Good science is key to protecting Hawai‘i’s streams. But according to Bill Devick, retired administrator for the state’s Division of Aquatic Resources, the state agencies charged with protecting streams are “too diffuse.”
At the Symposium on Hawaiian Streams and Estuaries held in Hilo in April, aquatic biologist Bob Nishimoto, head of the Big Island office of the Division of Aquatic Resources, relayed Devicks’ sentiments to the assembly of researchers, resource managers, and members of the public that had gathered at the Hilo Hawaiian Hotel to catch up on the latest research on Hawaii streams and stream organisms.
Devick was to have been the symposium’s final speaker, but was unable to attend. De- spite his absence, his message, read by Nishimoto, on the relevance of the public trust doctrine to the conservation of Hawaiian streams was clear: If the state is to set instream flow standards properly, it must build a bridge between the state Commission on Water Resource Management and the Department of Land and Natural Resources’ Division of Aquatic Resources.
Ed Sakoda, aWater Com mission staffer and one of the symposium’s 30 speak ers, agreed. “We need your help,” he said at the meeting.
The Water Commission is required to set instream flow standards – the mini mum amount of water that must be kept in streams to protect stream habitats and organisms and to address Hawaiian and riparian rights – for all Hawai‘i streams. But compared to the Division of Aquatic Resources, the com mission staff has little knowl edge of what healthy streams need.
The symposium, spon sored by the state Division of Aquatic Resources and the U.S. Fish and Wildlife Ser vice, did a lot to fill that gap, touching on everything from fish diets, to the impact of rain on hihiwai recruitment, to damselfly responses to simulated drought condi tions, and more. The following is a synopsis of just a few of the presentations.
Amphidromy
Hawai‘i’s stream fishes are technically not “stream fishes,” they’re amphidromous, meaning they spawn in freshwater, drift out -to sea upon hatching, and return to the stream, where most of their growth takes place. According to Robert McDowall, a researcher with New Zealand’s National Institute of Water and Atmospheric Research, amphidromy is common in the tropics, places like the Philippines and the Caribbean. While common on islands, it is a rare occurrence on continents.
Why are fish that live on small islands amphidromous? McDowall says that the un stable nature of island streams (i.e., flash floods) makes them high-risk habitats for fishes. The fish evolved to take advantage of that instability.
Hawai‘i has five amphidromous fish spe cies, four of which are found nowhere else in the world. These four species, however, are found throughout the island chain, which McDowall says suggests that stream commu nities are open, not closed, systems that in clude a marine dispersal component.
While seas are clearly important in con trolling recruitment, he says, more needs to be known about where larvae go and how they return to streams.
Knowing what the fish need to eat is also important. Evidence suggests fish tend to be carnivorous at lower elevations and herbivo rous upstream, McDowall says. Herbivory allows the good climbers to renew their en ergy as they work their way up waterfalls, he says.
Except for the native goby Lentipes concolor, a.k.a. “the climber,” all of Hawai‘i’s amphidromous fishes are found in the lower reaches of streams, below the first waterfall. Lentipes, on the other hand, have been found above the 1,100-foot Hi‘ilawe waterfalls in Waipi‘o valley on the island of Hawai‘i.
J. Mike Fitzsimons of Louisiana State University says that the native gobies Stenegobius hawaiiensis (naniha), Awaous guamensis (nakea), and Lentipes are omnivo rous; Sycopterus stimpsoni (o‘opu napili) are herbivorous, and the eleotrids, Eleotris sandwichensis (‘akupa), are carnivorous “sit-and-wait” predators that “will eat anything in the water that swims or crawls or wriggles.”
He adds that even when they are at sea, their source of nutrition is from streams. Once they reach the sea, he says, “They do not go far.”
Fitzsimons also points out the importance of boulders, where Lentipes graze and are also centers for social behavior.
