97 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
@ established in 1881 < 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Abstract—The genetic population 
structure of the polkadot skate (Dip- 
turus chinensis) around Japan was 
examined by using mitochondrial (mt) 
cytochrome (cyt) 6 gene sequences and 
polymorphic microsatellite (simple 
sequence repeat [SSR]) loci. Results 
of phylogenetic analysis based on mt 
cyt 6 gene sequences reveal 2 major 
lineages, clades A and B. Clade A con- 
sists of populations in the Sea of Japan 
and the East China Sea. Clade B con- 
tains 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 sup- 
ported 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 dis- 
tribution northward along the Pacific 
coast of Japan and divided into clades 
B1 and B2 in the Middle Pleistocene. 
The polkadot skate is clearly struc- 
tured into 3 genetically discrete pop- 
ulations around Japan that should be 
treated as independent management 
units for management of this species in 
the future. 
Manuscript submitted 4 February 2021. 
Manuscript accepted 23 June 2021. 
Fish. Bull. 119:97-111 (2021). 
Online publication date: 19 July 2021. 
doi: 10.7755/FB.119.2-3.1 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Genetic population structure of the polkadot 
skate (Dipturus chinensis) around Japan, based on 
mitochondrial DNA sequences and polymorphic 
microsatellite loci 
Takahiro Kusaka'*> 
Kojiro Hara” 
Keisuke Furumitsu? 
Shinji Uehara? 
Yuta Yagi* 
Atsuko Yamaguchi” 
Naoki Yagishita (contact author)? 
Email address for contact author: n-yagi@nagasaki-u.ac.|p 
' Laboratory for Aquatic Biology 
Graduate School of Agriculture 
Kindai University 
3327-204 Nakamachi 
Nara 631-8505, Japan 
? Graduate School of Fisheries and 
Environmental Sciences 
Nagasaki University 
1-14 Bunkyo-machi 
Nagasaki 852-8521, Japan 
3 Fisheries Data Sciences Division 
Fisheries Stock Assessment Center 
Fisheries Resources Institute 
Japan Fisheries Research and 
Education Agency 
2-12-4 Fukuura 
Kanazawa, Yokohama 236-8648, Japan 
The polkadot skate (Dipturus chin- 
ensis) is distributed along the coast 
of Japan from Hokkaido southward 
to Kyushu, the East China Sea, the 
Korean Peninsula, and Taiwan (Fig. 1). 
It inhabits sandy to muddy bottoms at 
depths of 20-320 m, mostly shallower 
than 150 m (Yamada et al., 2007, 2009; 
Hatooka et al., 2013; Last et al., 2016). 
Until recently, the species had been 
confused with the Kwangtung skate (D. 
kwangtungensis), which occurs in the 
South China Sea (Last and Lim, 2010). 
However, Last et al. (2016) reclassified 
the species as D. chinensis on the basis 
of the differences in morphological 
characteristics. 
“ Niigata Field Station 
Demersal Fish Resources Division 
Fisheries Stock Assessment Center 
Fisheries Resources Institute 
Japan Fisheries Research and Education 
Agency 
1-5939-22 Suido-cho 
Chuou-ku, Niigata 951-8121, Japan 
> Nishinihon Institute of Technology 
9-30 Wakamatsu-cho 
Kochi 781-0812, Japan 
The polkadot skate is caught mostly 
by bottom-trawl fishing vessels in the 
East China Sea (Jeong and Ishihara, 
2009) and processed mainly for dried 
and paste products (Yamada et al., 
2007). The annual catch of rajid spe- 
cies, including the polkadot skate, in 
the East China Sea peaked at 17,000 
metric tons (t) in 1948 but has declined 
to approximately 100 t in recent years 
(Tokimura et al., 1998; Hara et al., 
2014). Moreover, the polkadot skate 
was commonly found in Korean fish 
markets before 2000; however, pres- 
ently, very few can be found in those 
markets (Jeong and Ishihara, 2009). 
The decrease in abundance of skate 
