Upload
nicole-geer
View
214
Download
1
Tags:
Embed Size (px)
Citation preview
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