Carl J Walters

Carl J Walters
University of British Columbia - Vancouver | UBC · Institute for the Oceans and Fisheries

PhD

About

368
Publications
119,545
Reads
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41,188
Citations
Additional affiliations
July 1969 - present
University of British Columbia - Vancouver
Position
  • University of British Columbia
Education
July 1965 - July 1969
Colorado State University
Field of study
  • Fisheries

Publications

Publications (368)
Article
The salmon-eating Southern Resident killer whale (SRKW) (Orcinus orca) population currently comprises only 73 individuals, and is listed as ‘endangered’ under the Species at Risk Act in Canada. Recent evidence suggests that the growth of this population may be limited by food resources, especially Chinook salmon (Oncorhynchus tshawytscha). We prese...
Article
The demand for fish maw (i.e., dried swim bladder) has apparently intensified during the past decades in Hong Kong and mainland China; currently, maw has similar annual import volumes but far higher mean unit values than other important seafood delicacies like shark fins and sea cucumber. Escalated demand for seafood delicacies can significantly co...
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Full-text available
Abstract—Walleye (Sander vitreus) populations in Alberta, Canada collapsed by the mid-1990s and were a case study in the paper Canada’s Recreational Fisheries: The Invisible Collapse? Here we fit age-structured population dynamics models to data from a landscape-scale monitoring program to assess Walleye population status and reconstruct recruitmen...
Article
Significance Charging industries for exploiting natural resources ensures that the owner of the resources—the public—receives compensation for their usage. Although fishery resources within exclusive economic zones constitute most of the global marine capture production, it is unclear whether fishing industries harvesting these resources are charge...
Article
Increasing recruitment per mature adult as density declines is a key factor in being able to sustainably exploit populations and the extent of this increase is closely related to the sustainable exploitation rate of fish stocks. Stock-recruitment estimates typically show surprisingly large increases in egg to recruitment survival as density decline...
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Growth and recruitment overfishing can co-occur when a fishery is subjecting small and immature fish in conjunction with adult fish to excessive exploitation rates such that it reduces the spawning biomass to the point where recruitment is significantly impaired. Such conditions are generally evident in open-access fisheries and are especially detr...
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The reproductive biology of Indian halibut, Psettodes erumei, a commercially valuable flatfish species, in the northern Persian Gulf and Oman Sea was studied. A total of 433 specimens were collected monthly from October 2016 to November 2017, and their length, weight, sex, gonad and liver weight, and maturity status were recorded. Monthly variation...
Article
Inland fisheries managers must account for multiple competing uses for aquatic resources; using methods such as ecosystem‐based management allows for different priorities for aquatic ecosystems to be accounted for. Declining abundance of kokanee salmon Oncorhynchus nerka (Walbaum) in Arrow Lakes Reservoir in the 1990s led to the use of large‐scale...
Article
Fisheries in many developing nations commonly operate in an open access regime, largely due to fundamental factors like poor fisheries institutions and the need to maximize food security and employment. Such factors are evident in Hormozgan, the largest fishing province in Iran, rendering many fish stocks in precarious conditions. The catch of the...
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Dreissenid (zebra and quagga) mussels are spreading across North America and having an impact on freshwater ecosystems, through bottom-up impacts. Lakes in British Columbia are known to be at risk for mussel invasion due to favourable water chemistry and significant cross-border boat movements. This project uses Ecopath with Ecosim (EwE) to model a...
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Considerable effort is being deployed to predict the impacts of climate change and anthropogenic activities on the ocean's biophysical environment, biodiversity, and natural resources to better understand how marine ecosystems and provided services to humans are likely to change and explore alternative pathways and options. We present an updated ve...
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We develop a mechanistically motivated von Bertalanffy growth model to estimate growth rate and its predictors from spatial-temporal data, and compare this model’s performance to a suite of commonly used mixed-effects growth models. We test these models with simulated data and then apply them to test whether concerns that high density is causing gr...
