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

An update of the age and growth for juveniles of the short fin mako shark (I. oxyrinchus) from the Mexican Pacific is presented, based on the analysis of growth band counts from dorsal vertebrae of 198 individuals [110 females, 74-231 cm of total length (TL) and 88 males, 72-231 cm TL) caught during 2008-2018. New available information on vertebral growth band periodicity (biannual deposition in juveniles) and the convenience of using vertebrae form the dorsal region over the cervical region to count growth bands, as well as a multimodel approach, were used. The von Bertalanffy (VB) growth model, Gompertz, logistic and two parameters of VB (2-VB) were fitted to the length-at-age. Only ages <= 6 years were used for the fitting of the models and their performance was compared with the small-sample bias-corrected form of the Akaike information criterion (AICc), their differences (Delta(i)) and weights (w(i)). Following a multimodel inference approach, the model averaged asymptotic length ((L) over bar (inf)), length-at-age 0 ((L) over bar (0)) and their unconditional standard error ((SE) over bar), were estimated for each sex scenario using the three-parameter version of each model. The precision of growth band counts was acceptable for the different methods used and by two different readers. The centrum edge analysis (CEA) and marginal increment analysis (MIA) did not support the hypothesis of biannual band pair formation for juveniles, likewise for adults the periodicity could not be verified due to the small sample of large animals. Age was estimated assuming the formation of two pairs of growth bands per year during the first 5 years and one pair of bands per year afterwards considering direct validation information. The estimated ages in years ranged from 0-14 for females and 0-6 for males. The Kimura likelihood ratio test showed no differences in the growth curves of juveniles by sex (P > 0.05). According to the AICc, the 2-VB model better fitted the length-at-age data for combined sexes (L-inf = 386.4 cm, k= 0.12 years(-1), L0= 70 cm). The model averaged (L) over bar (inf) and (L) over bar (0) were 378.3 cm ((SE) over bar = 64:5) and 69.5 cm ((SE) over bar = 6:3), respectively. The growth parameters determined for juveniles of I. oxyrinchus are similar to those estimated in other

Automated summary

This study provides an updated understanding of the age and growth of juvenile short fin mako sharks from the Mexican Pacific based on the analysis of growth band counts from dorsal vertebrae. Multiple models were compared for their fit to the length-at-age data, and the two-parameter von Bertalanffy model was found to be the best fit. The precision of growth band counts was satisfactory, although the periodicity of growth bands in juveniles and adults could not be definitively determined due to limited sample size. Age was estimated based on the assumption of growth band pair formation, and the estimated ages ranged from 0-14 years for females and 0-6 years for males.