Effects of environmental variables on recruitment of Anguilla japonica glass eels in the Yangtze Estuary, China

The recruitment pattern of Anguilla japonica glass eels into the Yangtze Estuary, China was studied during five successive migration seasons (2012-2016). The variation in daily catch was analyzed in relation to environmental factors that affect inshore migration. Two large migration waves of glass eels were observed in each recruitment season: one in the winter (January/February) and the other in the spring (March/April). A generalized additive model indicated that daily changes in glass eel catch were partially affected by local water temperature and tidal range. Water temperature seemed to have a threshold effect in winter, and there were optimal temperature ranges of 6-8 degrees C and approximately 10.5-12.0 degrees C associated with different recruitment waves to the Yangtze Estuary. The influence of tides was complex, with an overall positive correlation. The annual glass eel catch fluctuated greatly, but generally did not show a significant downward trend. To achieve sustainable use of glass eels, it is proposed that relevant management and conservation activities be reinforced.