The effects of temperature and swimming speed on the metabolic rate of the nurse shark (Ginglymostoma cirratum, Bonaterre)

Abstract

Sharks and other top predators have a substantial impact on their ecosystems through trophically mediated effects, and understanding the scope of this impact is essential to forming an accurate picture of energy flow within an ecosystem. One of the most important factors to consider when assessing a predator's impact on their ecosystem is metabolic rate, which is dependent on a number of environmental factors including temperature, as well as underlying physiological and anatomical characteristics. Here the standard (SMR) and routine metabolic rates (RMR) and swimming dynamics of the nurse shark (Ginglymostoma cirratum, Bonaterre) were assessed using a static respirometer over two experimental temperatures (23 and 30°C). The metabolic rates measured here represent the lowest reported for any shark species to date. Mean (±SD) SMRs at 23°C and 30°C were 36±8 and 60±17mgO2kg-1h-1, and mean RMRs were 95±15 and 138±21mgO2kg-1h-1, respectively. The Q10 for SMR was 2.42 between 23 and 30°C. Minimum cost of transport (COTmin) at 23°C was 68mgO2kg-1km-1, where swimming speed was 0.33BLs-1. The COTmin increased to 81mgO2kg-1km-1 at 30°C, where swimming speed was 0.44BLs-1. The proportional cost of activity, or the cost of activity relative to SMR, was greater compared to other elasmobranchs, and nearly twice that of most ram ventilating shark species. These results highlight the sedentary nature of nurse sharks and suggest that they are energetically suited for a minimally active lifestyle.