Hawai‘i's native freshwater migratory animals include 5 fishes,
‘O‘opu ‘alamo‘o (Lentipes concolor) vary in color with age, and between males and females. They grow up to 5 inches and are omnivores.
‘O‘opu nōpili (Sicyopterus stimpsoni) vary in color between males and females, and with age. Males have white and black stripes, running from head to tail. Females are mottled brown or gray. They grow up to 7 inches and are herbivores.
‘O‘opu nākea (Awaous stamineus) have similar coloration between males and females. They are mottled brown and black, with white bellies, and vertical stripes on their dorsal and caudal fins. The largest of all ‘o‘opu, they grow up to 14 inches, and are omnivores.
‘O‘opu ‘akupa (Eleotris sandwicensis) are dark brown to black. They grow up to 12 inches, and are top predators in natural streams, eating both fishes and invertebrates. They often lie motionless and lunge at their prey when within striking range.
‘O‘opu naniha (Stenogobius hawaiiensis) have yellow-brown coloration, and often have 12 vertical black bands (sometimes faded). They have a distinct diagonal black band through their eyes. They grow up to 5 inches and are omnivorous.
Hawaiian Streams also have TWO native crustaceans, which we call ‘ōpae...
‘Ōpae ‘oeha‘a (Macrobrachium grandimanus) are brown with dark patterns along the side of their bodies and claws. Males will have one large claw and one small claw. They grow up to 3 inches (from nose to tail) and feed on plant and animal matter.
‘Ōpae kala‘ole (Atyoida bisulcata) vary in color, and can be golden brown, dark green, or black. They grow up to 2 inches and feed on both plant and animal matter.
Hawaiian Streams also have two freshwater mollusks...
Hīhīwai (Neritina granosa) have bumpy, dark brown to black shells, but are orange underneath. They grow up to two inches and are herbivorous.
Hapawai (Neritina vespertina) have smooth, thin shells, with wing-like projecdtions, and are flatter than Hīhīwai. They are light brown, but often have a pale, worn spot at the tip of their shell. They grow up to 1 inch and are herbivores.
Adults and juveniles of all nine species live in freshwater.
(modified illustration by Patrick Ching)
When old enough, animals lay eggs in freshwater. Newly hatched larvae travel to the ocean, where they will spend up to 6 months as zooplankton...
(modified illustration by Patrick Ching)
...before returned to freshwater, where they will swim upstream to the habitat they are best adapted to.
(modified illustration by Patrick Ching)
Both invertebrates and fishes can climb!
Some animals prefer habitats closer to the ocean, while others are able to climb high up into the mountains!
TWO SPECIES, ‘Ōpae kala‘ole and ‘o‘opu ‘alamo‘o are the highest climbers, traveling all the way from the ocean to the UPPER reaches of streams... sometimes climbing 1000s of feet of waterfalls!
THREE SPECIES, ‘o‘opu nopili, hīhīwai, and ‘o‘opu nākea migrate from the ocean to the MIDDLE reaches of the streams.
FOUR SPECIES, ‘O‘opu naniha, ‘o‘opu ‘akupa, hapawai, and ‘ōpae ‘oeha‘a are not great climbers, and are found at the LOWER part of Hawaiian Streams, often overlap habitat into estuaries.
QUIZ TIME!
1) How many species prefer to live in the lower stream habitat?
2) What species are they?
1) How many species prefer to live in the middle stream habitat?
2) What species are they?
1) How many species prefer to live in the upper stream habitat?
2) What species are they?
Natural Streams have fast flowing, cool, clear, water. The stream banks are naturally stable, and covered with native vegetation. The stream bottom is covered with boulders, rocks, and cobble, with little organic matter.
...Native species will always be found in high densities here.
Watershed alterations, water diversions, channelization, removal of riparian vegetation, sediment, and pollution all negatively affect habitat for native stream species.
Invasive species are often tolerant of such conditions, and can dominate heavily urbanized habitats like the one shown.
In addition to landscape changes, invasive species outcompete native species for food and habitat, and sometimes even feed on native fishes and invertebrates.
At every elevation, there is a fish or invertebrate that has been introduced that outcompetes native species.
Livebearers: Fishes of the family poeciliidae that give birth to live young and have internal fertilization via a special anal fin:
Armored catfishes of the family Loricariidae, are commonly referred to as plecostomus in the aquarium trade. They are most dominant fish in urban streams on O‘ahu, after their introduction to streams (likely as unwanted pets when they outgrow their aquarium) in the 1980s and 90s.
The two species are sometimes difficult to tell apart, especially when they are small:
Smallmouth bass (Micropterus dolomieu) are highly predatory fish that were introduced to Hawai‘i for recreational fishing, reaching > 12 inches in freshwater streams.
Fishes of the family Cichlidae are extremely popular aquarium fish, but many of them are extremely aggressive, and do not do well with others.
Japanese swamp shrimp (Neocaridina denticulata sinensis) is a popular shrimp sold in pet stores to feed to carnivorous aquarium fishes that only eat live food.
Unforntuately, they are able to climb as high as native shrimp, but do not require going to the ocean to complete their life cycle. Females hold onto their eggs and brood their larvae on their abdomen, until they disperse them as juveniles.
Tahitian prawns (Macrobrachium lar) were intentionally introduced to Hawai‘i as a food species. Juveniles can climb to the same habitat as ‘ōpae kala‘ole.
Swamp crayfish (Procambarus clarkii) are brown to dark red, and sometimes have blue coloration on their claws and body. Up to 5 inches, from nose to tail.
Numerous snails have been introduced to freshwater stream in Hawai‘i. Some were introduced through the aquarium trade, but others were imported for food.
As the most populated watershed in the Hawaiian Islands by people, the Ala Wai Watershed has some of the most drastic landscape changes and highest densities of invasive species.
After learning about native stream animals and the human induced problems they face, the students and educators in this community want to help.
After training at school, students visit the 1 of 20 study sites, to perform what they learned.
Two teams of students herd animals downstream, where they are captured by a third team with nets blocking the stream.
After capture, natives and invasives are separated, identified, and counted by students. Native species are returned to the stream. Invasives are iced and composted at Ho‘oulu ‘āina, in Kalihi Valley.
Joining forces with over 50 educational institutions, and 1000s of K-12+ students; 41,106 invasive species were removed, totaling > 1600 lbs, from Makiki, Mānoa, Pālolo Streams.
Summary of collected data from pa‘ēpa‘ē surveys across 20 sites (Click on mapped icons).
Aloha mai kākou and mahalo nui for your efforts in bringing health back to our watershed.
Thank you for listening to our story on how we have become Nā Wai ‘Ekolu!
Questions? Want to get involved?
Cory Yap
Environmental Educator / Researcher
‘Iolani School / University of Hawai‘i at Mānoa
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