*Excludes Observations that spanned multiple years
| Pre 1970 | 112 |
|---|---|
| 1970 | 0 |
| 1971 | 7 |
| 1972 | 3 |
| 1973 | 0 |
| 1974 | 3 |
| 1975 | 0 |
| 1976 | 1 |
| 1977 | 5 |
| 1978 | 3 |
| 1979 | 5 |
| 1980 | 5 |
| 1981 | 1 |
| 1982 | 2 |
| 1983 | 4 |
| 1984 | 1 |
| 1985 | 91 |
| 1986 | 77 |
| 1987 | 134 |
| 1988 | 275 |
| 1989 | 103 |
| 1990 | 45 |
| 1991 | 211 |
| 1992 | 262 |
| 1993 | 478 |
| 1994 | 472 |
| 1995 | 487 |
| 1996 | 290 |
| 1997 | 219 |
| 1998 | 75 |
| 1999 | 190 |
| 2000 | 117 |
| 2001 | 200 |
| 2002 | 95 |
| 2003 | 142 |
| 2004 | 162 |
| 2005 | 210 |
| 2006 | 150 |
| 2007 | 194 |
| 2008 | 176 |
| 2009 | 145 |
| 2010 | 171 |
| 2011 | 153 |
| 2012 | 193 |
| 2013 | 172 |
| 2014 | 174 |
| 2015 | 184 |
| 2016 | 203 |
| 2017 | 183 |
| 2018 | 125 |
| 2019 | 160 |
| 2020 | 74 |
| 2021 | 102 |
| 2022 | 223 |
| 2023 | 72 |
| 2024 | 20 |
| 2025 | 17 |
| 2026 | 0 |
| Total | 7378 |