*Excludes Observations that spanned multiple years
| Pre 1970 | 22 |
|---|---|
| 1970 | 1 |
| 1971 | 3 |
| 1972 | 10 |
| 1973 | 2 |
| 1974 | 1 |
| 1975 | 1 |
| 1976 | 17 |
| 1977 | 21 |
| 1978 | 1 |
| 1979 | 8 |
| 1980 | 6 |
| 1981 | 31 |
| 1982 | 3 |
| 1983 | 12 |
| 1984 | 15 |
| 1985 | 28 |
| 1986 | 91 |
| 1987 | 56 |
| 1988 | 255 |
| 1989 | 43 |
| 1990 | 18 |
| 1991 | 267 |
| 1992 | 293 |
| 1993 | 522 |
| 1994 | 381 |
| 1995 | 396 |
| 1996 | 204 |
| 1997 | 184 |
| 1998 | 102 |
| 1999 | 129 |
| 2000 | 79 |
| 2001 | 197 |
| 2002 | 146 |
| 2003 | 160 |
| 2004 | 226 |
| 2005 | 229 |
| 2006 | 158 |
| 2007 | 206 |
| 2008 | 138 |
| 2009 | 140 |
| 2010 | 683 |
| 2011 | 238 |
| 2012 | 142 |
| 2013 | 187 |
| 2014 | 228 |
| 2015 | 491 |
| 2016 | 393 |
| 2017 | 369 |
| 2018 | 291 |
| 2019 | 409 |
| 2020 | 220 |
| 2021 | 236 |
| 2022 | 263 |
| 2023 | 4 |
| 2024 | 0 |
| Total | 8956 |