FISH HANDLING

ERDC TN-DOER-E18

February 2005

ping to each buoy. Depending on environmental conditions, position accuracy is to within 1 or

2 meters. VRAP software gives the user the ability to process the true latitude and longitude

position of each tag. If standard acoustic pingers are used for tracking, VRAP software will

calculate the x and y position of the transmitter. If three-dimensional (3D) data are required, the z

(depth) coordinate can be determined in one or two ways: use of a depth transmitter, or manual

entering of the depth information if the animal is at a relatively constant water depth.

Lotek Wireless also employs a version of the MAP system to detect acoustically tagged fishes in

high noise environments. The MAP-600 is a multi-port receiver of tethered hydrophones.

Hydrophones are hard-wired to the receiver by a 600-m cable. Each receiver can support up to

eight paired hydrophones. Typically six or more hydrophones are deployed for 3D positioning at

sub-meter precision. This system has a tag identification capacity of tens of thousands on a

single frequency, and the ability to simultaneously track hundreds of transmitters with high

broadcast rates. Real-time data can be recorded directly to a PC or stored on an industrial Type 1

solid-state flash card.

All three systems are capable of giving real-time positioning data in high noise environments.

High-resolution tracking systems should be considered when data requirements dictate precise

movements of fishes around dams, hydroelectric facilities, and reservoirs. Costs are relatively

high, setting a limit on feasible spatial coverage.

FISH HANDLING: A fundamental aspect of tagging is survival of the fish during and after the

tagging process. Fish species vary greatly in their ability to be handled. While some species can

endure a considerable degree of handling stress, others such as the American shad (Alosa

sapidissima) can show stress response and potential mortality correlated with handling effects.

Many factors must be given adequate consideration when assessing potential handling effects on

a given species. One of the most important is the method of capture (netting, trawling, electro-

fishing). Trawls may cause considerable injury to fish stemming from rocks and other debris

that may be collected during the trawl as well as injury resulting from the spines of other fish.

Whenever trawling is employed as a method of capture for tagging studies, towing times should

be minimized. Netting (e.g., gill netting, seining, pound netting, fyke netting) will typically be

less invasive than trawling, but success will depend on the type of netting deployed and time

intervals between "fishing" the nets. An example of potential effects of netting on tag fish can

be seen in a pilot study involving upstream preproductive migration of American shad. In this

study, fewer detections were made at spawning grounds in the James River, Virginia of tagged

American shad for individuals captured by gill nets when compared to haul seines (Olney et al.

2004). Gill netting therefore must be considered a relatively stressful option unless "gilled" fish

are promptly removed. Various types of fish traps and bag nets may be preferable ways of

catching fish for tagging, but are not always possible. Electro-fishing has been used to catch fish

for telemetry studies. Although long-term effects may be minimal if used properly, injury and

mortality can result if the voltage and type of electrodes used are not properly considered. Fish

species and size, and environmental conditions such as conductivity (electro-fishing not feasible

in saline waters), depth, temperature and substrate are also determinants of the viability of

electro-fishing.