DataSheet_1_Impacts on biodiversity from codend and fisher selection in bottom trawl fishing.pdf

Fisheries have important impacts on marine biodiversity. In this work, combined information on the abundance, species richness, diversity indices, species composition, trophic level and vulnerability index were examined for the first-time to detect differences in five units related to trawl fishing: the fish assemblage entering the trawl codend, and the escaping, retained, discarded and landed fractions, derived by the gear and fisher selection practices. The work was based on a case study conducted in the Mediterranean Sea, using three different meshes in the trawl codend (40mm-40D and 50mm-50D diamond meshes, and 40 mm-40S square meshes) and a cover of the codends with small mesh size. In general, trawl fishing produces an escaping fraction that was always lower in abundance, richness, and vulnerability index, similar in diversity indices and trophic level, and different in species composition compared to the fish assemblage entering the codend. In almost all cases, fishers selected as landings a fraction that was the lowest in diversity indices, and the highest in trophic level. In contrast, fishers discarded a fraction that was the highest in diversity and vulnerability index, and the lowest in trophic level. Although the three codends did not differ significantly in the fraction of escapees in terms of diversity indices, trophic level, and vulnerability index, the 40S codend showed a significantly higher percentage in the escaping number of species and individuals, and less differences in the species composition; in addition, lower percentage in abundance of discards and higher of landings in the retained catch (0.6:1) than did the other two codends (0.9:1). It was suggested that an urgent modification of the trawl for the elimination of the discarded highly vulnerable species (e.g. Elasmobranchs) is needed, and that trawl species-selectivity should be improved by allowing escape or avoiding catch of the discarded fraction to minimize biodiversity losses.</p

Temporal patterns of the Shannon diversity H’ at six different Mediterranean bioregions using the MEDITS sampling carried out during 1994–2012.

<p>Temporal patterns of the Shannon diversity H’ at six different Mediterranean bioregions using the MEDITS sampling carried out during 1994–2012.</p

GAM outputs for partial effects for factor “year” (mean ± S.E.) on Shannon diversity (A) and species richness (B) of Mediterranean cephalopods collected during MEDITS sampling (2003–2008).

<p>GAM outputs for partial effects for factor “year” (mean ± S.E.) on Shannon diversity (A) and species richness (B) of Mediterranean cephalopods collected during MEDITS sampling (2003–2008).</p

Shannon diversity (A) and Species richness (B) per haul from MEDITS sampling (1994–2012), calculated for the following bioregions: Iberian-Lions (IL), Tyrrhenian Sea (TY), Strait of Sicily (SS), Adriatic Sea (AD), Ionian Sea (IO) and Southern Aegean Sea (AG).

<p>Shannon diversity (A) and Species richness (B) per haul from MEDITS sampling (1994–2012), calculated for the following bioregions: Iberian-Lions (IL), Tyrrhenian Sea (TY), Strait of Sicily (SS), Adriatic Sea (AD), Ionian Sea (IO) and Southern Aegean Sea (AG).</p

Boxplot of total species richness (S_rar) at different Mediterranean bioregions: Iberian-Lions (IL), Tyrrhenian Sea (TY), Strait of Sicily (SS), Adriatic Sea (AD), Ionian Sea (IO) and Aegean Sea (AG).

<p>Samples were included from 1994–2012 and rarefied to 35 hauls.</p

Boxplots of Shannon diversity (A) and Species richness (B) per haul, obtained using all MEDITS samples taken during 1994–2012.

<p>Boxplots of Shannon diversity (A) and Species richness (B) per haul, obtained using all MEDITS samples taken during 1994–2012.</p

Species accumulation curves of MEDITS sampling at different Mediterranean bioregions.

<p>Species accumulation curves of MEDITS sampling at different Mediterranean bioregions.</p

Map of the Mediterranean Sea showing the MEDITS stations sampled during 1994–2012.

<p>Plotted are 20463 hauls and colours correspond to the following bioregions: 1) Iberian-Lions, 2) Tyrrhenian Sea, 3) Adriatic Sea, 4) Ionian Sea, 5) Aegean Sea and 6) Strait of Sicily. Separation of bioregions is marked with thick black lines.</p

Temporal patterns of the Shannon diversity H’ at six different Mediterranean bioregions using the MEDITS sampling carried out during 1994–2012.

<p>Temporal patterns of the Shannon diversity H’ at six different Mediterranean bioregions using the MEDITS sampling carried out during 1994–2012.</p

GAM outputs of partial effects for 1) depth at the six bioregions investigated (A-F), 2) chlorophyll concentration (Chla; G) and 3) surface sea temperature (SST; H) on Mediterranean cephalopod diversity H’.

<p>Solid lines indicate the fitted partial effects and broken lines the 95% confidence intervals (CI).</p