A study by COB and UIB indicates that Mediterranean ecosystems are more sensitive to climate variability than thought so far

The researchers found that the combined effects of fishing and climate synergistically affect populations of several species

 A study conducted by scientists from the Balearic Oceanographic Centre (COB) of the Spanish Institute of Oceanography (IEO), in collaboration with researchers at the University of the Balearic Islands and the National Research Council has demonstrated the existence of synchronous responses in populations of several species in the Mediterranean as a result of the combined effects of fisheries and climate variability.The study was published recently in the journal ‘ICES Journal of Marine Science’ and analyzes the evolution of the marketed catch of the main species of the Balearic Islands between 1965 and 2008: three cephalopods (octopus, cuttlefish and squid), two bony fish (surmullet and hake), and two elasmobranch fish (catshark and skate).

 The fishing effort in the study area increased abruptly between 1965 and the late seventies as a result of the increased number of boats trolling. During the eighties, this increase put these species into a situation of overfishing, a change that altered the resilience and capacity of these communities to address possible adverse external factors, and increased their sensitivity to the effects of climate. Catches increased exponentially during the initial phase, before reaching overfishing, and then, since the eighties, they clearly show an oscillating behavior.

 To determine the origin of oscillations observed in catches, the researchers analyzed several different climate indices at various spatial scales. The results show that the local indices associated to the western Mediterranean and mesoscale indices associated to the North Atlantic affect the species that inhabit deeper waters (hake and elasmobranchii), while the global El Niño index affects those living at lesser depth (octopus, cuttlefish, squid and surmullet). El Niño is a weather phenomenon associated with ocean-atmosphere interactions taking place in the South Pacific, although its effects can be seen across the globe. In fact, its effects on terrestrial ecosystems in the Mediterranean have been documented in numerous studies. But so far their influence had not been recorded on marine ecosystems in the Mediterranean.

 The results of the study have led to two important conclusions. First, the combined effects of fishing and climate affects not only fished marine species, but also other species that share the same habitat and which are indirectly exploited. This results in synchronous responses at the community level, a phenomenon that has been observed in other oceans and, in the case of fisheries, can cause, as a lesser evil, variability and unpredictability of the catches. Second, it shows that the Mediterranean marine ecosystems are more sensitive to global climatic variability than thought so far.

 The study was done in the framework of the PROGECIB 48A project, financed by the Department of Universities, Research and Knowledge Transfer of the Regional Ministry of Education, Culture and Universities, Government of the Balearic Islands.

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