Science Serving Maryland's Coasts

Troy Gunderson, Boston University

Class Year: 

Project Title: 

Otolith Microchemical Analysis of Larval Bay Anchovy (Anchoa mitchilli) in Chesapeake Bay


The abundance and wide, euryhaline distribution of bay anchovy Anchoa mitchilli, make it difficult to monitor migration patterns throughout its complete life history. Otolith microchemical analysis was applied to larval bay anchovy from Chesapeake Bay with the objectives to (1) develop procedures, (2) determine if otoliths of larvae have Sr/Ca ratios that are directly related to the salinity level in their region of collection, and (3) determine if changes in Sr/Ca ration have occurred in the otoliths which are indicative of larval transport or migration across salinity zones during the first several weeks posthatch. Otolith Sr/Ca ratios were analyzed for 25 bay anchovy larvae collected from five areas throughout Chesapeake Bay in June and July 1993, representing upper, middle, and lower regions of the Bay. Microchemical analysis of otoliths was carried out with a wavelength dispersive electron microprobe. There was a weak, but significant, regression of otolith Sr.Ca ratios on salinity in larval bay anchovy. It was possible to distinguish most otoliths from larvae collected in low or high salinities (i.e. 5 or 25 ppt). Variation in the Sr/Ca ratio among juvenile and larval bay anchovy otolith data showed significant overlap in Sr/Ca levels at salinities below 15 ppt and a nearly 3 fold higher Sr uptake rate for juveniles than for larvae, suggesting a possible ontogenetic effect. Laboratory-rearing experiments using known salinities, as well as the need to analyze larger sample sizes from a wider range of salinities, are necessary to confirm whether otolith microchemical analysis is applicable to understanding migration or transport of larval bay anchovy.