Maximum sustainable swimming speeds of late-stage larvae of nine species of reef fishes

We examined the maximum sustainable swimming speed of late-stage larvae of nine species of tropical reef fishes from around Lizard Island, Great Barrier Reef, Australia. Larvae were captured in light traps and were swum in flumes at different experimental swimming speeds (of 5 cm s⁻¹ intervals) continuously for 24 h. Logistic regression was used to determine the speed at which 90% of larvae were able to maintain swimming, and this was used to indicate the maximum sustainable swimming speed for each species. Maximum sustainable swimming speeds varied among the species examined, with the lethrinid maintaining the fastest sustainable swimming speed (24 cm s⁻¹), followed by the Pomacentridae (10-20 cm s⁻¹) and the Apogonidae (8-12 cm s⁻¹). U-crit (maximum speed) explained 64% of the variation in sustainable speed among species, whereas total length only explained 33% of the variation in sustained swimming. A regression fitted across species suggests that 50% U-crit is a good approximation of the speed able to be maintained by these larvae for 24 h. A model based on a cubic relationship between sustained swimming time and speed was found to be more successful than either length or U-crit as a method of estimating sustainable swimming speed for most of the species examined. Overall, we found that swimming speed is an important factor when considering the potential for active swimming behaviour to influence dispersal patterns, recruitment success and levels of self-recruitment in reef fish larvae and needs to be carefully considered in models of larval dispersal.