6.6 Interactions among aquaculture, capture fisheries and the environment in coastal lagoon management

Interactions among aquaculture, capture fisheries and the environment in coastal lagoon management in Italy are quite strong, given the number and extent of these ecosystems along the Italian coastline. Interactions are sometimes on a conflict basis, but often result in positive interactions that allow to enhance the interactions. The most conflicting interactions are those that result in heavy environmental effects.

6.6.1 Interactions between commercial and recreational fisheries

In many coastal lagoons, no relevant interactions are reported to be present between commercial fishing and sport fishing, the latter representing a negligible activity. For example, in the Orbetello lagoon, recreational fishing does not bear any disturbance to commercial fishing for the low number of fixed fishing locations (around 42). Sport fishing in the lagoon is practiced from April to October in the 42 stations, allowed for three days a week (Friday, Saturday, Sunday), from 8 am to 6 pm. Only fishing rods are allowed. The fishing pressure may be considered for 110 fishers per week (three days) for the seven months of operation. The target species are the seabream, with eels as bycatch.
In the Lesina lagoon, interactions between commercial and recreational fishers (amateur fishers who are retired people) are peculiar, the second group exploiting the lagoon resources on the basis of civic uses without any further regulation. From these assumptions, it is clear that unavoidable frictions between the two teams, exacerbated or resolved often at a personal level, have often arisen.
Recreational fishing in the lagoons of the Veneto region (Venice, Caorle) is allowed on possession of a non-professional fishing licence and is regulated by a Provincial Regulation (Province of Venice, 2008). Besides the use of fishing rods with hooks and lines, the use of certain nets and traps, of the harpoon and the help of a light source (with a maximum power of 400 watts) is also allowed. Amateur fishing in the lagoons is practiced today by a consisting number of fishers. These can be ascribed to three types:

• Sporting fishers, usually equipped with adequate specific equipment for fishing, who focus primarily on catching valuable fish species. They are usually equipped with a fishing licence. The most common illegal catches are probably undersized specimens, fishing in areas that are not allowed and exceeding the maximum quota of fish.
• Fishers who operate similarly to those of commercial fishers, in terms of fishing effort (time allocated, gear, quantities caught). It is very likely that at least some of these fishers are retired professionals.
• Fishers/ gatherers, mainly dedicated to the harvest of bivalve molluscs, and who do not require special investments in equipment. The activity is practiced almost exclusively for direct consumption.
Of the more than 30 000 holders of a licence of B type in the Province of Venice, it is estimated that no fewer than 4 000 are operating in the lagoon or in the neighbouring sea. Many of these anglers catch valuable fish species (seabream, bream, croaker, seabass, etc.) by fishing rods or other fishing lines, operating both in the lagoon and at sea, depending on the tidal cycle. From May to September, many anglers concentrate daily in the vicinity of inlets, moving between the sea and the lagoon and vice versa by means of small boats with motor. The average number of fishing days each fisher was estimated at about thirty per year, with a catch average of about 2-
3 kg per day. It was thus possible to hypothesize a total catch of the order of 240–360 tonnes per year (Province of Venice, 2000; Pellizzato et al., 2006), a relevant share of the fish withdrawal.
Also relevant is the catch by the bilancioni (shore operated lift nets) in the lagoon of Venice; this type of gear is not allowed in other coastal lagoons of smaller size, but it is used in many rivers and channels in most regions. This gear targets nektonic species that make regular migrations (seasonal or related to the tide) between the lagoon and the sea. The relatively small mesh size, at least in the central portion of the gear, makes it vulnerable to the capture also the juvenile forms and undersize individuals. The bilancioni are usually placed strategically inside the tidal channels, also relatively shallow and narrow, close to sensitive habitats such as saltmarsh and mudflats areas, and they may represent a potential threat to fish moving between different lagoon habitats, or between the lagoon and the marine environment. The presence and impact of the bilancioni should also be evaluated taking into account other aspects, such as those related to the conservation of fragile habitats typical of the lagoon landscape (Provincia di Venezia, 2009).

6.6.2 Interactions among different fishers groups

In most coastal lagoons, no relevant interactions are reported among different fishers groups and conflicts between fishers/fish-farmers and public or private stakeholders. When touristic activities are present in the area, usually this creates a significant economic activity, also allowing some fishers to supplement the income with fishing tourism activities or other related activities.
Completely different is the interaction that arises in the lagoon of Venice due to the harvesting of Manila clam. The Province of Venice (1999) estimated the morphological damage consequent to R. philippinarum harvest in the lagoon of Venice in about 20 billion euros per year to collect and dispose residual materials and other 40 billion for the reconstruction of morphologies. 149
Harvest activities, lifting and suspending the sediment contribute to the erosion of salt marshes, also raising the bottom of the channels and promoting the loss of suspended material from the lagoon.
Conflicts also arise in relation to illegal fishing fight and prevention, based on seizures of the product either caught in prohibited waters or because it is under market size, boat confiscation, reporting and arresting.

6.6.3 Competition for space

The issue of competition for space between aquaculture and other uses of the lagoon, namely fisheries, is strongly felt with reference to the allocation of the concession areas for Manila clam culture and harvest in the lagoon of Venice.
In other coastal lagoons, the relationship between fisheries and the aquaculture industry has been constructive, as reported for the lagoon of Lesina, for example by providing hatchery seed for the restocking actions carried out by the Municipality of Lesina and by the Provinces. The shrimp farm (pens) present in the Lesina lagoon does not cause damage nor creates impacts on the fisheries, apart from the use of a limited area of the lagoon.

