*Excludes Observations that spanned multiple years
| Pre 1970 | 148 |
|---|---|
| 1970 | 3 |
| 1971 | 17 |
| 1972 | 2 |
| 1973 | 0 |
| 1974 | 0 |
| 1975 | 2 |
| 1976 | 2 |
| 1977 | 5 |
| 1978 | 7 |
| 1979 | 6 |
| 1980 | 8 |
| 1981 | 0 |
| 1982 | 6 |
| 1983 | 1 |
| 1984 | 4 |
| 1985 | 90 |
| 1986 | 122 |
| 1987 | 224 |
| 1988 | 722 |
| 1989 | 107 |
| 1990 | 64 |
| 1991 | 332 |
| 1992 | 226 |
| 1993 | 664 |
| 1994 | 346 |
| 1995 | 483 |
| 1996 | 339 |
| 1997 | 245 |
| 1998 | 55 |
| 1999 | 143 |
| 2000 | 142 |
| 2001 | 137 |
| 2002 | 105 |
| 2003 | 99 |
| 2004 | 146 |
| 2005 | 102 |
| 2006 | 65 |
| 2007 | 115 |
| 2008 | 153 |
| 2009 | 123 |
| 2010 | 129 |
| 2011 | 126 |
| 2012 | 148 |
| 2013 | 127 |
| 2014 | 141 |
| 2015 | 133 |
| 2016 | 108 |
| 2017 | 143 |
| 2018 | 97 |
| 2019 | 88 |
| 2020 | 66 |
| 2021 | 126 |
| 2022 | 121 |
| 2023 | 104 |
| 2024 | 133 |
| 2025 | 14 |
| 2026 | 1 |
| Total | 7365 |