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Greg Andrusak - One of the best experts on this subject based on the ideXlab platform.
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the fishing and Natural Mortality of large piscivorous bull trout and rainbow trout in kootenay lake british columbia 2008 2013
PeerJ, 2017Co-Authors: Joseph L Thorley, Greg AndrusakAbstract:BACKGROUND Estimates of fishing and Natural Mortality are important for understanding, and ultimately managing, commercial and recreational fisheries. High reward tags with fixed station acoustic telemetry provides a promising approach to monitoring Mortality rates in large lake recreational fisheries. Kootenay Lake is a large lake which supports an important recreational fishery for large Bull Trout and Rainbow Trout. METHODS Between 2008 and 2013, 88 large (≥500 mm) Bull Trout and 149 large (≥500 mm) Rainbow Trout were marked with an acoustic transmitter and/or high reward ($100) anchor tags in Kootenay Lake. The subsequent detections and angler recaptures were analysed using a Bayesian individual state-space Cormack-Jolly-Seber (CJS) survival model with indicator variable selection. RESULTS The final CJS survival model estimated that the annual interval probability of being recaptured by an angler was 0.17 (95% CRI [0.11-0.23]) for Bull Trout and 0.14 (95% CRI [0.09-0.19]) for Rainbow Trout. The annual interval survival probability for Bull Trout was estimated to have declined from 0.91 (95% CRI [0.76-0.97]) in 2009 to just 0.46 (95% CRI [0.24-0.76]) in 2013. Rainbow Trout survival was most strongly affected by spawning. The annual interval survival probability was 0.77 (95% CRI [0.68-0.85]) for a non-spawning Rainbow Trout compared to 0.41 (95% CRI [0.30-0.53]) for a spawner. The probability of spawning increased with the fork length for both species and decreased over the course of the study for Rainbow Trout. DISCUSSION Fishing Mortality was relatively low and constant while Natural Mortality was relatively high and variable. The results indicate that angler effort is not the primary driver of short-term population fluctations in the Rainbow Trout abundance. Variation in the probability of Rainbow Trout spawning suggests that the spring escapement at the outflow of Trout Lake may be a less reliable index of abundance than previously assumed. Multi-species stock assessment models need to account for the fact that large Bull Trout are more abundant than large Rainbow Trout in Kootenay Lake.
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the fishing and Natural Mortality of large piscivorous bull trout and rainbow trout in kootenay lake british columbia 2008 2013
bioRxiv, 2016Co-Authors: Joseph L Thorley, Greg AndrusakAbstract:Background. Estimates of fishing and Natural Mortality are important for understanding, and ultimately managing, commercial and recreational fisheries. High reward tags with fixed station acoustic telemetry provides a promising approach to monitoring Mortality rates in large lake recreational fisheries. Kootenay Lake is a large lake which supports an important recreational fishery for large Bull Trout and Rainbow Trout. Methods. Between 2008 and 2013, 88 large (≥ 500 mm) Bull Trout and 149 large (≥ 500 mm) Rainbow Trout were marked with an acoustic transmitter and/or high reward ($100) anchor tags in Kootenay Lake. The subsequent detections and angler recaptures were analysed using a Bayesian individual state-space Cormack-Jolly-Seber (CJS) survival model with indicator variable selection. Results. The final CJS survival model estimated that the annual interval probability of being recaptured by an angler was 0.17 (95% CRI 0.11 - 0.23) for Bull Trout and 0.14 (95% CRI 0.09 - 0.19) for Rainbow Trout. The annual interval survival probability for Bull Trout was estimated to have declined from 0.91 (95% CRI 0.77 - 0.97) in 2009 to just 0.45 (95% CRI 0.24 - 0.73) in 2013. Rainbow Trout survival was most strongly affected by spawning. The annual interval survival probability was 0.77 (95% CRI 0.68 - 0.85) for a non-spawning Rainbow Trout compared to 0.42 (95% CRI 0.31 - 0.54) for a spawner. The probability of spawning increased with the fork length for both species and decreased over the course of the study for Rainbow Trout. Discussion. Fishing Mortality was relatively low and constant while Natural Mortality was relatively high and variable. The results are consistent with Kokanee abundance as opposed to angler effort as the primary driver of short-term population fluctations in Rainbow Trout abundance. Multi-species stock assessment models need to account for the fact that large Bull Trout are more abundant than large Rainbow Trout in Kootenay Lake.
