\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**Ref** & **Contributions** & **Limitations** \\ \hline
[18] & -The role of the IoUT in preserving natural water resources is discussed. & -The integration of the IoUT with other advanced technologies are not explored. \\  & -The differences of the IoUT and IoT are highlighted. & -The security aspects of the IoUT applications are not explored. \\  & -The architecture and applications of the IoUT are presented. & -More emphasis is given to underwater communication and network protocols and BMD data handling. \\  & -The traditional challenges of using BMD processing is explored. & -Security and privacy aspects of handling BMD are not considered. \\  & -The use of ML in handling BMD is presented. & -BMD are not considered. \\  & -The potential scope of future research in the IoUT and BMD is highlighted. \\ \hline
[21] & -Underwater Network Management Systems (U-NMS) using acoustic communication and the IoUT are discussed. & -The viability of the prototype model in a real-world setup is not justified. \\  & -A prototype implementation of a U-NMS in a library environment is presented. & -Risk mitigation activities include the use of network protocols. \\ \hline
[23] & -Emphasizes the security threats related to UWSNs in IoUT implementations. & -Risk mitigation activities include the use of network protocols. \\  & -Alternative advanced approaches such as blockchain are not explored. \\ \hline
[24] & -Presents a review of existing research relevant to signal processing and routing for developing efficient IoUT systems. & -The MAC protocol, QoS metrics, and related performance issues are discussed. \\  & -The challenges mostly emphasize exploring various forms of network attacks and possible solutions along with research testbeds. & -Solutions focus on secured transmission of data and not on the storage aspect of the same. \\ \hline
[25] & -The use of WSNs and the IoUT in developing underwater vehicles (ROUVs), untethered Autonomous Underwater Vehicles (AUVs), Unmanned Autonomous Surface Vehicles (USVs/ASVs), and various other smart underwater technologies are explored. & -The scope of review includes only the African region while missing the security aspect. \\  & -Different UWSN-based IoUT implementations in the African region are analyzed. & -The role of a specific technology and its related contributions are not focused on, making the scope generic. \\ \hline
[16] & -Different network frameworks used in IoUT applications are discussed. & -The role of a specific technology and its related contributions are not focused on, making the scope generic. \\  & -The use of edge computing, data analytics, Optical Wireless Communications (OWCs), machine learning, and Intelligent Reflecting Surfaces (IRSs) in the IoUT is presented. & -Primarily emphasizes the target detection and tracking scheme. \\ \hline
[26] & -A survey on various unmanned water vehicles is presented. & -Primarily emphasizes the target detection and tracking scheme. \\  & -The use of cognitive acoustic networks, fog computing, the IoUT, and next-generation underwater networks is discussed. & -Security and privacy aspects of the collected data through the IoUT are not considered. \\ \hline
[27] & -Distinct forms of IoUT attacks in the form of black holes, routing, and Sybil are discussed. & -Focused primarily on IoUT network attacks and their prevention. -Security and privacy aspects of the collected data through the IoUT are not included. \\ \hline The present survey & -The first-of-its-kind survey on the application of blockchain for the IoUT. & - \\  & -Applications of blockchain in the IoUT are discussed. & -Challenges and future prospects of the integration of blockchain with the IoUT are highlighted. \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison with existing surveys.