Chinook Salmon Fishery Research Articles

Postrelease mortality of spring Chinook Salmon from a mark‐selective recreational fishery in the Yakima River, Washington

AbstractObjectiveFishery managers often implement mark‐selective fishing regulations that provide harvest opportunity on abundant hatchery salmon populations while requiring release of at‐risk natural‐origin populations. However, implementing these decisions requires fisheries managers to account for postrelease mortality of any natural‐origin fish caught and released by anglers, which can be variable and is unknown for spring Chinook Salmon Oncorhynchus tshawytscha recreational fisheries in eastern Washington. Therefore, the objective of this study was to estimate and examine the factors affecting, the postrelease mortality of spring Chinook Salmon caught and released from an inland recreational mark–selective fishery in the Yakima River, Washington.MethodsWe conducted a 2‐year paired control and treatment radio‐telemetry study using 171 treatment fish caught and released during a recreational fishery and 194 control fish captured in a nearby fishway. Subjects were subsequently tracked throughout the summer, and postrelease mortality was estimated on September 1. Stepwise logistic regression was used to analyze potential explanatory variables recorded at the time of capture.ResultThe estimated postrelease mortality of these fish was 12% (95% CI = 2–23%) just prior to the onset of spawning. We also inferred using logistic regression that anatomical hook location explained most of the variation in mortality rates of angled fish.ConclusionOur estimate of postrelease mortality is similar to estimates derived in other studies for recreational freshwater Chinook Salmon fisheries as well as the current 10% rate used to manage Columbia River spring Chinook Salmon recreational fisheries.

Parentage‐based tagging using mothers balances accuracy and cost for discriminating between natural and stocked recruitment for inland fisheries

AbstractHatchery programmes are frequently used to supplement inland fisheries, yet achieving successful management outcomes often requires information on stocked versus naturally reproduced fish abundance. Parentage‐based tagging – genetically assigning offspring to their parents – has potential to be an effective approach for distinguishing stocked and naturally reproduced fish. However, several challenges may limit its application to inland fisheries, including genetic relatedness among populations that can affect identification accuracy and high costs of genotyping large broodstocks. Here, we demonstrate the efficacy of parentage‐based tagging based on broodmothers in the Lake Ontario Chinook Salmon fishery, which uses thousands of broodparents and has potential for substantial relatedness between stocked and naturally reproduced fish. Restricting parent sampling to broodmothers reduced costs by two‐thirds, was logistically pragmatic, and achieved >95% accuracy in distinguishing stocked from naturally reproduced salmon. Combined, these results highlight the potential wide applicability of parentage‐based tagging for assessing stocking programmes in inland waters.

Modeling Chinook Salmon Run Timing in the Gulkana River, Alaska Using Environmental Indices

AbstractEnvironmental data from the Gulkana River, in conjunction with in‐season Chinook Salmon Oncorhynchus tshawytscha passage numbers, are among the many tools used by the Alaska Department of Fish and Game to assess in‐season run strength and timing in the upper Copper River drainage. In this study, we refine the modeling of Chinook Salmon run timing by comparing methods based on linear, exponential, and polynomial regressions of marine and freshwater environmental indices for the Gulkana River stock. A range of temporal subsets and measurement techniques for coastal upwelling, air temperature, river discharge, and water temperature was analyzed in a stepwise process to update the in‐season forecast model. Ultimately, Gulkana River water temperature proved to be the most important variable in predicting run timing. A model considering daily maximum water temperature and river discharge can accurately estimate the proportion of the total run that swam upriver before July (pseudo‐R2 = 0.97), allowing for efficient Chinook Salmon fishery management through the latter portion of the run.

