*Excludes Observations that spanned multiple years
| Pre 1970 | 185 |
|---|---|
| 1970 | 0 |
| 1971 | 12 |
| 1972 | 1 |
| 1973 | 0 |
| 1974 | 3 |
| 1975 | 7 |
| 1976 | 5 |
| 1977 | 3 |
| 1978 | 1 |
| 1979 | 7 |
| 1980 | 4 |
| 1981 | 0 |
| 1982 | 4 |
| 1983 | 3 |
| 1984 | 4 |
| 1985 | 65 |
| 1986 | 106 |
| 1987 | 195 |
| 1988 | 487 |
| 1989 | 102 |
| 1990 | 31 |
| 1991 | 246 |
| 1992 | 121 |
| 1993 | 634 |
| 1994 | 343 |
| 1995 | 319 |
| 1996 | 222 |
| 1997 | 182 |
| 1998 | 29 |
| 1999 | 181 |
| 2000 | 146 |
| 2001 | 147 |
| 2002 | 59 |
| 2003 | 94 |
| 2004 | 111 |
| 2005 | 94 |
| 2006 | 68 |
| 2007 | 95 |
| 2008 | 102 |
| 2009 | 76 |
| 2010 | 95 |
| 2011 | 88 |
| 2012 | 126 |
| 2013 | 114 |
| 2014 | 98 |
| 2015 | 99 |
| 2016 | 96 |
| 2017 | 104 |
| 2018 | 110 |
| 2019 | 128 |
| 2020 | 103 |
| 2021 | 123 |
| 2022 | 202 |
| 2023 | 174 |
| 2024 | 61 |
| 2025 | 66 |
| 2026 | 5 |
| Total | 6286 |