Age and growth analysis of the shortfin mako, Isurus oxyrinchus, in the western and central North Pacific Ocean

Yasuko Semba & Hideki Nakano & Ichiro AokiEnviron Biol Fish (2009) 84:377391speaker

Shortfin Mako

Kingdom AnimaliaPhylum ChordataClass ChondrichthyesSubclass ElasmobranchiiOrder LamniformesFamily LamnidaeGenus IsurusSpecies oxyrinchus

http://fishdb.sinica.edu.tw/chi/showpic.php?science=Isurus%20oxyrinchus http://fishdb.sinica.edu.tw/chi/newsearch/search.asp?search=order00

Introduction

Biology Habitats : OceanDeep SeaCoastal Habitats Depth : 0 - 740 M Max Lenth : 400 cm Size at birth estimated to be about 60-70 cm in TL. Ovoviviparous, with a uterine cannibal. http://fishbase.sinica.edu.tw/Photos/ThumbnailsSummary.php?ID=752

Characteristic

Wide distribution, and prefers temperatures of 17 to 22C. (Casey and Kohler 1992)Migration Sexual/ontogenetic stage segregation

Distribution http://www.aquamaps.org/receive.php

Sustainable Development The recent and rapid collapse of large predatory fish populations is a global concern (Myers and Worm 2003, 2005).Information on life history parameters derived from age and growth analyses plays an integral role. Age determination is an important component of population analyses.In addition, the growth curves generated in this study were compared to those for populations in other geographic regions.

Materials and methods

Sample collectionSampling period : 1992~2005 by the Japanese research vessels and tuna longline training vessels.Sampling amount : 275 individuals (128 males and 147 females).Sampling site : western and central North Pacific Ocean.

Fig. 1 Sampling locations for the shortfin mako (Isurus oxyrinchus) in the western and central North Pacific Ocean. Each point denotes a position where samples were collected.

Fig. 2 Length frequency of the specimen used for the analysis

species.wikimedia.org/.../Images/test

DL, TL, FL with PCLPCL : 57.2 to 186.5 cm

Step

Vertebral processingBoil the vertebraeStore it in 70% ethanolCut off a single centrumSoak it in 6N NaOHScrub it with apolishing buffEach centrum is cutinto two longitudinal sections after dryingThe halfcut centra with the focus were used for analysis after washing away the bone particle and drying for 1 day

Four techniques to enhance vertebral growth bandsshadowing (half-cut centra; Francis and Maolagin 2000)alizarin staining (section;Berry et al. 1977) silver nitrate staining (whole centra; Stevens 1975)soft X-radiography (whole or half-cut centra; Cailliet et al. 1983)

Method of age determination

The shadowing methodSimplicityVisual clarityRelative abundance of information amountLess time-consuming process

Fig. 3 Half of a vertebral centrum with lateral illumination from fiber-optic sources. The triangles indicate a convex structure or growth band. This example is from a 137 cm PCL female, with a vertebral centrum radius of 9.5 cm, and an estimated age of 4.6 years

Age determination In this way, the convex and concave structures were observed as light and dark regions, respectively. These structures correspond to the opaque (convex) and translucent (concave) regions observed in the sagittal section.

The vertebrae of neonates, which displayed only a birthmark, were excluded from this analysis.

CR with PCLThe centrum radius (CR) is the distance from the focus to the edge of the centrum perpendicular to the direction of the cutting plane. The CR was measured to the nearest 0.01 mm

Fig. 6 Age-bias plot of 275 shortfin mako vertebral counts from two independent readings by the first author. The open and solid mark indicate the observed counts and the mean counts assigned by the second count for all fish which was assigned a given count in the first count up to 12, respectively. The vertical bars for the solid mark up to the first count of 11 indicate the 95% confidence interval. The one to one equivalence line is also represented.

PA= [No. agreed/No. read]*100

Assuming that annuli (convex structures) are formed soon before or after 1 December, age in years was calculated as follows:x = the number of convex structurey = the month when the individual was caught (1y12).

Lt = PCL at time t (cm)L0 = size at birth (cm)(74 cm TL) (Joung and Hsu 2005)L =asymptotic length (cm) K = brody growth constant (year1).VBGE with size at birth

ResultsMale : 53~240 cm (PCL)Female : 57~300cm (PCL)

the allometric equation for regression analysis

Akaikes Information CriterionAIC = n ln(MSE) + 2K

model N (no bandperiodicity) : 312.44model A (annual periodicity) : 271.89model B (biannual periodicity) : 316.24

The estimated growth equationst = age (years)

The estimated S.E. of L for females was larger than that for males, whileS. E. of K for males was larger than for females

Discussion

Growth Fig. 7 Estimated von Bertalanffy growth curves for female and male shortfin mako in the western and central North Pacific Ocean

Growth band formationConvex dominant in the winter and concave dominant in the summer.Neonates captured in May and June suggested that the formation of the first convex concentric structure (birthmark) occurs after parturition.Branstetter (1987)We determined that the growth increment between the birthmark and the second annulus is approximately 7 months.

Fig. 8 Comparison of growth curves to those reported in previous studies for a males and b females. The curves reported by Pratt and Casey (1983) were recalculated assuming one growth band pair formation per year

Growth comparisons among geographical regionsEastern North Pacific (Cailliet and Bedford 1983; Ribot-Carballal et al. 2005)

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

South Pacific (Bishop et al. 2006)

ConclusionOur data from the western and central Pacific Ocean indicate that shortfin makos in this area grow slowly and mature late, and our results provide insight into the population structure.

A better understanding of the age structure in a unified regional framework will allow us to construct effective guidelines for the assessment and management of the shortfin mako population.

Thak you for your attention !