Experts Link Stream Flows To Kane`ohe Bay Productivity

posted in: September 1996, Water | 0

Since the second decade of the 20th century, the volume of fresh water flowing into Kane`ohe Bay has steadily dropped. Most scientists studying the bay agree that total freshwater input from streams and springs has dropped about 47 percent overall. The largest single loss may be attributed to the diversion of about 25 million gallons a day of fresh water into the Waiahole Ditch.

What this has meant for the bay’s function as one of just four great estuary systems in Hawai`i was debated at length in the contested case hearing on how water in Waiahole Ditch is henceforth to be apportioned. The evidentiary portion of the case, heard before the state Commission on Water Resource Management, began last November. Closing arguments will be made this month. A final decision by the commission may be made by the end of 1996.

Seafood Restaurants

When salt and fresh water mix along the coast, an estuary is formed. Estuaries are breeding grounds for many ocean fish, which makes them also feeding grounds for some of the larger nearshore fish. Kimberly Lowe, an aquatic biologist with the Department of Land and Natural Resources who has studied Kane`ohe Bay extensively, explained to the commission the importance of the bay as an estuary:

“Out of all the bait fishing in the state, Kane`ohe has 67 percent … And of that, the nehu [Hawaiian anchovy, used for bait in tuna fishing] is 61 percent…

“Now, it’s important to realize that nehu do not love purely fresh water. They sort of exist on the boundary between the fresh water and the marine. So they move into these areas, but they don’t go up the streams; they just kind of hang around at the edge. But that puts them in a position where the bait nets can catch them.”

Lowe also attempted to explain why estuaries are so attractive to fish — and to fishermen: “It is a nursery ground for fish, not only because of the fresh water, but because it’s shallow and there are places where they can refuge, they can get into shallow water … away from the papio that are going to chase them up as far as they can.” In addition, Lowe said, there’s “the food source that is coming down through the streams.”

“As the stream comes along, there are leaves that drop into the water, and those leaves start to break down and then little organisms get into them, including bacteria and bigger things [which] start to eat on the leaves and actually live inside of the leaves…

“Somebody once said to me, the reason the fish are in the estuary is like why do people eat in restaurants? That is where the food is. When the stream flows, it brings down the leaf litter, it brings down little clumps of mud… And they sift through that and they eat that.”

When the fresh water enters the ocean from the stream, “it will fan out over the water,” Lowe said. “And if you think about the edge of that boundary, the farther out it goes, the wider the edge. And if you look at all the fish studies that have been done in Kane`ohe Bay, you have your highest diversity and you have your highest biomass at that edge between the fresh and the saltwater, where the estuary ends. And the bigger the amount of water that is coming out, the bigger that edge is going to be.”

If the freshwater flows increase — as a result, say, of higher volume flows in Waiahole Stream — “the inshore fisheries will increase in Kane`ohe Bay,” Lowe testified. “I have no doubt about that.”

Non-linear Relations

Nor did Robert Livingston, who directs the Center for Aquatic Research and Resource Management in Florida. Livingston, perhaps the world’s foremost expert on estuaries, testified (unpaid) as a witness for the Waiahole-Waikane Community Association. “There is no doubt that a restoration of the fresh water will improve the productivity of Kane`ohe Bay,” he told the Water Commission.

It was Livingston who explained to the commission why relatively small changes in the flow of freshwater into estuaries can cause dramatic fluctuations in their productivity. The relation between flows and productivity, he told the commission, “approaches logarithmic — that is, it becomes many times more magnified in terms of the productivity relative to the amount of water going into the system.”

The experience of fishermen immediately after restoration of about 14 million gallons a day to Waiahole Stream in December 1994 tends to confirm the scientists’ predictions. Many old-timers noticed a marked increase in numbers of some fish observed in the northern end of Kane`ohe Bay.

George Uyemura, who has run, or helped run, Moli`i Fishpond nearly all his life, told the Water Commission that since the flow was restored to Waiahole Stream, “the amount of fish that came out is fantastic compared to the last ten years.

“This year, Christmas was the first day that mullet and aholehole started to come out. And we have so many different animals that came out. I thought that iao — that’s the nehu-looking animal — was extinct already. But about October, when I made some sampling, it was fantastic — big ones out there again. So the stream input must have done something to bring about all these new animals.”

Kaipo Faris, who fishes recreationally in Kane`ohe Bay, said he, too, noticed a difference. “This past year we had the largest `oama run that we’ve had in many years. People have commented on it over and over again.”

Even a witness for the various parties seeking to keep water in the Waiahole Ditch flowing to leeward O`ahu gave evidence that 1995 was an exceptional year for fishes in Kane`ohe Bay. The witness, Ken Leber, testified on behalf of Kamehameha Schools/Bishop Estate. Leber is a scientist with the Oceanic Institute who for several years has studied the abundance of fish near the mouths of windward streams.

