Annotated records of scombroid larvae distribution in northeastern Mediterranean waters

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1 8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας 937 Annotated records of scombroid larvae distribution in northeastern Mediterranean waters V. Vassilopoulou, A. Siapatis, C. Papaconstantinou, & E. Caragitsou, Hellenic Centre for Marine Research, Hellinikon 16777, Athens, Greece Abstract Data on the distribution of scombroid fishes larvae in northeastern Mediterranean are provided to contribute to our knowledge on spawning periods and locations of these highly migratory species. Samples were collected during a three-year survey conducted on a fortnight basis in summertime in the Thermaikos Gulf, the Thracean and the North Aegean Sea. Of the six scombroids known to dwell in Mediterranean waters, larvae of Thunnus alalunga, Euthynnus alleteratus, Auxis rochei and Xiphias gladius were present in our samples, while there was no sign of Thunnus thynnus and Sarda sarda. A. rochei larvae were relatively more frequently encountered, followed by E. alleteratus. T. alalunga and X. gladius exhibited a very scarce presence. All scombroid larvae were collected close to the sea surface (<25m). A. rochei larvae abundance peaked at the end of the summer. Στοιχεία και σχόλια σχετικά με την κατανομή προνυμφών σκομβροειδών ιχθύων στη βορειοανατολική Μεσόγειο περιληψη Στην εργασία αυτή παρουσιάζεται η κατανομή των προνυμφών των σκομβροειδών στη βορειοανατολική Μεσόγειο ώστε οι πληροφορίες αυτές να συνεισφέρουν στην καλύτερη γνώση των περιοχών και της περιόδου ωοτοκίας των μεταναστευτικών αυτών ψαριών. Τα δεδομένα προέρχονται από δειγματοληψίες οι οποίες έγιναν σε δεκαπενθήμερη βάση την περίοδο του καλοκαιριού, κατά τη διάρκεια μιας τρίχρονης έρευνας στην περιοχή του Θερμαϊκού, του Βόρειου Αιγαίου και του Θρακικού. Aπό τα έξι είδη της οικογενείας Scombridae που είναι γνωστό ότι ζουν σε νερά της Μεσογείου, στα δείγματα βρέθηκαν μόνον προνύμφες του Thunnus alalunga, του Euthynnus alleteratus του Auxis rochei και του Xiphias gladius ενώ απουσίαζαν το Thunnus thynnus και το Sarda sarda. Από τα τέσσερα είδη που αναγνωρίστηκαν, μόνον το A. rochei παρουσίασε σχετικά αυξημένη παρουσία, ακολουθούμενο μακράν από το E. αlleteratus, ενώ η παρουσία των υπολοίπων ήταν ιδιαίτερα περιορισμένη. Όλες οι προνύμφες συλλέχθηκαν κοντά στην επιφάνεια της θάλασσας (μέγιστο βάθος 25m). Το A. rochei παρουσίασε μέγιστη αφθονία στα δείγματα που προέρχονταν από το τέλος του καλοκαιριού. Λέξεις Κλειδιά: larvae / scombroids/ Greek Seas

2 938 8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας INTRODUCTION Ιchthyoplankton data on large pelagics are of primary importance for delineating their spawning grounds and seasons, contributing thus to a better knowledge of the biology of these highly migratory species. In the Mediterranean, there are ichthyoplankton data on Xiphias gladius and Sarda sarda (Demir, 1957; 1970, Sanzo, 1922; 1930; 1932 Sella, 1911; Tanning,1955), while there is also information on the distribution of the larvae of certain tuna species (Piccinetti & Manfrin, 1995). In Greek waters, since the time of the Danish Dana and Thor expedition (Fage, 1920; Schidt, 1918), limited ichthyoplankton surveys on pelagic fish species have been carried out. Very few data also exist on the abundance of eggs and larvae of scombroids (Caragitsou et al., 1993). The objective of the present study is to report on the distribution of the larvae of scombroids in northeastern Greek seas, in order to shed light on the time and locations of the species spawning activities in the study area. MATERIAL and METHODS Ichthyoplankton samples were collected at 113 stations (figure 1) in the Thermaikos Gulf (subarea I: 29 stations), the Thracean Sea (subarea II: 39 stations) and the north Aegean Sea (subarea III: 45 stations), during a three-years period, from 1992 to 1995, on a fortnight basis, from June through September, when spawning of scombroids is known to take place in Medi- Figure 1. Location of sampling stations in the Thermaikos Gulf (subarea I), the Thracean Sea (subarea II) and the NW. Aegean Sea (subarea III). (+ : tows, : Methot trawl tows)

