Ageing Methods
Appropriate hard parts for ageing (otoliths, vertebrae or spines) are removed from each fish that is subsampled and brought back to VIMS for further analysis. Otoliths are earbones located behind the brain in the skull of the fish which aid in balance and hearing. Fish lay down rings annually and we are able to count them like the rings of a tree. (The photo to the right is a Weakfish otolith extraction.)
Otolith and vertebrae samples are sectioned using a low-speed isomet saw (pictured below) and sanded to an appropriate thickness. Samples are read by three independent readers using a transmitted light microscope. Whole spines are read by three independent readers using a dissecting microscope with reflected light.
The samples processed allow us to determine the age of the fish when it was caught. With this data, we can get a clear picture of the age structure of the population present in the nearshore waters from Cape Hatteras, NC north to Cape Cod, MA.
Fish |
Whole Otolith |
Sectioned Otolith used for ageing fish |
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Winter Flounder Cut Otolith |
