Age, Growth, and Maturity of Chub Mackerel off Korea 韓國白腹鯖的年齡，成長和成熟期 North American Journal of Fisheries Management 28:1414–1425, 2008 Copyright by the American Fisheries Society 2008 DOI: 10.1577/M07-063.1 SUN-DO HWANG AND JIN-YEONG KIM National Fisheries Research and Development Institute, Busan 619-705, Korea TAE-WON LEE* Department of Oceanography, Chungnam National University, Daejeon 305-764, Korea Age, Growth, and Maturity of Chub Mackerel off Korea 韓國白腹鯖的年齡，成長和成熟期

Introduction

In the East China Sea, the Sea of Japan, and the Yellow Sea 1980~2004 年南韓就捕獲了10萬公噸。 捕撈的高峰在1990年初，在1996年的40萬公噸為最高峰，近年來則減少了18萬公噸 (NFRDI※ 2005)。 注：NFRDI (National Fishries Research & Development Insitute) 位於菲律賓

Tsushima Current stock East China Sea stock FIGURE 1. Seasonal migration of chub mackerel in the East China Sea, East/Japan Sea (Sea of Japan), and Yellow Sea(modified from NFRDI 2005). Two stocks have been indentified in these waters: the Tsushima Current stock and the East China Sea stock. Chub Mackerel overwinter and spawn in the southern area and migrate northward in early summer for feeding.

Tsushima Current stock 主要在濟州島(Jeju island)附近產卵和迴游。 比 East China Sea stock 更有經濟效益。 越冬時遷徙至南方水域並且產卵。 春季至夏初時向北迴游並索餌、攝食。

Moving out to the feeding ground in the open ocean chub mackerel 簡易生活史 Spawing in May to June Juveniles→ nursery ground in June to August Moving out to the feeding ground in the open ocean Migrating northward from spring to summer Overwinter around the Jeju island

Age composition of the catch Stock assessment models Virtual population analysis(VPA) (虛擬魚群分析法、 年級群分析) Estimates of growth parameters for YPR(yield per recruit) models

Ex:當棲地改變時，白腹鯖的耳石年輪也會跟著改變而產生非正確的年輪，導致讀輪時候之錯誤的判讀。 Estimate true age! Ex:當棲地改變時，白腹鯖的耳石年輪也會跟著改變而產生非正確的年輪，導致讀輪時候之錯誤的判讀。 在年齡和成長相關研究中，年齡的確認通常被粗略了。

這篇報告提供了每個月商業性捕撈的白腹鯖之體長、年齡和成熟期等資料。 在測定產卵季節和成長體長後，將與先前之報告相結合來互相比較。 這些資訊可以提供良好的基礎，用來評估族群動態、探討開發漁業作業場所受到的影響，並且可以依此來推動制定合理的漁業管理政策。

Methods

Samples of chub mackerel Collected from: Monthly from Korean purse-seine fishery Consists of over 40 vessels and catches mackerel throughout the year Fishing ground: Tsushima current stock Time: Sep. 1994 ~ Aug. 1995 Purse seines: 200 m* 1 km, 30mm stretched mesh Works: operated daily to catch mackerel between depths of 10–100 m

樣本的挑選 Randomly chosen Monthly 700 individuals from landed fish Measured to the nearest mm FL Subsamples of about 50 speciments Gonads were weighed to the nearest 0.1g Gonads for both sexes were staged macroscopically.

Macroscopic stages TABLE 1. Maturity stages of the gonads of chub mackerel off Korea. ※This classification of maturity stages was modified from Lagler (1978) and Gluyas-Milla´n and Quin˜onez- Vela´zquez (1997).

