*Excludes Observations that spanned multiple years
| Pre 1970 | 211 |
|---|---|
| 1970 | 1 |
| 1971 | 2 |
| 1972 | 2 |
| 1973 | 8 |
| 1974 | 2 |
| 1975 | 2 |
| 1976 | 3 |
| 1977 | 63 |
| 1978 | 2 |
| 1979 | 2 |
| 1980 | 1 |
| 1981 | 1 |
| 1982 | 1 |
| 1983 | 6 |
| 1984 | 3 |
| 1985 | 369 |
| 1986 | 842 |
| 1987 | 4 |
| 1988 | 1 |
| 1989 | 47 |
| 1990 | 154 |
| 1991 | 13 |
| 1992 | 3 |
| 1993 | 13 |
| 1994 | 83 |
| 1995 | 70 |
| 1996 | 749 |
| 1997 | 107 |
| 1998 | 253 |
| 1999 | 835 |
| 2000 | 424 |
| 2001 | 973 |
| 2002 | 819 |
| 2003 | 2697 |
| 2004 | 2135 |
| 2005 | 922 |
| 2006 | 1374 |
| 2007 | 2231 |
| 2008 | 1455 |
| 2009 | 3294 |
| 2010 | 4500 |
| 2011 | 2738 |
| 2012 | 2021 |
| 2013 | 4262 |
| 2014 | 2373 |
| 2015 | 2886 |
| 2016 | 1448 |
| 2017 | 1501 |
| 2018 | 2307 |
| 2019 | 863 |
| 2020 | 751 |
| 2021 | 1757 |
| 2022 | 1416 |
| 2023 | 4923 |
| 2024 | 1706 |
| 2025 | 130 |
| 2026 | 0 |
| Total | 55759 |