Climate change responses of Mediterranean fishes: Fishers' knowledge

Climate change is driving species ranges toward the poles, with substantial consequences on the structure and the functioning of marine communities. These changes are partially documented in the Mediterranean Sea, a... [ view full abstract ]

Climate change is driving species ranges toward the poles, with substantial consequences on the structure and the functioning of marine communities. These changes are partially documented in the Mediterranean Sea, a semi-enclosed and densely populated marine region, which urgently needs social and ecological information to appropriately conceive adaptation and mitigation measures. Here we present the results of a local ecological knowledge (LEK) survey aimed to investigate climate-related responses of Mediterranean fishes, in terms of spatial-temporal changes of abundance and distribution. The study was developed in 79 Mediterranean locations from 11 countries. Using a previously tested semi-structured questionnaire, 726 fishers were interviewed by asking the following main questions: what fish species increased in abundance in the last decades? Can you reconstruct your yearly catches for each of these species? The species whose abundance was perceived in increase (i.e. including new species arrived for the first time) were annotated and then fishers` perceptions on their yearly historical catches were reported in ranks (0-5) building a species-specific time series ranging from 1970 to 2016. Time series were subsequently analysed using breakpoint analysis to highlight years of significant structural changes. Overall, a total of 589 fishers (81%) answered that at least one species increased its abundance in the last decades, for a total of 1325 observations across 79 taxa. Non indigenous species of tropical origin represented 33% of observations (13 taxa in total), whilst indigenous species which already showed signs of northward expansion represented 52% of observations (20 taxa in total). Interestingly, in the North-western Mediterranean areas, perceived increases in abundances are mostly related to indigenous thermophilic taxa, whilst South-western areas are mostly characterized by the increase of non-indigenous species. Breakpoint analyses indicated significant positive breaks (i.e. sharp increases in perceived abundance) in 66% of time series across 48 taxa. Results indicated clear spatial-temporal dynamics of northwards expansion in species such as the bluefish Pomatomus saltatrix and the yellowmouth barracuda Sphyraena viridensis. For example, fishers reported a sharp increase of P. saltatrix in the Northwest of Sardinia around 1998 whilst in the north Adriatic Sea, such increase is reported only eleven years later (2009). A similar pattern emerged for S. viridensis, in fact the increase in its abundance between the Sicily strait and the North Tyrrhenian has been perceived with a delay of 12 years (i.e. from 1995 to 2007, respectively). The coherence and magnitude of these perceived signals provide a clear evidence of large scale responses of the Mediterranean biota, and agree with the expected consequences of climate change. It should be also highlighted that, the local ecological knowledge approach demonstrated to be effective in collecting data across different countries with considerable cultural diversities, demonstrating that LEK surveys can be successfully applied beyond the local scale, consolidating a standard methodology for monitoring current biotic responses to climate change.