In 1995, recruitment of striped mullet at Waiahole Stream in the months of August, September, and October was higher than in any previous year Leber had studied. Overall, more than twice as many mullet were collected at Waiahole then than in any previous year.

Yet Leber was reluctant to associate this with any change in stream flows, suggesting instead that fishing was down generally as a result of overfishing and pollution. To explain the 1995 figures, he said that 1995 may have been “a banner recruitment year throughout the bay… I have no statistical, no scientific basis for saying that this increase at Waiahole is larger than this increase at Kahalu`u. Absolutely no ground to stand on. Not a journal in this country would publish that information, if I claimed that this is evidence of a water flow.”

‘Building Condos’

Under cross-examination by Paul Achitoff, attorney for the windward parties, Leber was reminded that in a paper he wrote for a scientific journal, he had earlier claimed that the reduction in freshwater flows to the bay had degraded fish nursery habitats and had — quoting Leber’s article — “altered the primary refugia for Mugis cephalus — striped mullet — recruits.”

Achitoff: In the same paper, you concluded, didn’t you, that in areas where nursery habitats have been degraded, predation could have disproportionate impact on survival of smaller mullet, particularly if the degradation resulted in reduced access for juveniles to low salinity habitats?

Leber: Yes.

Achitoff: And the degradation that you’re referring to that results in reduced access for juveniles to low salinity habitats is, at least in significant part, the reduction of bay stream flows below natural levels, isn’t it?

Leber: Yes.

Achitoff: … Evidently, when you wrote that paper, you felt that there was an adequate basis to conclude that reductions in stream flow into Kane`ohe Bay have adversely affected mullet productivity, didn’t you?

Leber: I would like to put that into context. … My approach to the testimony here and the approach in my papers is that unless there’s a balanced approach, you are not going to have the kind of fishery management impact that you could have with a balanced approach… I maintain, and always will, that freshwater is a critical habitat for striped mullet. Clearly, if we bring back recruits, if we bring back the recruitment potential by increasing the number of spawning adults out there, which we can do in part if indeed there is overfishing and we control that — and I believe there is — then and only then would it be useful to have additional habitat back.

“Now, as I mentioned earlier, I’m an advocate of habitat restoration and habitat protection. What I see my role is — as in front of this commission — is to temper the claims that are being made that data and evidence exist to support the claims that we will see major increases in our fisheries if we put this water back.

“I am in no way saying that water is not important, and I’m in no way saying that it was unimportant that that water was taken through the mountains eighty years ago. And at that time, it may have had a severe impact on the fisheries on what the bay could support. It could indeed have been severe 80 years ago.

“Right now, because the recruitment potential is so low, it is not having anything like the impact that it must have had when it first happened. Just because you build more condos doesn’t mean there’s buyers there to jump in. And that’s the situation we have today.”

Still, Commission Chairman Mike Wilson pressed Leber to explain what Wilson said “seemed like a vast increase in the number of juvenile recruits” seen in 1995.

Leber responded by saying it could be attributed to “just annual variability. The stars lined up right… There was the right food at the right time when those eggs hatched and the current hadn’t swept them to the wrong places.”

A Dissenting View

Steven Dollar, an oceanographer who has a private consulting business (Marine Research Consultants), was hired by Kamehameha Schools/Bishop Estate to rebut some of the testimony from Lowe, Faris, and other windward witnesses.

In his prepared rebuttal testimony, Dollar claimed that the increase in flow of Waiahole Stream is insignificant in changing salinity — and thus estuarine — conditions of Kane`ohe Bay. In rebuttal of witnesses testifying that increased flow would therefore increase productivity of the bay, Dollar said: “When you look at it as an amount, as a quantity, it’s barely measurable.”

On the other hand, Dollar emphasized that any increase in freshwater flow could harm the corals in Kane`ohe Bay. “Kane`ohe Bay is primarily a coral reef system which works best without input from lands… [T[he nutrients that come in from the open ocean that cycle on the coral reefs, which are totally disconnected from land, are the primary habitats in the bay and, if anything, would be impacted in a negative sense from increased freshwater flow… From what we’ve seen, the coral reef areas … which are in the center of the bay, are more important in terms of productivity.”

Water Commissioner Lawrence Miike, who serves also as director of the state Department of Health, asked, “Am I also to believe you’re saying that Kane`ohe Bay would be better off without any streams entering into it?”

Dollar backed off the point, saying he meant only that he was speaking only to “the reef parts of the bay.”

Miike: So you were saying only in terms of the reef fish. But I’m asking about the total productivity of the bay. How important are streams, in your mind, to the productivity of the bay?

Dollar: Yes, that’s really not part of my testimony…. I haven’t done those calculations.

Volume 7, Number 3 September 1996

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