Oviduct Insertion of Radio Transmitters as a Means of Locating Northern Pike Spawning Habitat

Abstract

I inserted radio transmitters into the oviducts of northern pike Esox lucius in an attempt to find their spawning grounds. Oviduct insertion of miniature radio transmitters was quick and easy. I hoped that transmitters would be expelled with the eggs to aid in identifying critical habitat used for egg deposition. Ten transmitters were implanted in the egg masses of female northern pike that were staging for spawning. Four of the transmitters were expelled during the spawning period, two in emergent shoreline vegetation and two in submerged vegetation. Northern pike that retained transmitters were smaller than fish that expelled them, indicating that expulsion was influenced by the size of the transmitter in relation to the fish's size. Although transmitters were not expelled by all study fish, advances in miniaturization and refinements in transmitter shape hold promise for future application of this technique.