*Excludes Observations that spanned multiple years
| Pre 1970 | 88 |
|---|---|
| 1970 | 227 |
| 1971 | 254 |
| 1972 | 262 |
| 1973 | 80 |
| 1974 | 136 |
| 1975 | 120 |
| 1976 | 104 |
| 1977 | 302 |
| 1978 | 234 |
| 1979 | 255 |
| 1980 | 607 |
| 1981 | 180 |
| 1982 | 605 |
| 1983 | 163 |
| 1984 | 195 |
| 1985 | 191 |
| 1986 | 56 |
| 1987 | 76 |
| 1988 | 104 |
| 1989 | 48 |
| 1990 | 109 |
| 1991 | 76 |
| 1992 | 48 |
| 1993 | 98 |
| 1994 | 52 |
| 1995 | 50 |
| 1996 | 63 |
| 1997 | 65 |
| 1998 | 62 |
| 1999 | 54 |
| 2000 | 47 |
| 2001 | 37 |
| 2002 | 66 |
| 2003 | 57 |
| 2004 | 50 |
| 2005 | 108 |
| 2006 | 78 |
| 2007 | 552 |
| 2008 | 189 |
| 2009 | 206 |
| 2010 | 130 |
| 2011 | 152 |
| 2012 | 164 |
| 2013 | 763 |
| 2014 | 109 |
| 2015 | 252 |
| 2016 | 399 |
| 2017 | 80 |
| 2018 | 85 |
| 2019 | 116 |
| 2020 | 43 |
| 2021 | 47 |
| 2022 | 74 |
| 2023 | 50 |
| 2024 | 74 |
| 2025 | 5 |
| Total | 8897 |