Determination of Optimal Acoustic Passive Reflectors to Reduce Bycatch of Odontocetes in Gillnets

Frontiers in Marine Science

Ingo Schäfer¹  Arne Stoltenberg¹  Jérôme C. Chladek²  Daniel Stepputtis²  Lotte Kindt-Larsen³  Isabella M. F. Kratzer³  Finn Larsen³ 

[1] Bundeswehr Technical Center for Ships and Naval Weapons, Maritime Technology and Research, Eckernförde, Germany;Institute of Baltic Sea Fisheries, Thünen Institute, Rostock, Germany;National Institute of Aquatic Resources, Technical University of Denmark, Lyngby, Denmark;

关键词: bycatch;    odontocetes;    resonance;    target strength;    acrylic glass;    gillnet;   

DOI  :  10.3389/fmars.2020.00539

来源: DOAJ

【 摘 要 】

The need to minimize bycatch of toothed whales (odontocetes) in gillnets has long been recognized, because they are often top predators and thus essential to ecosystem resilience. It is likely that a key to achieving this goal is the improvement of gillnet acoustic visibility, because these species use underwater sonar for orientation. Previous work on increasing gillnet detectability for echolocating animals by making the nets more recognizable has been based on trial and error, without understanding the fundamental acoustic properties of the tested modifications. Consequently, these studies have produced mixed and sometimes contradictory results. We systematically identified small, passive reflective objects that can improve the visibility of gillnets at a broad range of frequencies, i.e., for many odontocetes. We simulated the acoustic reflectivity of a wide range of materials in different shapes, sizes, and environmental conditions, with a focus on polymer materials. We verified the simulation results experimentally and calculated detection distances of the selected modifications. For example, if 8 mm acrylic glass spheres are attached to the net at intervals smaller than 0.5 m, the spheres have the same target strength (TS) at 130 kHz as the most recognizable part of a gillnet, the floatline. Modifications of the netting material itself, e.g., using barium sulfate additives, do not substantially increase the acoustic reflectivity of the net.

【 授权许可】

Unknown