A Bayesian interpretation of target strength data from the Grand Banks

1997 ◽  
Vol 54 (10) ◽  
pp. 2323-2333 ◽  
Author(s):  
T Hammond
Keyword(s):  
Gadus Morhua ◽  
Research Effort ◽  
Target Strength ◽  
Grand Banks ◽  
Dual Beam ◽  
Northern Cod ◽  
Multiple Detection ◽  
Species Groups ◽  
Fish Detection

Knowledge of the target strength (TS) distribution of the fish being surveyed is necessary for accurate acoustic biomass estimates. Although dual-beam and split-beam transducers can measure TS in situ, these measurements are usually misleading because fish with higher TS are detected more readily, measurements are coming from several fish species, and measurements are made on the total echo from several unresolved targets. A Bayesian method of analysis was developed to extract information from TS data despite these problems. The first problem was addressed using a model of fish detection that was calibrated with data from a survey of northern cod (Gadus morhua) on the Grand Banks. The second problem, species composition, was dealt with by incorporating information about the relative abundance of species groups. Prior information about the concentration profile of the species assemblage was used to take into account the third problem, multiple detection. Results suggested that the difficulties mentioned above are serious sources of bias that should not be ignored. The method also indicated how research effort can be directed to improve acoustic surveys.

scholarly journals Monitoring coastal northern cod: towards an optimal survey of Smith Sound, Newfoundland

2003 ◽  
Vol 60 (3) ◽  
pp. 453-462 ◽  
Author(s):  
George A Rose
Keyword(s):  
Gadus Morhua ◽  
Sampling Error ◽  
Vertical Movement ◽  
Target Strength ◽  
Biomass Estimation ◽  
Night Time ◽  
Acoustic Measures ◽  
Rate Of Increase ◽  
Northern Cod ◽  
Age Structured

Abstract The extant, coastal northern cod (Gadus morhua) have over-wintered and spawned in Smith Sound, Newfoundland, since 1995, and acoustic surveys have been conducted in several seasons since then. Cod move into the Sound in late fall, over-winter in a dense, size- and age-structured aggregation, spawn between late March and early June and then disperse into and beyond Trinity Bay during summer to feed. The optimal survey time for biomass estimation is January–February, when the waters are ice-free and the cod are in mono-specific, relatively stationary, and well-defined aggregations with the highest densities and are typically clear of “bottom returns”. Biomass surveys have been conducted in mid-January since 1999. An error analysis indicated the main sources of uncertainty to be density variability and target strength (TS). Repeated quasi-synoptic (10 h) surveys were the optimal means of producing an estimate of uncertainty about population size. Some vertical movement led to night-time surveys consistently having higher estimates than day-time surveys by approximately 15%. Detectability ranged from 73 to 86% and deadzone-corrected, acoustic measures did not differ from swept-area densities found by bottom trawling. Biomass scaling by TS used length-dependant dB/kg to reduce the size-sampling error. Overall, population biomass doubled in approximately 7 years, consistent with a rate of increase around 0.2, largely through recruitment. The surveys are internally consistent and indicate instantaneous rates of mortality among year classes of 0.3 to >2 (very high on older fish) and provide a method for monitoring the annual biomass (cv<40%).

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 The relative frequency response derived from individually separated targets of northeast Arctic cod (Gadus morhua), saithe (Pollachius virens), and Norway pout (Trisopterus esmarkii)

2009 ◽  
Vol 66 (6) ◽  
pp. 1149-1154 ◽  
Author(s):  
Geir Pedersen ◽  
Rolf J. Korneliussen
Keyword(s):  
Frequency Response ◽  
Relative Frequency ◽  
Gadus Morhua ◽  
Target Strength ◽  
Reference Frequency ◽  
Acoustic Measurements ◽  
Arctic Cod ◽  
High Frequencies ◽  
Specific Frequency

