Multiple-Frequency Acoustic Backscattering and Zooplankton Aggregations in the Inner Scotian Shelf Basins

1991 ◽  
Vol 48 (3) ◽  
pp. 340-355 ◽  
Author(s):  
N. A. Cochrane ◽  
D. Sameoto ◽  
A. W. Herman ◽  
J. Neilson
Keyword(s):  
Target Strength ◽  
Scotian Shelf ◽  
Migration Patterns ◽  
Acoustic Backscattering ◽  
Large Populations ◽  
Order Of Magnitude ◽  
Silver Hake ◽  
Merluccius Bilinearis ◽  
Domain Dependence

Acoustic backscatter observations at 12, 50, and 200 kHz in the inner Scotian Shelf basins reveal large populations of silver hake (Merluccius bilinearis) and its principal prey, the euphausiid Meganyctiphanes norvegica. Multichannel sonar colour imagery facilitates separation of fish from euphausiids and delineation of their separate diurnal migration patterns. Silver hake acoustic abundances are consistent with midwater trawl sampling. Acoustic column densities for mature M. norvegica of approximately 1000/m2 exceed net sampling column densities by over 1 order of magnitude indicating strong net avoidance. Numerical simulation of euphausiid backscattering using a fluid cylinder model and natural distribution of scatterer orientations yields an approximate 20 log L target strength length dependence and little frequency domain dependence in the "geometric" scattering regime. Quantitative interpretation of euphausiid scattering in situ must account for randomness in their orientations.

Behavioral inferences from regulatory observer data: catch rate variation in the Scotian Shelf silver hake (Merluccius bilinearis) fishery

1999 ◽  
Vol 56 (2) ◽  
pp. 288-296 ◽  
Author(s):  
D M Gillis
Keyword(s):  
Interference Competition ◽  
Temporal Trends ◽  
Catch Rate ◽  
Rate Variation ◽  
Scotian Shelf ◽  
Apparent Contradiction ◽  
Fishing Vessels ◽  
Catch Rates ◽  
Silver Hake ◽  
Merluccius Bilinearis

The detailed spatial and temporal data collected for the regulation of the silver hake (Merluccius bilinearis) fishery on the Scotian Shelf provide a unique opportunity to test hypotheses about variability in catch rates on the scale of individual trawls. I used these data to examine vessel interactions and long-term temporal trends in catchability. An index of course linearity, derived from observed positions, times, and speeds of fishing vessels, indicated that interference competition was present in the fishery. However, catch rate did not decline with local vessel density. This apparent contradiction is consistent with fleet dynamic theory and suggests that the direct examination of catch rates is a poor test for interference in the retrospective analysis of fisheries data. The study of extended periods of high, localized fishing activity revealed a cycle in catch rates with periods of about 6 days. Such periods may represent an interaction between tidal, diel, and (or) technological factors. Although more study is required to identify the cause of these cycles, their existence should be considered in the design of surveys and other population studies using catch and effort data.

scholarly journals Response of Scotian Shelf silver hake (Merluccius bilinearis) to environmental variability

2018 ◽  
Vol 28 (3) ◽  
pp. 256-272 ◽  
Author(s):  
Daniel Reed ◽  
Stéphane Plourde ◽  
Adam Cook ◽  
Pierre Pepin ◽  
Benoit Casault ◽  
...  
Keyword(s):  
Environmental Variability ◽  
Scotian Shelf ◽  
Silver Hake ◽  
Merluccius Bilinearis

Diagnostic tools for unbiased in situ target strength estimation

2001 ◽  
Vol 58 (11) ◽  
pp. 2149-2155 ◽  
Author(s):  
Stéphane Gauthier ◽  
George A Rose
Keyword(s):  
Large Scale ◽  
Sample Volume ◽  
Target Strength ◽  
Diagnostic Tools ◽  
Threshold Density ◽  
Measurement Scales ◽  
Order Of Magnitude ◽  
Unbiased Estimates ◽  
Optimal Measure

In situ target strength (TS) is theoretically the optimal measure to scale echo-integration values to fish density. In practice, in situ TS is often biased. The number of fish per sample volume (Nv) has been used to set a threshold density to reduce the bias attributable to multiple targets. However, order of magnitude differences in the Nv threshold have been reported within the theoretical range 0 < Nv [Formula: see text] 1. To investigate the use and scale-dependence of the Nv index, with the objective of achieving unbiased estimates of in situ TS, redfish (Sebastes spp.) aggregations were measured in Newfoundland waters. When averaged over large horizontal distances (large scale), TS was biased upwards if Nv exceeded 0.04. However, TS could be estimated at higher densities without bias using smaller measurement scales. To deal with these scale-dependent variations, we develop diagnostic tools based on Nv and an echo-count index (Tv), which enable unbiased estimates of the Nv threshold and in situ TS.

