scholarly journals Correcting density-dependent effects in abundance estimates from bottom-trawl surveys

2014 ◽  
Vol 71 (5) ◽  
pp. 1107-1116 ◽  
Author(s):  
Stan Kotwicki ◽  
James N. Ianelli ◽  
André E. Punt
Keyword(s):  
Stock Assessment ◽  
Dead Zone ◽  
Walleye Pollock ◽  
Assessment Model ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
Negative Consequences ◽  
Catch Per Unit Effort ◽  
Density Dependent ◽  
Index Of Abundance

Abstract Indices of abundance are important for estimating population trends in stock assessment and ideally should be based on fishery-independent surveys to avoid problems associated with the hyperstability of the commercial catch per unit effort (cpue) data. However, recent studies indicate that the efficiency of the survey bottom trawl (BT) for some species can be density-dependent, which could affect the reliability of survey-derived indices of abundance. A function qe∼f(u), where qe is the BT efficiency and u the catch rate, was derived using experimentally derived acoustic dead-zone correction and BT efficiency parameters obtained from combining a subset of BT catch data with synchronously collected acoustic data from walleye pollock (Theragra chalcogramma) in the eastern Bering Sea (EBS). We found that qe decreased with increasing BT catches resulting in hyperstability of the index of abundance derived from BT survey. Density-dependent qe resulted in spatially and temporarily variable bias in survey cpue and biased population age structure derived from survey data. We used the relationship qe∼f(u) to correct the EBS trawl survey index of abundance for density-dependence. We also obtained a variance–covariance matrix for a new index that accounted for sampling variability and the uncertainty associated with the qe. We found that incorporating estimates of the new index of abundance changed outputs from the walleye pollock stock assessment model. Although changes were minor, we advocate incorporating estimates of density-dependent qe into the walleye pollock stock assessment as a precautionary measure that should be undertaken to avoid negative consequences of the density-dependent qe.

scholarly journals Factors affecting the availability of walleye pollock to acoustic and bottom trawl survey gear

2015 ◽  
Vol 72 (5) ◽  
pp. 1425-1439 ◽  
Author(s):  
Stan Kotwicki ◽  
John K. Horne ◽  
André E. Punt ◽  
James N. Ianelli
Keyword(s):  
Environmental Factors ◽  
Water Column ◽  
Dead Zone ◽  
Walleye Pollock ◽  
Bottom Trawl ◽  
Fish Length ◽  
Trawl Survey ◽  
Near Surface ◽  
Logistic Regression Models ◽  
Sediment Size

Abstract Abundances of semi-pelagic fish are often estimated using acoustic or bottom trawl surveys, both of which sample only a fraction of the water column. Acoustic instruments are effective at sampling the majority of the water column, but they have a near-surface blind zone and a near-bottom acoustic dead zone (ADZ), where fish remain undetected. Bottom trawls are effective near the seabed, but miss fish that are located above the effective fishing height of the trawl. Quantification of the extent of overlap between these gears is needed, particularly in cases where environmental factors play a role. We developed logistic regression models to predict the availability (qa) of walleye pollock (Gadus chalcogrammus) to both acoustic and bottom trawl gears using factors shown to affect qa (depth, light intensity, fish length) and introducing additional factors (tidal currents, surface and bottom temperature, sediment size). Results build on earlier studies and quantify the uncertainty associated with the estimation of the ADZ correction using Bayesian methods. Our findings indicate that on average during the day, walleye pollock are more available to the bottom trawl than to the acoustics. Availability to both gears depends mostly on bottom depth, light conditions, and fish size, and to a lesser extent sediment size. Availability to the acoustic gear is also related on surface temperature. Variability in availability to both gears also depends on environmental factors.

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

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.

scholarly journals Trends of white grouper landings in the Northeastern Mediterranean: reliability and potential use for monitoring

2020 ◽  
Vol 21 (1) ◽  
pp. 183
Author(s):  
SINAN MAVRUK
Keyword(s):  
Time Series ◽  
Age Groups ◽  
Monitoring Program ◽  
Bottom Trawl ◽  
Data Sets ◽  
Trawl Survey ◽  
Catch Per Unit Effort ◽  
Multiple Sources ◽  
Statistical Institute ◽  
The Status

