*Excludes Observations that spanned multiple years
| Pre 1970 | 13 |
|---|---|
| 1970 | 1 |
| 1971 | 1 |
| 1972 | 0 |
| 1973 | 2 |
| 1974 | 4 |
| 1975 | 5 |
| 1976 | 8 |
| 1977 | 5 |
| 1978 | 5 |
| 1979 | 2 |
| 1980 | 4 |
| 1981 | 1 |
| 1982 | 1 |
| 1983 | 12 |
| 1984 | 2 |
| 1985 | 18 |
| 1986 | 22 |
| 1987 | 29 |
| 1988 | 116 |
| 1989 | 20 |
| 1990 | 59 |
| 1991 | 191 |
| 1992 | 295 |
| 1993 | 234 |
| 1994 | 168 |
| 1995 | 235 |
| 1996 | 137 |
| 1997 | 65 |
| 1998 | 75 |
| 1999 | 73 |
| 2000 | 47 |
| 2001 | 127 |
| 2002 | 30 |
| 2003 | 95 |
| 2004 | 126 |
| 2005 | 64 |
| 2006 | 131 |
| 2007 | 142 |
| 2008 | 85 |
| 2009 | 102 |
| 2010 | 129 |
| 2011 | 225 |
| 2012 | 95 |
| 2013 | 135 |
| 2014 | 149 |
| 2015 | 158 |
| 2016 | 193 |
| 2017 | 194 |
| 2018 | 95 |
| 2019 | 228 |
| 2020 | 119 |
| 2021 | 129 |
| 2022 | 155 |
| 2023 | 2 |
| 2024 | 0 |
| Total | 4758 |