The Migratory Environmental History of Freshwater Resident Flathead Mullet Mugil cephalus L. in the Tanshui River, Northern Taiwan

migratory environmental history of freshwater resident flathead mullet Mugil cephalus L. in the Tanshui River, northern Taiwan. Zoological Studies 49(4): 504-514. The diversity of the migratory environmental history of freshwater resident flathead mullet Mugil cephalus was examined by analyzing the otolith elemental composition of mullet (n = 31) collected in midstream of the Tanshui River, northern Taiwan by laser-ablation inductively coupled plasma mass spectrometry. The mullet averaged 300 ± 33 mm in fork length and 410 ± 141 g in body weight, and all were sexually immature at 1+ and 2+ yr old. Strontium (Sr)/calcium (Ca) and barium (Ba)/Ca ratios in the otolith core indicated that the mullet in the river were from 2 different groups. Group 1 (18%) fish had higher Sr/Ca ratios and lower Ba/Ca ratios in the otolith core region. Group 2 fish (82%) were opposite to group 1, with higher Sr/Ca ratios and lower Ba/Ca ratios in the otolith core region, indicating that these mullet had resided in offshore waters in early life. Beyond the core region, the Sr/Ca and Ba/Ca ratios alternately varied, indicating that the mullet migrated between brackish and freshwater habitats after the juvenile stage. This study demonstrates that M. cephalus occupied diverse environments and migrated among marine, brackish, and freshwater habitats. More study is needed to determine whether the mullet in the Tanshui River of Taiwan is a local population and its relationship to the well-known offshore migratory population that migrates t