Fremadrettet forvaltning af tobis i Nordsøen

Sandeel in the North Sea is a priced commercial species and an ecological key species acting as prey for numerous predators from birds, through fish, to sea mammals. Sandeel is in particular important to the Danish fishery and fishmeal industry. However, large fluctuations in stock size and a complicated system of sub areas, where several have been deemed data poor by ICES, have been a challenge for the dependent industry.

The main aim of the present project was to provide a scientific basis for making a re-evaluation of the models and management regime used by ICES to provide advice for sandeel in the North Sea. This required (i) reviewing the literature to identify holes in our basic knowledge, (ii) investigating transport of sandeel larvae between fishing grounds and differences in population dynamics and productivity to guide decisions regarding management areas, (iii) developing a new survey index from the existing sandeel dredge survey, and (iv) make an effort to improve existing stock assessment models where possible.

Approximately half way through the project period, the ICES benchmark for sandeel took place. Here, all new results from the project was presented and used to facilitate a number of changes and improvements of the models and management regime. After the benchmark the project carried on to further underpin some of the decision made during the benchmark meeting.

These included conducting otolith analyses and population genetics, revealing novel insight, and the factual area divisions decided at the benchmark meeting was specifically evaluated using larval drift simulations. Studies of environmental drivers of sandeel recruitment and productivity were also finalized during the second half of the project.

The results revealed that the productivity of forage fish in the North Sea in general (sandeel included) has declined over time, explaining why the high fishing mortalities experienced during the 1990s cannot be maintained today. Correlative links were found between environmental variability and sandeel recruitment, suggesting that recruitment forecasting is potentially possible.

This work has therefore been presented before the members of the ICES WKS2D working group. This group is now planning to test an operational forecasting model in the coming years. Lastly, the process of evaluating a range of management strategies was initiated to support the ongoing process of developing a long-term management plan.

The MSE work is still ongoing and the continuousness of this work has been ensured by a new project initiated in 2017.