*Excludes Observations that spanned multiple years
| Pre 1970 | 71 |
|---|---|
| 1970 | 0 |
| 1971 | 7 |
| 1972 | 2 |
| 1973 | 0 |
| 1974 | 0 |
| 1975 | 1 |
| 1976 | 2 |
| 1977 | 2 |
| 1978 | 2 |
| 1979 | 3 |
| 1980 | 1 |
| 1981 | 0 |
| 1982 | 3 |
| 1983 | 1 |
| 1984 | 19 |
| 1985 | 138 |
| 1986 | 136 |
| 1987 | 275 |
| 1988 | 871 |
| 1989 | 72 |
| 1990 | 85 |
| 1991 | 350 |
| 1992 | 131 |
| 1993 | 539 |
| 1994 | 514 |
| 1995 | 195 |
| 1996 | 105 |
| 1997 | 72 |
| 1998 | 24 |
| 1999 | 147 |
| 2000 | 102 |
| 2001 | 48 |
| 2002 | 36 |
| 2003 | 111 |
| 2004 | 92 |
| 2005 | 109 |
| 2006 | 96 |
| 2007 | 94 |
| 2008 | 99 |
| 2009 | 103 |
| 2010 | 107 |
| 2011 | 102 |
| 2012 | 158 |
| 2013 | 130 |
| 2014 | 114 |
| 2015 | 98 |
| 2016 | 113 |
| 2017 | 107 |
| 2018 | 19 |
| 2019 | 55 |
| 2020 | 39 |
| 2021 | 55 |
| 2022 | 54 |
| 2023 | 73 |
| 2024 | 87 |
| 2025 | 98 |
| 2026 | 28 |
| Total | 6095 |