Effects of the introduction of the mesopelagic long line on catches and size structure of swordfish in the Ligurian Sea (Western Mediterranean)

In 2010 the new mesopelagic long line was introduced in the Ligurian Sea swordfish fishery, substituting the traditional surface long line. In 2010-2011 fishing seasons the main effects were: a) significant increasing of swordfish mean size, both for males and females b) great increasing of catches and CPUE values c) decreasing of by-catch. During the third year (2012) a great decline, both of mean size and CPUE, was recorded, followed by a small recovery in 2013. The introduction of this new gear revealed the presence of a fraction of the swordfish population, made up of large spawners, so far only partially exploited by commercial fishing, suggesting that swordfish SSB could be larger than previously expected. Effects of heavy exploitation on this fraction of the stock are discussed.