Risk analysis of a flatfish stock complex : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Mathematics at Massey University
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Date
2010
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Massey University
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Abstract
The New Zealand Ministry of Fisheries relies on fishery assessments to determine
suitable catch quotas for exploited fisheries. Currently, 628 fish stocks are managed
in New Zealand using the Quote Management System, which includes the 8 com-
mercial flatfish species caught within the Exclusive Economic Zone. These eight
species of flatfish, which includes four species of flounder, two species of sole, brill
and turbot, are currently managed using a combined catch quota. Since these eight
species are managed using a common catch quota, there is concern that some of the
individual species may be under or over-fished.
This thesis describes work involving the flatfish species caught in the FLA3 man-
agement area, around the south island of New Zealand. The FLA3 management area
contains three key species: New Zealand sole, lemon sole, and sand flounder. Due
to the nature and limitations of the data available, simple biomass dynamic models
were applied to these species. The maximum likelihood and Bayesian goodness of fit
techniques were used to estimate the model parameters. Three models were used:
the Fox model, the Schaefer model and the Pella-Tomlinson model with m = 3. As a
mathematical/statistical exercise, these models were used to conduct a risk analysis
to analyse the advantages and disadvantages of six management options for setting
a TACC. However, because of issues over the way that the parameter K has been
modelled (due to necessity caused by the lack of data), this should not be seen as
an appropriate method for estimating the fish stock. Conclusions were drawn from
the results regarding suitable future action for the assessment and management of
flatfish stock in FLA3.
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Keywords
New Zealand fisheries, Fisheries management, Fish stock assessment