*Excludes Observations that spanned multiple years
| Pre 1970 | 288 |
|---|---|
| 1970 | 6 |
| 1971 | 16 |
| 1972 | 10 |
| 1973 | 5 |
| 1974 | 11 |
| 1975 | 5 |
| 1976 | 5 |
| 1977 | 16 |
| 1978 | 13 |
| 1979 | 16 |
| 1980 | 11 |
| 1981 | 11 |
| 1982 | 5 |
| 1983 | 25 |
| 1984 | 9 |
| 1985 | 36 |
| 1986 | 51 |
| 1987 | 64 |
| 1988 | 297 |
| 1989 | 35 |
| 1990 | 51 |
| 1991 | 307 |
| 1992 | 438 |
| 1993 | 436 |
| 1994 | 329 |
| 1995 | 443 |
| 1996 | 227 |
| 1997 | 183 |
| 1998 | 145 |
| 1999 | 113 |
| 2000 | 93 |
| 2001 | 180 |
| 2002 | 94 |
| 2003 | 109 |
| 2004 | 217 |
| 2005 | 228 |
| 2006 | 148 |
| 2007 | 219 |
| 2008 | 119 |
| 2009 | 138 |
| 2010 | 403 |
| 2011 | 158 |
| 2012 | 97 |
| 2013 | 74 |
| 2014 | 105 |
| 2015 | 132 |
| 2016 | 174 |
| 2017 | 179 |
| 2018 | 76 |
| 2019 | 105 |
| 2020 | 68 |
| 2021 | 64 |
| 2022 | 82 |
| 2023 | 105 |
| 2024 | 28 |
| 2025 | 17 |
| 2026 | 0 |
| Total | 7019 |