Distribution Pattern, Age, and Growth of Blue Sharks in the South Atlantic Ocean

Abstract

The distribution pattern and the age and growth of Blue Sharks Prionace glauca were described based on 44,092 and 785 specimens, respectively, that were collected by scientific observers onboard Taiwanese longline fleets in the South Atlantic Ocean between December 2004 and December 2013. Size segregation was found, and the mean length of Blue Sharks was significantly larger in the equatorial–tropical area (0–15°S) than in the subtropical–temperate area (south of 15°S) during all seasons. Males predominated in both areas and during all seasons; the exceptions were seasons 2 (April–June) and 3 (July–September) in the equatorial–tropical area and season 2 in the subtropical–temperate area. The sex ratio increased with shark size in the equatorial–tropical area but decreased with size in the subtropical–temperate area. Growth band pairs (including translucent and opaque bands) were counted on images photographed from X‐ray films of vertebrae from the caudal peduncle region. The centrum edge analysis indicated that a growth band pair was formed on the vertebral centrum once per year. Corrected Akaike's information criterion values indicated that the von Bertalanffy growth function (VBGF) provided the best fit to the observed TL‐at‐age data. The likelihood ratio test indicated that the VBGF equations were not significantly different between the sexes. For both sexes combined, VBGF parameters were estimated as follows: asymptotic length was 352.1 cm TL, the Brody growth coefficient was 0.13/year, and the theoretical age at zero length was –1.31 years. Age at first maturity was estimated as 6.5 years for males and 6.7 years for females; theoretical longevity was estimated to be at least 21.4 years.

Age determination and growth of the blue shark (Prionace glauca) in the western North Pacific Ocean

“…Growth parameters we report for this study differ from those reported for sharks in the eastern North Pacific Ocean (Cailliet and Bedford, 1983;Blanco-Parra et al, 2008), possibly because few larger and older specimens (most individuals were less than 200 cm PCL) were represented in samples in those studies. The size range of specimens reported from the central South Pacific Ocean by Joung et al (2017) is similar to the range we report, as are estimates of growth parameters, especially asymptotic length (Table 5). However, our estimated female as- Table 4 Estimates, with 95% confidence intervals (95% CIs), of the parameters for the von Bertalanffy growth model used to examine differences in growth parameters between sexes for blue sharks (Prionace glauca) in the western North Pacific Ocean.…”

“…Furthermore, because we used the thin-sectioning method on older sharks, we minimized underestimation of age. The aging precision (IAPE and CV) that we achieved by combining techniques is comparable to that from the use of a single technique like thin sectioning (Lessa et al, 2004), silver nitrate impregnation (Blanco-Parra et al, 2008), or X-ray imaging (Joung et al, 2017;Joung et al, 2018). Consequently, our aging Table 5 Estimates of growth parameters of the von Bertalanffy growth function for blue sharks (Prionace glauca) from previous studies.…”

Development of an alternative ageing technique for blue shark (Prionace glauca ) using the vertebra

“…Also, those values for younger and smaller specimens (<200 cm PCL) were lowest in the burn method (3.0% and 4.2%), whereas those for older specimens were lowest in the unstained shadowing method (7.6% and 10.7%). The IAPE values for blue shark in other studies were 3.0% (silver nitrate [whole centra]: Blanco‐Parra, Galvan‐Magnna, & Marquez‐Farias, ), 7.9% (unstained whole centra: Jolly et al., ), and 3.8% and 9.0% (X‐ray [whole centra]: Joung, Lyu, Su, Hsu, & Liu, ; X‐ray [thin section]: Manning & Francis, ). Similarly, the CVs for blue shark in other studies were 5.0% and 12.8% (X‐ray [whole centra]: Joung et al., ; X‐ray [thin section]: Manning & Francis, ) and 15.0% (unstained thin section: Skomal & Natanson, ).…”

“…Also, those values for younger and smaller specimens (<200 cm PCL) were lowest in the burn method (3.0% and 4.2%), whereas those for older specimens were lowest in the unstained shadowing method (7.6% and 10.7%). The IAPE values for blue shark in other studies were Similarly, the CVs for blue shark in other studies were 5.0% and 12.8% (X-ray [whole centra]: Joung et al, 2017; X-ray [thin section]: Manning & Francis, 2005) and 15.0% (unstained thin section: Skomal & Natanson, 2003). The IAPE and CV reference values have been reported to be 5.5% and 7.6%, respectively (Campana, 2001).…”

Aspects of the reproductive biology of two pelagic sharks in the eastern Atlantic Ocean

“…In the Atlantic Ocean, the reproductive biology of blue shark has also been reported (Castro & Mejuto, 1995;Hazin et al, 2008;Kouamé et al, 2019;Pratt, 1979). Similarly, Joung et al (2005Joung et al ( , 2017 analysed the shark by-catch of the Taiwanese tuna longline fishery in the South Atlantic; Carvalho et al (2015) reported fishery selectivity for blue sharks in the South Atlantic based on satellite tagging; Coelho et al (2015Coelho et al ( , 2017 described the size, sex ratio and distribution pattern of blue sharks in the Atlantic and Indian Oceans based on observer data from major fishing fleets. Nonetheless, key reproductive parameters such as length at maturity and litter size of the blue shark were found to vary among different regions (Nakano & Stevens, 2008;Pratt, 1979).…”