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 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 Acoustic data collected during and between bottom trawl stations: consistency and common trends

2007 ◽  
Vol 64 (1) ◽  
pp. 166-180 ◽  
Author(s):  
Nicolas Bez ◽  
David Reid ◽  
Suzanna Neville ◽  
Yves Vérin ◽  
Vidar Hjellvik ◽  
...  
Keyword(s):  
Bottom Trawl ◽  
Vertical Profiles ◽  
Spatial Structures ◽  
Acoustic Measurements ◽  
Acoustic Data ◽  
Global Indices ◽  
Abundance Estimates ◽  
Before And After ◽  
Systematic Perturbation ◽  
Trawl Surveys

Acoustic data are often collected during bottom trawl surveys. Their use can potentially improve the precision and accuracy of fish abundance estimates if acoustic data collected between trawl stations are consistent with those collected during trawling operations. This question is addressed here through the analysis of 20 bottom trawl surveys (three survey areas and five different survey series) with coincident acoustic measurements during and between trawl stations. Firstly, on-station and underway acoustic data were compared using statistics computed globally over each survey (average vertical profiles, global indices of collocations, and spatial structures) for various combinations of depth layers. Secondly, we focussed on underway acoustic data recorded in the vicinity of stations, distinguishing between data recorded before and after the tows. On-station and underway acoustic data were highly consistent, and no systematic perturbation of the acoustic sign due to the presence of the gear a few hundred metres behind the vessel was observed.

scholarly journals Nursery areas and recruitment variation of Northeast Atlantic mackerel (Scomber scombrus)

2014 ◽  
Vol 72 (6) ◽  
pp. 1779-1789 ◽  
Author(s):  
Teunis Jansen ◽  
Kasper Kristensen ◽  
Jeroen van der Kooij ◽  
Søren Post ◽  
Andrew Campbell ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Bottom Trawl ◽  
Supporting Evidence ◽  
Geostatistical Model ◽  
Nursery Areas ◽  
Northeast Atlantic ◽  
Scomber Scombrus ◽  
Temporal Correlations ◽  
Catch Rates ◽  
Trawl Surveys

Abstract There are currently no dedicated recruitment survey data available in support of the assessment of the abundance and distribution of Northeast Atlantic (NEA) mackerel (Scomber scombrus), one of the most widespread and commercially important fish stocks in the North Atlantic. This is despite the fact that an estimate of recruitment is an important requirement for the provision of advice to fishery managers. The work here addresses this by compiling catch rates of juvenile mackerel from bottom-trawl surveys conducted between October and March during 1998–2012 and applying a log Gaussian Cox (LGC) process geostatistical model incorporating spatio-temporal correlations. A statistically significant correlation between the modelled catch rates in adjacent quarters 4 and 1 (Q4 and Q1) demonstrates that bottom-trawl surveys in winter are an appropriate platform for sampling juvenile mackerel, and that the LCG model is successful in extracting a population abundance signal from the data. In this regard, the model performed appreciably better than a more commonly used raising algorithm based on survey swept-area estimates. Therefore, the LCG model was expanded to include data from the entire survey time-series, and a recruitment index was developed for use in the annual ICES stock assessment. We hypothesize that catchability is positively density-dependant and provides supporting evidence from acoustic observations. Various density-dependant transformations of the modelled catch rates were furthermore found to improve the correlation between the derived annual recruitment index and recruitment estimated by backcalculation of adult mackerel data. Square root transformation led to the strongest correlation, so this is recommended for further analysis of mackerel abundance. Finally, we provide maps of spatial distributions, showing that the most important nursery areas are around Ireland, north and west of Scotland, in the northern North Sea north of 59°N and, to some extent, also in the Bay of Biscay.

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 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.

Anadromous Sturgeons: Habitats, Threats, and Management

2007 ◽  
Keyword(s):  
Relative Abundance ◽  
River Estuary ◽  
Hudson River ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
Atlantic Sturgeon ◽  
Stock Size ◽  
Bottom Trawl Survey ◽  
Spawning Stock ◽  
Mature Fish

<em>Abstract.</em>—Commercial harvest of Atlantic sturgeon <em>Acipenser oxyrinchus</em> from the Hudson River Estuary peaked in the late 1800s, declined precipitously soon after, and remained at low levels until the late 1970s when a resurgence in the fishery occurred. Preliminary analysis of the fishery suggested that the harvest was not sustainable. The state of New York banned possession of Atlantic sturgeon in 1996. A coastwide ban followed in 1998. We examined available data to determine whether the closures of the 1990s were warranted and to track stock recovery since the closure. We used an eggper-recruit model to determine an acceptable fishing rate (<EM>F</EM><sub>50%</sub>). We assumed a maximum age of 60 and a natural mortality rate <EM>M</EM> of 0.07 and obtained an <EM>F</EM><sub>50%</sub> of 0.03. The fishing rates <EM>F</EM> estimated during the recent fishery were 0.33 for males and 0.17 for females, well over the <EM>F</EM><sub>50%</sub>. We set an abundance target for spawning females at 3,000 animals, which was 50% of the estimated maximum abundance in the late 1800s. We estimated mean annual spawning stock size during the fishery as mean annual harvest divided by exploitation rate. Estimated numbers of mature fish were approximately 600 males and 270 females (less than 10% of the abundance threshold). Our estimates of fishing rate and female stock size suggest that the stock was severely overfished prior to and during the recent fishery. We used changes in relative abundance of juveniles to infer changes in recruitment. Relative estuarine abundance of premigrant juveniles declined in the late 1970s in the bycatch of the American shad <em>Alosa sapidissima </em>commercial gill-net fishery and in the mid-1980s in a 3-m bottom trawl survey. Both in-river indices suggest a slight improvement since the late 1990s. Relative abundance of postmigrant juveniles in a bottom trawl survey off the coast of northern New Jersey declined from the late 1980s through the present.

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.

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