Age and growth of the shortfin mako (Isurus oxyrinchus)

in the south-eastern Pacific off Chile

學生：曾正豪學號： M98310003

Francisco Cerna, and Roberto Licandeo

Marine and Freshwater Research, 2009, 60, 394–403

東南太平洋智利外海灰鯖鮫之年齡與成長研究

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Shortfin mako

Kingdom Animalia

Phylum Chrodata

Subphylum Vertebrata

Class Chondrichthyes

Subclass Elasmobranchii

Order Lamniformes

Family Lamnidae

Genus Isurus

http://fishdb.sinica.edu.tw/chi/showpic.php?science=Isurus%20oxyrinchus

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Distribution

http://fishbase.sinica.edu.tw/summary/SpeciesSummary.php?id=752

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Introduction

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• 1. By-catch in longline fisheries of swordfish. (Xiphias gladius Linnaeus, 1758)

• 2. Longline non-industrial fishery developed

in northern Chile, between 25◦ and 35◦S.

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• Unlike blue sharks, most of the shortfin makos are retained.

• Reported commercial landings

◎maximum peak of ~1000 t in 2002.

◎ decline to 400 and 500 t between

2001 and 2005. (SERNAPESCA, 2005)

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Age and growth

• Northern Atlantic (Pratt and Casey 1983; Natanson et al. 2006)

• Northern Pacific (Cailliet and Bedford 1983; Ribot-Carballal et al. 2005)

• South-western Pacific (Chan 2001; Bishop et al. 2006)

• South-eastern Pacific (Acuña et al. 2001)

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Age and growth

• Two band-pairs were formed every year. (Pratt and Casey 1983; Chan 2001)

• Band-pair forms annually.

(Hsu 2003; Bishop et al. 2006)

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• In recent years, there has been a growing shark fishery in Chilean waters.

• A lack of age validation, the use of whole vertebrae for ageing and a lack of large specimens have still left considerable uncertainty about growth and maximum ages for this species.

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Materials and methods

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Sampling

• Collected in waters from 18◦S to 40◦S during 2004 and 2005.

• For every shark caught, sex, fork length (FL) and total length (TL) were recorded.

TL

FL

PCL

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vertebral columns were washed

connective tissue and muscle were cut away

soaked in formic acid (10%) for 2~4 min

rinsed in boric acid and distilled water

air-dried

http://www.eva.mpg.de/evolution/files/luminescence.htm

http://wormatlas.psc.edu/glossaries/pglossary.htm

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• A band-pair consisted of one highly calcified (opaque) band and one less-calcified (translucent) band.

• The first band-pair near the focus was defined as a birth band. (i.e. age zero)

(Wintner and Cliff 1999)

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• Band-pairs were counted by two readers without knowledge of the length of the specimens.

• The between-reader bias was determined from age-bias plots and the reproducibility was evaluated with the coefficient of variation (CV) and average percent error (APE).

(Campana et al. 1995) (Beamish and Fournier 1981; Chang 1982)

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• Growth parameters were estimated with the von Bertalanffy growth model(VBGM).

• Length–frequency data were obtained from commercial captures of the swordfish fishery during 2003–2006.

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Results

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• In total, 562 shortfin makos were sampled. (313 females and 249 males).

Females ranged from 75 to 330 cm TL;

males ranged from 76 to 285 cm TL.

Female:

FL=0.905TL+1.345 (n=5542, R2 =0.99, P <0.0001)Male:

FL=0.894TL+2.912 (n=5149, R2 =0.99, P <0.0001)

18 TL=25.192VR0.823 (n=545, R2 =0.91, P <0.0001)

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• From the original 562 vertebral samples, 15 samples were discarded because they were unreadable.

(304 females and 243 males)

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• The oldest estimated age for both sexes in the present study was 25+ years old, at size 270 cm (female) ; 265 cm TL (male).

• The largest female was estimated to be 22 years old (330 cm TL), male was 24 years old (285 cm TL).

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• L∞ values for both sexes corresponded fairly closely with the greatest observed maximum lengths (Lmax).

• Lengths estimated at birth for females and males were 70.0 and 79.3 cm TL.

• Close to typically observed lengths of embryos at birth (70 cmTL).

(Bass et al. 1975; Stevens 1983)

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(mean=156.52 cm TL±46.76, n=11687)

Most sharks caught during the 4-year study (2003–2006) were in the length range 70–220 cm TL or approximately 0–13 years of age.

`

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Discussion

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• The relationship between TL and VR was similar to that found in several other studies.

(Bishop et al. 2006; Natanson et al. 2006)

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Age-bias plots

APE and CV

(9.8% and 13.8%)

(Ribot-Carballal et al. 2005)

Bishop et al. (2006) ; Natanson et al. (2006)

similiar

higher

CV exceed 10%(Campana 2001)

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This studyOne band-pair per year

Campana et al. 2002 Ribot-Carballal et al. 2005 Ardizzone et al. 2006 Natanson et al. 2006

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Edge-analysis

• Similar to Ribot-Carballal et al. (2005)

→summer

• Close correlation with SST

→environmental changes

temperature, photoperiod, food availability

(Cailliet et al. 1986; Branstetter 1987)

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Comparison with previous studies

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Maximum observed age (25+years) for both sexes

New Zealand (29 years, Bishop et al. 2006)

North Atlantic Ocean (29–32,Ardizzone et al. 2006; Natanson et al. 2006)

lower

Eastern coast ofCanada in the Atlantic (24 years, Campana et al. 2005)

similiar

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The bands become more tightly at the outer edge, particularly in larger specimens.

(MacNeil and Campana 2002)

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• Growth curves showed significant differences between sexes for this species.

→ L∞ , growth rates (female) (Bishop et al. 2006; Natanson et al. 2006)

• For other elasmobranchs (e.g. Skomal and Natanson 2003;

Goldman et al. 2006;

Francis et al. 2007).

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• In the North Atlantic Ocean, after the age of 11 years, there was a dramatic difference in growth between the sexes.

( Natanson et al. 2006)

• This could be due to the differences in age-at-maturity with populations of North Atlantic Ocean.

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Von Bertalanffy growth model parameters

• Values of Lmax were lower than other studies.

• Growth parameters reported previously in Chilean waters seem to be closer to those in our study.

(Acuña et al. 2001)

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• L∞ (182–243 cmTL) obtained for this model was unrealistically low.

( Acuña et al. 2001)

→ Number of ages used in the fit (1–13 years old).

• The differences with the other studies

(e.g. Bishop et al. 2006; Natanson et al. 2006)

→ larger Lmax larger L∞

because of a lack of older individuals.

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The estimated size-at-birth in this study

70 cm for female; 79 cm for male (TL)

Mollet et al. 2000 ( 70 cm T∼L)Duffy and Francis 2001 (77 cm TL)Joung and Hsu 2005 (79 cm TL)

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The estimated L∞ 325 cm (female) ; 296 cm (male)

Maximum size observed (Lmax) off Chilean waters (330 and 285 cm TL)

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The first year growth rates in the present study

between 16 and 19 cm year−1

Bishop et al. 2006 (38 cm year−1 ) Natanson et al. 2006 (40 cm year−1)

Overestimation of the size-at-birth

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Stock status of mako sharks

• No quotas or gear restrictions have been established.

• Wide distribution and the highly mobile.

• The status of this population in the south-eastern Pacific is largely unknown.

• Need for directed life-history studies and conservation measures for pelagic sharks.

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Thanks for your attention！