Growth and mortality of the brushtooth lizardfish (Saurida undosquamis) in Iskenderun Bay (eastern Mediterranean Sea) using length frequency analysis

Abstract

and the exploitation ratio was0.51, indicating that the brushtooth lizardfish stock is on theverge being overfished.IntroductionThe brushtooth lizardfish, Saurida undosquamis (Richardson,1848), is a demersal species inhabiting sandy and muddybottoms, at depths generally above 100 m (Golani et al.,2002). Lengths of up to 50 cm SL were reported for the species,although specimens ranging from 20 to 30 cm TL are common(Sulak, 1984). The natural distribution range of S. undosqu-amis includes the Indo-West Pacific Ocean (Red Sea, PersianGulf, Eastern Africa to Japan and Australia) (Froese andPauly, 2006), but it has penetrated into the eastern Mediter-ranean Sea via the Suez Canal. First specimens were collectedduring 1953 along the coast of Israel and 266 tonnes werelanded by commercial local trawlers during 1956 (Ben-Yamiand Glaser, 1974). Catches have since remained high, withsome fluctuations (Golani, 1993). This alien species is one ofthe most successful colonizers throughout the Levant basin,which extends as far as the Aegean Sea (Bilecenoglu et al.,2002). The brushtooth lizardfish is currently the most exploitedalien fish in Turkey, comprising almost one-third of thecommercial trawl catch in the northeastern Levant (Cinaret al., 2005).In the eastern Mediterranean Sea, S. undosquamis was thesubject of few biological studies. The pioneering study wascarried out by Ben-Yami and Glaser (1974), who providedgeneral biological information and the invasion process of thespecies in relation to environmental factors. Morphometricseparation of brushtooth lizardfish stocks was studied atMersin coasts (Avsar et al., 1990). Feeding habits, maturityand fecundity of the species were examined by Bingel andAvsar (1988), Golani (1993) and Ismen (2003) respectively.Concerning growth of S. undosquamis, only Anonymous(1981), Tu¨reli and Erdem (1997) and Ismen (2002) provideddata from the Turkish coasts, based on otolith readings. Thisinvestigation was undertaken to improve knowledge of growthparameters and mortality rates of brushtooth lizardfish byusing length frequency analysis.Materials and methodsThe brushtooth lizardfish specimens were collected during2004 at monthly intervals from Iskenderun Bay, onboard thecommercial trawler Canan Kaptan (26 m length, 450 HPengine) using a conventional bottom trawl with a cod-endmesh size of 22 mm. A total of 36 valid trawling hauls weremade at depths ranging from 45 to 60 m; 4711 specimens werecollected. Towing speed varied between 2.5 and 2.8 knots, withtowing durations from 90 to 180 min. Fish were measured tothe nearest 1.0 cm TL immediately after capture and monthlylength–frequency distributions for use in growth estimationwere constructed. The von Bertalanffy growth function(VBGF) was used to estimate growth parameters, using theELEFAN I routine incorporated in the