*Excludes Observations that spanned multiple years
| Pre 1970 | 126 |
|---|---|
| 1970 | 4 |
| 1971 | 16 |
| 1972 | 20 |
| 1973 | 5 |
| 1974 | 3 |
| 1975 | 3 |
| 1976 | 3 |
| 1977 | 21 |
| 1978 | 2 |
| 1979 | 6 |
| 1980 | 3 |
| 1981 | 1 |
| 1982 | 3 |
| 1983 | 3 |
| 1984 | 24 |
| 1985 | 234 |
| 1986 | 173 |
| 1987 | 250 |
| 1988 | 864 |
| 1989 | 92 |
| 1990 | 104 |
| 1991 | 336 |
| 1992 | 145 |
| 1993 | 662 |
| 1994 | 416 |
| 1995 | 280 |
| 1996 | 178 |
| 1997 | 156 |
| 1998 | 23 |
| 1999 | 150 |
| 2000 | 99 |
| 2001 | 53 |
| 2002 | 48 |
| 2003 | 107 |
| 2004 | 92 |
| 2005 | 99 |
| 2006 | 99 |
| 2007 | 117 |
| 2008 | 116 |
| 2009 | 123 |
| 2010 | 94 |
| 2011 | 128 |
| 2012 | 189 |
| 2013 | 131 |
| 2014 | 124 |
| 2015 | 113 |
| 2016 | 117 |
| 2017 | 108 |
| 2018 | 27 |
| 2019 | 33 |
| 2020 | 31 |
| 2021 | 34 |
| 2022 | 55 |
| 2023 | 35 |
| 2024 | 25 |
| 2025 | 12 |
| 2026 | 0 |
| Total | 6515 |