*Excludes Observations that spanned multiple years
| Pre 1970 | 79 |
|---|---|
| 1970 | 2 |
| 1971 | 10 |
| 1972 | 2 |
| 1973 | 2 |
| 1974 | 2 |
| 1975 | 4 |
| 1976 | 7 |
| 1977 | 2 |
| 1978 | 3 |
| 1979 | 3 |
| 1980 | 10 |
| 1981 | 9 |
| 1982 | 4 |
| 1983 | 7 |
| 1984 | 3 |
| 1985 | 10 |
| 1986 | 81 |
| 1987 | 75 |
| 1988 | 533 |
| 1989 | 445 |
| 1990 | 13 |
| 1991 | 100 |
| 1992 | 134 |
| 1993 | 184 |
| 1994 | 614 |
| 1995 | 362 |
| 1996 | 257 |
| 1997 | 205 |
| 1998 | 48 |
| 1999 | 45 |
| 2000 | 41 |
| 2001 | 135 |
| 2002 | 81 |
| 2003 | 155 |
| 2004 | 234 |
| 2005 | 212 |
| 2006 | 136 |
| 2007 | 167 |
| 2008 | 166 |
| 2009 | 247 |
| 2010 | 242 |
| 2011 | 190 |
| 2012 | 137 |
| 2013 | 141 |
| 2014 | 157 |
| 2015 | 154 |
| 2016 | 179 |
| 2017 | 188 |
| 2018 | 124 |
| 2019 | 164 |
| 2020 | 93 |
| 2021 | 125 |
| 2022 | 230 |
| 2023 | 54 |
| 2024 | 4 |
| Total | 7011 |