Several marking methods are available that will facilitate monitoring rehabilitated sea otters after release. Sea otters are routinely marked by securing colored flipper tags to the hind flippers Jameson, 1989; DeGange and Williams, 1990). Tag colors should be conspicuous and different from colors already in use on free-ranging sea otters in the release area. Because tag loss is known to occur, sea otters are also routinely marked with a small transponder chip for permanent identification (Thomas et a1., 1987; DeGange and Williams, 1990). Transponder chips are usually injected beneath the skin in the groin area.
Abdominally implanted radio transmitters (Garshelis and Siniff, 1983; Ralls et a1., 1989) provide the most dependable means of marking sea otters for studies requiring frequent observations of individuals. It may be important that some of the released sea otters carry such transmitters as part of a natural resource damage assessment to monitor their movements following release and to estimate survivorship and reproduction (Bayha and Kormendy, 1990). The radio-tagged animals should be released together with the majority of the rehabilitated sea otters, thereby assuring adequate sampling of the released population. Ideally, follow-up studies should be designed to evaluate stresses associated with implant surgery, capture, treatment, and long-term holding. Although it can be argued that the results of follow-up studies will not affect whether or not oiled sea otters are rehabilitated and released, an indication of postrelease survival and movements is important to guide future release efforts.
