Presentation on theme: "Age and growth of Sebastes vulpes in the coastal waters of western Hokkaido, Japan Takeshi SEKIGAWA,ToyomiTAKAHASHI, *Tetsuya TAKATSU,Syuichi NISHIUCHI,"— Presentation transcript:
Age and growth of Sebastes vulpes in the coastal waters of western Hokkaido, Japan Takeshi SEKIGAWA,ToyomiTAKAHASHI, *Tetsuya TAKATSU,Syuichi NISHIUCHI, Masayoshi SASAKI AND Fumiyasu SHIOKAWA FISHERIES SCIENCE 2003;69: 575–580 Reporter: 莊京儒
INTRODUCTION Chen and Barsukov classified Sebastes vulpes complex into three species: S.vulpes ( 帶斑平鮋 ),S.zonatus ( 帶平鮋 ), and S.ijimae ( 黑背平鮋 ), and described these three species as being sympatric ( 共域的 )around Japan. Thereafter, Kanayama and Kitagawa, and Ishida recognized them as the same species (S.vulpes) because of the occurrence of intermediate individuals.
‘Fox jacopever’(Sebastes vulpes complex) is distributed in the coastal waters from Funka Bay in Hokkaido to near Bousou Peninsula in the Pacific Ocean, from Ishikari Bay in Hokkaido to southern Korea in the Japan Sea. The annual catch in Japan was approximately 500–1000 tons in the 1960s,but decreased to 100–200 tons in the 1990s. INTRODUCTION
MATERIALS AND METHODS Samples were collected with commercial bottom set nets and gill nets at depths of 30–100 m in the coastal waters of Shimamaki and Suttsu, western Hokkaido, from April 1998 to May 1999 (Fig.1;Table 1). Because of its low abundance,the number of specimens collected was not large, especially for large fish.
MATERIALS AND METHODS Fig. 1 Map showing sampling area (striped area) and contours of depth in the coastal waters of western Hokkaido.
The S. vulpes collected were sexed and recorded along with total length(TL,mm), standard length (SL,mm), eviscerated body weight (EBW,nearest0.1 g), and gonad weight (GW, nearest 0.01 g). The paired sagittal otoliths were removed then cleaned with water, and stored dry in plastic trays.
MATERIALS AND METHODS Because the SL of S.vulpes taken in April 1998 were not measured, these values were calculated from the following equations: Male : SL = 0.819 TL - 1.40, r = 0.995, P < 0.001, n = 124 Female: SL = 0.796 TL - 4.27, r = 0.994, P <0.001, n = 117
MATERIALS AND METHODS The otoliths were placed on wood blocks and embedded in clear epoxy, and sectioned through the nucleus using a low-speed diamond wafering saw. Thin sections (0.5 mm) of otoliths were mounted on microscope slides with sticky wax, sanded with wet 600- and 1500- grade sandpaper, and polished on a 4000- grade emery paper. Procedure of cross-sections
MATERIALS AND METHODS The surface of the whole otolith was observed and whether the outer perimeter of the otolith had an opaque zone or not was recorded. Opaque zones were counted under a binocular dissecting microscope at ｘ 20–40 magnification with reflected light. In contrast, sectioned otoliths were observed with transmitted and/or reflected light and the opaque zones were counted.
MATERIALS AND METHODS Because no difference in the number of opaque zones was found between right and left otoliths, the right otolith was used as a rule. Von Bertalanffy growth curves for both sexes and both methods (surface and cross-section) were calculated from age–length data using the least-squares, non-linear regression procedure.
MATERIALS AND METHODS In order to determine the period of the first annulus formation, the otoliths of 1-year-old cultured S.vulpes (51 individuals) (parturition date: 26 May - 4 June 1997) were sampled and observed in June 1998. The parturition and birth season was examined from seasonal change in gonadosomatic index (GSI) for female fish. GSI ＝ GW ｘ 10^2 / EBW
RESULTS: Time of annulus formation No significant difference in percentage occurrence of otoliths with an opaque edge was found between sexes (G-test,Gadj=0.65,P=0.42) through the sampling periods, the percentages for both sexes were combined.
Fig. 2 Monthly change in percentage occurrence of opaque edge in otolith of Sebastes vulpes.
Seasonal change in gonadosomatic index Fig. 3 Seasonal change in gonadosomatic index (GSI) of female Sebastes vulpes (X) with and ( ❍ ) without spent ovary.
Comparison of annulus counts between the surface method and the cross-section method
Growth curves Male: SLt = 354.6(1 – exp -0.167(t+0.580) ), r = 0.815, P < 0.001, n = 136 Female: SLt = 403.4(1 – exp -0.114(t+1.579) ), r = 0.755, P < 0.001, n = 130 SLt = 358.6(1 –exp -0.156(t+0.820) ),r = 0.791,P < 0.001, n = 266 Combined
DISCUSSION In the present study the aging of S.vulpes was conducted by the surface and the cross-section methods. As a result, the underestimation of aging occurred for fish older than 6 years using the surface method. The cause of this was that in older fish the annuli that were layered lengthwise in sectioned otoliths could not be distinguished by the surface method.
Hayashi et al. stated on otoliths of marbled rockfish, Sebastiscus marmoratus( 石狗公 ), Beamish stated the otolith growth pattern of Pacific ocean perch,Sebastes alutus( 革平 鮋 ),Kelly et al. the crosssection of otoliths of bluemouth rockfish,Helicolenus d.dactylopterus( 黑腹無鰾鮋 ), Fujiwara and Hankin stated that the growth in the otolith radius of sablefish,Anoplopoma fimbria( 銀鱈魚 ) decreased dramatically with age, but growth of otolith thickness continued to increase inearly with age.
Comparison of Sebastes vulpes growth curves for the present study area with that for Hachinohe region given by Iizuka.
As aforementioned,however, ages of old fish based on the surface method were underestimated and the oldest fish was 35 years (354 mm SL). It seems likely that S.vulpes grows more slowly and lives longer than previously thought.