New model provides better insights into the lobster stock

The new model has been developed through a so-called benchmarking process, which involves a comprehensive review of available data, model structure, assumptions, and uncertainty testing. The work has been led by researchers at the Department of Aquatic Resources (SLU Aqua) and has involved representatives from the Swedish Agency for Marine and Water Management, county administrative boards, the fishing industry, and an external lobster expert.

"This year’s review was conducted to ensure data quality, improve our index calculations, and evaluate the model itself. Additional data has also been incorporated, including catch index data from 2023, more size classes, and a fishery-independent catch index. This results in a more flexible model that better captures uncertainties in parameters and data," says Andreas Sundelöf, researcher at SLU Aqua.

Signs of recovery

In the previous assessment, which was based on data up to and including 2022, the lobster stock was considered to be very weak. At the same time, SLU observed substantial catches during the fishing season, with many reports of larger catches than in previous years.

"Now that we have supplemented the data up to 2023, we believe that the large catches in recent years likely reflect a real increase in the lobster stock, which is a positive sign," says Andreas Sundelöf.

Some concerns remain, particularly regarding how climate change and rising sea temperatures might affect catchability. Each year, however, the information on the size structure of the stock (are all sizes and ages represented?), improves rhe robustness of the model. This type of information about individual sizes in the stock makes it easier to rule out climate effects and determine whether improvements in stock status indicate a real increase in the population.

Uncertainties in the fishery

The future development of the lobster stock depends on the level of catches, which in turn is influenced by several factors—not least the number of people participating in lobster fishing. Since there is no fixed quota, the fishery is regulated more indirectly, and estimating total catches is difficult.

"This comprehensive review of data and models has given us a more reliable picture of the stock, but it has also highlighted its weaknesses. To ensure sustainable fishing, better knowledge of recreational fishing catches is needed. Improved reporting of both gear usage and catches would provide managers with better tools to monitor the developments," says Andreas Sundelöf.

Read more about the status of the lobster stock and the latest stock assessment in the Fiskbarometern (only in Swedish)

Read more about the benchmarking process in the report  Benchmark of European Lobster (Homarus gammarus) in Swedish areas of Skagerrak, Kattegat and Öresund