Ontogeny of critical swimming speeds for larval and pelagic juvenile rockfishes (Sebastes spp., family Scorpaenidae)

Abstract

Understanding the mechanisms that affect larval dispersal is critical to management of marine populations. Rockfishes Sebastes spp. do not settle to benthic habitats immediately after metamorphosis, but instead remain in the water column for weeks to months. Movements of larvae and pelagic juveniles during their months at sea are largely unknown. It is traditionally thought that young rockfishes are planktonic, moving at the mercy of ocean currents, but this assumption is unverified. In this study, swimming capabilities (critical speed) of larval and pelagic juvenile stages of 6 rockfish species (blue [S. mystinus], yellowtail [S. flavidus], brown [S. auriculatus], kelp [S. atrovirens], gopher [S. carnatus], and splitnose [S. diploproa]) were evaluated to determine their ability to behaviorally influence dispersal. Rockfish larvae have critical speeds of 0.5 to 1.8 cm s-1 (1 to 3 body lengths per second [bl s-1]) at parturition, whereas newly settled juveniles are capable of swimming 8.6 to 53.5 cm s-1 (5 to 9 bl s-1). Swimming ability increases throughout ontogeny and postflexion rockfishes can swim faster than typical water motions in their natural habitat (i.e. mean ocean currents off central California). Critical speeds for Sebastes spp. are substantially lower than those for larvae and juveniles of tropical species at similar body sizes. Rockfishes, however, have swimming speeds at settlement comparable to some tropical species, as rockfishes settle at larger sizes. The increasing ability of rockfishes to outswim currents during their pelagic phase (acting as nekton rather than plankton) may promote individual survival as well as enhance retention and/or long-distance dispersal-thus swimming has important implications for population connectivity and sustainability. © Inter-Research 2014.