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Hazardous Species Sharks and other large or venomous fishes are potentially dangerous to the investigator, and thus require special methods of restraint that must involve a compromise be- tween potential injury to the handlers and injurious re- straint of the animal. The particular method chosen will vary with the species and purpose of the project. Adherence to the following general guidelines is recommended when working with hazardous fishes: a. Procedures chosen should minimize the amount of han- dling time required and reduce or eliminate contact between handler and animal. b. One should never work alone. A second person, knowl- edgeable in capture and handling techniques and emer- gency measures, should be present at all times. ' c. Prior consultation with workers experienced with these species, as well as a review of the relevant literature, is of particular importance since much of the information on han- dlingdangerous species has not been published, but is sim- ply passed from one investigator to another. Prolonged distressful restraint should be avoided. In some cases, utilization of general anesthesia for restraint in the field may be advisable. If so, the anesthetic chosen should be a low risk compound that permits rapid return to normal physiological and behavioral status, and the anima! must be kept under observation until appropriate recovery oc- curs. The relatively unpredictable response of some poikil- otherms to immobilants or anesthetics under field condi- tions may contraindicate field use of these chemicals under certain conditions. Chemical Restraint Many chemicals used for restraint or immobilization of fishes are controlled by the Federal Bureau of Narcotics and Dangerous Drugs/Drug Enforcement Administration (DEA). A DEA permit is required for purchase or use of these chemicals. Extensive information on these substances and their use is available (22,23), and permit application pro- cedures are available from regional DEA offices. Investi- gators should choose the chemical for immobilization with consideration of the impacts of that chemical on the target organism. The potent drugs available for wildlife immobilization when properly used are, with the exception of succinyl- choline, safe for target animals but can be extremely dan- gerous if accidentally administered to humans. The degree of danger varies according to the drug, and users must be aware of the appropriate action to take in the event of ac- cident (9). 3. Animal Marking Fish marking, by a variety of techniques, provides one of the most important methods of analyzing fish move- ments, abundance, and population dynamics (cf. 24). It is basic to all field studies. Important considerations in choos- ing amarking technique are its effect on behavior, physi- ology and survival of the target species or a close relative. Investigators must consider the nature and duration of re- straint, the amount of tissue affected, whether distress is momentary or prolonged, whether the animal, after mark- ing, will be at greater than normal risk, whether the animal's desirability as a mate is reduced, and whether the risk of infection or abscess formation is minimal. Careful testing of markers on preserved or captive animals before use on wild animals may reveal potential problems and is recom- mended. Marking techniques for fishes have been exten- sively reviewed (25) and are summarized below. Fin-clipping is relatively easy, may have minimal impact on survival and social structure of the marked fish, and is a recommended procedure for many studies. Fins used for clipping or removal would depend upon the species se- lected, i.e., clipping of the anal fin of poeciliid males would be inappropriate, but removal of the adipose fin of a salmonid would have negligible impact. The importance of fins to the survival and well-being of fishes varies so widely that specific guidelines are not possible. Marking techniques involving tissue removal or modifi- cation (branding, etc.) should be preceded by local anes- thetic (aerosols containing benzocaine, such as Cetacaine, may be applied) and followed by the application of topical antiseptic. Chilling of fishes prior to marking maybe ef- fective for immobilization. Electrocauterization of a number, letter, or pattern on the skin, in which deep layers of skin are cauterized to prevent regeneration, provides a marking system that, if performed properly, heals rapidly and seldom becomes infected. Brand marks typically, however, are not visible in captive fishes after a few months. Freeze branding is often the preferred branding technique. Tattooing and acrylic paint injections have been used with success on fishes. Two potential problems that must be resolved prior to marking are: (1) the selection of a dye which will be visible against the pigmentation of the skin, and (2) the loss of legibility due to diffusion or ultraviolet degradation of the dye. Tagging is perhaps the most widely used and best in- vestigated means of fish marking. Several logical constraints should be considered in planning any tagging program. Tags that cause projections from the body could produce physical impairment and enhance the risk of entanglement in underwater vegetation. Brightly colored tags may com- promise afish's camouflage. The size, shape, and place- ment of tags should permit normal behavior of the animal to the greatest extent possible. Radiotelemetry Radiotelemetry is a specialized form of animal marking, and the same general procedures apply. Underwater telem- etry, however, is primarily limited to acoustic rather than radio frequency transmission. Radio transmission is only practical in freshwater and at relatively shallow depths. Radio transmission is regulated by the Federal Communi- cations Commission, and investigators should inquire about availability of frequencies they plan to use. General telem- etry techniques are summarized by Mackay (2fi), Amlaner and MacDonald (2~, and Stasko and Pincock (28). Many fishes are unsuitable for radiotelemetricstudles be- cause of their small size and habit of living in confined spaces. Component miniaturization will undoubtedly fa- cilitate the future use of radiotelemetry in studies of small 20 . Fisheries, Vol. 13, No. 2