On 26 maart 2018 at 16:00 Klaas Sys defends his doctoral thesis
“Exploitation dynamics of the Belgian beam trawl fleet targeting hotspots of flatfish.”
The defense takes place at the Faculteit van de Bio-ingenieurswetenschappen, Academieraadzaal, A0.030, Coupure Links 653, 9000 Gent. Promotors are prof. dr. ir Jeroen Buysse van UGent and dr. ir. Jef Van Meensel en dr. ir. Hans Polet of ILVO.
From quotas to effort management: information is needed about the relationship between management, fleets and catches
The management of fishing systems - through fishing quotas – has seen great progress in recent decades. The increased availability of data and new scientific insights and analysis methods allowed us to better understand the relationship between fish stocks, the fishing industry and fisheries management. And that is paying off: a number of fish stocks, such as the sole and plaice stock in the North Sea, are once again being exploited in a sustainable way.
But there remain two major problems concerning mixed trawl fisheries: the discarding of unwanted fish and the disturbance of the seabed.
Through the landing obligation, which must be fully implemented for Belgian fishing in 2019, Europe hopes to reduce the discarding problem. Landings will cost money and will be counted in the quota, so the fishermen will automatically have to search for systems with less unwanted bycatch, according to the lawmakers reasoning. However, a number of studies show that a landing obligation can have negative socio-economic consequences for many fisheries sectors. In other words: less income and fewer jobs. For when the quota of a particular species in an area is exhausted, the fishery has to close there, even if there are still quotas for other species. Such a scenario could be avoided if the fishermen were to be given a management that would rely more on the fishing effort per area and per period, rather than on the amount of fish caught by species and by area. By using the catch and location data that fishermen supply themselves via the electronic logbook and GPS, the fishing effort can then be adjusted in function of the catch composition and impact on the ecosystem.
The idea of effort management has been on the table for years as a principle, but the applications in practice remain unanswered. An important reason for this is that it is still unclear how fishermen, and by extension fishing fleets, will react to this. ILVO-UGent researcher Klaas Sys therefore extensively researched the relationship between the dynamics of fishing fleets, the behavior of fishermen and the catches. He based his research on logbook and location data of Belgian fishing vessels. Klaas Sys examined cases, among others, including the race between fishermen after the opening of closed areas, the competition between the Dutch pulse fishermen and the Belgian beam trawlers in the North Sea, and the behavior of fishermen who are guided by (traditional) personal knowledge of the stalk. He discovered that decisions by individual fishermen and interactions between entire fleets have a strong impact on catches.
Dutch pulse fishing fleet causes shifts in catches
The more fish, the bigger the catch, you might think. And vice versa: the less fish, the smaller the catch. Yet that relationship does not always appear to be straightforward, especially when competition is at stake. In that case, the catches often appear to decrease faster than the amount of fish. In the Belgian fisheries, this happened, for example, after the Dutch beam trawl fleet switched to pulse fishing in 2012. By using the lighter electric pulse fishing gear, they were able to fish areas that were previously only fished by Belgian fishermen. Through analysis of catches and the activity of the vessels on weekdays (Dutch vessels do not fish during the weekend), Klaas Sys could demonstrate that the catches of sole by Belgian vessels were remarkably lower during weekdays than during the weekend. Dutch pulse fishing caused important shifts in catches as a result of changed interactions between the fleets. Belgian sole fishermen therefore experience more competition in the North Sea since 2012, which can translate into a lower income and underutilized quota.
Temporary closures cause races between fishermen
Sometimes there are "hotspots" of fish - and how does that affect the catches? To investigate this, Sys focused on data about the seasonal closure in the Celtic Sea and about the sole catches in that area. Since 2005, the main fishing grounds in the Celtic Sea have been closed during the months of February and March, to encourage recovery of the cod stock. After the reopening of the fishery, the catch of the target species (sole) appeared to be 1.5 to 2 times higher in the first two weeks of April. This resulted in an annual race to this area, with the result that most of the annual sole quota was fished up during the first two weeks of April. During this period of intensive fishing, the catch of sole always fell back to a normal level. Just before the reopening of the area there was a local hotspot of sole, but it disappeared very quickly after the opening due to the race between vessels. As soon as the catches decreased, the vessels spread out again.
Technical knowledge and tactical choices of fishermen in the model
For good fisheries management it is essential that the origin of the fish is determined as accurately as possible. This is currently done on the basis of GPS data from the vessels and on the basis of their logbook data, but the results are not so precise. Klaas Sys was able to determine the origin more accurately by modeling the tactical choices of a fisherman in his search for fish. In order to find fish, fishermen must continue their experience and knowledge of fishing grounds - there are no technical tools to detect flat fish, the target species of beam trawling. Klaas Sys thus identified the tactical choices, and he linked this behavior to the landing data of the fleet. He did this based on data about commercial vessels. Using this method, he was able to describe more accurately the relationship between the catches and the spatial distribution of vessels.
Knowledge about the behavior of fishermen and fleets can be incorporated into fisheries management
Interactions between vessels and behavioral patterns of fishermen at sea were not taken into account in the design of traditional fisheries management systems. This is because they were not known or because it was not clear how great their effect is. "However, that effect can be decisive for catches, especially if several factors are at play at the same time and when scaling up to large areas or longer periods," says Klaas Sys. "Thanks to the increased availability of data from commercial vessels, and new modeling techniques, the behavior and interactions between fleets can now be described.” With this information, the researcher helps overcome the obstacles that prevent a change from a quota management to an effort management.