Larvae Survival
“In their first week or so, fresh water is a requirement for larval gobies,” says Kim Bell, a researcher with Memorial University in New foundland. Bell’s studies in the West Indies on larval gobies found that their biology is domi nated by cycles, both lunar and daily. Bell also found that in one study area, 50 percent of the larvae died in the first hour after hatching. While he did not know the exact cause of mortality, Bell suggested that “some fish pick off their own larvae. I don’t think many fish will refuse a high protein opportunity.”
Another study by Japanese researcher Keiichiro Iguchi of the National Research In stitute of Fisheries Science may have the answer to why many larvae die before they reach the sea: Starvation.
Iguchi’s studies on gobies in three Japanese streams found that the larvae’s small size limits their ability to swim in running water. Once they reach a stream’s lower course, where the water moves more slowly, the larvae don’t start swimming, but instead “waste time” hanging around while they deplete their yolk sacks, Iguchi says.
After the yolks are exhausted, many of the larvae sink and die, he says. The longer the stream, the more likely the larvae are to die of starvation. In the Shimanto River, which is 190 km long, most larvae can’t reach the sea alive, he says. In the short Mina River, 7 kilometers long, most larvae reach the sea alive.
Louisiana State University’s Mark McRae adds that anything that slows migration – slow water speed, or plunge pools that are wide, deep, long, and hold predatory inva sive populations – threatens larvae survival.
As far as freshwater endurance goes, Japa nese larvae seem to last about seven days, while Hawai‘i larvae can go for about five days, he says, adding that the sea isn’t exactly a haven, as larvae encounter the same threats there as they do in streams: predators and low-velocity flow.
Given the larvae’s average endurance, are shorter streams better habitat than longer streams?
“Yes and no,” McRae says. “It depends on the species.” For Lentipes, which has to brave steep waterfalls in addition to making it to and from sea, short is better. But long streams are also important because they provide food for other species of fish and allow for broader diversity, he says.
He adds that larvae may not always return to their stream of origin and may drift from one stream to another. Some streams may be sources of populations, while others – where more larvae are coming in than going out – may be sinks.
For this reason, he says, population size alone is not the only indicator of habitat quality. “Proximity to the ocean is at least as important.”
Power Climbing
Studying differences in the shape and climb ing style of fishes, as well as differences in stream courses, is essential to proper resource management — especially for streams where water is being diverted, Heiko Schoenfuss of Minnesota’s St. Cloud State University has found.
Hawaii’s climbing stream fishes don’t all climb the same way: Sicyopterus climbs next to flowing water, not in it, and inches its way up a waterfall. Awaous and Lentipes, on the other hand, engage in “power-burst” climb ing, swimming vigorously in the water stream. Schoenfuss says it’s a terribly inefficient way of climbing that, with the drag from the water, burns s lot of energy. However, the method does allow the fish to escape predation, he says.
These faster climbers make few climbing cycles, he says, adding that a 2.5-degree in crease in temperature – due, perhaps to a water diversion – decreases the efficiency of their wide muscle by 50 percent. This could ham per their journeys home, particularly in steeper Big Island streams, where climbing ability is an important factor in survival. On Kaua‘i, where the streams are slower and wider, Schoenfuss says predator avoidance is a bigger factor.
Hihiwai Recruitment
Rainfall in the first few months of a given year will spur hihiwai (Neritina granosa) recruit ment by the summer, says Skippy Hau, a biologist with the state Division of Aquatic Resources. Hau studied hihiwai populations in East Maui’s Honomanu and West Maui’s ‘Iao streams for the past several years.
‘Iao is diverted most of the year and has no surface flow. There is, however, some ground water upwelling in places. Large North Pacific ocean swells sometimes build a sand berm that cuts Honomanu’s flow into the ocean.
Between 1999 (2001 for Honomanu) and 2004, Hau collected hihiwai for one hour, once a month from the streams. >From Honomanu, he’d collect between 100 and 600 animals each time. From ‘Iao, numbers would peak in the summer months, but the rest of the year, there would be no hihiwai. After studying rainfall patterns, Hau found that for both streams, there was delayed re cruitment after heavy rains in the early parts of the years.
— Teresa Dawson
Volume 15, Number 12 June 2005
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