As a consequence of national fishery statistics showing a sharp decline in the landings of white groupers (WG), Epinephelus aeneus (Geoffroy Saint-Hilaire, 1817) after 2010, the decision to ban any further fishing of the species was implemented by the Turkish management authority in 2016. Stakeholders have since strongly objected to this decision claiming that the trends of landing statistics are unreliable. Here, this assertion is questioned using multiple sources of data. The catch per unit effort (CPUE) from the fishery independent bottom trawl survey (2004-2018) officially reported landing statistics (2002-2017) and the microdata set of landings (2012-2016) gathered by the Turkish Statistical Institute (TUIK). Based on the results of this study, there was a clear parallelism amongst the data sets. Landing records and the CPUE time series revealed unimodal non-linear patterns along the time (p<0.001). Landings increased until 2010 and decreased thereon after, whereas CPUE values started to decrease after 2009. In segmented time series, there were no statistically significant differences between the direction and magnitude of slopes of landings and fishery independent data. Cross-correlations between landings and CPUE were statistically significant with one and two-year lag distances. This was because the earlier age groups were sampled with coastal bottom trawl operations. Combined with further efforts, this finding may help to develop a monitoring program for the status of white grouper populations in the northeastern Mediterranean and contribute to a better management strategy.

A length-based Bayesian stock assessment model for the New Zealand abalone Haliotis iris

2003 ◽  
Vol 54 (5) ◽  
pp. 619 ◽  
Author(s):  
Paul A. Breen ◽  
Susan W. Kim ◽  
Neil L. Andrew
Keyword(s):  
New Zealand ◽  
Stock Assessment ◽  
Assessment Model ◽  
Data Sets ◽  
Catch Per Unit Effort ◽  
Commercial Catch ◽  
Data Set ◽  
Future Directions ◽  
Common Component ◽  
Joint Posterior Distribution

We describe a length-based Bayesian model for stock assessment of the New Zealand abalone Haliotis iris (paua). We fitted the model to five data sets: catch-per-unit-effort (CPUE) and a fishery-independent survey index, proportions-at-length from both commercial catch sampling and population surveys, and tag–recapture data. We estimated a common component of error and used iterative re-weighting of the data sets to balance the residuals, removing the arbitrary data set weightings used in previous assessments. Estimates at the mode of the joint posterior distribution were used to explore sensitivity of the results to model assumptions and input data; the assessment itself was based on marginal posterior distributions estimated from Markov chain–Monte Carlo simulation. Assessments are presented for two stocks in the south of New Zealand. One may be recovering after recent catch reductions; the other is over-exploited and likely to decline further. Assessment for the first stock was robust; assessment for the second stock was sensitive to the CPUE data and may be too optimistic. We discuss future directions and potential problems with this approach.

scholarly journals Standardization of CPUE for walleye pollock in the Okhotsk Sea with inclusion of some environmental factors

2020 ◽  
Vol 200 (4) ◽  
pp. 819-836
Author(s):  
V. V. Kulik ◽  
A. I. Varkentin ◽  
O. I. Ilyin
Keyword(s):  
Linear Models ◽  
Stock Assessment ◽  
Generalized Additive Models ◽  
Total Yield ◽  
Walleye Pollock ◽  
Additive Models ◽  
Okhotsk Sea ◽  
Catch Per Unit Effort ◽  
Bayesian Criterion ◽  
In The Beginning

Catch of walleye pollock by Russia is the highest in the northern Okhotsk Sea where on average 0.94 million metric tons were caught annually in the period between 1962 and 2017, or around 24 % of the total yield of Russian fishery. The total stock and spawning stock of pollock grow there since 2002, though the catch per unit effort (CPUE) has significantly decreased in the beginning of 2018 despite expected high levels of both total and spawning stocks. The sea surface temperature, ice cover and storms frequency were examined as possible reasons of low fishing efficiency in 2018. For this purpose, the generalized linear models (GLM) and generalized additive models (GAM) of catch dynamics are compared. GAM with addition of temperature and storms factors has the lowest Schwarz’s Bayesian criterion and the highest explained deviance (61.6 %). Efficiency of fishing gears has nonlinear relationship with the towing time. CPUE has hypersensitivity to the stock biomass presented as the power dependence (γ = 0.94, r = 0.923). Standardized CPUE is recommended for using in the final GAM for the pollock stock assessment in the northern Okhotsk Sea, hypersensitivity of CPUE should be estimated and corrected if necessary.

