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Recovering Fish Population in a Marine Reserve: No Easy Matter

Por: | 18 de diciembre de 2013


By Rosa Martínez, University of Barcelona Press

The recovery of fish populations in the Mediterranean coast is not an easily resolved issue. Quite the contrary: it is a long-term process that lasts for decades and, after many years of protection, only some fish species reach total recovery. Indeed, recent research reveals that fish populations that are more vulnerable to fishing will be destroyed if protection failures.

Protection policies started more than 25 years ago in the Medes Islands, a marine reserve of high ecological value in western Mediterranean. From 1992 to 2009, scientists from the University of Barcelona (UB) and the Centre for Advanced Studies of Blanes (CEAB-CSIC) tracked some species strongly affected by fishing practices in order to check the effect of protection in the marine reserve. 

Bernat Hereu, an expert from UB, points out that “research is focused on six fish species that are good indicators of protection effects: dusky grouper, common dentex, European seabass, zebra seabream, brown meagre and gilthead seabream. They are vulnerable to fishing, they have long lives and a common habitat and, due to protection, they are more abundant in the protected area than outside”.


What’s the Effect of Marine Protection?

In order to find answers, scientists compared abundance and size among these species in the marine reserve, partial reserve and the unprotected area. Do protection results in the marine reserve differ among species?

According to the study, dusky grouper, zebra seabream and European seabass have practically reached total recovery; brown meagre is close to population stabilization and common dentex is still increasing. The situation of other species does not look so good. The gilthead seabream population, for example, is decreasing even in protected areas. This phenomenon may be caused by their spillover — in other words, their movement from the protected area to the coast. “Gilthead seabream”, explains Hereu, “is a species that lives in different habitats. In autumn, it aggregates to spawn. One of these aggregations is located very close to the marine reserve and is well known by fishermen in the area. An overfishing of aggregations for reproduction may reduce gilthead seabream populations”.


Threats to Marine Ecosystems

Antoni Garcia Rubies (CEAB-CSIC) concludes, “Those species which are more vulnerable to fishing need longer protection in order to recover totally. If protection is not ensured”, he adds, “populations will be destroyed in a matter of days. The comparison between protected and exploited populations gives us an idea of how much are these species exhausted in areas open to fishing”. The research, published on PLOS ONE, was funded by the Government of Catalonia and supported by the Montgrí, Medes Islands and Baix Ter Natural Park.

The scientific community shares worries about making marine reserves more successful around the world. Thirty years ago, UB set up these studies in the Medes Islands, a unique reserve in Mediterranean marine ecosystems because of its landscape and biodiversity richness. In Medes Islands’s scenario, Hereu and Garcia state that “in order to improve environmental policies, it is necessary to promote a surveillance system to control furtive fishing, foster new studies focused on species biology (reproduction aggregations of gilthead seabream, relationship between different habitats, etc.), and develop more strategies to protect biodiversity”. Scientists propose that, without protection, the destruction of some fish populations will be only a matter of time.

Image: The study warns that the total recovery of fish populations in the Mediterranean coast lasts for decades (Copyright: Josep Clotas and Marta Cunillera).

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