leon said.

“On the east coast, that stock decline started earlier than 2007 in each of the three stock assessment areas between Eddystone Point and Southport, which are used for modelling purposes.

“Modelling showed that biomass and the total quantity of eggs produced by the stock – which is an indicator of the stock’s ability to reproduce and its future sustainability – declined from 2002 in Area 3 between Eddystone and Friendly Beaches. They also declined from 2005 for Area 1 between Eaglehawk Neck and Southport and Area 2 from Friendly Beaches to Eaglehawk Neck.”

Consequently, the State Government introduced the 10-year East Coast Stock Rebuilding Strategy (ECSRS) in July 2013, ahead of the 2013/14 season. The initial goal was to return biomass in these three areas to above 20% of unfished stock by 2023.

This initial target of 20% was chosen because it’s widely used as the lower acceptable limit for fished stocks, which would ideally be double this at over 40%. The 20% rebuilding target was also based on ecological modelling of interactions between rock lobsters and urchins, with IMAS recommending the rebuilding strategy also address this issue.

While some delays occurred, the 20% rebuilding target is now due to be achieved in all three assessment areas by 2025 after the State Government implemented a suite of management changes. These changes, which aimed to keep more stock in the water to rebuild biomass on the east coast, included:

• Staged reduction in statewide total allowable catch, from 1,523 tonnes in 2008/09 to the current level of 1,050.7 tonnes in 2014/15
• Shortened east coast recreational fishing season, with the daily recreational bag limit in the eastern zone reduced to two lobsters per person, with a daily boat limit of 10
• East coast commercial fishery catch cap, which limits commercial catch and closes the region when that limit has been reached
• An ongoing translocation program, which has moved undersized lobsters from the plentiful south west to the east coast to boost numbers in each of the three assessment areas
• New size limits for all fishers in November 2022, including an increased minimum size limit for females on the east coast, protecting females from being caught for longer and increasing stock productivity and biomass.

“Rock lobster on the east coast have always been fished harder than other areas due to its high accessibility and sheltered boating conditions for both commercial and recreational fishers,” IMAS Human Dimensions and Modelling Team Leader, Dr Klaas Hartmann said.

“As a result, when rock lobster stocks dropped across Tasmania in the late 2000s, the east coast stock fell to the lowest and most alarming levels. A decade later, through the development of the ECSRS, we’ve seen a substantial recovery in the region’s lobster stocks.

“IMAS modelling has been key to informing the government’s management decisions throughout this strategy.

“Our initial modelling in 2012 showed that rebuilding over a decade would require catch to be maintained to about a third of the most recent peak catch in 2005. Much of this reduction had already occurred due to catch rates plummeting, so the strategy was developed to keep catches around this reduced level rather than increasing catches as stock recovery occurred.

“Progress has been monitored annually, and adjustments made. Biomass is now above 20% of the unfished stock in Areas 1 and 3, which is a fantastic outcome to date and shows how the research and management have worked in collaboration with the fishing industry.”

Benefits of translocation

Since 2015, over 325,600 rock lobsters have been translocated from deeper, colder and slower-growing south west waters to shallower, warmer and faster-growing waters around Tasmania, including the east coast.

“Rock lobster that would ordinarily take a long time to reach commercial and recreational minimum legal size limits will grow faster in their new east coast habitat,” Dr Leon said.

“Translocation is a way of increasing recruitment to the east coast region and will inevitably accelerate the increase in biomass and egg production, provided that total catch is limited.”

The Department of Natural Resources and Environment Tasmania provided project funding through the Sustainable Marine Research Collaboration Agreement between the Tasmanian Government and the University of Tasmania.

Images:

• Top right: Associate Professor Scott Ling with a Southern rock lobster on the east coast (Photo: Lachie Tainsh)
• Top left: Southern rock lobster in an east coast cave (Photo: Scott Ling)
• Middle right: Associate Professor Scott Ling with a Southern rock lobster on the east coast
• Bottom left: Southern rock lobster being translocated to Tasmania's east coast. (Photo: Scott Ling) 

Published 6 March 2024