Age validation of juvenile Shortfin Mako (Isurus oxyrinchus) tagged and marked with oxytetracycline off southern California

Abstract

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Size, Age, and Spatial–Temporal Distribution of Shortfin Mako in the Mexican Pacific Ocean

“…Because the scientific observers determined sexual stage data using only external features, which can jeopardize the accuracy of female sexual stage data, this study only assessed the mean size of males at sexual maturity. Our results agree with Maia et al (2007), Semba et al (2011), and Bustamante and Bennett (2013), who reported males matured at 185-217 cm TL, and with Wells et al (2013) who calculated the length at sexual maturity of males at 190 cm TL Shortfin Makos in southern California, a study area near to the Mexican Pacific. Size at sexual maturity may vary according to sample size, length range sampled, and different models for estimations; however, it can also be affected by geography, such as differences between the hemispheres (Mollet et al 2000).…”

“…Juvenile Shortfin Makos appear to have higher growth rates during the first years of life (Natanson et al 2006;Barreto et al 2016). This rapid growth in the early stages of life could explain the high growth rate (k = 0.17-0.19 cm/year) reported by Wells et al (2013), which contrasts with that (k = 0.05 cm/year) reported by Ribot-Carballal et al (2005). In any case, because accuracy in age and growth parameters is important for fishery management and conservation, more age and growth studies covering all size and age ranges of Shortfin Makos will be necessary in the western North Pacific to confirm the periodicity of ring formation in vertebrae.…”

“…Although Shortfin Makos displayed large displacements in the western North Pacific (Medina Trujillo 2013), another study carried out by Wells et al (2013) along the California coast (north of the Mexican Pacific coast) reported the deposition of two age rings per year, based on the oxytetracycline (OTC) age-validation technique. The difference in ring deposition (i.e., periodicity), and consequently dissimilar growth patterns in sharks between nearby study areas (northern Mexican Pacific versus California waters), could be a consequence of the low sample size of the OTC-marked vertebrae analyzed (n = 29) and the maturity stages that were dominated by juveniles in the study of Wells et al (2013). Juvenile Shortfin Makos appear to have higher growth rates during the first years of life (Natanson et al 2006;Barreto et al 2016).…”

“…Maia et al (2007), Semba et al (2011), andBustamante andBennett (2013) determined that male Shortfin Makos mature at 185-217 cm TL. In southern California, Wells et al (2013) determined length at maturity at 190 cm TL for males and 303 cm TL for females. More recently, Groeneveld et al (2014) measured length at sexual-maturity at 206 cm TL for males and 271 cm TL for females from the southwestern Indian Ocean.…”

A fishery-independent survey of juvenile shortfin mako (Isurus oxyrinchus) and blue (Prionace glauca) sharks in the Southern California Bight, 1994–2013

“…The proportion of males caught (sex ratio) for each 10 cm length bin was also calculated and tested for departures from 1:1 using a Chi-Square Goodness of Fit test. Mako sharks were considered young-of-the-year (age-0) if they were smaller than 100 cm FL (Wells et al, 2013;Pratt and Casey, 1983). Blue sharks were considered young-of-the-year if they were smaller than 90 cm FL (Cailliet and Bedford, 1983;Blanco-Parra et al, 2008;Stevens, 1975).…”