Studying the effects of an introduced predatory grouper, roi (Cephalopholis argus) on a native

Hawaiian reef fish assemblage

Charles Birkeland, University of Hawai'i and USGSEric Conklin, The Nature Conservancy of Hawai'iAlan Friedlander, University of Hawai'i and USGSJonatha Giddens, University of Hawai'i at HiloChad Wiggins, The Nature Conservancy of Hawai‘i

TopicsRoi (C. argus) in HawaiiRoi removal study design Study objectives

o Approacho Progress

Next steps

Roi (Cephalopholis argus) in HawaiiEstimated population

7.8 km2 reef = 56,290 roi consume 8.3 mil. fish/year

Surpass biomass of all other reef fish predators

Increasing with prey populations (DAR)

Dierking, 2007

Managers: • Science is equivocal

Community members:• Roi are a big part of why there

are so few native fish

What do roi ACTUALLY do to Hawaii’s reefs???

Experimental roi removal design

Experimental roi removal goals

Address the following questions: Can we reduce roi

populations with removal efforts?

How do nearby roi populations respond?

Do we know how many roi are out there?

Does reducing roi populations change the native reef assemblage?

Can we work with the fishing community on this project in a collaborative spirit that builds relationships and trust?

Objective) Begin to experimentally assess the actual affect that roi have on native reef communities

Approach: Collect baseline data on

the structure and composition of benthic and reef fish communities

Continue monitoring quarterly (for multiple years)

Average fish abundance by feeding guild at three study sites

Reference Treatment Control0

20

40

60

80

100

120

140

160

Apex predator

Apex predator (roi)

Zooplanktivore

Secondary consumer

Primary consumer

Ave

rage

cou

nt (1

00m

2)

A

B

B

F=10.4, p<0.001

Objective) Create an independent estimate of roi populations via a depletion experiment

Approach: Calculate the

original population density of roi in the removal area

Track catch per unit effort (CPUE) of fishers

Objective) Quantify immigration into cleared areasApproach: Externally tag roi

around removal site “Recapture” tagged

individualso Inside removal areao Via visual surveys o Via tag returns

from community members

Pre-removal tagging:

Objective) Evaluate the efficacy of roi removal as a management tool

Approach: Quantify the level

of effort (time and money) required to fish roi down to <10% of original population.

Spearfishing!Local spearfishermen

dispatch roi and record information to determine:o Catch per unit efforto Length/weight ratioso Geographic

distributiono Re-colonization

rates/dynamics

Caught roi are used for:

oCiguatera research

oAge/growth studies

oOrganic fertilizer

Next steps:

Objective) Build stronger ties between coral reef managers, researchers, and the fishing community through an open collaborative approach

Approach: Contract two fisherman

to help with experimental removal

Present project broadly within the community before, during, and after implementation

Mahalo nui loaWe are truly grateful for the opportunity

to do this work, and especially want to thank:

HCRI, NOAA, DAR Kona, Russell Amimoto, Kydd Pollock and all of TNC, Kosta Stamulous, Paolo Usseglio and UH manoa, Jim Beets, Bill Mautz, Cam Muir and UH Hilo, TCBES ohana, Kawika, Mike, Rob White and the Roi Rally, Mike Kawamoto and the Hilo Dive Club, Darrell Tanaka and the Roi Round-up gang, The Puakō Community Association, Liz and Michael Morris family and friends and all of the community volunteers and supporters of marine conservation in Hawai’i.

Questions?

Photo: Rob Shallenberger