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

Abstract

Accurate estimation of growth parameters is vital for stock assessments and management of exploited species. To determine if changes in sex-specific growth parameters of the blue shark (Prionace glauca) have occurred in the North Pacific Ocean following population declines in the 1980s and 1990s, we analyzed data obtained from the vertebrae of 659 male and 620 female sharks that had precaudal lengths (PCLs) of 33.4-258.3 cm and were captured over a wide geographic area between 2010 and 2016. Maximum counts of growth bands were 18 for males and 17 for females. Significant (P<0.001) between-sex differences were detected in growth parameters. We estimated parameters of the von Bertalanffy growth function: for males, the theoretical asymptotic length (L ∞ ) was 284.9 cm PCL, the growth coefficient (k) was 0.117/year, and the theoretical age at zero length (t 0 ) was −1.35 years, and, for females, L ∞ was 257.2 cm PCL, k was 0.146/year, and t 0 was −0.97 years. Sexual discrepancies in growth rates are likely a function of differences in energy allocation relating to reproduction between sexes. Given that no remarkable change in growth parameters was observed over 3 decades, life history parameters of this population do not appear to have been affected by shifts in stock abundance or environmental fluctuation.

Re‐estimation of juvenile Isurus oxyrinchus growth in the Mexican Pacific through a multimodel inference approach and verification of growth band periodicity

“…Based on our age data from the MP, it can be concluded that juveniles of I. oxyrinchus have a relatively fast growth rate, as has previously been reported for the species in the NPO (Kai et al ., 2015) and Northwest Atlantic (Branstetter, 1990), with implications for their biological productivity and resilience to fishing. The growth of the species is similar to that of other oceanic species, such as blue ( Prionace glauca ) and thresher sharks ( Alopias pelagicus ), with similar growth coefficients reported for both females ( k = 0.15/0.09 year −1 ) and males ( k = 0.12/0.12 year −1 ) (Fujinami et al ., 2019; Liu et al ., 1999). Our results provide an insight into the population structure, with greater precision for neonates and juvenile growth.…”

Age and Growth of Southern Bluefin Tuna, Thunnus maccoyii, Based on Otolith Microstructure

“…There would be the differences between otolith processing methods and its interpretation. Accurate estimation of growth parameters is vital for stock assessments and management of exploited species (Fujinami et al 2019). Mendoza (2006) also noted that accurate size-at-age and age-at-first maturity estimations are highly important for conservation and management of exploitable fishery resources.…”

Size structure, age, and growth of the blue shark, Prionace glauca (Linnaeus, 1758) in southern Brazil

“…The birthmark was identified by a change in the angle of the inner margin of the corpus calcareum , exhibiting the transition from pre‐ to postnatal growth, thus, established as age zero (Goldman et al, 2012) (Figure 2). The vertebral radius (VR) was measured from the focus to the edge of the centrum of the vertebrae perpendicular to the direction of the cutting plane (Fujinami et al, 2019) using the measuring programme ImageJ (Schneider et al, 2012). The VR to FL relationship was estimated by using a linear regression and was compared by sex using the ANCOVA.…”

“…2). The vertebral radius (VR) was measured from the focus to the edge of the centrum of the vertebrae perpendicular to the direction of the cutting plane (Fujinami et al, 2019) using the measuring programme ImageJ (Schneider et al, 2012). The VR to FL relationship was estimated by using a linear regression and was compared by sex using the ANCOVA.…”

“…The most common method for studying growth in elasmobranchs is by interpreting band pairs (one obscure and one opaque) in vertebral centra to estimate growth parameters such as asymptotic length (L∞) and growth coefficient (k) using available growth models (Goldman et al, 2012). Accurate information about growth-related life history is crucial for the sustainable management of an exploited species and for monitoring how these parameters may change over time (Fujinami et al, 2019). Montealegre-Quijano (2007) estimated the growth parameters for blue sharks in the southwestern Atlantic region during the 2004-2006 period (Table 1).…”