*Excludes Observations that spanned multiple years
| Pre 1970 | 151 |
|---|---|
| 1970 | 21 |
| 1971 | 17 |
| 1972 | 15 |
| 1973 | 17 |
| 1974 | 32 |
| 1975 | 23 |
| 1976 | 15 |
| 1977 | 22 |
| 1978 | 38 |
| 1979 | 17 |
| 1980 | 24 |
| 1981 | 22 |
| 1982 | 13 |
| 1983 | 34 |
| 1984 | 50 |
| 1985 | 24 |
| 1986 | 38 |
| 1987 | 44 |
| 1988 | 55 |
| 1989 | 56 |
| 1990 | 54 |
| 1991 | 54 |
| 1992 | 64 |
| 1993 | 67 |
| 1994 | 60 |
| 1995 | 168 |
| 1996 | 169 |
| 1997 | 123 |
| 1998 | 106 |
| 1999 | 113 |
| 2000 | 108 |
| 2001 | 112 |
| 2002 | 103 |
| 2003 | 127 |
| 2004 | 128 |
| 2005 | 116 |
| 2006 | 160 |
| 2007 | 106 |
| 2008 | 118 |
| 2009 | 154 |
| 2010 | 230 |
| 2011 | 217 |
| 2012 | 190 |
| 2013 | 182 |
| 2014 | 197 |
| 2015 | 218 |
| 2016 | 214 |
| 2017 | 190 |
| 2018 | 148 |
| 2019 | 144 |
| 2020 | 158 |
| 2021 | 174 |
| 2022 | 95 |
| 2023 | 3 |
| 2024 | 7 |
| 2025 | 5 |
| Total | 5310 |