Parentage-based tagging and genetic stock identification applied to assessment of mixed-stock fisheries and hatchery broodstocks for Chinook salmon in British Columbia, Canada

Genetic stock identification (GSI) and parentage-based tagging (PBT) are being increasingly applied to salmon fisheries and hatchery broodstock management and assessment in Canada. GSI and PBT with single nucleotide polymorphisms (SNPs) were applied in assessment of 2020 Chinook salmon fisheries and hatchery broodstocks in British Columbia (BC), Canada, with 9234 individuals successfully genotyped in fishery samples and 2250 PBT identifications made (24.4% individual identification rate). As PBT identifications provided age of the individual and sex was determined from a SNP in the SNP panel, it was possible to evaluate sex ratios by age observed in the fishery sampling. Fishery catch sex ratios at age two and three years were male-biased, whereas those at age four and five years were female-biased. The combined age and sex information derived from genetics-based fishery sampling illustrates the ancillary information that becomes available relative to coded-wire tag (CWT) sampling if biological sampling of the catch is not conducted. There were 20,342 individuals genotyped in 65 hatchery broodstocks from which 6080 PBT identifications were made. Population-specific contributions to mixed-stock fisheries and exploitation rates were estimated with CWTs and GSI-PBT technologies for 13 populations, and close agreement of estimated population-specific exploitation rates between CWT and genetic methods for the 13 populations was observed (r2(11)= 0.951, P < 0.001). We conclude that a genetic approach can improve upon the results available from the current CWT program for assessment and management of Chinook salmon fisheries and hatchery broodstocks in BC, as well as provide ancillary information to improve wild Chinook salmon assessment and conservation by providing fishery impacts by conservation unit for any fishery in Canada.

Cumulative Impacts of Water Abstraction on a Recreational Salmon Fishery on the Rangitata River, New Zealand

AbstractThis study investigates factors contributing to the unexpected loss of a recreational Chinook salmon fishery in a reach of the Rangitata River in Canterbury, New Zealand. The Rangitata is o...

Fishers' perception of the interaction between the South American sea lions and the Chinook salmon fishery in southern Chile

We studied how the South American sea lion (SASL, Otaria flavescens) interacts with the operation of an artisanal fishery of Chinook salmon, a non-native species in Chile, using a combination of biological and social approaches, including a valuation by fishers about this interaction. During austral summer of 2019, an observer onboard artisanal fishing boats characterized the attack behavior of SASLs to gillnet-captured Chinook salmon during 33 hauls and analyzed which factors may affect the intensity of attacks. To analyze the relationship between fishers and SASLs, a Likert scale about the perception and views about nature was applied. A total of 23 interviews—including 35 open and 16 closed questions—with fishers were conducted to describe how they perceived the interactions with SASLs. Interactions with SASLs were recorded in 35% of the fishing events and varied depending on both operational factors, such as the number of boats, as well as environmental factors, such as moon’s luminosity. Even though SASL interactions resulted in seven fish (~ 70 kg) damaged of a total catch of 2815 kg (2.5%) during the survey, boats with a damaged catch by SASL lost up to 11% of their revenue. This is consistent with 87% of the interviewed fishers who considered that the conflict with the SASL negatively impacts their activity and results in economic losses. A negative perception towards SASLs likely results from personal experience and revenue loss, even though impacts of SASL interactions at the scale of the entire fishery may be less important. While older fishers with less formal education have a productivist and instrumental focus, younger fishers with a more sustainable and conservationist view of fishing offer an opportunity to lead an improved local understanding of the relationship between salmon, SASLs, and humans.

Parentage-based tagging combined with genetic stock identification is a cost-effective and viable replacement for coded-wire tagging in large-scale assessments of marine Chinook salmon fisheries in British Columbia, Canada.

