11th ICRS Abstract book - Nova Southeastern University

22-41
Using Length-Frequency Data To Identify Management Options: A Case-Study
Based On Five Years Monitoring Of The Large Seine Net Fishery Of Rodrigues
Island, Indian Ocean
Alasdair EDWARDS* 1 , Emily HARDMAN 2 , Jovani RAFFIN 2
1 School of Biology, Newcastle University, Newcastle upon Tyne, United Kingdom,
2 Shoals Rodrigues, Pointe Monier, Mauritius
The large seine-net fishery in the 240 km² shallow lagoon of Rodrigues Island is of great
socio-economic importance in terms of both protein and employment. Seine net fishing is
undertaken by teams of 15 and 30 fishers, using four to eight boats. Annual landings from
the fishery of 190 to 300 tonnes have been recorded since 2000. Working with local
fishing cooperatives, the NGO Shoals Rodrigues has monitored the seine catch since
2002, recording the species and total length of each fish caught during 125 sampled
fishing days. A total of over 68,000 fish in 110 species have been sampled with data on
each individual entered on a specially designed database to facilitate analysis. The fishery
is diverse and the most commonly caught species include Siganus sutor, Valamugil
seheli, Naso unicornis, Acanthurus triostegus, Lethrinus nebulosus, Mulloidichthys
flavolineatus, Caranx melampygus and Gerres longirostris.
Analysis of the length-frequency distributions for the primary species in the catch
suggests that several of the main species caught are being severely overexploited but that
others are being exploited sustainably at close to optimal levels of effort. The
overexploited species tend to be those that are deeper bodied (e.g. Siganus sutor) and thus
caught at a younger age, whereas the sustainably exploited species tend to be those that
are shallow-bodied (e.g. goatfish and mullet) and thus caught much later in life.
A surplus yield model based on government fisheries statistics suggests that the fishery
may be at a sustainable level overall. However, the length-frequency data shows that
several species are heavily overexploited. Data on length at first capture shows that an
increase in mesh size is unlikely to be practical. A network of marine reserves and an
MPA are being implemented in an effort to ensure sustainability in the face of excess
fishing pressure.
22-43
Patterns in A Catch-And-Release Sport Fishery Targeting A Pristine Stock Of
Caranx Ignobilis At Midway Atoll
Raymond BOLAND* 1 , Frank PARRISH 1
1 NMFS/NOAA, Pacific Islands Fisheries Science Center, Honolulu, HI
From 1996 to 2001, a catch-and-release charter fishery was conducted in waters of the
U.S. Fish and Wildlife Service Wildlife Refuge at Midway Atoll in the Northwestern
Hawaiian Islands. In the history of the coral atoll, this was the first and only organized
fishing directed at giant trevally (Caranx ignobilis) and it caught a total of 751 fish.
Fishing logs indicated an overall trend of increased fishing effort throughout the 6-year
period. Catch per unit of effort (CPUE) derived as catch per day, per trip, per boat hour,
and per hook-hour declined between one-half and one-third of initial levels, then
increased from 1999 to 2001. The increase of CPUE during the later part of the study
corresponded to wider spatial distribution of the fishing effort throughout the atoll. In
1998 the U.S. Fish and Wildlife Service implemented a tagging study at Midway Atoll,
tagging 356 C. ignobilis of which 24 were recaptured, 4 more than once. Time periods at
liberty for the fish ranged from 0 to 389 days and movement was seen across the atoll.
Recapture data for fish tagged at Midway and at neighboring atolls showed no movement
of jacks between atolls. Treating the adult jacks at Midway Atoll as a closed population
and assuming a constant capture probability, the number of resident jacks was estimated
at 2590 (± 793 SE). The data from Midway indicates catch and release fishing has a
measurable effect on the atoll’s jack assemblages. It is not known whether the decline is
a result of post release mortality from capture events; or the result of experienced jacks
avoiding fishers.
