Dating fishermen

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The lead-radium measurements are performed in Hawaii and the carbon-14 readings are done at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAM) at Woods Hole Oceanographic Institution.

Bomb radiocarbon dating can determine the age of individual fish with high precision (± 1 to 2 years).

It can be used to determine ages for fish ranging from a few years to about 100 years.

The approach relies on a conserved record of the rapid increase in radiocarbon (14C) that occurred in the oceans of the world as a result of atmospheric testing of thermonuclear devices in the 1950's and 1960's.

An example of how this works is if a fish was captured in 1995 and its otolith core radiocarbon matched the coral record from 1965.

This fish was 30 years old."The coral records are a nice time-specific record of marine chemistry including the radiocarbon signal created by the bomb tests in the 50's and 60's," said Allen H.

Andrews, a Ph D ichthyologist who works as a Research Fisheries Biologist at the Pacific Islands Fisheries Center of NOAA Fisheries.

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Overall, the age and growth calculated for young fish by other methods remained valid up to about 5-10 years, but the extrapolated maximum ages underestimated true age.

This recently turned out to be the case with the bluespine unicornfish (Naso unicornis), a fish commonly seen by snorkelers in Hawaii and known locally as Kala.

This fish may seem like a small to medium-sized reef fish to most people, but it can be a regular part of fish markets reaching a maximum size of up to 27 inches.

Lead-radium dating, on the other hand, can be used for fish of any age but detection limits require the pooling of otoliths from many fish to attain measureable lead-radium levels.

A group of fish of similar size is used, and the result is an estimate of average age for the group.

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