Wireless sensor network is commonly used to monitor certain region and to collect data for several applications, Normally, in wireless sensor network, data are routed in a multi-hop fashion towards a static sink. In this scenario, nodes closer to the sink become heavily involved in packet forwarding and their battery power is exhausted quickly. In this paper, an Infrastructure based Data Gathering Protocol (IDGP) and a Distributed Data Gathering Protocol (DDGP) are proposed to plan the data gathering path for a mobile sink. A k-hop, relay mechanism is introduced to limit the number of hops for routing data to a mobile sink. In Order to increase the efficiency of the data gathering, a cooperative environment among the sensor nodes and the mobile robot is proposed to formulate the data gathering path. Simulation results show that our data gathering protocols enable the nodes to transmit data with least number of hops and simultaneously reduce the data gathering path length traced by the mobile sink. (C) 2009 Elsevier B.V. All rights reserved.