Abstract Pedersen, G., and Korneliussen, R. J. 2009. The relative frequency response derived from individually separated targets of northeast Arctic cod (Gadus morhua), saithe (Pollachius virens), and Norway pout (Trisopterus esmarkii). – ICES Journal of Marine Science, 66: 1149–1154. The concept of relative frequency response r(f) of fish is an important feature used to characterize acoustic targets. It is defined as the volume-backscattering coefficient at a specific frequency f relative to that of a reference frequency. When based on volume backscattering, r(f) reliably distinguishes several acoustic categories if the insonified volumes are reasonably comparable between the frequencies, and that enough samples and targets are measured to constrain stochastic variations in the data within acceptable limits. Therefore, r(f) distinguishes different fish species with swimbladders poorly if they appear as single targets. Using target-strength (TS) data, the acoustic measurements are more spatially comparable, and averaging the TS over an echotrace of a single fish improves the ability to distinguish between different species. Frequency response was estimated using TS data from in situ measurements, collected using Simrad EK60 echosounders with split-beam transducers transmitting simultaneously at 18, 38, 70, 120, and 200 kHz. Selected series with nearly pure catches of northeast Arctic cod (Gadus morhua), saithe (Pollachius virens), and Norway pout (Trisopterus esmarkii) were analysed using a target-tracking algorithm. The frequency response of northeast Arctic cod and saithe did not differ significantly, but at high frequencies, the response of both northeast Arctic cod and saithe differed from that of Norway pout. However, in the latter case, northeast Arctic cod and saithe could be separated, because of their different TS magnitudes.

Acoustical Assessment of Squid (Loligo opalescens) off the Central Oregon Coast

1987 ◽  
Vol 44 (6) ◽  
pp. 1261-1267 ◽  
Author(s):  
Katharine Jefferts ◽  
Janusz Burczynski ◽  
William G. Pearcy
Keyword(s):  
Geographic Distribution ◽  
Distribution Density ◽  
Strength Distribution ◽  
Target Strength ◽  
Adjacent Area ◽  
Density Estimates ◽  
Oregon Coast ◽  
Loligo Opalescens ◽  
Dual Beam

Squid (Loligo opalescens) were surveyed acoustically in an area off the Oregon coast using dual-beam and echo integrator techniques. The method developed is shown to be feasible for in situ estimation of target strength, distribution, and abundance of midwater squids. Average target strength was estimated both while drifting with a squid school and cruising over one. The values derived, −58.6 to −58.7 dB, are much lower than previous estimates, but more realistic in relation to the target strength of fishes. Schools judged to be fish or squid showed little difference in depth or size, but varied significantly in geographic distribution. Density estimates ranged from 9.9 t/km2 in a known spawning area to 0.93 t/km2 in an adjacent area.

On Recruitment and Distribution of Atlantic Cod (Gadus morhua) off Newfoundland

1993 ◽  
Vol 50 (12) ◽  
pp. 2729-2741 ◽  
Author(s):  
B. deYoung ◽  
G. A. Rose
Keyword(s):  
Population Dynamics ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Life Cycles ◽  
Grand Banks ◽  
Larval Retention ◽  
The Past ◽  
Northern Cod ◽  
Poor Recruitment ◽  
The Right

The Atlantic cod (Gadus morhua) populations located off Labrador and Northeastern Newfoundland (NAFO areas 2G–3L) have recently declined to the lowest levels of abundance on record. These "northern" cod have historically comprised several geographically recognizable populations with independent migratory life cycles on the shelf from the Grand Banks to Labrador. A reappraisal of past and recent work suggests that fundamental changes have taken place in the population dynamics of these cod during the past several decades. We focus on two key elements: distribution and recruitment. Distributions have become more southerly and recruitment failures prevail. We argue that these features are related and that northerly spawning and warm ocean conditions are prerequisites for strong recruitment. Cold ocean temperatures are associated with southerly distributions and poor recruitment. We propose the "right site" hypothesis, that egg and larval retention and survival are spatially dependent and that in cold years, spawning tends to occur at southerly locations where larval retention will be poor. We make several testable predictions: regeneration of the northern populations will occur slowly at time scales of decades, regeneration of southern populations will occur more quickly given warming conditions, and the 1991–93 year classes will be poor because of southerly distributions.

