**4. Results**

### *4.1. Data from FAO Official Statistics*

During the period 1994–2019, the bulk of the deep-water catches in the Mediterranean Sea was due to the species *M. merluccius*, *P. longirostris*, *A. foliacea*, *A. antennatus*, *N. norvegicus*, *Lophius* spp., *G. melastomus*, *C. conger*, *H. dactylopterus*, *P. bogaraveo*, *Phycis blennoides*, and *P. americanus*. The average total landing for the whole basin was 57,774 (±1857) tonnes per year (7% on average of the Mediterranean total landing; 788,000 tonnes). In the Ionian Sea (FAO subdivision 37.2.2), the average total landing of deep-water species was equal to 23,153 (±1859) tonnes (40% on average of the total landing of Mediterranean deep-water species) (Table 1), thus being the most important area for the exploitation of deep-water resources (Figure 1). A marked fluctuation in landings of the deep-water resources over time has been detected both in the whole Mediterranean and in the Ionian Sea, without any significant trends (Figure 3).


**Table 1.** Total landing (in tonnes and %), with mean and standard error (SE), in the Mediterranean (MED) and Ionian Sea (ION), and by species, in the period 1994–2019. *ρ* = Spearman's rank correlation coefficient; *p* = *p*-value; n.s.: non-significant values.

**Figure 3.** Landings (in tonnes) of deep-sea commercial species in the Mediterranean Sea (black line) and the Ionian Sea (dashed line) in the period 1994–2019, based on official FAO statistics.

The main harvested species in the Ionian Sea are the European hake (9865 ± 1445 tonnes and 43% on average), the deep-water rose shrimp (7597 ± 521 tonnes, 33%), the deepwater red shrimps (*A. foliacea* and *A. antennatus*, 1921 ± 177 tonnes, 8%), the Norway lobster (1673 ± 117 tonnes, 7%), and anglers (*Lophius* spp., 1330 ± 207 tonnes, 6%). For *M. merluccius*, *N. norvegicus*, and *Lophius* spp. significant negative temporal trends have been detected (*p* < 0.001, *p* < 0.01, and *p* < 0.05, respectively). In contrast, the landings of the shrimp *P. longirostris* and deep-water red shrimps showed significant positive trends (*p* < 0.05) (Table 1, Figure 4a,b). For the European conger, a clear landing decrease was shown from 2006 (991 tonnes) to 2019 (172 tonnes) (Figure 4c). The exploitation of other deep-water commercial species has increased in this period, as is the case of the blackmouth catshark, with an increase in the landings from a minimum of 193 tonnes in 2009 to a maximum of 1465 tonnes in 2018 (*p* < 0.001). Similarly, *H. dactylopterus* showed a landing increase in the last five years of the time series (*ρ* = 0.584; *p* < 0.01), as did *P. bogaraveo* (*ρ* = 0.681; *p* < 0.001) and *P. blennoides* (*ρ* = 0.542; *p* < 0.01) (Table 1, Figure 4c,d).

**Figure 4.** Landings (in tonnes) by deep-sea commercial species—(**a**) *M. merluccius* and *P. longirostris*; (**b**) *A. foliacea*, *A. antennatus*, *N. norvegicus*, and *Lophius* spp.; (**c**) *C. conger*, *G. melastomus*, and *H. dactylopterus*; (**d**) *P. bogaraveo*, *P. blennoides*, and *P. americanus*—caught in the Ionian Sea (FAO subdivisions 37.2.2) during the period 1994–2019.

In the Ionian Sea, the Italian fleet shows the highest exploitation of the deep-water resources, with an average landing value of 19,504 tonnes per year in the period 1994–2019, equal to an average of 84% of the total landing from this basin, followed by Tunisia (1418 tonnes; 6%), Albania (1109 tonnes; 5%), and Greece (1062 tonnes; 5%). Marked

fluctuations have been observed in the Italian annual landing, with a non-significant decrease, while significant increases have been observed in landings in Tunisia and Albania (*p* < 0.001). A stable trend of landing was shown for Greece (Table 2, Figure 5).

**Table 2.** Total landing (in tonnes and %), with mean and standard error (SE), by Ionian countries in the period 1994–2019. *ρ* = Spearman's rank correlation coefficient; *p* = *p*-value; n.s.: non-significant *p*-values.


**Figure 5.** Landings by country ((**a**) Italy; (**b**) Albania, Tunisia and Greece) in the Ionian Sea (FAO subdivisions 37.2.2).

