Dispersal of yellow phase Japanese eels Anguilla japonica after recruitment in the Kojima Bay-Asahi River system, Japan

Abstract

The density, size and age distribution were investigated for 233 eels, Anguilla japonica, sampled in fresh and brackish water areas of the Kojima BayAsahi River system, Okayama, Japan, to evaluate the possible patterns of dispersal of eels that recruit to this area. Migratory histories of 183 eels were categorized into 5 types depending on the Sr and Ca concentrations in their otoliths: (1) brackish water residents (74 fish, 40.4%), which settled in saline water and remained until capture; (2) freshwater residents (46 fish, 25.1%), which settled in freshwater and remained until capture; (3) upstream shifters (3 fish, 1.6%), which settled in saline water and moved upstream into freshwater; (4) downstream shifters (53 fish, 29.0%), which settled in freshwater and moved downstream into saline water; (5) multiple habitat shifters (7 fish, 3.8%), which shifted their habitats between freshwater and saline water more than twice. For eels captured in the brackish water area, fish density decreased with distance in the downstream direction, while the size and age of eels increased. For eels captured in the freshwater area, size and age were greater than those in the upper-most brackish site. These observations suggest that eels in this system initially accumulate in the lower reaches of the river and then disperse in both upstream and downstream directions following their growth.

Growth differences of Japanese eels Anguilla japonica between fresh and brackish water habitats in relation to annual food consumption in the Kojima Bay‐Asahi River system, Japan

“…For another temperate species, Japanese eel Anguilla japonica, a similar tendency has been reported, even though the differences shown in the studies were not statistically significant or were limited to a certain growth stage (Kotake et al 2005;Yokouchi et al 2008). However, a recent study has indicated the likelihood that Japanese eels have faster growth in saline water than in fresh water within the Kojima Bay-Asahi River system, where this study was conducted (Kaifu et al 2010). Faster growth enhances many fitness-related aspects of fishes, including a shorter amount of time to reach the adult stage and reproductive maturation and a decreased risk of predation (Hutchings 2006;Edeline 2007).…”

“…Anguillid species use both fresh and saline water habitats in their growth phase. A considerable number of studies found consistent divergences of life history patterns in five species of temperate eels that include river, estuarine and marine residents, and multihabitat users that move from one habitat to another once or more during their growth phase (Jessop et al 2002;Tzeng et al 2002;Arai et al 2003;Daverat et al 2005;Kotake et al 2005;Daverat & Tomas 2006;Shiao et al 2006;Kaifu et al 2010). A considerable number of studies found consistent divergences of life history patterns in five species of temperate eels that include river, estuarine and marine residents, and multihabitat users that move from one habitat to another once or more during their growth phase (Jessop et al 2002;Tzeng et al 2002;Arai et al 2003;Daverat et al 2005;Kotake et al 2005;Daverat & Tomas 2006;Shiao et al 2006;Kaifu et al 2010).…”

Synergistic patterns of threat and the challenges facing global anguillid eel conservation

“…Most glass eels enter fresh water, migrating to the upper limits of tidal flow which in the old, flat continents occupied by A. anguilla and A. rostrata represents exclusively fresh water but for A. japonica can be either fresh or brackish water as mountains and the ocean stand adjacent to one another (Kaifu et al, 2010). Once freshwater is detected, this can trigger a range of behaviours: individuals either continue up-river, return to brackish water, or adopt a nomadic life-history where they use a range of saline habitats (Daverat et al, 2006;Cairns et al, 2009).…”

Modeling individual growth trajectories of the female European eel in relation to temperature and habitat-use history in the Gironde River, France

“…In addition, some eels change habitats during their growth phase (e.g. Tsukamoto et al 1998, Tsukamoto & Arai 2001, Jessop et al 2004, Daverat & Tomas 2006, Kaifu et al 2010, Yokouchi et al 2012. Studies on growth of anguillid eels showed that eels living in brackish habitats had a higher growth rate than eels living in freshwater habitats (e.g.…”