Age and growth of the blue shark, prionace glauca Linnaeus, 1758, in the northwest coast off Mexico

The blue shark is one of the main species caught in the artisanal fisheries in the northwest coast of Mexico. The age and growth was estimated by counting the growth bands on vertebral centra stained with silver nitrate from 204 sharks. Shark sizes ranged from 81 to 270 cm total length (TL), with a mean of 165 ± 35 cm and a sex ratio of 2:1 between males and females. Male lengths ranged from 81 to 270 cm TL (mean 150.4 ± 32.3 cm, n=593) and female lengths ranged from 90 to 252 cm TL (mean 162.7 ± 37.5 cm, n=324). The relationship between TL and the vertebral centrum radio (CR) was linear indicating a positive relationship between the vertebral centrum growth and body growth. IAPE estimated value was 3.0%. Maximum age estimated for males was 16 years and for females, 12 years. The majority of the sharks in the catches were juveniles of age four (134 ± 13 cm TL) and age seven (174 ± 21 cm TL) from which 19% were males and 22% were females. The von Bertalanffy growth parameters were: L_∞ = 299.85 cm TL, K = 0.10 years^-1 and t₀ = -2.44 years for males and L_∞ = 237.5 cm TL, K = 0.15 years^-1 and t₀ = -2.15 years for females; differences in growth were found between sexes. Growth parameters were within the range of previous values reported for blue sharks in the Pacific Ocean.