Two New Large-scale Acoustic Techniques Aim to Study Fisheries - High-frequency fish finding sonars are widely used to locate ocean fish, but they can only "see" a 10m-wide section of water at a time. A new system, Ocean Acoustic Waveguide Remote Sensing, uses low frequency signals to track large groups of fish over thousands of square kilometers, enabling researchers to watch as schools and shoals form, divide, and scatter. The system uses lower-powered signals than those emitted by naval submarine-seeking sonars. After initial tests in 2003, the system is due for further testing this fall in the Gulf of Maine. Another new system, the proposed Ocean Tracking Network, is being tested off the western coast of Canada. The network is centered on acoustic receivers deployed at sea, which listen for signals emitted by acoustic tags surgically implanted in fish. The tags last from six months to two years; some simply note the presence of the fish, while others can collect more detailed data including daily locations, temperature, and depth, to better track long-term movement of individuals. Scientists hope to deploy such networks of receivers in 14 ocean regions throughout the world. Source: Science, 8/11/06 [READ ARTICLE]
Kauai Crickets Develop Silent Wings to Avoid Parasite - On Kauai, male field crickets have quickly evolved female-like wings incapable of creating their characteristic chirping sound. In only 20 generations, 90 percent of male crickets have become silent, and so avoid predation by a parasitic fly that uses cricket song to find hosts. The flies deposit larvae in the crickets, which are later killed when the flies emerge. The now-silent males have made behavioral adaptations to be able to attract mates: they congregate near the few remaining calling males and intercept females attracted by the calls. "While we were surprised by the extraordinary speed at which the mutation spread, what is more interesting is that, ordinarily, you would expect such a change in wing morphology to quickly disappear, because males couldn't attract mates," researcher Marlene Zuk said. "Instead, the behavior of the flatwings allows them to capitalize on the few callers that remain, and thus escape the fly and still reproduce. This is seeing evolution at work." The end of this evolutionary story is yet to be written: are the remaining singing males too rare to support the wasp population, or will they die off completely, and if so, will the silent males be able to find mates? Source: ScienceDaily, 9/26/06 [READ ARTICLE]
Ship Noise Stresses Freshwater Fish
Wysocki, L.E. et. al. Ship noise and corisol secretion in European freshwater fishes. Biological Conservation 128:501-508. 2006
A striking study, confirming what many have suspected: exposure to noise significantly increases the secretion of stress hormones in fish. If this result is replicated for other species, it could dramatically shift the debate about ocean noise, because stress has been widely shown to make animals dramatically more susceptible to disease, toxins, and other health threats. The study at hand involved three freshwater fish (carp, gudgeon, perch) exposed to recordings of ships on the Danube and two Austrian lakes. The researchers measured the level of the cortisol in the water before and after noise exposure. Cortisol is the primary stress-related hormone in fish and many other animals. After thirty minutes of exposure to the ship noise, secretions of cortisol roughly doubled, ranging from 80-120% depending on the species of fish. Interestingly, there was no increase in cortisol when the fish were exposed to a steady white noise as intense as the loudest boat sounds, suggesting that the variability of the ship noise is more important than the intensity.
Pile-Driving Noise Can Mask Dolphin Calls Over Several Kilometers
J.A. David. Likely sensitivity of bottlenose dolphins to pile-driving noise. Water and Environment Journal 20 (2006) 48-54
This paper is a literature survey of research that has looked at the sound profile and propagation of noise from pile-driving in water. Pile-driving is used to construct sturdy anchors for piers, bridges, and, increasingly, wind turbines. Pile-driving noise is loudest in frequency ranges that coincide with dolphin whistles, and so are likely to mask whistles at the long ranges, up to 10-15km for sounds at 9kHz. The 50kHz component of dolphin whistles can be masked at ranges of about 6km. At higher frequencies (115kHz), pile-driver noise dissipates more quickly and is loud enough to mask higher-frequency dolphin clicks only at ranges of 1.2km or less. The impact of such potential masking is likely reduced by dolphins' directional hearing, the intermittent nature of pile driving noise, and behavioral modifications in calling patterns by the dolphins (changing the frequency and amplitude of their calls, as well as the content of the signals). The author suggests several mitigation measures: avoiding pile-driving during calving season, ramped-up warning signals, and the use of bubble-curtains to reduce pile-driving impulsive noise.
Human Noise Favors Frogs That Take Advantage of Lulls in Calls of Other Species
Sun, Jennifer and Narins, Peter. Anthropogenic sounds differentially affect amphibian call rate. Biological Conservation 121 (200) 419-427.
This study, apparently the first in twenty years to address the effects of human noise on amphibian call rates, suggests that human noise may increase reproductive success of some frog species, while decreasing success in its neighbors, thus perhaps changing the overall species mix in a given noisy location. The study took place in central Thailand, where researchers measured the call rates of several species of frogs, before, during, and after two noise intrusions: airplane overflights and playback of recorded motorcycle noise. Three of the most acoustically active species decreased their call rates during noise intrusions, but one increased its call rate. The species that increased its call rate, R. taipehensis, was one that uses natural lulls in local frog choruses to make itself heard to its species-mates. Thus, this study suggests that the intrusion of human noise may increase the number of lulls in the chorus of mixed species, and so offer R. taipehensis an increased number of opportunities to successfully advertise to potential mates. The implication is that human noise may differentially favor some species (such as R. taipehensis, which uses chorus lulls to be heard), while putting other species (such as ones that reduce or stop calling during noise intrusions) at a reproductive disadvantage--because, as the researchers note, "it is well established that individual reproductive success is directly proportional to calling effort in numerous frog species."
Possible Mechanisms to Explain Beaked Whale Sensitivity to Anthropogenic Sound
T.M. Cox et al. Understanding the impacts of anthropogenic sound on beaked whales. J. Cetacean Res. Manage. 7(3):177-187, 2006. [DOWNLOAD PAPER(pdf)]
This comprehensive review paper is the result of a special workshop on beaked whales convened in 2004 by the Marine Mammal Commission, and is coauthored by an all-star team of 36 diverse cetacean researchers. It begins by offering a good summary of a series of mass strandings stretching from Greece in 1996 to the Gulf of California in 2002. It then reviews some recent papers that have identified shared characteristics in some of the strandings, including near-shore canyons, acoustic waveguides, and certain transmission pattern similarities. The heart of the paper is an extended discussion of several possible mechanisms by which active sonar might lead to strandings. These range from simply "chasing" whales into shallow water to a variety of ways in which the whales' behavior might be altered in ways that could affect nitrogen bubble formation in their tissues. The latter include the fairly well-known concern that whales may surface too quickly and cause tissue damage much like "the bends" in human divers (some deep-diving whales seem to ascend more slowly than they descend, unlike most cetaceans, suggesting this is possible), as well as some lesser-considered variations: staying too long at depth during dives (perhaps delaying surfacing due to sound?), or having their rest time at the surface--or the poorly-understood series of shallow dives often seen between deep dives--interrupted (so that tissues may retain more nitrogen at the start of the dive than is healthy). They also summarize other physiological factors that could contribute to observed hemorrhaging, including a sensitivity to stress or disorientation caused by a vestibular response. Finally, they summarize current research into the possibility of direct tissue damage caused by exposure to intense sound waves. Recommendations from the panel focus on the obvious need for more research of dive patterns, beaked whale anatomy and hearing sensitivity, as well as a call for a detailed retrospective review of stranding records and for new controlled-exposure experiments to get a better sense of what received levels can trigger potentially dangerous behavioral changes.
Note: Several other recently published research papers have shed light on beaked whale dive patterns and acoustic behavior. See the Recent Research page for more....