Joseph L Thorley - One of the best experts on this subject based on the ideXlab platform.
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the fishing and Natural Mortality of large piscivorous bull trout and rainbow trout in kootenay lake british columbia 2008 2013
PeerJ, 2017Co-Authors: Joseph L Thorley, Greg AndrusakAbstract:BACKGROUND Estimates of fishing and Natural Mortality are important for understanding, and ultimately managing, commercial and recreational fisheries. High reward tags with fixed station acoustic telemetry provides a promising approach to monitoring Mortality rates in large lake recreational fisheries. Kootenay Lake is a large lake which supports an important recreational fishery for large Bull Trout and Rainbow Trout. METHODS Between 2008 and 2013, 88 large (≥500 mm) Bull Trout and 149 large (≥500 mm) Rainbow Trout were marked with an acoustic transmitter and/or high reward ($100) anchor tags in Kootenay Lake. The subsequent detections and angler recaptures were analysed using a Bayesian individual state-space Cormack-Jolly-Seber (CJS) survival model with indicator variable selection. RESULTS The final CJS survival model estimated that the annual interval probability of being recaptured by an angler was 0.17 (95% CRI [0.11-0.23]) for Bull Trout and 0.14 (95% CRI [0.09-0.19]) for Rainbow Trout. The annual interval survival probability for Bull Trout was estimated to have declined from 0.91 (95% CRI [0.76-0.97]) in 2009 to just 0.46 (95% CRI [0.24-0.76]) in 2013. Rainbow Trout survival was most strongly affected by spawning. The annual interval survival probability was 0.77 (95% CRI [0.68-0.85]) for a non-spawning Rainbow Trout compared to 0.41 (95% CRI [0.30-0.53]) for a spawner. The probability of spawning increased with the fork length for both species and decreased over the course of the study for Rainbow Trout. DISCUSSION Fishing Mortality was relatively low and constant while Natural Mortality was relatively high and variable. The results indicate that angler effort is not the primary driver of short-term population fluctations in the Rainbow Trout abundance. Variation in the probability of Rainbow Trout spawning suggests that the spring escapement at the outflow of Trout Lake may be a less reliable index of abundance than previously assumed. Multi-species stock assessment models need to account for the fact that large Bull Trout are more abundant than large Rainbow Trout in Kootenay Lake.
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the fishing and Natural Mortality of large piscivorous bull trout and rainbow trout in kootenay lake british columbia 2008 2013
bioRxiv, 2016Co-Authors: Joseph L Thorley, Greg AndrusakAbstract:Background. Estimates of fishing and Natural Mortality are important for understanding, and ultimately managing, commercial and recreational fisheries. High reward tags with fixed station acoustic telemetry provides a promising approach to monitoring Mortality rates in large lake recreational fisheries. Kootenay Lake is a large lake which supports an important recreational fishery for large Bull Trout and Rainbow Trout. Methods. Between 2008 and 2013, 88 large (≥ 500 mm) Bull Trout and 149 large (≥ 500 mm) Rainbow Trout were marked with an acoustic transmitter and/or high reward ($100) anchor tags in Kootenay Lake. The subsequent detections and angler recaptures were analysed using a Bayesian individual state-space Cormack-Jolly-Seber (CJS) survival model with indicator variable selection. Results. The final CJS survival model estimated that the annual interval probability of being recaptured by an angler was 0.17 (95% CRI 0.11 - 0.23) for Bull Trout and 0.14 (95% CRI 0.09 - 0.19) for Rainbow Trout. The annual interval survival probability for Bull Trout was estimated to have declined from 0.91 (95% CRI 0.77 - 0.97) in 2009 to just 0.45 (95% CRI 0.24 - 0.73) in 2013. Rainbow Trout survival was most strongly affected by spawning. The annual interval survival probability was 0.77 (95% CRI 0.68 - 0.85) for a non-spawning Rainbow Trout compared to 0.42 (95% CRI 0.31 - 0.54) for a spawner. The probability of spawning increased with the fork length for both species and decreased over the course of the study for Rainbow Trout. Discussion. Fishing Mortality was relatively low and constant while Natural Mortality was relatively high and variable. The results are consistent with Kokanee abundance as opposed to angler effort as the primary driver of short-term population fluctations in Rainbow Trout abundance. Multi-species stock assessment models need to account for the fact that large Bull Trout are more abundant than large Rainbow Trout in Kootenay Lake.
