Abstract
BackgroundThe flathead grey mullet Mugil cephalus has the widest distribution among mugilid species. Recent studies based on mitochondrial DNA sequences showed that the species comprises at least 14 different groups, three of which occur in the northwest Pacific. We analyzed the otolith microchemistry of M. cephalus at several locations in Korea to improve understanding of migration pattern and population origin.ResultsWe collected 123 sagittal otoliths from seven locations and determined their concentrations of eight elements (7Li, 24Mg, 55Mn, 57Fe, 60Ni, 63Cu, 88Sr, and 138Ba) using laser ablation inductively coupled plasma mass spectrometry. Mean otolith elemental ratios differed significantly among the locations. The Sr:Ca, Fe:Ca, and Ba:Ca ratios were significantly higher than others, and useful chemical signatures for investigating the habitat use of M. cephalus populations. We identified five diverse and complicated migration patterns using the otolith data that we collected: estuarine resident (type I), freshwater migrant (type II), estuarine migrant (type III), seawater resident (type IV), and seawater migrant (type V). A canonical discriminant analysis plot revealed separation of two groups (type II in the Yellow Sea vs. other types in remaining locations). Two locations on Jeju Island, despite their close proximity, had fish with quite different migration patterns, corroborating previous molecular studies that distinguished two groups of fishes.ConclusionWe successfully showed that the migration patterns of the Korean mullet varied by location. Only fish from the western sector of Jeju had a unique migration pattern, which is likely confined population in this area. Among the eight otolith elements measured, the Sr:Ca ratio was found to be the best indicator of migration pattern and population origin.
Highlights
The flathead grey mullet Mugil cephalus has the widest distribution among mugilid species
We found that otolith Sr:Ca, Ba:Ca, and Fe:Ca ratios are useful natural markers for distinguishing among M. cephalus specimens from diverse environments
The influence of environmental factors on migratory patterns Our study provided the first evidence for the five migratory patterns in Korean M. cephalus
Summary
The flathead grey mullet Mugil cephalus has the widest distribution among mugilid species. We analyzed the otolith microchemistry of M. cephalus at several locations in Korea to improve understanding of migration pattern and population origin. Otolith microchemistry has recently provided increasingly important signals for reconstructing and tracking the environmental histories of fish. The deposition of otolith carbonate may be regulated by a range of factors, such as age, physiology, environmental stress, food availability, ambient temperature, diurnal and seasonal cycles, and the movement of individual fishes (Radtke and Shafer 1992). Because of these effects, otolith microchemistry can provide important data on migratory behavior and environmental factors. The level of gene flow can be discerned when these data are combined with information on neutral genetic makers
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