This week I am attending the joint meeting of the Animal Behavior Society and the International Ethological Conference, which is being held at Indiana University in Bloomington, Indiana. One of the symposia on the first day of the conference focused on the idea of "sensory pollution," a new buzz-term collectively describing the negative effects of human activities and products on the ability of animals to accurately perceive the world around them. In addition to the noise pollution that I have often described in previous posts, experts spoke on the impacts of pollution from light, chemicals, and sources of magnetism. While most of the discussion focused on the ways in which sensory pollution is harmful, there was also some mention of how "pollution" might be used to the advantage of wild animals.---
(Pile-driving, one of many sources of aquatic noise pollution. I can attest from personal experience that, on land at least, it is very, very loud. Considering that sound is transmitted even better in water, I'm guessing things get quite unpleasant for aquatic animals exposed to this racket.)NOISE
Legendary aquatic bioacoustician Arthur Popper discussed recent experimental work on the physical effects of pile-driving noise on fish. He and his lab built a small indoor setup where they could mimic both the frequency (e.g., pitch) and amplitude of pile-driving sounds. Those who have heard this intense sound in the field will probably not be surprised to learn that the initial run of the testing arena resulted in vibrations so intense that they shook the entire building. After a bit of tweaking, the machinery was back on track and the researchers were able to proceed with their tests. One of their surprising findings was that, at low and moderate levels of pile-driving noise, fish were able to recover from the bleeding and tissue hemorrhaging caused by the disturbance. Further, only species with a swim bladder exhibited truly irreparable damage in response to the noise. Overall, these are fairly encouraging results, since they suggest that many animals may be more tolerant of pile-driving than expected--good news given that this particular form of aquatic sound disturbance is fairly common worldwide.
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(Light pollution in the continental US.)LIGHT
Next up was light pollution expert Sidney Gauthreaux, author of Ecological Consequences of Artificial Night Lighting. NPR listeners may recognize his name (and message) from a piece on bird migration that aired in 2009. Gauthreaux discussed the many sources of artificial night lighting (lighthouses, lightships, tall buildings, street lights, spotlights, flares, communication and broadcast towers) and the various ways in which they can affect birds (e.g., by causing blindness, singing feathers, increasing collisions, and leading to death). Since most birds are diurnal, lighting is a particular problem during spring and fall migrations, when many species fly through the night in order to reach their breeding and wintering grounds, respectively. Steady lights have been shown to attract three times as many birds as flashing lights. Results of studies on the effects of light color are a bit more mixed; while some findings suggest that red light and white light are not as attractive as blue lights, other research indicates that red and white light are actually worse than green and blue. One particularly interesting part of Gauthreaux's talk focused on the interaction between magnetic orientation and lighting. Evidently, birds navigate best when light is at or below the intensity of a sunset; when lighting becomes more intense, their magnetic senses are confounded and they become disoriented. Young birds appear to be particularly susceptible to light pollution, which is discouraging since these are the animals that are needed to replenish populations and carry on breeding in years to come. Another sad aspect of light pollution is that "captured" birds--those that have been drawn to a light and are too bedazzled to leave--appear to attract other birds, and many animals end up dead not only from colliding with anthropogenic structures, but also from colliding with each other midair.
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(A reflective surface, which causes light to polarize. This unnatural source of polarized light can trick animals, especially insects, into thinking they are seeing water.)POLARIZED LIGHT
One subset of light pollution is polarized light, which is light that has bounced off a surface in such a way that its wavelengths are oriented in the same direction--or, at the very least, are less randomly directed than previously. This "specialty" form of light pollution was discussed by Bruce Robertson of the Smithsonian Conservation Biology Institute. According to Robertson, there are only two natural sources of polarized light: the sky, which contains water droplets that cause polarization, and bodies of water. Many animals are sensitive to polarization because it helps them orient themselves so that the sky is above and behind them, and/or because this sensitivity enables them to seek out bodies of water where they may feed and breed. Unfortunately for these animals, humans have changed the polarized light landscape by using construction materials that are smooth and dark--the two characteristics that cause the highest levels of polarization. Objects like blacktop, crude oil spills, plastic tarps, metals, and glass all mimic water, causing animals--particularly insects--to aggregate in inappropriate places (Robertson says that an increasingly noticeable phenomenon is the presence of water insects on cars, which they mistake for ponds. Next time you go for a drive, check your vehicle for evidence of this trend!). Obviously, this is quite bad for the animals that are lured astray, but other animals may capitalize on their mistakes. Birds such as magpies and house sparrows, for instance, have been observed eating insects that are mindlessly flinging themselves at reflective windows. Fortunately, the negative impacts of polarized light can be mitigated fairly easily. Adding a bit of roughness to a surface--by faint etching in glass, for instance, or a handful of pebbles in asphalt mix--can dramatically reduce polarization. Likewise, using materials that are lighter in color or are criss-crossed by gridding in order to create many small, less attractive "islands" of habit, can also diminish the likelihood that animals will mistake anthropogenic building materials for water.
