HISTORICAL RECONSTRUCTION OF FISHERY CATCHES FOR THE LAKE GARDA

Fishery activities in the Garda lake had historically played a very important role for the people living along the coasts of the lake. In this work we present updated time series of catches, that could be useful to describe the evolution of the fishery, linking landings with the changes of environmental conditions and biological communities reported in the literature. Total catches peaked in the mid ’60s (ca. 700 metric tons) and then smoothly decreased until the ‘90s, when they started oscillating around a total production of about 400 metric tonnes, similarly to the situation observed before the ‘50s. However, catches composition shows more complex dynamics over time, with the disappearance over the years of species very important for the lake ecosystem and for the fishery itself, both in terms of catches or economic value (e.g. the Common bleak Alburnus alborella or the Carpione del Garda Salmo carpio). Even if some of the zooplankivourous species showed strong declines over time, this feeding category has always been very important for the lake fishery, representing at least 50% of the total caught biomass and reaching more than 80% of total catches since 1980. This is due to the large contribution of the Agone Alosa agone, that has been very important in the whole history of the fishery of the lake, and of the European whitefish Coregonus lavaretus, whose contribution changed over the decades, but that is characterized by an increase in the last period, becoming the most important species during the last decade

Influence of Seascape on Coastal Lagoon Fisheries: the Role of Habitat Mosaic in the Venice Lagoon

Fisheries are a staple human activity supported by coastal lagoons. Together with water quality and trophic status, lagoon morphology is acknowledged as one of the main ecological drivers of fishery yields; however, the role of lagoon seascape structure is still poorly understood. This paper investigates how morphological variables, habitat distribution and seascape diversity and complexity affect yields of artisanal fishery performed with fyke nets in the Venice Lagoon (northern Adriatic Sea, Italy). Two spatial scales were considered in the analysis, with water quality parameters (temperature, salinity, dissolved oxygen, turbidity, water residence times, N, P and chlorophyll-a concentrations) being measured at a fine, fyke-net scale and morphological (average bottom elevation and sediment grain size) and habitat features (habitat proportion, diversity and complexity) being measured at a broader, seascape scale. Generalised linear mixed models were employed to model 8 years of nekton and green crab catches, disentangling the role of broad-scale morphology and seascape from that of fine-scale water quality. Broad-scale variables clearly influenced fishery target species. Among them, lagoon residents were associated with specific morphological and habitat characteristics, while marine migrants showed a stronger link with overall habitat diversity and complexity. This evidence emphasises how artisanal fishery in the Venice Lagoon relies on the conservation of morphological and habitat heterogeneity. Moreover, it highlights how habitat restoration performed at the seascape level should also be taken into account, in addition to controlling hydrology and water quality, when managing fishery resources in coastal lagoons

IMPLEMENTATION OF THE HABITAT FISH BIO-INDICATOR IN TWO WATER BODIES OF THE VENICE LAGOON: THE ROLE OF SEASONAL AND ENVIRONMENTAL VARIABILITY IN THE ASSESSMENT OF ECOLOGICAL STATUS OF FISH FAUNA

Under the Water Framework Directive (WFD; Dir. 2000/60/EC), fish are one of the Biological Quality Elements that need to be taken into account when evaluating the Ecological Status of transitional water bodies. The Habitat Fish Bio-Indicator (HFBI), a multi-metric index composed of six descriptors based on functional traits of fish assemblages, was recently developed to assess Italian transitional waters. In this study, HFBI was applied, following the national application protocol, to two water bodies in the Venice lagoon featuring different water and sediment physco-chemical properties and habitat distribution. The analysis highlighted that, in addition to seasonality, environmental variability along confinement gradients and presence and extent of seagrass meadows strongly influence the six metrics, the HFBI score and the subsequent assessment outcome. The selection of number and location of sampling sites must then be based on environmental characteristic and variability found within each water body, and is therefore a crucial step in the evaluation of Ecological Status in transitional water ecosystems

Fish Response to Multiple Anthropogenic Stressors in Mediterranean Coastal Lagoons: A Comparative Study of the Role of Different Management Strategies

Transitional waters are among the most productive ecosystems of the world and their biotic communities show high diversity and complex mechanisms of self-regulation that provide valuable ecosystem services and societal goods and benefits. In this work a comparison of the fish assemblages of three non-tidal Mediterranean coastal lagoons is carried out in order to evaluate the impacts of alternative management strategies. The anthropogenic pressures acting on the lagoons were quantified by means of categorical indicators, while the characteristics of the fish assemblages were summarized in multi-metric indices (MMIs). Two MMIs were developed using data collected with a beach seine net and with fyke nets, following an empirical approach that selects, from a pool of 73 metrics, the combination that maximizes the MMI/pressure relationship. The two MMIs include four metrics each, most of which are based on feeding mode functional guilds and habitat use functional guilds, and they are sensitive to anthropogenic pressures. The human activities directly or indirectly affecting water quality are the ones that most influence the fish assemblage, while the presence of artisanal fisheries, a typical and relevant resource use in these lagoons, seems to play a beneficial role. Lagoon fisheries management relies on the maintenance of infrastructures that guarantee the hydraulic functioning of the lagoon, thus ensuring exchanges with the adjacent coastal sea, and therefore indirectly contributing to the habitat quality

