Bias in Hydroacoustic Estimates of Fish Abundance due to Acoustic Shadowing: Evidence from Day–Night Surveys of Vertically Migrating Fish

1992 ◽  
Vol 49 (10) ◽  
pp. 2179-2189 ◽  
Author(s):  
A. R. Appenzeller ◽  
W. C. Leggett
Keyword(s):  
Fish Community ◽  
Acoustic Scattering ◽  
Fish Abundance ◽  
Diel Changes ◽  
Light Levels ◽  
Abundance Estimates ◽  
Acoustic Quantification ◽  
Acoustic Methods ◽  
Acoustic Surveys ◽  
Acoustic Shadowing

We investigated the hypothesis that fish schooling behavior leads to underestimation of fish abundance when assessed by acoustic methods. Current methods for acoustic quantification of fish abundance rely on the assumption that fish biomass and numerical fish abundance are linearly related to acoustic scattering under all natural fish densities. However, cage experiments as well as field observations have indicated that acoustic shadowing effects occur at very dense and large aggregations of fish. Acoustic surveys of the pelagic fish community of Lake Memphremagog, Quebec, were conducted when fish were aggregated and dispersed. These differences in aggregation were related to diel responses to light levels. We found that estimates of fish abundance, as measured by echo integration, were consistently and significantly lower when fish were aggregated in dense schools. This bias was not due to diel changes in average echo level per fish, which exhibited no relationship to diel changes in vertical and hortizontal distributions. We conclude that the reduced abundance estimates obtained when fish were aggregated resulted from acoustic shadowing. Our data suggest that this bias may be as large as 50%.

Cluster Sampling Estimation of the Variance of Abundance Estimates Derived from Quantitative Echo Sounder Surveys

1982 ◽  
Vol 39 (1) ◽  
pp. 229-231 ◽  
Author(s):  
Neal J. Williamson
Keyword(s):  
Data Analysis ◽  
Confidence Intervals ◽  
Serial Correlation ◽  
Simulation Analysis ◽  
Fish Abundance ◽  
Simple Random Sample ◽  
Cluster Sampling ◽  
Abundance Estimates ◽  
Acoustic Surveys ◽  
Precision And Accuracy

Serial correlation in data collected from fisheries acoustic surveys may have an effect on the precision and accuracy of fish abundance estimates. A simple random sample approach to the data analysis yields unreliable confidence intervals for mean population density when the degree of serial correlation in the data is high. The results of a simulation analysis indicate that more reliable confidence intervals can be obtained using cluster sampling estimation techniques.Key words: acoustic surveys, fish abundance estimates, cluster sampling, serial correlation

Jellyfish distribution and abundance in relation to the physical habitat of Jellyfish Lake, Palau

2018 ◽  
Vol 34 (1) ◽  
pp. 17-31 ◽  
Author(s):  
Megan A. Cimino ◽  
Sharon Patris ◽  
Gerda Ucharm ◽  
Lori J. Bell ◽  
Eric Terrill
Keyword(s):  
Autonomous Underwater Vehicle ◽  
Size Fraction ◽  
Underwater Vehicle ◽  
Habitat Associations ◽  
Physical Habitat ◽  
Uv Damage ◽  
Tourist Destination ◽  
Novel Approach ◽  
Abundance Estimates ◽  
Acoustic Surveys

Abstract:Animals often select for habitats that increase their chance of survival by balancing the need to acquire food, reproduce and avoid predation. Perennial blooms of golden jellyfish (Mastigias papua etpisoni) are present in Jellyfish Lake, Palau, a popular tourist destination. Based on the species’ economic importance and unusual behavioural complexity, increased understanding of jellyfish habitat selection is necessary. We used a novel approach, a REMUS autonomous underwater vehicle, to quantify jellyfish distribution, abundance and habitat, and compared these findings to traditional methods. Midday acoustic surveys showed jellyfish distribution was patchy and the population resided mainly on the eastern side of the lake, as it is known that jellyfish migrate eastward towards the sun. Highest vertical densities of jellyfish were at 6–7 m, potentially to mitigate UV damage or photoinhibition of their photosymbionts, suggesting a coupling exists between their vertical distribution and water properties. Abundance estimates of jellyfish were ~2.75 and ~7.1 million (~2 million excluding bell diameters <1 cm) from acoustic and net samples, suggesting the methodology employed underestimated the population's smaller size fraction and non-synoptic surveys could impact estimates due to unresolved patchiness. Our approach could investigate population dynamics, behaviour or habitat associations on fine scales.

