Environmental Engineering Reference
In-Depth Information
heavy metals and to a lesser extent PAHs and PCBs. In a similar manner, the environmental
quality of the Corno River seems better than the Aussa one, both in terms of contaminants
and measured concentrations.
4.2.3 Exploitation of aquatic resources
The Lagoon of Marano and Grado hosts the two most important fishery ports of the Region
Friuli Venezia Giulia: Marano Lagunare and Grado. Together they represent almost 80% of
the fishery fleet of the region as number of vessels. Fishermen operate at sea by trawling,
seine, hydraulic dredge for bivalves (mainly
Chamelea gallina
,
Callista chione
and
Ensis minor
),
trammel and gill nets, longlines, fish traps adapted to catch cuttlefishes (
Sepia officinalis
) and
mantis (
Squilla mantis
). Most of fishermen in Marano Lagunare work both at sea and lagoon;
in the latter case they use prevalently a very old method to catch fish in the northern
Adriatic lagoons: a barriers system ending in the fyke nets (locally named
cogolli
). This very
ancient method is tightly linked to the tide regime. Moreover in the lagoon there is a so
much ancient tradition (arising to 16
th
century in the Lagoon of Grado) to farm fishes inside
pools such as sea bream (
Sparus aurata
), sea bass (
Dicentrarchus labrax
), eel (
Anguilla anguilla
)
and mullet (
Mugil
sp.).
The spreading of Manila clam in the Adriatic lagoons led to a consistent abandonment of
traditional fishery, because of the massive abundance of this species, its easiness of
harvesting and overall the considerable market of this resource. In this way at the beginning
of 90
th
almost 50% of fishermen in Marano Lagunare started to harvest these clams. In the
first time they were harvested by hand from spring to autumn and a maximal daily quota
per person of about 50 kg was established. In 1992 a special dredge was introduced to collect
clams during the winter in the Lagoon of Marano. This gear was studied and built in
Marano Lagunare and it is locally known as “maranese rake” (Fig. 3.). This method
permitted to harvest Manila clams in the cold season and these gears were hauled on the
shallow lagoon bottoms by boats with a power engine ranging between 80 and 120 Hp. A
quota of 50 kg/day was established for each boat, excepting for about twenty days during
the Christmas celebrations when a quota of 70 kg/day was permitted (Zentilin & Orel,
2009). No specific limitations were established to access the Manila clam natural banks with
this method of fishery. Thus until December 2006 almost 150 fishermen could harvest freely
this resource from October to March using this mechanical gear in the most part of the
Lagoon of Marano. In the Lagoon of Grado Manila clam had not a massive spreading such
as Marano basin and this species is manually harvested only by local or leisure fishermen;
although an illegal harvesting and sale occur nowadays in both lagoons.
The Table 2. shows how the exploitation with “maranese rake” increased enormously since
1995, when the contribution of farm to the total production in the market of Marano
Lagunare was only 3%, whereas the biggest production was recorded in 1996. In those years
each natural bank of Manila clams was freely overexploited until the biomass dropped
below 0.01 or even 0.005 kg/m
2
. This impulsive and uncontrolled exploitation of the
resource, accompanied to mobilization of sediments and potential contaminants, led the
authority to stop definitively this free practice with the rake in January 2007, after many
years of tacit assent. This sudden decision caused social disorders and resentments between
the citizens of Marano Lagunare where, due to the general crisis of marine resources too,
half of fishermen community was employed till then to this kind of harvesting. This occurs
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