24 
National Marine 
Fisheries Service 
NOAA 
Abstract —The population structure 
of the ocellate spot skate (Okamejei 
kenojei), distributed in the western 
North Pacific, was assessed on the 
basis of genetic variations in the 
mitochondrial DNA control region 
(mtCR) and differences in morpho¬ 
logical characters and features. Sig¬ 
nificant genetic differentiation in 
mtCR was observed among 6 region¬ 
al populations along the Japanese 
Archipelago and Korean Peninsula. 
Unique haplotypes found in Osaka 
Bay and off the east coast of Kyushu 
Island suggested an absence of gene 
flow from the other 5 regions. In ad¬ 
dition, comparisons of morphological 
characters and features, including 
measurements, nuchal thorn counts, 
differences in maturity size, and col¬ 
oration, indicated that populations 
of ocellate spot skate from Osaka 
Bay and from off the Pacific coast of 
northern Japan were clearly distin¬ 
guishable from 4 other regional pop¬ 
ulations. Together with molecular 
differentiation among the regional 
populations, they suggest that the 
straits, ocean currents, and limited 
migrations are significant barriers 
to gene flow between populations. 
Future fisheries management of the 
species is discussed on the basis of 
the present findings. 
Manuscript submitted 6 July 2018. 
Manuscript accepted 26 November 2018. 
Fish. Bull. 117:24-36 (2019). 
Online publication date: 4 December 2018. 
doi: 10.7755/FB.117.1.4 
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. 
Fishery Bulletin 
fir established in 1881 •<?> 
Spencer F. Baird 
First U S Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Population structure of the ocellate spot skate 
(Okamejei kenojei) inferred from variations in 
mitochondrial DNA (mtDNA) sequences and from 
morphological characters of regional populations 
Ryo Misawa (contact author ) 1 
Yoji Narimatsu 2 
Hiromitsu Endo 3 
Yoshiaki Kai 1 
Email address for contact author: batoideafish@gmail.com 
1 Maizuru Fisheries Research Station 
Field Science Education and Research Center 
Kyoto University, Nagahama, Maizuru, 
Kyoto 625-0086, Japan 
2 Tohoku National Fisheries Research Institute 
Fisheries Research and Education Agency 
25-259 Same-machi, Flachinohe, 
Aomori 031 -0841, Japan 
3 Laboratory of Marine Biology 
Faculty of Science and Technology 
Kochi University, 
2-5-1 Akebono-cho, 
Kochi 780-8520, Japan 
Many elasmobranch fishes (sharks, 
rays, and skates) are particularly 
vulnerable to overfishing because of 
their large size, slow growth, late 
maturity, and low fecundity (Brand- 
er, 1981; Dulvy et ah, 2000; Griffiths 
et ah, 2010; Griffiths et ah, 2011). 
These life-history traits translate 
into low rates of reproduction and 
low potential rates of population in¬ 
crease (Walker and Hislop, 1998). 
Elasmobranch fishes are also target¬ 
ed by fisheries because their meat, 
fins, and liver oil are commercially 
valuable (Dulvy et al., 2014; David¬ 
son et ah, 2016). In addition, elasmo¬ 
branch fishes are often caught as by- 
catch of fisheries that focus on more 
commercially valuable teleost fish 
species, such as tunas and demersal 
fishes (Dulvy et ah, 2014). The fish¬ 
ing pressure on elasmobranchs is in¬ 
creasing and therefore their extinc¬ 
tion risk and conservation interest 
are being discussed on a global scale 
(e.g., Dulvy et ah, 2014; Davidson 
et ah, 2016). Shallow-water elasmo¬ 
branchs particularly have a higher 
risk of extinction or decrease in 
population because of their constant 
exposure to coastal fisheries (Dulvy 
et ah, 2014). The ocellate spot (or 
spiny) skate Okamejei kenojei (fam¬ 
ily Rajidae) is widely distributed 1) 
in shallow coastal waters of 20-230 
m depth (mainly 30-100 m) in the 
western North Pacific: 2) from the 
coastal waters off southern Hokkai¬ 
do, Japan, southward to waters off 
northern Taiwan, including 3) along 
the Pacific coast of Japan; 4) within 
the Sea of Japan; 5) the East China 
Sea; and 6) the Yellow Sea (Ishihara, 
1987; Hatooka et ah, 2013; Last et 
ah, 2016). The age at maturity of 
the species has been estimated to 
be about 3 years, and females pro¬ 
duce at least 300 egg capsules during 
