Underwater infrared video system for behavioral studies in lakes

Abstract

We propose the use of infrared (IR) video systems for the underwater behavioral study of animals at night, at depth, and/or in colored aquatic systems. This system is composed of a black-and-white video camera coupled with four projectors, each equipped with 50 IR light-emitting diodes (LEDs). The use of LEDs is energetically far more efficient than the use of halogen lights equipped with IR filters, and therefore allows automatic long-term video recording at low cost. Laboratory testing of one LED spot at increasing humic acid concentrations indicates that this system can be used for short-range underwater observation in colored lakes. We applied this system to the study of scavenger/carcass interactions. Under field conditions, the setup is not easily detected by animals and allows direct and continuous observation of animal interactions during a full daily cycle. Note that, to our knowledge, this video system provides the first published night movies of freshwater fish behavior filmed in highly colored lakes, without using visible light. Our results indicate that this nonintrusive system can be successfully used for scientific studies in freshwater ecology, even in the presence of significant concentrations of light-absorbing humic substances in the water.