For as much as Hawai`i is known for rainforests and waterfalls, freshwater streams seem surprisingly depauperate compared to continental ecosystems. They like many other native Hawaiian habitats are imperilled, making this encounter with a fairly healthy stream with native fish a real treat.

While windward and montane slopes certainly have the rainfall totals to create perennial streams, flow can fluctuate wildly with frequent flash flood events. These flash floods clear the streambed of organic debris and sedimentation buildup. On a longer period of time, streams themselves a limited to the island’s lifespan above the surface of the ocean and ability to capture rainfall. These constraints may help to understand why Hawaiian freshwater stream ecosystems developed the way they did.

4 gobies and 1 eleotrid make up the native freshwater fish of Hawai`i. All species are diadromous. The adults live, breed and spawn in fresh or brackish water. Eggs and recently hatched juveniles make their way downstream, where they spend a portion of their lives in an oceanic stage before returning to freshwater as adults. The native freshwater fish seem to be adapted to the frequent flash floods as the high flow events clear their habitat and spawning grounds which they readily recolonize.

Here at Limahuli stream, conditions are not nearly as degraded as other streams in Hawai`i, making for excellent viewing of our native freshwater creatures. In the 2 previous videos above, I was able to observe some `O`opu naniha (Stenogobius hawaiiensis). This species can be readily identified by the prominent black “tear” from the orbit down its cheek. We saw several individuals very close to the stream mouth.

`O`opu nakea (Awaous stamineus formerly within A. guamensis sensu lato) is the other species of `O`opu we came across further upstream. This species is the largest species of freshwater fish in Hawai`i, reaching up to 14 inches.

Channelization, runoff, chemical intrusion have all wrecked havoc on freshwater ecosystems where I live in Honolulu. But because Hawaiian freshwater biota seems to be pre-adapted to taking advantage of fresh habitat via flash floods, they maybe able to recolonize restored streams if given the chance. It probably doesn’t matter to the fish if the habitat was created by a flash flood or a volunteer workday.Spending meaningful time at a quality ecosystem such as Limahuli stream allow my mind to imagine high quality streams throughout the state in a better future.

—Ref

Nishimoto, Robert T., and J. Michael Fitzsimons. “Status of native Hawaiian stream fishes, a unique amphidromous biota.” American Fisheries Society Symposium. Vol. 53. 2007.

Native Stream Animals