Old fish caught in Samoa
This is hard to believe -- an 18 year old alogo was caught in American Samoa. That's old enough to get a drivers license.
We're talking about the alogo, also known as the bluelined surgeonfish Acanthurus lineatus. Nothing unusual about its size -- it was the standard 8-inch alogo you see in the stores. And I ate it. All that remained were the little bones that scientists use to determine the age of the fish. These bones, when looked at under a microscope, have concentric circles, one for each year, just like tree rings. You just count the rings and that's how old the fish is.
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| Rob Meyers, Coral Graphics, Guam |
What's even more astonishing is that an alogo caught in Australia's Great Barrier Reef was 44 years old. I am not kidding. Reputable scientists determined the age of that fish. There were also other alogo in the Australian sample that were 20-40 years old, so the record age of 44 is believable. These old fish were not unusually large, just the standard size alogo.
It turns out that this is not unusual for coral reef fish. Recent studies show that several other species of surgeonfish (pone), unicornfish (ume), groupers (gatala) and snappers (mu) can also live up to 20-40 years. These findings are beginning to reshape our understanding about the ecology of coral reef fishes and their vulnerability to overfishing. The occurrence of many long-lived fish in a population indicates that the coral reef fish community is fairly stable, with a low replacement of individual fish. Once a young fish gets to the reef, it may be there for decades.
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| I’asina in a basket trap |
Why would these fish live so long? The answer provides some key information about the environment that the fish live in. Fish typically exhibit this type of life cycle (long life span and repeat spawning) when few of their young survive. That's certainly the case for coral reef fish – their thousands of eggs and larvae drift around with the ocean currents for weeks or months. Very few of them make it back to the reefs. So, if all their young usually die, the fish need to live a long time and spawn repeatedly to make sure that at least some young survive. If the adults lived only a short time, the population might disappear altogether.
Every so often however, during years when the ocean currents and conditions are just right, massive numbers of young fish survive and appear on our reefs, like pala'ia (young pone surgeonfish) or i'asina (young goatfish).
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| Fish for dinner - Photo by Eva Pasko |
While this is, of course, all very interesting, there is an important take-home message. It is easy to overfish populations with these life history characteristics. Having a long life span and spawning repeatedly may be a successful strategy under natural conditions, but it also makes these fish extra vulnerable to overfishing. That's because fishermen tend to harvest the larger (older) fish in the population. Under heavy fishing pressure, all the old fish may be taken, leaving only the smaller, younger fish. That would put the population in a very precarious situation, because the younger fish left may not yet be old enough to spawn. This type of overfishing probably occurred on Tutuila's coral reefs in the 1990s and may be continuing. It is a common belief that fish on our reefs are fewer and smaller than they used to be, and there is some scientific evidence to support this.
Two fisheries in American Samoa target these coral reef fish -- the subsistence fishery and the artisanal (small-scale commercial) fishery. Subsistence fishing includes the multiple ways that Samoans have always caught nearshore fish. These catches declined significantly in the early 1990s, but the current status is not known.
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| Roadside fish seller |
The artisanal fishery that sells reef fish to local stores is a relatively recent development. It is conducted by teams of night divers who use underwater flashlights and spears to catch sleeping fish. In the mid 1990s, many of these divers switched from free-diving to scuba diving, which greatly increased the number of fish they could take. It is likely that this type of fishing had a significant impact on our reef fish populations, so the use of scuba gear while spear fishing was banned in the Territory in early 2000.
So, that 18 year old alogo was not just an unusual trophy – it was also a vital member of the fish community that spawned year after year (for about 14 years after it reached maturity at age 4), thereby insuring that some young fish survived to maintain a healthy population of alogo on our reefs.
P. Craig, NPS