Article
The commercially, recreationally and culturally important Fraser River Sockeye Salmon Oncorhynchus nerka have experienced a productivity decline over the last three decades, which along with greater temporal variation in annual abundance (i.e. cyclic dominance) may at least partly be due to Steller Sea Lion Eumetopias jubatus (SSL) predation on ret...
Article
• Predator–prey models are often used to represent consumptive interactions between species but, typically, are derived using simple experimental systems with little plasticity in prey or predator behaviours. However, many prey and predators exhibit a broad suite of behaviours. Here, we experimentally tested the effect of density‐dependent prey and...
Article
When fish stocks migrate across multiple exclusive economic zones (EEZs), they compel managers to examine management at both national and international levels. A strategic interaction emerges when the fishing activity of one country impacts fishing opportunities available for other countries sharing the stock. Left unaddressed, strategic interactio...
Article
Salmon populations harvested in mixed-stock fisheries can exhibit genotypic, behavioral, and life history diversity that can lead to heterogeneity in population productivity and size. Methods to quantify this heterogeneity among populations in mixed-stock fisheries are not well-established but are critical to assessing harvest-biodiversity trade-of...
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We address the problem of optimal size‐selective exploitation in an age‐structured fish population model by systematically examining how density and size dependency in growth, mortality and fecundity affect optimal harvesting patterns when judged against a set of fisheries objectives. The study offers five key insights. First, while minimum‐length...
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Quantifying ecosystem-level processes that drive community structure and function is key to the development of effective environmental restoration and management programs. To assess the effects of large-scale aquatic vegetation loss on fish and invertebrate communities in Florida estuaries, we quantified and compared the food webs of two adjacent s...
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Several studies have shown that mean length is only slightly biased and hence a robust indicator of the total mortality (fishing and natural mortalities). However, these studies use models that typically assume equilibrium conditions and are expected to predict a much stronger relationship between mean length and fishing mortality than would be obt...
Preprint
We address the problem of optimal size-selective exploitation in an age-structured fish population model by systematically examining how density- and size-dependency in growth, mortality and fecundity affect optimal harvesting patterns when judged against a set of common fisheries objectives. Five key insights are derived. First, while minimum-leng...
Preprint
Full-text available
Saving big and old fish from harvest constitutes an increasingly popular idea from a conservation perspective. But does it pay off also from a fisheries perspective. Or does the presence of old fish in a stock indicate the poor fisheries management by protecting fish that cost yield? Our paper systematically investigates optimal sizes limits, in pa...
Article
The population dynamics of forage fish are often ‘boom or bust’, and variation in recruitment may be a contributing factor to changes in abundance. Here we applied several methods for identifying stock recruit relationships (SRR) to 52 forage fish stocks: a time-invariant Ricker model and two time-varying methods (dynamic linear models and regime-b...
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Seasonal fisheries emerge due to a variety of mechanisms: ontogenetic shifts of fish life stages, regulatory initiatives (e. g., fishing seasons) and/or biomass dynamics where there can be a strong seasonal reduction in stock biomass as fisheries harvest a single or double recruiting cohorts each year. The latter mechanism involves targeting specie...
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...
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Attempts to model the giant mud crab Scylla serrata fishery in the Northern Territory (Australia), have often been complex and the results difficult to interpret, leading to divergent estimates of fishing mortality. This has hindered the development of meaningful management policy. Additionally, analyses based on the entire Northern Territory fishe...
Article
Many modern stock assessments estimate age- or length-based selectivity, often using simple parametric functions describing asymptotic or dome-shaped selectivity. We present a length-based stock reduction analysis (Length-SRA), which bypasses the requirement of estimating selectivity by calculating exploitation rate at length directly from observed...
Article
Commercial salmon harvests have declined dramatically for all Pacific salmon species in British Columbia, mainly over the period 1995–2000. Much of this decline is attributable to declining abundance, but some of it has been due to deliberate reduction in allowable exploitation rates. Various reasons have been given for this reduction, but the main...
Article
In complex dynamic systems like fisheries, recognizing fishing-effort responses is as critical as understanding the biology of the exploited species for making sensible management decisions. In highly seasonal fisheries, it is theoretically possible for an “interannual bionomic equilibrium” to develop under open-access, where fleet dynamics may res...