Joseph E Hightower - One of the best experts on this subject based on the ideXlab platform.
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an integrated tagging and catch curve model reveals high and seasonally varying Natural Mortality for a fish population at low stock biomass
Fisheries Research, 2020Co-Authors: Jacob R Krause, Joseph E Hightower, Stephen J Poland, Jeffrey A BuckelAbstract:Abstract Rebuilding of exploited fish stocks at low biomass requires accurate Mortality estimates. Weakfish (Cynoscion regalis) abundance is at historical lows caused by an increasing instantaneous total Mortality (Z) in recent years, but uncertainty exists regarding the relative importance of instantaneous fishing Mortality (F) and Natural Mortality (M) to Z. Data from a tag-return study and catch-curve of weakfish in North Carolina were analyzed jointly using a Bayesian statistical framework to estimate seasonal and annual Mortality (i.e., F, M, and Z). We accounted for key auxiliary parameters in the tag-return portion of the model (i.e., tag-reporting rate and tag loss) through field studies and an experimental design, including use of high-reward tags and double tagging. Estimates of Z from the joint model were similar in magnitude to the weakfish stock assessment. From mid-2014 to 2017, we estimated a constant annual instantaneous Mortality rate of 0.05 yr−1 (95 % credible interval [CrI]: 0.04, 0.07) for F and 2.33 yr−1 (CrI: 2.10, 2.6) for M. In the most recent stock assessment, estimates of M had an upper bound of 1.0; thus, our findings suggest that these estimates of M are biased low and F biased high. Our seasonal analyses showed that a large portion of Mortality occurred from fall to spring, coinciding with weakfish migration and overwintering periods on the continental shelf. Through an integrated modeling approach, our study provides insights into the magnitude, timing, and sources of weakfish Mortality, and enhances understanding of weakfish population dynamics to guide management strategies.
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relative importance of fishing and Natural Mortality for spotted seatrout cynoscion nebulosus estimated from a tag return model and corroborated with survey data
Fisheries Research, 2018Co-Authors: Timothy A Ellis, Joseph E Hightower, Jeffrey A BuckelAbstract:Abstract The spotted seatrout (Cynoscion nebulosus) is one of the most economically important sportfish in the U.S. South Atlantic and Gulf of Mexico, including at its northern distributional extent in North Carolina and Virginia. The recent stock assessment for this region used an assumed fixed rate of Natural Mortality (M), obtained from a general life-history relationship based on weight. However, biased estimates of fishing Mortality (F) could result if the life-history proxy failed to capture either the magnitude or temporal variation in M. Data from the first comprehensive tag-return study of spotted seatrout in this region were used in a Bayesian statistical modeling framework to estimate F and M. Both laboratory and field studies, including high-reward and double tagging, were conducted to obtain estimates of auxiliary parameters (i.e., tag-reporting rate, tag loss, and tagging Mortality) necessary for the tag-return model. There was no measured Mortality associated with tagging, but reporting rate and loss of internal anchor tags limited returns in this study. From 2008 to 2012, tag-return model estimates of bimonthly instantaneous Mortality rates ranged from 0.003 to 0.067 2-mo−1 for F and from 0.002 to 2.850 2-mo−1 for M. Annual estimates of F were much lower than M for the three years studied, and annual M-estimates were higher than those used for spotted seatrout in this region’s recent stock assessment. Bimonthly estimates of total Mortality rate (Z) from tag-return data were similar to bimonthly estimates of Z from an independent analysis of concurrent gill net survey data, which corroborates the variability and magnitude of Mortality estimates determined from tagging. A strong seasonal influence (i.e., winter severity) on annual loss of spotted seatrout was observed, suggesting that future assessments and management measures for this stock would be improved by explicitly accounting for temporal variation in M in models of fishery population dynamics.
