Operating at constant depth, various embodiments are provided equipped with automatic depth-control mechanisms in dynamic devices such as lures and carriers that acquire and maintain a constant target depth when pulled through a medium such as water. The depth-control mechanism incorporates a mechanical pressure measurement of depth using a bladder with changing dimensionality and mechanical coupling to a variable angle dive plane. The measured pressure is compared with the target depth pressure causing the dive plane angle to adjust and converge to an adjustable target depth with forward motion due to retrieval or trolling. The dive plane extension is optionally a variable angle lip or bill protruding from the front of the lure or a pectoral fin-like configuration. Multi-purpose carriers are provided that can perform various underwater sensing and measuring tasks. Included are systems and methods for using a lure or platform equipped with a depth-controlling device.
