Methods for estimating detection efficiency and tracking acoustic tags with mobile transect surveys.

Area of Science:

• Marine Biology
• Acoustic Telemetry
• Fisheries Science

Background:

• Mobile transect surveys are vital for estimating fish populations using acoustic tags.
• Accurate inferences on fish presence depend on reliable tag detection, which is often challenging.
• A significant proportion of deployed acoustic tags go undetected, complicating population assessments.

Purpose of the Study:

• To quantify detection efficiencies in mobile acoustic tag surveys conducted in a deep fjord.
• To develop and assess methods for estimating and improving tag detection rates.
• To identify factors influencing detection efficiency and explore strategies for enhancing data acquisition in underwater tracking.

Main Methods:

• Conducted 5-year mobile transect surveys in a deep fjord, focusing on detecting weak acoustic tags on the seabed.
• Assessed transect widths using cumulative probabilities of perpendicular distances from transect lines to tag locations.
• Employed three methods for estimating detection efficiencies: fitting attenuation functions, using dual receiver systems, and conducting test tag surveys.

Main Results:

• Quantified detection efficiencies, revealing significant variability influenced by boat speed, tag depth, tag type, and receiver system.
• Demonstrated a trade-off between detection efficiency per unit area and area swept, primarily related to boat speed.
• Identified factors affecting acoustic tag detection ranges and efficiency, including hydrophone-receiver system variations.

Conclusions:

• Accurate fish presence estimations require rigorous quantification of detection efficiencies in acoustic telemetry.
• Optimizing boat speed and selecting appropriate equipment are critical for maximizing detection rates in mobile surveys.
• Proposed methods can enhance decoding efficiencies, improving data quality in challenging underwater acoustic tracking studies.