Pacific Grenadier, An Old-Growth Fish? by Mari N. Jensen
Knowing a fish's age is crucial for proper fisheries management, but until recently, scientists did not know whether the Pacific grenadier was six or sixty.
In the Monterey Bay area, Pacific grenadier used to be considered a junk fish. But as near-shore fish species get fished out or regulations become stricter, commercial fishers must turn to new species."In the '70s, people started fishing sablefish [black cod], in the '80s, they started fishing thornyhead," Gregor Cailliet, an ichthyologist at Moss Landing Marine Laboratories in Salinas, California, says. "And in '90s, now they're going farther offshore for grenadier."
Jim Glock, fishery management coordinator for the Pacific Fishery Management Council, says, "There's no specific management for grenadier: There's no annual quota, there's no restriction on vessels, there's no closed season."
There was never a need for it before; no one wanted to buy the ugly, bug-eyed fish known as Pacific rat-tail. But even with that unappetizing appearance, the mild-tasting white fillets of Pacific grenadier, the fish scientists call Coryphaenoides acrolepis, are increasingly popular with customers at the local Safeway.
Long-lived animals that mature and reproduce slowly produce fewer offspring than fast-growing, fast-reproducing animals like rabbits. Some deep-water fish grow slowly. If scientists find that the Pacific grenadier matures slowly and reproduces infrequently, increases in the Pacific grenadier catch off the central California coast could damage the fish population.
Traditional methods of determining a fish's age require scientists to capture live fish and collect years' worth of growth records: either the detainees are kept in aquaria for years to observe growth rates or the fish are measured, tagged, released, and recaptured years later and re-measured.
Such methods do not work with the Pacific grenadier. One reason is that dragging the fishes topside from their 600-meter-deep (2,000 feet) homes gives them "big, big pressure problems," says Allen Andrews, a researcher at Moss Landing Marine Laboratories. Gases in the fishes' bladders expand rapidly, popping their stomachs out their mouths and making their eyes bug out. The result: a lot of dead, ugly fish of indeterminate age.
For dead fish, biologists have estimated ages by counting annual rings on scales or annual rings on otoliths (fish earbones). But unlike trees, the rings on fish scales and otoliths may or may not be annual: it depends on the species. With Pacific grenadier and other deep-water fish, calibrating the ring-counting method by tracking live fish is impossible. Researchers cannot be sure how many years one ring represents, and age estimates for the Pacific grenadier range from six to 60 years old.
"If they are 60 years old," Andrews says, "You're cutting down the old-growth fish."
Rapid exploitation of slow-growing deep-water fish can be the recipe for a crash - which is what happened in New Zealand's orange roughy fishery in the 1980s. Ellen Pikitch, Director of Fisheries Programs at the Wildlife Conservation Society in New York City, says, "The longer lived the fish is, the lower the fraction of the population you can harvest on a sustainable basis."
When people began fishing orange roughy commercially, fisheries biologists assumed the fish lived 20 to 30 years. That meant biologists set the catch limits too high, because orange roughy actually lives over 100 years. That first - discovered orange roughy population got overfished in fewer than five years. When people finally realized their mistake, "There wasn't very much you could do about that stock," Pikitch says "It will take a very long time to come back."
Andrews is conquering the Pacific grenadiers' reluctance to reveal their correct ages. He finds that a 70 centimeter (27 inches) grenadier can be 60 years old; which means it's a slow-growing fish.
To determine the age of this new dinner from the deep, Andrews and his colleagues use a so-called radioactive clock that was incorporated into the fish's earbone, or otolith, when the fish was born. Just as sand flows from top to bottom of an hourglass at a constant rate, radioactive elements steadily transform into other elements. In the grenadier, radium-226 which is incorporated into the fisn's otolith at birth decays into another element, lead-210. Andrews can tell how long ago the fish was born by measuring the amount of lead-210 that accumulates as the fish ages and comparing that to the amount of radium-226 that remains.
Andrews has teamed up with Pete Holden, a geochemist at the University of California, Santa Cruz, to measure the radium-226 in Pacific grenadier otoliths. It's an unusual collaboration,Holden's equipment, a thermal ionization mass spectrometer, is more typically used for aging ancient rocks. Using such mass spectrometry on fish otoliths is so new, says Kenneth Coale, a geochemist at Moss Landing Marine Laboratories, that no one has published on it. The Moss Landing group hopes to be the first.
Andrews is conquering the Pacific grenadiers' reluctance to reveal their correct ages. He finds that a 70 centimeter (27 inches) grenadier can be 60 years old; which means it's a slow-growing fish.
To determine the age of this new dinner from the deep, Andrews and his colleagues use a so-called radioactive clock that was incorporated into the fish's earbone, or otolith, when the fish was born. Just as sand flows from top to bottom of an hourglass at a constant rate, radioactive elements steadily transform into other elements. In the grenadier, radium-226 which is incorporated into the fisn's otolith at birth decays into another element, lead-210. Andrews can tell how long ago the fish was born by measuring the amount of lead-210 that accumulates as the fish ages and comparing that to the amount of radium-226 that remains.
Andrews has teamed up with Pete Holden, a geochemist at the University of California, Santa Cruz, to measure the radium-226 in Pacific grenadier otoliths. It's an unusual collaboration; Holden's equipment, a thermal ionization mass spectrometer, is more typically used for aging ancient rocks. Using such mass spectrometry on fish otoliths is so new, says Kenneth Coale, a geochemist at Moss Landing Marine Laboratories, that no one has published on it. The Moss Landing group hopes to be the first.
To regulate deep-water fisheries, the National Marine Fisheries Service gets advice from the regional fisheries management councils, groups composed of state and industry representives. California regulations are suggested by the Pacific Fishery Management Council (PFMC), which covers California, Oregon, and Washington. As the Pacific grenadier catch increases, people are beginning to notice.
PFMC's Glock says, "Fishermen have started to talk about Pacific grenadier at meetings. That's typically how it starts." Regulations may follow.
Andrews and his colleagues at Moss Landing Marine Laboratories are discovering just the information Glock will need to set limits on the Pacific grenadier catch. "Size and age of the fish in the population," Glock says, "is pretty critical."
If, or maybe when, Glock must set quotas on Pacific grenadier, Andrews expects to be able to tell him what a conservative harvest level is. No one at Moss Landing Marine Laboratories wants to see Monterey Bay's Pacific grenadier population cited as the newest example of an over- exploited fishery.