scholarly journals Influence of improved performance monitoring on the consistency of a bottom trawl survey

2003 ◽  
Vol 60 (4) ◽  
pp. 818-826 ◽  
Author(s):  
Mark Zimmermann ◽  
Mark E Wilkins ◽  
Kenneth L Weinberg ◽  
Robert R Lauth ◽  
Franklin R Shaw
Keyword(s):  
Time Series ◽  
Performance Monitoring ◽  
Bottom Trawl ◽  
Data Sets ◽  
Trawl Survey ◽  
Performance Measurements ◽  
Bottom Contact ◽  
Technological Advances ◽  
Improved Performance ◽  
Trawl Surveys

Abstract Numerous trawl hauls, made during the triennial bottom trawl surveys (1977–1998) conducted by the National Marine Fisheries Service off the U.S. West Coast, had unusually small catch rates of benthic fish and invertebrates (cpueB), probably because the trawl failed to contact the seabed (off-bottom). Technological advances in the equipment used to monitor trawl performance since 1986 have increased our ability to recognize off-bottom tows, and cpueB has risen. As direct trawl performance measurements were not available in earlier surveys, a minimum cpueB derived from the survey with the best monitoring of bottom contact of the time-series (1998) was used as a criterion to eliminate trawls with poor bottom contact from earlier surveys. The truncated data sets produce significantly larger biomass indices, especially in 1980, with increases of 43, 45, and 56% for Dover sole, petrale sole, and Pacific sanddab, respectively. The analysis suggests that changes in cpueB over the time-series may be related more to changing survey fishing methods than to changes in abundance. Other bottom trawl surveys, which have also added trawl monitoring equipment during their time-series, may have experienced similar changes in trawl performance.

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.

Calculation of untrawlable areas within the boundaries of a bottom trawl survey

2003 ◽  
Vol 60 (6) ◽  
pp. 657-669 ◽  
Author(s):  
Mark Zimmermann
Keyword(s):  
Relative Abundance ◽  
Species Group ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
Gis Analysis ◽  
Target Species ◽  
Abundance Estimates ◽  
Original Target ◽  
Catch Rates ◽  
Trawl Surveys

A geographic information system (GIS) analysis of 5039 bottom trawl events from U.S. west coast bottom trawl surveys (1977–1998) estimated that the survey area was about 77% trawlable but five of the 30 strata were less than 50% trawlable. Untrawlable areas, by definition, cannot be surveyed with the bottom trawl; however, there has never been a means of identifying and excluding these areas from relative abundance estimates, which are calculated only from hauls completed in the trawlable portions of each stratum. Unknown amounts of untrawlable habitat are a problem for relative abundance estimation in many bottom trawl surveys. This manuscript describes one method of using the bottom trawling events of a survey, such as ripped-up hauls and abandoned stations, to calculate the amount of area that is untrawlable. A comparison of catch rates between undamaged tows and a limited number of damaged tows, which are normally discarded as faulty samples, showed that Sebastes catch rates were generally higher in damaged tows. Thus untrawlable areas may have substantial importance on relative abundance estimates of Sebastes, the original target species group for this survey.

scholarly journals An application of two techniques for the analysis of short, multivariate non-stationary time-series of Mauritanian trawl survey data

2005 ◽  
Vol 62 (3) ◽  
pp. 353-359 ◽  
Author(s):  
Karim Erzini ◽  
Cheikh A. O. Inejih ◽  
Kim A. Stobberup
Keyword(s):  
Time Series ◽  
Factor Analysis ◽  
Fishing Effort ◽  
Stationary Time Series ◽  
Dynamic Factor ◽  
Data Sets ◽  
Trawl Survey ◽  
Explanatory Variables ◽  
Nao Index ◽  
Complementary Techniques

Abstract Min/max autocorrelation factor analysis (MAFA) and dynamic factor analysis (DFA) are complementary techniques for analysing short (>15–25 y), non-stationary, multivariate data sets. We illustrate the two techniques using catch rate (cpue) time-series (1982–2001) for 17 species caught during trawl surveys off Mauritania, with the NAO index, an upwelling index, sea surface temperature, and an index of fishing effort as explanatory variables. Both techniques gave coherent results, the most important common trend being a decrease in cpue during the latter half of the time-series, and the next important being an increase during the first half. A DFA model with SST and UPW as explanatory variables and two common trends gave good fits to most of the cpue time-series.

scholarly journals Extracting groundfish survey indices from the Ocean Biogeographic Information System (OBIS): an example from Fisheries and Oceans Canada

2009 ◽  
Vol 67 (4) ◽  
pp. 638-645 ◽  
Author(s):  
Daniel Ricard ◽  
Robert M. Branton ◽  
Donald W. Clark ◽  
Peter Hurley
Keyword(s):  
Time Series ◽  
Information System ◽  
Trawl Survey ◽  
Independent Information ◽  
Stock Assessments ◽  
The World ◽  
Abundance Trends ◽  
Selected Subset ◽  
Temporal Abundance ◽  
Trawl Surveys

