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1. Introduction
Incidental catch or bycatch represents 8% of global fisheries production [1]. Bycatch is defined as any unwanted species caught during normal fishing operations and may include nontarget fish species, marine mammals, turtles, sharks, and seabirds [2, 3].
Dolphinfishes (Coryphaena hippurus and Coryphaena equiselis) are highly migratory pelagic species which inhabit tropical, subtropical, and temperate waters. They constitute a valuable seasonal resource for small-scale fleets. Traditionally, dolphinfish has been an important food resource for the Mediterranean people. The Mediterranean landings of these species have increased regularly in the last decade [4]. Nevertheless, the assessment and management of dolphinfish is difficult mainly due to the scarcity of data on biology, migratory patterns, and exploitation of these species in the Mediterranean.
Dolphinfishes in the Mediterranean support both commercial small-scale fishing and recreational fisheries [5, 6]. In Malta, Tunisia, Sicily, and Balearic Islands from the end of summer to autumn, dolphinfish juveniles are caught using Fish Attracting Devices [7–9]. These species are also caught as a bycatch of commercial longline fisheries [10, 11]. The Western Mediterranean Sea is an important fishing ground where the Spanish drifting longline fishery operates targeting mainly swordfish Xiphias gladius, bluefin tuna Thunnus thynnus, and albacore T. alalunga. In this context, identification of the principal factors that determine this bycatch is basic to improve the assessment and management of the Mediterranean dolphinfish stocks.
The aim of this paper is to describe the dolphinfish bycatch rates in the longline fisheries from Western Mediterranean and modeling the nominal bycatch abundance and distribution of dolphinfish from the Spanish Mediterranean as a function of technical, geographical, and seasonality factors.
2. Material and Methods
Catch and effort data for longline fisheries were collected by the Spanish Oceanographic Institute (IEO) on-board observer training program, planned according to International Commission for the Conservation of Atlantic Tunas (ICCAT) recommendations. The positions of the fishing grounds and spatial distribution of gear effort are shown in Figure 1. We classified the fleet into six strata (Table 1), according to differences in target species, operational depth, and technical characteristics (more detailed information in [12]). The positions of the fishing grounds and spatial distribution of gear effort are shown in detail in García-Barcelona et al. [12].
Table 1
Six boats...