*Excludes Observations that spanned multiple years
| Pre 1970 | 255 |
|---|---|
| 1970 | 2 |
| 1971 | 6 |
| 1972 | 2 |
| 1973 | 3 |
| 1974 | 21 |
| 1975 | 15 |
| 1976 | 3 |
| 1977 | 7 |
| 1978 | 6 |
| 1979 | 0 |
| 1980 | 1 |
| 1981 | 1 |
| 1982 | 1 |
| 1983 | 1 |
| 1984 | 4 |
| 1985 | 0 |
| 1986 | 3 |
| 1987 | 1 |
| 1988 | 0 |
| 1989 | 1 |
| 1990 | 1 |
| 1991 | 66 |
| 1992 | 22 |
| 1993 | 85 |
| 1994 | 122 |
| 1995 | 284 |
| 1996 | 214 |
| 1997 | 231 |
| 1998 | 281 |
| 1999 | 270 |
| 2000 | 302 |
| 2001 | 709 |
| 2002 | 639 |
| 2003 | 657 |
| 2004 | 733 |
| 2005 | 220 |
| 2006 | 325 |
| 2007 | 130 |
| 2008 | 169 |
| 2009 | 163 |
| 2010 | 251 |
| 2011 | 114 |
| 2012 | 75 |
| 2013 | 113 |
| 2014 | 77 |
| 2015 | 79 |
| 2016 | 92 |
| 2017 | 65 |
| 2018 | 76 |
| 2019 | 92 |
| 2020 | 83 |
| 2021 | 85 |
| 2022 | 84 |
| 2023 | 94 |
| 2024 | 25 |
| Total | 7361 |