*Excludes Observations that spanned multiple years
| Pre 1970 | 69 |
|---|---|
| 1970 | 0 |
| 1971 | 0 |
| 1972 | 0 |
| 1973 | 1 |
| 1974 | 1 |
| 1975 | 5 |
| 1976 | 2 |
| 1977 | 6 |
| 1978 | 2 |
| 1979 | 4 |
| 1980 | 3 |
| 1981 | 1 |
| 1982 | 2 |
| 1983 | 4 |
| 1984 | 2 |
| 1985 | 5 |
| 1986 | 19 |
| 1987 | 22 |
| 1988 | 20 |
| 1989 | 37 |
| 1990 | 324 |
| 1991 | 72 |
| 1992 | 31 |
| 1993 | 45 |
| 1994 | 31 |
| 1995 | 97 |
| 1996 | 38 |
| 1997 | 909 |
| 1998 | 737 |
| 1999 | 450 |
| 2000 | 2422 |
| 2001 | 2854 |
| 2002 | 1661 |
| 2003 | 6084 |
| 2004 | 2166 |
| 2005 | 3478 |
| 2006 | 1844 |
| 2007 | 1626 |
| 2008 | 1762 |
| 2009 | 5013 |
| 2010 | 3525 |
| 2011 | 2373 |
| 2012 | 1380 |
| 2013 | 1764 |
| 2014 | 1668 |
| 2015 | 1313 |
| 2016 | 1699 |
| 2017 | 2178 |
| 2018 | 1618 |
| 2019 | 847 |
| 2020 | 1348 |
| 2021 | 1735 |
| 2022 | 1045 |
| 2023 | 1526 |
| 2024 | 1 |
| Total | 55869 |