Adriatic Sea (North Central) - Exploitation

Small pelagic fish, mainly sardine and anchovy, constitute the principal component of the catches from the north-central Adriatic Sea and are mainly caught by purse seiners and mid water trawlers (Arneri 1996, Mannini and Massa 2000). The demersal fishery mainly comprises juveniles of several target species, e.g. hake and red mullet, principally caught by the bottom trawling and the beam trawling fleets. Invertebrates (cephalopods, crabs and scallops) also constitute an important proportion of the catch.

Important changes in landings have been recorded in the north-central Adriatic from mid 1970s till the present, with a dramatic increase in catches from the mid 1970s to the mid 1980s, mainly due to the increase of small pelagic fish in the catch (Coll et al. 2007, 2009, 2010). This was followed by marked fluctuations in landings until catches progressively declined from late 1980s to the present, primarily because of the decrease in small pelagic fish, especially of anchovy and sardine (Cingolani et al. 1996, Azzali et al. 2002, Santojanni et al. 2003, 2005). Total official landings from 2000 were lower than those attained in the late 1970s. Existing data show a significant decrease in fish landings with time, coupled with a non significant increase in invertebrate landings.

In fact, ecological modelling highlighted that fishing activities inflicted notable impacts on the ecosystem during the 1990s, with a high consumption of fishable production and high exploitation rates for various target and non target species. Moreover, the analysis of ecological indicators highlighted that the ecosystem was in a low-medium developmental stage (Coll et al. 2007). A supplementary ecosystem model representing the 1970s suggested that, in fact, the north-central Adriatic Sea was already highly impacted by the fisheries in the late 1970s. Important changes in the biomass of various species have been described from the 1970s to 2000s by matching data from catch records and results from temporal dynamic modelling simulating the fishing effort dynamics in the area (Coll et al. 2009). Importantly, dynamic simulations suggested that large decreases in demersal and pelagic target fish species were produced during these three decades, in parallel with an increase in demersal invertebrates (e.g. crabs and shrimps) and pelagic organisms (e.g. jellyfishes). Predictions from the model adequately matched observed biomass and catch data for each year. Observed trends and predicted data for biomasses decreased with time for several species, including Norway lobster, hake, red mullets, flatfish, and anchovy. The environmental functions resulting from the fitting procedure predicted that primary production and nutrients increased beyond the baseline from 1975 level, and then showed a decrease. They were negatively correlated with mean sea surface temperature and positively correlated with the Mediterranean Oscillation Index. Results suggested that the NC Adriatic ecosystem became more degraded over time due to expanding fishing effort, bottom-up effects, and climatic anomalies.

In another study, data from catch statistics, scientific surveys and results from ecosystem models was analyzed to assess main changes in marine resources of the North-Central Adriatic Sea (Central Mediterranean) from the mid 1970s to the early 2000s (Coll et al. 2010). Results illustrated a general decrease in the biomass and catch of target species with time, with a first phase of increasing catch and biomass of some organisms from the 1970s to the 1980s, a ‘fishing down the food web’ process during the 1980s, and a clear trend towards biomass and catch reductions during the late 1990s and early 2000s. These changes occurred in parallel with an increase in fishing effort and human development in the basin and changes in environmental factors such as an increase in the average annual sea water temperature, a decrease in the inflow of highly saline Mediterranean water into the Adriatic Sea, and changes in the atmospheric pressure at sea level. A high and significant correlation between ecological indicators and abiotic factors (in particular with human factors: fishing effort and the human development index) was found. In fact, historical data highlights important ecosystem changes of the north-central Adriatic Sea far back in the past (Fortibuoni et al. 2010; Lotze et al. 2011).

Currently, fishing has a notable impact on benthic habitats (Pranovi et al. 2000, 2001, 2003, Morello et al. 2006); various target demersal species are reported as overexploited while scientific concern is raised about the status of small pelagic fish (Papaconstantinou and Farrugio 2000, Jukic-Peladic et al. 2001, Vrgoc et al. 2004, Bombace and Grati 2007) and important amounts of discards are produced (Wieczorek et al. 1999, Pranovi et al. 2000, 2001, Tudela 2004). The application of a new index of ecosystem effects of fishing (Tudela et al. 2005, Libralato et al. 2008) suggests high probabilities of ecosystem overfishing for the north-central Adriatic Sea. Recent analysis of biodiversity patterns and threats in the Mediterranean Sea identified the Adriatic Sea as an important area hosting a high degree of marine biodiversity but also highly threatened by numerous human activities (Coll et al. 2010b, Coll et al. 2011). Moreover, marine protected areas in the region hardly cover any of this biodiversity (Mouillot et al. 2011).