Biologists who study fish behavior in the main Hawaiian islands, particularly off the Big Island, are having unexpected encounters with large reef fish in the Northwestern Hawaiian chain. After diving off of Nihoa and Necker Islands and in and around the atoll of French Frigate Shoals, these fish specialists are beginning to question a few long held theories of fish behavior back home.

"Everywhere we go we are swarmed by large schools of nenue," said Steve Cotton, an aquatic biologist working with the University of Hawaii Hilo and the State of Hawai'i's Department of Land and Natural Resources (see pictures above and below). "These fish literally follow us and surround us during our dives." Aside from the nenue, Cotton and his colleagues have found this behavior common with other fish like the milletseed butterflyfish (lauwiliwili or Chaetodon miliarias).

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In the main Hawaiian Islands this kind of behavior has been frequently observed. The common theory has been that this swarming behavior is due to fish feeding for ocean tourism purposes. The theory contends that over time, in areas where fish are being fed regularly, the fish become conditioned to associate divers with food. As a result, when divers enter the waters in these areas, the fish display a swarming like behavior.

The divers first noticed this behavior at Nihoa but didn't know what to make of it until they continued to see the same behavior at other sites during the expedition. "Our observations may suggest that instead of a solely learned response, this kind of swarming behavior may be a natural response to a stimulus in the water that's enhanced by fish feeding," suggests Cotton.

"Why fish like nenue do this, we don't know. But what we now do know, is that this behavior is often characteristic of the species, whether they are being artificially fed or not. The implications of this kind of behavior aren't clear yet, but the more time we spend up here in the future, the more we may understand this behavior," said Cotton.

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Throughout the world there is controversy over fish feeding and whether or not it alters fish behavior. While these fish scientists are not suggesting that artificial feeding doesn't alter fish behavior, nor that they are in favor of it, they say that it's important to separate the issues.

"While swarming may not be caused by fish feeding, fish feeding does cause other impacts. For one, the food that is fed is not part of a natural diet. Feeding also attracts fish that would not normally be found in certain reef areas," said Cotton. Most significantly, feeding can cause fish to be more aggressive and encourage them to come into close proximity to humans. Too close for comfort when the fish have teeth, like eels and barracudas.

Nenue weren't the only type of fish to demonstrate this behavior, but because it's a schooling species, the behavior was more noticeable to the divers.

"Another species to demonstrate this curious behavior were the giant ulua (trevally), a fish eating predator," said Brent Carman another fisheries specialist. "During many dives these large fish followed us along our transect lines. Because their home ranges may be wide, they may have also followed us to multiple dive areas."

Noticing and accounting for this kind of behavior has practical considerations for research when one counts fish. Divers have to hone their observation skills when counting fish like ulua and learn to recognize the large fish as individuals so they aren't counted twice. "If they follow you around and you don't recognize that you already counted them, your data will be skewed," explained Carman.

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At times, the divers were surrounded by 30 to 50 large ulua (above) at the same time, making counting very difficult. But understanding this behavior, the fish team is now sensitive to the fact that they're being followed. With the use of video cameras, the fish team can now cross reference the data they collect with the video to make sure that the fish they record are not being counted more than once, ensuring the accuracy of their research.

From a management perspective, this attractiveness to divers concerns the fish team. "If these top level predators are attracted to divers, this behavior makes them particularly vulnerable to activities like spearfishing." explained Carman.

According to Carman, this may explain why these larger fish are no longer found in the shallow reef areas of the main Hawaiian Islands. "These naïve fish may already have been fished beyond what their populations could sustain. And when, by chance, a fish is able to grow to large size, because of their curious nature, they'd probably get caught fairly easily,"

Carman suspects. The strange 'attraction' behavior was noticed primarily with bony fish, not sharks. According to these divers, while some sharks, like gray reefs, would sometimes come close to take a look, they'd usually only stay around for a little while. "They seem to be a little more circumspect. But its too early to tell," said Carman.

"In areas like these, where there are a large number of these fish still present, we need to take a conservative approach to managing them," said lead fish investigator, Bill Walsh. "Especially since we haven't seen many juvenile fish up here. We've seen nothing that suggests if these animals were removed from these reefs, they would be replaced by younger fish.

Therefore we have to be very careful in the way we set policy regarding these northwestern waters. "We need to investigate this issue of recruitment further, as this expedition will not provide us with the opportunity to do that. If, however, it turns out to be true that juvenile fish are not found in abundance up here, these northwestern waters may be even more fragile and vulnerable than we imagined," concluded Walsh.

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