Evaluating techniques for determining elasmobranch body size: a review of current methodologies

Area of Science:

• Marine Biology
• Conservation Science
• Zoology

Background:

• Elasmobranchs possess life history traits making them vulnerable to overexploitation.
• Accurate biometric data (growth rate, age, size at maturity) are vital for elasmobranch conservation and management.
• Traditional capture-based methods for data collection can be invasive or lethal.

Purpose of the Study:

• To review and analyze existing non-invasive techniques for collecting zoometric data in elasmobranchs.
• To highlight the advantages and limitations of each technique for fieldwork application.
• To guide researchers in selecting appropriate non-invasive measurement methods.

Main Methods:

• Systematic review of 49 articles on elasmobranch measurement techniques.
• Analysis of seven non-invasive techniques: photogrammetry (distance, bar, laser), stereo-DOV, stereo-BRUV, stereo-ROV, and aerial photogrammetry.
• Evaluation of technique requirements, costs, limitations, and features.

Main Results:

• Stereo-DOV, stereo-BRUV, stereo-ROV, and aerial photogrammetry are identified as excellent, minimally invasive alternatives to capture-based methods.
• These techniques are practical, simple to use, and potentially highly accurate for elasmobranch size measurement.
• Detailed information on equipment, cost, limitations, and features of each technique is presented.

Conclusions:

• Non-invasive photographic techniques significantly advance elasmobranch research and conservation efforts.
• The reviewed methods provide valuable alternatives for collecting essential demographic data without harming animals.
• This review serves as a guide for selecting optimal non-invasive tools for elasmobranch zoometric studies.