5:15 PM - 6:45 PM
[HTT16-P10] Otolith Sr isotopes can identify natal sites of migratory fish endemic to Lake Biwa
Keywords:Strontium stable isotope, Otolith, Natal homing, Migration, Carassius buergeri grandoculis, Lake Biwa
Carassius buergeri grandoculis in a migratory crucian carp endemic to Lake Biwa. This fish generally spawns in coastal flood plains, while it has also utilized rice paddies as alternative spawning habitat. After installation of modern irrigation system in which irrigation waters are pumped up from the lake basin but not from rivers, its population drastically declined due to physical barrier to channels connecting between the lake and spawning habitats. For the sake of biodiversity conservation, Shiga Prefecture implemented a nursery rice paddy project in 2006.
The Shiga Prefectural Fishery Experiment Station released larval crucian carps with chemically labeled otolith into the nursery rice paddy and revealed that the fish can perform natal homing at high spatial resolution. Our previous study revealed that strontium stable isotope ratio (87Sr/86Sr) of otolith core which was formed during the larval stage of adults was linearly correlated with that of environmental waters where the adults migrated for spawning. These results strongly suggest that the fish has the natal homing ability.
For a wild population of C. buergeri grandoculis, however, its migration ecology and spatial resolution at which it identifies and returns to its natal habitat has been poorly understood. Therefore, we would like to evaluate the spatial resolution of natal homing ability that wild C. buergeri grandoculis has, with stable isotope ratios of strontium. The previous study reported that there are strong correspondences of 87Sr/86Sr between juvenile otoliths and ambient waters within a watershed, showing the possibility that natal sites of spawning adults can be identified on the basis of their otolith core 87Sr/86Sr on the catchment scale. In this study, we aim to investigate the migration ecology of C. buergeri grandoculis and the spatial scale, especially on the habitat scale within the catchment, of its natal homing.
We conducted a field survey in a lake coastal district, Taduke, into which the nursery rice paddy was introduced. We collected juveniles and ambient waters in two drainage canals, A connected to nursery rice paddies and B connected to conventional rice paddies, which prevent fish from spawning migration. In parallel, we collected a variety of environmental samples within the catchment: irrigation waters and soils of nursery rice paddies, groundwaters, river and coastal lake waters. We measured 87Sr/86Sr for fish otoliths and environmental samples using TIMS in RIHN.
Environmental samples showed distinctly different isotope signatures among sample types within the catchment though some overlapped with each other. The 87Sr/86Sr values of drainage canal waters overlapped with those of lake waters rather than of river waters and did not differ between the two canals. These results corroborate that the canal waters were mostly derived from lake coastal waters via the modern pump-up irrigation. By contrast, irrigation waters of nursery rice paddies had lower 87Sr/86Sr than those of canal waters, suggesting the possibility that Sr derived from the paddy soils with low 87Sr/86Sr is mixed during the retention.
Juvenile otolith 87Sr/86Sr individually varied within the range of isotope values between the nursery rice paddy and canal waters. The juveniles collected from the canal A had significantly lower 87Sr/86Sr than that of ones from the canal B. This result suggests that some of juveniles collected from the canal A inhabited the nursery rice paddies and moved to the canal after the mid-summer drainage.
In the present study, we demonstrated that there are marked differences in isotope signatures of individual juveniles and environmental samples even within the catchment, depending on the hydrological processes of rice paddy irrigation. In conclusion, we could show the utility of otolith Sr isotope approach to identify natal sites of spawning adults in the wild fish population at the high spatial resolution.
The Shiga Prefectural Fishery Experiment Station released larval crucian carps with chemically labeled otolith into the nursery rice paddy and revealed that the fish can perform natal homing at high spatial resolution. Our previous study revealed that strontium stable isotope ratio (87Sr/86Sr) of otolith core which was formed during the larval stage of adults was linearly correlated with that of environmental waters where the adults migrated for spawning. These results strongly suggest that the fish has the natal homing ability.
For a wild population of C. buergeri grandoculis, however, its migration ecology and spatial resolution at which it identifies and returns to its natal habitat has been poorly understood. Therefore, we would like to evaluate the spatial resolution of natal homing ability that wild C. buergeri grandoculis has, with stable isotope ratios of strontium. The previous study reported that there are strong correspondences of 87Sr/86Sr between juvenile otoliths and ambient waters within a watershed, showing the possibility that natal sites of spawning adults can be identified on the basis of their otolith core 87Sr/86Sr on the catchment scale. In this study, we aim to investigate the migration ecology of C. buergeri grandoculis and the spatial scale, especially on the habitat scale within the catchment, of its natal homing.
We conducted a field survey in a lake coastal district, Taduke, into which the nursery rice paddy was introduced. We collected juveniles and ambient waters in two drainage canals, A connected to nursery rice paddies and B connected to conventional rice paddies, which prevent fish from spawning migration. In parallel, we collected a variety of environmental samples within the catchment: irrigation waters and soils of nursery rice paddies, groundwaters, river and coastal lake waters. We measured 87Sr/86Sr for fish otoliths and environmental samples using TIMS in RIHN.
Environmental samples showed distinctly different isotope signatures among sample types within the catchment though some overlapped with each other. The 87Sr/86Sr values of drainage canal waters overlapped with those of lake waters rather than of river waters and did not differ between the two canals. These results corroborate that the canal waters were mostly derived from lake coastal waters via the modern pump-up irrigation. By contrast, irrigation waters of nursery rice paddies had lower 87Sr/86Sr than those of canal waters, suggesting the possibility that Sr derived from the paddy soils with low 87Sr/86Sr is mixed during the retention.
Juvenile otolith 87Sr/86Sr individually varied within the range of isotope values between the nursery rice paddy and canal waters. The juveniles collected from the canal A had significantly lower 87Sr/86Sr than that of ones from the canal B. This result suggests that some of juveniles collected from the canal A inhabited the nursery rice paddies and moved to the canal after the mid-summer drainage.
In the present study, we demonstrated that there are marked differences in isotope signatures of individual juveniles and environmental samples even within the catchment, depending on the hydrological processes of rice paddy irrigation. In conclusion, we could show the utility of otolith Sr isotope approach to identify natal sites of spawning adults in the wild fish population at the high spatial resolution.