Reproductive Biology and Embryonic Diapause as a Survival Strategy for the East Asian Endemic Eagle Ray Aetobatus narutobiei

Batoids comprise five of the seven most threatened families of sharks and rays. The East Asian endemic Naru eagle ray Aetobatus narutobiei is a large bodied ray whose estuarine habitat overlaps with an economically valuable bivalve fishery. In response to decreased bivalve yields, the government initiated a predator control program and as a result, Naru eagle rays have faced intense and targeted fishing pressure during the last two decades. The long-term impacts of the predator control program on the population of rays and bivalves and their balance in the ecosystem are unknown because the life history of the Naru eagle ray has not been characterized. To begin to fill these critical knowledge gaps, the reproductive life history of the Naru eagle was described. Females mature at a larger size than males and require nearly twice as many years to reach maturity (DW50, 952.0 mm vs. 764.2 mm; Age50, 6.0 years vs. 3.5 years). Both males and females reproduce annually and their reproductive cycles are synchronized and seasonal. Females have a single ovary and paired uteri, are viviparous, and reproduce via matrotrophic histotrophy. Mating occurs in August and September and gestation lasts approximately 12 months including a 9.5-month diapause that begins soon after mating and ends in June of the following year, leaving 2.5 months for embryos to complete development. Fecundity ranged from 1 to 7 embryos per brood (n = 158, mean ± SD = 3.36 ± 1.26) and was positively correlated with female disc width (linear regression; F = 105.73, d.f. = 151, P < 0.05). Naru eagle rays are vulnerable to overfishing because of their low fecundity, long reproductive cycle and long time to reach sexual maturity. Obligate embryonic diapause during overwintering and seasonal migrations is a survival strategy that benefits the adults and neonates. This research is a valuable resource to help guide science-based management, conservation and protection of the endemic Asian A. narutobiei and its nursery areas

Takifugu rubripes predation on the venomous stingray Dasyatis akajei : gut content evidence from an estuary in the western Seto Inland Sea, Japan

瀬戸内海の河口干潟域でトラフグTakifugu rubripes 稚魚による刺毒魚アカエイDasyaris akajei の捕食を初めて確認した。2012年9～11月と2014年10月に山口市椹野川河口で採集したトラフグ27個体（9.8～14.0cm SL, 11.9～17.5cm TL の食性を調査し2012年10月に採集した1個体（12.1cm SL, 15.1cm TL）の消化管内容物からアカエイ1個体を同定した。アカエイ被食部位は，尾部を含めた体後部で，計40個の断片として検出された。異なる2通りの復元方法により，体盤幅はそれぞれ11.1 ±2.4cm (±95% 信頼区間），12.8±3.7cm（同）と推定された。被食量は，前者ではアカエイ体重の18.6%，後者では11.8% に及ぶと考えられた。Tiger pufferfish, Takifugu rubripes (Family: Tetraodontidae), is an important commercial fish in Japan. Landings of Tiger pufferfish at the Shimonoseki fish market, Yamaguchi Prefecture, where ca. 60% of the pufferfish caught in Japan is landed has decreased remarkably from 1,841 metric tons at the peak of catch in 1987 to 111 metric tons in 2013. This reduction in stock indicates the pufferfish population of Japan has reached a critical condition. As a result, the local population in Ariake Bay, East China Sea has been evaluated as an endangered local population by the Nagasaki Prefectural local government (Red List 2011, category: LP). Necessarily, it is desired that the resources should recover from the present state. It is known that juvenile tiger pufferfish grow in estuaries until late fall. They forage on small benthic animals there. Therefore, it is necessary to clarify the feeding habits of the juvenile pufferfish in the intertidal area in detail. In this report, we clarified the predation on the Whip stingray, Dasyatis akajei by juvenile Tiger pufferfish in the estuary area. Because the stingray is well-known as a venomous species, it has been considered that no fish species could prey on stingrays in this area. In September-November 2012 and October 2014, 27 individuals of T. rubripes (9.8-14.0cm SL, 11.9-17.Scm TL) were collected in the Fushino River estuary in Yamaguchi Prefecture, western Seto Inland Sea to examine their feeding habits. A D. akajei was identified from the gut contents of the juvenile T. rubripes, 12.1 cm SL (15.1 cm TL), which was collected in October 2012. The prey, the stingray's body was detected as a total of 40 only partially digested pieces including 4 distinct pieces of the tail being the posterior portions of the stingray's body. By two different restoring methods, the disc width of the stingray was estimated to be 11 .1 ± 2.4cm (± 95% confidence interval) and as 12.8 ± 3.7cm. The amount of stingray body tissue consumed to total stingray body weight was estimated to be 18.6% of the former restoring method and 11.8% by the latter. In the Seto Inland Sea of Japan, resources of benthotrophic fish species, such as flatfishes and pufferfishes, which use the estuary in their early life history, have decreased remarkably. For recovery and regeneration of these critical resources, it is necessary to clarify the relationships between organisms and the estuarine ecosystem

