Between waterfalls and coral reefs: assessing the overlooked Hawaiian

estuarine fish habitat

Peyton, Kimberly A.1; Sakihara, Troy1; Shimoda, Troy1; Nishiura, Lance1; Shindo, Timothy1; Hau, Skippy1; Higashi, Glenn1; Lapp, Eko1; Infante, Dana2; Tingley, Ralph2; Tsan,

Yin-Pahn2; Mackenzie, Rich3; Smith, Gordon4 1Hawaii Division of Aquatic Resources; 2Michigan State;

3USFS; 4Hawaii FHP

Overarching goal: To describe and understand how estuaries in Hawaii function as juvenile fish habitat.

Aquatic Habitat Assessments in Hawaii The Hawaii Fish Habitat Partnership has participated in developing the following aquatic habitat assessments:

• Atlas of Hawaiian Watersheds

• Statewide Inventory of Barriers to Fish Passage

• Hawaii Portion of the 2010 National Assessment of Fish Habitat

• Marine assessments linking upstream/downstream habitat condition – initiated in 2014

• 9 streams along the North Hilo and Hamakua districts of Hawaii Island

• streams span a steep precipitation gradient • Started regionally now expanding to state

wide stream ecological classifaqtio system

Richard MacKenzie rmackenzie@fs.fed.us

Hawaiian estuaries

C. Glenn UH-Manoa SOEST

Undertaking a census of Hawaiian estuaries

Juvenile habitat – Cast net surveys

10 sites total for 3 years – 4 times per year Kauai, Oahu, Maui and Hawaii Island

Results all years and sites pooled

16,864 fish sampled >170 kilograms (>376 pounds)

75 species sampled

63 fish species 32 families

12 invertebrate species 7 families

Hawaiian estuaries are diverse

Relative Abundance

Kuhlia xenura

Valamugil engeli

Atherinomorus insularum

Mugil cephalus

Mulloidichthys flavolineatus

Herklotsichthys quadrimaculatus

Sarotherodon melanotheron

Polydactylus sexfilis

Caranx ignobilis

Caranx melampygus

Acanthurus triostegus

Scomberoides lysan

Kuhlia sandvicensis

Selar crumenophthalmus

Abudefduf abdominalis

Hemichromis elongatus

Sport fish and invasive fish are the most abundant juveniles

Relative biomass is also composed of sport fish and invasive fish

Relative Biomass

Kuhlia xenura

Valamugil engeli

Mulloidichthys flavolineatus

Mugil cephalus

Sarotherodon melanotheron

Herklotsichthys quadrimaculatus

Atherinomorus insularum

Polydactylus sexfilis

Acanthurus triostegus

Caranx ignobilis

Caranx melampygus

Kuhlia sandvicensis

Abudefduf abdominalis

Scomberoides lysan

Selar crumenophthalmus

Hemichromis elongatus

Invasive fish are a problem in estuaries

Relative Abundance

Native speciesInvasive species

Invasive species make up an even greater proportion of relative biomass because adults co-occur with juveniles.

Relative Biomass

Native speciesInvasive species

Emergent plants are important habitat for juvenile fishes

Hawaii is a sedge based system

Urochloa mutica California grass/para grass

Objective: conserve and restore juvenile fish habitat

How do these two habitats function as juvenile fish habitat?

Urochloa mutica California grass/para grass

Mapped the invasion of

California grass in Hilo estuary

• Opportunistic study • Original question compared relative

abundance mullet species • 9-year study • Concluded study because of

sampling access problems • Growth rate: 1.3 - 36.0 m2 d-1

CPUE declined for

juvenile native mullet

with the invasion of California

grass

Native species

For juvenile invasive

mullet CPUE is

independent of the

invasion of California

grass Exotic species

California grass smothers juvenile striped mullet habitat

Native species Exotic species

Striped mullet feed on benthic diatoms

Open canopy formed by sedges creates benthic diatom habitat

Mahalo