Alessandro Mannini

Large-Scale Diversity of Slope Fishes: Pattern Inconsistency between Multiple Diversity Indices

Large-scale studies focused on the diversity of continental slope ecosystems are still rare, usually restricted to a limited number of diversity indices and mainly based on the empirical comparison of heterogeneous local data sets. In contrast, we investigate large-scale fish diversity on the basis of multiple diversity indices and using 1454 standardized trawl hauls collected throughout the upper and middle slope of the whole northern Mediterranean Sea (36°3′- 45°7′ N; 5°3′W - 28°E). We have analyzed (1) the empirical relationships between a set of 11 diversity indices in order to assess their degree of complementarity/redundancy and (2) the consistency of spatial patterns exhibited by each of the complementary groups of indices. Regarding species richness, our results contrasted both the traditional view based on the hump-shaped theory for bathymetric pattern and the commonly-admitted hypothesis of a large-scale decreasing trend correlated with a similar gradient of primary production in the Mediterranean Sea. More generally, we found that the components of slope fish diversity we analyzed did not always show a consistent pattern of distribution according either to depth or to spatial areas, suggesting that they are not driven by the same factors. These results, which stress the need to extend the number of indices traditionally considered in diversity monitoring networks, could provide a basis for rethinking not only the methodological approach used in monitoring systems, but also the definition of priority zones for protection. Finally, our results call into question the feasibility of properly investigating large-scale diversity patterns using a widespread approach in ecology, which is based on the compilation of pre-existing heterogeneous and disparate data sets, in particular when focusing on indices that are very sensitive to sampling design standardization, such as species richness.

A medium-term, stochastic forecast model to support sustainable, mixed fisheries management in the Mediterranean Sea

A medium-term (10 year) stochastic forecast model is developed and presented for mixed fisheries that can provide estimations of age-specific parameters for a maximum of 10 stocks and 10 fisheries. Designed to support fishery managers dealing with complex, multi-annual management plans, the model can be used to quantitatively test the consequences of various stock-specific and fishery-specific decisions, using non-equilibrium stock dynamics. Such decisions include fishing restrictions and other strategies aimed at achieving sustainable mixed fisheries consistent with the concept of maximum sustainable yield (MSY). In order to test the model, recently gathered data on seven stocks and four fisheries operating in the Ligurian and North Tyrrhenian Seas are used to generate quantitative, 10 year predictions of biomass and catch trends under four different management scenarios. The results show that using the fishing mortality at MSY as the biological reference point for the management of all stocks would be a strong incentive to reduce the technical interactions among concurrent fishing strategies. This would optimize the stock-specific exploitation and be consistent with sustainability criteria.

Effects of environmental and anthropogenic drivers on the spatial distribution of deep-sea shrimps in the Ligurian and Tyrrhenian Seas (NW Mediterranean)

In the Mediterranean Sea, Aristaeomorpha foliacea and Aristeus antennatus are the most important target species of deep-sea trawl fisheries. Previous studies performed in several areas of the Mediterranean highlighted the key role played by both environmental factors, such as temperature, and anthropogenic activities, such as fishing, in affecting the abundance and distribution of the two species. The present study is aimed at investigating the effects of environmental and anthropogenic drivers on the abundance and spatial distribution of A. foliacea and A. antennatus in the Ligurian and northern and central Tyrrhenian Seas (NW Mediterranean). To this end, the time series of MEDITS trawl survey data (1994–2015) were analyzed together with environmental variables, namely sea surface temperature, current speed, and fishing effort by means of GAM. The results show that fishing plays an important role in shaping the spatial distribution of the two species. A. antennatus is prevalent where fishing effort is higher; this can be related to the higher resilience of blue and red shrimp to fishery impact. In contrast, high temperatures are associated to the prevalence of A. foliacea. Therefore, the abundance and spatial distribution of this species is mainly driven by temperature.