Subsequent developments have involved the addition of sensors to monitor the maximum depth of each dive and environmental parameters such as the water temperature at that depth (Fig. A8).
Logical extensions of these developments include the addition of numerous other sensors to permit simultaneous monitoring of multiple aspects of the animal's environment and the transmission of these data first to aircraft and subsequently to satellites for relay to shore-based laboratories.
In addition to permitting scientists to define movement patterns and daily diving patterns of cetaceans, the use of such devices offers an exciting means of determining the environmental parameters that trigger changes in their behavior.
Radio transmitter tags, in a variety of configurations, may be constructed and attached for short-term studies or for long-term monitoring of migrating animals. In either case, depending on their size and methods of attachment, radio transmitter tags may be visible on a free-swimming animal even at a considerable distance.
[Illustration: Appendix Figure A7.--A saddleback dolphin wearing a radio tag transmitter surfaces to breathe off southern California. (_Photo courtesy of W. E. Evans._)]
[Illustration: Appendix Figure A8.--A radio transmitter package attached to the dorsal ridge of a California gray whale. This yearling animal, captive for most of the first year of its life, was released into the ocean off San Diego, Calif., in March 1972 and subsequently tracked from shipboard and aircraft for over 30 days. The sensor transmitter package, shown in detail in the inset, was designed to measure the maximum depth of the animal's dive and the water temperature at that depth. (_Photo by S. Leatherwood._)]
In addition to these man-made and applied tags, variations in natural markings and unusual appearances may be used to identify individuals and herds on repeated encounters. Although many species of cetaceans are characterized by changes in color pattern with age, individuals occasionally differ radically in their coloration from their fellows (App. Figs. A9, A10). In addition, individuals are sometimes seen with unusually shaped dorsal fins or scarring patterns (App. Fig. A11). These unusually marked animals should stand out in repeated encounters and can be a help in identifying a herd from one encounter to another.