Abstract Ricard, D., Branton, R. M., Clark, D. W., and Hurley, P. 2010. Extracting groundfish survey indices from the Ocean Biogeographic Information System (OBIS): an example from Fisheries and Oceans Canada. – ICES Journal of Marine Science, 67: 638–645. Scientific trawl surveys have been conducted in different regions of the world and by a variety of countries and agencies since the mid-1900s. Although the data are collected in a scientifically and statistically appropriate context and represent an important source of fishery-independent information for agency-specific stock assessments, their use and dissemination has often been limited to the agencies conducting the surveys. In recent years, Internet data portals such as the Ocean Biogeographic Information System have provided an arena for the wider distribution and use of marine fish data. Despite the increased accessibility of such data, their scientific acceptability has been limited by a lack of reproducibility in data analyses. We present a methodology for the computation of time-series of groundfish stock indices using publicly available trawl survey data derived from the Canadian Department of Fisheries and Oceans Maritimes region. Potential pitfalls associated with the computation of time-series are discussed and proper stratified random estimates of temporal abundance trends are compared with other methods for a selected subset of species. Also, the broader applicability of the methods for datasets collected under similar sampling designs is discussed, along with the reproducibility of the analyses and results.

scholarly journals Anglerfish discard estimates and patterns in Spanish Northeast Atlantic trawl fisheries

2008 ◽  
Vol 65 (7) ◽  
pp. 1350-1361 ◽  
Author(s):  
Paz Díaz ◽  
Juan Santos ◽  
Francisco Velasco ◽  
Alberto Serrano ◽  
Nélida Pérez
Keyword(s):  
Atlantic Ocean ◽  
Length Distribution ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
Marine Science ◽  
Target Species ◽  
Northeast Atlantic ◽  
Northeast Atlantic Ocean ◽  
Trawl Fisheries ◽  
Trawl Surveys

Abstract Díaz, P., Santos, J., Velasco, F., Serrano, A., and Pérez, N. 2008. Anglerfish discard estimates and patterns in Spanish Northeast Atlantic trawl fisheries. – ICES Journal of Marine Science, 65: 1350–1361. Estimates of Spanish bottom trawl discards of anglerfish Lophius budegassa and Lophiuspiscatorius in the Northeast Atlantic Ocean are presented. Both species are commercially valuable in ICES Subareas VI and VII, and Divisions VIIIc and IXa. Information was obtained from observers on board during discard-monitoring programmes. Raising by effort, rather than by landings and target species, was used to determine the total annual discards by weight and number, the discard percentage, and the discard length distribution by stock throughout the dataseries. By weight and number, discards varied interannually, ranging from 4 to 600 t (∼28 000–7 000 000 fish) in northern stocks of anglerfish, and from 1 to 100 t (∼20 000–400 000 fish) in southern stocks. The discard percentage for both species and northern and southern stocks therefore ranged between 2 and 76% by number. Length distributions of the discarded anglerfish show that most were juveniles, although the pattern differed in years with high or with low rates of discarding. The number of juveniles caught apparently increased in most areas after 2000. Correlations between the quantities discarded and recruitment indices from French and Irish trawl surveys were found for northern stocks and with Spanish trawl survey indices for southern stocks.

scholarly journals Relevance of using the equipment for control of fishing gear to reduce inaccuracy in evaluation of marine organisms abundance

2016 ◽  
Vol 186 (3) ◽  
pp. 198-206
Author(s):  
Egor A. Zakharov ◽  
Pavel O. Emelin
Keyword(s):  
Bering Sea ◽  
Marine Organisms ◽  
Geometric Parameters ◽  
Bottom Trawl ◽  
Actual Data ◽  
Fishing Gear ◽  
Trawl Survey ◽  
Fixed Constant ◽  
Trawl Surveys ◽  
The Bering Sea

Geometric parameters of the bottom trawl DT 27.1/24.4 were tested aboard RV TINRO in the Bering Sea using the acoustic equipment «Scanmar» (Norway). Possible errors in the estimates of marine organisms abundance by bottom trawl survey are calculated for different species by comparing the actual data on the trawl geometry with the fixed constant value of its horizontal opening. The obtained data can be used for evaluation of the hauled area in bottom trawl surveys.

scholarly journals Evaluation of sampling strategies for age determination of cod (Gadus morhua) sampled at the North Sea International Bottom Trawl Survey

2020 ◽  
Vol 77 (3) ◽  
pp. 859-869
Author(s):  
N O A S Jourdain ◽  
O Breivik ◽  
E Fuglebakk ◽  
S Aanes ◽  
J H Vølstad
Keyword(s):  
North Sea ◽  
Age Distribution ◽  
Age Determination ◽  
Length Distribution ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
The North ◽  
The North Sea ◽  
Trawl Surveys

Abstract The North Sea cod stock assessment is based on indices of abundance-at-age from fishery-independent bottom trawl surveys. The age structure of the catch is estimated by sampling fish for otoliths collection in a length-stratified manner from trawl hauls. Since age determination of fish is costly and time consuming, only a fraction of fish is sampled for age from a larger sample of the length distribution and an age–length key (ALK) is then used to obtain the age distribution. In this study, we evaluate ALK estimators for calculating the indices of abundance-at-age, with and without the assumption of constant age–length structures over relatively large areas. We show that the ALK estimators give similar point estimates of abundance-at-age and yield similar performance with respect to precision. We also quantify the uncertainty of indices of abundance and examine the effect of reducing the number of fish sampled for age determination on precision. For various subsampling strategies of otoliths collection, we show that one fish per 5-cm-length group width per trawl haul is sufficient and the total number of fish subsampled for age from trawl surveys could be reduced by at least half (50%) without appreciable loss in precision.

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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