*Excludes Observations that spanned multiple years
| Pre 1970 | 26 |
|---|---|
| 1970 | 2 |
| 1971 | 6 |
| 1972 | 3 |
| 1973 | 1 |
| 1974 | 0 |
| 1975 | 0 |
| 1976 | 0 |
| 1977 | 14 |
| 1978 | 4 |
| 1979 | 10 |
| 1980 | 2 |
| 1981 | 1 |
| 1982 | 1 |
| 1983 | 19 |
| 1984 | 8 |
| 1985 | 33 |
| 1986 | 50 |
| 1987 | 63 |
| 1988 | 296 |
| 1989 | 31 |
| 1990 | 47 |
| 1991 | 302 |
| 1992 | 431 |
| 1993 | 431 |
| 1994 | 325 |
| 1995 | 439 |
| 1996 | 221 |
| 1997 | 180 |
| 1998 | 133 |
| 1999 | 110 |
| 2000 | 90 |
| 2001 | 179 |
| 2002 | 93 |
| 2003 | 108 |
| 2004 | 216 |
| 2005 | 225 |
| 2006 | 148 |
| 2007 | 212 |
| 2008 | 93 |
| 2009 | 99 |
| 2010 | 397 |
| 2011 | 157 |
| 2012 | 82 |
| 2013 | 69 |
| 2014 | 102 |
| 2015 | 132 |
| 2016 | 174 |
| 2017 | 176 |
| 2018 | 74 |
| 2019 | 98 |
| 2020 | 66 |
| 2021 | 56 |
| 2022 | 74 |
| 2023 | 5 |
| 2024 | 0 |
| Total | 6314 |