*Excludes Observations that spanned multiple years
| Pre 1970 | 10 |
|---|---|
| 1970 | 0 |
| 1971 | 4 |
| 1972 | 0 |
| 1973 | 1 |
| 1974 | 0 |
| 1975 | 2 |
| 1976 | 0 |
| 1977 | 4 |
| 1978 | 3 |
| 1979 | 0 |
| 1980 | 0 |
| 1981 | 0 |
| 1982 | 2 |
| 1983 | 1 |
| 1984 | 3 |
| 1985 | 80 |
| 1986 | 64 |
| 1987 | 206 |
| 1988 | 408 |
| 1989 | 59 |
| 1990 | 32 |
| 1991 | 223 |
| 1992 | 184 |
| 1993 | 430 |
| 1994 | 208 |
| 1995 | 288 |
| 1996 | 286 |
| 1997 | 210 |
| 1998 | 39 |
| 1999 | 112 |
| 2000 | 51 |
| 2001 | 157 |
| 2002 | 67 |
| 2003 | 71 |
| 2004 | 97 |
| 2005 | 91 |
| 2006 | 49 |
| 2007 | 74 |
| 2008 | 64 |
| 2009 | 78 |
| 2010 | 94 |
| 2011 | 80 |
| 2012 | 109 |
| 2013 | 90 |
| 2014 | 86 |
| 2015 | 87 |
| 2016 | 86 |
| 2017 | 81 |
| 2018 | 49 |
| 2019 | 132 |
| 2020 | 99 |
| 2021 | 79 |
| 2022 | 90 |
| 2023 | 55 |
| 2024 | 3 |
| Total | 4878 |