Refining Crossbow Deployment Techniques of Suction Cup Attached Tags for Cetacean Field Studies

Abstract

Remote deployment of non-invasive suction cup attached tags on free ranging cetaceans continues to be problematic for researchers. In an effort to increase the chances of success, the factors affecting the velocity, range, and drop of crossbow deployed tags were examined. The exit velocity of a tag is primarily governed by the tag's weight and can be predicted for a particular bow. Higher exit velocities correspond to a smaller drop for a given range. Compound crossbows are able to achieve higher exit velocities and hence longer ranges for a given tag weight than simple re-curve bows of the same draw weight. Varying the position of the tag's center of mass has a greater effect on the drop of the tag than arrow length, shaft material, diameter or wall thickness. Raising the height of the center of mass increases the induced departure angle of the tag, giving the tag a vertical velocity component. This upward velocity helps to counteract negative gravitational forces and extends the range of the tag. Thus, researchers could potentially manipulate various parameters of their arrow/tag system to increase the range of their tag and their chances of successfully tagging cetaceans in the field.