Light Pollution Impacts Fish and Wildlife

Cheryl Lovato Niles coordinates the WSU Extension Watershed Master/Beach Watchers and also the Shore Stewards for Whatcom County.

When we think about pollution, we tend to think of things like antifreeze, or paint thinners or garbage — tangible things that either act as poisons, or destroy the life-sustaining qualities of the environment that fish and wildlife depend on. We don’t usually think of something as intangible and omnipresent as light. 

Light is so familiar and, in the form of artificial lights, such a commonplace part of our world that we forget how powerfully it affects living things. Yet, the 24-hour cycle of light and dark, called the circadian cycle, impacts the biology and behavior of most of the world’s living things, including humans. And like a chemical or physical pollutant, light can harm fish and wildlife by confusing or disrupting the environment to which they’ve evolved. 

The plight of sea turtle hatchlings on developed beaches is familiar. The tiny hatchlings are hardwired to immediately set out in the direction of light on the horizon. For millennia, that instinct served them well as the bright reflections of the moon and stars on the water drew the baby turtles to the sea. In the last several decades, however, their instinct has too often drawn them to patio lighting on seaside condos in Florida.

In Washington state, we don’t have such dramatic reminders of light’s influence on the natural world, prodding us to carefully consider how we light up our shoreline property. But research shows that artificial night lighting does have the power to impact the fish that live in our waters. And, because of its economic value to the Northwest, a lot of that research has been done on salmon. 

Night lighting doesn’t just impact fish and wildlife, it also changes our experience of the night. Sometimes those changes are very positive and enhance our safety and mobility. But excessively bright or poorly directed lighting creates a harsh glare, makes it harder for us to see our way, and can rob us of the starry night sky.

In this article I’ll first explore some of the ways night lighting affects fish and then I’ll consider ways to enhance our experience of the night along the shoreline with appropriate lighting that creates a safe and beautiful environment for both people and fish.

A few lights here or there wouldn’t merit a lot of attention. But when you consider that more than half of the world’s population lives within 45 miles of an ocean you can begin to imagine the profound effect that our homes and towns and streets can have on the biology of fishes living in the shallow waters of the nearshore. 

Moonlight, starlight and bioluminescence are the only forms of night lighting to which fishes are naturally adapted, and light intensity, or brightness, governs important natural behaviors such as feeding, schooling and migration. Some types of light attract some species of salmon; this is a phenomenon used at hydroelectric dams to draw the fish to safe passage routes.

Strobe lights, on the other hand, are generally disturbing to fish, perhaps because the rapid change in light intensity makes it impossible for their eyes to adapt to either darkness or bright light. This piece of information wouldn’t seem to have any real world application, since fish seldom frequent discos, until you consider the appearance of cars traveling around the bend of a road along the shoreline, or a motion detection light triggered by branches swaying in the wind. 

Different species of salmon respond differently to night-lighting experiments. Coho and steelhead tend to be still at night and remain still when artificial lights are turned on. Chinook, pink and chum salmon, however, are typically active in schools after dark and will move away from light. Salmon response to night lighting also changes with age. As fry mature to smolts, they react more strongly to being suddenly illuminated. They dart around more wildly and seek cover for a longer time.

When we look outside of the laboratory, beyond salmon, and into the waters of Puget Sound, we find that the complex and varied responses to night lighting can drive changes to the community of fishes. For some fish more light means more time to forage for food, while others find that they have become the now bounteous meal.

In a study conducted around over-water security lighting, spiny dogfish, a Puget Sound shark, appeared to be attracted to the bright light, probably because it illuminated schooling fishes. Pacific herring and sand lance numbers declined in the area as they presumably filled the sharks’ bellies.

Juvenile salmon often outmigrate at night and changes in lighting have been shown to interrupt the outmigration of sockeye fry. In a field study similar to the one described above, salmon fry became food for sculpins at lighted areas along their migratory route. It would appear that darkness provides important cover for these small fishes.

