Annual bottom trawling hours and hotspots in the Mediterranean for 2019

An enhanced  version of the R4AIS workflow (Galdelli et al., 2021) was used to process T-AIS data, with a poll frequency of 5 min, of fishing vessels operating in the Mediterranean Sea in 2019. Data of vessels categorized as bottom trawlers were aggregated to obtain yearly fishing hours at 0.1° and 0.5° resolution. Besides information of the number of vessels involved in the fishing activity and their nationality were retrived.

Besides, statistically significant trawling hotspots of fishing activities in the Mediterranean were identified by the application of the Getis-Ord Gi statistic (Getis and Ord 2010) though the statistical software R using the globalG.test function (spdep package). The function computes a global test for spatial autocorrelation using a Monte Carlo simulation approach. It tests the null hypothesis of no autocorrelation against the alternative hypothesis of positive spatial autocorrelation. Then the local spatial autocorrelation was tested calculating the Gi statistic, using the local_g_perm function (dfdep package), which indicates the strength of the clustering.

Categorization of hotspots was performed, according to the Gi value and the p-value of a folded permutation test obtained for each grid cell, as follows:

Gi>0 and p_value <=0.01 as Very hot

Gi>0 and p_value <=0.05 as Hot

Gi>0 and p_value <=0.1 as Somewhat hot

Gi<0 and p_value <=0.1 as Somewhat cold

Gi<0 and p_value <=0.05 as Cold

Gi<0 and p_value <=0.01 à Very cold

Grid cells with a p-value > 0.1 were categorized as Insignificant.

The present dataset includes layers of the annual bottom trawling activity and their hotspot in the Mediterranean (.shp; .csv) at both resolutions (0.1°; 0.5°)