Estimation of differential growth of the protandrous hermaphrodite marine gastropod Trochita trochiformis (Littorinimorpha: Calyptraeidae) using Schnute model cases

Abstract

The snail Trochita trochiformis is a mollusk captured on the coasts of Jalisco and Guerrero of the Mexican Pacific. Despite its importance in artisanal fisheries, information on its population parameters is still being determined. This research aimed to determine the diameter-weight relationship, sex ratio, cohorts, and growth of this species. Specimens were captured from October 2019 to September 2021. Shell diameter (Sd), total weight (Tw), and the sex of the organisms were gathered from a total of 1763 females and 956 males. The sex ratio was 1.84:1, and the X2 test (P < 0.05) indicated significant differences. The Sd-Tw relationship for females and males was potential-type. The values of the allometry coefficient for both sexes were b = 2.61, b = 2.60 for females, and b = 2.62 for males. In all three cases, the t-Student test indicated negative allometric growth, which indicates that the species first grows in shell diameter, then in body weight. The ANCOVA did not show significant differences in the Sd-Tw relationships between sexes (P = 0.902). The Kolmogorov-Smirnov test applied to the Sd data showed differences between sexes (P < 0.001). In females, differences were observed in 71.5% by monthly comparisons, while in males, differences were found in 58.1%. Multinomial analysis showed three modal groups and 14 individual cohorts for both females and males. Case 2 of the Schnute model was the best for females (wi = 0.39) and males (wi = 0.53), showing sigmoidal Gompertz-type growth. The resulting growth curves showed that females exhibit accelerated growth concerning males and that both sexes reach their maximum size, 88.04 and 86.23 mm, respectively, at approximately 10 years of age.