On the Puntledge River in British Columbia, harbor seals became the beneficiaries of a well-lit bridge. The seals enjoyed an all-night dinner until researchers tried a “lights-out” experiment. The number of seals feeding in the immediate area dropped significantly. But the savvy seals repositioned themselves to take advantage of the glow from a nearby urban area and resumed their nighttime feasting.

Shorelines are special not only because we share them with fish that we value but also because of the added beauty of light reflected on the water. Water amplifies the beauty of moonlight as well as the glare of excessively bright or poorly directed light. And light over open water is free to travel long distances, giving what would be a minor nuisance in a shady neighborhood the power to simultaneously annoy many neighbors. 

Not just on shorelines but everywhere we live, and more with each passing year, the glow from our night lighting obscures the beauty of the night sky. We call this light pollution. The changes are so gradual that we don’t even realize what we’re missing until we happen to find ourselves in some remote location, look up at the heavens and are dazzled by the amazing and unfamiliar brilliance of starlight. 

One common night-lighting mistake is over-lighting. When going from a bright room to a dark one, we find it very hard to see for a while. But given time, our eyes adjust amazingly well to the darkness. The human eye is incredibly sensitive and can see a single candle 10 miles away.

Exposure to bright light actually makes it harder to see at night; we squint in the unexpected brightness and then feel blind again when we move away from it. Softening the light works with the natural functioning of our eyes and results in greater nighttime visibility. 

Another related problem is glare. Whenever light shines directly from a fixture into your eyes it causes unnecessary glare and makes it harder to see. Shielding light fixtures so that all of the light is directed either down onto a path or onto a door, for example, creates much better visibility for you for a lot less wattage. Shielding fixtures in this way also minimizes light pollution and sky glow.

By becoming more careful and conscious of our night lighting choices and by following some simple guidelines we can illuminate paths, keep our property secure and enhance the night for fish and stargazers alike.

Provide adequate light for the task but don’t over-light. A full moon can be so bright that it casts shadows and you can read by it (or at least I could as a girl), yet some modern lighting systems are 100 times brighter than the full moon. 

Shield lighting fixtures so that the light is directed down and none of the direct rays of light can reach your eye. Light fixtures of this type are called “full cut-off” fixtures. It’s not necessary to purchase entirely new fixtures — you can retrofit existing lights with cutoff “sky caps” or in some cases small pieces of aluminum sheeting fitted to the fixture. Never use an insulating material that might cause overheating. 

Be mindful of your neighbors and ensure that your night lighting doesn’t encroach on their property unless it’s welcome. 

Avoid all-night security lights. A more effective approach to security lighting is a motion detector. A moving person suddenly illuminated will be more noticeable to neighbors. When considering security lighting, also keep in mind that very bright lighting and glare creates deep shadows. 

When lighting signs, shine the light from above and in front, keeping the light aimed at the sign surface. Here too, note that very bright signs are actually harder to read.

Being savvy about lighting can save money, too. While you’re making the most out of your night lighting by softening it and keeping it out of your eyes, consider saving yourself a bunch of money on your electricity bills by using high-efficiency bulbs. 

To learn more about night lighting, I recommend the resources listed below. The David Owen article, “The Dark Side: Making War on Light Pollution.” published in The New Yorker magazine is wonderfully well written. To learn more about light pollution in general, good light fixtures and to see examples of lighting ordinances from around the country, check out the International Dark Sky Association Web site: http://www.darksky.org/resources. §

• Liebl, David S., and Robert Korth. Wisconsin. University of Wisconsin Extension. Sensible Shoreland Lighting. Sept. 2000. 10 Sept. 2007. http://www.uwsp.edu/cnr/uwexlakes/humanimpact/lighting.pdf.

• Rich, Catherine, and Travis Longcore, eds. Ecological Consequences of Artificial Night Lighting. Washington, D.C.: Island P, 2006. 254-276.

• Owen, David. “The Dark Side: Making War on Light Pollution.” The New Yorker, 20 Aug. 2007. 14 Sept. 2007. http://www.newyorker.com/reporting/2007/08/20/070820fa_fact_owen.