Seasonal occurrence pattern of leptocephali in the north Satsunan area, southern Japan FIS-P-14042 Gen Kume1, Satoru Jinno1, Toru Kobari1, Kazuhiro Shiozaki2, Atsushi Narumi1, Shuya Ito1, Kei Nakaya1, Mutsuo Ichinomiya3 and Tomohiro Komorita3 1 Aquatic Sciences, Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima 890-0056, Japan. Email: [email protected] 2 Food and Life Sciences, Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima 890-0056, Japan. 3 Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto, Japan.

Introduction nMany leptocephali are found in the Satsunan area, southern Japan throughout the year. nThey may include important fishery-targeting species. (e.g. Anguilla spp., spp., Muraenesox spp.) nThe purpose is to clarify the seasonal and spatial occurrence pattern of leptocephali in the north Satsunan area in relation to the Kuroshio.

Materials and methods n Field surveys • Field surveys were condected from February in 2015 to August in 2018 by RV Nansei-maru and in November in 2015 and November in 2017 by RV Kagoshima-maru. • Study stations were fixed 15 stations in the inshore of Kuroshio path, 2 stations in Kuroshio path and 2 stations in the offshore of Kuroshio path. A. .Inshore of Kuroshio path • Specimens were collected by the ORI net (diameter, 160 cm; mesh size, 335 µm) which was obliquely towed from the bottom (ca. 10 m above the depth) to the surface at approximately 2 knots for 30 min.

• Specimens were preserved in 99.5 % ethanol. B. Kuroshio path n Analyses Kuroshio • Species identification by morphological and genetic methods (16SrRNA)* and morphological measurements *16Sar-L (CGCCTGTTTATCAAAAACAT), 16Sbr-H (GGTCTGAACTCAGATCACGT) (Kurogi et al. 2016) C. Offshore of Kuroshio path

Fig.1 Stations in Satsunan area Results and discussion 35 Kuroshio path n=31 Offshore of Kuroshio path n=36

) 30 Table 1. Seasonal occurrence of leptocephali in inshore of Kuroshio path ㎥ Family Species Spring Summer Autumn Winter Total 25 Synaphobranchidae Congrinae spp. 1 9 - 10 20 Gnasophis spp. 13 5 66 - 84 Gnasophis 15 Ariosoma spp. 4 26 5 - 35

Unidentified 23 11 11 1 46 10 Ophichchidae

Kaupichthys japonicus - - 1 - 1 Chlopsidae Abundance(n/1000 5 Nettastomatidae Robinsia catherinae - 2 - - 2

Muraeninae spp. 2 4 1 1 8 0 Muraenidae

Gymnothorax minor 3 2 - - 5 Spring Summer Autumn Winter Muraenidae Enchelycore lichenosa - 1 - - 1 Fig. 3 Srasonal abundance of leptocephali in inshore of Kuroshio path Unidentified - 2 1 - 3 Fig. 5 Species composition of leptocephali in Kuroshio path and offshore of Kuroshio path in 100 Ophichthinae spp. - 12 1 - 13 autumn 100 Ophichchidae Myrophinae spp. 2 - 1 - 3 90 90 80 Inshore of Kuroshio path Unidentified 3 3 1 - 7 70 80 60 n=84 Saurenchelys lateromaculata - 3 4 - 7 50 (%) Saurenchelys stylura - - 3 - 3 40 Nettastomatidae 70 30 Saurenchelys spp. - 3 1 - 4 Inshore of Kuroshio path 20 n=121 10 Unidentified - 3 3 - 6 60 0 100 44 46 48 Nemichthys scolopaceus - 2 - - 2 90 Nemichthyidae 80 Nemichthys spp. - 1 - - 1 50 70 Kuroshio path Muraenesocidae Muraenesox spp. 2 118 1 - 121 60 40 50 n=7 Derichthyidae Derichthys serpentinus - 3 - - 3 40 30 Synaphobranchidae Unidentified - - 24 - 24 30 20 Frequency ofoccurrence Frequency 10 0 20 Frequency of occurrence (%) 100 Spring n=54 Summer n=202 90 80 10 70 60 Offshore of Kuroshio path 50 n=11 0 40 4 6 8 10 12 14 16 18 20 30 20 Body length (mm) 10 0 Fig. 4 Body length composition of Muraenesox spp. in inshore of 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Kuroshio path Body length (mm) Table 2. Occurrence of leptocephali in Kuroshio path (B) Fig. 6 Body length composition of spp. in Satsunan area and offshore of Kuroshio path (C) in autumn 100 Family Species B C 90 Inshore of Kuroshio path 80 n=24 Congrinae spp. - - 70 60 Gnasophis spp. 7 11 50 Congridae - - 40 Ariosoma spp. 30 Autumn n=133 Winter n=2 Unidentified - - 20 10 Kaupichthys japonicus - - 0 Chlopsidae Robinsia catherinae - - 100 90 Muraeninae spp. 1 - 80 Kuroshio path Gymnothorax minor - - 70 n=16 Muraenidae 60 Enchelycore lichenosa - - 50 Unidentified - - 40 30 Ophichthinae spp. 6 2 20 10

Ophichchidae Myrophinae spp. - - Frequency of occurrence (%) 0 Unidentified - - 100 Saurenchelys lateromaculata - - 90 80 Saurenchelys stylura 1 - 70 Offshore Kuroshio path Nettastomatidae Saurenchelys spp. - - 60 n=23 50 Unidentified - - 40 Nemichthys scolopaceus - - 30 Nemichthyidae 20 Nemichthys spp. - - 10 Congridae Gnathophis Muraenesox Synaphobranchidae Congrinae Muraenesocidae Muraenesox spp. - - 0 6 8 10 12 14 16 18 20 22 24 26 28 30 Ophichthidae Ariosoma Nettastomatidae Muraenidae Others Derichthyidae Derichthys serpentinus - - Body length (mm) Fig. 2 Seasonal species composition of leptocephali in inshore of Kuroshio path Synaphobranchidae Unidentified 16 23 Fig. 7 Body length composition of Dysomma spp. in Satsunan area

Ø Leptocephali were identified to 22 taxonomic groups and the most dominant species were Gnathophis spp., Dysomma spp. and Muraenesox spp. Ø Most of larvae were thought to be dispersed from the East China Sea, where their main spawning grounds exist, to the study area by the Kuroshio Current. Ø Muraenesox spp. are composed of M. cinereus and M. bagio, both of which are important fishery-targetting species. Leptocephali of Muraenesox spp. included a substantial number of small individuals (< 10 mm body length), suggesting that their spawning ground would exist adjacent to the study area.

Reference Kurogi H, Chow S, Yanagimoto T, Konishi K, Nakamichi R, Sakai K, Ohkawa T, Saruwatari T, Takahashi M, Ueno Y, Mochioka N (2016) Adult form of a giant anguilliform leptocephalus Thalassenchelys coheni Castle and Raju 1975 is Congriscus megastomus (Günther 1877). Ichthyol Res 63:239–246