Atmospheric depression as the final trigger for the seaward migration of the Japanese eel Anguilla japonica

Abstract

Despite the absence of rainfall or of any rise in river water level, the seaward migration of Japanese silver eels frequently occurs after the passage of a 'dry depression', suggesting that the migratory behavior of the eels is influenced by the atmospheric depression rather than by rainfall or elevated water level, as is usually thought. Our analyses showed that seaward migration of silver eels takes place mainly during the new moon in autumn to winter as water temperature decreases, suggesting the possibility that their migratory behavior depends on at least 3 independent environmental factors: water temperature, lunar phase and the passage of an atmospheric depression. However, water temperature and lunar phase were insufficient to cause the eels to start their migration. The passage of a depression was required as the final event to begin the seaward migration. These findings strongly suggest that the passage of a depression may be the only trigger that begins the seaward migration of silver eels.

Movement patterns of barramundi Lates calcarifer, inferred from 87Sr/86Sr and Sr/Ca ratios in otoliths, indicate non-participation in spawning

“…Rather, it appears that the proximate cues for migration of barramundi from freshwater are complex (McDowall 1988) or are linked to rare climatic events. Rainfall, temperature, moon phase, olfaction and fish condition have all been identified as important cues for migration of many freshwater and marine fishes (McDowall 1988, Naslund et al 1993, Boubee et al 2001, Hodgson & Quinn 2002, Okamura et al 2002. Similar cues are probably involved in barramundi migration.…”

Seasonal variation in the migratory history of the Japanese eel Anguilla japonica in Mikawa Bay, Japan

“…However, there is a general lack of knowledge about the age, growth, maturation, and migration of the silver eels that leave their juvenile habitats in East Asia and migrate towards the offshore spawning area. Some recent studies have been done on the environmental triggers of migration, ovarian morphology, and Sr:Ca ratios of silver eels in Mikawa Bay, Japan (Okamura et al 2002, Tzeng et al 2003a, Utoh et al 2004), on the occurrence of silver eels in the East China Sea (Sasai et al 2001), and the growth rates (Tzeng et al 2003b) and morphology (Han et al 2003) of silver eels. However, basic studies on many aspects of the ecology and reproductive migration of the Japanese eel are still lacking compared to other anguillid species such as the Atlantic eels.…”

“…Okamura et al (2002) reported that the fine-scale timing of migration of the silver eels captured in set nets in Mikawa Bay in the autumn appeared to be related to low pressure systems moving over Japan. The ovarian morphology of these migrating silver eels has also been documented over a 4 yr period (Utoh et al 2004).…”

Inhibitory Effects of Testosterone on Downstream Migratory Behavior in Masu Salmon, Oncorhynchus masou

“…They then drastically switch their resident life in continental waters to a migratory life in the ocean. Many studies have suggested that downstream migration of eels is triggered by various environmental factors, such as lunar cycle (Lowe, 1952), river flow (Haro, 2003), or atmospheric depression (Okamura et al, 2002). Although there is information on environmental conditions that cause downstream migration in eels (Haro, 2003;Bruijs and Durif, 2009), the endocrinological mechanisms involved in eel downstream migration are largely unknown (Han et al, 2003a, b).…”