Up-estuary dispersal of young-of-the-year bay anchovy Anchoa mitchilli in the Chesapeake Bay: Inferences from microprobe analysis of strontium in otoliths

Abstract

Young-of-the-year (YOY) bay anchovy Anchoa mitchilli occur in higher proportion relative to larvae in the upper Chesapeake Bay. This has led to the hypothesis that up-bay dispersal favors recruitment. Here we test whether recruitment of bay anchovy to different parts of the Chesapeake Bay results from differential dispersal rates. Electron microprobe analysis of otolith strontium was used to hind-cast patterns and rates of movement across salinity zones. Individual chronologies of strontium were constructed for 55 bay anchovy aged 43 to 103 d collected at 5 Chesapeake Bay mainstem sites representing upper, middle, and lower regions of the bay during September 1998. Most YOY anchovy were estimated to have originated in the lower bay. Those collected at 5 and 11 psu sites exhibited the highest past dispersal rates, all in an up-estuary direction. No significant net dispersal up- or down-estuary occurred for recruits captured at the polyhaline (≥18 psu) site. Initiation of ingress to lower salinity waters (<15 psu) was estimated to occur near metamorphosis, during the early juvenile stage, at sizes ≥25 mm standard length (SL) and ages ≥50 d after hatch. Estimated maximum upstream dispersal rate (over-the-ground speed) during the first 50 to 100 d of life exceeded 50 mm s-1.