The first ecosystem model that encompasses the entire food web of the western Baltic Sea anticipates how marine life in the region might react to various fishing scenarios and extra stressors introduced by humans. The model simulations demonstrate that ecosystem-based fisheries management would recover stocks of economically significant fish species and the imperiled harbor porpoise population. In a paper published in Frontiers in Marine Science, a team of marine scientists led by GEOMAR Helmholtz Centre for Ocean Research Kiel (Germany) argues that marine life would become more resilient and alternatives for further carbon sequestration would become available.
Decades of overfishing, coupled with nutrient pollution, a rapid increase in hypoxia, ocean warming, and acidification, have placed fish and harbour porpoises (Phocoena phocoena) at risk of extinction in the western Baltic Sea. According to a team of marine scientists from GEOMAR Helmholtz Centre for Ocean Research Kiel (Germany), the German Federal Agency for Nature Conservation (Bundesamt für Naturschutz, BfN, Germany), and the Institute of Biosciences and Bioresources at the National Research Council (CNR) of Italy, commercially significant stocks of cod (Gadus morhua), herring (Clupea harengus), and sprat (Sprattus sprat) (Sprattus spratt) (G.
The researchers investigated five scenarios, ranging from no fishing to ecosystem-based fisheries management, using model simulations. This method takes into account the roles of species in their environment and adjusts catches accordingly to maintain healthy, productive, and resilient fish stocks. Ecosystem-based fisheries management might allow the endangered harbour porpoise population to recover and dramatically increase herring and cod catches within a decade, according to a study recently published in the scientific journal Frontiers in Marine Science. In addition to being more capable of supporting carbon sequestration, the food web would become less susceptible to eutrophication and climate change than in a business-as-usual scenario that assumes current fishing practices continue.
The study benefits from GEOMAR’s years of data collection. The researchers have created the first model for the western Baltic Sea that includes top predators such as harbour porpoises and seals, diverse fish species and other marine creatures, plankton, algae, and seaweed, as well as their interactions under various scenarios. Dr. Marco Scotti, a marine ecologist at GEOMAR and CNR and the lead author of a new paper, says that a holistic view of the food web helps find ways to manage important food resources and the businesses that depend on them.
Ecosystem-based fisheries management would entail stopping the capture of juvenile cod, reducing catches of herring and sprat to 50 percent of the maximum sustainable yield—the highest possible annual harvest that can be sustained over time—and catching 80 percent of the maximum sustainable yield of adult cod and flatfish. This plan was compared to a status quo scenario in which the average number of fish killed by fishing for all exploited stocks from 2015 to 2019 stayed the same.
In the business-as-usual scenario, cod stocks collapse slightly below 2019 levels by 2050, while herring stocks decrease to nearly half their 2019 levels. Sprague and flatfish populations are increasing, indicating a considerable regime shift. In contrast, ecosystem-based fisheries management would boost cod catches by 70 percent and herring catches by 50 percent by 2050, compared to the period from 2015 to 2019. The catch of flatfish would increase by over 20%, while fishing effort and expenses would be drastically decreased. Carbon sequestration would be more than three times as likely under ecosystem-based fisheries management as it would be under business as usual.
Dr. Rainer Froese, a fisheries biologist at GEOMAR and co-author of the study, explains, “Europe’s Common Fisheries Policy mandates an end to overfishing by 2020, followed by the restoration of healthy, resilient ecosystems.” “The recent collapse of herring, cod, and profitable western Baltic fisheries in general was mostly caused by past and current overfishing, not climate change. In addition, continued business as usual would bring the critically endangered harbour porpoise to the edge of extinction. In contrast, ecosystem-based management would restore healthy stocks and fisheries, as well as aid us in combating climate change. To save the western Baltic, cod and herring fishing must be halted for a few years while their stocks recover. The fishermen must be paid for their losses during this period. In the interim, fishing for plaice and other flatfish can continue. “
