Characterizing growth patterns of bottlenose dolphins (Tursiops truncatus) in Sarasota Bay

Abstract

Growth patterns of specific body structures provide insight into the physiological and developmental processes underlying their function; however, collecting morphological data on these body structures is challenging for large animals in the marine environment due to the logistics of collecting hands-on measurements and the limitations of data provided by other methods (e.g., photogrammetry). Despite these challenges, the Sarasota Dolphin Research Program has more than 50 years of morphometric data collected on the resident common bottlenose dolphin ( Tursiops truncatus ) in Sarasota Bay. Other studies have documented sexual dimorphism for some morphological features within this dolphin community; however, most have focused on maximum length and girth, and few have considered variation in growth at the individual level. This study developed growth models using repeated measurements of individuals to examine growth patterns and potential sexual dimorphism of twenty less-studied body traits of Sarasota Bay bottlenose dolphins. Measurements were collected during catch-and-release projects (n = 218) and necropsies (n = 59) during 1988 through 2024. Gompertz and Richards growth curves were used to model measurements, and growth parameters were bootstrapped with 95% confidence intervals to determine whether sexual dimorphism was present for each measurement. Sexual dimorphism existed for all measurements assessed, with males typically growing larger than females and females reaching maximum size earlier in life. All measurements exhibited generally low within- and among-individual variation, with standard deviations and random effect residuals being less than 10% of the population averages. Understanding the growth of individual morphological features can help us recognize sex-specific challenges and adaptations driven by size and morphology.