*Excludes Observations that spanned multiple years
| Pre 1970 | 19 |
|---|---|
| 1970 | 222 |
| 1971 | 252 |
| 1972 | 262 |
| 1973 | 76 |
| 1974 | 135 |
| 1975 | 118 |
| 1976 | 103 |
| 1977 | 301 |
| 1978 | 233 |
| 1979 | 254 |
| 1980 | 604 |
| 1981 | 180 |
| 1982 | 603 |
| 1983 | 162 |
| 1984 | 195 |
| 1985 | 186 |
| 1986 | 54 |
| 1987 | 75 |
| 1988 | 103 |
| 1989 | 42 |
| 1990 | 110 |
| 1991 | 76 |
| 1992 | 48 |
| 1993 | 97 |
| 1994 | 52 |
| 1995 | 49 |
| 1996 | 53 |
| 1997 | 63 |
| 1998 | 62 |
| 1999 | 49 |
| 2000 | 32 |
| 2001 | 33 |
| 2002 | 64 |
| 2003 | 41 |
| 2004 | 43 |
| 2005 | 68 |
| 2006 | 41 |
| 2007 | 485 |
| 2008 | 155 |
| 2009 | 185 |
| 2010 | 114 |
| 2011 | 133 |
| 2012 | 146 |
| 2013 | 742 |
| 2014 | 86 |
| 2015 | 224 |
| 2016 | 373 |
| 2017 | 32 |
| 2018 | 62 |
| 2019 | 112 |
| 2020 | 41 |
| 2021 | 26 |
| 2022 | 65 |
| 2023 | 22 |
| Total | 8163 |