Benefits to Waiahole Stream Life Are Seen Following Restored Flows

posted in: September 1996, Water | 0

Around 24 million gallons a day of water are trapped by the windward tunnels that feed into the Waiahole Ditch. Until December 1994, all of this water was taken to the leeward side of the island. Following an agreement negotiated among all the parties to the Waiahole contested case (except Bishop Estate and the state of Hawai`i), about 15 million gallons a day was allowed to flow into Waiahole Stream.

This has put more water back into the stream than at any time since the ditch was constructed (it was completed in 1916). Since then, biologists have been attempting to study the impacts that the additional flow has had on stream life. Their findings — albeit still tentative — were presented during testimony taken at the Waiahole contested case hearing before the state Commission on Water Resource Management.

Almost all experts agreed that it will take years to determine the full effects of restored stream flow. Several witnesses for the windward parties predicted long-term and far-ranging benefits. Robert J. Livingston, professor of biological science and director of the Center for Aquatic Research and Resource Management at Florida State University — widely regarded as one of the world’s foremost experts on estuaries — stated in his written testimony: “In general, it is my opinion that restoration, partial or whole, will have beneficial effects on (1) the stream ecosystem… (2) the vegetation of the basins and sub-basins (watersheds)… (3) the estuary and marine waters… and (4) specifically, the stream ecosystems, vegetation, estuary and marine waters affected by the restoration.”

Confirmation of most of those benefits awaits longer-term scientific studies. However, several immediate benefits to stream life were observed within days of the release of ditch water to Waiahole Stream.

* * *
Preliminary Results

Bill Devick, head of the state Department of Land and Natural Resources’ Division of Aquatic Resources, described what occurred soon after the increased flow began:

“Due to the short notice and insufficient funding, there was no opportunity to collect meaningful baseline data prior to the flow restoration or to conduct a thorough follow-up investigation of changes in the stream associated with the increased flows. Only the most basic factors could be evaluated, with native o`opu recruitment at the top of the priority list.

“Because it was hypothesized that increased flow would attract native o`opu post-larvae from January to June, DAR biologists … put traps overnight once per month near the mouths of Waiahole Stream and nearby Waikane Stream, which did not have a flow restoration [and] which had also been impacted by the original Waiahole Ditch diversion.

“To everybody’s surprise, given the dearth of native fishes in Waiahole Stream and their generally low populations as a whole, substantial new recruitment of all five of the native stream fishes, along with the native atyid shrimp into Waiahole Stream was discovered and recruitment was substantially higher in Waiahole than Waikane.

“The findings are already significant because, first, two of the species, Lentipes concolor and Sicyopterus stimpsoni, have not been found as adults in the stream in prior samples. Second, one species — Awaous guamensis — was found only occasionally as an adult. And third, all three of these are inland species that require suitable upstream habitat conditions for growth and reproduction.

“The findings with regard to Lentipes concolor have added significance because that species, until a few years ago, was thought to be extinct on O`ahu and is still known to exist in only a few streams…

“There was no opportunity to incorporate monitoring for aholehole, or mullet, another valuable native species associated with stream mouths and which have become uncommon in the area, but fishers below this area claim that both species were increasing in abundance.

“Now that we know we have recruitment of the native gobiids, the question is whether this new recruitment will result in the re-establishment of mature adult fishes and emergence of reproductively viable populations in the stream. About two to three additional years of restored flow along with continued studies will be required to reach any definitive conclusions.”

* * *
Roundworms, Tapeworms, And Leeches…

Another dramatic and immediate impact of increased flow in Waiahole Stream was the elimination of many non-native fish. The native species are adapted to live in heavy stream flows, while the non-native species are habituated to slower currents. The non-natives pose a host of problems for the native species, and one of the biggest of these problems is the fact that they infect the natives with parasites.

William Font, a professor of biology at Southeastern Louisna University, specializes in the study of fish parasites. Over the last four years, he has been under contract with the state Division of Aquatic Resources to study parasites in Hawaiian stream fishes as part of a program to develop a management plan for conservation of the five native gobies. Font testified on behalf of the Waiahole-Waikane Community Association, the Hakipu`u Ohana, and the Kahalu`u Neighborhood Board.

“With a nod towards serendipity,” Devick told the Water Commission, “Dr. William Font happened to be working in Waiahole Stream … when flows were restored… He reported an obvious and dramatic reduction, based on his qualitative observations, on the abundance of exotic fishes in a sample area following flow restoration. He also sighted several o`opu akupa, which is a near-mouth species, farther upstream than the species had ever before been observed.”


Font himself told the Water Commission that when he began his study, he expected to find very few native parasites in the gobies. “And the reason I thought that,” Font said, “is because … these native stream fishes are all amphidromous. That means when they are hatched out of the eggs, they are immediately swept out to sea, not feeding at all in the streams, not having an opportunity to acquire freshwater parasites. They spend a required period of time in the ocean as planktonic larvae, and then move back into the streams as post-larvae. So it’s very unlikely that they would come back into the streams with any freshwater helminth, or worm, parasites.”

