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Reconstructing lingcod biomass in Georgia Strait and the effect of marine reserves on lingcod populations in Howe Sound Martell, Steven James Dean
Abstract
Commercial lingcod fishing in Georgia Strait was closed in 1990 due to severely depressed catches. Seasonal closures and size restrictions were added to sports fisheries in an attempt to rebuild the stock. There have been no fishery independent surveys to estimate lingcod abundance in Georgia Strait. The rate of recovery is monitored through changes in sports fishery catch rates. In this thesis, I use catch statistics and commercial catch and effort data to reconstruct the lingcod biomass time series for statistical area 4B (Georgia Strait and surrounding areas). This reconstruction was carried out using a technique called Stock Reduction Analysis (SRA), where the dynamics of an agestructured model is driven by annual removals. The SRA model was tested using a fake time series of relative abundance data and known parameter values. The model was able to estimate, within 10%, the correct parameter values used to generate the fake data. Catch and effort data (CPUE) are used as a relative abundance index to estimate unfished biomass and stock productivity. It is assumed that the relationship between CPUE and stock size is hyperstable in commercial fisheries. Results of the SRA indicate that Georgia Strait lingcod stock have been depleted by over 90%, and that their reproductive capacity is much lower than that of other temperate fish stocks. Lingcod in Howe Sound are part of the Georgia Strait Stock. There are 3 small Marine Protected Areas (MPAs) in Howe Sound that are closed to fishing. An in-situ mark-recapture study was carried out to evaluate responses of lingcod populations in closed areas, and to determine whether or not lingcod move across reserve area boundaries. Changes in underwater encounter rates and length frequencies in each of 13 different survey sites provide evidence of small-scale seasonal movement patterns in lingcod. Densities and average lengths of lingcod have higher means in reserve areas compared to fished areas, but the differences are not significantly different. Lingcod in the oldest reserve area are significantly larger than lingcod in recently established reserve areas. However, this result may be due to artificial reefs that are present in the oldest reserve area. The idea of using marine reserves as a fisheries management tool is relatively new in fisheries science. Current ecological questions focus on ideal reserve location and reserve area size. Until contentious issues surrounding the use of marine reserves have been resolved, and proper large-scale field experiments have been conducted to evaluate reserves, computer models can be used to speculate how reserve areas will perform. A spatially explicit computer model (FISHMOD) was used to evaluate the current network of "no-take" areas in Howe Sound. Specifically, the model was used to answer questions pertaining to movement rates in lingcod, spatial distribution of fishing effort, and to compare alternative management policies. Simulation results suggest that a disproportionate amount of fishing effort will be distributed along boundaries of reserve areas, especially at low stock sizes. As exchange rates between reserve area and fished area increase, more fishing effort is distributed along reserve boundaries. In comparison to increasing size limits or reducing fishing season length, a system of MP As in Howe Sound is more effective.
Item Metadata
Title |
Reconstructing lingcod biomass in Georgia Strait and the effect of marine reserves on lingcod populations in Howe Sound
|
Creator | |
Publisher |
University of British Columbia
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Date Issued |
1999
|
Description |
Commercial lingcod fishing in Georgia Strait was closed in 1990 due to severely
depressed catches. Seasonal closures and size restrictions were added to sports fisheries
in an attempt to rebuild the stock. There have been no fishery independent surveys to
estimate lingcod abundance in Georgia Strait. The rate of recovery is monitored through
changes in sports fishery catch rates. In this thesis, I use catch statistics and commercial
catch and effort data to reconstruct the lingcod biomass time series for statistical area 4B
(Georgia Strait and surrounding areas). This reconstruction was carried out using a
technique called Stock Reduction Analysis (SRA), where the dynamics of an agestructured
model is driven by annual removals. The SRA model was tested using a fake
time series of relative abundance data and known parameter values. The model was able
to estimate, within 10%, the correct parameter values used to generate the fake data.
Catch and effort data (CPUE) are used as a relative abundance index to estimate unfished
biomass and stock productivity. It is assumed that the relationship between CPUE and
stock size is hyperstable in commercial fisheries. Results of the SRA indicate that
Georgia Strait lingcod stock have been depleted by over 90%, and that their reproductive
capacity is much lower than that of other temperate fish stocks.
Lingcod in Howe Sound are part of the Georgia Strait Stock. There are 3 small
Marine Protected Areas (MPAs) in Howe Sound that are closed to fishing. An in-situ
mark-recapture study was carried out to evaluate responses of lingcod populations in
closed areas, and to determine whether or not lingcod move across reserve area
boundaries. Changes in underwater encounter rates and length frequencies in each of 13 different survey sites provide evidence of small-scale seasonal movement patterns in
lingcod. Densities and average lengths of lingcod have higher means in reserve areas
compared to fished areas, but the differences are not significantly different. Lingcod in
the oldest reserve area are significantly larger than lingcod in recently established reserve
areas. However, this result may be due to artificial reefs that are present in the oldest
reserve area.
The idea of using marine reserves as a fisheries management tool is relatively new
in fisheries science. Current ecological questions focus on ideal reserve location and
reserve area size. Until contentious issues surrounding the use of marine reserves have
been resolved, and proper large-scale field experiments have been conducted to evaluate
reserves, computer models can be used to speculate how reserve areas will perform. A
spatially explicit computer model (FISHMOD) was used to evaluate the current network
of "no-take" areas in Howe Sound. Specifically, the model was used to answer questions
pertaining to movement rates in lingcod, spatial distribution of fishing effort, and to
compare alternative management policies. Simulation results suggest that a
disproportionate amount of fishing effort will be distributed along boundaries of reserve
areas, especially at low stock sizes. As exchange rates between reserve area and fished
area increase, more fishing effort is distributed along reserve boundaries. In comparison
to increasing size limits or reducing fishing season length, a system of MP As in Howe
Sound is more effective.
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Extent |
9690529 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-06-12
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0074836
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1999-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.