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Understanding density-dependent changes in juvenile survival and growth rates is of great importance because these rates determine recovery rates for imperiled populations and/or sustainable harvest rates. Unfortunately, the mechanisms leading to density dependent survival and growth are among the least understood process in biology and fisheries....
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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
Predation risk and competition among conspecifics significantly affect survival of juvenile salmon, but are rarely incorporated into models that predict recruitment in salmon populations. Using densities of harbour seals (Phoca vitulina) and numbers of hatchery-released Chinook salmon (Oncorhynchus tshawytscha) smolts as covariates in spatially str...
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We describe an unbiased length-based, age-structured mark-recapture (LAMR) model for estimating length-based abundance and recruitment of fish populations. Many mark-recapture studies employ capture gear that is size-selective, leading to a larger and faster growing marked sub-population with a different capture probability than the unmarked sub-po...
Preprint
Full-text available
We describe an unbiased length-based, age-structured mark-recapture (LAMR) model for estimating length-based abundance and recruitment of fish populations. Many mark-recapture studies employ capture gear that is size-selective, leading to a larger and faster growing marked sub-population with a different capture probability than the unmarked sub-po...
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Full-text available
Most stocks of Atlantic cod (Gadus morhua) in the Northwest Atlantic collapsed in the early 1990s, with little sign of recovery since then. In the southern Gulf of St. Lawrence (sGSL), the failed recovery is due to severe increases in the natural mortality of adult Atlantic cod. We examined the role of predation by grey seals (Halichoerus grypus) i...
Article
Like fishing, natural regime shifts and human-induced environmental changes are often equally important factors in driving fish stock declines. In the Northwestern Arabian Gulf, many fish stocks are declining, raising questions about the reduction in the flow of Tigris-Euphrates rivers. Here we investigate the relationship between Tigris-Euphrates...
Preprint
Full-text available
Understanding density-dependent changes in juvenile survival and growth rates is of great importance because these rates determine recovery rates for imperiled populations and/or sustainable harvest rates. Unfortunately, the mechanisms leading to density dependent survival and growth are among the least understood process in biology and fisheries....
Article
Declining catches are typically taken to be a warning sign of overfishing. But in fact, many such declines have been driven by recruitment changes unrelated to stock size, as evidenced by the failure of stocks to recover after reduction in fishing or recovery despite the failure to reduce fishing. Given a declining pattern, supposedly precautionary...
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We introduce introduce a Lagrangian movement model that can be used to characterize cyclic migrations of iteroparous fish populations. We demonstrate how movement parameters can be estimated using conventionally available catch at age data and provide a description of the potential bias that may arise from model misspecification, data aggregation a...
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This paper explores the impact of fishing low trophic level “forage” species on higher trophic level marine predators including other fish, birds and marine mammals. We show that existing analyses using trophic models have generally ignored a number of important factors including (1) the high level of natural variability of forage fish, (2) the wea...
Article
Simple predator-prey models make widely divergent predictions about impact on piscivores of harvesting forage fish species, depending on structural assumptions about the fine-scale spatial structure of trophic interactions (presence or absence of foraging arena structure in prey availability) and about limitation in predator or prey recruitment due...
Article
Simple predator-prey models make widely divergent predictions about impact on piscivores of harvesting forage fish species, depending on structural assumptions about the fine-scale spatial structure of trophic interactions (presence or absence of foraging arena structure in prey availability) and about limitation in predator or prey recruitment due...
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The approach to fisheries termed “balanced harvesting” (BH) calls for fishing across the widest possible range of species, stocks, and sizes in an ecosystem, in proportion to their natural productivity, so that the relative size and species composition is maintained. Such fishing is proposed to result in higher catches with less negative impact on...
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Selectivity in fish is often size-dependent, which results in differential fishing mortality rates across fish of the same age, an effect known as "Lee’s Phenomenon". We extend previous work on using length composition to estimate the spawning potential ratio (SPR) for data-limited stocks by developing a computationally efficient length-structured...
