The triple threat of overfishing, pollution and climate change has been cited as the reasons behind the decline in pilchard, anchovy and hake fish stocks that make up the European fisheries sector.
Along with a reduction in important fish species (34%) the report also identified a reduction in top predator numbers (41%), as well as increases of the organisms at the bottom of the food web (23%).
“Since climate change and fishing pressure are expected to intensify in the Mediterranean Sea, there is a serious risk that these may push the system beyond the ‘point of no-return,’” the report stated.
In the report that appears in Nature's Scientific Reports, researchers from the Joint Research Centre (JRC), the European Commission's science and knowledge service, highlight the impact environmental drivers and fishing efforts have had on the Mediterranean Sea’s food web.
The largest reductions were found in the Western Mediterranean Sea and the Adriatic Sea (-50%), while the reduction was much less in the Ionian Sea (-8%).
Food web modelling
Using a food web modelling approach, the team from were able to evaluate progressive responses of species numbers and ecosystem dynamics to changes in primary productivity (PP) and fisheries.
Results indicated that both changes in PP and fishing pressure played an important role in driving species dynamics.
However, PP was the strongest driver upon the Mediterranean Sea ecosystem. According to the team, this highlighted the importance of a bottom-up processes in controlling the biological characteristics of the region.
"These characteristics render the Mediterranean Sea highly vulnerable to impacts such as climate change, marine litter and invading alien species, and it is very easy to overfish the existing stocks,” warned Jann Martinsohn, leader of the fisheries research group at the JRC.
“When fish stocks are fished intensively, they do not have the time to reproduce to keep up the population levels.”
The decline in fish stocks is an issue that scientists and fisheries experts have been monitoring over many years.
An analysis carried out by the Scientific Technical Economic Committee for Fisheries (STECF), the European Commission's scientific advisory body in collaboration with the JRC, found that 93% of the assessed fish stocks in the Mediterranean Sea were currently over-exploited.
These findings hold true despite the lack of data for many fish stocks. A significant number of catches are still not legally recorded or the catches are from data-deficient stocks.
MedFish4Ever program
Last year, the European Commission responded by launching the MedFish4Ever initiative to rebuild the fisheries sector.
The initiative included securing strong political leadership to rebuild a sustainable fisheries sector, and ensuring the strong commitment of all stakeholders to contribute to its long-term sustainability.
The results of the assessments are documented in 36 JRC Science for Policy reports in which the JRC have been collecting, compiling and assessing information on fisheries in the Mediterranean and Black Seas since 2007.
Source: Nature Scientific Reports
Published online ahead of print: doi:10.1038/srep44491
“Historical changes of the Mediterranean Sea ecosystem: modelling the role and impact of primary productivity and fisheries changes over time.”
Authors: Chiara Piroddi, Marta Coll, Camino Liquete, Diego Macias, Krista Greer, Joe Buszowski, Jeroen Steenbeek, Roberto Danovaro & Villy Christensen