*Excludes Observations that spanned multiple years
| Pre 1970 | 156 |
|---|---|
| 1970 | 17 |
| 1971 | 8 |
| 1972 | 20 |
| 1973 | 28 |
| 1974 | 72 |
| 1975 | 52 |
| 1976 | 33 |
| 1977 | 33 |
| 1978 | 30 |
| 1979 | 40 |
| 1980 | 23 |
| 1981 | 35 |
| 1982 | 36 |
| 1983 | 35 |
| 1984 | 89 |
| 1985 | 32 |
| 1986 | 54 |
| 1987 | 50 |
| 1988 | 54 |
| 1989 | 48 |
| 1990 | 53 |
| 1991 | 57 |
| 1992 | 62 |
| 1993 | 75 |
| 1994 | 63 |
| 1995 | 120 |
| 1996 | 110 |
| 1997 | 96 |
| 1998 | 84 |
| 1999 | 96 |
| 2000 | 104 |
| 2001 | 109 |
| 2002 | 115 |
| 2003 | 96 |
| 2004 | 114 |
| 2005 | 96 |
| 2006 | 90 |
| 2007 | 87 |
| 2008 | 103 |
| 2009 | 114 |
| 2010 | 131 |
| 2011 | 187 |
| 2012 | 227 |
| 2013 | 189 |
| 2014 | 205 |
| 2015 | 167 |
| 2016 | 162 |
| 2017 | 126 |
| 2018 | 124 |
| 2019 | 128 |
| 2020 | 189 |
| 2021 | 149 |
| 2022 | 101 |
| 2023 | 4 |
| 2024 | 0 |
| Total | 4878 |