11th ICRS Abstract book - Nova Southeastern University

22-5
Fishing Pressure, Productivity, And Competition For Resources: Malthusian
Overexploitaton And Efforts To Overcome It On Kenyan Coral Reefs
Tim MCCLANAHAN 1 , Christina HICKS* 2,3 , Emily DARLING 4
1 Marine Program, WCS, New York, NY, 2 Coral Reef Conservation Project, Mombasa,
Kenya, 3 Marine Sciences and Technology, University of Newcastle, Newcastle, United
Kingdom, 4 Simon Fraser University, Burnaby, BC, Canada
Trends in an artisanal coral reef fishery were examined using a ten year time series along
a gradient of fishing intensity spanning 75 km of Kenya’s most populated coastline. As
predicted by Malthusian scenarios; catch per unit effort (CPUE), mean trophic level,
functional diversity of fished taxa, and diversity of gear declined, while total annual catch
and catch variability increased with increasing fishing pressure. The fishery was able to
sustain high (~16 tons km-2 year-1) but variable yields at high fishing pressure due to the
dominance of a few productive herbivorous fish in the catch. The effect of two separate
management strategies to overcome this Malthusian pattern was investigated: fisheries
area closure and elimination of the dominant and most “competitive” gear (pulled seine
nets). We found that sites within 5 km of the enforced closure showed significantly lower
total catch and catch per unit effort (CPUE), but increased yield stability and trophic level
of catch than predicted by regression models normalized for fishing effort. Sites that had
excluded illegal beach seine use through active gear management exhibited increased
total catch and CPUE. Time for space substitutions confirmed positive correlations
between time since closure and trophic level and between time since pull seine removal
and CPUE. There was a strong interaction between closure and gear management, which
indicates that for closures to be effective at increasing catch, there must be simultaneous
efforts at gear management around the periphery of the closures. We propose that
Malthusian effects are responsible for the variation in gear and catch and that active
management through reduced effort and reductions in the most competitive gear have the
greatest potential to increase the functional and trophic diversity and per-person
productivity.
22-6
Demographic Shifts in Coral Reef Fish Communities Across A Gradient Of Human
Disturbance
Benjamin RUTTENBERG* 1,2 , Stuart SANDIN 1 , Sheila WALSH 1 , Scott HAMILTON 3 ,
Mary DONOVAN 3
1 Scripps Institution of Oceanography, La Jolla, CA, 2 Marine Science Institute, University
of California Santa Barbara, Santa Barbara, 3 Marine Science Institute, University of
California Santa Barbara, Santa Barbara, CA
Over the past few decades, direct human impacts have been increasing on coral reefs
worldwide. Researchers have documented changes in individual size and community
structure, and declines in the yield of reef-based fisheries resulting from these impacts.
Still, there have been fewer studies of demographic shifts driven by anthropogenic
effects, and nearly all of these have examined only fishery species. We examine
demographic patterns from five species from a variety of trophic levels on two nearby
atolls in the Line Islands, Kiritimati Island and Palmyra Atoll. These islands are similar
biogeographically and oceanographically, and yet differ greatly in the level of human
impacts. We present age-based demographic data, obtained using standard techniques in
otolith ageing from collections of the study species from both islands. We found striking
differences in demography among islands, and these patterns differed across trophic
groups. On unfished Palmyra, top predators (piscivores) were larger and longer-lived
than on more heavily-fished Kiritimati, though individual growth rates were comparable.
In contrast, species in lower trophic groups, including mid-level predators, were smaller,
experienced higher rates of mortality, and grew faster on Palmyra than on Kiritimati. Our
data suggest that anthropogenic impacts lead to indirect demographic changes; on
relatively impacted Kiritimati Island, the removal of piscivores leads to lower rates of
predation on lower trophic groups and increased sizes and longevity, whereas on
relatively pristine Palmyra, the presence of large populations of top predators results in
greater predation pressure, higher rates of mortality, and faster growth for lower trophic
groups. Similar data from other atolls in the Line Islands chain corroborate these
findings. Improving our understanding of species specific changes that result from human
disturbance can help us develop more functional approaches to managing reef fisheries.
