The effect of autotrawl systems on the performance of a survey trawl

Three aspects of a survey bottom trawl performance—1) trawl geometry (i.e., net spread, door spread, and headrope height); 2) footrope distance off-bottom; and 3) bridle distance off-bottom—were compared among hauls by using either of two autotrawl systems (equal tension and net symmetry) and hauls conducted with towing cables of equal length and locked winches. The effects of environmental conditions, vessel heave, crabbing (i.e., the difference between vessel heading and actual vessel course over ground), and bottom current on trawl performance with three trawling modes were investigated. Means and standard deviations of trawl geometry measures were not significantly different between autotrawl and locked-winch systems. Bottom trawls performed better with either autotrawl system as compared to trawling with locked winches by reducing the variance and increasing the symmetry of the footrope contact with the bottom. The equal tension autotrawl system was most effective in counteracting effects of environmental conditions on footrope bottom contact. Footrope bottom contact was most inf luenced by environmental conditions during tows with locked winches. Both of the autotrawl systems also reduced the variance and increased the symmetry of bridle bottom contact. Autotrawl systems proved to be effective in decreasing the effects of environmental factors on some aspects of trawl performance and, as a result, have the potential to reduce among-haul variance in catchability of survey trawls. Therefore, by incorporating an autotrawl system into standard survey procedures, precision of survey estimates of relative abundanc

Monitoring Alaskan Arctic shelf ecosystems through collaborative observation networks

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Danielson, S. L., Grebmeier, J. M., Iken, K., Berchok, C., Britt, L., Dunton, K. H., Eisner, L., V. Farley, E., Fujiwara, A., Hauser, D. D. W., Itoh, M., Kikuchi, T., Kotwicki, S., Kuletz, K. J., Mordy, C. W., Nishino, S., Peralta-Ferriz, C., Pickart, R. S., Stabeno, P. S., Stafford. K. M., Whiting, A. V., & Woodgate, R. Monitoring Alaskan Arctic shelf ecosystems through collaborative observation networks. Oceanography, 35(2), (2022): 52, https://doi.org/10.5670/oceanog.2022.119.Ongoing scientific programs that monitor marine environmental and ecological systems and changes comprise an informal but collaborative, information-rich, and spatially extensive network for the Alaskan Arctic continental shelves. Such programs reflect contributions and priorities of regional, national, and international funding agencies, as well as private donors and communities. These science programs are operated by a variety of local, regional, state, and national agencies, and academic, Tribal, for-profit, and nongovernmental nonprofit entities. Efforts include research ship and autonomous vehicle surveys, year-long mooring deployments, and observations from coastal communities. Inter-program coordination allows cost-effective leveraging of field logistics and collected data into value-added information that fosters new insights unattainable by any single program operating alone. Coordination occurs at many levels, from discussions at marine mammal co-management meetings and interagency meetings to scientific symposia and data workshops. Together, the efforts represented by this collection of loosely linked long-term monitoring programs enable a biologically focused scientific foundation for understanding ecosystem responses to warming water temperatures and declining Arctic sea ice. Here, we introduce a variety of currently active monitoring efforts in the Alaskan Arctic marine realm that exemplify the above attributes.Funding sources include the following: ALTIMA: BOEM M09PG00016, M12PG00021, and M13PG00026; AMBON: NOPP-NA14NOS0120158 and NOPP-NA19NOS0120198; Bering Strait moorings: NSF-OPP-AON-PLR-1758565, NSF-OPP-PLR-1107106; BLE-LTER: NSF-OPP-1656026; CEO: NPRB-L36, ONR N000141712274 and N000142012413; DBO: NSF-AON-1917469 and NOAA-ARP CINAR-22309.07; HFR, AOOS Arctic glider, and Passive Acoustics at CEO and Bering Strait: NA16NOS0120027; WABC: NSF-OPP-1733564. JAMSTEC: partial support by ArCS Project JPMXD1300000000 and ArCS II Project JPMXD1420318865; Seabird surveys: BOEM M17PG00017, M17PG00039, and M10PG00050, and NPRB grants 637, B64, and B67. This publication was partially funded by the Cooperative Institute for Climate, Ocean, & Ecosystem Studies (CICOES) under NOAA Cooperative Agreement NA20OAR4320271, and represents contribution 2021-1163 to CICOES, EcoFOCI-1026, and 5315 to PMEL. This is NPRB publication ArcticIERP-43

Combining bottom trawl and acoustic data to improve survey derived abundance estimates of semipelagic species

