*Excludes Observations that spanned multiple years
| Pre 1970 | 17 |
|---|---|
| 1970 | 1 |
| 1971 | 3 |
| 1972 | 1 |
| 1973 | 1 |
| 1974 | 0 |
| 1975 | 0 |
| 1976 | 4 |
| 1977 | 16 |
| 1978 | 3 |
| 1979 | 8 |
| 1980 | 3 |
| 1981 | 6 |
| 1982 | 1 |
| 1983 | 5 |
| 1984 | 4 |
| 1985 | 31 |
| 1986 | 10 |
| 1987 | 31 |
| 1988 | 164 |
| 1989 | 20 |
| 1990 | 65 |
| 1991 | 272 |
| 1992 | 319 |
| 1993 | 349 |
| 1994 | 66 |
| 1995 | 266 |
| 1996 | 103 |
| 1997 | 151 |
| 1998 | 46 |
| 1999 | 105 |
| 2000 | 71 |
| 2001 | 152 |
| 2002 | 38 |
| 2003 | 79 |
| 2004 | 145 |
| 2005 | 35 |
| 2006 | 84 |
| 2007 | 113 |
| 2008 | 159 |
| 2009 | 167 |
| 2010 | 153 |
| 2011 | 132 |
| 2012 | 127 |
| 2013 | 209 |
| 2014 | 172 |
| 2015 | 154 |
| 2016 | 250 |
| 2017 | 232 |
| 2018 | 276 |
| 2019 | 315 |
| 2020 | 139 |
| 2021 | 173 |
| 2022 | 216 |
| 2023 | 3 |
| 2024 | 0 |
| Total | 5665 |