Year	Number
1970	766
1971	871
1972	1019
1973	1026
1974	1111
1975	1312
1976	1463
1977	1409
1978	1057
1979	826
1980	734
1981	640
1982	319
1983	331
1984	277
1985	292
1986	256
1987	0
1988	0
1989	0
1990	0
1991	0
1992	0
1993	0
1994	0
1995	0
1996	0
1997	0