The exploration of the seabed is of strategic importance for various applications, including military, scientific, and commercial purposes. However, underwater communication is limited by the poor propagation of radio waves and the low data rates of acoustic communication. This leads to the topic of retrieving large amounts of data over a long range. To address this challenge, the concept of data muling-which involves the use of mobile agents to physically carry data from underwater nodes or Autonomous Underwater Vehicles (AUVs)-seems to be an interesting solution. In this paper, we focus on the scenario of a fixed data source and sink point separated by a large distance. We propose a relay system that uses mobile agents assigned to specific areas. Each agent can communicate with neighbouring agents and travel within its assigned area to transport data and act as a moving relay. We evaluate the performance of this data muling solution using three metrics: equivalent throughput, latency, and energy. We compare our solution with a scenario inspired by previous work and show that our relay system can extend the range and data rate of underwater communication. The paper provides a detailed system model and presents experimental results to implement muling along testing scenarios.