*Excludes Observations that spanned multiple years
| Pre 1970 | 210 |
|---|---|
| 1970 | 1 |
| 1971 | 2 |
| 1972 | 2 |
| 1973 | 7 |
| 1974 | 2 |
| 1975 | 2 |
| 1976 | 1 |
| 1977 | 61 |
| 1978 | 1 |
| 1979 | 2 |
| 1980 | 1 |
| 1981 | 1 |
| 1982 | 1 |
| 1983 | 6 |
| 1984 | 3 |
| 1985 | 369 |
| 1986 | 842 |
| 1987 | 5 |
| 1988 | 1 |
| 1989 | 54 |
| 1990 | 154 |
| 1991 | 13 |
| 1992 | 3 |
| 1993 | 15 |
| 1994 | 83 |
| 1995 | 70 |
| 1996 | 749 |
| 1997 | 110 |
| 1998 | 253 |
| 1999 | 835 |
| 2000 | 386 |
| 2001 | 909 |
| 2002 | 819 |
| 2003 | 2694 |
| 2004 | 2135 |
| 2005 | 922 |
| 2006 | 1373 |
| 2007 | 2230 |
| 2008 | 1452 |
| 2009 | 3293 |
| 2010 | 4499 |
| 2011 | 2738 |
| 2012 | 2020 |
| 2013 | 4260 |
| 2014 | 2371 |
| 2015 | 2879 |
| 2016 | 1440 |
| 2017 | 1483 |
| 2018 | 2209 |
| 2019 | 736 |
| 2020 | 34 |
| 2021 | 0 |
| Total | 44741 |