Stereophotography for the field biologist: measurement of lengths and three-dimensional positions of free-swimming sharks

Klimley, A. P.; Brown, S. T.

doi:10.1007/bf00413921

Cited by 69 publications

(53 citation statements)

References 11 publications

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“…This compares well with the 55% precision obtained by Klimley & Brown (1983). An advantage of our method is that it corrects not only for non-parallel optical axes (which the distance correction is assumed to do), but also for spherical aberration of the lenses (distortion in the X-and y-dimension) and for sources of bias that may vary between sessions (separate correction factors per session).…”

Section: Discussionsupporting

confidence: 77%

“…Klimley & Brown (1983) describe such a set up and point out an important source of bias, which occurs when the optical axes of the two cameras are not exactly parallel. To correct for such bias they present a method that is based on the empirical determination of the linear change in axis separation and the hyperbolic change in image dimension, both in relation to the distance from the camera.…”

Section: Introductionmentioning

confidence: 99%

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A simple field method for stereo-photographic length measurement of free-swimming fish: merits and constraints

Rooij

Videler

1996

Journal of Experimental Marine Biology and Ecology

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A simple field method to correct for bias in stereo-photographic underwater measurements is presented and its usefulness to improve the accuracy of length estimates of free-swimming fish is tested. The calibration is based on the inclusion of stereo exposures of a slate of known dimensions at the beginning and end of each measuring session. and it allows correction for non-parallel optical axes, spherical aberration of the lenses. and for other sources of bias that may vary between sessions. A precision of t3% for replicate length measurements of a 30 cm slate is obtained at distances between 0.7 and 2.0 m. This compares well with reported values that are obtained with more sophisticated (laboratory) methods.However, application of this calibration does not significantly improve the accuracy of stereo measurements of the length of free-swimming fish (22.5 cm or 7-11% of actual fish length). The limitations are caused by difficulties in recognizing identical extreme points at the body of fish that are photographed under field conditions. By averaging three or more replicate measurements the accuracy is improved to il cm (2.7-4.5%).We conclude that effort should be aimed at increasing sample size. rather than at improving equipment and correction procedures, when measuring free-swimming fish in their natural habitat.

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Section: Discussionsupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

A simple field method for stereo-photographic length measurement of free-swimming fish: merits and constraints

Rooij

Videler

1996

Journal of Experimental Marine Biology and Ecology

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“…The use of accurate length-measurement devices such as stereophotogrammetry (Klimley and Brown 1983;Spitz et al 2000) or laser metrics (Durban and Parsons 2006;Rohner et al 2011) will allow a more precise evaluation to be made. As the latter technique is now being employed on both the Seychelles and Djibouti aggregations, this will open up avenues for more detailed analysis of membership periods and annual population estimates.…”

Section: Further Analysismentioning

confidence: 99%

Long-term membership of whale sharks (Rhincodon typus) in coastal aggregations in Seychelles and Djibouti

Rowat

Brooks

March

et al. 2011

Mar. Freshwater Res.

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Abstract. In coastal waters of several locations globally, whale sharks (Rhincodon typus) form seasonal aggregations, most of which largely comprise juvenile males of 4-8 m length. Evaluation of the period that individuals stay within these size-and age-specific groupings will clarify our understanding of the transition between life-stages in this species and how this might affect their long-term conservation. Long-term photo-identification studies in Seychelles and Djibouti provided data to evaluate this.

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“…Calibration of the 3-D optic-To assess the accuracy and precision (Kellner et al 2004) of the optical system in terms of size measurements, calibration experiments were carried out according to the established procedures of analog stereo photography (Cook 1986;Klimley 1980;Rebikoff 1984).…”

Section: Fischer Et Almentioning

confidence: 99%

“…In contrast to analog stereoscopic photography, where the parallelism of the two optical axes of a pair of cameras has to be estimated by calibration pictures of an object at infinity (Cook 1986;Klimley 1980;Rebikoff 1984) and later corrected during image processing, in digital photography this can be done prior to the measurements by adjusting the two cameras on the mounting rack to an object at infinity. To do this in the system…”

Section: Fischer Et Almentioning

confidence: 99%

Habitat structure and fish: assessing the role of habitat complexity for fish using a small, semiportable, 3‐D underwater observatory

Fischer

Weber

Heine

et al. 2007

Limnology & Ocean Methods

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In contrast to terrestrial ecology, three-dimensional (3-D) imaging technology is not well established as a method for studying species-habitat interactions in aquatic ecology. In this study, we used a semi-portable, digital, 3-D underwater observatory designed for long-term exposure in shallow water habitats to assess fish-habitat interactions to artificial structures of different complexity. The observatory was mounted on a cable-car system and was moved along a 50 m transect parallel to five artificial structures of different complexity and one control site. The optical unit took high-resolution digital images, in pairs, from each structure and the control site at a frequency of 30 min over 24 h and was then moved remotely to the next structure. The system was operated for 2 mo without being recovered and took a total of 2160 stereoscopic image pairs. The system proved highly valuable in assessing small-scale temporal patterns in fish-habitat interactions, as well as changes in habitat preferences of fish over the diel cycle. Such small-scale temporal and spatial patterns are important for a detailed understanding of specieshabitat interactions, not only in fish but also in most aquatic macro-organisms. Nevertheless, such patterns can hardly be assessed using classical sampling devices due to labor and animal protection restrictions. However, the possibility of a significant increase in quantity of sampling through the use of remote imaging technology is accompanied by a significant increase in labor costs for image analysis. Therefore, further progress in semi-and fully automated systems for image analysis is needed, including 3-D imaging tools, for ecological studies.

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Stereophotography for the field biologist: measurement of lengths and three-dimensional positions of free-swimming sharks

Cited by 69 publications

References 11 publications

A simple field method for stereo-photographic length measurement of free-swimming fish: merits and constraints

A simple field method for stereo-photographic length measurement of free-swimming fish: merits and constraints

Long-term membership of whale sharks (Rhincodon typus) in coastal aggregations in Seychelles and Djibouti

Habitat structure and fish: assessing the role of habitat complexity for fish using a small, semiportable, 3‐D underwater observatory

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