Angela Granzotto

Comparison between artisanal and industrial fisheries using ecosystem indicators

Artisanal fishery in the lagoon of Venice is a multi-target activity with an old tradition. It was the only fishing activity since a new one with most features of an industrial fishery flourished following the introduction of the Manila clam in 1983. To compare the two fishing activities, a set of ecosystem indicators (landings, catches, discards, biomass of the system, mean Trophic Level of the system and exergy) obtained by a model approach, was applied. The model used was a mass-balance model of the lagoon ecosystem developed with the software package Ecopath with Ecosim. The 73 scenarios obtained by changing the fishing effort of the two different fisheries were used to explore the impact of fishing activity on the ecosystem. The results showed that the two activities are strongly interrelated, even if they do not exploit the same resources, and that the mechanical clam harvesting is the driving force able to affect the ecosystem state fundamentally. All this produces a strong conflict between the two kinds of fisheries. The ecosystem and social optimisation depend mainly upon a reduction of clam fishery, while the optimisation of the economic aspects is strictly linked to the maintenance of this fishing activity.

Comparison between Artisanal Fishery and Manila Clam Harvesting in the Venice Lagoon by Using Ecosystem Indicators: An Ecological Economics Perspective

Artisanal fishery in the Venice lagoon is a multi-target activity with a long tradition. It was the main fishing activity till the late ’80s when, after the introduction and spread of the Manila clam (Tapes philippinarum), the mechanical clam harvesting started. A mass-balance model of the lagoon ecosystem was developed using the Ecopath with Ecosim software. 73 scenarios, obtained by changing the fishing effort of the two different types of fishery, were used to explore their impact on the ecosystem. A set of indicators was applied in order to compare the two fishing activities. The results obtained showed that the two activities are strongly interlinked, even through they don’t exploit the same resources. The mechanical clam harvesting could reasonably be considered to be the driving force; it is capable of determining the state of lagoon ecosystem. The above mentioned factors create a lot of conflict between the two types of fishery.

Marginal increment analysis and Sr/Ca ratio in otholiths of the grass goby, Zosetrisessor ophiocaphalus

Abstract Monthly changes in marginal increments, determined from alternation of macroscopic opaque and translucent bands, of Zosterisessor ophiocephalus sagittae were examined. The time of an‐nulus completion proved to be annual, occurring around June both for females and males, and coinciding with the end of the breeding season and a period of larger body condition. The translucent band is likely to start depositing in summer. Since Sr/Ca peaks coincided with annulus completion, the most likely hypothesis is that the Sr/Ca ratio is influenced by the reproductive season.