The Japanese Eel Does Not Climb Back up

Tuesday, August 19, 2014: 10:50 AM
206B (Centre des congrès de Québec // Québec City Convention Centre)
Wann-Nian Tzeng , Department of Environmental Biology & Fisheries Science, National Taiwan Ocean University, Taipei, Taiwan
Taiwan is the first station of Japanese eel Anguilla japonica recruitment to the eastern Asian countries, which provides the advantage in monitoring the recruitment level of the eel. The long-term catch data of the glass eel from Taiwan in relation to the number of sunspot during the period from 1972-2014 were used to monitor the population status of Japanese eel by trend analysis, autocorrelation and cross- correlation. Results indicated that the recruitment of glass eel exponentially decreased [Catch = a *exp(b*Year), b = -0.03, R2 = 0.12 and p = 0.014 ], with a 11-year cyclic change (p = 0.0204). The maximal number of sunspot is well-known to occur every 11.2 year. The glass eel catch was found positively cross-correlated with the number of sunspot at alag of -1, 0 and 1 year, respectively ( p = 0.0268, 0.006 and 0.01). The peak catches of glass eel corresponding to the maximal sunspot decreased from 40 tons in 1979, through 31.3 tons (1990), 18.3 tons (2001), and to 6.7 tons in 2014. The decrease in peak catch implies that the Japanese eel population is still in the status of slippery slope.