Corroborating the ages of walleye pollock (Theragra chalcogramma)

2006 ◽  
Vol 57 (3) ◽  
pp. 323 ◽  
Author(s):  
Daniel K. Kimura ◽  
Craig R. Kastelle ◽  
Betty J. Goetz ◽  
Christopher M. Gburski ◽  
Alexander V. Buslov
Keyword(s):  
Walleye Pollock ◽  
Theragra Chalcogramma ◽  
Age Validation ◽  
Eastern Bering Sea ◽  
Walleye Pollock Theragra Chalcogramma ◽  
Unbiased Manner ◽  
Marginal Increment ◽  
Reading Methodologies ◽  
Made In ◽  
Age Reading

Fish ageing researchers have long recognised the importance of validating age-reading methodologies. The strongest age validations require the acquisition of ageing structures from fish of known-ages, or specimens whose ages are appropriate for bomb carbon validation. Often such specimens are extremely difficult or impossible to acquire so researchers have sought alternatives to validation. The alternative to age validation is age corroboration. Corroboration of a fish ageing method occurs when fish ages are found to be consistent with some ancillary information when comparisons are made in an unbiased manner. The question pursued in this study is how desirable are such comparisons from a scientific viewpoint. Information is presented that corroborates otolith ages for walleye pollock (Theragra chalcogramma), one of the largest groundfish fisheries in the world. Walleye pollock ages were corroborated using marginal increment analysis, ages following the strong 1978 year class in the eastern Bering Sea, and a comparison of ages read from otoliths with ages read from vertebrae. A new statistical method is suggested for comparing otolith and vertebra age readings. The walleye pollock example demonstrated that corroborating evidence can improve confidence in fish ages and ageing techniques.

scholarly journals Evaluating management strategies for eastern Bering Sea walleye pollock (Theragra chalcogramma) in a changing environment

2011 ◽  
Vol 68 (6) ◽  
pp. 1297-1304 ◽  
Author(s):  
James N. Ianelli ◽  
Anne B. Hollowed ◽  
Alan C. Haynie ◽  
Franz J. Mueter ◽  
Nicholas A. Bond
Keyword(s):  
Climate Change ◽  
Bering Sea ◽  
Management Strategies ◽  
Walleye Pollock ◽  
Status Quo ◽  
Theragra Chalcogramma ◽  
Recruitment Pattern ◽  
Control Rules ◽  
Eastern Bering Sea ◽  
Walleye Pollock Theragra Chalcogramma

Abstract Ianelli, J. N., Hollowed, A. B., Haynie, A. C., Mueter, F. J., and Bond, N. A. 2011. Evaluating management strategies for eastern Bering Sea walleye pollock (Theragra chalcogramma) in a changing environment. – ICES Journal of Marine Science, 68: 1297–1304. The impacts of climate change on fish and fisheries is expected to increase the demand for more accurate stock projections and harvest strategies that are robust to shifting production regimes. To address these concerns, we evaluate the performance of fishery management control rules for eastern Bering Sea walleye pollock stock under climate change. We compared the status quo policy with six alternative management strategies under two types of recruitment pattern simulations: one that follows temperature-induced trends and the other that follows a stationary recruitment pattern similar to historical observations. A subset of 82 Intergovernmental Panel on Climate Change climate models provided temperature inputs from which an additional 100 stochastic simulated recruitments were generated to obtain the same overall recruitment variability as observed for the stationary recruitment simulations. Results indicate that status quo management with static reference points and current ecosystem considerations will result in much lower average catches and an increased likelihood of fishery closures, should reduced recruitment because of warming conditions hold. Alternative reference point calculations and control rules have similar performance under stationary recruitment relative to status quo, but may offer significant gains under the changing environmental conditions.

scholarly journals Expected declines in recruitment of walleye pollock (Theragra chalcogramma) in the eastern Bering Sea under future climate change

2011 ◽  
Vol 68 (6) ◽  
pp. 1284-1296 ◽  
Author(s):  
Franz J. Mueter ◽  
Nicholas A. Bond ◽  
James N. Ianelli ◽  
Anne B. Hollowed
Keyword(s):  
Climate Change ◽  
Bering Sea ◽  
Late Summer ◽  
Walleye Pollock ◽  
Future Climate ◽  
Future Climate Change ◽  
Theragra Chalcogramma ◽  
Climate Projections ◽  
Eastern Bering Sea ◽  
Walleye Pollock Theragra Chalcogramma

Abstract Mueter, F. J., Bond, N. A., Ianelli, J. N., and Hollowed, A. B. 2011. Expected declines in recruitment of walleye pollock (Theragra chalcogramma) in the eastern Bering Sea under future climate change. – ICES Journal of Marine Science, 68: 1284–1296. A statistical model is developed to link recruitment of eastern Bering Sea walleye pollock (Theragra chalcogramma) to variability in late summer sea surface temperatures and to the biomass of major predators. The model is based on recent advances in the understanding of pollock recruitment, which suggest that warm spring conditions enhance the survival of early larvae, but high temperatures in late summer and autumn are associated with poor feeding conditions for young-of-year pollock and reduced recruitment in the following year. A statistical downscaling approach is used to generate an ensemble of late summer temperature forecasts through 2050, based on a range of IPCC climate projections. These forecasts are used to simulate future recruitment within an age-structured stock projection model that accounts for density-dependent effects (stock–recruitment relationship), the estimated effects of temperature and predation, and associated uncertainties. On average, recruitment in 2040–2050 should expectedly decline by 32–58% relative to a random recruitment scenario, depending on assumptions about the temperature relationship, the magnitude of density-dependence, and future changes in predator biomass. The approach illustrated here can be used to evaluate the performance of different management strategies and provide long-term strategic advice to managers confronted with a rapidly changing climate.

