Sunday, April 5, 2015

Hāpu`upu`u and `ōpakapaka are way older than anyone knew

Groupers are among the grandfathers of the Hawaiian reef. And in the deep waters, pink snappers are right up there with them.

Some of them live for as many as five decades.

(Image: The Hawaiian grouper hāpu`upu`u or Hyporthodus quernus. Credit: NOAA.)

And you can thank the nuclear bomb testing of the 1950s and 60s for knowing that. The nuclear testing put a pulse of radiation into the environment that scientists are using to date biological material.

It has extended dramatically the previously believed maximum age of both the  hāpu`upu`u and the `ōpakapaka.

A group of researchers led by Allen Andrews from the Pacific Fisheries Science Center (PIFSC) used radioactive carbon signatures in the bony parts of fish—like the ear bones or otoliths—to determine their age.

Previously, fish ages have been estimated by counting the growth zones in the otoliths. But earlier tests indicated that otolith age testing was of questionable value for determining grouper ages when it came to the bigger, older fish. The age of young fish worked out well, but as the animals reached maturity, the otolith growth zone technique delivered more challenging results.

“Age estimates were dubious for the largest fish,” said a NOAA report on the subject in 2012.

But the nuclear testing inserted known data point into the mix. Researchers know when the ocean radioactivity increased as a result of the bomb testing, and in older fish, they could see that radioactivity signature in the bones.

“As they grow, otoliths reflect the ocean chemistry during the time they are formed. Thus by comparing measurements of radiocarbon in the otolith to a marine radiocarbon reference, the fish's age can be determined,” the PIFSC paper says.

(Image: an otolith or fish earbone, which can be used to determine the fish’s age. Credit: NOAA.)

So by adding the valid growth zone data from before the radioactivity spike to the time since the spike, they were able to accurately age groupers. It is a type of study that had previously been performed on the bottomfish `ōpakapapa, also known as pink snapper or Pristipomoides filamentosus

With respect to the hāpu`upu`u, the oldest fish found using growth zone counting was 34. But the bomb counting technique brought an oldest age of 43. And since there are bigger fish than the 43-year-old, the researchers assume there are still older groupers.

In the `ōpakapaka paper, researchers Andrews, Robert L. Humphreys, Edward E. DeMartini, Ryan S. Nichols and Jon Brodziak found that previous estimates of a maximum 18-year longevity for the pink snapper was wrong. There was a similar problem as with the hāpu`upu`u with difficulty of aging older fish.

“Bomb radiocarbon dating requires birth year otolith material to have formed between
approximately 1955 and 1970 for age determination, and recently collected fish would need to be between 40 to 55 years old for the method to be applicable,” they wrote in their 2011 paper

They came up with a mean age of 45.6 years for the largest Hawaiian `ōpakapaka—more than twice as old as previously assumed. And some of them, too, may be way older than that.

© Jan TenBruggencate 2015

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