Review article

The long-term decline of the Chamelea gallina L. (Bivalvia: Veneridae) clam fishery in the Adriatic Sea: is a synthesis possible?

Michele ROMANELLI ; ISPRA (formerly ICRAM), Via di Casalotti 300, 00166 Rome, Italy
Cristina Angela CORDISCO ; ISPRA (formerly ICRAM), Via di Casalotti 300, 00166 Rome, Italy
Otello GIOVANARDI ; ISPRA (formerly ICRAM), Località Brondolo, 30015 Chioggia, Italy

Abstract

Since the early 1970s a comparatively large clam fishery based on hydraulic dredgers has beendeveloping, though later declining, along the Italian coast of the Adriatic Sea (Central Mediterranean).In the late 1970s the fishery yielded 80,000-100,000 metric tons per year (at least accordingto the best available estimates, based on confidential interviews with fishermen, fish retailers as wellas examination of trade sheets) but later progressively decreased in most recent years to one sixthof the previous level.
In Italy it was the first fishery to be controlled through licences whose number had been set at thenational level to keep the fleet and the fishing effort nearly unchanged, but the number of authorisedvessels actually increased during the 1980s and technical improvements on the fishing gear allowedthe boats to sweep greater ground areas per unit time. This explains why various measures weresought to reduce the fishing pressure on clam beds (such as withdrawal of vessels, imposition ofclosed seasons, larger open spaces in the sieves), and a limited reduction of the fleet was pursued inthe late 1990s after large mortality events were recorded during late summer-early autumn of 1996.
At the same time the influence of unknown environmental factors was occasionally assumed forthe fishery, and the greater abundance of clam beds as well as other fish and shellfish resources inthe Adriatic in comparison with other Mediterranean areas was tied to the large freshwater inflowfrom the Po and other rivers.
Because of such discrepancies in the literature we reviewed all available papers (or nearly so)on the Adriatic clam fishery (including national laws, reports on the eutrophication of the coastalareas of NE Italy, and others) in order to understand the role of environmental factors (i.e. unrelatedto the fishing effort) vs. fishing pressure for determining causes of the clam decline. Althoughthe low qualitative level of many data makes it difficult to disentangle the decline’s causes, indirectclues show that the progressive reduction of freshwater flow into the Adriatic Sea, as well as of itsphosphate content, have been playing a relevant role in the matter.

Keywords

Chamelea gallina; bivalves; Po; phytoplankton; productivity

Hrčak ID:

45928

URI

https://hrcak.srce.hr/45928

Publication date:

1.12.2009.

Article data in other languages: croatian

Visits: 2.238 *