Oral Mini-Symposium 22: Coral Reef Associated Fisheries
22-7
Distribution Pattern, Habitat Overlap And Trophic Interaction Of Trawl Catches Within
The Ragay Gulf, Philippines Coastal Fisheries Ecosystem
Lualhati LACHICA-ALIÑO* 1 , Laura DAVID 1 , Matthias WOLFF 2 , Porfirio ALIÑO 1 ,
Catalina RAÑOLA 1
1 University of the Philippines, Marine Science Institute, Quezon City, Philippines, 2 University
of Bremen, 2 Center for Tropical Marine Ecology (ZMT), Bremen, Germany
A comprehensive resource and ecological assessment was done in Ragay Gulf, Philippines.
Exploratory trawl-fishing surveys characterized the distribution patterns of trawl fish catch and
assessed the external factors influencing the variability of the catch within the gulf. Species
composition of commercial and municipal fish catches was compared to those found within coral
reef, seagrass, mangrove and soft bottom communities, to determine the degree of overlap of their
associated species within the gulf’s fisheries catches. Mass-balanced trophic models using speciesspecific
ecological groups were developed to quantify the trawl fisheries’ impact on the temporal
biomass budget of the ecosystem. Cluster analysis based on the 38 commonly occurring and
abundant species in the trawl catches revealed northern (less exposed) and southern (exposed)
species clusters associated with the prevailing circulation pattern and phytoplankton density in
the gulf. Further analysis of the trawl catches composition revealed two other distinct clusters
indicative of the spatial distribution and intensity of the trawl fishery in the gulf. We
differentiated these areas as “highly fished” and “less fished” areas. Fifty percent of the
multigear fisheries catch overlapped with the four coastal habitats. Species associated with soft
bottom habitats had the highest overlap with the trawl fishing areas while overlap of municipal
fisheries catch was highest with species associated with coral reefs and seagrass habitats. Fortyfive
years historical reconstruction of the trawl fisheries using ECOSIM showed a significant
decrease in the biomass of the large high value fisheries groups together with an increase of
cephalopod biomass. Subsequent 10-year simulation scenarios of a trawl fishery ban revealed
that important resources such as large and medium sized carnivores would not have been
significantly reduced had there been a timely application of fisheries gear regulations.
22-8
Impacts of Non-Professional Fisheries on Reef Fish Communities. A Case Study in New
Caledonia (Western Pacific)
Nicolas GUILLEMOT* 1 , Pascale CHABANET 2 , Marc LEOPOLD 1 , Olivier LE PAPE 3 ,
Marion CUIF 1
1 Institut de Recherche pour le Développement, CRISP Program, Noumea, New Caledonia,
2 Institut de Recherche pour le Développement, Ste Clothilde, Reunion, 3 Pôle Halieutique,
Agrocampus Rennes, Rennes, France
The imminent creation of a massive nickel mining complex will soon increase demographic
pressure on the rural Northwest coast of New Caledonia (Western Pacific Ocean). As a
consequence, fishing pressure is expected to significantly rise. Our objectives were 1) to assess
to what extent six years (2002-2007) of underwater visual censuses (UVC), conducted over 60
permanent transects, reflected the fishing pressure characterised by 165 surveys of nonprofessional
fishermen conducted in 2007 ; 2) to plan for an optimized long-term monitoring
program (adequate methodologies and sampling design) to monitor the predicted fishing
impact. In the study area, including three villages and five Melanesian tribes, surveys showed
that non-professional fishing uptakes (~171 tons) are far more important than professional
uptakes (~35 t). Non-professional fishermen target a large diversity of biotopes (barrier,
intermediate and fringing reefs, mangroves, soft bottoms) and fish families. The main families
targeted are Lethrinidae, Acanthuridae, Scaridae, Mugilidae, Siganidae, Serranidae,
Haemulidae, Ludjanidae, Carangidae, Sparidae, Gerreidae and Kyphosidae. Furthermore,
fishing practices (gear, targeted species, yearly landings) differed strongly between tribes and
villages, which underlines the necessity to monitor every aspects of these non-professional
activities. UVC reflected partially the effects of this complex fishery landscape. After that
survey information was translated into spatially-explicit information and integrated into a GIS,
UVC results compiled by biotopes and species reflected 36% of the survey information.
Specifically, several key landing indicators (yield, species mid-size) were successfully related to
UVC indicators (biomass, species mid-size), and both proved to be consistent for a long-term
monitoring. However, UVC’s sensitivity remains not completely appropriate to fully measure
non-professional fishery impacts. Adequate quantification could be partially based on UVC but
methods such as video observations (avoiding diver biases) could provide complementary data
on targeted species. Furthermore, validation should still be based on surveys, especially
targeting non-professional fishermen.
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