Fleet dynamics of herring trawlers—change in gear size and implications for interpretation of catch per unit effort

2002 ◽  
Vol 59 (3) ◽  
pp. 531-541 ◽  
Author(s):  
Mika Rahikainen ◽  
Sakari Kuikka
Keyword(s):  
Stock Assessment ◽  
Fish Stock ◽  
Catch Per Unit Effort ◽  
Unit Effort ◽  
Fish Stock Assessment ◽  
Fleet Dynamics ◽  
Changes Over Time ◽  
Index Of Abundance ◽  
Over Time ◽  
Stock Abundance

Catch per unit effort (CPUE) is widely used as an index of stock abundance. It is as widely acknowledged that CPUE can be a misleading index of abundance owing to a multitude of factors including fish behavior, fishing fleet interaction, and the increase in catchability over time caused by improvement in fishing technology. Based on information concerning the size of herring trawls manufactured in Finland since the early 1980s, an increase in fishing power of the fleet was postulated. Because we lacked direct information about the size of trawls aboard, we applied a model to estimate the changes over time. In the analysis, an analogy between fish and trawls was created by adopting the concepts and algorithms from fish stock assessment into assessment of the trawl "population", where both the total number of trawls and the size of individual trawls were being analyzed. The results indicate that the average gear size has nearly tripled in 20 years. Accepting the assumption that larger trawls are generally more effective than smaller ones, a substantial increase in fishing power has taken place. As a result, sequential population models calibrated with CPUE data will be severely biased as well.

Combining bottom trawl and acoustic data to model acoustic dead zone correction and bottom trawl efficiency parameters for semipelagic species

2013 ◽  
Vol 70 (2) ◽  
pp. 208-219 ◽  
Author(s):  
Stan Kotwicki ◽  
Alex De Robertis ◽  
James N. Ianelli ◽  
André E. Punt ◽  
John K. Horne
Keyword(s):  
Dead Zone ◽  
Light Level ◽  
Walleye Pollock ◽  
Modeling Method ◽  
Bottom Trawl ◽  
Acoustic Measurements ◽  
Habitat Features ◽  
Acoustic Data ◽  
Eastern Bering Sea ◽  
Pelagic Habitat

We present a modeling method that combines acoustic and bottom trawl abundance measurements and habitat data to estimate acoustic dead zone (ADZ) correction and bottom trawl efficiency parameters. Bottom trawl and acoustic measurements of walleye pollock (Theragra chalcogramma) abundance and available habitat data from the eastern Bering Sea are used to illustrate this method. Our results show that predictions of fish abundance in the ADZ can be improved by incorporating bottom habitat features such as depth and sediment particle size, as well as pelagic habitat features such as water temperature, light level, and current velocity. We also obtain predictions for trawl efficiency parameters such as effective fishing height, density-dependent trawl efficiency, and catchability ratio between trawl and acoustic data by modeling bottom trawl catches as a function of acoustic measurements and the environmentally dependent ADZ correction. We conclude that catchability of walleye pollock for either survey is spatially and temporarily variable. Our modeling method can be applied to other semipelagic species to obtain estimates of ADZ correction and bottom trawl efficiency parameters.

Population structure, reproduction and exploitation of the greater forkbeard Phycis blennoides (Brünnich, 1768) from the Algerian basin

2020 ◽  
Vol 33 ◽  
pp. 20
Author(s):  
Zakia Alioua ◽  
Soumia Amira ◽  
Ghollame Ellah Yacine Khames ◽  
Ulla Fernandez-Arcaya ◽  
Beatriz Guijarro ◽  
...  
Keyword(s):  
Population Distribution ◽  
Stock Assessment ◽  
Bottom Trawl ◽  
Fish Stock ◽  
Commercial Fisheries ◽  
Trawl Survey ◽  
Bottom Trawl Survey ◽  
First Maturity ◽  
Density And Biomass ◽  
Trawl Surveys

The objective of this study was to determine the population distribution and some biological aspects for fish stock assessment of the greater forkbeard Phycis blennoides along the Algerian basin. The distribution of P. blennoides (3418 individuals) was studied using data collected between 170–779 m depth during two bottom trawl surveys developed on 2003 and 2004. Additionally, some biological parameters were obtained from 1050 individuals sampled from commercial fisheries in Algerian ports (i.e. Annaba, Azeffoun, Dellys, Cap Djinet, Zemmouri, Bouharoun, Algiers, La Madrague, Cherchell, Tenes and Mostaganem) during the period 2013–2017. P. blennoides sampled from bottom trawl surveys showed a depth related distribution with the largest individuals being found at 600–800 m depth and the smallest at shallower depths. Density and biomass varied with depth and density also with longitude, while biomass showed no pattern with longitude. Recruitment was recorded in the eastern sector of Algeria during winter, for individuals sampled by bottom trawl surveys. Young P. blennoides entered commercial fisheries in summer, with an overall sex ratio skewed towards males (1F:2.18M). The size at first maturity (L 50) was 24.30 cm and 30.39 cm for males and females, respectively. The age at 50% maturity was 2–3 years for specimens collected by a bottom trawl survey in 2003 and commercial fisheries, but 3–4 years for the bottom trawl survey in 2004.

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