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a combined telemetry tag return approach to estimate fishing and Natural Mortality rates of an estuarine fish
Canadian Journal of Fisheries and Aquatic Sciences, 2009Co-Authors: Nathan M Bacheler, Joseph E Hightower, Jeffrey A Buckel, Lee M Paramore, Kenneth H PollockAbstract:A joint analysis of tag return and telemetry data should improve estimates of Mortality rates for exploited fishes; however, the combined approach has thus far only been tested in terrestrial systems. We tagged subadult red drum (Sciae- nops ocellatus) with conventional tags and ultrasonic transmitters over 3 years in coastal North Carolina, USA, to test the efficacy of the combined telemetry - tag return approach. There was a strong seasonal pattern to monthly fishing Mortality rate (F) estimates from both conventional and telemetry tags; highest F values occurred in fall months and lowest levels occurred during winter. Although monthly F values were similar in pattern and magnitude between conventional tagging and telemetry, information on F in the combined model came primarily from conventional tags. The estimated Natural Mortality rate (M) in the combined model was low (estimated annual rate ± standard error: 0.04 ± 0.04) and was based pri- marily upon the telemetry approach. Using high-reward tagging, we estimated different tag reporting rates for state agency and university tagging programs. The combined telemetry - tag return approach can be an effective approach for estimat- ing F and M as long as several key assumptions of the model are met.
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tag return models allowing for harvest and catch and release evidence of environmental and management impacts on striped bass fishing and Natural Mortality rates
North American Journal of Fisheries Management, 2007Co-Authors: Honghua Jiang, Kenneth H Pollock, Cavell Brownie, John M Hoenig, Robert J Latour, Brian K Wells, Joseph E HightowerAbstract:Abstract Catch-and-release fisheries have become very important in the management of overexploited recreational fish stocks. Tag return studies, where the tag is removed regardless of fish disposition, have been used to assess the effectiveness of restoration efforts for these fisheries. We extend the instantaneous rate formulation of tag return models to allow for catch and release as well as harvest. The key point of our methods is that, given an estimate of the tag reporting rate, the fishing Mortality rate (F) is separated into two components: the Mortality on harvested fish and the “Mortality” on tags (because the tags are removed) of fish released alive. The total fishing Mortality rate for untagged fish is the sum of the Fs due to harvest and hooking Mortality suffered by fish released alive. Natural Mortality rates can also be estimated. Both age-independent models and age-dependent models are constructed, and the age-dependent models are illustrated by application to data from a study of striped ...
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fishing and Natural Mortality of adult largemouth bass in a tropical reservoir
Transactions of The American Fisheries Society, 2005Co-Authors: Scott D Waters, Richard L Noble, Joseph E HightowerAbstract:Abstract Largemouth bass Micropterus salmoides, an intensively studied sport fish of temperate North America, has been introduced into tropical regions, but with little evaluation of fishing or Natural Mortality rates. Previous research in Puerto Rico suggested that annual Mortality rates are high, but whether the extended spawning season (nearly 6 months annually), high angler harvest, or a combination was the cause of the elevated Mortality was unresolved. Using ultrasonic telemetry, we tracked 44 adult largemouth bass over an 18-month period to quantify patterns of Natural, fishing, and total Mortality. Using a general capture–recapture model, we estimated the annual instantaneous rates of fishing (0.584, SE = 0.164) and Natural Mortality (0.310, SE = 0.122). Natural Mortality varied seasonally and generally increased during periods of spawning activity; however, fishing Mortality was fairly consistent throughout the study. Given the relatively high fishing Mortality rate, restrictions on harvest could...
