Diurnal variation in acoustic densities: why do we see less in the dark?

2004 ◽  
Vol 61 (11) ◽  
pp. 2237-2254 ◽  
Author(s):  
Vidar Hjellvik ◽  
Olav Rune Godø ◽  
Dag Tjøstheim
Keyword(s):  
Barents Sea ◽  
Dead Zone ◽  
Model Development ◽  
Demersal Fish ◽  
Target Strength ◽  
Trawl Survey ◽  
Diurnal Changes ◽  
Density Profiles ◽  
Vertical Density ◽  
Acoustic Surveys

Diurnal fluctuations in total integrated echo abundance and in vertical density profiles were examined using data from the Norwegian combined acoustic and bottom-trawl survey for demersal fish during winter in the Barents Sea. The total echo abundance was about 40%–50% higher at day than at night. An unknown amount of fish was lost close to the seabed in the acoustic dead zone, but the systematic changes in the near-bottom vertical density profiles did not indicate that migration in and out of the dead zone was the major reason for the large diurnal differences in echo abundance. A more plausible explanation could be that diurnal changes in fish behaviour affect the mean acoustic target strength. Based on the present study, we recommend that the time series of acoustic surveys should be re analysed, taking the diurnal bias into account. Any comparison of the fish densities indicated by trawl and acoustic surveys will suffer if this bias is not corrected. We believe that model development utilizing this type of information is crucial for future ecosystem-based monitoring.

scholarly journals Methods and results of in situ target-strength measurements of Atlantic cod (Gadus morhua) during combined trawl-acoustic surveys

2009 ◽  
Vol 66 (6) ◽  
pp. 1225-1232 ◽  
Author(s):  
Viacheslav A. Ermolchev
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Atlantic Cod ◽  
Biological Data ◽  
Target Strength ◽  
Fish Length ◽  
The Barents Sea ◽  
Total Fish ◽  
Acoustic Surveys

Abstract Ermolchev, V. A., 2009. Methods and results of in situ target-strength measurements of Atlantic cod (Gadus morhua) during combined trawl-acoustic surveys. – ICES Journal of Marine Science, 66: 1225–1232. This paper presents methods for collecting acoustic and biological data, including in situ target-strength (TS) estimates of fish, with results presented for Atlantic cod (Gadus morhua) obtained from combined trawl-acoustic surveys. These include fish in the small, average, and maximum length classes, within the range 5–136 cm (total fish length, LT). The investigations were done using Simrad EK500/EK60 echosounders with split-beam transducers and special post-processing software. Based on an analysis of data collected in the Barents Sea during 1998–2007, a relationship TS = 25.2 log10(LT) − 74.8 was obtained for Atlantic cod at 38 kHz, with TS in dB and LT in centimetres. Seasonally, and for depths between 50 and 500 m, the variability in cod TS was 3.1 dB, decreasing with depth. The largest day–night difference in mean TS was in August–September, with changes as large as 1.0–1.7 dB. In the other seasons, the day–night difference was <1.0 dB.

scholarly journals Estimating gear efficiency in a combined acoustic and trawl survey, with reference to the spatial distribution of demersal fish

2009 ◽  
Vol 67 (4) ◽  
pp. 668-676 ◽  
Author(s):  
Mathieu Doray ◽  
Stéphanie Mahévas ◽  
Verena M. Trenkel
Keyword(s):  
Spatial Distribution ◽  
Demersal Fish ◽  
Target Strength ◽  
Fish Length ◽  
Trawl Survey ◽  
Acoustic Backscattering ◽  
Scattering Coefficients ◽  
Fishing Vessels ◽  
Gear Efficiency ◽  
The Mean

Abstract Doray, M., Mahévas, S., and Trenkel, V. M. 2010. Estimating gear efficiency in a combined acoustic and trawl survey, with reference to the spatial distribution of demersal fish. – ICES Journal of Marine Science, 67: 668–676. Few analyses have been performed to estimate the efficiency of trawls targeting demersal fish using the ratio of catches and acoustic densities. In summer 2006, acoustic and fishing data were collected simultaneously over 3 d by three fishing vessels equipped with identical pelagic trawls in the Bay of Biscay. Variography identified moderate spatial autocorrelation in the acoustic backscatter at a mean scale of 3 km, a scale slightly smaller than the mean haul length (3.5 km), indicating that fish horizontal availability did not influence trawl efficiency. Acoustic backscattering densities expressed as nautical area scattering coefficients (NASCs) recorded in the trawled layer were compared with equivalent NASC (ENASC) values calculated from the species composition in the trawl, fish-length structure, and available relationships between target strength and fish length. Estimates of trawl efficiency for hake-dominated trawls were computed as the slopes of the relationships ENASC = 0.008 NASC and ENASC = 0.18 NASC0.31 for trawls made by day and night, respectively. For the whole demersal community, the relationships were ENASC = 0.022 NASC and ENASC = 0.17 NASC0.33 for trawls made by day and night, respectively.

