The research, promoted by the Fisheries Foundation, Ca’ Foscari and the Region looked at the food preferences of the invasive crustacean, which threatens the valuable green crab. The blue crab’s high reproductive capacity is also confirmed: females lay more than 2 million eggs with each single deposit
By Elisabetta B. Anzoletti
January 26 , 2024
[Ed. Note: Blue crabs are invasive in the Mediterranean and have reached the lagoon of Venice in recent years, creating a crisis for fisherman. They damage fishers’ nets and catches, as well as have negative impacts on native ecosystems, especially on organisms living close to the seafloor.]
Moeche are among the blue crab’s favorite prey. This was confirmed by the research commissioned by the Fisheries Foundation and the Region to the Ca’Foscari Department of Environmental Sciences.
The results of the first structured study on the invasion of the blue crab will be made available to the ministry so that they become useful to the entire sector.
“For six months (June-November 2023) we carried out on-site surveys, studies and comparisons to understand the life and behavior of the blue crab”, explains Professor Piero Franzoi of the Environmental Sciences department.
“The research involved both sampling with pots and monitoring of artisanal fishing with fixed nets and bertovelli [a fixed gill net, which is used both at sea and in fresh waters, consisting of an external net in the shape of a long cone, with other conical nets within, allowing fish to enter but not exit]. The crab pots were highly selective, capturing mainly adult individuals. The greatest abundances were observed in the summer months and the sex ratio was shifted in favor of males.”
Egg-bearing females were caught from June to September, with a peak catch at sea in August.
The fertility analysis confirmed the species’ high reproductive capacity, with females laying on average more than 2 million eggs with each single deposit.
Catches with fixed nets and bertovelli were sporadic at the beginning of the survey period, and then increased at the end of summer (5-7 individuals weighing 1.6-1.7 kg, per line per day), when blue crabs were in almost all of the lines examined.
The abundance of blue crabs in the bertovelli seems to negatively influence catches of other species, in particular the green crab, which until now has represented the primary species for lagoon fishing with fixed nets. Individuals that have just molted (moeche) and mature females (masanete) represent valuable products.”
“If this trend were to become established”, continues Franzoi, “it would lead to a replacement of species in the ecosystems of the Upper Adriatic, with the serious risk of an even more drastic reduction in green crab numbers. Certainly, the efforts implemented in 2023 by fishermen to catch the blue crab and reduce their abundance will need to be strengthened and coordinated in the near future.”
Source: La Nuova di Venezia e Mestre
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