The hake deepwater semi-pelagic ("pedra-bola") longline fishery in the Algarve (southern Portugal)

A 2-year study of the European hake (Merluccius merluccius) semi-pelagic ("pedra-bola) longline fishery was carried out in the Algarve (southern Portugal). This fishery takes place on the continental slope at 200-700 m depths. using monofilament longlines that are lifted off the bottom at regular intervals by glass balls. Hook selectivity trials were carried out with four hook sizes (SIAPAL brand numbers 10, 9, 7 and 5) from March to August 1997 and May to August 1998. At least 32 species of fish and invertebrates were caught, with hake dominating the catch (41 and 45% of the catch in numbers), followed by Galeus melastomus (23 and 19%), Micromesistius poutassou (10 and 7%), Benthodesmus elongatus (8 and 5%), Etmopterus pusillus (6 and 9%) and Scyliorhinus canicula (5 and 4%). Apart from the hake, and some species of commercial value such as G. melastomus (only the large individuals), Ray's bream (Brama brama, 1.4 and 4%), silver scabbard fish (Lepidopus caudatus. 1 and 2.5%), swordfish (Xiphins gladius, <1%), wreckfish (Polyprion americanus, <1%). conger eel (Conger conger. <1%), and bluemouth rockfish (Helicolenus dactylopterus, <1%)- most of the other species are discarded, used as bait in traps or consumed by the fishermen. Catch rates (number of fish per 100 hooks) for hake and for all species combined decreased significantly with hook size. Hake catch size frequency distributions for the different hook sizes in 1997 and 1998 were highly overlapped, with the four different hooks catching a wide range of sizes. Although catch size frequency distributions for the different sized hooks were not significantly different in 1997, hake caught in 1998 were characterised by smaller sizes and size ranges. (C) 2001 Elsevier Science B.V. All rights reserved.