*Excludes Observations that spanned multiple years
| Pre 1970 | 94 |
|---|---|
| 1970 | 0 |
| 1971 | 9 |
| 1972 | 1 |
| 1973 | 0 |
| 1974 | 0 |
| 1975 | 1 |
| 1976 | 0 |
| 1977 | 4 |
| 1978 | 5 |
| 1979 | 2 |
| 1980 | 3 |
| 1981 | 0 |
| 1982 | 1 |
| 1983 | 4 |
| 1984 | 7 |
| 1985 | 86 |
| 1986 | 73 |
| 1987 | 120 |
| 1988 | 405 |
| 1989 | 69 |
| 1990 | 68 |
| 1991 | 153 |
| 1992 | 212 |
| 1993 | 272 |
| 1994 | 86 |
| 1995 | 233 |
| 1996 | 200 |
| 1997 | 191 |
| 1998 | 72 |
| 1999 | 168 |
| 2000 | 141 |
| 2001 | 116 |
| 2002 | 48 |
| 2003 | 72 |
| 2004 | 112 |
| 2005 | 43 |
| 2006 | 95 |
| 2007 | 132 |
| 2008 | 152 |
| 2009 | 132 |
| 2010 | 103 |
| 2011 | 65 |
| 2012 | 138 |
| 2013 | 147 |
| 2014 | 113 |
| 2015 | 90 |
| 2016 | 105 |
| 2017 | 93 |
| 2018 | 111 |
| 2019 | 118 |
| 2020 | 75 |
| 2021 | 150 |
| 2022 | 139 |
| 2023 | 69 |
| 2024 | 76 |
| 2025 | 50 |
| 2026 | 1 |
| Total | 5225 |