Some Characteristics of the Bluefin Tuna. Its Geographical Distribution, Areas and Fishing Systems

Abstract

Some characteristics of bluefin tuna are described relating to its biology (growth, reproduction, migrations and ethology), physiology, geographical distribution and fishing. Regarding the latter, the evolution of bluefin tuna fisheries over the last seven decades is analyzed, with descriptions of the various fleets working in different regions over this period. The Atlantic bluefin tuna belongs to the family of the Scombrid fishes (Scombridae) (Collette and Nauen 1985). It can weigh over 725 kg (Crane 1936; Lebedeff 1936; Heldt 1938), reach lengths of 3.3 m (Cort et al. 2013) and live over thirty years (Neilson and Campana 2008). In general, during its fattening phase in the first year of life it reaches 53 cm (4 kg); at age 10, 204 cm (170 kg); at 20 years, 273 cm (410 kg); and at 30 years, 301 cm (550 kg). The official record of the largest ABFT captured in the western Atlantic is 679 kg, a fish caught in Nova Scotia waters (Canada) in 1979 (Fraser 2008). This catch also stands as the current Guinness world record. It forms large shoals and feeds mainly on other fishes, cephalopods, small crustaceans such as krill (Euphausiacea) and pelagic crabs, Polybius henslowii (Leach), (Estrada et al. 2005; Sarà and Sarà 2007; Logan et al. 2010). Its shape is highly hydrodynamic, as it is entirely adapted to mobility. ABFT inhabits temperate waters of the North Atlantic and Mediterranean Sea (ICCAT 2010). It is found in the eastern Atlantic from Senegal (Ngon Sow and Ndaw 2010) and Cabo Verde (15º N), the Mediterranean and Black Sea (Zaitsev 2003), almost as far as the Arctic Circle (75º N) where temperatures of 5 ºC are recorded (De Metrio et al. 2002; MacKenzie and Myers 2007; Di Natale 2012a), and in the western part from Brazil (Takeuchi et al. 1999, 2009) to Newfoundland (Hurley and Iles 1980). It is also found in the southern Atlantic (Di Natale et al. 2013). Its bloodstream forms the core of a highly evolved heat exchange system, and so its internal temperature can be maintained at up to 21 ºC higher than that of the water surrounding it (Carey et al. 1969; Carey and Lawson 1973). This is one of the reasons for its wide distribution in the ocean. ABFT can appear in the warm waters of the Bahamas at close to 30 ºC (Rivas 1954) and 50 days later in Norwegian waters, where the temperature hardly rises above 10 ºC (Mather III 1962).