A multifrequency method to classify and evaluate fisheries acoustics data

2006 ◽  
Vol 63 (10) ◽  
pp. 2225-2235 ◽  
Author(s):  
J Michael Jech ◽  
William L Michaels
Keyword(s):  
Clupea Harengus ◽  
Biological Information ◽  
Classification Algorithms ◽  
Atlantic Herring ◽  
Population Abundance ◽  
Acoustic Data ◽  
Video Images ◽  
Abundance Estimates ◽  
Fisheries Acoustics ◽  
Acoustic Surveys

Acoustic surveys have been conducted on Georges Bank from 1998 to present to estimate Atlantic herring (Clupea harengus) population abundance. Acoustic data were collected with a 12 or 18, 38, and 120 kHz Simrad EK500 scientific echo sounder. A pelagic trawl and underwater video images were used to collect biological information and to verify the species composition of acoustic backscatter. A multifrequency classification method was developed to improve the efficiency and accuracy of classifying species from acoustic echograms. In this method, a volume backscatter (Sv) threshold was applied equivalently to all echograms, and then a composite echogram was created based on which frequencies had Sv greater than or less than the Sv threshold. The results of this method were compared with the standard method of visually scrutinizing regions, and metrics were developed to evaluate the accuracy of classification algorithms relative to current methods, as well as to assess the effects of classification methods on population abundance estimates. In general, this method matched visually scrutinized Atlantic herring regions, but with consistent biases in classifying 38 kHz backscatter. The metrics highlighted spatial and temporal changes in the acoustic landscape, which may be indicative of intra- and inter-annual biological changes.

It’s complicated…Environmental DNA as a predictor of trout and char abundance in streams

2020 ◽  
Author(s):  
Adam J. Sepulveda ◽  
Robert Al-Chokhachy ◽  
Matthew B Laramie ◽  
Kyle Crapster ◽  
W Ladd Knotek ◽  
...  
Keyword(s):  
Cutthroat Trout ◽  
Environmental Dna ◽  
Fish Abundance ◽  
Bull Trout ◽  
Intermountain West ◽  
Salvelinus Confluentus ◽  
Oncorhynchus Clarkii ◽  
Habitat Monitoring ◽  
Abundance Estimates ◽  
Random Site

The potential to provide inferences about fish abundance from environmental (e)DNA samples has generated great interest. However, the accuracy of these abundance estimates is often low and variable across species and space. A plausible refinement is the use of common aquatic habitat monitoring data to account for attributes that influence eDNA dynamics. We therefore evaluated the relationships between eDNA concentration and abundance of bull trout (Salvelinus confluentus), westslope cutthroat trout (Oncorhynchus clarkii lewisi) and rainbow trout (O. mykiss) at 42 stream sites in the Intermountain West (USA and CAN) and tested if accounting for site-specific habitat attributes improved the accuracy of fish abundance estimates. eDNA concentrations were positively associated with fish abundance but these relationships varied by species and site and there was considerable variation unaccounted for. Random site-level differences explained much of this variation, but specific habitat attributes of those sites explained relatively small amounts of this variation. Our results underscore that either eDNA sampling or environmental characterization will require further refinement before eDNA can be used reliably to estimate fish abundance in streams.

scholarly journals Acoustic observations of micronekton fish on the scale of an ocean basin: potential and challenges

2009 ◽  
Vol 66 (6) ◽  
pp. 998-1006 ◽  
Author(s):  
Rudy J. Kloser ◽  
Tim E. Ryan ◽  
Jock W. Young ◽  
Mark E. Lewis
Keyword(s):  
Fishery Management ◽  
Size Structure ◽  
Acoustic Scattering ◽  
Ocean Basin ◽  
Fishing Vessel ◽  
Large Spatial Scale ◽  
Top Predators ◽  
Basin Scale ◽  
Acoustic Methods ◽  
Marine Planning

