*Excludes Observations that spanned multiple years
| Pre 1970 | 65 |
|---|---|
| 1970 | 2 |
| 1971 | 7 |
| 1972 | 4 |
| 1973 | 1 |
| 1974 | 0 |
| 1975 | 1 |
| 1976 | 1 |
| 1977 | 7 |
| 1978 | 8 |
| 1979 | 2 |
| 1980 | 4 |
| 1981 | 0 |
| 1982 | 4 |
| 1983 | 6 |
| 1984 | 11 |
| 1985 | 180 |
| 1986 | 205 |
| 1987 | 232 |
| 1988 | 870 |
| 1989 | 228 |
| 1990 | 109 |
| 1991 | 381 |
| 1992 | 193 |
| 1993 | 479 |
| 1994 | 1023 |
| 1995 | 746 |
| 1996 | 455 |
| 1997 | 517 |
| 1998 | 65 |
| 1999 | 203 |
| 2000 | 114 |
| 2001 | 93 |
| 2002 | 63 |
| 2003 | 240 |
| 2004 | 292 |
| 2005 | 229 |
| 2006 | 232 |
| 2007 | 238 |
| 2008 | 326 |
| 2009 | 317 |
| 2010 | 240 |
| 2011 | 234 |
| 2012 | 269 |
| 2013 | 322 |
| 2014 | 271 |
| 2015 | 253 |
| 2016 | 236 |
| 2017 | 212 |
| 2018 | 95 |
| 2019 | 90 |
| 2020 | 34 |
| 2021 | 198 |
| 2022 | 69 |
| 2023 | 11 |
| 2024 | 5 |
| Total | 10692 |