TAG ATTACHMENT METHODS

ERDC TN-DOER-E18

February 2005

Properly transferring fish from the net or trawl to the tagging station is also important in reducing

stress. If fish are to be transported from the catch site to a tagging location, water-filled plastic

bags or suitable containers will minimize injury to the fish. Whenever possible exposure of the

fish to air should be avoided. Two studies indicated that the use of in-water transfers reduced 96-

hour mortality from 82 percent to 15 percent in American shad (Murai et al. 1979) and reduced

long-term mortality from 52 percent to 15 percent in Atlantic salmon (Flagg and Harrell 1990).

During tagging, the use of tagging cradles, troughs, or holders to keep fish immobilized is

recommended. If anesthesia is used, type and exposure dosage will vary between species, as well

as recovery times. In many situations newly tagged fish should be monitored in a holding tank

until there is evidence of full recovery (e.g., resumption of normal swimming behavior and

respiration). When fish are kept in a holding tank, water quality, temperature, and duration held

must be monitored.

TAG ATTACHMENT METHODS: The method of tag attachment (external or internal) is

another consideration when planning a telemetry study. External attachment typically involves

the use of barb darts, pins or sutures, whereas internal tagging requires the insertion of the tag

through the esophagus into the stomach, or the surgical implantation in muscle or the abdominal

cavity. Both attachment methods have advantages and disadvantages, which depend on the type

of transmitter selected, the species and behavioral characteristics of the fish species to be studied,

and the type of data required from the research.

External Tagging. External attachment typically involves suturing the tag directly to the body

of the fish, or using fine wires or nylon cords, which pass through the body musculature, and are

anchored by plastic discs or plates on the opposing side of the fish. The most common position

for external attachment is along the base of the dorsal fin as described by Gray and Haynes

(1979), who used this method to attach radio tags to salmonids. Other methods of external

tagging include single-point attachments, which have been widely used with sharks and tethered

tags that require a strong permanent anchor point. For fish species that are not easily captured,

tethered tags typically consist of a dart with an arrowhead that resists extraction from muscle

tissues. Detailed descriptions and variations to external tagging procedures are described in

Thorsteinsson (2002). For some species, like flatfishes (e.g., plaice, Pleuronectes platessa)

external tagging may be the only option due to a tightly coiled gut and small peritoneum,

eliminating internal tagging as an option. External tagging may also be necessary with species

that may be difficult to bring onboard, such as sharks, and large pelagic fish (e.g., tuna, marlin).

There are both advantages and disadvantages to external tagging. Most notably external tagging

is usually simpler and can be performed much faster than internal tagging methods. In addition,

it can be done without surgery or anesthesia. The primary disadvantage with external tagging

may be adverse effects on behavior and physiology of swimming animals caused by

hydrodynamic drag. Chafing, abrasion, and ulcerated wounds may also be problematic, primarily

with tags that have extended battery life, most notably archival tags.

Internal Tagging. Internal tagging can be accomplished through insertion of a radio or

acoustic tag into the stomach, oviduct, or through intra-peritoneal surgery. Stomach insertion

may be voluntary or forced ingestion. In voluntary ingestion, acoustic transmitters are embedded

in bait and ingested by the species of interest. This is usually confirmed by viewing the bait with