Feeding Ecology of Juvenile (Age-0) Silver Hake (Merluccius bilinearis) on the Scotian Shelf

1989 ◽  
Vol 46 (10) ◽  
pp. 1762-1768 ◽  
Author(s):  
P. A. Koeller ◽  
L. Coates-Markle ◽  
J. D. Neilson
Keyword(s):  
Prey Selection ◽  
Fish Length ◽  
Feeding Patterns ◽  
Migration Patterns ◽  
Early Juvenile Stage ◽  
Class Strength ◽  
Different Depths ◽  
Silver Hake ◽  
Merluccius Bilinearis ◽  
Survival Differences

Feeding patterns of juvenile silver hake (Merluccius bilinearis) (length range 19–90 mm) captured by midwater trawl were compared between seasons (fall and winter), years (1980 and 1981), fish lengths, and depth and time of capture. Prey selection shifted gradually with increasing fish length, from copepods at the smaller size ranges, to amphipods, euphausiids and silver hake at the larger sizes. An abrupt shift in the feeding pattern occurred as larvae metamorphosed into juveniles, but there were no similar "critical" changes during the juvenile phase itself. Cannibalism of juveniles by juveniles was pronounced and could be an important factor influencing year-class strength. Silver hake juveniles did not prey on the larvae or juveniles of other fish species, nor did they compete with them for available food, mainly because the juveniles of other species were rare during the period of greatest silver hake abundance in the pelagic zone. Evidence from abundance surveys and the feeding study suggests that increased size-at-date at the early juvenile stage, possibly due to more favourable growth and feeding conditions, resulted in increased survival. Differences in feeding patterns among fish in different size categories, and captured at different depths and times generally substantiate diet migration patterns inferred from previous vertical distribution experiments.

Growth variation and water mass associations of larval silver hake (Merluccius bilinearis) on the Scotian Shelf

2000 ◽  
Vol 57 (8) ◽  
pp. 1728-1738 ◽  
Author(s):  
Jennifer A Jeffrey ◽  
Christopher T Taggart
Keyword(s):  
Water Mass ◽  
Age And Growth ◽  
Scotian Shelf ◽  
Growth And Survival ◽  
Growth Variability ◽  
Wet Biomass ◽  
Growth Variation ◽  
Silver Hake ◽  
Age Relations ◽  
Merluccius Bilinearis

Otolith microstructure is shown to be ideal for assessing age and growth in silver hake (Merluccius bilinearis) larvae and is used to examine growth among individuals and cohorts. Larvae collected from Western Bank, Scotian Shelf, in September, October, and November 1997 defined three monthly cohorts identified using inferred hatch dates. Total length-at-age relations did not differ between the September and October cohorts despite substantial differences in growing degree-day (435 versus 318°C·d) and zooplankton (potential prey index) wet biomass (0.15 versus 0.27 g·m-3). Larvae collected off-bank in September exhibited a growth advantage of >0.10 mm·d-1 relative to larvae collected on-bank. Greater variability in growth rate within cohorts and among water masses implies that cohort-averaged growth and survival (based on growth) estimates can be biased by overrepresentation of a single water mass. The focus on growth variability, and its relationship to survival, should be on individuals within cohorts and not on cohort-averaged estimates. We hypothesize that growth, and perhaps survival, in silver hake larvae on the Scotian Shelf is most easily explained by variation in physical oceanographic processes.

Convergence of Acoustic, Optical, and Net-Catch Estimates of Euphausiid Abundance: Use of Artificial Light to Reduce Net

1993 ◽  
Vol 50 (2) ◽  
pp. 334-346 ◽  
Author(s):  
D. Sameoto ◽  
N. Cochrane ◽  
A. Herman
Keyword(s):  
Target Strength ◽  
Sampling System ◽  
Remotely Operated Vehicle ◽  
Acoustic Backscattering ◽  
Video Cameras ◽  
Acoustic Target ◽  
Avoidance Reactions ◽  
Theoretical Scattering ◽  
System Operating

