Decline of the Manila clams stock in the northern Adriatic lagoons

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.

Spatial and seasonal variability of human and fish viruses in mussels inside and offshore of Ravenna’s harbour (Adriatic Sea, Italy)

“…2010; Ponti et al . 2017). Moreover some fish farms are present in other lagoons along the Adriatic coast, of which the closest is the Valli di Comacchio lagoon complex; however, no direct water connection exists between these lagoons and the Ravenna’s harbour.…”

Sea level and temperature extremes in a regulated Lagoon of Venice

“…Munari (2011) investigated considerable changes in the benthic community structure and relative composition, persisting until the year 2005, in Comacchio Lagoon (Northern Adriatic Sea, Italy). In a close area, Ponti et al (2017) report the decline of the available stock of Manila clam in a coastal lagoon due to overfishing and heat exposure. From this short and non-exhaustive list, we can assume that the main biological impacts verified in previous MHW in the world are the geographical species shift, the widespread changes in species composition and the mass mortalities of particular species.…”

Optimizing Hard Clam Production in Taiwan by Accounting for Nonlinear Effects of Stocking Density and Feed Costs on Farm Output of Clams

“…This process promotes the ingestion of nutrient substances in the feed for hard clam and thus, helps to increase feed digestibility [12][13][14], increase the culture production output and survival rates [15,16], enhance disease resistance and immunity [17,18], as well as compete with pathogens for the growing environment [16,19], consequently inhibiting pathogens and improving the culture environment by stabilizing water quality [20,21]. Bordignon et al (2021) [22] demonstrated in their study that increases in stocking density lead to reduced clam growth and, depending on the water quality, may also cause mortality [23][24][25][26][27]. Previous studies also reported that decreasing the natural seed stocks of clam cultures may encourage the usage of hatchery-produced seeds [28][29][30][31].…”