ANNALES • Ser. hist. nat. • 12 ■ 2002 ■ 2 original scientific paper UDC 597:591.13(262.4) received: 2002-06-03 STOMACH CONTENTS OF THE LONGNOSE SPURDOG, SQUALUS BLAIN-VILLEKRISSO, 1826) FROM THE NORTH-EASTERN AEGEAN SEA Hakan KABASAKAL Ichthyotogicai Research Society, Ataturk mahallesi, Mentejoglu caddcsi, ¡dil apt.. No 30, O 4, TR Ùmraniye 8 f J30 Istanbul E-maii: hakankabasakai^hotmait.com ABSTRACT Examination of the stomach contents of the kingpost spurdogs, Squalus blainvillei (Risso, 1826), captured iri the NE Aegean Sea suggests that they mainly consumed, in order of importance, crustaceans and teleost fishes (I.R.I. -7098.59 and 2734.8, respectively). Liocarcinus spp. and Parapenaeus iorign ostris were the most frequent prey items of the examined specimens of long nose spurdogs (¡.R.I. ~ 2072.74 and 1143.2, respe< lively). Key words: Squalidae, longnose spurdog, Squalus blainvillei, stomach contents, Aegean Sea CONTENUTi STOMACAL! DELLO SPiNAROLO BRUNO, SQUALUS Bl.AINVlLLEI {RISSO, 1826) DELL'EGEO NORD-ORIENTALE sinusi L'esame de; contenuti stomacali di spinarolo bruno, Squalus blainvillei (Ri s so, 1826), catturato nell'Egeo nordorientale, suggerisce che la sua alimemazione si basi, in ordine di importanza, su crostacei e teleostei (I.R.I. -7098,59 e 27.14.8, rispettivamente). Liocarcinus spp. e Parapenaeus longlrostris sono risultati le prede più frequenti degii esemplari esaminsti di spinarolo brunu 'I.R.I. - 2072.74 e i 14.1.2, rispettivamente). Parole chiave: Squalidae, spinarolo bruno, Squalus blainvillei, contenuti stomacal), mar L'geo 173 ANN ALES ■ Ser. hist. nat. • 12 • 2002 • 2 Hakar» KA6ASAKAI: STOMACH CONTENTS Or l ilt lONGNOSk' Sf'UKOOC. SQUALUS ÙLiMNVtUtl(RISSO, 1S2W .... 173.176 INTRODUCTION The longnose spurdog, Squalus blainvillei (P.isso, 1826) (Fig. 1) is a widespread member of the family Squalidae and it generally occurs at depths between 16 and 440 m (Compagno, 1984). The occurrence of this shark in the Mediterranean Sea as well as along the Turkish coast is well documented by several researchers (e.g.. Ale?!ray, 1987; Kabasakal 2002a, in press; McEac-hran & Branstetter. 1984; Slastenenko, 1955-1956; and Torlonese, 1956). Elasmobranchs are among the top predators in the marine environment and have an important role in the marine ecosystem in relation to the populations of both fish and invertebrates at lower trophic levels (Ellis et a!., 1996), Furthermore, there is always a competition between the fishermen and the marine predators feeding on commercially valuable species, and the Interactions among these predators and the populations of commercially important marine species should therefore be carefully examined (Kabasakal, 2002b, in press). There have been several studies describing the stomach contents of the squaliforrn sharks of a specific area in the Mediterranean Sea, for example, jardas (1972a, 1972b) in the Adriatic Sea, Kabasakal & Unsa! (1999) and Kara-gam et a I. (1996) in Turkish seas, and Macpherson (1980) in the western Mediterranean. The aim of the present study is to provide some preliminary data on the stomach contents of 5. blainvillei, captured in the NE Aegean Sea. Fig. 1: Longnosc spurdog, Squalus blainvillei (Risso, 1826). (Drawing: A. DeMaddalena) SI. 1: Rjavi trnez, Squalus blainvillei (Risso, 1826). (Risba: A. De Maddalena) MATERIAL AND METHODS In November 2000, specimens of S. blainvillei were collected by means of a commercial fishing trawler with a cod-end mesh opening of 22 mm from knot to knot, in the NE Aegean Sea (Station 1: 40°28' N - 26°00' €, depth = ÔO m, n = 20; Station 2: 40°33' N - 25°59't', depth = 70 m, n = 25; Fig. 2). All haulings were carried out during the day time. Total length (TOT; according to Compagno, 1984) of the sharks was measured to the nearest mm with a mesurlng tape. Total lengths of the examined sharks ranged between 350 to 420 mm. Di- Fig. 2: Sampling stations in the north-eastern Aegean Sea iir. indicates St. 1 and indicates St. 2); (&) on the small map indicates the area investigated. SI. 2: Vzorčišča v severovzhodnem Egejskem morju (A ponazarja 1. vzorčišče, ® 2. vzorčišče); (•=>) na malem zemljevidu označuje raziskovano območje. gesti ve tracts of the specimens were removed arid immediately fixed in 5 percent formalin in sea water. The fixed stomach