This paper describes a novel routing mechanism for a network of highly mobile sensor nodes that routes data over dynamically changing topologies, using only information from nearest neighbours. The preferred forwarding directions of mobile sensor nodes are modelled as vectors, and a scalar trigger is used to determine data forwarding. Simulations have demonstrated that this technique operates successfully in sparse networks, where node movements are unpredictable, and data generation by nodes is nonuniform. The application scenario is a self-configuring network of mobile nodes, floating in the sea, that is tracking the movements of a shoal of fish. The requirements of the technique in terms of memory are minimal, with very few parameters and very little code being needed, as is appropriate for the lowpowered microprocessors envisaged.