*Excludes Observations that spanned multiple years
| Pre 1970 | 3 |
|---|---|
| 1970 | 0 |
| 1971 | 0 |
| 1972 | 1 |
| 1973 | 0 |
| 1974 | 0 |
| 1975 | 0 |
| 1976 | 1 |
| 1977 | 2 |
| 1978 | 3 |
| 1979 | 1 |
| 1980 | 1 |
| 1981 | 5 |
| 1982 | 2 |
| 1983 | 2 |
| 1984 | 1 |
| 1985 | 0 |
| 1986 | 3 |
| 1987 | 2 |
| 1988 | 1 |
| 1989 | 2 |
| 1990 | 5 |
| 1991 | 5 |
| 1992 | 6 |
| 1993 | 6 |
| 1994 | 22 |
| 1995 | 11 |
| 1996 | 56 |
| 1997 | 12 |
| 1998 | 19 |
| 1999 | 29 |
| 2000 | 46 |
| 2001 | 29 |
| 2002 | 63 |
| 2003 | 550 |
| 2004 | 529 |
| 2005 | 278 |
| 2006 | 222 |
| 2007 | 153 |
| 2008 | 279 |
| 2009 | 4432 |
| 2010 | 201 |
| 2011 | 369 |
| 2012 | 307 |
| 2013 | 206 |
| 2014 | 266 |
| 2015 | 345 |
| 2016 | 248 |
| 2017 | 373 |
| 2018 | 221 |
| 2019 | 198 |
| 2020 | 271 |
| 2021 | 180 |
| 2022 | 1687 |
| 2023 | 344 |
| 2024 | 249 |
| 2025 | 33 |
| 2026 | 0 |
| Total | 12280 |