Font sampled the little post-larvae, or hinana, as they’re called in Hawaiian. “And the samples … were parasite-free, they had no freshwater parasites when they moved in from the ocean.”

“However,” Font went on to say, “over 20 years ago, Bill Devick, of the Division of Aquatic Resources, predicted that there were parasites that could cause disease in Hawaiian fishes, and that these were associated with accidental or purposeful introductions of exotic fishes. Now, he predicted this over 20 years ago, but until I began my studies, we had absolutely no data to either support or refute these predictions.”

When Font finally undertook his studies, he said, he found 14 different parasites associated with introduced species, 11 of which can become established in native species. Of those 11, Font’s testimony focused on the three worst: a roundworm, a tapeworm, and a leech. These were introduced to Hawaiian streams when swordtails and other freshwater fish were released into streams — some by the state in a past effort to control mosquitoes, others by people dumping their aquaria.

In surveying streams, Font found that those having “a robust, strong current had usually few exotic fishes directly in the streams.” Rather, the exotics were confined to slower side streams or pools, where infestation by parasites was generally very high. In the stronger currents of the main stream, however, the native fishes showed only light infection with parasites and thus were at less risk for disease, Font testified. “Often we think that if an individual is parasitized, that individual must have a disease,” he added. “That’s not necessarily true. Very often the disease is a manifestation of how many worms, how many parasites,” rather than the mere presence of parasites.

“So,” Font went on to say, “if we compare parasite levels in streams with a strong current, like Hakalau Stream, we find an average in the o`opu nakea, Awaous guamensis, we find an average of about two worms per fish; whereas in Wai`ula`ula Gulch … those same o`opu are extremely heavily infected, with an average of about 17 worms per fish. And these are tiny little fish just moving into the stream.”

Exotic Departures

Font told the Water Commission that there was “a strong connection with stream flow and parasite abundance. And this has implications for what may occur in diverted streams.” He went on to explain how this related to Waiahole:

“Since December 1994, I’ve studied Waiahole Stream and some other streams of the windward coast. And I found in general, in these streams, there were larger populations of exotics, mainly poeciliids, than I found in the other streams on the other islands; and also there were other exotic species of fish present, like cichlids, tilapia, et cetera. And the roundworm, the tapeworm, and the leech … are widespread in these streams…

“I collected fishes in the Waiahole and Waianu Streams prior to restoration of flow to the Waiahole in December of 1994. And at that time, I found that both streams were very similar. They both were very shallow, they both had weak currents, and they both had high population densities of exotic, poecillid fishes.

“Then I collected fishes in the Waiahole immediately after the restoration of flow and into January for several weeks into 1995 after flow was restored. And what I saw was that there was an immediate and dramatic reduction in the exotics in Waiahole Stream … associated with the restoration of flow to Waiahole Stream.”

The smaller exotics, young-of-the-year and guppies, were especially affected by the increased flow, Font said. This “makes sense,” he added, “because these are the weakest swimmers.” Reduction in numbers of these small fishes is important, too, Font said, since they serve as the best host for roundworms.

About six months after flow was restored, Font continued, “we returned and quantified the differences in the number of poeciliids in Waiahole Stream and in Waianu Stream… For every one [exotic] fish that we caught in Waiahole Stream, we caught ten exotic fishes in Waianu Stream…

“Now, there are several potential advantages to reduction of exotic fishes, advantages that would accrue to native fishes. Firstly, if exotic fishes interfere with courtship or other aspects of the behavior of native fishes, then their reduced numbers would be beneficial.

“Secondly, in looking at intestinal contents for parasites, I’ve also had an opportunity to look at what these fishes feed on. And I have seen that both exotic fishes and native fishes eat mainly diatoms — they are both eating the same thing. Therefore, there is potential for competition for food. If diatoms are limited in these streams — and I don’t know that they are … then there is competition going on, and removal of the exotics would lessen that competition with the native fish.

“But I think most important is the parasite situation. Many parasites were immediately lost from Waiahole Stream when their hosts were eliminated with the restoration of stream flow.”

* * *
Swimming Against The Current

In response to a question from Water Commission Chairman Mike Wilson, Font explained what allowed the o`opu to withstand the current that flushes out exotic species. “If you go to a stream like Hakalau and look, say, at where Sicyopterus lives, if we look at the stream with human eyes, we see a horrendous flow coming over you. In fact, as we try to observe these fishes, we’re just hanging on as hard as we can. When you stick your face in the water and look at the fish, the fish is in a little crevice between a couple of rocks, and it’s just sitting there as happy as can be, hardly exerting energy at all… The exotic fish don’t have that sucker cup” — fused pelvic fins — “to hold in one place; they have to constantly use their fins and muscles, burning energy, to maintain a position in a stream. And you can increase flow to the point that they cannot maintain their position anymore and they’re swept backward.”

The ability of increased flows to eliminate non-native species of fish was identified by other witnesses as a key to allowing gobies to re-establish themselves in windward streams. Devick testified that even though o`opu exist with exotic species in some streams, “we know that the exotics are depressing the abundance of the [native] species.”

