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

Abstract

Basic population parameters such as age, size, and distribution have been poorly evaluated for the Shortfin Mako Isurus oxyrinchus in the Mexican Pacific Ocean. According to data collected by scientific observers on board medium‐size fishing vessels during the period of 2006–2013, size as TL was obtained for 5,740 individual sharks. The range of TL was 70–362 cm for females and 71–296 cm for males. Weight (W), measured randomly from 1,409 individuals, ranged from 2 to 90 kg for females and from 2 to 80 kg for males. The weight‐to‐TL ratio was best fitted by the equation W = 4 × 10⁻⁵(TL)^2.59 (r² = 0.6532). No sex‐specific difference was found in the weight‐to‐TL relationship between males and females, nor in W or TL separately. By using the inverse von Bertalanffy equation and parameters described by other authors for the same study area, we determined the age range for individuals captured on the basis of their TL. The age ranged from 0 to 39 years in females and from 0 to 21 years in males. Using a logistic model, the mean length at sexual maturity was obtained for 2,532 males (TL = 190 cm). The quarterly distribution of young of the year and 1‐year‐old juveniles showed that there is a tendency for these sharks to move northward as sea surface temperature increases. Our findings shed new light on how Shortfin Mako juveniles use a habitat that has been proposed by other authors as a nursery area for this species, information that is valuable for the sustainability of the Mexican Pacific fisheries.