Table 2. Snail distribution in the monitoring sites of the Yangtze River in Hunan section from 2003 to 2015.

Year	Bottomlands outside the embankment of Yangtze River (7 sites)						Polder ditches inside the protective embankment of Yangtze River (7 sites)						Bottomlands on diversion channels (5 sites)						Overall (12 sites)
	A	B	C	D	E	F	A	B	C	D	E	F	A	B	C	D	E	F	A	B	C	D	E	F
2003	308.6	7710	26.36	0.9000	1.31	0.0145	18.3	3894	8.17	0.3246	0	0	189.4	3571	48.39	2.8617	1.82	0.0218	516.3	15175	26.87	1.2140	1.09	0.0125
2004	869.0	9768	21.46	0.4486	1.48	0.0150	23.7	4730	9.43	0.4693	0.04	0.0004	411.9	2720	33.79	0.7643	0.07	0.0011	1304.6	17218	20.10	0.5042	0.87	0.0088
2005	740.6	18542	8.74	0.1619	0.44	0.0044	21.7	4928	10.78	0.2121	0.12	0.0012	389.4	8809	19.13	0.5293	0.23	0.0023	1151.7	32279	11.88	0.2698	0.33	0.0033
2006	742.6	18604	9.61	0.1958	0.78	0.0084	19.7	4360	11.65	0.2222	0	0	379.4	8749	31.43	0.8755	0.16	0.0032	1141.6	31713	15.91	0.3869	0.50	0.0058
2007	640.0	16095	14.10	0.3420	0.14	0.0014	20.9	5462	5.58	0.0639	0	0	371.9	8114	21.00	0.4275	0.01	0.0001	1032.8	29671	14.42	0.3142	0.08	0.0008
2008	679.0	17100	10.17	0.2522	0.06	0.0008	23.1	7322	5.41	0.0593	0	0	311.9	6398	17.36	0.3448	0.03	0.0003	1014.0	30820	10.53	0.2256	0.04	0.0005
2009	769.0	19380	10.61	0.2389	0.01	0.0002	22.6	7321	1.58	0.0228	0	0	367.4	6673	19.65	0.4009	0.12	0.0015	1159.0	33374	10.44	0.2239	0.03	0.0004
2010	909.0	22844	12.40	0.2481	0.07	0.0007	23.1	7497	1.28	0.0191	0	0	387.4	8494	16.11	0.3397	0.04	0.0004	1319.5	38835	11.06	0.2239	0.05	0.0005
2011	909.0	22802	10.98	0.2237	0.00	0	19.9	7014	0.09	0.0010	0	0	321.5	8275	13.00	0.2620	0	0	1250.4	38091	9.41	0.1910	0	0
2012	339.8	7570	8.35	0.1219	0	0	17.9	13280	0	0	0	0	156.0	4091	12.71	0.2095	0	0	513.7	24941	4.62	0.0714	0	0
2013	310.0	7750	7.45	0.0990	0	0	24.9	6300	0	0	0	0	156.0	4031	13.79	0.2322	0	0	490.9	18081	6.27	0.0942	0	0
2014	310.0	7750	6.72	0.0901	0	0	46.0	6300	0	0	0	0	156.0	4031	9.48	0.1253	0	0	512.0	18081	4.99	0.0665	0	0
2015	310.0	7750	6.25	0.0841	0	0	46.0	6300	0	0	0	0	156.0	4031	9.18	0.1459	0	0	512.0	18081	4.72	0.0686	0	0
G	-	-	11.30	17.92	-	-	-	-	-	-	-	-	-	-	12.94	21.97	-	-	-	-	13.49	21.29	-	-
H	-	-	76.29	90.66	100	100	-	-	100	100	100	100	-	-	81.03	94.90	100	100	-	-	82.43	94.35	100	100

Note: A, monitored area (hm²); B, number of frames (0.11 m²); C, occurrence rate of frames with living snails (%); D, mean density of living snails (snails/ 0.11m²); E, occurrence rate of frames with infected snails (%); F, mean density of infected snails (snails/ 0.11m²); G, yearly reduction rate (%); H, total reduction (%).