Spatio-temporal trends in diversity of demersal fish assemblages in the Mediterranean

Abstract

The high species richness, coupled with high proportion of endemism, makes the Mediterranean one of the world’s ‘biodiversity hotspots’. However, the continuous increase in fisheries in the last few decades has led to the overexploitation of their main commercial stocks. Using fishery-independent data collected under the framework of the MEDITS trawl surveys carried out over the last 20 years, we study the demersal fish diversity pattern in the Mediterranean at a large spatial and temporal scale to determine whether it is being affected by the general fishing overexploitation of the demersal resources. The detected diversity trends are compared with the spatio-temporal variation in bottom trawl fishing effort in the Mediterranean. Our results show a stability and even recovery of demersal fish diversity in the Mediterranean together with higher diversity values on the continental shelves of the Balearic Islands, Sardinia, Sicily and the Aegean Sea. At large temporal and spatial scales, the high diversity of demersal assemblages in the Mediterranean is associated with a reduction in bottom trawl fishing effort. The inclusion of species other than target ones through diversity indices is important in the implementation of an ecosystem-based fisheries management.

Spatial Management Units as an Ecosystem-Based Approach for Managing Bottom-Towed Fisheries in the Central Mediterranean Sea

“…Other studies have shown that the spatial patterns of demersal fish diversity associated to the continental shelf and upper/lower slope in the Mediterranean are dependent on differences in the distribution of cumulative threats to marine biodiversity, which are mainly concentrated in coastal areas and on the continental shelf of the Mediterranean (Danovaro et al, 2010;Coll et al, 2012;Farriols et al, 2019). A generally stable, or a slight recovering, trend has been highlighted for some areas of the Mediterranean Sea (see Farriols et al, 2019), which further confirms our findings for SMU1. Moving away from land toward the continental slope, SMU2 is found between 70 and 250 m depth (Figure 9); here the species composition is dominated by the valuable deep-water rose shrimp that shows a persistent spawning ground located on the south-eastern side of the Adventure Bank (Fortibuoni et al, 2010).…”

Πρότυπα Και Τάσεις Των Βενθοπελαγικών Κοινωνιών Στις Ελληνικές Θάλασσες

“…The above findings are opposed to the "fishing down food web" theory, which assumes that intense fishing depletes larger predators and subsequently favors the dominance of low trophic level species (Pauly et al 1998). However, they are in line with previous Mediterranean studies, based on survey data, which indicate that environmental (e.g temperature and salinity) and biological parameters (e.g., productivity) are the main assemblages structuring factors, while trawling pressure plays a minor role (Farriols et al 2019, Merigot et al 2019. Recent studies indicate the important contribution of primary productivity to the determination of marine community structure in the Mediterranean (Pirrodi et al 2017, Merigot et al 2019.…”

“…Furthermore, species diversity remained stable over the study period, suggesting that environmental or anthropogenic pressure, such as climate change, fishery or tourism development, has not dramatically affected community structure during the last decade. Similar findings are reported from studies based on the MEDITS survey data in different Mediterranean areas (Gaertner et al 2013, Granger et al 2015, Keller et al 2016, Merigot et al 2019, Farriols et al 2019, Quetglas et al 2019.…”

“…The MEDITS data have been used for joint publications, which have elucidated several aspects related to abundance and biomass indices of demersal species, their length-/age-frequency distribution (by sex and maturity stages) and life history parameters, the latter especially related to total and fishing mortality (e.g., Abella et al 1999, Colloca et al 2003, Gaertner et al 2007, Granger et al 2015, Druon et al2015, Brind'Amour et al 2016, Keller et al 2016, Merigot et al 2019. Population and community indicators and spatial occupation indices have also been estimated (e.g., Trenkel et al 2007, Farriols et al 2019. All these results have provided information among the various GFCM geographical sub-areas of the Mediterranean for a range of target species and thematic areas.…”

Resilience dynamics and productivity‐driven shifts in the marine communities of the Western Mediterranean Sea

“…Additionally, the impact of fishing has been suggested as a key chronic stressor in the Mediterranean increasing the ecosystems’ sensitivity to productivity changes (Damalas et al., 2021 ; Fu et al., 2018 ). However, a recent decrease in fishing effort and displacement of fishing activity to deeper strata in the Western Mediterranean allowed a relative recovery of highly vulnerable species in the shelf such as elasmobranchs (Ramírez‐Amaro et al., 2020 ) and benefitted regional fish diversity (Farriols et al., 2019 ). This is consistent with our results in Northern Spain and the increase in the relative contribution of some periodic commercial and equilibrium species in recent years, and also with the recent increase in commercial species of short life cycle in the Alboran Sea.…”