*Excludes Observations that spanned multiple years
| Pre 1970 | 326 |
|---|---|
| 1970 | 227 |
| 1971 | 179 |
| 1972 | 201 |
| 1973 | 70 |
| 1974 | 110 |
| 1975 | 114 |
| 1976 | 59 |
| 1977 | 97 |
| 1978 | 108 |
| 1979 | 45 |
| 1980 | 40 |
| 1981 | 134 |
| 1982 | 51 |
| 1983 | 32 |
| 1984 | 73 |
| 1985 | 65 |
| 1986 | 49 |
| 1987 | 9 |
| 1988 | 167 |
| 1989 | 185 |
| 1990 | 166 |
| 1991 | 174 |
| 1992 | 136 |
| 1993 | 627 |
| 1994 | 360 |
| 1995 | 310 |
| 1996 | 197 |
| 1997 | 161 |
| 1998 | 128 |
| 1999 | 209 |
| 2000 | 359 |
| 2001 | 272 |
| 2002 | 232 |
| 2003 | 181 |
| 2004 | 110 |
| 2005 | 223 |
| 2006 | 235 |
| 2007 | 475 |
| 2008 | 435 |
| 2009 | 244 |
| 2010 | 309 |
| 2011 | 181 |
| 2012 | 203 |
| 2013 | 230 |
| 2014 | 165 |
| 2015 | 120 |
| 2016 | 130 |
| 2017 | 71 |
| 2018 | 75 |
| 2019 | 104 |
| 2020 | 89 |
| 2021 | 48 |
| 2022 | 73 |
| 2023 | 38 |
| 2024 | 13 |
| Total | 9424 |