*Excludes Observations that spanned multiple years
| Pre 1970 | 49 |
|---|---|
| 1970 | 2 |
| 1971 | 11 |
| 1972 | 5 |
| 1973 | 1 |
| 1974 | 0 |
| 1975 | 1 |
| 1976 | 2 |
| 1977 | 8 |
| 1978 | 8 |
| 1979 | 3 |
| 1980 | 3 |
| 1981 | 0 |
| 1982 | 4 |
| 1983 | 4 |
| 1984 | 24 |
| 1985 | 233 |
| 1986 | 241 |
| 1987 | 251 |
| 1988 | 1034 |
| 1989 | 221 |
| 1990 | 142 |
| 1991 | 417 |
| 1992 | 201 |
| 1993 | 540 |
| 1994 | 1184 |
| 1995 | 668 |
| 1996 | 576 |
| 1997 | 539 |
| 1998 | 132 |
| 1999 | 235 |
| 2000 | 152 |
| 2001 | 70 |
| 2002 | 74 |
| 2003 | 232 |
| 2004 | 260 |
| 2005 | 230 |
| 2006 | 231 |
| 2007 | 234 |
| 2008 | 266 |
| 2009 | 286 |
| 2010 | 237 |
| 2011 | 221 |
| 2012 | 269 |
| 2013 | 253 |
| 2014 | 243 |
| 2015 | 253 |
| 2016 | 234 |
| 2017 | 199 |
| 2018 | 50 |
| 2019 | 65 |
| 2020 | 30 |
| 2021 | 71 |
| 2022 | 52 |
| 2023 | 15 |
| 2024 | 14 |
| 2025 | 6 |
| Total | 10986 |