*Excludes Observations that spanned multiple years
| Pre 1970 | 19 |
|---|---|
| 1970 | 7 |
| 1971 | 4 |
| 1972 | 11 |
| 1973 | 20 |
| 1974 | 20 |
| 1975 | 11 |
| 1976 | 9 |
| 1977 | 4 |
| 1978 | 18 |
| 1979 | 31 |
| 1980 | 22 |
| 1981 | 66 |
| 1982 | 55 |
| 1983 | 97 |
| 1984 | 102 |
| 1985 | 98 |
| 1986 | 91 |
| 1987 | 109 |
| 1988 | 71 |
| 1989 | 82 |
| 1990 | 125 |
| 1991 | 121 |
| 1992 | 96 |
| 1993 | 68 |
| 1994 | 89 |
| 1995 | 79 |
| 1996 | 77 |
| 1997 | 60 |
| 1998 | 80 |
| 1999 | 90 |
| 2000 | 48 |
| 2001 | 129 |
| 2002 | 63 |
| 2003 | 64 |
| 2004 | 54 |
| 2005 | 70 |
| 2006 | 79 |
| 2007 | 71 |
| 2008 | 97 |
| 2009 | 136 |
| 2010 | 103 |
| 2011 | 156 |
| 2012 | 196 |
| 2013 | 171 |
| 2014 | 196 |
| 2015 | 171 |
| 2016 | 204 |
| 2017 | 132 |
| 2018 | 94 |
| 2019 | 72 |
| 2020 | 142 |
| 2021 | 136 |
| 2022 | 44 |
| 2023 | 0 |
| 2024 | 0 |
| Total | 4460 |