**Acknowledgements**

 Funding for this work was provided by Kenya Marine and Fisheries Research Institute, KMFRI) and RAF 7008, 7009, 7015 Project and CRP-K41016 projects jointly funded by International Atomic Energy Agency, IAEA and Government of Kenya. We are greatly indebted to the Directors of these Institutions for supporting this work. We also appreciate the efforts of KMFRI staff that assisted in field samples collection and analysis in one way or the other.