6.6.4 Product interaction on the market

Market interactions often have resulted in positive initiatives. In Orbetello, the company Orbetello Pesca Lagunare aimed to enhance local productions and diversify products from the lagoon, supported up to now by funding from the Regional Administration. In addition to artisanal fisheries, fish barriers management and management of one of the hatcheries also sustain processing initiatives of some typical products, such as the production of mullet roe (bottarga) and mullet smoked fillets, and manage a fish restaurant. In the Lesina lagoon, the fishers cooperatives have often set up initiatives and programmes to protect and enhance fish production of the lagoon, with the support of the Municipality of Lesina, through a mixed public-private partnership that also managed in the past a small shop and a processing unit for mullet roe production. The most relevant market interaction in recent years is the one occurring between fish from the valli and imported product (seabream and seabass), which caused a sharp fall in prices, also accentuated by the difficulty to label this product with appropriate marketing techniques (Persona et al., 1996; Donati et al., 1999).

6.6.5 Organic input from aquaculture activities

The most relevant situation of organic input from aquaculture activities is the one present in the lagoon of Orbetello, because of the presence of intensive fish farms discharging in the past in the lagoon, concurring to eutrophication and consequent dystrophic crises that occurred in 1991–1993. At present, the problem has been remediated by effluent waters treatment.

6.6.6 Environmental effects of aquaculture and capture fisheries on biodiversity conservation

With regards to the environmental effects of capture fisheries on biodiversity conservation, in most lagoons fishing gear is selective up to a certain measure, and this applies in particular to the fish barrier, that allows juveniles and sub-adult fish to escape. Thus, the environmental effects are to be ascribed to fishing effort intensity and result mostly in a depletion of fish stocks in conditions of intense fishing.
A relevant environmental effect of aquaculture on the lagoon environment is the one reported for the Manila clam harvesting in the lagoon of Venice, because the operation of the gear during harvest strongly affects the bottom, primarily by suspending the sediment. The greater part of the sediment lifted by the fishing gear resettles in the lagoon, thus increasing the silting of traits of the navigation channels, and is partly transported to the sea through the inlets. Manila clam harvesting was estimated to cause the loss of one billion cubic meters of sediments per year from the Venice Lagoon. These direct effects on the sediment may cause indirect effects on aquatic organisms and the ecosystem. Most authors (Pranovi and Giovanardi, 1994; Fontolan et al. 1995; Pranovi et al. 1998; Province of Venice, 1998) agree that the action of the gear for clam harvesting cause a general depletion of species and total biomass of the benthic community.
On the contrary, positive relationships can be described between extensive aquaculture activities carried out in the valli and the environment. In addition to farming, wildlife presence and hunting activities, the valli are of still of considerable importance because of their environmental and naturalistic value. The management of a valle foresees a number of interventions, the aim of which is ultimately to ensure habitat conservation (Donati et al., 1999). The maintenance of a substantial ecological stability is the basis of long-term profitability of a valle (Ardizzone et al., 1988). An average of about 30 percent of the maintenance works being carried out in a valle are estimated to present a high environmental value.
Environmental effects linked to the presence of intensive aquaculture facilities discharging directly into the lagoon have been heavy in the past, and have brought about negative consequences to the whole ecosystem of the Orbetello lagoon, and to its biodiversity. A substantial impact on the environment, even if hardly measurable, is due to the wastewaters from the aquaculture facilities in other lagoons, such as the lagoon of Lesina, where some culture facilities discharge into the lagoon their effluent waters. This situation could bring about, apart from an increase of the trophic level of the lagoon, also the spreading of pathologies. The occurrence of the allochthonous species Tilapia niloticus, which has reached the lagoon from a nearby fish farm, is now established, and there is evidence that this species has now adapted to the lagoon environment.

6.6.7 Pathology spread

Pasteurella piscicida pathologies, probably derived from cultured European seabass and gilthead seabream in the surrounding fish farms, were reported in the Orbetello lagoon for some years for the large grey mullet (Mugil cephalus) specimens during spring and autumn.

6.6.8 Juveniles/spat collection in the wild for culture and/or restocking purposes

Fry specialist fisheries are a traditional harvesting activity in the lagoon of Venice surroundings that provide seed for stocking the valli and therefore sustain extensive culture practices. Details on fishing, quantities and use can be found in Granzotto et al. (2001).

6.6.9 Genetic impact of restocking actions / escape events on wild stocks

See above, the reporting of the Nile tilapia in the lagoon of Lesina that can survive in this lagoon also in winter owing to the presence of some warmer areas where spring water is hot.

6.6.10 Impact of ichthyophagous birds (species, migration routes, entity of predation, bird control)

This impact is unanimously reported to be present in all Italian coastal lagoons, mostly to be ascribed to great cormorants. In the area of the Fogliano coastal lake, about 2 000 cormorants were estimated to be present, and 800 of them wintering there, but the impact of their presence on the fish community has not been directly estimated. The impact of their presence is remarkable also in the Orbetello lagoon, given the presence of about 2 500–3 000 wintering cormorants since 2000 (Ceccarelli et al., 2005). Cormorants are the greatest negative impact that fishers have to endure also in the lagoon of Lesina, with some thousands of birds every year that during the migration period can cause the loss of large quantities of product. Over 11 700 cormorants were recorded in the Sardinian wetlands in 1995 (Cannas et al., 1995).
Ichthyophagous birds have a strong impact in the area of the lagoon of Venice and in all the northern Adriatic area, mainly in relation to fish predation in the valli, and represent one of the main causes of product loss. Predation by ichthyophagous birds represents the main factor limiting fish productions in these extensive aquaculture situations. On the other hand, the presence of other water birds represents a main attraction in these same sites as preys for hunting.