Anadromous Sturgeons: Habitats, Threats, and Management

2007 ◽  
Keyword(s):  
Sand Dunes ◽  
Demersal Fish ◽  
Lake Sturgeon ◽  
Fish Distribution ◽  
Trawl Survey ◽  
Atlantic Sturgeon ◽  
Potential Threat ◽  
Two Phase ◽  
Good Correspondence ◽  
Acoustic Surveys

Abstract.—Atlantic sturgeon <em>Acipenser oxyrinchus</em> and lake sturgeon <em>A. fulvescens </em>in the middle St. Lawrence estuary are under consideration for designation as “endangered” or “vulnerable” species. A potential threat to these species is the disposal of dredged sediments in an area where young-of-the-year and juvenile Atlantic sturgeon concentrate. The objectives of this study were (1) to study the short-term and cumulative impacts, if any, of the dumped sediments on the abundance, distribution, and movements of the two sturgeon species downstream of the disposal area, and (2) to investigate the usefulness of acoustic surveys for assessing sturgeon density and distribution. A two-phase, combined acoustic-trawl survey was conducted to describe sturgeon distributions and produce concurrent acoustic and trawl estimates of the relative abundance of demersal fish within the area (lake sturgeon and Atlantic sturgeon were presumed to dominate the acoustic echoes). This series of surveys was the first known attempt to quantify sturgeon abundance and distribution with a vertically deployed echo sounder. The results showed good correspondence between the two methods. Replicated sampling also showed the repeatability of the acoustic technique and stability in demersal fish distribution on a scale of days. The acoustic surveys indicated that the spatial distribution of demersal fishes was dependent on substrate, as these fishes avoided areas of dredged sediment dumping and associated sand dunes. Our study showed that under certain conditions, acoustic-trawl surveys can reliably assess sturgeon density and distribution.

Density and Size Estimates of Cisco (Coregonus artedii) Using Analysis of Echo Peak PDF from a Single-Transducer Sonar

1987 ◽  
Vol 44 (4) ◽  
pp. 811-821 ◽  
Author(s):  
Lars G. Rudstam ◽  
Clarence S. Clay ◽  
John J. Magnuson
Keyword(s):  
Probability Density Functions ◽  
Target Strength ◽  
Fish Length ◽  
Density Functions ◽  
Density Profiles ◽  
Gill Nets ◽  
Vertical Density ◽  
Coregonus Artedii ◽  
Size Estimates

We estimated size and density of fish in three Wisconsin lakes from echo peak probability density functions (PDFs) obtained at night with a single-transducer 70-kHz echosounder. At night, cisco (Coregonus artedii) dominated the pelagic zone in all three lakes. The beam pattern effect was removed with a deconvolving filter technique. Fish size was estimated by fitting a combination of Rice PDFs to the deconvolved fish scattering PDF. Vertical density profiles and size estimates obtained acoustically corresponded to distributions and lengths of fish caught in vertical gill nets. The proportion of different size classes caught in gill nets agreed fairly well with the proportions determined acoustically. This analysis can be applied to signals from noncalibrated sonars and can be used to calibrate simultaneously obtained echo squared integration values. With calibrated sonars, target strength can be estimated in situ. For Cisco, TS = 21.9 log10L − 67.2, where TS is target strength in (decibels) and L is fish length (centimetres). The average number of Cisco in the three lakes ranged from 89 to 1551 fish/ha, corresponding to a biomass of 2–223 kg/ha. Maximum densities range from 12 to 49 fish/1000 m3.

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.

Growth of Stegophiura nodosa (Echinodermata, Ophiuroidea) in the Pechora Sea

2020 ◽  
Vol 100 (7) ◽  
pp. 1129-1133
Author(s):  
Ekaterina A. Stratanenko ◽  
Stanislav G. Denisenko
Keyword(s):  
Growth Rate ◽  
Barents Sea ◽  
Specific Growth ◽  
Food Resource ◽  
Demersal Fish ◽  
Brittle Star ◽  
Arctic Seas ◽  
Gompertz Equation ◽  
Biological Patterns ◽  
Growth Features

AbstractThe brittle star Stegophiura nodosa is one of the most abundant ophiuroid species living in Arctic seas and serves as a food resource for demersal fish. The study of autecological and biological patterns of S. nodosa is important for understanding the species reaction to environmental change. The growth features and growth rate of this brittle star from the Pechora Sea were estimated using the Gompertz equation as the basic mathematical model and compared with Bertalanffy equation parameters. Individual age was evaluated by counting the ring-shaped growth marks in the calcite structure of the animal's vertebral ossicle, where each visible ring was considered to be an annual growth mark. The calculations indicated: the theoretical limiting radius of the brittle star's ossicle (R∞) averages 318 ± 18 μm, and the exponential deceleration of the specific growth rate (g) is found to be 0.46 ± 0.02. The initial hidden growth marks were found to vary from 1–3, and the maximum lifespan of S. nodosa in the Pechora Sea (SE of the Barents Sea) is evaluated to be 9–10 years.

