Sinking rates of late-stage fish larvae: Implications for larval ingress into estuarine nursery habitats

Many species spawn in oceanic waters yet their juvenile stages use nearshore and estuarine habits and the bio-physical mechanisms by which late-larvae enter these juvenile habitats may be an important bottleneck in the population dynamics of these species. To provide parameters for the development of larval ingress models, sinking rates were measured of the late-stage larvae of six fish species: Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus), Atlantic menhaden (Brevoortia tyrannus), summer flounder (Paralichthys dentatus), southern flounder (P. lethostigma), and gulf flounder (P. albigutta). Species-specific differences were found in sinking rates; Atlantic croaker had the slowest sinking rates and Atlantic menhaden and the three flounder species had the fastest sinking rates. Additionally, sinking rates increased for all species as length increased. The total amount of variability explained in sinking rates was low (20–50%), indicating a large amount of variability at the level of the individual. The observed patterns in sinking rates were then combined with previous studies on the mechanisms of larval ingress to present species-specific conceptual models of ingress.