Age and growth of Sebastes vulpes in the coastal waters of western Hokkaido, Japan

1. 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

2. INTRODUCTION • Actinopterygii 條鰭魚綱 • Neotperygii 新鰭亞鋼 • Scorpaeniformes 鮋形目 • Scorpaenoidei 鮋亞目 • Scorpaenoidae 鮋科 • Sebastes 平鮋屬 • Sebastesvulpes 帶斑平鮋 http://www.scuba4u.net/?document_srl=4877&mid=oceanic_life&listStyle=&cpage=

3. INTRODUCTION • Chen and Barsukov classifiedSebastes vulpescomplex into three species:S.vulpes(帶斑平鮋),S.zonatus(帶平鮋), andS.ijimae(黑背平鮋 ), and described these three speciesas being sympatric (共域的)around Japan. • Thereafter,Kanayama and Kitagawa, and Ishida recognizedthem as the same species (S.vulpes) because of theoccurrence of intermediate individuals.

4. INTRODUCTION • ‘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 Japanwas approximately 500–1000 tons in the 1960s,but decreased to 100–200 tons in the 1990s.

5. MATERIALS AND METHODS • Samples were collected with commercial bottomset nets and gill nets at depths of 30–100 m in thecoastal waters of Shimamaki and Suttsu, westernHokkaido, from April 1998 to May 1999 (Fig.1;Table 1). • Because of its low abundance,the numberof specimens collected was not large, especiallyfor large fish.

6. MATERIALS AND METHODS • Fig. 1 Map showing sampling area (striped area) and contours of depth in the coastal waters of western Hokkaido.

7. MATERIALS AND METHODS

8. MATERIALS AND METHODS • TheS. vulpescollected were sexed and recordedalong with total length(TL,mm), standard length(SL,mm), eviscerated body weight (EBW,nearest0.1 g), and gonad weight (GW, nearest 0.01 g). • Thepaired sagittal otoliths were removed then cleanedwith water, and stored dry in plastic trays.

9. MATERIALS AND METHODS • Because theSLofS.vulpestaken in April 1998 were notmeasured, these values were calculated from thefollowing 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

10. MATERIALS AND METHODS Procedureofcross-sections • The otoliths were placed on wood blocks and embedded in clear epoxy,andsectioned 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.

11. MATERIALS AND METHODS • The surface of the whole otolith wasobserved and whether the outer perimeter of theotolith had an opaque zone or not was recorded. • Opaque zones were counted under a binocular dissectingmicroscope atｘ20–40magnification withreflected light. • In contrast, sectioned otoliths wereobserved with transmitted and/or reflected lightand the opaque zones were counted.

12. MATERIALS AND METHODS • Because no differencein the number of opaque zones was found betweenright and left otoliths, the right otolith was used asa rule. • Von Bertalanffy growth curves for both sexesand both methods (surface and cross-section)were calculated from age–length data using the least-squares, non-linearregression procedure.

13. MATERIALS AND METHODS • In order to determine the period of the first annulus formation, the otoliths of 1-year-old culturedS.vulpes(51 individuals) (parturition date: 26 May - 4June 1997) were sampled and observed in June1998. • The parturition and birth season was examined from seasonal change in gonadosomatic index (GSI) for female fish. • GSI＝GWｘ10^2 / EBW

14. RESULTS:Time of annulus formation • No significant difference in percentageoccurrence of otoliths with an opaque edge wasfound between sexes (G-test,Gadj=0.65,P=0.42) through the sampling periods, the percentages forboth sexes were combined.

15. Fig. 2Monthly change in percentage occurrence ofopaque edge in otolith ofSebastes vulpes.

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

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

19. 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

20. DISCUSSION • In the present study the aging of S.vulpes was conductedby the surface and the cross-section methods. • As a result, the underestimation of aging occurred for fish older than 6 years using the surfacemethod. • The cause of this was that in older fishthe annuli that were layered lengthwise in sectionedotoliths could not be distinguished by thesurface method.

21. Hayashi et al.stated on otolithsof marbled rockfish, Sebastiscus marmoratus(石狗公),Beamish stated the otolith growth pattern ofPacific ocean perch,Sebastes alutus(革平鮋),Kelly et al.the crosssectionof otoliths of bluemouth rockfish ,Helicolenusd.dactylopterus(黑腹無鰾鮋), Fujiwara and Hankin stated that the growth in theotolith radius of sablefish ,Anoplopoma fimbria(銀鱈魚) decreased dramatically with age, but growth ofotolith thickness continued to increase inearlywith age.

22. Comparison of Sebastes vulpes growth curves forthe present study area with that for Hachinohe regiongiven by Iizuka.

23. As aforementioned ,however, ages of old fish based on the surfacemethod were underestimated and the oldest fishwas 35 years (354 mm SL). • It seems likely thatS.vulpes grows more slowly and lives longer thanpreviously thought.

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