*Excludes Observations that spanned multiple years
| Pre 1970 | 125 |
|---|---|
| 1970 | 1 |
| 1971 | 6 |
| 1972 | 3 |
| 1973 | 1 |
| 1974 | 1 |
| 1975 | 2 |
| 1976 | 3 |
| 1977 | 1 |
| 1978 | 5 |
| 1979 | 9 |
| 1980 | 4 |
| 1981 | 1 |
| 1982 | 4 |
| 1983 | 6 |
| 1984 | 9 |
| 1985 | 90 |
| 1986 | 90 |
| 1987 | 146 |
| 1988 | 604 |
| 1989 | 48 |
| 1990 | 54 |
| 1991 | 250 |
| 1992 | 117 |
| 1993 | 166 |
| 1994 | 113 |
| 1995 | 259 |
| 1996 | 86 |
| 1997 | 121 |
| 1998 | 13 |
| 1999 | 97 |
| 2000 | 149 |
| 2001 | 80 |
| 2002 | 47 |
| 2003 | 54 |
| 2004 | 67 |
| 2005 | 34 |
| 2006 | 63 |
| 2007 | 78 |
| 2008 | 103 |
| 2009 | 90 |
| 2010 | 81 |
| 2011 | 81 |
| 2012 | 82 |
| 2013 | 79 |
| 2014 | 68 |
| 2015 | 66 |
| 2016 | 65 |
| 2017 | 64 |
| 2018 | 39 |
| 2019 | 22 |
| 2020 | 18 |
| 2021 | 32 |
| 2022 | 45 |
| 2023 | 8 |
| 2024 | 2 |
| 2025 | 0 |
| 2026 | 0 |
| Total | 3952 |