Thesis (Ph.D.)--University of Washington, 2014Abundances of semipelagic fishes are often estimated using acoustic or bottom trawl (BT) surveys, both of which sample a fraction of the water column. Acoustic instruments are effective at sampling the water column, but they have a near-bottom acoustic dead zone (ADZ), where fish near the seafloor cannot be detected. Bottom trawl surveys cannot account for fish that are located above the effective fishing height (EFH) of the trawl. In this dissertation I develop methods for combining BT and acoustic data to improve abundance estimates of semipelagic species. Semipelagic walleye pollock (Gadus chalcogrammus) was chosen as a case study because they are a dominant species with important commercial and ecological roles in the North Pacific. A model combining a subset of acoustic and BT data was developed to estimate ADZ correction and BT efficiency parameters. Fitting this model to the data provided estimates of the catchability ratio between BT and acoustics, the EFH of the BT, and the density dependent efficiency of the BT. Estimates of experimentally-derived ADZ correction and BT efficiency parameters were then used to develop a model predicting BT efficiency as a function of BT catch rate. It was found that BT efficiency decreased with increasing bottom trawl catches resulting in hyperstability of the abundance index derived from BT survey. Density-dependent BT efficiency resulted in spatially and temporarily variable bias in survey CPUE and biased population age structure derived from survey data. Logistic regression models were developed to predict the availability (qa) of pollock to both acoustic and BT gears using environmental predictors and fish length. Findings indicated that on average, availability of pollock in the EBS to the BT was larger than to the acoustics. Availability to both gears depended mostly on bottom depth, light conditions, and fish length, and to a lesser extent on sediment size. Availability to the acoustic gear also depended on surface temperature. A method was developed for combining pollock abundance estimates from BT and acoustic surveys using estimates of efficiency and availability to the BT and acoustic gears. Coefficients of variation (CV) obtained for combined estimates were generally lower than those obtained from either BT, or acoustic surveys. Although this work specifically addresses the assessment of walleye pollock in the EBS it has general applicability in the assessment of other semipelagic species. Methods presented in this dissertation can be applied to other semipelagic species to obtain estimates of ADZ correction or BT efficiency parameters. Similarly, methods for estimating density dependence of the BT, availability to the BT and acoustic gears, and combining BT and acoustic abundance estimates can be applied to other species

Combining bottom trawls and acoustics in a diverse semipelagic environment: What is the contribution of walleye pollock (Gadus chalcogrammus) to near-bottom acoustic backscatter in the eastern Bering Sea?

The abundance of walleye pollock (Gadus chalcogrammus) in the eastern Bering Sea (EBS) is estimated through fisheries-independent acoustic trawl (AT) surveys, which currently use acoustic backscatter data down to 3 m above the bottom. A large portion of adult pollock are demersal and these estimates will become more accurate if the survey is extended closer to bottom. The purpose of this project was to assess the feasibility of extending the AT survey closer to the bottom by estimating the contributions of each fish species to observed acoustic backscatter in the highly diverse near-bottom region. This was accomplished by fitting a regression model to simultaneously collected acoustic backscatter and bottom trawl (BT) catch data. Pollock were the dominant source of acoustic backscatter among demersal species accounting for 85.9 ± 4.8 % of acoustic backscatter (mean ± standard deviation). A method was developed to extend the AT survey to within 0.5 m of the bottom and applied to the 1994-2014 surveys, pollock biomass increased by an average of 35 ± 12 %.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Improved estimation of age composition by accounting for spatiotemporal variability in somatic growth

Age composition is defined as the proportion of a fish population belonging to each age class and is an informative input to stock assessment models. Variations in somatic growth rates may lead to larger errors in age composition estimates. To reduce this source of error, we compared the performance of four methods for estimating age compositions of a simulated fish population: two methods based on age–length keys (ALK, pooled and annual) and two model-based approaches (generalized additive models (GAMs) and continuation ratio logits (CRLs)). CRL was the most robust and precise method, followed by annual ALKs, particularly when significant growth variability was present. We applied these methods to survey age subsample data for Pacific cod (Gadus macrocephalus) in the eastern Bering Sea, estimating age compositions that were then incorporated in its stock assessment model. The model that included age compositions estimated by CRL displayed the highest consistency with other data in the model. CRL approach has utility for estimating age compositions employed in stock assessment models, especially when substantial variation in somatic growth is present.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Combining data from bottom trawl and acoustic surveys to estimate an index of abundance for semipelagic species.

Fishery-independent surveys are useful for estimating abundance of fish populations and their spatial distribution. It is necessary in the case of semipelagic species to perform acoustic-trawl (AT) and bottom-trawl (BT) surveys to assure that sampling encompasses both midwater and demersal components of the population. Abundance estimates from both survey types are negatively biased because of the blind zones associated with fish vertical distribution. These biases can vary spatially and temporally, resulting in confounded trends and additional variation in abundance estimates. To improve abundance estimates for semipelagic species we propose a new method for combining BT and AT survey data using environmental variables to predict the vertical overlap. On an example of pollock AT and BT surveys in the eastern Bering Sea we show that combined estimates provide more reliable whole water column and spatial distribution estimates than either survey can by itself. Although the combined estimates are still relative they account for the uncertainty in the bias ratio between two survey methods and uncertainty associated with the extent of the water column sampled by both surveys. Our method of combining BT and AT data can be extended to other semipelagic species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author