Thomas Carruthers

Thomas Carruthers
University of British Columbia - Vancouver | UBC · Institute for the Oceans and Fisheries

Doctor of Philosophy

About

34
Publications
10,163
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808
Citations
Introduction
Tom is the CEO of Blue Matter Science, a quantitative fishery consultancy based in Vancouver, and an Adjunct Professor at the UBC Institute for the Oceans and Fisheries. Tom works on assessment and Management Strategy Evaluation frameworks for both data-rich and data-limited fisheries. He is a developer of R packages such as DLMtool and MSEtool and Apps such as MERA, Slick, SSES and the Atlantic bluefin MSE framework.

Publications

Publications (34)
Technical Report
Full-text available
The three main robustness tests, senescence, growth curve for eastern stock, "Brazilian" catches, had already been coded in July 2020 (with 4 Operating Models (OMs) each), but the "Brazilian" catches test needed to be redone. Robustness tests on time-varying mixing and persistent change in mixing have now also been coded (with 2 OMs each) and will...
Article
Stock assessments are often used to provide management advice, such as a total allowable catch (TAC), to fishery managers. Many stocks are not assessed annually, and the TAC from the previous assessment is often maintained in years between assessments. We developed two interim management procedures (MPs) that update the estimate of current vulnerab...
Article
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Common uncertainties in stock assessment relate to parameters or assumptions that strongly determine both the estimates of quantities of management interest (e.g. stock depletion) and related reference points (e.g. biomass at maximum sustainable yield). The risks associated with these uncertainties are often presented to managers in the form of dec...
Article
Potential users of the model proposed by Froese et al. (2018) should be aware of several issues. First, the method to calculate equilibrium numbers-at-length is incomplete and leads to negatively biased estimates of fishing mortality. Second, inadequate simulation testing fails to reveal that the method is highly sensitive to assumptions of equilib...
Article
Full-text available
Specifying annual catch limits for artisanal fisheries, low economic value stocks, or bycatch species is problematic due to data limitations. Many empirical management procedures (MPs) have been developed that provide catch advice based on achieving a stable catch or a historical target (i.e., instead of maximum sustainable yield). However, a thoro...
Article
Full-text available
1.A simulation‐based approach known as Management Strategy Evaluation (MSE) is increasingly used by resource managers to identify management procedures that are robust to uncertainties in system dynamics. 2.The majority of global fish populations are data‐limited and there is large uncertainty over their population and exploitation dynamics. 3.The...
Article
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The first relatively complete landscape-scale social–ecological system (SES) model of a recreational fishery was developed and ground-truthed with independent angling effort data. Based on the British Columbia multistock recreational fishery for rainbow trout (Oncorynchus mykiss), the model includes hundreds of individual lake fisheries, hundreds o...
Article
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A new indicator is described that uses multivariate posterior predictive data arising from management strategy evaluation (MSE) to detect operating model misspecification (exceptional circumstances) due to changing system dynamics. The statistical power of the indicator was calculated for five case studies for which fishery stock assessments have e...
Article
Full-text available
Qualitative risk assessment frameworks, such as the Productivity Susceptibility Analysis (PSA), have been developed to rapidly evaluate the risks of fishing to marine populations and prioritize management and research among species. Despite being applied to over 1,000 fish populations, and an ongoing debate about the most appropriate method to conv...
Article
A simple approach is described that uses the ratio of catches among a reference and a target stock to estimate their relative depletion. The catch-ratio estimator was simulation tested to identify conditions under which it can be expected to provide precise and unbiased estimates of relative depletion. The catch-ratio estimator is strongly affected...
Article
Full-text available
Virtual population analysis (VPA) is used in many stock assessment settings and requires a total catch-at-age data set where an age is assigned to each fish that has been caught. These data sets are typically constructed using ad hoc methods that rely on numerous assumptions. Although approaches are available to account for observation error in the...
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A method is described that uses stock-specific movement to impute stock-of-origin for electronic tags. A simple example of the approach was tested using cross-validation of electronic tags of known stock-of-origin. The imputation model achieved a failure rate of 3% and a success rate of 88%. In 9% of cases the imputation model did not classify stoc...
Article
Full-text available
Rebuilding depleted fish populations is a priority of modern fisheries management. In the U.S., strong statutory mandates extend to both the goals and process by which stocks are to be rebuilt. However, the National Standard Guidelines that govern the implementation of the Magnuson-Stevens Fishery Conservation and Management Act may change to incre...
Article
Full-text available
Using a management strategy evaluation approach, we compare a range of new and established anagement procedures (MPs) for setting catch-limits in fisheries. Performance is evaluated with respect to fish life history type, level of stock depletion, data quality, and autocorrelation in recruitment strength. We quantify the robustness of each MP with...
Article
Full-text available
We develop and test spatial population dynamics models that estimate age-dependent offshore movement of fish populations from spatial fishery data. Spatially aggregated population dynamics models produced biased estimates of maximum sustainable yield (MSY) reference points when spatial dynamics were simulated. Spatial population dynamics models pro...
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Full-text available
Estimates of tag reporting rates are necessary in order to estimate tag-recovery rates and interpret tagging data in terms of movement rates, exploitation rates and abundance. We describe a Bayesian framework for the estimation of reporting rates for multiple fleets using coincidental tagging and catch data disaggregated by fish size, species, loca...
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Full-text available
The majority of global fish stocks lack adequate data to evaluate stock status using conventional stock assessment methods. This poses a challenge for the sustainable management of these stocks. Recent requirements to set scientifically based catch limits in several countries, and growing consumer demand for sustainably managed fish have spurred an...
Technical Report
Full-text available
In January 2014, the Natural Resources Defense Council (NRDC) convened a group of experts from NMFS, state agencies, academic institutions, and non-governmental organizations for a Workshop on the science and management of data-limited fisheries. The goal of the Data-Limited Methods (DLM) Workshop was to evaluate and seek to improve current methods...
Article
Full-text available
Methods that use only fisheries catch records to determine the status of exploited fish populations have been used to draw important conclusions regarding the world's fisheries. The reliability of two such approaches is evaluated by simulating a range of fisheries development and overfishing scenarios. The success rate and bias of stock status clas...
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Full-text available
We formulate and simulation-test a spatial surplus production model that provides a basis with which to undertake multispecies, multi-area, stock assessment. Movement between areas is parameterized using a simple gravity model that includes a "residency" parameter that determines the degree of stock mixing among areas. The model is deliberately sim...
Article
Full-text available
When deriving relative abundance indices on the basis of fishery catch-per-unit-effort (CPUE) data, biases may be introduced by systematic changes in the spatial distribution of fishing. We present and simulation test an integrated approach that combines the conventional generalized linear modelling (GLM) approach to CPUE standardization with data...
Article
Full-text available
Uncertainty about reporting rates of tags returned by fishermen has often prevented tagging data from being used in stock assessments. In this study we conduct a meta-analysis to estimate tag reporting rates of commercial tuna fleets by comparing their tag return data with those of the USA longline pelagic observer program. The longline fleets of V...
Article
Full-text available
Relative abundance indices derived from nominal catch-per-unit-effort (CPUE) data are a principle source of information for the majority of stock assessments. A particular problem with formulating such abundance indices for pelagic species such as tuna is the interpretation of CPUE data from fleets that have changed distribution over time. In this...

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Projects

Projects (5)
Project
Develop software to support landscape-scale decision making for freshwater fisheries
Project
Streamlined implementation of strategic fishery management
Project
Provide rapid specification of operating models and testing of data-rich management procedures.