*Excludes Observations that spanned multiple years
| Pre 1970 | 42 |
|---|---|
| 1970 | 0 |
| 1971 | 3 |
| 1972 | 0 |
| 1973 | 2 |
| 1974 | 1 |
| 1975 | 1 |
| 1976 | 1 |
| 1977 | 3 |
| 1978 | 3 |
| 1979 | 1 |
| 1980 | 1 |
| 1981 | 1 |
| 1982 | 1 |
| 1983 | 0 |
| 1984 | 4 |
| 1985 | 14 |
| 1986 | 50 |
| 1987 | 96 |
| 1988 | 410 |
| 1989 | 22 |
| 1990 | 107 |
| 1991 | 231 |
| 1992 | 103 |
| 1993 | 113 |
| 1994 | 354 |
| 1995 | 358 |
| 1996 | 341 |
| 1997 | 351 |
| 1998 | 68 |
| 1999 | 50 |
| 2000 | 29 |
| 2001 | 10 |
| 2002 | 49 |
| 2003 | 96 |
| 2004 | 123 |
| 2005 | 114 |
| 2006 | 75 |
| 2007 | 72 |
| 2008 | 132 |
| 2009 | 125 |
| 2010 | 74 |
| 2011 | 68 |
| 2012 | 169 |
| 2013 | 362 |
| 2014 | 467 |
| 2015 | 392 |
| 2016 | 369 |
| 2017 | 165 |
| 2018 | 28 |
| 2019 | 16 |
| 2020 | 75 |
| 2021 | 101 |
| 2022 | 73 |
| 2023 | 32 |
| 2024 | 0 |
| Total | 5948 |