Trap nets are designed for live release, making them an invaluable tool in measuring biological characteristics of fish species that inhabit the littoral zone. Trap nets are set perpendicular to shore and capture fish as they move along the ‘leader’ into the ‘head’.
Trap nets consist of two main parts: the leader and the head. The leader is set closest to shore and impedes the fishes’ path. The lead will then “lead” the fish into the head. The head funnels into the crib, once in the crib the fish cannot escape. The crib is the section of the trap net where fish await sampling and release.
Trap nets allow for the biological sampling of fish including: catch, fish length, weight, girth, sex, maturity, and age samples (scales, pectoral/ pelvic rays, pectoral/dorsal spines). Data collection allows for comparisons, and is valuable in determining the health of lakes, fish population, and to establish a base line of fish growth and characteristics.
One issue affecting the function of trap nets is selectivity, as the traps may not allow for the capture of fish less than 90 mm in length and extremely large fish (that cannot swim into the crib). Standardized methods are practiced to deter any bias in studies such as an End of Spring Trap Netting (ESTN).
Standard methods include: size of nets, set times, minimum water depth, minimum net separation, orientation from shore, water temperature, and number of sets per lake. Also, randomly selected net locations are determined by a random sampling grid and are selected before heading out into the field. During random selection, a chosen location cannot be excluded without valid reason (shallow water or obstructing boating lanes). During an ESTN study, a net cannot be set within 500 meters of where other trap nets were in the previous 48 hours.
Go To : Setting a Trap Net