Year	Number
1960	0
1965	0
1970	0
1975	0
1976	0
1977	0
1978	0
1979	0
1980	0
1981	0
1982	0
1983	0
1984	0
1985	0
1986	0
1987	0
1988	0
1989	0
1990	0
1991	0
1992	0
1993	0
1994	0
1995	0
1996	0
1997	0
1998	0
1999	0
2000	0
2001	0
2002	0
2003	0
2004	500
2005	1300
2006	1600
2007	1800
2009	1000
2010	1600
2011	2130
2012	2800
2013	3400
2014	3800
2015	6600
2016	7600
2017	8000
2018	8500
2019	9000
2020	9000
2021	9000