scholarly journals Diurnal variation in bottom trawl survey catches: does it pay to adjust?

2002 ◽  
Vol 59 (1) ◽  
pp. 33-48 ◽  
Author(s):  
Vidar Hjellvik ◽  
Olav Rune Godø ◽  
Dag Tjøstheim
Keyword(s):  
Correction Term ◽  
Bottom Trawl ◽  
Melanogrammus Aeglefinus ◽  
Fish Length ◽  
Small Fish ◽  
Trawl Survey ◽  
Moderate Increase ◽  
Bottom Trawl Survey ◽  
Abundance Estimate ◽  
Diurnal Amplitude

The diurnal bias of bottom trawl survey catches is studied with the purpose of adjusting for it and thereby improving the accuracy of abundance estimates. The correction term is estimated with uncertainty and thus increases the variance of the resulting abundance estimate. To investigate this adequately, we use a stochastic model describing diurnal fluctuations and examine the annual variation of the diurnal amplitude as a function of species and length. The diurnal amplitude is fairly stable for large fish, and for these, the bias-corrected estimate leads to a moderate increase in variance. For small fish, the diurnal amplitude is unstable, however, and the correction of diurnal bias occurs at the expense of a large increase in variance. This unstable amplitude also leads to a large year-to-year variation in catchability for small fish. For haddock (Melanogrammus aeglefinus), the diurnal amplitude depends heavily on fish length, indicating a strong decrease in catchability with decreasing fish length.

scholarly journals Accounting for length- and depth-dependent diel variation in catchability of fish and invertebrates in an annual bottom-trawl survey

2003 ◽  
Vol 60 (6) ◽  
pp. 1298-1317 ◽  
Author(s):  
Hugues P Benoít ◽  
Douglas P Swain
Keyword(s):  
Bottom Trawl ◽  
Small Fish ◽  
Trawl Survey ◽  
Diel Variation ◽  
Statistical Control ◽  
Bottom Trawl Survey ◽  
Significant Length ◽  
Spatio Temporal ◽  
Depth Dependency ◽  
Species Specific

Abstract Diel variation in the catchability of 51 species of fish and 13 invertebrate taxa from an annual bottom-trawl survey of the southern Gulf of St. Lawrence was examined using generalized linear (Poisson) models. Two approaches were used: comparative fishing based on spatially paired day and night tows, and statistical control of spatio-temporal effects in regular survey data. The two approaches provided remarkably similar results. Furthermore, species-specific results were consistent between survey time periods where different vessels were used, and were quite comparable to results from other studies conducted in separate geographic areas. Where sufficient data existed, we considered both length and depth dependencies in diel variation in catchability. We commonly found significant length dependency for groundfish species and the pervasive pattern was for higher nighttime catches of small fish, the magnitude of the effect generally decreasing with increasing length. In contrast, water depth had a much less important impact, except for a few species. When considered jointly, however, patterns in length/depth dependency were not always clear. Given length-dependent geographic and bathymetric patterns in species distribution, the potential for confounding length and depth dependencies exists and correction factors for diel variation in catchability need to be applied cautiously.

scholarly journals Decadal‐Scale Variation in Mean Trophic Level in Beibu Gulf Based on Bottom‐Trawl Survey Data

2021 ◽  
Vol 13 (3) ◽  
pp. 174-182
Author(s):  
Li Su ◽  
Zuozhi Chen ◽  
Kui Zhang ◽  
Youwei Xu ◽  
Shannan Xu ◽  
...  
Keyword(s):  
Survey Data ◽  
Trophic Level ◽  
Bottom Trawl ◽  
Beibu Gulf ◽  
Trawl Survey ◽  
Bottom Trawl Survey ◽  
Decadal Scale ◽  
Mean Trophic Level ◽  
Scale Variation

scholarly journals The influence of warp length on trawl dimension and catch of walleye pollock Theragra chalcogramma in a bottom trawl survey

2005 ◽  
Vol 71 (4) ◽  
pp. 738-747 ◽  
Author(s):  
Yasuzumi FUJIMORI ◽  
Kenji CHIBA ◽  
Tatsuki OSHIMA ◽  
Kazushi MIYASHITA ◽  
Satoshi HONDA
Keyword(s):  
Walleye Pollock ◽  
Bottom Trawl ◽  
Theragra Chalcogramma ◽  
Trawl Survey ◽  
Bottom Trawl Survey ◽  
Walleye Pollock Theragra Chalcogramma

scholarly journals Protocols of the EU bottom trawl survey of Flemish Cap

2014 ◽  
Vol 46 ◽  
pp. 3-51
Author(s):  
A Vazquez ◽  
J M Casas ◽  
A Alpoim
Keyword(s):  
Bottom Trawl ◽  
Trawl Survey ◽  
Bottom Trawl Survey ◽  
The Eu