Abstract Kloser, R. J., Ryan, T. E., Young, J. W., and Lewis, M. E. 2009. Acoustic observations of micronekton fish on the scale of an ocean basin: potential and challenges. – ICES Journal of Marine Science, 66: 998–1006. Acoustic methods of characterizing micronekton communities (∼2 to 20 cm length) on the scale of an ocean basin could provide valuable inputs to ecosystem-based fishery management, marine planning, and monitoring the effects of climate change. The micronekton fish are important forage for top predators (e.g. tunas), and information on their diversity, distribution, size-structure, and abundance is needed to increase accuracy of top-predator distribution and abundance predictions. At the scale of an ocean basin, four years of Tasman Sea transects using a fishing vessel provide fine-scale maps of acoustic backscatter at 38 kHz that reveal detailed spatial patterns and structure to depths of 1200 m. Research-vessel data provide detailed biodiversity, density, size structure, and acoustic-scattering information from depth-stratified net sampling and a lowered acoustic probe. Wet-weight biomass estimates of the micronekton fish in the region vary considerably by a factor of 5–58 between acoustics (16–29 g m−2), nets (1.6 g m−2), and large spatial-scale, ecological models (0.5–3 g m−2). We demonstrate the potential and challenges of an acoustic basin-scale, fishing-vessel monitoring programme, including optical and net sensing, which could assist in characterizing the biodiversity, distribution, and biomass of the micronekton fish.

Sperm whale abundance estimates from acoustic surveys of the Ionian Sea and Straits of Sicily in 2003

2007 ◽  
Vol 87 (1) ◽  
pp. 353-357 ◽  
Author(s):  
T. Lewis ◽  
D. Gillespie ◽  
C. Lacey ◽  
J. Matthews ◽  
M. Danbolt ◽  
...  
Keyword(s):  
Sperm Whale ◽  
Western Mediterranean ◽  
Small Sample ◽  
Line Transect ◽  
Ionian Sea ◽  
Sperm Whales ◽  
Detection Function ◽  
Abundance Estimate ◽  
Abundance Estimates ◽  
Acoustic Surveys

Acoustic surveys for sperm whales, using line-transect methodology, were carried out in the Ionian Sea and Straits of Sicily, Mediterranean Sea, in 2003. A total of 17 whales were detected along 3846 km of designed survey track in the Ionian Sea, and no whales along 892 km in the Straits of Sicily. This total was insufficient to estimate a detection function, so further data were obtained from quasi-random passages made elsewhere in the western Mediterranean in the same year. The encounters included several tight aggregations with inter-animal spacing less than 1 km, primarily from the western Mediterranean. Including individuals from these aggregations distorted the detection function due to the small sample sizes. No such aggregations were found during formal survey of the two areas of interest, and the aggregations were therefore excluded from detection function estimation. The resultant effective strip half-width was 10.0 km (n=40). On the assumption that g(0)=1, the resulting abundance estimates for the Ionian Sea were 62 (with 95% lognormal confidence limits of [24,165]), and 0 for the Straits of Sicily. The low abundance estimate for the Ionian Sea indicates that careful monitoring of the population is needed in the future. During passages along the Hellenic Trench, that were not part of the designed survey, several sperm whales including two aggregations were detected, suggesting that this may be a higher density area and ought to be considered as a separate stratum when designing future surveys.

scholarly journals The influence of natural flow and temperature and introduced brown trout on the temporal variation in native fish abundance in a “reference” stream

2019 ◽  
Vol 76 (5) ◽  
pp. 705-722 ◽  
Author(s):  
John W. Hayes ◽  
Eric O. Goodwin ◽  
Joanne E. Clapcott ◽  
Karen A. Shearer
Keyword(s):  
Temporal Variation ◽  
Life Histories ◽  
Fish Community ◽  
River Flow ◽  
Fish Population ◽  
Large River ◽  
Fish Abundance ◽  
Native Fish ◽  
Natural Flow ◽  
Upper South

Understanding what drives variation in fish abundance at reference sites provides perspective for assessing the effects of human alterations to river flow and land use. We examined temporal variation in fish community abundance in a headwater tributary of a large river in the upper South Island (New Zealand) over 10 years. We were interested in the influence of natural flow variation and temperature on native fish abundance within the context of potential competition/predation pressure from juvenile introduced trout. Results from biannual sampling highlighted the dominating influence of floods on fish population dynamics, overriding biotic effects. We found no evidence for adverse effects of trout on native fish, and flow-related habitat performed more poorly in explaining variation in fish abundance than low- and median-flow statistics. Differences in temporal variation in abundance between species were largely consistent with life histories that provide resistance and (or) resilience to flood flows and relative insensitivity to low flows. Long-term data (≥10 years) are needed for detecting meaningful trends and quantifying the effects of human activities on fish community abundance.

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