The long term success of marine reserves, and their benefits to nearby fished areas, depends on how well populations inside reserves are connected to those outside and to other nearby reserves. Answering that question requires an understanding of 1) how far adult individuals travel, and 2) how far their offspring drift on oceanic currents before settling to the bottom and maturing into breeding adults. If adults occasionally move outside reserve boundaries and their larvae often travel to other reserves and to fished areas, the individuals in an area can be considered a single, multi-part population, and even a small network of reserves can have substantial benefits.
Enter the European lobster! Much like the lobsters found on both the west and east coast of the United States, lobsters are a favorite target for recreational and commercial fishers along European coastlines, and in the early 2000’s their populations were beginning to decline. In 2006, a series of small MPAs were established along the Norwegian coast, and by 2010 the densities of adult lobsters had tripled and the average individual size of lobsters had increased. The no-take lobster reserves were clearly benefitting the lobsters protected within their borders, but what about the lobster populations outside?
A team of Norwegian and Swedish scientists embarked on a 4-year study to determine if these reserves offered long-term protection, to what extent adult lobsters moved outside the reserve borders, and if the lobsters along this stretch of coastline were a single population. They used radio transmitters to track the movements of 30 individual lobsters, then tagged close to 2000 additional lobsters and documented the distance traveled between tagging and recovery. They also sampled tissues along the Skagerrak coast of Norway for genetic studies.
What they found bodes well for lobster fishers along the rugged Norwegian coast. The Skagerrak network of lobster reserves is protecting the adult lobsters within its boundaries. On average, the radio-tagged lobsters survived for nearly the entire one-year study duration. In fact, the tagged lobsters probably survived well beyond that initial year, but the transmitters were only able to track movements until the lobster’s next molt; an annual event in which lobsters shed their hard exterior shell (and in this case, the attached radio transmitter). The small size of the reserves matched the scale of lobster movement; individuals within reserves largely stayed within reserves, although occasionally an individual would move a much greater distance. Just under 5% of the lobsters tagged within the reserve were recaptured outside the reserve boundaries, indicating that there is some spillover of lobsters into fishable waters. Genetic studies showed that lobster young often drift far from the site where they were born, suggesting that the lobsters along the Skagerrak coast are one large population rather than multiple separate enclaves. The research done by these scientists gives reason to hope. Despite recent declines in lobster catches outside of the reserves, the small amount of spillover and the connectedness of these populations suggests that over time, the protected lobster aggregations will benefit lobsters along the entire Skagerrak coast and increase lobster catches.
For More Information:
Huserbråten M.B.O., E. Moland, H. Knutsen, E.M. Olsen, C. André, and N.C. Stenseth. 2013. Conservation, spillover and gene flow within a network of Northern European marine protected areas. PLoS One 8:e73388 (553K PDF)