Year	Number
1971	11500
1972	19700
1973	23700
1974	25600
1975	32600
1976	33700
1977	42300
1978	50200
1979	53900
1980	45500
1981	60800
1982	43800
1983	34500
1984	55000
1985	32400
1986	52400
1987	17000
1988	0
1989	0
1990	0
1991	0