A digital stereo-video camera system for three-dimensional monitoring of free-swimming Pacific bluefin tuna,Thunnus orientalis, cultured in a net cage

Abstract Lundgren, B., and Nielsen, J. R. 2008. A method for the possible species discrimination of juvenile gadoids by broad-bandwidth backscattering spectra vs. angle of incidence. – ICES Journal of Marine Science, 65: 581–593. Measurements were made of the broad-bandwidth (80–220 kHz) acoustic backscattering from free-swimming juvenile gadoids at various orientations and positions in an acoustic beam, under controlled conditions. The experimental apparatus consisted of a stereo-video camera system, a broad-bandwidth echosounder and echo-processor system, a narrowband 120 kHz split-beam echosounder, a large tank, and a fishnet cage. The net cage was centred on the acoustic beams and was virtually transparent, both acoustically and optically. Accurate three-dimensional positions and angular orientations of individual fish were estimated from stereo-images captured synchronously when broad-bandwidth echoes were received from passing fish. Fish positions were also estimated from data collected with a synchronized split-beam echosounder. Software was developed for image analysis and modelling, including calibration, alignment of acoustic and optical-reference frames, and automatic position-fitting of fish models to manually marked fix-points on fish images. The software also performs Fourier spectrum analysis and pulse-shape analysis of broad-bandwidth echoes. Therefore, several measurement series on free-swimming juvenile gadoids were evaluated. The method and data may be used to improve the acoustic identification of fish species and sizes, and thereby improve investigations of spatial prey–predator relationships, and the accuracy and efficiency of acoustic surveys.

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A Comparison of the Accuracy and Precision of Measurements from Single and Stereo-Video Systems

Marine Technology Society Journal ◽

10.4031/002533202787914106 ◽

2002 ◽

Vol 36 (2) ◽

pp. 38-49 ◽

Cited By ~ 65

Author(s):

Euan Harvey ◽

Mark Shortis ◽

Mathew Stadler ◽

Mike Cappo

Keyword(s):

Video Camera ◽

The Other ◽

Fish Length ◽

Camera System ◽

Stereo Video ◽

Accuracy And Precision ◽

Video Systems ◽

Subject Orientation ◽

Video Camera System

Underwater tests using plastic silhouettes of fish were used to compare the accuracy and precision of measurements made with a single video camera system to those made from two stereo-video systems (one using digital camcorders, the other using Hi8 camcorders). Test measurements made across a variety of ranges and angles of silhouette orientation in the fields of view showed the length estimates from both the digital and Hi8 stereo-video systems were substantially more accurate and precise than those obtained by the single video camera system, and had the great advantage that the position (range and bearing) and orientation of a fish target could be measured directly. Measurements made with stereo-video were much less restricted by range and subject orientation than those made with single video. The data resulting from these trials are used to propose a set of guidelines to optimize the accuracy and precision of underwater measurements of fish length using single and stereo-video systems.

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Error and bias in size estimates of whale sharks: implications for understanding demography

Royal Society Open Science ◽

10.1098/rsos.150668 ◽

2016 ◽

Vol 3 (3) ◽

pp. 150668 ◽

Cited By ~ 9

Author(s):

Ana M. M. Sequeira ◽

Michele Thums ◽

Kim Brooks ◽

Mark G. Meekan

Keyword(s):

Body Size ◽

Conservation Status ◽

Video Camera ◽

Data Sets ◽

Large Species ◽

Camera System ◽

Stereo Video ◽

Whale Sharks ◽

Large Animals ◽

Video Camera System

Body size and age at maturity are indicative of the vulnerability of a species to extinction. However, they are both difficult to estimate for large animals that cannot be restrained for measurement. For very large species such as whale sharks, body size is commonly estimated visually, potentially resulting in the addition of errors and bias. Here, we investigate the errors and bias associated with total lengths of whale sharks estimated visually by comparing them with measurements collected using a stereo-video camera system at Ningaloo Reef, Western Australia. Using linear mixed-effects models, we found that visual lengths were biased towards underestimation with increasing size of the shark. When using the stereo-video camera, the number of larger individuals that were possibly mature (or close to maturity) that were detected increased by approximately 10%. Mean lengths calculated by each method were, however, comparable (5.002 ± 1.194 and 6.128 ± 1.609 m, s.d.), confirming that the population at Ningaloo is mostly composed of immature sharks based on published lengths at maturity. We then collated data sets of total lengths sampled from aggregations of whale sharks worldwide between 1995 and 2013. Except for locations in the East Pacific where large females have been reported, these aggregations also largely consisted of juveniles (mean lengths less than 7 m). Sightings of the largest individuals were limited and occurred mostly prior to 2006. This result highlights the urgent need to locate and quantify the numbers of mature male and female whale sharks in order to ascertain the conservation status and ensure persistence of the species.

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