Hawaiian streams have characteristics that distinguish them from typical U.S. mainland streams. Key characteristics are (https://dlnr.hawaii.gov/dar/habitat/about-streams/):
- They are small compared to many of the larger streams on the US mainland. Hawaiian streams resemble a mainland trout stream but are generally shorter. Only 28 or 7.4% of the streams are 10 miles or longer.
- Numerous waterfalls characterize many Hawaiian streams. This feature gives the stream a steep profile and is especially evident in streams in the geologically younger islands, such as on the “Big Island” of Hawai‘i.
- Stream flow tracks rainfall pattern. Although year round orographic rainfall is the primary source of stream water, localized heavy rainfall and storms passing through the islands cause frequent flooding, called freshets or spates. These flow spikes, often lasting only a couple of days, contribute to the flashy (as in flash flood) characteristic of Hawaiian streams.
The website explains that Hawaiian streams have a limited but unique fauna: only five native species of fishes (four endemic, one native but also found elsewhere), two species of crustacean (all endemic) and three species of mollusk (all endemic).
The image below is part of a DLNR poster (https://dlnr.Hawaiʻi.gov/dar/files/2017/08/native_stream_animals.pdf). The poster also includes a wonderful painting by Patrick Ching of the Hawaiian stream environment.
Adaptations of Hawaiian Freshwater Gobies to Stream Life is described here: https://dlnr.hawaii.gov/dar/habitat/about-streams/adaptation/. Descriptions of amphidromy and Hawaiian stream fish migration up streams that are described below are taken from the DLNR-DAR website.
Most native Hawaiian stream animals share a unique life cycle pattern, called amphidromy. This is a specialized pattern where the animals lives in two different environments (diadromy) during different life stages…The gobies lay their eggs in the stream, and upon hatching, the larvae migrate downstream and are swept out to sea. After living in the ocean plankton community for a time, the postlarvae, called hinana, return to the adults habitat by migrating upstream, often climbing numerous waterfalls. Unlike the salmon, the gobies do not return to the streams that they were born in.
The diagram below depicts the amphidromus life cycle of Hawaiian stream gobies.
Once in the estuaries each species employs a different survival mechanism. Larvae of Eleotris sandwicensis and Stenogobius Hawaiiensis (‘o‘opu naniha) will remain in the estuaries for the rest of their life as they are not capable of climbing the waterfalls, which often obstruct the passage into the upper stream reaches. Awaous guamensis (‘o‘opu nākea), Lentipes concolor (‘o‘opu ‘alamo‘o), and S. stimpsoni [‘o‘opu nōpili] will pass through the estuaries and are adapted to climb waterfalls to reach their adult habitats. Once past the terminal waterfall these three species will separate over the remainder of the stream according to their climbing ability. A. guamensis will remain in the lower to mid stream reaches, S. stimpsoni will climb into the mid stream reaches, and L. concolor can be found above even the highest waterfalls of Hawai‘i.
A nice table summary with short descriptions and key features of streams throughout Hawaiʻi is here: https://www.nps.gov/subjects/rivers/Hawaii.htm.
Below are links to various other sources of information:
An excellent lecture presentation on Hawaiʻi streams and other aspects of freshwater by David Hyrenbach is here: http://www.pelagicos.net/BIOL3010/lectures/Biol3010_Lecture19_sp2016.pdf.
Hawaiʻi Watershed Atlas: http://www.hawaiiwatershedatlas.com/intro_streams.html.
Biology of Hawaiian Streams and Estuaries (Symposium Volume): http://hbs.bishopmuseum.org/pubs-online/strm/bces3.html
Stream assessment report published 1990: https://histategis.maps.arcgis.com/home/webmap/viewer.html?useExisting=1
Waipio Valley stream restoration study: http://hbs.bishopmuseum.org/waipio/
The Hawaiʻi Stream Research Center website: http://www.hawaii.edu/hsrc/home/welcome.htm. (This organization and website may no longer be active.)
Some relatively recent evolutionary research on one of the gobies by J. Cullen et al. (2012) titled Evolutionary Novelty versus Exaptation: Oral Kinematics in Feeding versus Climbing in the Waterfall-Climbing Hawaiian Goby Sicyopterus stimpsoni is here: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0053274.
Native stream animal photos and descriptions are here: https://dlnr.hawaii.gov/dar/habitat/about-streams/native-animals/.
The National Park Service Inventory and Monitoring Program Stream Monitoring Protocol document for the Pacific (includes other islands besides Hawaiʻi) also has photos and much information on Hawaiian streams and monitoring: https://irma.nps.gov/Datastore/DownloadFile/441522.
A recent development in stream assessment methodologies is the High Definition Stream Assessment. Check out an informative powerpoint presentation on the methodology here: http://www.ofwim.org/wp-content/uploads/2017/11/Parham-High-Definition-Stream-Surveys.pdf.