Genetic population structure of the polkadot skate (Dipturus chinensis) around Japan, based on mitochondrial DNA sequences and polymorphic microsatellite loci

The genetic population structure of the polkadot skate (Dipturus chinensis) around Japan was examined by using mitochondrial (mt) cytochrome (cyt) b gene sequences and polymorphic microsatellite (simple sequence repeat [SSR]) loci. Results of phylogenetic analysis based on mt cyt b gene sequences reveal 2 major lineages, clades A and B. Clade A consists of populations in the Sea of Japan and the East China Sea. Clade B contains populations in the Pacific Ocean and is divided into 2 subclades, clades B1 and B2, which correspond to the populations along the southern and northern coasts of Japan, respectively. This genetic differentiation is also supported by results from SSR analysis. The divergence of clades A and B may reflect isolation of the East China Sea from the Pacific Ocean in the Early Pleistocene. After diverging from clade A, clade B might have extended its distribution northward along the Pacific coast of Japan and divided into clades B1 and B2 in the Middle Pleistocene. The polkadot skate is clearly structured into 3 genetically discrete populations around Japan that should be treated as independent management units for management of this species in the future

A New Species of Eagle Ray Aetobatus narutobiei from the Northwest Pacific: An Example of the Critical Role Taxonomy Plays in Fisheries and Ecological Sciences

Recent taxonomic and molecular work on the eagle rays (Family Myliobatidae) revealed a cryptic species in the northwest Pacific. This species is formally described as Aetobatus narutobiei sp. nov. and compared to its congeners. Aetobatus narutobiei is found in eastern Vietnam, Hong Kong, China, Korea and southern Japan. It was previously considered to be conspecific with Aetobatus flagellum, but these species differ in size, structure of the NADH2 and CO1 genes, some morphological and meristic characters and colouration. Aetobatus narutobiei is particularly abundant in Ariake Bay in southern Japan where it is considered a pest species that predates heavily on farmed bivalve stocks and is culled annually as part of a \u27predator control\u27 program. The discovery of A. narutobiei highlights the paucity of detailed taxonomic research on this group of rays. This discovery impacts on current conservation assessments of A. flagellum and these need to be revised based on the findings of this study

Biology of Herbivorous Fish in the Coastal Areas of Western Japan

Seaweed beds in Japanese coastal waters have significantly declined in recent years and feeding by herbivorous fish has been identified as one of the potential causes of this decline. In the western coastal areas of Kyushu, seaweed consumption by fish species such as the mottled spinefoot (Siganus fuscescens), sea chubs (Kyphosus spp.), and the Japanese parrotfish (Calotomus japonicus) has become a matter of concern. Our research group has been investigating the biology of herbivorous fish in the coastal waters around western Kyushu and Okinawa. This paper presents some of the results of our work with a focus on the biology of herbivorous fish, including their distribution, age, growth, sexual maturity, sex change, feeding, behavioral ecology, and population structure. Investigation of the stomach contents of herbivorous fish revealed that Kyphosus bigibbus fed mainly on the seaweed sargassum throughout the year. In contrast, other fish supplemented their diet of seaweed with amphipods and other organisms. Experiments to determine food preference were performed on captive K. bigibbus, and their results supported the results of the stomach content analysis. Both experiments showed that the fish selectively fed on Sargassum fusiforme and Undaria pinnatifida. Herbivorous fish off the west coast of Kyushu were tracked using a biotelemetry technique, which indicated that the fish inhabited seaweed beds during the daytime. The activity of S. fuscescens and K. bigibbus markedly declined when the water temperature decreased to approximately 20°C and 17°C, respectively, but it was observed that these fish overwintered in these areas. This study demonstrates that the recent rise in winter ocean temperatures has extended the period of activity of herbivorous fish. The results contradict the hypothesis that herbivorous fish species migrate southward during colder periods.Nagasaki University Major Research Project: Restoration of Marine Environment and Resources in East Asi

Clasper and clasper skeleton of adult male <i>Aetobatus narutobiei</i>.

<p>Outline illustration of the left clasper. A: dorsal view of intact clasper (holotype FFNU-P-2001); B: dorsal view of clasper skeleton (paratype FFNU-P-2015). Abbreviations: apo – apopyle; axc – axial cartilage; cgr – clasper groove; hyp – hypopyle; mcd – dorsal marginal cartilage; mcv – ventral marginal cartilage; p2– pelvic fin; psp – pseudopera; pss - pseudosiphon; tcd – dorsal terminal cartilage; tcv – ventral terminal cartilage; vcp – ventral covering piece.</p