*Excludes Observations that spanned multiple years
| Pre 1970 | 43 |
|---|---|
| 1970 | 2 |
| 1971 | 11 |
| 1972 | 1 |
| 1973 | 2 |
| 1974 | 0 |
| 1975 | 1 |
| 1976 | 2 |
| 1977 | 9 |
| 1978 | 0 |
| 1979 | 1 |
| 1980 | 0 |
| 1981 | 5 |
| 1982 | 0 |
| 1983 | 5 |
| 1984 | 6 |
| 1985 | 71 |
| 1986 | 131 |
| 1987 | 194 |
| 1988 | 407 |
| 1989 | 361 |
| 1990 | 33 |
| 1991 | 203 |
| 1992 | 73 |
| 1993 | 422 |
| 1994 | 819 |
| 1995 | 412 |
| 1996 | 345 |
| 1997 | 233 |
| 1998 | 23 |
| 1999 | 53 |
| 2000 | 47 |
| 2001 | 60 |
| 2002 | 32 |
| 2003 | 96 |
| 2004 | 92 |
| 2005 | 107 |
| 2006 | 79 |
| 2007 | 98 |
| 2008 | 85 |
| 2009 | 84 |
| 2010 | 105 |
| 2011 | 89 |
| 2012 | 101 |
| 2013 | 120 |
| 2014 | 98 |
| 2015 | 101 |
| 2016 | 79 |
| 2017 | 92 |
| 2018 | 35 |
| 2019 | 23 |
| 2020 | 29 |
| 2021 | 54 |
| 2022 | 31 |
| 2023 | 38 |
| 2024 | 2 |
| Total | 5645 |