While total elimination of exotics may not be possible, Devick told the commission, reducing their numbers is a key element in stream restoration: “Just about every stream has exotics,” Devick said under cross-examination by Waiahole Irrigation Company attorney Alan Oshima. “But the densities are quite important in this case.”

Oshima went on to ask Devick what would constitute “an adequate restoration of native biota in any stream.”

Devick: Adequate is a judgment word, of course. I think what we would like to do is see streams returned to their original pristine condition, which obviously is not going to happen. And so what we would like to see, wherever possible, is at least existence of reproductively viable populations — that is, where we can identify significant number of, in the case of fish, fish which are reproducing and stream flow patterns which are assuring that the larvae can make it to the sea.

Oshima: Okay. Would the number of fish in the reproducing mode be the same for every stream?…

Devick: I think, first of all, you have to look — consider each stream as being a unique habitat. And so the actual relative densities of the fish in the stream are probably going to be controlled by whatever the characteristics of that particular habitat may be. So I think, to try to respond to your question, what we would be looking for would be whatever species are present in significant enough numbers so we can have some assurance that they are, in fact, reproducing and have some evidence that we’re getting both a contribution to the oceanic pool and some recruitment to the stream.

Oshima: So, even one reproducing pair might constitute a restoration of that species?

Devick: Well, no. I don’t think — you know, again, we’re talking about a qualitative judgment, and so we would have to have enough fish to have some idea that these things would be sustainable year to year.

Exactly why there should be a connection between increased flow and increased recruitment of o`opu was explained by Devick and other witnesses. What attracts the recruiting post-larvae to a stream, Devick said, is “an olfactory response in which the post-larvae actually smell the fresh water coming into the ocean.” When several streams empty into the ocean all in the same vicinity — as occurs in the northern end of Kane`ohe Bay — “you should, most likely, have a larger [freshwater] plume that would attract the post-larvae and therefore, in fact, better recruitment,” Devick said.

* * *
Rare Species May Benefit

Two rare native species stand to gain ground, or lose it, depending on the eventual decision of the Water Commission.

The Hawaiian moorhen, or koloa, is one of four endangered waterbird species found in the Kane`ohe Bay area. While most of the natural wetlands that it would use for habitat have been destroyed, it has taken refuge in Waiahole taro patches. Restoration of flows to windward streams would almost certainly benefit the koloa.

According to Reginald David, an expert on birds who testified for the windward parties, the number of acres of wetland bird habitat in just the Kane`ohe area declined from roughly 1,300 acres around the turn of the century to a mere 83 acres in 1977. Without taro and lotus wetlands, David testified, the koloa would probably go extinct.

Even the leeward parties’ chief expert on biological issues, Ron Englund, in his written testimony, reported that “the highest densities of moorhens in the study area were observed at the Reppun taro fields adjacent to Waianu Stream.”

The black-lined damselfly, Megalagrion nigrolineatum, is a candidate for listing as an endangered species. Whether restoration of flows to windward streams would benefit the damselfly was the subject of much debate in the Waiahole contested case hearing.

In December 1995, Englund, testifying on behalf of Kamehameha Schools/Bishop Estate, told the commission that a damselfly population along Waiawa Stream, on the leeward side, could be damaged if any less water leaked from Waiahole ditch. Also, he said, wetland habitat for some waterbirds on the leeward side might be harmed if leaks in the ditch were repaired.

But under questioning from Water Commissioner Lawrence Miike, Englund acknowledged that his assumption of a connection between flows in the ditch, on the one hand, and flows in Waiawa Stream and other leeward watercourses was not based on any evidence. “We’re erring on the side of conservation biology,” Englund said in an effort to explain his position. In fact, he eventually conceded, “there is no direct indication that the base flow of upper Waiawa Stream is being augmented by the proximity of Waiahole Ditch.”

Adam Asquith, an entomologist with the U.S. Fish and Wildlife Service, rebutted Englund’s testimony on behalf of the windward parties. Asquith advised the commission that if it wanted to create maximum habitat for the damselfly, it restore “a judicious amount of water … to as many drainages as possible on the windward side.”

According to Asquith, two major factors account for the decline of damselflies on O`ahu — alien fish and the change in hydrology of the Ko`olau mountains that followed construction of the Waiahole ditch system.

“Alien fish exist in both of those drainages [Waiahole-Waikane valleys] in the lower reaches. That means the native damselflies have been pushed upstream. Historically, they went all the way down to the ocean, basically. So the damselflies are existing at the upper elevations,” Asquith testified.

“In Waiahole-Waikane,” he continued, “we know, from historical records, that those upper elevation patterns have been reduced and, in many cases, eliminated. Springs dried up, seeps dried up, for example, from the ditch. So we know that there has been a loss of habitat available at the upper elevations. So, yes, I would — I am advocating attempts to restore some of that available habitat at those upper elevations.”

Volume 7, Number 3 September 1996

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