Atmosphere–Ocean Coupling and Atlantic Cod Migrations: Effect of Wind-Forced Variations in Sea Temperatures and Currents or Nearshore Distributions and Catch Rates of Gadus morhua

1988 ◽  
Vol 45 (7) ◽  
pp. 1234-1243 ◽  
Author(s):  
G. A. Rose ◽  
W. C. Leggett
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Analysis Model ◽  
Sea Temperature ◽  
The North ◽  
Dual Beam ◽  
Ocean Coupling ◽  
Catch Rates ◽  
Alongshore Wind

Coastal upwellings and downwellings forced by alongshore winds on the north shore of the Gulf of St. Lawrence were associated with variability in onshore movements and inshore daily catches of Atlantic cod (Gadus morhua). Mean cod densities in the zone offshore from the trap sites, determined by hydroacoustic integration scaled by an in situ dual beam determined mean backscatter, ranged from 2.6 to 82.7 fish/105 m3. Cod were located where sea temperatures ranged from −0.5 to 8.5 °C. Catches were nil where temperatures were outside this range. Cod were located at depths which correlated with the strength of alongshore currents (r = −0.55). A path analysis model with predictors alongshore wind stress and current, sea temperature, and cod density accounted for 76% of the variance in catch. Cod abundance in the offshore zone accounted for the most variance independent of other factors (27%). Sea temperature and currents accounted for 15 and 13%, respectively. Peaks in catch (to 1500 kg/d) coincided with maximum rates of decline in sea temperatures and with NE upwelling currents. Low catches coincided with maximum rates of increase in temperatures and with SW currents. In a regression model, four lags of alongshore wind accounted for 83% of the variance in catch.

scholarly journals Variations in the target strength of Atlantic cod during vertical migration

2009 ◽  
Vol 66 (6) ◽  
pp. 1205-1211 ◽  
Author(s):  
George A. Rose
Keyword(s):  
Vertical Migration ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Multivariate Model ◽  
Ex Situ ◽  
Target Strength ◽  
Conventional Model ◽  
Close Range ◽  
The Mean

Abstract Rose, G. A. 2009. Variations in the target strength of Atlantic cod during vertical migration. – ICES Journal of Marine Science, 66: 1205–1211. Experiments conducted at sea in June 1999 and January 2000 indicated that the mean target strength (TS) of Atlantic cod (Gadus morhua) varies not just with length, but also with pressure (depth) and fish orientation, particularly during vertical migration. In June, when fish were migrating and spawning, vertical migration was pronounced, extending up to 150 m off the seabed, and the associated TS declined by as much as 5 dB. In January, when the fish were located nearer the seabed, mean TS was more stable and matched a conventional model of TS vs. length [L, cm; i.e. TS = 20 log(L) − 66] based on measurements of ex situ fish orientated horizontally and positioned at close range. This paper demonstrates that mean TS is inversely related (p < 0.05) to the range off the seabed (r, m), which includes 90% of fish. Based on this finding, a new multivariate TS model is proposed: TS = 20 log(L) − 65 − 0.05 r. In this model, r is a proxy for swimbladder volume and fish orientation. A survey in May 2007 found that cod (mean L = 63 cm) dispersed in such a way that single targets could be resolved up to 100 m from the seabed. Measurements of TS of in situ individual fish (TSindividual) and mean TS inferred from a comparison of area-backscattering coefficients (sa) and count-based densities (TSindirect) were positively correlated with a slope not different from unity. Means of these TS estimates were −32.4 and −32.2 dB, respectively, or ∼2.3 dB less than that predicted by the conventional model. In contrast, the new multivariate model predicts TS = −32.5 dB, which is nearly identical with the means of TSindividual and TSindirect.

To Eliminate Curtain Effect of FIB TEM Samples by a Combination of Sample Dicing and Backside Milling

2014 ◽  
Author(s):  
Jian-Shing Luo ◽  
Hsiu Ting Lee
Keyword(s):  
Sample Preparation ◽  
Focused Ion Beam ◽  
Preparation Method ◽  
Low Cost ◽  
Ion Beam ◽  
Sample Preparation Method ◽  
Site Specific ◽  
Dual Beam ◽  
Transmission Electron

Abstract Several methods are used to invert samples 180 deg in a dual beam focused ion beam (FIB) system for backside milling by a specific in-situ lift out system or stages. However, most of those methods occupied too much time on FIB systems or requires a specific in-situ lift out system. This paper provides a novel transmission electron microscopy (TEM) sample preparation method to eliminate the curtain effect completely by a combination of backside milling and sample dicing with low cost and less FIB time. The procedures of the TEM pre-thinned sample preparation method using a combination of sample dicing and backside milling are described step by step. From the analysis results, the method has applied successfully to eliminate the curtain effect of dual beam FIB TEM samples for both random and site specific addresses.

Sign in / Sign up

Export Citation Format

Share Document