ANALYSIS OF THE TRAWL-FISHERY WITHIN 3 MILES OFF THE COAST-LINE IN THE CHIOGGIA MARITIME COMPARTMENT (ADRIATIC SEA).
O. Giovanardi, ICRAM , Viale Stazione, 5 30015 CHIOGGIA (Ve)
Key-words: coastal trawl-fishery, small scale fishery, Adriatic sea, Lagoon of Venice, A. boyeri.
Data and information collected in this work let us draw a framework of the situation of the trawl fishery carried out within 3 miles from the coast-line in the Chioggia Maritime Compartment, related to the November-March period, when this “special fishery” is permitted by the present italian law in the Northern Adriatic sea.
After describing the main points of the present knowledge on the subject of our study, the incidence of the fleet devoted to this activity compared to the vessels dedicated to other types of trawl fisheries has been estimated; moreover, the different levels of catch have been described: wholesale fish market, major cooperatives associating this category of fishermen, before, during and after the derogation period model vessels, samplings on-board model boats both making and not making use of the opportunity of fishing given by the derogation, samplings on fixed stations in the sea and the Lagoon of Venice.
Therefore it has been possible to define the abundance and to study the biology and dynamics of the sand smelt (Atherina boyeri, which is the main target species for this activity.
The importance of this type of resource most of all for the smaller fishing vessels has come to light.
The larger vessels, allowed to fishing during the derogation period, depending on the fluctuations of meteo-marine conditions and the yield of their usual trawl-fishing activity on target species located in off-shore areas (e.g. Eledone species), in December and January usually decide whether change type of net and move inshore. Actually, even in this case, the total daily catch for those species is rather limited sometimes.
The number of boats really carrying out inshore trawl-fishing activities during the derogation period greatly varies from year to year, as a result of the fluctuations of the target species, particularly sand-smelt and cuttle-fish (Sepia officinalis). In the last seasons, this number has wavered around half of the total of allowed vessels which can dedicate to the sand-smelt fishery with a reduced-mesh-size net for a continuative period of at least a few weeks. The change of the net can produce remarkably great variations in the catch. For example, some fishermen state that the use of the net for the sand-smelt fishery (12-mm-mesh size) leads to a reduced speed in fishing, and a lesser amount in the catch of the species usually more abundant when the fishing speed is higher.
A problem related to the derogation period for trawl-fishery activity indicated by local fishermen comes out from the present legislation, lacking in some points in defining this type of activity. Sometimes it happens that in the on-board controls the Authorities observe a considerable presence of commercial species different from whom (sand-smelt and cuttlefish) the derogation period has been established, and quite often tend to fine the fishermen.
On the other hand, it is clear that this type of fishery cannot be monospecific and the catch of other species is inevitable. The average incidence of sand-smelt has been observed to be at least 50% of the weight during the period of our investigation. In some cases, it reaches even 90%.
Anyway it is better to point out that the remaining part of the catch mainly consists of adults of several species of Gobidae, characterised by small size, short vital cycle and longer inshore presence. Juveniles of other species are not observable.
Moreover, in the Lagoon of Venice a small-size net is employed (“coccetta di porto con ciocioli”), trawled by two boats in shallow areas, particularly suitable for the catch of A. boyeri (“acquadelle”), but also Mugilidae, cuttlefish, anchovies, etc. In this case, the fishing daily pattern has a different cycle from the classic one, with boats going out at sunset and coming back to the harbour, for the market, at 5.00 am.
There are only a few couples able to operate both in the Lagoon and the open sea, but in quite inshore areas, due both to the size of the boat and to the type of the gear. For those vessels, the sand-smelt fishery is very important; they follow the species in its migration, fishing in the Lagoon until November and in the open sea as soon as the species moves to the coastal sea areas.
The phase of the vital cycle spent in the Lagoon has been observed as extremely important for the A. boyeri stock. Therefore, any sort of management measure must necessarily start mainly from that area. According to what comes out from the data obtained, at present there seem to not be risks for this resource related to the type and level of its actual exploitation.
The set of data of the genetic analyses emphasises how the sand-smelt flows between the open sea and the Lagoon are important and the importance of the mixing for the conservation of its genetic biodiversity.
In the April-June period the target species of the trawl fishery carried out within 3 miles is the cuttlefish, which comes inshore for its reproduction. This activity is allowed up to 600 m from the coast, but there is a conflict of interests with the operators employing traps, pots and fixed nets. Also that activity is strongly variable according to the annual fluctuations of the species, but in the Chioggia Compartment it is always actively performed.
This subject has been faced particularly by other 2 research projects on the theme of “Fisheries within 3 miles from the coastline in the Adriatic Sea”, financed, as our research, within the IV Triennial Plan for Fisheries and Aquaculture of the Ministry for Agricultural Policies. In general the trawl fishery on cuttlefish performed inshore presents some problems making this activity hard to justify.
- PR94 