Catchability of snow crab (Chionoecetes opilio) by the eastern Bering Sea bottom trawl survey estimated using a catch comparison experiment

2013 ◽  
Vol 70 (12) ◽  
pp. 1699-1708 ◽  
Author(s):  
David A. Somerton ◽  
Kenneth L. Weinberg ◽  
Scott E. Goodman
Keyword(s):  
Experimental Data ◽  
Bering Sea ◽  
Weighted Average ◽  
Assessment Model ◽  
Bottom Trawl ◽  
Snow Crab ◽  
Trawl Survey ◽  
Chionoecetes Opilio ◽  
Bottom Trawl Survey ◽  
Eastern Bering Sea

Catchability of the eastern Bering Sea (EBS) bottom trawl survey for snow crab (Chionoecetes opilio) was estimated from experimental data to provide a constraint on the survey catchability parameters in the stock assessment model. The experiment utilized a second fishing vessel to conduct side-by-side trawling with each of two survey vessels at 92 stations using an experimental trawl assumed to capture all crabs in its path. Trawl efficiency, or the captured proportion of crabs in the trawl path, was estimated for the 83-112 Eastern otter trawl from experimental data using a nonparametric smooth function of carapace width, sediment size, and depth. Survey catchability was then estimated as the catch-weighted average of the predicted trawl efficiency at all 275 survey stations where snow crabs were captured. The fitted model indicated that trawl selectivity was greater in sand than mud and greater in shallow water than deep. At a carapace widths >95 mm, the minimum commercial size limit, the estimated survey catchability of males is considerably less than previously reported.

Validation of deep-sea coral and sponge distribution models in the Aleutian Islands, Alaska

2017 ◽  
Vol 75 (1) ◽  
pp. 199-209 ◽  
Author(s):  
Christopher N Rooper ◽  
Rachel Wilborn ◽  
Pamela Goddard ◽  
Kresimir Williams ◽  
Richard Towler ◽  
...  
Keyword(s):  
Survey Data ◽  
Deep Sea ◽  
Goodness Of Fit ◽  
Bottom Trawl ◽  
Aleutian Islands ◽  
Trawl Survey ◽  
Bottom Trawl Survey ◽  
Spatial Management ◽  
Model Predictions ◽  
Deep Sea Corals

Abstract Spatial management of vulnerable benthic ecosystem components such as deep-sea corals and sponges requires adequate maps of their distribution. These maps are often based on statistical models of survey data. The objective of this project was to validate the predictions of existing presence or absence and abundance models of deep-sea corals and sponges in the Aleutian Islands that were based on bottom trawl survey data. Model validation was conducted by comparing bottom trawl survey model predictions to the observations of an in situ camera survey conducted at randomly selected locations. The measures of goodness of fit (area-under-the-receiver-operator-curve, AUC) for the bottom trawl survey model predictions of camera survey observations ranged from 0.59 to 0.77 (for sponges and coral, respectively) and indicated that the bottom trawl survey models predicted the probability of presence for corals accurately across the Aleutian Islands. The bottom trawl survey models explained as little as 3% of the variability in Stylasteridae density and up to 17% of the variability in coral density. These results indicate that models of deep-sea coral distributions based on presence and absence data from bottom trawl surveys can be accurate and can provide useful information for spatial management of these vulnerable taxa. However, for some other taxa, such as sponges, care should be taken interpreting the results of bottom trawl survey models. An interesting finding of this study was that the residuals from the bottom trawl survey model-camera density relationships were negative in areas that remained open to fishing after 2005, possibly indicating an effect of continued bottom trawling on the abundance of corals in these areas. This study highlights the importance of validating models of species distribution using independent surveys, so that the results can be used with confidence to support decision-making processes.

20 Years of the German small-scale bottom trawl survey (GSBTS): A review

2007 ◽  
Vol 37 (1) ◽  
pp. 13-82 ◽  
Author(s):  
Siegfried Ehrich ◽  
Sara Adlerstein ◽  
Uwe Brockmann ◽  
Jens Floeter ◽  
Stefan Garthe ◽  
...  
Keyword(s):  
Bottom Trawl ◽  
Small Scale ◽  
Trawl Survey ◽  
Bottom Trawl Survey
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