FISH FAUNA IN THE VENICE LAGOON: UPDATING THE SPECIES LIST AND REVIEWING THE FUNCTIONAL CLASSIFICATION

This work aims at reviewing the existing ecological classification of fish fauna in the Venice lagoon, and updating the list of species found during 15+ years of research in this ecosystem. The checklist encompass all fish life stages including ichthyoplankton, and contains 94 taxa, with 14 recorded only after 2010. The new functional classification, made of eight guilds including two guilds of lagoon residents and two of marine migrants, highlights the differences in species’ use of lagoon habitats in different seasons

DISTRIBUTION OF THE ALIEN SPECIES PALAEMON MACRODACTYLUS RATHBUN, 1902 IN THE VENICE LAGOON

Palaemon macrodactylus Rathbun (1902) is an estuarine shrimp native to north-western Pacific which, due to its wide environmental tolerance to chemical-physical conditions and its long breeding period, from 1957, probably carried by ship ballast water, massively colonized estuarine ecosystems worldwide. After its first record, in 2012, P. macrodactylus appears to have rapidly colonized the entire Venice lagoon, showing higher abundance in the confined saltmarsh stations of the northern sub-basin, probably due to the relatively low salinities values of this area. Records collected from 2014 to 2020 confirm the long reproductive period, comprised between Spring (mid-April) and Autumn (October), and the potential large invasion capacity of this species, which in the future could provoke competition with autochthonous species of the genus Palaemon and Crangon crangon

APPLICATION OF THE HABITAT FISH BIOLOGICAL INDEX (HFBI) FOR THE ASSESSMENT OF THE ECOLOGICAL STATUS OF PO DELTA LAGOONS (ITALY)

Fish fauna is one of the biological quality elements useful for assessing the ecological status of European transitional water bodies, for the purposes of applying the Water Framework Directive. For the assessment of the ecological status of Italian transitional aquatic ecosystems, the multimetric index “Habitat Fish Bio-Indicator” (HFBI), based on fish fauna, was developed and validated at national level. This paper reports the results of a study on the shallow-water fish fauna of 5 lagoon environments of the Po Delta (Northern Adriatic, Italy) which aimed to evaluate the ecological status of these water bodies by calculating the HFBI. The results made it possible to describe the taxonomic composition and the functional and trophic structures of the fish community characteristic of these delta lagoons. The shallow water fish assemblage was characterized by the presence of juvenile stages of marine migrating species (i.e., grey mullets of the genus Chelon, the sea bream Sparus aurata and the sea bass Dicentrarchus labrax) and by species of estuarine residents (i.e., small gobies Knipowitschia panizzae, Pomatoschistus marmoratus, and P. canestrinii, the silverside Atherina boyeri and the killfish Aphanius fasciatus). The guilds of hyperbentivores/zooplanktivores, microbentivores and detritivores were the most represented in the fish assemblage of the of investigated lagoons. The HFBI index, applied on an annual basis, made it possible to highlight marked differences in the ecological status of the Po Delta lagoons. Only Caleri lagoon resulted in a good state, Marinetta and Canarin lagoons in a moderate state, while Barbamarco and Scardovari lagoons resulted in a poor ecological state. Eutrophication, resulting from the large inputs of nutrients with freshwater from the Po River branches, and the modification of lagoon morphologies, a consequence of anthropogenic activities, are the main pressure factors that determine the ecological status of these transitional water bodies

Using fish assemblage to identify success criteria for seagrass habitat restoration

A fish-based multimetric index was applied to assess the ecological status of fish fauna in both natural and newly restored seagrass meadows in the Venice lagoon (northern Adriatic Sea, Italy), using natural habitats as reference sites. Fish assemblages were then compared, and community attributes of recreated and natural habitats were evaluated. Ecological status resulted higher in natural meadows, and a multivariate analysis showed that an increase in the relative proportion of seagrass specialists at restored sites could represent an indicator of success of seagrass restoration

Expected Shifts in Nekton Community Following Salinity Reduction: Insights into Restoration and Management of Transitional Water Habitats

Abstract: A restoration project is planned to take place in the northern Venice lagoon (northern Adriatic Sea, Italy), aiming at introducing freshwater into a confined shallow water lagoon area and recreating transitional water habitats. This work describes the shifts in the nekton (fish and decapods) community structure to be expected following the future salinity decrease in the restoration area. Nekton was sampled at a series of natural shallow water sites located along salinity gradients in the Venice lagoon. A multivariate GLM approach was followed in order to predict species biomass under the salinity and environmental conditions expected after restoration. Biomass of commercially important species, as well as species of conservation interest, is predicted to increase following salinity reduction and habitat changes. From a functional perspective, an increase in biomass of hyperbenthivores-zooplanctivores, hyperbenthivores-piscivores and detritivores is also expected. This study emphasises the ecacy of a predictive approach for both ecological restoration and ecosystem management in transitional waters. By providing scenarios of community structure, the outcomes of this work could be employed in future evaluations of restoration success in the Venice lagoon, as well as to develop management tools to forecast the eects of alterations of salinity regimes in coastal lagoons due to climate change