Oral Mini-Symposium 22: Coral Reef Associated Fisheries
22-44
Behavioral Effects Of Fishing On Coral Reefs
Elizabeth MADIN* 1,2 , Steven GAINES 3,4 , Robert WARNER 1,2
1 Dept. of Ecology, Evolution, and Marine Biology, University of California - Santa Barbara,
Santa Barbara, CA, 2 Marine Science Institute, University of California - Santa Barbara, Santa
Barbara, 3 Marine Science Institute, University of California - Santa Barbara, Santa Barbara,
CA, 4 Dept. of Ecology, Evolution, and Marine Biology, University of California - Santa
Barbara, Santa Barbara
The community-level consequences of predator removal, and indeed the mechanisms behind
them, are poorly understood in coral reef systems. However, the majority of coral reefs globally
experience some degree of fishing pressure, much of which is focused on predatory fishes. To
date, most research on this topic has been focused on changes in the density of prey species as
the principal mechanism causing the effects of fishing to cascade through coral reef
communities. However, an entirely different pathway exists by which fishing, and therefore
predator removal, could fundamentally alter marine ecosystems: changes in the behavior of prey
species. The Line Islands represent a gradient in human influence that ranges from nearly
pristine coral reefs to ones with key upper trophic levels functionally removed. We used this
system to ask whether prey fishes behave differently over a gradient of fishing intensity and
thus predator biomass. We quantified behaviors of a suite of prey fishes spanning different
functional groups, focusing on behaviors that are subject to a risk-reward trade-off and play a
potentially important role in mediating benthic community structure. We found that these prey
fishes exhibit demonstrable shifts in behavior over the gradient of predator biomass. In
particular, time spent foraging versus sheltering and patterns of movement over feeding areas
appear to be constrained by the level of predation risk imposed by predators. Our findings
demonstrate that fishing on coral reefs may strongly affect prey species’ behavior, and further
suggest that these behavioral responses may have important implications for benthic community
structure in ways not predicted from traditional density-mediated trophic cascade models.
22-45
Reproduction, Habitat Utilization, And Movements Of Hogfish (lachnolaimus Maximus)
in The Florida Keys: A Comparison From Fished Versus Unfished Habitats
Roldan MUNOZ* 1 , Michael BURTON 1 , Kenneth BRENNAN 1 , R. O. PARKER, JR. 1
1 National Marine Fisheries Service, National Oceanic and Atmospheric Administration,
Beaufort, NC
Few studies conducted within reserves have examined the reproductive behavior of exploited
reef fishes. We tested the hypothesis that reproductive output should be greater in a marine
reserve (i.e., greater density and sizes of inhabitants) relative to a fished area. Our study took
place in the Florida Keys National Marine Sanctuary in the Western Sambos Ecological
Reserve (closed to fishing) and the Middle Sambos (fishing permitted). At these sites we
gathered detailed information on microhabitat utilization of hogfish (Lachnolaimus maximus),
their movements, encounter rates, and their reproductive behavior. Most of the data were
collected with focal animal observations and the behavioral data geographically logged with a
hand-held GPS. Multivariate analyses of microhabitats present on home ranges and utilized by
hogfish indicate no overall differences between study sites, yet hogfish movements were greater
at the fished site. Furthermore, despite a greater survey effort at the fished study site, no
reproductive activity was seen there. In marked contrast, spawning was readily observed at the
reserve site where 55 spawns were recorded from 6 different harems. Encounters with the
potential to be inherently disruptive (i.e., male-male) tended to occur at a higher rate at the
fished site. Conversely, encounters capable of stabilizing social groups (i.e., male-female)
tended to occur at a higher rate in the reserve. These data suggest a breakdown of social
structure at the fished site and highlight the role that marine reserves may play in the
maintenance of reproductive output by site-attached fishes, particularly those with complex
social and mating systems that experience intense fishing pressure; the easily-speared L.
maximus, characterized by harem territories and female-to-male sex change, is a good example
of such a species.
193