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

Young-of-the-year (YOY) bay anchovy Anchoa mitchilli occur in higher propor tion relative to larvae in the upper Chesapeake Bay. This has led to the hy pothesis that up-bay dispersal favors recruitment. Here we test whether rec ruitment of bay anchovy to different parts of the Chesapeake Bay results fr om differential dispersal rates. Electron microprobe analysis of otolith st rontium was used to hind-cast patterns and rates of movement across salinit y zones. Individual chronologies of strontium were constructed for 55 bay a nchovy aged 43 to 103 d collected at 5 Chesapeake Bay mainstem sites repres enting upper, middle, and lower regions of the bay during September 1998. M ost YOY anchovy were estimated to have originated in the lower bay. Those c ollected 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-es tuary occurred for recruits captured at the polyhaline (greater than or equ al to 18 psu) site. Initiation of ingress to lower salinity waters (<15 psu ) was estimated to occur near metamorphosis, during the early juvenile stag e, at sizes <greater than or equal to>25 mm standard length (SL) and ages g reater than or equal to 50 d after hatch. Estimated maximum upstream disper sal rate (over-the-ground speed) during the first 50 to 100 d of life excee ded 50 mm s(-1).