The submerged structures for the restocking and fishing ("artificial barriers")

Part 1: Considerations on the effectiveness of the artificial reefs based on the specialized bibliography

We examined about 350 scientific papers dealing with the underwater structures named “artificial reefs” (“ARs”). ARs are clustered solid structures set on shallow marine grounds that attract fishes and other motile animals through visual and sound stimuli and, at the same time, may offer  protection from predators and  additional food sources.

Our analysis shows that most papers on ARs are mainly descriptive because changes through time in the composition of faunal assemblages are recorded but the underpinning relationships (predation, spatial competition, new hydrological parameters, and so on) are often neglected.

Moreover, ARs should be differently planned according to the expected prominent “functions”, for instance conspicuous and tall buildings are required for visual attraction whereas sparse small structures, holding holes and interstices, are preferred to protect small-sized and juveniles of target species.

In view of the complex relationships between ARs and the surrounding marine environment the effects of ARs on local fish and benthic assemblages result to be hardly predictable. Finally we observe that in Italy ARs may be of more interest to recreational fishermen, provided that these sites are often not managed by professional ones, although they result to be the beneficiaries within the project.

Part 2: Veneto’s case study: artificial reefs in shallow water in front of the Sacca of Canarin (Rovigo)

In this report results are summarised from distinct investigations carried out during 2005-2010, before and after the settlement of ARs on shallow marine grounds facing the coast of Veneto near the Sacca of Canarin. The sinking of the artificial structures aimed both to hamper illegal trawling in proximity of a mussel farm and to promote passive restocking of the area.

The reported data refer to geophysical surveys of the seabed and hard bottom and fish communities investigations carried out before and after artificial reefs deployment.

Local benthic and fish communities show high species richness levels, but reduced biomass values. Furthermore, large spatial and temporal fluctuations are observed in both qualitative and quantitative terms. This study area seems much more influenced by natural variations than by the presence of ARs.

These evidences are linked partly to the small volumes of the structures themselves and partly to the constant presence of illegal trawl fishing, as shown by acoustic survey of the seabed, that limit or even reduce the attractive effect of the ARs.

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