Wild Pacific salmon, including Chinook salmon Oncorhynchus tshawytscha, have been supplemented with hatchery propagation for over 50 years in support of increased ocean harvest, mitigation for hydroelectric development, and conservation of threatened populations. In Canada, the Wild Salmon Policy for Pacific salmon was established with the goal of maintaining and restoring healthy and diverse Pacific salmon populations, making conservation of wild salmon and their habitats the highest priority for resource management decision‐making. For policy implementation, a new approach to the assessment and management of Chinook salmon and the associated hatchery production and fisheries management are needed. Implementation of genetic stock identification (GSI) and parentage‐based tagging (PBT) for marine fisheries assessment may overcome problems associated with coded‐wire tag‐based (CWT) assessment and management of Chinook salmon fisheries, providing at a minimum information equivalent to that derived from the CWT program. GSI and PBT were used to identify Chinook salmon sampled in 2018 and 2019 marine fisheries (18,819 individuals genotyped) in British Columbia to specific conservation units (CU), populations, and broodyears. Individuals were genotyped at 391 single nucleotide polymorphisms via direct sequencing of amplicons. Very high accuracy of assignment to population and age (>99.5%) via PBT was observed for 1994 Chinook salmon of ages 2–4 years, with a 105,722–individual, 380–population baseline available for assignment. Application of a GSI‐PBT system of identification to individuals in 2019 fisheries provided high‐resolution estimates of stock composition, catch, and exploitation rate by CU or population, with fishery exploitation rates directly comparable to those provided by CWTs for 13 populations. GSI and PBT provide an alternate, cheaper, and more effective method in the assessment and management of Canadian‐origin Chinook salmon relative to CWTs, and an opportunity for a genetics‐based system to replace the current CWT system for salmon assessment.

Application of Genetic Stock Identification and Parentage‐Based Tagging in a Mixed‐Stock Recreational Chinook Salmon Fishery

AbstractGenetic methods can guide and improve the management of recreational mixed‐stock fisheries by informing stock‐specific estimates of harvest. We applied genetic stock identification and parentage‐based tagging to a recreational Chinook Salmon Oncorhynchus tshawytscha fishery in the Columbia River to illustrate the value of genetic analysis in management. We sampled landed catch in 2017 and 2018, assigned the fish to genetic reporting groups, explored temporal trends in harvest composition within and between seasons, and assessed the accuracy and precision of genetic methods against estimates from conventional tagging methodology. The genetic stock identification and parentage‐based tagging produced concordant stock assignments, and the harvest composition estimates were validated with independent data. High assignment rates, relative to expended sampling effort, and precise harvest composition estimates with adequate sample sizes demonstrate that both genetic methods can be complementary, effective tools in advancing harvest assessment and recreational fisheries management. The success of genetic stock identification and parentage‐based tagging supports the expanded application of genetics to similar fisheries, potentially alongside existing or emerging assessment methods, and guides future improvements in data collection and analysis.

Climate effects on size‐at‐age and growth rate of Chinook Salmon (Oncorhynchus tshawytscha) in the Fraser River, Canada

AbstractDecline in size‐at‐age of Chinook Salmon (Oncorhynchus tshawytscha) has been observed for many populations across the entire Northeast Pacific Ocean, and identifying external drivers of this decline is important for sustainable management of these ecologically, economically, and culturally valuable resources. We assessed size‐at‐age of 96,939 Chinook Salmon sampled in the Fraser River watershed (Canada) from 1969 to 2017. A broad decline in size‐at‐age was confirmed across all population aggregates of Fraser River Chinook Salmon, in particular since year 2000. By developing a novel probability‐based approach to calculate age‐ and year‐specific growth rates for Fraser River Chinook Salmon and relating growth rates to environmental conditions in specific years through a machine learning method (boosted regression trees), we were able to disentangle multi‐year effects on size‐at‐age and thus identify environmental factors that were most related to the observed size‐at‐age of Chinook Salmon. Among 10 selected environmental variables, ocean salinity at Entrance Island in spring, the Aleutian Low Pressure Index and the North Pacific Current Bifurcation Index were consistently identified as important contributors for four of the seven age and population aggregate combinations. These top environmental contributors could be incorporated into future stock assessment and forecast models to improve Chinook Salmon fisheries management under climate change.

