Acoustical properties of fishing gear: possible relationships to baleen whale entrapment

• Main Author: Todd, Sean Kevin
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1991
• Subjects: Newfoundland; baleen whale; baleen whales; Gadus morhua; Humpback Whale; Megaptera novaeangliae
• Online Access: https://research.library.mun.ca/5875/; https://research.library.mun.ca/5875/1/Todd_SeanKevin.pdf; https://research.library.mun.ca/5875/3/Todd_SeanKevin.pdf

The incidental entrapment in passive fishing gear of mysticetes, including the humpback whale Megaptera novaeangliae, is examined, with specific reference to the role of acoustics as a mechanism in perception. The acoustics of capelin traps and other common net types involved in entrapment are investigated. -- Many marine mammals, particularly humpback whales, are incidentally entrapped in fishing gear in Newfoundland and Labrador inshore waters. Explanations of these collisions are complex, and the fundamental question of how a whale perceives a net has yet to be answered. It is clear that the whale fails to detect the net in time to avoid it. It has been argued that the mechanism of sound remains as the most probable primary system of orientation to targets such as nets. -- The present state of knowledge on the use of sound by baleen whales is discussed, including the possibility that humpback whales might possess a crude form of echolocation. It is also shown that a potential exists for the use of sound as a passive navigation system. Thus while humpbacks might use sound for orientation purposes, their apparent failure to detect nets might result from the target being acoustically cryptic. -- The acoustics of a capelin (Mallotus villosus) trap are investigated. It was found that capelin trap mesh produces a wide band signal, which is significantly reduced in level once the trap is filled with capelin. Acoustic damping by schools of bait are discussed. -- Capelin trap mesh produces the strongest acoustic signal, while larger mesh sized cod (Gadus morhua ) trap mesh produces the least detectable signature. It is shown that net noise production can be correlated to the drag that a net imposes in a current. Differences in net acoustic signature are discussed in terms of anecdotal entrapment evidence; there is a negative correlation between probability of entrapment and the strength of acoustic signature of that net type.