Scales and Otoliths
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Don Mortensen
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries
Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau AK 99801
(907)789-6088
Don.Mortensen@noaa.gov
Scales are protective plates which grow on the skin of most fish. Scales
are made of layers of calcium and fibrous collagen. Otoliths, or ear stones, are bone-like structures found in the heads of
most fishes. Otoliths provide the fish with a sense of balance and
orientation and also aid in hearing.
To the fisheries biologist, fish scales and otoliths are important
tools for understanding the life of fish and fish populations. As
fish grow, scales and otoliths also grow proportionally, with circuli laid down much like the growth rings of a tree. As fish
growth slows during the winter, the circuli of scales and otoliths bunch
closer together and form darker bands known as annuli. These circuli and annuli record age and growth patterns of the fish in
surprising detail. Virtually the entire growth history of a fish
is recorded in its scales and otoliths.
Scale and otolith research at the Auke Bay Laboratory centers around
developing and using methods for interpreting and using fish scales and otoliths in studies of fish biology, fish population dynamics, and fish
stock assessments. We are involved in many aspects of this
research, from routine age determinations to the latest advances in mass
marking and chemical isotope dilutions using of electron
microprobes and mass spectrophotometers.
For more information on recent research, see:
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