生殖腺指數Gonadosomatic index (GSI) GSI =[gonad weight / total fish weight] * 100 A. Samples during 1995 Mar. to Aug. B. 120 Female (range=21.9-39.0cm ; 0-3 years) C. Estimate length at 50% maturity D. Classified an individual as ‘‘mature’’and as ‘‘immature’’ otherwise E. Fit the binary data to a logistic regression model by the method of maximum likelihood. F. Estimated length at 50% maturity and its 95% confidence intervals (CI),. Age at 50% maturity was also calculated by the same method. 測定方法步驟：

Estimating sagittal otoliths A. Sagittal otoliths were removed from 50 individuals/month. B. use Canada balsam(加拿大安息油)and examined at 50 ,100 ,200X magnification from a light microscope C. Measured otolith radius (R[mm]) and distance to i th annuli (Ri). D. Examined the right sagittal for consistency. E. Marginal increment analysis. MI(marginal index)= (R-Rn) / [Rn - (Rn-1)] X 100

Marginal Increment Radius

Relationship between otolith radius and FL( L [mm] ) 公式: L=a+bR 下列有三種方法可以推估在i歲時的體長Li 1. Li - a = (Ri / R)X (L – a) 2. 使用i歲時的Ri，亦即Li = a + bRi 3. 配合捕捉的月份直接觀察。

The size-at-age estimates for ages 0–4 from all three approaches were used to : fit von Bertalanffy growth curves for males, females estimate their 95% CIs by the NLIN procedure of SAS version 8 (SAS 1999). The length–weight relationship was calculated by means of the exponential function : W=aLb

Results Chub mackerel samples Size composition: Range: 12~43cm Total: 13,041(Fig.2) FIGURE 2. Length frequency distributions of chub mackerel caught by the Korean purse-seine fishery off Korea from September 1994 to August 1995; n = the number of individuals measured.

Age and growth Sectioned otoliths Adult chub mackerel False annuli Several opaque(暗帶) and translucent(明帶) zones were alternated between annuli. True annuli were formed continuously all around the sagittal plane. False annuli True annuli (Ri) Adolescent chub mackerel False annuli FIGURE 3.—Microphotographs of false annuli (R’ and R’’)and annuli (Ri) on the otolith of an adult chub mackerel (upper photograph) caught by purse seine in the offshore waters of Korea under transmitted light and false annuli on the otolith of an adolescent chub mackerel (lower photograph) caught by trap net in the inshore waters of Korea in August 1995 under dark field illumination.

Age and growth Of 747 otoliths examined, 701 (93.8%) were considered readable, and the oldest was age 4. 因兩位判讀者在判讀過程之間產生了不同的意見： 他們發現有46顆耳石樣本無法清楚判斷年齡，故捨棄之。

Intensive fishing

成長率快速 成長率緩慢 Li - a = (Ri / R)X (L – a) Li = a + bRi

Fork length was proportional to otolith growth. Linear regression indicated no significant difference (P< 0.05) in the relationship between otolith radius and FL for males and females, so the data were pooled. L=146.35R – 27.91 ( r2=0.73 ; n= 701)

Highest Mean MI 形成輪紋（暗帶） Lowest Mean MI FIGURE 4. Monthly variation in the means and 95% Cis (vertical lines) of the marginal index (ratio of the distance outside the last annulus to the distance between the last two annuli) of chub mackerel collected off Korea from September 1994 to August 1995.

Fraser-Lee預估之L∞ ，也略小於實際高齡魚的最大體長。 Lt=34.4(1-e(-1.67[ t +0.0045 ]) ) (r2= 0.58) Lt=34.6(1-e(-1.51[ t +0.0050 ]) ) (r2= 0.51) FIGURE 5.—Von Bertalanffy growth curves (solid lines and their 95% confidence intervals indicated by dotted lines)derived from back-calculated lengths at age according to (a) the Fraser–Lee equation, (b) the regression of FL on otolith radius, (c) the observed lengths of chub mackerel collected off Korea from September 1994 to August 1995. Juvenile data from a previous study (Hwang and Lee 2005) were also included in the last approach. Lt=34.1(1-e(-2.19[ t +0.0035 ]) ) (r2= 0.88)

The weight–length relationship for chub mackerel W = 0.0012L3.692 (r2 = 0.97 ; n=747) W為體重(g)

在Equation(3)式中，K值(2.19)大於(a)、(b)兩式之K值的原因為作者加入了幼年時期的資料。 TABLE 3. Estimates and 95% confidence intervals (CIs) for the von Bertalanffy growth parameters in three equations for chub mackerel off Korea: L∞=the asymptotic length, K=the growth coefficient, t0=the theoretical age when the fish has length 0. (t0 為魚體長度為0之當時理論年齡) Confidence intervals are not given for t0 because the length at hatch was fixed when fitting the growth equations.