Barbara A Block - One of the best experts on this subject based on the ideXlab platform.
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estimating Natural Mortality of atlantic bluefin tuna using acoustic telemetry
Scientific Reports, 2019Co-Authors: Barbara A Block, Rebecca Whitlock, Robert J Schallert, Mike Castleton, Michael J. W. Stokesbury, Steve Wilson, Andre BoustanyAbstract:Atlantic bluefin tuna (Thunnus thynnus) are highly migratory fish with a contemporary range spanning the North Atlantic Ocean. Bluefin tuna populations have undergone severe decline and the status of the fish within each population remains uncertain. Improved biological knowledge, particularly of Natural Mortality and rates of mixing of the western (GOM) and eastern (Mediterranean) populations, is key to resolving the current status of the Atlantic bluefin tuna. We evaluated the potential for acoustic tags to yield empirical estimates of Mortality and migration rates for long-lived, highly migratory species such as Atlantic bluefin tuna. Bluefin tuna tagged in the Gulf of St. Lawrence (GSL) foraging ground (2009–2016) exhibited high detection rates post release, with 91% crossing receiver lines one year post tagging, 61% detected after year two at large, with detections up to ~1700 days post deployment. Acoustic detections per individual fish ranged from 3 to 4759 receptions. A spatially-structured Bayesian mark recapture model was applied to the acoustic detection data for Atlantic bluefin tuna electronically tagged in the GSL to estimate the rate of instantaneous annual Natural Mortality. We report a median estimate of 0.10 yr−1 for this experiment. Our results demonstrate that acoustic tags can provide vital fisheries independent estimates for life history parameters critical for improving stock assessment models.
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estimating fishing and Natural Mortality rates for pacific bluefin tuna thunnus orientalis using electronic tagging data
Fisheries Research, 2012Co-Authors: R E Whitlock, Murdoch K Mcallister, Barbara A BlockAbstract:Abstract This paper presents estimates of fishing and Natural Mortality rates derived from a spatially- and seasonally structured Bayesian mark-recapture model for electronically tagged Pacific bluefin tuna (PBFT) (Thunnus orientalis). Fishing Mortality rates (F) were estimated by age group, year, quarter and area and ranged between 0.02 and 1.92 quarter−1 for the northeastern Pacific Ocean (EPO) and 0.18 and 0.54 quarter−1 for the northwestern Pacific Ocean. Annual Fs in the EPO were on average 2–3 times higher than the estimated rate of Natural Mortality for Pacific bluefin tuna aged 2 and 3 and 4–6 times higher than the estimated rate of Natural Mortality for Pacific bluefin tuna aged 4 and older. The estimate of M for PBFT aged 5 and above (median 0.15 yr−1, standard deviation = 0.10) was lower than the value currently used in the PBFT stock assessment (i.e. 0.25 yr−1). In addition to estimating age-group specific Natural Mortality rates (M), the plausibility of alternative values for M was evaluated by fixing it at the age-specific schedules tested in the PBFT stock assessment and computing a Bayesian model selection criterion (the Deviance Information Criterion, DIC) for alternative M configurations. For models in which M was fixed, the lowest DIC was obtained for the M scenario that assumed the lowest value of M for PBFT aged 4 and above (i.e. 0.12 yr−1).
Douglas P. Swain - One of the best experts on this subject based on the ideXlab platform.