Euphausiid concentrations in the Scotian Shelf basins were sampled with BIONESS, a multinet sampling system, and quantitatively assessed simultaneously with an in situ optical zooplankton counter (OPC) mounted on BIONESS and with an acoustic backscattering system operating simultaneously at 50, 122, and 200 kHz. Supplementary observations were made with vertically dropped video cameras and video and 35-mm frame cameras mounted on a remotely operated vehicle (ROV). The use of a light source on BIONESS during sampling increased the catch of euphausiids by 10–20 times by reducing active avoidance reactions to the net. Consequently, conventional net sampling has greatly underestimated euphausiid concentrations, a conclusion suggested by previous acoustic measurements. Experimental acoustic target strengths for 28-mm euphausiids averaged −77.5, −73.4, and −68.4 dB at 50, 122, and 200 kHz, respectively, using measured Sv levels and assuming 100% net sampling efficiency. Theoretical scattering models based on randomly oriented cylinders require the euphausiids to be oriented within about 5° of the horizontal to approximate both the experimentally observed target strength amplitudes and their frequency dependence. Acoustic interpretation has been enhanced by incorporation of transducer sensitivity versus temperature corrections and modeling techniques that allow for finite transducer beam widths.

Individual variability in sub-Arctic krill material properties, lipid composition, and other scattering model inputs affect acoustic estimates of their population

2021 ◽  
Author(s):  
Brandyn M Lucca ◽  
Patrick H Ressler ◽  
H Rodger Harvey ◽  
Joseph D Warren
Keyword(s):  
Lipid Composition ◽  
Material Properties ◽  
Acoustic Scattering ◽  
Gulf Of Alaska ◽  
Individual Variability ◽  
Target Strength ◽  
Frequency Independent ◽  
Lipid Mass ◽  
Order Of Magnitude

Abstract Target strength model inputs including morphometry, material properties, lipid composition, and in situ orientations were measured for sub-Arctic krill (Euphausia pacifica, Thysanoessa spinifera, T. inermis, and T. raschii) in the eastern Bering Sea (EBS, 2016) and Gulf of Alaska (GOA, 2017). Inter-species and -regional animal lengths were significantly different (F1,680 = 114.10, p &lt; 0.01), while animal shape was consistent for all species measured. The polar lipid phosphatidycholine was the dominant lipid, comprising 86 ± 16% (mean ± SD) and 56 ± 22% of total lipid mass in GOA and EBS krill, respectively. Krill density contrasts varied by species and region rather than with morphometry, lipid composition, or local chla fluorescence. Mean in situ krill orientation was 1 ± 31°, with 25% of observed krill within ±5° of broadside incidence. Modelled target strength sensitivity was frequency independent for variations in material properties but was primarily sensitive to morphometry and orientation at lower (38 kHz) and higher (200 kHz) frequencies, respectively. Measured variability in material properties corresponded to an order of magnitude difference in acoustic estimates of biomass at 120 kHz. These results provide important inputs and constraints for acoustic scattering models of ecologically important sub-Arctic krill species.

scholarly journals Modelling the acoustic effect of swimbladder compression in herring

2003 ◽  
Vol 60 (3) ◽  
pp. 548-554 ◽  
Author(s):  
Natalia Gorska ◽  
Egil Ona
Keyword(s):  
Orientation Distribution ◽  
Target Strength ◽  
Acoustic Effect ◽  
Acoustic Backscattering ◽  
Cylinder Model ◽  
Acoustic Surveys ◽  
The Mean ◽  
Theoretical Results

Abstract Obtaining accurate data on fish target strength (TS) is important when determining the quality of the results from acoustic surveys. However, this requires an improved understanding of both behavioural and environmental influences on the acoustic backscattering by fish. It is well known that the increased pressure with depth compresses the swimbladder of herring, and it has been confirmed by in situ measurements that the TS of adult herring (30–34 cm) is 3–5 dB weaker at 300 m than that of fish close to the surface. Understanding exactly how swimbladder compression may influence herring TS is, therefore, of great interest, and is the main motivation behind this study. Taking account of swimbladder volume changes with depth, we obtained analytical solutions using the Modal-Based, Deformed-Cylinder Model (MB-DCM). The mean-backscattering cross-section is then computed with selected orientation patterns, length distributions, and contrast parameters. The depth-dependence of TS at different acoustic frequencies has been studied. We conducted a sensitivity analysis to show how TS is dependent on the contraction rates of the bladder dimensions and on the fish-orientation distribution. Our theoretical results are compared with TS measured at 38 kHz.

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