The sex ratio did not differ significantly from 1:1 (P>0.05). Black bars = 310(Female) White bars = 301(Male) The sex ratio did not differ significantly from 1:1 (P>0.05). Females classified as ripe, spawning, and spent were observed mainly from April to July. Spent males were observed only in June and July (100%) 3 4 5 3 4 5 6 7 FIGURE 6. Relative frequencies of maturity stages by month for female (black bars) and male (white bars) chub mackerel collected off Korea from September 1994 to August 1995; n = the number of specimens examined.

GSI=4.31±1.70 GSI=3.51±1.61 GSI=0.83±0.40 GSI=0.41±0.07(95%) 9 10 11 12 1 2 3 4 5 6 7 8 FIGURE 7. Monthly variation in the means and 95% Cis (vertical lines) of the gonadosomatic index (GSI) for (a)female and (b) male chub mackerel collected off Korea from September 1994 to August 1995.

雌魚50%成熟的： 體長： 28.6 cm (95%CI, 27.8–29.9 cm) 第一次產卵年齡： 1.01歲(95% CI, 0.83–1.19) FIGURE 8. Scatter diagram of maturity (ML) versus FL (L) for female chub mackerel off Korea. The binary data were fitted to the logistic function, and the 95% CIs were calculated by the method of maximum likelihood.

假定五月為白腹鯖產卵期： Spawning proportions： 0歲：15.6% 1歲：87.7% 2歲：93.5% The mean GSI for ripe and spawning stages： 0歲：4.8 1歲：4.5 2歲：7.6 3歲：9.8

Discussion

Size and Age Composition 判讀耳石第一輪是非常困難的，可能是因為白腹鯖在幼年(juvenile)至成魚(adolescent)階段中，從近岸水域游向離岸的海水。 白腹鯖在5月孵化後即成長快速(17-18cm in July and over 20cm as age 0 in September)，原因為白腹鯖大量消耗自己的能量來成長，以便在隔年時候能順利產卵。

Size and Age Composition 漁獲強度在12~2月時候為最大，4~7月為最低(NFRDI 2005) 所以可解釋在Fig.2中，12月~2月時候大魚樣本數很少的原因。 過漁也造成在Table2.中，3歲以上成魚數量非常稀少。 不過在1990年代，TAC(total allowable catch)的制定，將可以減緩過漁造成魚群數量減低的壓力。

TABLE 4. Comparison of fork lengths (cm) at age of chub mackerel estimated by the von Bertalanffy growth model in this study and previous studies.

FIGURE 9. Comparison of the growth curve for chub mackerel obtained in this study with those of Ann (1971), Ouchi (1978),Kondo (1966), Chen and Li (1978), Knaggs and Parrish (1973), and Gluyas-Milla´n and Quin˜onez-Vela´zquez (1997).

Conclusion 這篇報告將可以立即的提供了韓國白腹鯖的資源現況，並且進一步來評估並制定合理的韓國漁業管理政策。 同時作者也建議其他地區，同樣在做白腹鯖資源管理的學者，也可以重新檢視該地區白腹鯖之年齡與資源評估，特別是重新確認並判讀錯誤或正確的年輪。 在韓國地區，秋季的白腹鯖漁撈作業應減少，以保存剛出生的稚魚數量，如此一來，TAC的制定也就有它存在的意義了。

Thanks for your attention! OVER Thanks for your attention!