Simulating the indirect handline jigging effects on the European squid Loligo vulgaris in captivity

The European squid Loligo vulgaris is an important target species of commercial and recreational fisheries in the NW Mediterranean. Handline jigging is one of the most common fishing gears used by both of these fisheries to catch squid, which are trapped when they try to seize the lure with their tentacles. An unknown but possibly significant number of squid are able to escape from this gear by losing one or both of their tentacles (drop off rate). Between April and July 2010, two sets of experiments under controlled laboratory conditions were carried out to test (n = 15 squid) the indirect effects of tentacle loss on predation success and predation behaviour. The first set of experiments consisted of estimating the number of attacks and time spent until a squid with no (n = 5), one (n = 5) or two tentacles (n = 5) successfully caught a prey item. Independent trials were carried out with two prey types with very different swimming capabilities (fish and shrimp). The second set of experiments consisted of prey-selectivity trials to determine whether squid prefer fish or shrimp when both are available. The results obtained clearly demonstrate not only that squid missing tentacles have a reduced predation performance but also that they can change predation preferences and predation behaviour. These changes might negatively affect the condition of injured squid (reduced fitness). Consequently, the possibility of squid losing their tentacles deserves more attention in the management decisions for the squid fishery. This indirect handline jigging effect may imply unreported fishing mortality (ghost fishing) that should be considered when making management decisions for this important fishery.

► Handline jigging causes indirect effect on injured squid decreasing their predation effectiveness.
► The injured squid change predation preferences and predation behaviour.
► The condition of the injured squid might be negatively affected.
► The drop off rate may imply unreported fishing mortality (ghost fishing).