*Excludes Observations that spanned multiple years
| Pre 1970 | 25 |
|---|---|
| 1970 | 0 |
| 1971 | 0 |
| 1972 | 0 |
| 1973 | 2 |
| 1974 | 1 |
| 1975 | 2 |
| 1976 | 1 |
| 1977 | 1 |
| 1978 | 0 |
| 1979 | 0 |
| 1980 | 1 |
| 1981 | 1 |
| 1982 | 2 |
| 1983 | 1 |
| 1984 | 1 |
| 1985 | 3 |
| 1986 | 5 |
| 1987 | 6 |
| 1988 | 12 |
| 1989 | 28 |
| 1990 | 10 |
| 1991 | 35 |
| 1992 | 20 |
| 1993 | 22 |
| 1994 | 42 |
| 1995 | 53 |
| 1996 | 23 |
| 1997 | 20 |
| 1998 | 63 |
| 1999 | 73 |
| 2000 | 74 |
| 2001 | 53 |
| 2002 | 51 |
| 2003 | 800 |
| 2004 | 1312 |
| 2005 | 409 |
| 2006 | 325 |
| 2007 | 337 |
| 2008 | 407 |
| 2009 | 5363 |
| 2010 | 644 |
| 2011 | 927 |
| 2012 | 898 |
| 2013 | 570 |
| 2014 | 470 |
| 2015 | 393 |
| 2016 | 516 |
| 2017 | 624 |
| 2018 | 486 |
| 2019 | 157 |
| 2020 | 346 |
| 2021 | 341 |
| 2022 | 3039 |
| 2023 | 300 |
| 2024 | 290 |
| 2025 | 5 |
| Total | 19590 |