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evaluating the potential for grey seal predation to explain elevated Natural Mortality in three fish species in the southern gulf of st lawrence
Marine Ecology Progress Series, 2011Co-Authors: Hugues P Benoit, Mike O. Hammill, Douglas P. Swain, Don W Bowen, Greg A Breed, Valerie HarveyAbstract:Despite 2 decades of very low fishing levels, numerous NW Atlantic demersal fish stocks have failed to recover from collapsed states or are presently collapsing. In the southern Gulf of St. Lawrence, adult Natural Mortality (M) appears to be the demographic rate that most limits population productivity in at least 3 species: Atlantic cod Gadus morhua, white hake Urophycis tenuis and winter skate Leucoraja ocellata. The causes of elevated M are not well understood, though there is indirect evidence consistent with an effect of predation by grey seals Halichoerus grypus. However, direct evidence is lacking due to uncertainty in the seal diet. Consequently, Monte Carlo simulations were undertaken using data on the spatial overlap between the seals and the fishes and a seal food-consumption model, to estimate the plausibility that different seal-diet compositions could explain observed M levels. Under the simulation assumptions, we find that predation could explain up to 20 to 50% of M in adult white hake and cod even if these species comprise a small percentage of grey seal diets (<25%). If seals consume some of these fish only partially, by selectively feeding on soft tissues, a predation effect becomes more plausible. Preda- tion can also plausibly explain the observed elevated M in adult winter skate, even if they com- prise a negligible (<0.1%) percentage of the grey seal diet. Though the simulations deal with the factors that shape the potential for predation, a greater understanding of prey selection is required to conclude whether grey seals are actually adversely impacting these fish populations.
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life history evolution and elevated Natural Mortality in a population of atlantic cod gadus morhua
Evolutionary Applications, 2011Co-Authors: Douglas P. SwainAbstract:Fisheries-induced evolution has been hypothesized to delay the recovery of collapsed fish stocks through effects on their productivity. The cod stock in the southern Gulf of St. Lawrence (SGSL) collapsed in the early 1990s and has shown no recovery since then, due mainly to high Natural Mortality of adult cod. Age and size at maturation of SGSL cod decreased sharply over time in cohorts produced in the 1950s and 1960s, likely reflecting an evolutionary response to intensified fishing, and have remained low since then, despite severe reductions in fishing Mortality over the past 15 years. A predicted consequence of early maturation is increased Natural Mortality due to higher costs to reproduction. Early maturation may be a cause of increases in Natural Mortality of SGSL cod in the 1970s but does not appear to be related to the much larger increases since then. Instead, the current high Natural Mortality of SGSL cod appears to be primarily a cause, rather than a consequence, of the continued early maturation in this population, now replacing fishing Mortality as the agent of selection favouring early maturity. This striking example of the failure to reverse fisheries-induced evolution by relaxing fishing pressure emphasizes the need for management strategies that minimize the chances of harvest-induced genetic change.
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covariation between grey seal halichoerus grypus abundance and Natural Mortality of cod gadus morhua in the southern gulf of st lawrence
Canadian Journal of Fisheries and Aquatic Sciences, 2005Co-Authors: G A Chouinard, Mike O. Hammill, Douglas P. Swain, G A PoirierAbstract:More than 10 years after the collapse of Atlantic cod (Gadus morhua) fisheries in Canada, the role of increased seal populations in the decline and lack of recovery of the stocks continues to be discussed. Using removals and abundance indices from synthetic populations, we found that sequential population analysis can uncover trends in Natural Mortality. We used this approach to examine variation in Natural Mortality (M) of southern Gulf of St. Lawrence cod. M increased from the late 1970s to the mid-1990s but declined slightly recently. Results were consistent with previous work indicating that M increased in the 1980s. Changes in estimated M for this cod stock matched fluctuations in grey seal (Halichoerus grypus) abundance. The increase in grey seal abundance from the late 1970s to the mid-1990s corresponded with the increase in estimated M of cod over this time period. The correspondence between seal abundance and M of cod supports the hypothesis that seal predation may be a cause of increased M. Howe...