contents were finally preserved In 70% ethanol. Prey items found in the stomachs were identified to the possible lowest taxon. Preys were dried on the pa[>er towel at room temperature for one hour, weighed to the nearest 0.05 g on precision balance and then counted. Percent numerical (PN%), weight (PW%) and frequency of occurrence (PO%) values of prey items were calculated, and these values were used to calculate the Index of Relative Importance "I.R.I." of each prey item, according to the following formulae (Cailllet etal1986); I.R.I. = (PN% + PW%) x PO% According to Cailliet et al. (1986), the maximum value of I.R.I. would be 20000. The number of fish with empty stomachs was expressed as a percentage of the total number examined (the Index of Vacuity, IV; Ellis et al. 19%). RESULTS AND DISCUSSION The aim of the stomach content analysis is to provide information on the contribution of different prey to the diet, indicating the position of a fish within the genera! trophic web. Thirty-three (73.3%) of the 45 examined stomachs of S. blainvillei were found to contain food (IV = 26.6%). Dietary composition of full stomachs is summarised in Table 1 and graphically expressed in Fig. 3. 174 ANN ALES ■ Ser. hist. nat. • 12 • 2002 • 2 H»U> KABASAKAL: STOMACH COWTIN is Of THC lONGNOSt SF'URPOC. squalus blainvillei fflSSO, 1526»..., 173-176 Tab. 1: Composition of the stomach contents of the examined specimens of Squalus blainvillei, and numerical (PN%i, weight (PW%), and frequency of occurrence (PO%) values of prey items. Tab. 1: Struktura hrane v želodcih pregledanih primerkov rjavih trnežev Squalus blainvillei in vrednosti, kar zadeva numeričnost (PN%), težo (PW%) in frekvenco pojavljanja (PO%) enot plena. The data in this study suggest that S. blainvillei mainly consumed, in order of importance, crustaceans and teleost fishes il.R.I. ~ 7098.59 and 2734.8, respectively, Tab. 1). Crustaceans were found ir all or the examined stomachs and the epibenthic decapods consisted the major part of the identified c rustac.eans. Liocarcinus spp. and Parapenaeus longirostris were the most frequent prey items of the examined specimens of longnose spur-dog {I.R.I. w 2072.74 and 1143.2, respectively, lab. 1 and Fig. 3). Regarding its I.R.I value, Sepia ehgans occupies the third rank (I.R.I. = 445.57) after Liocarcinus spp. and Parapenaeus longirostris. In comparison with the most frequent prey organisms. I.R.I. values of tire poly chaete, tuphrosine foliosa, and the lesser spotted est shark, Scyliorhinus catucula, were remarkably lower (I.R.I. - 7.38 and 5.37, respectively, Tab. 1 and Fig. 3), and in the light of this result, both animals can be considered as accidental preys oi 5. blainvillei. lardas (1cJ72a) examined 4.3 Adriatic specimens of 5. blainvillei and recorded three species of henthic and epibenthic teleost fishes, five species of crustaceans and four species of cephalopoda in the stomachs, jardas (1972a) also reported that 5. blainvillei has a preference for Cephalopoda and Crustacea in its diet. However, in the present study, by contrast, cephalopods occupy the third rank (I.R.I. - .308.79, Tab. 1) after crustaceans and teleost fishes. Predation on the eggs and juveniles of the scyllo-rhinids by squaliform sharks has been well documented in some species (Barrull & Mate, 2001, in Oxynotus centring and Macpherson, 1980, in Da I alias licha). Tiie continental shelf and slope of the northern Aegean Sea is recognized as a breeding and nursery ground for several elasmobrandts, including scyliorhinids by D'Onghia et at. (1995) and Kabasakal (2002a, in press). Because of their high fat and protein content as well as the easy ac-cesibllty, cat shark eggs and neonates can be an important nutritional source for bottom-dwelling sharks. It would be worth finding out how this predation by squalirorm sharks could affect the caishark population over this nursery ground. Although preliminary, the analysis of the stomach contents of S. blainvillei indicates that the longnose spurdog is a generalist predator feeding mainly on crustaceans and teleost fishes, as well as cephalopods and polyohaeles. ACKNOWLEDGEMENTS The author wishes to thank the crew of the fishing trawler "$EKERBAVA 2" for their help during the sampling. i^-iKuvAa Him --„■■--, ,--.....-.......; ([.»•«a.liij Jm.