98 
Fishery Bulletin 119(2-3) 
Stéphan et al.’; Frodella et al., 2016; Im 
et al., 2017; Vargas-Caro et al., 2017; 
/ 
/ 
{ 
‘ 
/ 
Hf 
( \ Tsushima 
(7% Current — 
Sea of Japan }§ - 
—“@4 / Honshu .{ 
> c f onsnu 
Yellow Sea¥ Penin SNS 
9. 
Ryukyu Isls. 
BA *— Tsugaru Warm Current 
| 
Ferrari et al., 2018; Weltz et al., 2018; 
Misawa et al., 2019a, 2019b, 2020). The 
results of most studies reveal significant 
population structuring shaped by histor- 
ical, geographical, and environmental 
factors, indicating that Rajidae gener- 
ally have low dispersal ability. 
Japan is surrounded by complicated 
oceanic currents (Fig. 1): the Kuroshio 
—| Current flows from east of the Phil- 
ippines past Taiwan and the Ryukyu 
Islands to the Pacific coast of Kyushu, 
Shikoku, and southern Honshu of 
Japan; the Tsushima Current, which 
branches off from the Kuroshio Current 
off southern Kyushu, flows northward 
along the western coast of Honshu; 
and the Oyashio Current originates in 
the Arctic Ocean and flows southward 
past the Bering Sea to the Pacific coast 
of Hokkaido and northern Honshu. The 
population structures of rajid species 
as well as of various marine animals 
around Japan, it has been suggested, 
are affected by those currents (Kojima 
Figure 1 
Map of the 7 locations (black circles) around Japan where polkadot skate 
(Dipturus chinensis) were collected during 2010-2017. Also shown are the 
2 locations (gray circles) of the populations for which DNA sequences were 
obtained through the International Nucleotide Sequence Database Collab- 
oration. The dark and light gray lines with arrows indicate the flow and 
direction of oceanic currents. The numerals next to the circles correspond 
to the 9 locations: (1) Danjo Islands, (2) Goto Islands, (3) Koshiki-jima 
Islands, (4) Kyoto Prefecture, (5) Niigata Prefecture, (6) Kochi Prefecture, 
(7) Aomori Prefecture, (8) Taiwan, and (9) Korean Peninsula. Isls.=Islands; 
Penin.=Peninsula. 
species, including the polkadot skate, may result from 
their life history traits; as members of Elasmobranchii, 
they have slow growth rates, late attainment of sexual 
maturity, long life spans, and low fecundity (Brander, 
1981; Dulvy et al., 2000; Hara et al., 2018a), making them 
vulnerable to exploitation. 
Recently, basic life history traits, such as age, growth, 
and age at sexual maturity, and dietary habits of the 
polkadot skate were examined to establish conserva- 
tion and management strategies for this species (Hara 
et al., 2018a, 2018b). Genetic information, such as 
population structure, is important for fisheries man- 
agement and development of conservation policies for 
elasmobranch species (Domingues et al., 2018). To date, 
several studies on genetic population structure have 
been conducted for several species of Rajidae (Chevolot 
et al., 2006a, 2006b, 2007; Griffiths et al., 2010, 2011; 
et al., 1997, 2004; Akihito et al., 2008; 
Kokita and Nohara, 2011; Han et al., 
2012; Hirase et al., 2012; Hirase and 
Ikeda, 2014). For the ocellate spot skate 
(Okamejei kenojei), the distribution of 
which is similar to that of the polkadot 
skate, the force of warm currents, the 
Tsushima and Kuroshio Currents, has 
been reported to prevent dispersal of 
individuals (Misawa et al., 2019b). The 
Tsushima Current, as a dispersal bar- 
rier, has shaped the population struc- 
ture of the mottled skate (Beringraja 
pulchra), according to Misawa et al. 
(2019a). There is a possibility that the 
population structure of the polkadot skate is also affected 
by the currents around Japan. 
In this study, we examined the genetic population struc- 
ture of the polkadot skate around Japan by using partial 
sequences of mitochondrial (mt) cytochrome (cyt) b gene 
and polymorphic microsatellite (simple sequence repeat 
[SSR]) loci because those molecular markers will provide 
information that can help guide fishery management and 
! Stéphan, E., C. Hennache, A. Delamare, N. Leblanc, V. Legrand, 
G. Morel, E. Meheust, and J. L. Jung. 2014. Length at maturity, 
conversion factors, movement patterns and population genetic 
structure of undulate ray (Raja undulata) along the French 
Atlantic and English Channel coasts: preliminary results, 16 p. 
Working paper presented at the 2014 Working Group on Elas- 
mobranch Fishes (WGEF) meeting; Lisbon, 17—26 June. [Avail- 
able from ICES Secretariat, H. C. Andersens Blvd. 44-46, 1553 
Copenhagen, Denmark.] 