scholarly journals Age validation of walleye pollock (Theragra chalcogramma) from the Gulf of Alaska using the disequilibrium of Pb-210 and Ra-226

2006 ◽  
Vol 63 (8) ◽  
pp. 1520-1529 ◽  
Author(s):  
Craig R. Kastelle ◽  
Daniel K. Kimura
Keyword(s):  
Accurate Determination ◽  
Gulf Of Alaska ◽  
Growth Zone ◽  
Walleye Pollock ◽  
Theragra Chalcogramma ◽  
Age Validation ◽  
Important Species ◽  
The North ◽  
Walleye Pollock Theragra Chalcogramma ◽  
Radiometric Ages

Abstract The walleye pollock (Theragra chalcogramma) is a commercially important species in the North Pacific, and harvest quotas are dependent upon accurate determination of ages. The two techniques (called methods A and B) currently used to interpret the growth zone patterns in walleye pollock otoliths were compared. The age distributions from these two techniques differed; method B produced ages twice that of method A. Validation of ages from walleye pollock has not been done previously. Radiometric ageing based on the ratio of Pb-210/Ra-226 was used to evaluate the accuracy of otolith growth zone counts, and it demonstrated that method A, which produced younger ages between 3 and 8 years, was correct. Walleye pollock grow older than the 3–8 year (method A) age range validated in this study. The experimental design was limited to a maximum method A age of 8 years, because available samples did not provide the minimum of 40 fish required for estimating a radiometric age. Our radiometric ageing study on walleye pollock appears to be the first to use the Pb-210/Ra-226 radiometric age-validation method in a boreal fish species where all samples were potentially young, 8 years or less. In previous studies, radiometric ages often approached 100 years. Also, only one presumed year class was used, which was sampled in successive years. Therefore, Ra-226 sample measurements were averaged to provide lower error.

scholarly journals Length-selective retention of walleye pollock, Theragra chalcogramma, by midwater trawls

2010 ◽  
Vol 68 (1) ◽  
pp. 119-129 ◽  
Author(s):  
Kresimir Williams ◽  
André E. Punt ◽  
Christopher D. Wilson ◽  
John K. Horne
Keyword(s):  
Gulf Of Alaska ◽  
Light Level ◽  
Walleye Pollock ◽  
Theragra Chalcogramma ◽  
Eastern Bering Sea ◽  
Walleye Pollock Theragra Chalcogramma ◽  
Abundance Estimates ◽  
Selective Retention ◽  
Survey Estimates ◽  
Hierarchical Bayesian Methods

Abstract Williams, K., Punt, A. E., Wilson, C. D., and Horne, J. K. 2011. Length-selective retention of walleye pollock, Theragra chalcogramma, by midwater trawls. – ICES Journal of Marine Science, 68: 119–129. Midwater trawls are commonly used during acoustic surveys of fish abundance to determine species and length compositions of acoustically sampled fish aggregations. As trawls are selective samplers, catches can be unrepresentative of sampled populations and lead to biased abundance estimates. Length-dependent retention of walleye pollock was estimated using small recapture nets, so-called pocket nets, attached to the outside of the trawl. Experimental haul sets comprising eight hauls each were conducted in the Gulf of Alaska in 2007 and 2008 and in the eastern Bering Sea (EBS) in 2007. Pocket-net catches were then modelled by fitting parameters for selectivity and escapement location along the trawl. Within- and between-haul variability was jointly estimated using hierarchical Bayesian methods. There was significant undersampling of juvenile (<25 cm) pollock, with the length-at-50%-retention (L50) estimated between 13.5 and 26.1 cm among haul sets. In the EBS set, L50 values were correlated with light level, escapement being greater at night. Trawl selectivity may be a significant source of error in acoustic-survey estimates of the abundance of pollock.

A probabilistic cellular automata approach for predator–prey interactions of arrowtooth flounder (Atheresthes stomias) and walleye pollock (Theragra chalcogramma) in the eastern Bering Sea

2012 ◽  
Vol 69 (2) ◽  
pp. 259-272
Author(s):  
Kun Chen ◽  
Kung-Sik Chan ◽  
Kevin M. Bailey ◽  
Kerim Aydin ◽  
Lorenzo Ciannelli
Keyword(s):  
Cellular Automata ◽  
Bering Sea ◽  
Environmental Changes ◽  
Spatial Scales ◽  
Walleye Pollock ◽  
Theragra Chalcogramma ◽  
Predator Prey ◽  
Eastern Bering Sea ◽  
Walleye Pollock Theragra Chalcogramma ◽  
Arrowtooth Flounder

We developed a hybrid cellular automata (CA) modelling approach to explore the dynamics of a key predator–prey interaction in a marine system; our study is motivated by the quest for better understanding of the scale and heterogeneity-related effects on the arrowtooth flounder (Atheresthes stomias) and walleye pollock (Theragra chalcogramma) dynamics during the summer feeding season in the eastern Bering Sea (EBS), but can be readily extended to other systems. The spatially explicit and probabilistic CA model incorporates individual behaviours and strategies and local interactions among species, as well as spatial and temporal heterogeneity due to geographical and (or) environmental changes in the physical environment. The model is hybridized, with an individual-based model (IBM) approach for increasing its capacity and continuum and for balancing between computational efficiency and model validity, which makes it suitable for simulating predator–prey dynamics in a large, complex ecological environment. We focus on the functional and aggregative responses of predators to prey density at different spatial scales, the effects of individual behaviours, and the impacts of systematic heterogeneity. Simulations from the model with suitable parameter values share qualitatively similar features found in field observations, e.g., local aggregations around hydrographical features. Spatial heterogeneity is an important aspect of whether local-scale functional and aggregative responses reflect those operating over large, or global, scales.

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