Abstract
In this paper, the usefulness of different kinds of ‘target’ and ‘threshold’ reference points, their practical application for Nephrops norvegicus, the accuracy of their estimates and uncertainty levels are discussed. This study refers to the stock settled on the northern Tyrrhenian grounds around the Tuscan archipelago north of Elba island. Growth and mortality rates as well as some reproductive aspects (age at first maturity, fecundity at age, etc.) were incorporated into stock assessment models and allowed to estimate the present status for the Nephrops fishery and to define the more safe and productive fishing strategy for the species. The estimated current F value is well under the values of the target reference points F(Fmsy = M) and F0.1 suggesting that the species is only lightly exploited. The stock replacement analysis suggests that, with the current fishing strategy, the surviving adult stock biomass is able to ensure population self-renewal. This paper demonstrates the inadequacy of Fmax as a threshold reference point for Nephrops norvegicus. In fact, with current fishing strategy, the yield-per-recruit curves are very flat over a relatively moderate rate of fishing mortality and hence a very high (and economically inefficient) effort increase should be necessary in order to reach the maximum yield-per-recruit. At this high mortality rate, the probability of population rebuilding should be extremely reduced and risk of stock collapse increased.
Published Version
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