Central Valley Spring-Run Chinook Salmon and Ocean Fisheries: Data Availability and Management Possibilities

Author(s): Satterthwaite, William H.; Cordoleani, Flora; O'Farrell, Michael R.; Kormos, Brett; Mohr, Michael S. | Abstract: Central Valley spring-run Chinook Salmon (CVSC) are designated threatened by state and federal authorities. Although CVSC are caught in ocean fisheries, their harvest is not actively managed, because it is assumed that measures currently in place to protect endangered Sacramento River winter-run Chinook Salmon (SWRC) will also sufficiently protect CVSC. Recoveries of tags and genetically-identified CVSC suggest these fish have a more northerly distribution than SRWC. Further, escapement data and cohort reconstructions suggest that CVSC mature later than SRWC. Thus, regulations (time/area restrictions and minimum size limits) crafted to protect SRWC alone may not adequately protect CVSC; on the other hand, regulations to constrain impacts on Klamath River and California coastal Chinook Salmon populations may also reduce impacts on CVSC. Trends in CVSC escapement were deemed acceptable in recent status updates, but concerns remain because of the negative effects caused by recent drought and ocean conditions. Should more active management of CVC be desired, current options are limited. The most promising approach is based on estimating age-specific ocean fishing mortality rates by using cohort reconstructions applied to tagged Chinook Salmon that originate from the Feather River Hatchery. At a minimum, ocean fishing mortality rates could be monitored and compared to proxy thresholds. If reference harvest rates were established, harvest models could be developed to predict how CVSC would be affected by fishing regulations, similar to the way fall-run Chinook Salmon fisheries are evaluated. Abundance forecasts would require improved juvenile production data (e.g., from genetic sampling of juvenile emigrants), since sibling-based forecasts commonly used for fall-run Chinook Salmon would not be available in time for pre-season planning. It is unclear if ocean fishing mortality rate estimates derived from hatchery proxies for natural-origin fish are truly representative, but existing data do not demonstrate obvious differences in ocean distribution or size-at-age fish. Substantial new investments in tagging or sampling would be needed to directly estimate ocean fishing mortality rates for natural-origin CVSC. Establishing specific harvest targets or limits for CVSC requires an improved understanding of production throughout their life cycle through juvenile production estimates and long-term information on spawner age structure.

Genetic Mixture Analysis Supports Recalibration of the Fishery Regulation Assessment Model

Management of the commercially important Washington coastal Chinook Salmon Oncorhynchus tshawytscha troll fishery depends on the Chinook Salmon Fishery Regulation Assessment Model (FRAM). The Chinook Salmon FRAM uses historical and contemporary coded wire tag recoveries to estimate abundance and exploitation rates for particular indicator stocks. Those estimates are used to set limits on overall harvest and protect sensitive stocks. Current efforts are underway to implement a newer “base period” (time period on which exploitation rates are based). Our collaboration of science, management, and industry used genetic mixture modeling to provide independent stock composition estimates supporting FRAM recalibration. Genetic modeling suggested that total catch includes a much smaller proportion of a limiting Columbia River stock, a larger fraction of Canadian stocks, and an abundant Oregon coastal stock not previously included in the FRAM. Our results focus attention on particular stocks that will benefit from refinements in the Chinook Salmon FRAM.

A Multi-regional Economic Impact Analysis of Alaska Salmon Fishery Failures

Recently, the harvest of Chinook salmon (Oncorhynchus tshawytscha) in some areas of Alaska was severely curtailed due to a significant reduction in the salmon runs. This generated adverse economic impacts in the areas. Unlike previous studies of impacts of changes in fisheries, which often rely on single-region economic impact models, this study uses a multi-regional social accounting matrix (MRSAM) model of three US regions – Alaska, West Coast, and the rest of US – to calculate the multi-regional economic impacts of the Chinook salmon fishery failures, considering the countervailing effects of federal disaster funds paid to commercial salmon fishermen. To estimate the negative effects of the reduced salmon harvest, this study uses “adjusted demand-driven MRSAM model”, which avoids the double-counting problem encountered when a demand-driven model is used to compute the effects of exogenous output change, and overcomes the weakness of Ghosh (1958) approach in estimating the forward-linkage effects. To calculate the positive effects of federal relief payments, this study uses a Leontief demand-driven MRSAM model. Results indicate that the salmon fishery failures have significant adverse economic impacts including both intra-regional (Alaska) and inter-regional (West Coast and the rest of US) impacts, and that the disaster relief mitigates only a small portion of the adverse impacts.

