*Excludes Observations that spanned multiple years
| Pre 1970 | 45 |
|---|---|
| 1970 | 3 |
| 1971 | 6 |
| 1972 | 13 |
| 1973 | 9 |
| 1974 | 37 |
| 1975 | 30 |
| 1976 | 25 |
| 1977 | 18 |
| 1978 | 15 |
| 1979 | 17 |
| 1980 | 36 |
| 1981 | 32 |
| 1982 | 50 |
| 1983 | 64 |
| 1984 | 148 |
| 1985 | 90 |
| 1986 | 94 |
| 1987 | 58 |
| 1988 | 89 |
| 1989 | 184 |
| 1990 | 266 |
| 1991 | 237 |
| 1992 | 290 |
| 1993 | 274 |
| 1994 | 342 |
| 1995 | 455 |
| 1996 | 349 |
| 1997 | 291 |
| 1998 | 383 |
| 1999 | 484 |
| 2000 | 443 |
| 2001 | 668 |
| 2002 | 771 |
| 2003 | 428 |
| 2004 | 556 |
| 2005 | 317 |
| 2006 | 481 |
| 2007 | 465 |
| 2008 | 603 |
| 2009 | 522 |
| 2010 | 654 |
| 2011 | 585 |
| 2012 | 1091 |
| 2013 | 1250 |
| 2014 | 829 |
| 2015 | 782 |
| 2016 | 708 |
| 2017 | 516 |
| 2018 | 500 |
| 2019 | 475 |
| 2020 | 881 |
| 2021 | 699 |
| 2022 | 378 |
| 2023 | 2 |
| 2024 | 0 |
| Total | 19038 |