Thursday, November 11, 2010


A quick view of the website for the Herring Alliance gives the impression that the biggest issue impeding the recovery of river herring stocks is by catch from the Atlantic herring fishery.  While there are certainly other factors contributing to the consistently low levels of river herring, including habitat loss and direct commercial catches, there is no doubt that by catch is a major factor.  The dilemma that occurs when attempting to restrict or manage river herring by catch is that so little is known about their marine migrations. 

Enter otolith microchemistry.

I have already written, and it has been well documented in the literature, about the ability of otoliths to record the natal origins of fish.  Theoretically, as long as there is data about the elemental signature of individual watersheds, river herring caught in the open ocean could be classified to natal rivers.  Knowing the natal origins of a fish captured in the open ocean is an incredible piece of information but is incredibly difficult to obtain.  Traditional tagging studies, where the fish is physically given some type of mark or tag, are difficult because of the large sample size, and amount of effort that is needed to carry out these studies.  Capturing small juvenile fish, while they are still in their natal area, and marking them is pretty much a death sentence and in most instances probably not practical.  The most effective larval/juvenile tagging studies utilize hatchery raised fish that have been marked with fin clips or been given chemical marks on their otoliths.  However, marking and recapturing hatchery-raised fish gives us no information about the behaviors of wild spawned fish.    

Knowing the natal origins of ocean caught fish (combined with age data also obtained from otoliths)  can provide valuable information about migration patterns, schooling behavior, stock structure, recruitment, and exploitation rates.  This data can then be used to strengthen management decisions.  As research on elemental signatures in otoliths continues to progress networks of signatures for rivers along the east coast can be built up so that some of these questions can be answered.    

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