Jodie L. Rummer

Body condition is an important proxy for the overall health and energetic status of fishes. The classically used Fulton's condition factor requires length and mass measurements, but mass can be difficult to obtain in large species. Girth measurements can replace mass for wild pelagic sharks. However, girth‐calculated condition has not been validated against Fulton's condition factor intraspecifically, across ontogeny or reproduction, or in a controlled setting. We used the epaulette shark ( Hemiscyllium ocellatum ), because they are amenable to captive reproduction, to track fine‐scale body condition changes across life stages, oviparous reproduction and between condition indices. We measured four girths, total length and mass of 16 captive epaulette sharks across 1 year and tracked female reproduction daily. We also collected length and mass data from an additional 72 wild‐caught sharks and 155 sharks from five previous studies and two public aquaria to examine the relationship between length and mass for this species. Even though data were derived from a variety of sources, a predictable length–mass relationship ( R 2 = 0.990) was achievable, indicating that combining data from a variety of sources could help overcome knowledge gaps regarding basic life history characteristics. We also found that condition factor decreased during early life stages, then increased again into adulthood, with predictable changes across the female reproductive cycle. Finally, we determined that both Fulton's and girth condition analyses were comparable. Outcomes from this study uniquely provide body condition changes across the complete life history, including fine‐scale female reproductive stages, and validate the use of girths as a nonlethal whole‐organism energetic assessment for fishes.

Accelerative manoeuvres, such as fast-starts, are crucial for fish to avoid predation. Escape responses are fast-starts that include fundamental survival traits for prey that experience high predation pressure. However, no previous study has assessed escape performance in neonate tropical sharks. We quantitatively evaluated vulnerability traits of neonate tropical sharks by testing predictions on their fast-start escape performance. We predicted (1) high manoeuvrability, given their high flexibility, but (2) low propulsive locomotion owing to the drag costs associated with pectoral fin extension during escape responses. Further, based on previous work on dogfish, Squalus suckleyi, we predicted (3) long reaction times (as latencies longer than teleosts, >20 ms). We used two-dimensional, high-speed videography analysis of mechano-acoustically stimulated neonate blacktip reef shark, Carcharhinus melanopterus (n=12), and sicklefin lemon shark, Negaprion acutidens (n=8). Both species performed a characteristic C-start double-bend response (i.e. two body bends), but single-bend responses were only observed in N. acutidens. As predicted, neonate sharks showed high manoeuvrability with high turning rates and tight turning radii (3–11% of body length) but low propulsive performance (i.e. speed, acceleration and velocity) when compared with similar-sized teleosts and S. suckleyi. Contrary to expectations, escape latencies were <20 ms in both species, suggesting that the neurophysiological system of sharks when reacting to a predatory attack may not be limited to long response times. These results provide a quantitative assessment of survival traits in neonate tropical sharks that will be crucial for future studies that consider the vulnerability of these sharks to predation.