3 8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας 939 terranean waters (Megalofonou et al., 1995). Plankton hauls were made using a with mesh sizes of 300 and 500 μm. Hauls were taken obliquely at a ship s speed of 2.5 knots, from just above the sea bottom to the surface or to a maximum depth of 150 m where the bottom is deeper. In Sporades basin (N.W. Aegean sea) known to be an important nursery ground for scombroids (Megalofonou, 1990), additional data were gathered from horizontal surface tows using the s and Methot trawl (3mm mesh size net) during the summer of All samples were preserved in 4% neutralized formalin. In the laboratory all larvae were removed, identified to the lowest possible taxon, counted and measured (standard length (SL)). The absolute number of larvae per haul was recorded and the relative number per 100 m 3 filtered water was calculated. RESULTS and DISCUSSION In all, 68 fish taxa were identified in the samples collected in the study area. Of the scombroid species existing in Mediterranean waters (Collette & Nauen, 1983), only Thunnus alalunga, Euthynnus alleteratus, Auxis rochei and Xiphias gladius appeared in the ichthyoplankton samples of the present survey. Scombroid larvae comprised 4.1% of the total number of all fish larvae collected during this study. Thunnus alalunga was represented by only one specimen (Table I), which was collected in subarea III, off the NE coast of Euboea Island, in late August The specimen was 4.4 mm long (SL) and was captured by a during a horizontal tow. Two postlarvae of X. gladius were caught by the Methot trawl in August and September. This seems to be consistent with another observation regarding the existence of increased spawning activities of swordfish in east Mediterranean in June and July (De Metrio et al., 1989). As shown in Table 1, the first postlarva was 15.1mm SL and was caught off the Table I.- Sampling gear, number of larvae and body size (SL) of E. alleteratus, T. alalunga, X. gladius and A. rochei larvae collected in the study area from 1992 to Sampling gear Number of larvae Length range (SL,mm) E. alleteratus T. alalunga X. gladius , 15.1 A. rochei

