*Excludes Observations that spanned multiple years
| Pre 1970 | 110 |
|---|---|
| 1970 | 38 |
| 1971 | 18 |
| 1972 | 11 |
| 1973 | 6 |
| 1974 | 18 |
| 1975 | 12 |
| 1976 | 6 |
| 1977 | 5 |
| 1978 | 9 |
| 1979 | 123 |
| 1980 | 65 |
| 1981 | 42 |
| 1982 | 81 |
| 1983 | 24 |
| 1984 | 21 |
| 1985 | 47 |
| 1986 | 9 |
| 1987 | 10 |
| 1988 | 45 |
| 1989 | 221 |
| 1990 | 262 |
| 1991 | 84 |
| 1992 | 42 |
| 1993 | 73 |
| 1994 | 60 |
| 1995 | 65 |
| 1996 | 76 |
| 1997 | 55 |
| 1998 | 51 |
| 1999 | 101 |
| 2000 | 107 |
| 2001 | 100 |
| 2002 | 116 |
| 2003 | 78 |
| 2004 | 63 |
| 2005 | 62 |
| 2006 | 43 |
| 2007 | 98 |
| 2008 | 81 |
| 2009 | 101 |
| 2010 | 170 |
| 2011 | 140 |
| 2012 | 155 |
| 2013 | 417 |
| 2014 | 101 |
| 2015 | 166 |
| 2016 | 130 |
| 2017 | 57 |
| 2018 | 41 |
| 2019 | 77 |
| 2020 | 45 |
| 2021 | 53 |
| 2022 | 113 |
| 2023 | 67 |
| 2024 | 97 |
| 2025 | 128 |
| Total | 4596 |