*Excludes Observations that spanned multiple years
| Pre 1970 | 35 |
|---|---|
| 1970 | 2 |
| 1971 | 0 |
| 1972 | 16 |
| 1973 | 12 |
| 1974 | 31 |
| 1975 | 18 |
| 1976 | 22 |
| 1977 | 16 |
| 1978 | 17 |
| 1979 | 20 |
| 1980 | 29 |
| 1981 | 25 |
| 1982 | 31 |
| 1983 | 25 |
| 1984 | 62 |
| 1985 | 50 |
| 1986 | 59 |
| 1987 | 15 |
| 1988 | 13 |
| 1989 | 87 |
| 1990 | 91 |
| 1991 | 97 |
| 1992 | 116 |
| 1993 | 135 |
| 1994 | 98 |
| 1995 | 167 |
| 1996 | 131 |
| 1997 | 104 |
| 1998 | 121 |
| 1999 | 121 |
| 2000 | 111 |
| 2001 | 145 |
| 2002 | 208 |
| 2003 | 168 |
| 2004 | 153 |
| 2005 | 137 |
| 2006 | 167 |
| 2007 | 187 |
| 2008 | 236 |
| 2009 | 214 |
| 2010 | 215 |
| 2011 | 178 |
| 2012 | 412 |
| 2013 | 540 |
| 2014 | 343 |
| 2015 | 388 |
| 2016 | 709 |
| 2017 | 212 |
| 2018 | 194 |
| 2019 | 199 |
| 2020 | 339 |
| 2021 | 216 |
| 2022 | 75 |
| 2023 | 0 |
| 2024 | 0 |
| Total | 7512 |