Abstract
The Manila clam, Ruditapes philippinarum, introduced in the Venice lagoons in 1983 and rapidly spread to the nearby coastal lagoons represents one of the most important commercially-exploited resources of this area. Abundance, size-class and biomass distribution of the wild population living in the Pialassa Baiona lagoon were assessed and related to the hydrological and sediment characteristics. Despite the lagoon being affected by eutrophication, chemical and thermal pollution, the clams were harvested by about thirty professional fishermen until 2003. The commercially available stock was estimated at 36.8 10 3 kg in July 2002, 29.3 10 3 kg in April 2003, and 10.3 10 3 kg in October 2003. Stock estimations and observed mortality were in good accordance with the fishermen data. The decline of the available stock could be due to both overfishing and the extraordinary summer heat wave occurred in 2003, which may have reduced larval recruitment and increased the mortality. Overall, the juvenile recruitment appeared insufficient to annually restore the natural stock. Although the national and regional high relevance of clams market, local harvesting of wild populations appeared marginal and inadequate to support a remunerative commercial activity, due to the variability and unpredictability of the annual yield and the lack of a sustainable management based on a production chain’s approach.
Highlights
The Manila clam, Ruditapes philippinarum (Adams and Reeve, 1850), is native to the Indo-Pacific region and as a results of aquaculture activities and human transport it is widely distributed along the Pacific coast of America, the Atlantic coast of Europe, until 50° latitude N, in the northern Adriatic and Aegean Seas (JENSEN et al, 2004; HUMPHREYS et al, 2007)
Sympatric coexistence of the two congeneric species or the predominance of R. philippinarum over R. decussatus may depend by local environmental conditions and less narrow requirements of the introduced ones (BIDEGAIN et al, 2016; NERLOVIĆ et al, 2016)
Despite being a very hardy species, well adapted to the changing conditions that occur in coastal lagoons, Manila clam may be affected by adverse environmental conditions, including the most important as the prolonged anoxia and excessive heating of the water
Summary
The Manila clam (or Japanese carpet shell), Ruditapes philippinarum (Adams and Reeve, 1850), is native to the Indo-Pacific region and as a results of aquaculture activities and human transport it is widely distributed along the Pacific coast of America, the Atlantic coast of Europe, until 50° latitude N, in the northern Adriatic and Aegean Seas (JENSEN et al, 2004; HUMPHREYS et al, 2007). It was introduced for marine farming on the Mediterranean and Atlantic coast of the France at the beginning of ‘70s of last century (BODOY et al, 1981).
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