Does Your Light Cause Critters Harm?

It was during early attempts at macro photography at night at Grand Turk's reef wall that I first discovered the hazardous effect of artificial light on small critters. Every time I lined up my camera on one, it would disappear before I had time to record it. It was some time before I realized a big grouper had taken up station next to me and was literally sucking my subjects, mesmerized by the light, out of my picture. In Egypt's Red Sea, lionfish have learned to do the same at night in a commensal relationship with divers' flashlights.

Stéphan G. Reebs of the Université de Moncton, Canada, wrote in 2007 how fishes at night exposed to a bright light suffer 'light shock' -- becoming motionless and often sinking to the bottom [where it is shallow]. "This may give the illusion of sleep when in fact it is only a short-lived reaction to a temporally abnormal stimulus."

At Manuelita (Cocos Island), great hordes of white-tip reef sharks follow divers at night like packs of hounds, picking off small creatures that are temporarily immobilized by beams of light from divers. It's a spectacular experience for the divers but catastrophic for small fish that were hiding in the darkness.

Clearly, illuminating a small fish or critter with a bright light at night can make it vulnerable to predation. But, can the light itself do direct harm to those creatures caught in its beam? Subscriber Harvey S. Cohen (Middletown, NJ) wonders about this possible harm from a light beam and in an email to Undercurrent. He said, "I wish dive operators would discuss torch [lighting] etiquette in briefings for night dives.

Divers become aware that light-sensitive animals like crinoids only spread their fronds in the darkness and to point a beam of light at them makes them curl up in shyness, but is there any science to Harvey Cohen's concern? Does the beam of your light damage critters in some way? Some modern video lights push out a fantastic amount of light in lumens.

Is There a Physiological Effect?

Well, there doesn't seem to be a lot of science on fish, critters and night lights, but we may extrapolate.

The International Dark Sky Association website says "Nocturnal animals sleep during the day and are active at night. Light pollution radically alters their night-time environment by turning night into day. According to research scientist Christopher Kyba, for nocturnal animals, "the introduction of artificial light probably represents the most drastic change human beings have made to their environment."

The Florida Fish and Wildlife Conservation Commission tells us that "the effect on diurnal creatures is that it alters their sleep patterns, resulting in them not getting enough sleep, not having enough downtime for the body to repair itself, altering reproductive cycles."

Dr. Anika Brüning of Freie Universität Berlin wrote her Ph.D. thesis Disruptive light: when night becomes day for fish (recorded on the website of the Leibniz-Institute of Freshwater Ecology and Inland Fisheries). She concluded that light pollution influences biological rhythms of fish [and presumably other marine creatures] ... the hormone melatonin is mainly responsible for these rhythms ... Melatonin is mainly produced at night and ... constantly provides fish with information about the season and time of day. Night light suppresses the nocturnal increase in the melatonin level, which may disrupt processes that follow this hormonal rhythm." She says that the suppression of the melatonin rhythm that might affect the immune system, growth, development, and behavior may not only affect individual fish, but also whole populations, even their reproductive biology, and could lead to "altered predator-prey relationships, and could, therefore, have an impact on species communities and entire ecosystems."

However, this doesn't really apply to bursts of light, but when unnaturally turning night into day with long periods of light.

Furthermore, we do know that lights attract some fish. For centuries, hunters and fishermen have used flames and bright lights to attract quarry to their nets, so powerful is the effect of light on some species. The inshore waters across many oceans are dotted at night with the lights of squid fishing fleets in the darkness.

So far as we know, there has been one study of the effect of photographers' strobes on White's seahorses, conducted by the University of Technology, Sydney (UTS) Australia, under lead researcher David Harasti. He found that flash-photography-based tagging had no long-term effect -- that is, the animals did not exhibit any short-term behavioral changes.

Some Ideas to Ease the Stress on Animal Life

So, while we do know that isolating a fish in a beam of light or strobe, can set it up for instant death by an opportunistic predator that has learned to use a diver unnaturally in its hunt, we may not know much more. That said, this is the behavior I would strongly suggest (if your comfortable knowing that some of the critters you isolate will become prey).

1) Don't allow the beam of your light to dwell on a critter for long periods and if you are shooting video, be discerning about the length of a shot.

2) If your video or spotting light has a red light mode, use it. Few marine creatures can see by red light and are undisturbed by it. Careful photographers use it to line up their cameras on shy critters such as mandarin fish and then ambush them with a pulse of white light from their strobe lights. A red mode also allows divers to watch behavior that would otherwise be unseen at night.

3) Let's follow a few suggestions put forth by subscriber Cohen, which seem to make common sense. "Light up critters mostly with the dimmer edge of your beam-- not the hot spot. Point out an item of interest by circling the hot spot around it. Never leave your hot spot on a critter for more than a couple of seconds. And, if you see someone shooting photos, or especially video, take your beam away from their subject."

-- John Bantin