Age, growth, and age at sexual maturity of the commercially landed skate species,Dipturus chinensis(Basilewsky, 1855), in the northern East China Sea

Abstract

SummaryAge, growth, and age at sexual maturity of the polkadot skate Dipturus chinensis, in the northern East China Sea were determined for a total of 614 specimens collected from thereafter, females grew larger than males. Maximum age recorded was 13 years for males and 15 years for females. Age at 50% sexual maturity was 8.22 years for males and 9.39 years for females. These results indicate that D. chinensis is slow growing, relatively long-lived, and late maturing, and therefore vulnerable to exploitation.

Length–Weight Relationships, Growth Models of Two Croakers (Pennahia macrocephalus and Atrobucca nibe) off Taiwan and Growth Performance Indices of Related Species

“…A growth ring is a part of an otolith that consists of one translucent zone and one opaque zone [115]. When the annual formation of the growth ring is validated, the age is usually determined by the number of ring counts [20,116,117]. However, this method ignores valuable information contained within a year's growth.…”

Age, growth parameters, and reproductive characteristics of the sharpspine skate (Okamejei acutispina) in the East China Sea

“…A total of 331 sharpspine skate (161 females and 170 males) were captured from April 2009 through November 2022 at depths of approximately 100-200 m in the central and northern East China Sea, off southwestern Japan (approximately between 27°30′N, 125°50′E and 32°20′N, 128°00′E). Skates were caught with bottom-trawl nets deployed from the commercial fishing vessels of the Yamada Suisan Co. Ltd. 2 (Nagasaki City, Japan) and the training ship of Nagasaki University (Hara et al, 2016(Hara et al, , 2018a(Hara et al, , 2018b. The TL (to the nearest 1 mm), disc width (DW, to the nearest 1 mm), body weight (BW, to the nearest 0.01 g), and sex of each individual were recorded in the laboratory.…”

“…Clasper length (to the nearest 0.01 mm), the distance from the posterior part of the cloaca to the tip of the clasper; oviducal gland width (to the nearest 0.01 mm); and the weights of the testes and ovaries (to the nearest 0.01 g) were recorded. Maturity stages were assigned on the basis of the scale of Hara et al (2018a). The maximum diameter of oocytes (to the nearest 0.01 mm) in mature females was measured, and the presence or absence of egg cases in oviducts was recorded.…”

“…For age determination, approximately 10 large vertebrae were extracted from the posterior portion of the abdominal cavity of specimen and immersed in 70% ethanol for 1-2 weeks. Each vertebral centrum was sectioned, following the procedure described by Hara et al (2018a), with whetstones (#400-3000; Kai Corp. and Kai Industries Co. Ltd., Tokyo, Japan) (Fig. 1).…”

“…Despite concerns about declining populations in the East China Sea, information on the life history of the sharpspine skate is extremely limited. Furthermore, published studies on its biology and ecology are scarce, even more than those on the polkadot skate, about which our recent studies have been published (Hara et al, 2018a(Hara et al, , 2018b. In a previous study (Joung et al, 2011), the age and growth parameters of the sharpspine skate in the coastal waters of Taiwan, the southern limit of its range, were estimated; however, young of the year were not included in the estimation.…”