*Excludes Observations that spanned multiple years
| Pre 1970 | 70 |
|---|---|
| 1970 | 1 |
| 1971 | 5 |
| 1972 | 3 |
| 1973 | 1 |
| 1974 | 1 |
| 1975 | 3 |
| 1976 | 3 |
| 1977 | 24 |
| 1978 | 9 |
| 1979 | 8 |
| 1980 | 9 |
| 1981 | 1 |
| 1982 | 4 |
| 1983 | 4 |
| 1984 | 11 |
| 1985 | 119 |
| 1986 | 163 |
| 1987 | 246 |
| 1988 | 781 |
| 1989 | 375 |
| 1990 | 98 |
| 1991 | 350 |
| 1992 | 238 |
| 1993 | 561 |
| 1994 | 1440 |
| 1995 | 729 |
| 1996 | 540 |
| 1997 | 593 |
| 1998 | 104 |
| 1999 | 160 |
| 2000 | 75 |
| 2001 | 86 |
| 2002 | 76 |
| 2003 | 270 |
| 2004 | 323 |
| 2005 | 252 |
| 2006 | 233 |
| 2007 | 272 |
| 2008 | 307 |
| 2009 | 309 |
| 2010 | 291 |
| 2011 | 259 |
| 2012 | 269 |
| 2013 | 308 |
| 2014 | 268 |
| 2015 | 244 |
| 2016 | 257 |
| 2017 | 214 |
| 2018 | 59 |
| 2019 | 60 |
| 2020 | 46 |
| 2021 | 111 |
| 2022 | 57 |
| 2023 | 24 |
| 2024 | 19 |
| 2025 | 5 |
| 2026 | 0 |
| Total | 11348 |