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Population structure and reproductive biology of jumbo squid Dosidicus gigas from the Gulf of California

after the 1997–1998 El Niño event

加利福尼亞海灣在 1997-1998 聖嬰事件之後，對美洲大赤魷的族群結構與生殖的影響

Unai Markaidaª,* Fisheries Research(2006) : 79 ， 28-37

Reporter : huang xiao ting

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反聖嬰 (1988 年 12 月 )

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Dosidicus gigasPhylum Mollusca

Class : Cephalopoda ( 頭足綱 ) Order : Teuthida ( 管鱿目 ) Family : Ommastrephidae ( 真鱿科 ) Genus : Dosidicus ( 美洲大赤鱿屬 ) Scientific Name :Dosidicus gigas

Common Name : Jumbo flying squid

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1、 Introduction

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a small group predominantly occurring in the equatorial area (males maturing at 13-26 cm ， females 14-34 cm).

a medium-sized group occurring over the whole species range.(24-42 cm, 28-60 cm).

a large size group occurring at the northern and southern peripheries of the range.(>40-50 cm, >55-65 cm).

7• Banned owing to a 50cm ML mimimum size imposed by the Mexican Fisheries Institure.

• El Niño effect. (upwelling 、 pelagic environment 、 sperm whale).

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• reports the population structure, size at maturity, and reproductive aspects of jumbo squid in the Gulf of California in 1998-2000.

• differences between these maturity indices and those calculated for large maturing jumbo squid described for 1995-1997.(Markaida and Sosa-Nishizaki, 2001).

objective

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2、Material and methods

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2-1、 Sampling :

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• Sampled squid : Mantle length. sex, and maturity.Stages : According to the classification of Lipinski and Underhill (1995) ( i.e. I-II, immature ； III,maturing ； IV-V, mature ； VI, spent).

• Collected squid : body weight and reproductive organs.females : ovary weight. nidamental gland weight (length) , Oviductal complex weight (length).Males : testis weight (length) , spermatophoric complex weight.

sampling

Data analysis

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Maturity indices ( 成熟指標 )sampling

Data analysis

X2 – test ( 卡方 )

ANOVA( 變異數分析法 )

Mann-Whitney U-test ( 曼 -惠特尼檢定 )

body weight , mantle length and reproductive organs

Female to male ratio

Mean size of mature indivitiduals

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OW ovary weight 卵巢重NGW nidamental gland weight 纏卵腺重NGL nidamental gland length 纏卵腺長OCW Oviductal complex weight 輸卵管重OCL Oviductal complex length 輸卵管長

TW testis weight 精巢重

TL Testis length 精巢長

SCW spermatophoric complex weight 精莢囊重

K2testis weight to spermatophoric compl

ex weight ratio精巢重與精莢

重比RSWI Reproductive system weight index 產卵腺重比

females :

males :

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Maturity indices calculation :• For females: OWI ( 卵巢重比 )= 100×OW/(BW−OW), NGWI ( 纏卵腺重比 )= 100×NGW/(BW−NGW), NGLI ( 纏卵腺長比 )= 100×NGL/ML, OCWI ( 輸卵管重比 )= 100×OCW/(BW−OCW), OCLI ( 輸卵管長比 )= 100×OCL/ML, RSWI ( 生殖腺重比 )= 100×(OW+NGW+ OCW)/(BW−OW−NGW−OCW).• For males: TWI ( 精巢重比 ) = 100×TW/(BW−TW), TLI ( 精巢長比 ) = 100× TL/ML, SCWI ( 精莢囊重比 ) =100×SCW/(BW−SCW), K2 ( 精巢重與精莢囊重比 )= TW/SCW, RSWI = 100×(TW + SCW)/(BW−TW−SCW).

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3、 Results

• 3-1、 population structure • 3-2、 Size at maturity comparison • 3-3、Maturity indices

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3-1、 population structure

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• 1999 May (Rosalia) --- the sex ratio for mature individuals to

0.7:1, not significantly different form 1:1 (X2=2.6; P>0.05).

• 1999 August (Rosalia) --- the sex ratio was equal 0.75:1

(X2=0.29; P>0.05) not significantly.

• No differences were found for size distribution of mature individuals of both sexes of squid caught in different days

(ANOVA; P＞ 0.05). not significantly.

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• 1999 May (Topolobampo) – all but six females had non-mated.• 1999 May (Rosalia) – immature females <32 cm ML had not mated, while above that size almost all observed females had mated. • 1999 August --- half of females below 46 cm ML had not mated.

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3-2、 Size at maturity comparison

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纏卵腺重比

輸卵管重比

卵巢重比

纏卵腺長比

輸卵管長比

產卵腺重比

3-3、Maturity indices

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精巢重比

精莢囊重比

纏卵腺比

精巢長比

精巢重與精莢重比

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4、 Discussion• Large maturing form of jumbo squid were observed in the cali

fornia,1995-1997.• Belongeg to the medium size maturing group in 1998-2000. 1、 Large squid are the result of inhabiting areas of upwelling ,durin

g El Niño (Nisis, 1983). 2、Medium size squid would had been hatched during the transitio

n in summer 1998. warmer conditions during early life could accelerate maturation (Forsythe, 2004). 3、 Overfishing.

• Restoration to a large size maturing squid in 2000, although catches did not reach the levels of the 1995-1997 period.

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• Dominance of meted mature

females off topolobampo strongly

suggests a spawning jumbo squid

aggregation in this area in May 1999.

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• The cold La Niño event in 1996 caused jumbo squid to migrate to northern, warmer water off Peru. (Taipe et al., 2001).

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• Cephalopod population dynamicity appear to be determined mainly by phenotypic plasticity in response to environmental variability. (warmer temperatures, decreasing food supply).

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Thanks

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• 變異數分析 (analysis of variance) ANOVA

類似 t檢定的延伸，比較兩組或兩組以上的獨立組別 平均數有沒有差異。