The understanding of fish communities' changes over the past centuries has important implications for conservation policy and marine resource management. However, reconstructing these changes is difficult because information on marine communities before the second half of the 20th century is, in most cases, anecdotal and merely qualitative. Therefore, historical qualitative records and modern quantitative data are not directly comparable, and their integration for long-term analyses is not straightforward. We developed a methodology that allows the coding of qualitative information provided by early naturalists into semi-quantitative information through an intercalibration with landing proportions. This approach allowed us to reconstruct and quantitatively analyze a 200-year-long time series of fish community structure indicators in the Northern Adriatic Sea (Mediterranean Sea). Our analysis provides evidence of long-term changes in fish community structure, including the decline of Chondrichthyes, large-sized and late-maturing species. This work highlights the importance of broadening the time-frame through which we look at marine ecosystem changes and provides a methodology to exploit, in a quantitative framework, historical qualitative sources. To the purpose, naturalists' eyewitness accounts proved to be useful for extending the analysis on fish community back in the past, well before the onset of field-based monitoring programs.

In the Mediterranean Sea, structured and standardized monitoring programs of marine resources were set only in the last decades, so the analysis of changes in marine communities over longer time scale has to rely on other sources. In this work, we used seven decades (1945-2014) of disaggregated landings statistics for the Northern Adriatic Sea (Mediterranean) to infer changes in the ecosystem. Analysis of landings composition was enriched with the application of a suite of ecological indicators (e.g., trophodynamic indicators, such as the primary production required to sustain the catches-PPR; size-based indicators, such as the large species indicator-LSI; other indicators, such as the elasmobranchs-bony fish ratio-E/B ratio). Indicators were further compared with main ecosystem drivers, i.e., fishing capacity, nutrient loads and climate change. Species most vulnerable to fishing (i.e., elasmobranchs and large-sized species) dramatically declined at the beginning of the industrialization of fishery that occurred right afterwards World War II, as can be inferred by the negative drop of LSI and E/B ratio in the mid-1950s. However, until the mid-1980s landings and PPR increased due to improvements in fishing activities (e.g., the introduction of more efficient fishing gears) increasing fishing capacity, high productivity of the ecosystem. Overall, the effects of fishing were buffered by an increase in productivity in the period of high nutrient discharge (up to mid-1980s), while significant changes in fish community structure were already occurring. From the mid-1980s, a reduction in nutrient load caused a decline in productivity but the food-web structure was already modified and unable to support, or recover from, such unbalanced situation, resulting in the collapse of landings. This collapse is coherent with alternative stable states hypothesis, typical of complex real systems, that implies drastic interventions that go beyond fisheries management and include regulation of nutrient release for recovery. The work highlights that, despite poor capabilities to track species dynamics, landings and applied indicators might help to shed light on the long-term dynamics of marine communities, thus contributing to place current situation in an historical framework with potential for supporting management.

By-catch is one of the main sources of anthropogenic mortality in marine species of conservation concern worldwide. Between 2006 and 2008, the Consorzio Nazionale Interuniversitario per le Scienze del Mare (CoNISMa) coordinated a monitoring programme of cetacean by-catch in Italian pelagic trawlers, funded in compliance with European Regulation 812/2004. Sixteen independent observers monitored a total of 3141 hauls. The observation coverage ranged between 0.9 and 6.3% of the regional fishing effort. Almost all by-catch events were recorded in the northern Adriatic Sea. By-catch rates of bottlenose dolphins (Tursiops truncatus) and loggerhead turtles (Caretta caretta) were 0.0006 and 0.0255 individuals per haul, respectively. Given the low number of observed deaths, reliable estimates of total mortality for these two species were not obtained. The annual number of by-caught turtles was 863 (CV=0.15), with 99% released alive. A ‘hotspot’ for turtle captures was found off Goro (south Venice). The existence of lethal interactions makes it important to understand whether the scale of this mortality is sufficient to pose a threat at population level. Finally, annual by-catch estimates for rays and sharks were 5436 (CV=0.08) and 5414 (CV=0.15), respectively. Thintail threshers (Alopias vulpinus), piked dogfish (Squalus acanthias) and smooth-hounds (Mustelus mustelus), which are both commercial and vulnerable to overfishing, were taken in large numbers

Among the 19 non-native species of marine invertebrates which have invaded the Venice Lagoon and have established populations, Ruditapes philippinarum, deliberately introduced in 1983, is surely the most successful species. According to the hypothesis that alien species invasion could be favoured by an altered ecological, chemical or physical state of the system induced by anthropogenic disturbance, R. philippinarum turned out to be 'the right species at the right moment'. By comparing historical data (1968, 1985, 1990) with 1999 data, changes in macrobenthic community, in particular bivalve molluscs, of the lagoon induced by R. philippinarum introduction and subsequent clam exploiting activity were assessed. It has been possible to describe a sharp reduction, both in terms of distribution area and density, of all other filter feeder bivalves. Moreover, by using the clearance rate of the most abundant bivalve species in 1990 and 1999 (Cerastoderma glaucum and R. philippinarum, respectively), it was possible to estimate that the filtration capacity, expressed as l h )1 m )2 , has more than doubled. This has altered the functioning of the ecosystem, resulting in a stronger benthic-pelagic coupling. In this context, R. philippinarum attains control of the system. Considering all this, it is possible to state that the Venice Lagoon ecosystem has entered into a new state, probably more resistant but less resilient, with implications for future management choices.