age and growth of sebastes vulpes in the coastal waters of western hokkaido, japan takeshi...

Age and growth of Age and growth of Sebastes vulpesSebastes vulpes in the in the

coastal waters of western coastal waters of western Hokkaido, JapanHokkaido, Japan

Takeshi SEKIGAWA,ToyomiTAKAHASHI,*Tetsuya TAKATSU,Syuichi NISHIUCHI,

Masayoshi SASAKI AND Fumiyasu SHIOKAWAFISHERIES SCIENCE 2003;69: 575–580

Reporter: 莊京儒

INTRODUCTIONINTRODUCTIONActinopterygii 條鰭魚綱Neotperygii 新鰭亞鋼Scorpaeniformes 鮋形目Scorpaenoidei 鮋亞目Scorpaenoidae 鮋科Sebastes 平鮋屬Sebastes vulpes 帶斑平鮋http://www.scuba4u.net/?

document_srl=4877&mid=oceanic_life&listStyle=&cpage=

INTRODUCTIONINTRODUCTIONChen 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.

INTRODUCTIONINTRODUCTION

MATERIALS AND MATERIALS AND METHODSMETHODS

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.


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.


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


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


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.


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.


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:RESULTS:Time of annulus Time of annulus formationformationNo 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 Seasonal change in gonadosomatic indexgonadosomatic index

Fig. 3 Seasonal change in gonadosomatic index (GSI) of female Sebastes vulpes (X) with and ( ) without spent❍ ovary.

Comparison of annulus counts Comparison of annulus counts between the surface method and the between the surface method and the cross-section methodcross-section method

Growth curvesGrowth 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

DISCUSSIONDISCUSSION 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.

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