Age and growth of the shortfin mako ( Isurus oxyrinchus ) in the south-eastern Pacific off Chile

1. Age and growth of the shortfin mako (Isurus oxyrinchus)in the south-eastern Pacific off Chile Francisco Cerna,and Roberto Licandeo Marine and Freshwater Research, 2009, 60, 394–403 學生：曾正豪 學號：M98310003 東南太平洋智利外海灰鯖鮫之年齡與成長研究

2. 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

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

4. Introduction

5. 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.

6. 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)

7. 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)

8. 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)

9. 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.

10. Materials and methods

11. PCL FL TL 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.

12. http://www.eva.mpg.de/evolution/files/luminescence.htm http://wormatlas.psc.edu/glossaries/pglossary.htm 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

13. 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)

14. 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)

15. 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.

16. Results

17. 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)

19. From the original 562 vertebral samples, 15 samples were discarded because they were unreadable. (304 females and 243 males)

21. 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).

24. 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)

25. ` (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.

27. Discussion

28. The relationship between TL and VR was similar to that found in several other studies. (Bishop et al. 2006; Natanson et al. 2006)

29. APE and CV (9.8% and 13.8%) Bishop et al. (2006) ; Natanson et al. (2006) CV exceed 10% (Campana 2001) (Ribot-Carballal et al. 2005) Age-bias plots higher similiar

30. This study One band-pair per year Campana et al. 2002 Ribot-Carballal et al. 2005 Ardizzone et al. 2006 Natanson et al. 2006

31. 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)

32. Comparison with previous studies

33. 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) Eastern coast of Canada in the Atlantic (24 years, Campana et al. 2005) lower similiar

34. The bands become more tightly at the outer edge, particularly in larger specimens. (MacNeil and Campana 2002)

35. 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).

36. 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.

37. 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)

38. 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.

39. The estimated size-at-birth in this study 70cm for female; 79 cm for male (TL) Mollet et al. 2000 (∼70 cm TL) Duffyand Francis 2001 (77 cm TL) Joung and Hsu 2005 (79 cm TL)

40. The estimated L∞ 325 cm (female) ; 296 cm (male) Maximum size observed (Lmax) off Chilean waters (330 and 285 cm TL)

41. 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

42. 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.

43. Thanks for your attention！