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Ecopath with Ecosim (EwE) models are easier to construct and use compared to most other ecosystem modelling techniques and are therefore more widely used by more scientists and managers. This, however, creates a problem with quality assurance; to address this we provide an overview of best practices for creating Ecopath models. We describe the diag...
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In a recent publication (Froese et al., ICES Journal of Marine Science; doi:10.1093/icesjms/fsv122), we presented a critique of the balanced harvesting (BH) approach to fishing. A short section dealt with the size-spectrum models used to justify BH, wherein we pointed out the lack of realism of these models, which mostly represented ecosystems as c...
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Full-text available
Ecopath with Ecosim (EwE) models are easier to construct and use compared to most other ecosystem modelling techniques and are therefore more widely used by more scientists and managers. This, however, creates a problem with quality assurance; to address this we provide an overview of best practices for creating Ecopath, models. We describe the dia...
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
Catch and release (CR) is an increasingly common strategy for recreational fisheries in which sustaining high catch rates is important. The success of this strategy is reduced if the released fish are temporarily invulnerable to capture due to behavioral changes, as recent research suggests. Here, we explore how temporary fishing closures with shor...
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Rainbow trout (Oncorhynchus mykiss) have been purposely introduced in many regulated rivers, with inadvertent consequences on native fishes. We describe how trout growth rates and condition could be influencing trout population dynamics in a 130 km section of the Colorado River below Glen Canyon Dam based on a large-scale mark–recapture program whe...
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Diagnosing causal factors of change at the ecosystem level is challenging because multiple drivers often interact at various spatial and temporal scales. We employ an integrated natural and social science approach to assess potential mechanisms leading to the collapse of an estuarine social-ecological system, and recommend future paths to increased...
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The Apalachicola Bay, Florida, eastern oyster (Crassostrea virginica) industry has annually produced about 10% of the U.S. oyster harvest. Today’s simple individual-operator, hand-tonging, small-vessel fishery is remarkably similar to the one that began in the 1800s. Unprecedented attention is currently being given to the status of oyster resources...
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Food web dynamics consist of processes that affect ecosystem structure and functioning. EcoTroph (ET) is a recently developed approach and software for modeling aquatic eco - systems, articulated entirely around the trophic level concept. Here, we used ET to investigate impacts of 2 trophic controls (i.e. foraging arena and top-down controls) on ma...
Article
Bioenergetics models are commonly used to predict effects of changes in metabolic rates and food availability on growth. However, food intake rate generally is assumed to vary asWd, where d = 2/3, an assumption based on observations from feeding trials in laboratory studies. Further, the von Bertalanffy growth function (VBGF) is specifically integr...
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Increased population sizes of Double-crested Cormorants (Phalacrocorax auritus) and small-bodied (<15 cm total length) yellow perch (Perca flavescens) have occurred at Lac la Biche, Alberta, Canada, since fisheries collapsed the walleye (Sander vitreus) population. A walleye restoration program was introduced in 2005, but uncertainty around the eco...
Article
Ecosystem-based fisheries management seeks to consider trade-offs among management objectives for interacting species, such as those that arise through predator-prey linkages. In particular, fisheries-targeting forage fish (small and abundant pelagic fish) might have a detrimental effect on fisheries-targeting predators that consume them. However,...
Article
Dynamic programming is used to construct harvest control rules that account for persistent changes in productivity, exploitation rate constraints that prevent extinction of nontarget weak stocks, and an economic objective that recognizes moderate income to be more important to fishermen than maximization of total profit. Persistent productivity cha...
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AimThere has been considerable effort allocated to understanding the impact of climate change on our physical environment, but comparatively little to how life on Earth and ecosystem services will be affected. Therefore, we have developed a spatial-temporal food web model of the global ocean, spanning from primary producers through to top predators...
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Why are marine species where they are? The scientific community is faced with an urgent need to understand aquatic ecosystem dynamics in the context of global change. This requires development of scientific tools with the capability to predict how biodiversity, natural resources, and ecosystem services will change in response to stressors such as c...