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In the present research project, the effects due to the fry (bianchetto) fishery of sardine (Sardina pilchardus) in the Gulf of Manfredonia on the Adriatic stock of adults of this species were evaluated for the time interval 1996-2008, by means of population dynamics methods. These sardine bianchetto catches, composed mainly of post-larvae and also by juveniles (the length range is between 25 and 45 mm), by far represented the most important small pelagic fry fishery in the Adriatic Sea. These were landed in the months from January to April by bottom trawlers vessels and, in some years of the time interval investigated, resulted to be over 100 tonnes. In the analyses carried out, two scenarios for the catch levels and eight different functions to calculate the daily rate of natural mortality M were taken into account for bianchetto, along with the values of abundance at sea of sardines of the age class 1, estimated by means of population dynamics methods applied in the stock assessment of adults. The analyses performed yielded a series of possible impacts due to the bianchetto fishery on the abundance at sea of adult sardines of the age class 1. The average impacts, for the most likely natural mortality function, one of two derived from the model proposed by Pepin (1991), were 0,4% and 1,7%, with the latter case being obtained at the higher level of bianchetto catches. Less likely natural mortality functions yielded higher impacts: for example, when the two functions derived from the model proposed by McGurk (1986) for juveniles were used, the average impacts obtained at the higher level of bianchetto catches were 15,9% and 13,8%. |