A Spatially Explicit Assessment of Changes in Chinook Salmon Fisheries in Lakes Michigan and Huron from 1986 to 2011

AbstractWe produced a spatially explicit assessment of the changes in stocking, catch, fishing effort, and catch per effort (CPE) for Chinook Salmon Oncorhynchus tshawytscha in Lakes Michigan and Huron from 1986 to 2011. We focused on describing spatial differences in the changes that occurred during three well‐known episodes of rapid change: (1) a decline in abundance during 1986–1994 in Lake Michigan, (2) a recovery in abundance during 1994–2006 in Lake Michigan, and (3) a decline in abundance during 2002–2010 in Lake Huron. We used a spatial grid system to describe and contrast trends in fishing effort and CPE among the main lake basins (Michigan, Huron, and Georgian) and subregions within those basins. We applied linear regressions, ANCOVAs, and Tukey's tests to assess differences. We found that trends differed among and within basins during all three episodes, which resulted in changes in the distribution of fishing effort and CPE. Fishing effort generally decreased in all basins and subregions over the entire 25 years, but it decreased less in areas where CPE had increased. The timing of the recovery episode and second mortality episode overlapped, so CPE simultaneously increased from 79 to 139 fish/1,000 h of fishing in the Michigan basin and decreased from 65 to 35 fish/1,000 h of fishing in the Huron basin. Movement of fishing effort and Chinook Salmon from the Huron basin to the Michigan basin probably occurred during this time. The CPE did not change significantly in the Georgian basin. Within basins, CPE exhibited sharp declines of more than 80% in some subregions during both mortality episodes but declined much less or not at all in others. After the recovery episode, areas of highest CPE in the Michigan basin had shifted from eastern subregions to western subregions.Received February 2, 2016; accepted April 23, 2016 Published online August 30, 2016

Length‐ and Age‐Selective Fishing on Chinook Salmon of the Columbia River Basin, 2002–2012

AbstractFisheries can influence the size and age of exploited stocks if they selectively remove fish. In this study, we quantified length and age selectivity of the commercial and recreational fisheries on upriver spawning stocks of Chinook Salmon Oncorhynchus tshawytscha in the lower Columbia River from 2002 to 2012. Length and age data were sampled from fish (hatchery and wild individuals together) that were caught by the fisheries and from fish that escaped and then entered a trap in a dam immediately upstream of the fisheries. We found that age‐ and length‐based standardized selection differentials (SSDs) were generally small compared with other fisheries and varied over time. Across all years, fish that were caught were, on average, 0.006 years older and 0.19 cm longer than fish in the total return. These results were consistent with the low harvest rates over the 11 years (recreational fishery harvest rate = 4.9%, commercial fishery harvest rate = 3.7%). However, in some years the SSDs during certain fishing periods or overall were larger than in other years and harvested fish were significantly older and longer than the average fish in the total return. For most years and periods, these larger SSDs appeared to be driven by higher harvest rates by recreational fishing gear (hook and line). The SSDs were influenced by how many Chinook Salmon were available to be caught when and where fisheries were occurring, the size and age distribution of those fish, and the selectivity of the gear. We conclude that the SSDs for contemporary lower Columbia River Chinook Salmon fisheries have generally been small in magnitude and variable over time, though in some years and periods the fisheries caught larger‐ and older‐than‐average fish. Thus, the 2002–2012 lower Columbia River fisheries likely had a low influence on the fitness or potential changes in length and age at maturation of upriver Chinook Salmon.Received December 16, 2015; accepted March 30, 2016 Published online July 19, 2016

Otolith microchemistry reveals spatio-temporal heterogeneity of natal sources and inter-basin migrations of Chinook salmon in Lake Huron

