Year	Number
1970	30516
1971	30942
1972	28231
1973	27944
1974	23835
1975	35826
1976	42145
1977	32278
1978	33136
1979	33128
1980	39540
1981	36071
1982	28612
1983	27649
1984	28817
1985	28706
1986	29053
1987	18792
1988	21866
1989	16249
1990	24173
1991	30463
1992	31278
1993	33926
1994	33082
1995	31364
1996	30950
1997	30978
1998	28285
1999	26063
2000	24857
2001	27533
2002	34855
2003	34765
2004	28183
2005	30545
2006	32286
2007	31991
2008	30316
2009	33343
2010	32795
2011	32019
2012	33733
2013	36422
2014	37942
2015	31757
2016	29285
2017	31104
2018	33669