*Excludes Observations that spanned multiple years
| Pre 1970 | 252 |
|---|---|
| 1970 | 5 |
| 1971 | 13 |
| 1972 | 3 |
| 1973 | 3 |
| 1974 | 8 |
| 1975 | 6 |
| 1976 | 13 |
| 1977 | 20 |
| 1978 | 11 |
| 1979 | 16 |
| 1980 | 10 |
| 1981 | 17 |
| 1982 | 3 |
| 1983 | 21 |
| 1984 | 8 |
| 1985 | 30 |
| 1986 | 94 |
| 1987 | 134 |
| 1988 | 528 |
| 1989 | 84 |
| 1990 | 87 |
| 1991 | 455 |
| 1992 | 482 |
| 1993 | 532 |
| 1994 | 136 |
| 1995 | 552 |
| 1996 | 244 |
| 1997 | 281 |
| 1998 | 122 |
| 1999 | 181 |
| 2000 | 174 |
| 2001 | 288 |
| 2002 | 101 |
| 2003 | 130 |
| 2004 | 200 |
| 2005 | 115 |
| 2006 | 117 |
| 2007 | 184 |
| 2008 | 213 |
| 2009 | 270 |
| 2010 | 426 |
| 2011 | 240 |
| 2012 | 151 |
| 2013 | 204 |
| 2014 | 174 |
| 2015 | 135 |
| 2016 | 272 |
| 2017 | 333 |
| 2018 | 302 |
| 2019 | 390 |
| 2020 | 292 |
| 2021 | 367 |
| 2022 | 416 |
| 2023 | 387 |
| 2024 | 97 |
| 2025 | 56 |
| 2026 | 6 |
| Total | 10391 |