Year	Number
1970	11200
1971	11200
1972	11000
1973	11300
1974	11200
1975	11300
1976	12700
1977	12100
1978	11600
1979	11800
1980	12000
1981	12200
1982	12600
1983	13100
1984	12600
1985	12300
1986	12300
1987	12500
1988	11000
1989	10700
1990	10400
1991	11300
1992	10800
1993	10900
1994	12000
1995	12000
1996	7100
1997	10000
1998	10100
1999	7300
2000	7445
2001	7492
2002	7474
2003	7990
2004	8342
2005	8505
2006	8524
2007	9057
2008	5654
2009	5423
2010	7516.15985130111
2011	3002
2012	1553
2013	0
2015	2765
2016	2305