4 940 8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας Pelion peninsula in early August 1992, while the second one was 12.6 mm SL and was caught off the southern coast of Skopelos in mid-september E. alletteratus numbered 16 larvae, whose lengths ranged from 4.1mm (larva caught at the end of July) to 10.2 mm (larva caught at the end of August). Four of these were collected by Methot trawl, six by Bongo, during horizontal tows in depths from the surface to 25 m, and six by Bongo, during oblique tows (Table I). All specimens came from Subarea III (Figure 1). These catches suggest the presence of a spawning ground for the species in the study area, that was previously thought to be limited only in the Central part of the Mediterranean (Piccinetti & Manfrin, 1995). Auxis rochei larvae were encountered more frequently than all the rest. 354 specimens (334 by Bongo, with SL ranging from 2.2 to 10.5 mm, and 20 by Methot trawl, with SL from 5 to 11 mm) were collected during the whole survey study (table I). Most of these specimens were collected in tows conducted till depths of m. The 82.5% of the A. rochei larvae were found in subarea III, while this is the only species, whose larvae appeared also in subarea I. Relative abundance values of A. rochei larvae peaked from late August till mid-september, which possibly suggests that spawning activities in the Aegean peak at the end of the summer. The limited number of scombroid larvae, particularly of T. alalunga and X. gladius as compared to E. alleteratus and A. rochei could be related to the fact that the latter two are known to be more coastal, in relation at least to Thunnus and Xiphias (W. J. Richards, personnal communication), and during the present survey our sampling stations were concentrated rather close to the shore. The fact that N. Aegean comprised more scombroid larvae as compared to the other two study areas could result by their drifting there due to the southward surface current along the northeastern Greek coasts in the Aegean (Theocharis & Georgopoulos, 1989). Thunnus thynnus and Sarda sarda were not collected in the framework of the present study. S. sarda appears to migrate for spawning, from the Aegean to the Black Sea in April and returns to the Aegean in October (Demir, 1957), which could justify the reason for not catching any samples of this species during this survey. On the other hand, T. thynnus eggs and larvae occur in Mediterranean waters from mid- June till early August (Cavallaro et al., 1998), which suggests that the species larvae were probably missed during our samplings. Our study underlines the necessity to conduct a new survey based on a sampling scheme, specially designed to fill sampling gaps identified herein, which could then clarify specific points raised by current findings. REFERENCES Caragitsou E., Siapatis A., Giagnisi M., Papaconstantinou C., Distribution and abundance of the ichthyoplankton (eggs and larvae) in the N. and W. Aegean Sea, Proc. 4th Congress Oceanography and Fisheries, Rhodes (1993) 6 p. Cavallaro, G., Cephali, A., Potoschi, A, Alcunni aspetti biologici e pesca di pesces pada, tonno ed alalunga in studi eseguititra il 1984 ed il 1996 nel Tirreno meridionale e nello Ionio. Biol., Mar. Mediter., 5(3) (1998) Collette B.B., Nauen C.E., Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date, FAO Fish. Synops. 125, 1983, 137 p. De Metrio G., Megalofonou P., Tsellas S., Fishery and biology of the swordfish Xiphias gladius L., 1758, in Greek waters, FAO Fish. Rep. 412 (1989) Demir M., Migrations of Sarda sarda Bloch in Black, Marmara, and Aegean sea: the probable spawning places and times, FAO Tech. Pap. 4 (1957)

5 8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας 941 Demir N., Contribution to the knowledge of the Swordfish (Xiphias gladius L.) Egg, Journees Etud. Planctonol. (1970) Fage L., Engraulidae, Clupeidae, Rep. Dan. Oceanogr. Exped. Mediterr (Biology) A 9 (1920) Megalofonou P., Size distribution, lengthweight relationships, age and sex of albacore, Thunnus alalunga Bonn., in the Aegean Sea, Collect. Vol. Sci. Pap. ICCAT, 33 (1990) Megalofonou P., Dean J. M., De Metrio G., Wilson C., Berkeley S., Age and growth of juvenile swordfish, Xiphias gladius Linnaeus, from the Mediterranean sea, J. Exp. Mar. Biol. Ecol. 188 (1995) Piccinetti C., Manfrin G. P., Distribution des larves des thonides en Mediterranee, FAO Fish. Rep. 494 (1995) Sanzo L., Uova e larve di Xiphias gladius L., Mem. Com. Talassogr. Ital. 79 (1922) 17 p. Sanzo L., Giovanissimo stadio larvale di Xiphias gladius L., di mm. 6,4, Mem. Com. Talassogr. Ital. 79 (1930) 17 p. Sanzo L., Uova e primi Stadi Larvali di Petamis sarda C. V., R. Mem. Com. Talassogr. Memoria CLXXV 1, 1932, 21 p. Schmidt J., Argentinidae, Microstomidae, Ophistoproctidae, Odontostomidae, Rep. Dan. Ocean. Exped Medit. adjac. Seas (1918) Sella M., Contributo alla conoscenza della riproduzione e dello sviluppo del pesce-spada (Xiphias gladius L.). Mem. Com.Talassogr. Ital. 2 (1911) 16 p. Tanning A. V On the breeding of the swordfish (Xiphias), Pap. Mar.. Biol. Oceanogr. 3 (1955) Theocharis A., Georgopoulos D., Physical Parameters: Hydrology, in: National Centre for Marine Research (Ed.), Pollution Research and Monitoring programme in the Aegean and Ionian Seas, Athens, 1989, 175 p.

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