Abstract The Chinook salmon fishery in Lake Huron is comprised of approximately 20% hatchery-reared fish and 80% fish from wild populations. However, finer-scale stock composition remains poorly understood because of the lack of lake-wide research and monitoring of this species and logistical constraints of mass-marking wild fish. This lack of information has resulted in a common assumption made by management agencies and used in fisheries models of a homogeneous mixture of hatchery and wild populations in the fishery. Using otolith microchemistry (multi-element concentrations and 87 Sr/ 86 Sr isotopic ratios), we identified natal sources of Chinook salmon opportunistically sampled through space and time in the 2008 and 2010 recreational fisheries. Our findings demonstrated extensive spatio-temporal variability in sample composition, providing the first direct evidence of heterogeneous mixing of hatchery and wild populations in the fishery. Our data also suggest that > 90% of all fish in the recreational fishery originate in rivers and hatcheries in Southern Georgian Bay (46%) and Northern Lake Huron (46%). The majority of wild fish appear to originate from rivers in Southern Georgian Bay (55%) and Northern Lake Huron (35%); whereas the majority (67%) of hatchery fish appear to originate from Michigan hatcheries. Analysis of 87 Sr/ 86 Sr ratios suggests that

Fishermen, markets, and population diversity

Fishing impacts biodiversity on multiple levels, potentially resulting in unintended feedbacks to the economic performance of the fishery over time. For example, targeting observable traits within a population can impact genetic diversity and targeting valuable species can impact biodiversity at the ecosystem level. The bioeconomic literature, however, has given little attention to the effect of fishing on population diversity, even though population diversity contributes to ecosystem services and estimates of population extinction rates are three orders of magnitude higher than species extinction rates. Here we develop a stochastic bioeconomic model that links the harvest of multiple salmon populations in a single commercial fishery to the trajectory of population diversity in a salmon stock complex. We parameterize our model with biological and economic data from the Copper River Chinook salmon fishery. We show that markets can incentivize the degradation of population diversity, reducing infra-marginal fishery rents, and increasing variability in economic returns. We also show that second-best management can conserve population diversity and improve welfare. Furthermore, depending on fishermen׳s time preferences, this management strategy is potentially self-financing.

Stock composition and ocean spatial distribution inference from California recreational Chinook salmon fisheries using genetic stock identification

We apply genetic stock identification (GSI) data and models of the catch and sampling process to describe spatial and temporal patterns in the stock composition and stock-specific catch-per-unit-effort (CPUE) of both tagged and untagged stocks encountered in California recreational ocean Chinook salmon fisheries during the period 1998–2002. Spatial and temporal distributions inferred from GSI sampling of stocks with tagged hatchery components were broadly consistent with those previously inferred from studies of tag recoveries alone, while GSI provided additional insight into untagged stocks of conservation concern. The catch in all times and areas was dominated (typically ≥90%) by the “Central Valley Fall” genetic reporting group, which is comprised primarily of Sacramento River fall run Chinook. Other contributing stocks were more spread out in space and time with the exception of Central Valley winter run Chinook, which were rarely encountered by boats fishing in port areas north of Point Reyes. Localized stock-specific CPUE appeared to increase near a stock's respective natal river while decreasing in other port areas at the time of adult return to freshwater for spawning. We describe methods for quantifying uncertainty in stock proportions, stock-specific catch, and determining the statistical support for proposed management boundaries hypothesized to represent “break points” in the spatial distributions for stocks of concern, and find at most equivocal support for a proposed delineation line at Point Reyes in north-central California.