### *4.2. Data from MEDITS Trawl Surveys (NorthWestern Ionian Sea, GSA 19)*

The European hake and the deep-water rose shrimp are the most abundant species in weight and number, respectively. Highly significant increases in abundance in weight and number over time were detected for the deep-water rose shrimp (*P. longirostris*) (*p* < 0.001, *ρ* = 0.737 and 0.804, respectively), the giant red shrimp (*A. foliacea*) (*p* < 0.001, *ρ* = 0.692 and 0.599, respectively), and the blackspot seabream (*P. bogaraveo*) (*p* < 0.01, *ρ* = 0.538 and *p* < 0.001, 0.634, respectively). A highly significant negative trend for abundance in both weight and number was detected for *N. norvegicus* (*p* < 0.001, *ρ* = −0.766 and −0.785 respectively). A biomass decrease was only shown for *A. antennatus* (*p* < 0.05, *ρ* = −0.391). Fluctuating abundances with no significant trends were observed for the European hake, greater forkbeard, anglers, and blackmouth catshark over the study period (Table 3, Figure 6a,b).

**Figure 6.** *Cont*.

**Figure 6.** (**a**) Time series of biomass (kg/km2) index by species sampled during experimental trawl surveys carried out in the northwestern Ionian Sea from 1994 to 2020. (**b**) Time series of abundance (N/km2) index by species sampled during experimental trawl surveys carried out in the nortwestern Ionian Sea from 1994 to 2020.

**Table 3.** Mean values of biomass (kg/km2) and density (N/km2) indices with standard deviation (s.d.), computed by species on the 1994–2020 time series of experimental trawl surveys carried out in the northwestern Ionian Sea. *ρ* = Spearman's rank correlation coefficient; *p* = *p*-value; n.s.: non-significant *p*-value.


A significant positive relationship was shown between the abundance and SBT in *A. foliacea* (*p* < 0.01, *ρ* = 0.580) and *P. longirostris* (*p* < 0.05, *ρ* = 0.464), while there was a significant negative relationship for *N. norvegicus* (*p* < 0.01, *ρ* = −0.642).

Furthermore, a significant increase in abundance in weight (kg/km2) in relation to the decreasing FE was observed for *A. foliacea* and *P. longirostris* (*p* < 0.001, *ρ* = −0.736 and −0.746 respectively), as well as for *P. bogaraveo* (*p* < 0.005, *ρ* = −0.520).

The estimated regression coefficients β0 and β1 for each model, applied to the logtransformed abundances of *A. foliacea* and *P. longirostris*, are reported in Table 4.

**Table 4.** Effect of fishing effort and temperature covariates on *P. longirostris* and *A. foliacea* abundance indices in biomass (kg/km2) and density (N/km2). Estimate = Estimated coefficient; SE = Standard Error; *t* = *t*-value; *p* = *p*-value.


Results highlight the significant effects of both covariates on the abundances of the two species. In particular, for both species, increased abundances significantly depend on a decrease in FE, while significant positive effects are estimated for abundances in relation to the increase in SBT.

Regardless of the type of tool used and the type of habitat investigated, the relationships between the sizes and depths show the occurrence of the largest individuals at the

greatest depths, with these results being highly significant for all species on soft bottoms, and only for *H. dactylopterus* in VMEs (Figure 7). The sizes were greater in VMEs than on soft bottoms, but this cannot be properly compared due to the different sampling methods and tools (Figure 8).

**Figure 7.** Relationships of total length (TL) with depth of deep-sea species collected on soft bottoms (**left**) and in vulnerable marine ecosystems (VMEs) (**right**) of the central Mediterranean.

For all of the deep-sea species considered, the abundances in weight and number for an area near the SML CWC province were greater than those for the area far from this coral province (Figure 9). However, the differences were significant for the abundance in both weight and number of *A. foliacea*, *H. dactylopterus*, and *P. bogaraveo*. The differences between the two areas were significant for the abundance in number of *P. blennoides* and for the abundance in weight of *M. merluccius* (Figure 9). All of these differences are even more significant due to the fact that the fishing effort is significantly greater near the SML CWC province than in the area far from this province in terms of both the number (*p* < 0.001) and the GT of vessels (*p* < 0.05) (Figure 10).

**Figure 9.** Boxplots of biomass (kg/km2) and abundance (N/km2) by species collected in two areas of the northwestern Ionian Sea, near and far from the SML fishery restricted area, from 1994 to 2020.

**Figure 10.** Boxplots of the fishing effort in terms of number (N) (**a**) and gross tonnage (GT) (**b**) of trawl vessels operating near to and far from the SML CWC province during the period 1994–2020.
