Field validation of an inexpensive time‐depth recorder

Abstract

Time-depth recorders (TDRs) have proven to be an essential tool in studying the at-sea behavior of marine and aquatic animals (Kooyman 2004, Shaffer and Costa 2006). While their use is often limited by the difficulty of capturing and tagging the animal, in many cases the cost of the tag is the limiting factor (Wilson et al. 1989, Ropert-Coudert and Wilson 2004). Reduced instrument costs could benefit research on diving vertebrates by affording increased sample sizes, extending the scope of research objectives within and among species, and opening this technology to a larger segment of the research community. One reason that the currently available TDRs are expensive is that they are developed explicitly for the animal tagging research market. Relatively small demand coupled with large investments in research, development, and quality control has led to increased precision, accuracy, and reliability. One way of reducing the cost of TDRs is to take advantage of products designed for a high-volume market, such as the dive computers used for recreation sport divers. While these have been bulky and limited to a few dives over a period of hours, new devices are available that can provide an inexpensive alternative to existing animal tags (approximately one-tenth of the price). With the exception of maximum readable depth, the Sensus Ultra TDR (ReefNet Inc., Mississauga, Ontario, Canada) has pressure and temperature sensor specifications similar or superior to most other commercially available electronic TDRs (Table 1). Memory capacity, depth rating, and additional sensor options are limited by comparison, but the Sensus Ultra TDR remains compatible with the diving behavior of many species. Here, we conduct an in-field comparison of the Sensus Ultra TDR against a purpose-built marine animal TDR (Wildlife Computers,