LIHU‘E — Six fish-aggregation devices (FADs) were installed off Kaua‘i last week, restoring the local portion of a statewide buoy array to nearly full strength.
FADs attract several desirable pelagic fish, including tuna, billfish, mahimahi and ono.
“They’re very important to the small-boat fishers,” said Hawai‘i Institute of Marine Biology Researcher Kim Holland, director of the state FAD program.
“Those are guys that are mostly doing it for recreation,” Holland continued. “But there’s some people that do it at a small-scale subsistence level, for food and making a few bucks on the side.”
FADs are also frequently utilized by charter boats whose operators can rely on the buoys to increase their clients’ chances of landing desirable fish.
Hawai‘i’s public FAD array, which will total more than 50 buoys when complete, is currently operated by the Hawai‘i Institute of Marine Biology, the School of Ocean and Earth Science and Technology and the University of Hawai‘i in cooperation with the state Department of Land and Natural Resources Division of Aquatic Resources.
Kaua‘i has nine designated FAD locations. As of Feb. 16, all but two are active.
Researchers are unsure why fish congregate near FADs, which are comparable to floating marine debris.
Small schools of mahimahi and ono may be attracted by smaller fishes, but that’s not the case for skipjack and ahi tuna, Holland said.
“There simply isn’t enough food attracted by the FAD to support those schools of fish,” he explained. “In fact, if you look at the published gut contents of fish caught around floating objects, they don’t eat things that are sometimes found around floating objects.”
Two major hypotheses account for the phenomenon, according to Holland.
One, the indicator-log hypothesis, suggests logs floating in or near nutrient-rich river-mouths effectively signal a corresponding presence of food. Attracted fish would have therefore gained a feeding advantage, and evolution would have ingrained this behavior in tuna millions of years before humanity first exploited it.
“The other hypothesis is the meeting-point hypothesis,” Holland said. “Tunas are schooling animals. Even though they may split up at night to go hunting more or less by themselves, they want to rejoin a flock for protection.”
Floating debris and FADs serve as rendezvous points under this second hypothesis, which doesn’t necessarily preclude the first.
“There’s no reason they both can’t be working at the same time, so to speak,” Holland said.
Other factors play into tunas’ changing preferences in FADs: a given buoy can be “hot” one week and “cold” the next.
These shifts probably reflect the presence or absence of transient food supplies, like groups of shrimp, squid and fish species, grouped near a FAD’s anchor blocks. Tuna within the vicinity of the buoy would be well-positioned to eat when their prey rises from the deep at night.
Private and fishing-industry FADs are not allowed in Hawai‘i waters, but are legal elsewhere.
DLNR named these devices commonly used by the purse-seine fishery, known as drifting FADs or dFADs, a new marine-debris item of concern in September 2021.
Drifting FADs, unlike the state program’s stationary buoys, are free-floating.
“Sometimes these dFADs will drift outside the feasible range of the fishing fleet or the GPS tracking devices will fail,” DLNR announced last year. “These lost dFADs become derelict fishing gear, one of the most common and problematic categories of marine debris … Floating and submerged components are hazards for navigation and entanglement, especially for marine mammals, birds and turtles.”
For maps and coordinates of state-sanctioned FADs near Kaua‘i and other Hawaiian islands, visit himb.hawaii.edu/FADS/.
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Scott Yunker, reporter, can be reached at 245-0437 or syunker@thegardenisland.com.
Source: The Garden Island
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