Ammonia vertical density profiles in Jupiter and Saturn from their radioelectric and infrared emissivities

Icarus ◽  
1980 ◽  
Vol 41 (3) ◽  
pp. 410-422 ◽  
Author(s):  
André Marten ◽  
Régis Courtin ◽  
Daniel Gautier ◽  
Anne Lacombe
Keyword(s):  
Density Profiles ◽  
Vertical Density

Abrupt transitions between gyroscopic and internal gravity waves: the mid-latitude case

2008 ◽  
Vol 598 ◽  
pp. 67-80 ◽  
Author(s):  
HANS VAN HAREN
Keyword(s):  
Large Scale ◽  
Deep Ocean ◽  
Internal Gravity Waves ◽  
Buoyancy Frequency ◽  
Neutral Stability ◽  
Density Profiles ◽  
Geostrophic Balance ◽  
Convective Mixing ◽  
Vertical Density ◽  
Wave Limit

The large-scale vertical density stratification, represented by buoyancy frequency N, is generally very stable in the upper half of the ocean, and relatively weak in the lower half. However, closer inspection of density profiles demonstrates steps rather than a smooth increase with depth. As is demonstrated here using Richardson number, geostrophic balance and slantwise convective mixing arguments, these layers have a limited set of minimum, weak stratification, N-values Nmin indicating the transition between stably stratified and convective ‘homogeneous’ layers. Adopting the viewpoint that the transition occurs for neutral stability in the direction of Earth's rotation Ω instead of gravity g, three discrete states are hypothesized for mid-latitudes: (i) Nmin = 2fh under linear stability conditions, (ii) Nmin = fh(|ϕ| < 45°) and (iii) Nmin = 4fh, both under nonlinear stability, where horizontal component fh = 2Ω cos ϕ at latitude ϕ. The Nmin are not in terms of inertial frequency f = 2Ω sin ϕ, because the effect of fh is the tilting of vortex tubes away from the local vertical in the direction of Ω. The above explains very well deep-ocean North-Atlantic and Mediterranean observations on transitions in conductivity-temperature with depth profiles, inertial polarization and near-inertial shear. The latter peaks at sub-inertial 0.97f, which is associated with the lower inertio-gravity wave limit for Nmin = 4fh, thereby stressing the importance of fh for the dominant physics associated with mixing in the ocean.

Penetration of a Rate Sensitive Geological Target by the Compaction Ring Theory

2002 ◽  
Author(s):  
Martin R. Gilmore ◽  
S. E. Jones ◽  
Joseph C. Foster
Keyword(s):  
Model Development ◽  
Target Material ◽  
Rate Sensitivity ◽  
Target Strength ◽  
Strain Rates ◽  
Linear Rate ◽  
Cat Scan ◽  
Strain And Strain Rate ◽  
Simplifying Assumptions ◽  
Made In

In an earlier paper, the authors presented a theory for the penetration of geologically based semi-infinite targets [5]. This theory was suitable for application to targets in which compaction due to the crushing of voids is the primary deformation mechanism. This phenomenon has been observed in concrete targets with a ring of dense material around the tunnel region, see figure 1 for a cat scan of a concrete target after penetration. This was the motivation for the model development. A number of simplifying assumptions were made in the application of the theory to data from concrete penetration experiments. One of the assumptions was that the target strength was constant, or independent of strain and strain rate. This assumption leads to generally consistent results for the same ogive nose geometry. However, it was noted that there was a discrepancy between the strength predictions when two different ogive nose geometries were used. This paper investigates the discrepancy by assuming that the target material is rate sensitive. The results indicate that the strain rates in the target are indeed affected by the nose geometry. A detailed analysis for a target material with linear rate sensitivity is provided in the paper and the results provide a favorable comparison with available experimental evidence.

Abundance of demersal fish resources in the Persian Gulf and Oman Sea

2006 ◽  
Vol 86 (6) ◽  
pp. 1455-1462 ◽  
Author(s):  
T. Valinassab ◽  
R. Daryanabard ◽  
R. Dehghani ◽  
G.J. Pierce
Keyword(s):  
Persian Gulf ◽  
Central Area ◽  
Demersal Fish ◽  
Total Biomass ◽  
Trawl Survey ◽  
Important Species ◽  
Fish Resources ◽  
Oman Sea ◽  
Commercially Important ◽  
The Persian Gulf

We report on results of a trawl survey during 2003–2004 to assess the abundance of demersal fish resources in the Persian Gulf and Oman Sea. Samples were taken at a total of 316 trawl stations selected following a stratified random procedure. Catch rates (catch per unit area, CPUA) and total biomass were estimated. Total demersal fish biomass was estimated to be approximately 73,000 tonnes in Persian Gulf waters and approximately 39,000 tonnes in the Oman Sea. The lowest CPUA was recorded in the west of the study area (stratum A, approximately 1700 kg/n.m.2) and the highest in the east (stratum Q, 13943.4 kg/n.m.2), although density of commercially important species was higher in the central area (stratum K). Catch rate and biomass varied significantly in relation to seabed depth. Commercially important demersal species made up around 60% of the estimated total biomass. The most abundant species groups were rays, catfish, grunts, nemipterids and carangids. Several important species (e.g. silver pomfret, croakers and sharks) appear to have declined since the late 1970s while others, such as rays and catfish, have increased.

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