Creel Survey Sampling Designs for Estimating Effort in Short‐Duration Chinook Salmon Fisheries

AbstractChinook Salmon Oncorhynchus tshawytscha sport fisheries in the Columbia River basin are commonly monitored using roving creel survey designs and require precise, unbiased catch estimates. The objective of this study was to examine the relative bias and precision of total catch estimates using various sampling designs to estimate angling effort under the assumption that mean catch rate was known. We obtained information on angling populations based on direct visual observations of portions of Chinook Salmon fisheries in three Idaho river systems over a 23‐d period. Based on the angling population, Monte Carlo simulations were used to evaluate the properties of effort and catch estimates for each sampling design. All sampling designs evaluated were relatively unbiased. Systematic random sampling (SYS) resulted in the most precise estimates. The SYS and simple random sampling designs had mean square error (MSE) estimates that were generally half of those observed with cluster sampling designs. The SYS design was more efficient (i.e., higher accuracy per unit cost) than a two‐cluster design. Increasing the number of clusters available for sampling within a day decreased the MSE of estimates of daily angling effort, but the MSE of total catch estimates was variable depending on the fishery. The results of our simulations provide guidelines on the relative influence of sample sizes and sampling designs on parameters of interest in short‐duration Chinook Salmon fisheries.Received February 5, 2013; accepted July 1, 2013

Unbiased Methods for Calculating Mortality in Mark‐Selective Fisheries Models for Ocean Salmon

AbstractMark‐selective fisheries (MSF) are increasingly being used as a strategy for managing fisheries for Coho Salmon Oncorhynchus kisutch and Chinook Salmon O. tshawytscha on the west coast of North America. Mark‐selective fisheries allow anglers to keep legal‐size Coho Salmon or Chinook Salmon with a missing adipose fin (typically hatchery fish) and require the release of those with an adipose fin (unmarked fish, which are usually wild fish). The objective of MSF is to provide meaningful fisheries on abundant stocks of hatchery salmon while reducing the impact on wild (unmarked) salmon stocks. As has been previously shown, the model currently used in the Pacific Fishery Management Council's preseason planning process to project mortalities for proposed Coho Salmon and Chinook Salmon fisheries underestimates the number of unmarked salmon mortalities occurring in MSF and concurrent nonselective fisheries. We propose equations that provide unbiased estimates of salmon mortalities that occur in these fisheries due to the release of fish. The performance of the proposed methods is evaluated and compared to the current methods using a simulation model. The methods are shown to provide unbiased calculations of total mortalities for unmarked salmon in both mark‐selective and concurrent nonselective fisheries. The unbiased methods are able to incorporate different release‐mortality and mark‐recognition rates for the fisheries modeled.Received July 24, 2012; accepted November 26, 2012

Effect of Survey Design and Catch Rate Estimation on Total Catch Estimates in Chinook Salmon Fisheries

AbstractRoving–roving and roving–access creel surveys are the primary techniques used to obtain information on harvest of Chinook salmon Oncorhynchus tshawytscha in Idaho sport fisheries. Once interviews are conducted using roving–roving or roving–access survey designs, mean catch rate can be estimated with the ratio‐of‐means (ROM) estimator, the mean‐of‐ratios (MOR) estimator, or the MOR estimator with exclusion of short‐duration (≤0.5 h) trips. Our objective was to examine the relative bias and precision of total catch estimates obtained from use of the two survey designs and three catch rate estimators for Idaho Chinook salmon fisheries. Information on angling populations was obtained by direct visual observation of portions of Chinook salmon fisheries in three Idaho river systems over an 18‐d period. Based on data from the angling populations, Monte Carlo simulations were performed to evaluate the properties of the catch rate estimators and survey designs. Among the three estimators, the ROM estimator provided the most accurate and precise estimates of mean catch rate and total catch for both roving–roving and roving–access surveys. On average, the root mean square error of simulated total catch estimates was 1.42 times greater and relative bias was 160.13 times greater for roving–roving surveys than for roving–access surveys. Length‐of‐stay bias and nonstationary catch rates in roving–roving surveys both appeared to affect catch rate and total catch estimates. Our results suggest that use of the ROM estimator in combination with an estimate of angler effort provided the least biased and most precise estimates of total catch for both survey designs. However, roving–access surveys were more accurate than roving–roving surveys for Chinook salmon fisheries in Idaho.Received May 14, 2012; accepted July 23, 2012