Age and growth of the blue shark (Prionace glauca) in the Indian Ocean

Abstract

Obrigada ao Dr. Rui Coelho por ter aceite orientar este trabalho e por toda a ajuda imprescindível, assim como ao Dr. Karim Erzini. À Daniela Rosa, obrigada por toda a ajuda e pela paciência durante estes meses de trabalho, e também ao Rubén Muñoz-Lechuga pela sua disponibilidade. Obrigada aos observadores do IPMA, Carlos Barbosa e Sérgio Goes, que recolheram as amostras sem as quais esta tese não seria possível, e também à restante equipa do IPMA por me terem feito sentir integrada. Aos meus pais e à minha irmã, obrigada por terem estado sempre presentes mesmo quando eu não estava, e por todo o apoio incondicional. À minha restante família, um grande abraço e obrigada por tudo. Obrigada à Inês por estares presente em tudo quase desde sempre, à Mariana que chegaste mais tarde, mas para ficar para sempre e ao Diogo que mesmo quando estiveste longe estiveste sempre perto. To all the friends I met in Faro, but I feel like I have known for so long, thank you for making these two years so much fun even when times were harder. I wish you all the best.

Age, Growth, and Sexual Maturity of the Crocodile Shark, Pseudocarcharias kamoharai, From the Eastern Atlantic Ocean

“…Age and growth studies for most shark species have used the three-parameter VBGF (3-VBGF) to describe growth (Jolly et al, 2013;Drew et al, 2015;Lessa et al, 2015;Baje et al, 2018;Liu et al, 2018;Andrade et al, 2019). In this study, the 3-VBGF, as well as the other three models, presented good fit to the observed length-at-age data for P. kamoharai since their AICc values were <2 showing all models had great support (Burnham and Anderson, 2002).…”

“…The X-ray radiography approach on whole and coronally sectioned centra for P. kamoharai failed to present clear growth bands in this study. Sectioned vertebral centra embedded in resin are the most widely used technique to age sharks (Matta et al, 2017;Andrade et al, 2019). Lessa et al (2015) used sectioned vertebral centra on P. kamoharai specimens captured in the south-western Atlantic and obtained positive results, so its failure in the present study may be because of improper handling or processing of samples.…”

“…Vertebrae are the most used structures to age sharks, though they are at times difficult to read on account of the poor contrast between opaque and translucent growth bands, especially for species such as the blue shark (Manning and Francis, 2005;Jolly et al, 2013;Andrade et al, 2019). Therefore, to enhance the readability of these growth patterns on elasmobranchs vertebrae, alternative methods such as staining and X-ray radiography are sometimes applied; image analysis and editing software are also used to enhance images and increase visual contrast between growth zones (Megalofonou et al, 2009;Ainsley et al, 2011;Jolly et al, 2013;Campana, 2014;Tribuzio et al, 2016;Matta et al, 2017;Andrade et al, 2019). In the current study, a comparison of age determination was made between unstained (longitudinal) and stained (whole centra) vertebral sections.…”

“…Also, growth models without small individuals or young ages are generally less accurate which may be another factor that influenced the changes in k. According to Branstetter (1987), the growth rate of species with a growth coefficient between 0.10 and 0.20 is considered moderate. Therefore, k = 0.18 means that P. kamoharai grows faster than other pelagic shark species with larger body sizes, such as the blue shark (k (males) = 0.13; k (female) = 0.12; Andrade et al, 2019), and the Shortfin Mako shark (k combinedsexes = 0.123; Liu et al, 2018). Our result suggests that the P. kamoharai in the TEA Ocean may have a faster growth rate than those in the south-western Atlantic Ocean.…”

Life history parameters of the crocodile shark, Pseudocarcharias kamoharai, in the tropical Atlantic Ocean

“…Additionally, Harry (2018) alerts to the fact that many validation studies have reported underestimation in shark and ray ageing studies, especially in the larger and presumably older sharks. Ages can be underestimated if vertebrae cease to grow as maximum size is approached (Andrade et al ., 2019), therefore estimated maximum ages in this study should be considered as low estimates of maximum age for this species. Age validation through a species' lifespan is of extreme importance, as incorrect age and growth parameters will influence longevity, mortality estimates and other biological processes, which are important input parameters for stock assessments and fisheries management (Goldman et al ., 2012; Cailliet, 2015).…”