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(Ocean acidification is caused by changes in carbon dioxide levels. The oceans have absorbed almost half the excess carbon dioxide we humans have pumped into the atmosphere. This has reduced the amount of carbonate in the water, which means that shellfish have fewer materials with which to make their shells.)CHEMICALS
Recent PhD graduate Danielle Dixson discussed the effects of rising marine carbon dioxide levels on the ability of fish to use their sense of smell. She found that increases in carbon dioxide cause clownfish to prefer useless scent cues and to ignore important cues. This latter effect was seen in response to predator scents, which fish should pay attention to if they want to make sure they aren't eaten. Responses to carbon dioxide are dose-dependent, which means that as humans continue to alter global chemistry, things will only get worse for the clownfish (and probably other species, as well). Not only did the chemical pollution disrupt the fishes' sense of smell, but it also altered their "personalities": larvae treated with carbon dioxide were both bolder and more active, which means they could be more conspicuous to predators. Dixson reported that hearing and learning were also affected by carbon dioxide; cumulatively, this suggests that the chemical pollution may have an impact early on in development, and/or may affect brain functioning, thus affecting all these characteristics simultaneously. The only good news for the clownfish is that predators are similarly impacted by carbon dioxide, and under high levels of pollution they are less aggressive and quickly lose interest in their prey. Perhaps the most interesting--though very discouraging--finding was that marine larvae actively avoid scents of both oil palm and coconut, but are attracted to the scent of decomposing detritus. Why is this important? In the Pacific island archipelagos where Dixson conducted most of her research, larvae find their habitats (the shallow waters around each island) by sniffing out leaves that have fallen into the water from overhanging native trees. These species are increasingly being replaced with crops like oil palm and coconut. Thus, larvae will not only have trouble finding an attractive scent--and therefore a good home--but they will actively be repelled from the very same sites that they should be moving towards.
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(Sharks can be both a type of bycatch and a deterrent to other types of bycatch.)FINALLY, SOME GOOD NEWS
Some relief from all this depressing news was offered by Richard Brill of the Virginia Institute of Marine Science, a branch of my very own alma mater, the College of William and Mary. He discussed how sensory pollution has been used to discourage bycatch, and therefore preserve the health and population numbers of marine organisms such as fish, sharks, turtles, and pelagic seabirds. One early attempt at "positive" sensory pollution was the use of colored streamers on fishing lines in order to alarm potential bycatch, thereby keeping them away from fish hooks. When this failed to get the job done adequately, researchers got a bit more fancy and studied the sensory abilities of specific bycatch species. This eventually led them to discover differences between sea turtles--which fishermen don't want to catch--and edible fish such as swordfish--which they do. Specifically, sea turtles can see in the ultraviolet range, but swordfish cannot. Thus, an ultraviolet warning signal should keep turtles away from fishing lines, while leaving swordfish unaffected. Because turtles have a strong panic reaction to sharks, researchers came up with the idea of creating a UV shark silhouette that can be placed periodically along fishing lines in order to send the turtles running (or, in this case, swimming). Since plexiglass reflects UV light, it seems to be a good candidate material for the cut-outs. This particular plan is hot off the press,and researchers haven't yet had a chance to test whether it really works--but stay tuned. Another potential technique that hasn't been investigated is the use of electropositive metals to create a "zone of repulsion" around fishing lines. This should cause electrosensitive animals--namely sharks, another unwanted species--to avoid becoming snagged on a fishing hook. Magnets could also be used for this purpose, but so far they appear to cause avoidance behavior over the short-term, whereas the metals cause longer-term avoidance. One added bonus of the metals is that they are small, abundant, and cheap, which should make this technique easy to employ if it turns out to work well.
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Thanks to the following websites for providing the images used in this post:
https://www.chicap.org/p08.asp
http://laps.noaa.gov/albers/slides/ast/places.html
http://www.ehow.com/info_8242388_determines-light-polarized-not.html
http://www.macroevolution.net/ocean-acidification.html
http://www.flmnh.ufl.edu/fish/sharks/statistics/2007attacksummary.htm
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