*Excludes Observations that spanned multiple years
| Pre 1970 | 57 |
|---|---|
| 1970 | 0 |
| 1971 | 0 |
| 1972 | 0 |
| 1973 | 1 |
| 1974 | 1 |
| 1975 | 6 |
| 1976 | 2 |
| 1977 | 3 |
| 1978 | 2 |
| 1979 | 4 |
| 1980 | 4 |
| 1981 | 2 |
| 1982 | 2 |
| 1983 | 6 |
| 1984 | 1 |
| 1985 | 2 |
| 1986 | 1 |
| 1987 | 3 |
| 1988 | 2 |
| 1989 | 8 |
| 1990 | 5 |
| 1991 | 54 |
| 1992 | 48 |
| 1993 | 12 |
| 1994 | 11 |
| 1995 | 108 |
| 1996 | 14 |
| 1997 | 72 |
| 1998 | 46 |
| 1999 | 193 |
| 2000 | 1239 |
| 2001 | 1765 |
| 2002 | 296 |
| 2003 | 2292 |
| 2004 | 1148 |
| 2005 | 2195 |
| 2006 | 1130 |
| 2007 | 939 |
| 2008 | 1099 |
| 2009 | 2631 |
| 2010 | 2245 |
| 2011 | 3034 |
| 2012 | 1426 |
| 2013 | 1113 |
| 2014 | 1008 |
| 2015 | 1217 |
| 2016 | 2093 |
| 2017 | 973 |
| 2018 | 1183 |
| 2019 | 1057 |
| 2020 | 583 |
| 2021 | 1052 |
| 2022 | 320 |
| 2023 | 840 |
| 2024 | 0 |
| Total | 33548 |