*Excludes Observations that spanned multiple years
| Pre 1970 | 164 |
|---|---|
| 1970 | 2 |
| 1971 | 5 |
| 1972 | 1 |
| 1973 | 1 |
| 1974 | 1 |
| 1975 | 3 |
| 1976 | 1 |
| 1977 | 5 |
| 1978 | 3 |
| 1979 | 5 |
| 1980 | 3 |
| 1981 | 1 |
| 1982 | 3 |
| 1983 | 3 |
| 1984 | 3 |
| 1985 | 80 |
| 1986 | 65 |
| 1987 | 208 |
| 1988 | 410 |
| 1989 | 59 |
| 1990 | 39 |
| 1991 | 228 |
| 1992 | 185 |
| 1993 | 433 |
| 1994 | 213 |
| 1995 | 295 |
| 1996 | 289 |
| 1997 | 211 |
| 1998 | 42 |
| 1999 | 115 |
| 2000 | 51 |
| 2001 | 158 |
| 2002 | 68 |
| 2003 | 71 |
| 2004 | 97 |
| 2005 | 92 |
| 2006 | 49 |
| 2007 | 94 |
| 2008 | 89 |
| 2009 | 115 |
| 2010 | 117 |
| 2011 | 80 |
| 2012 | 128 |
| 2013 | 108 |
| 2014 | 86 |
| 2015 | 88 |
| 2016 | 86 |
| 2017 | 81 |
| 2018 | 52 |
| 2019 | 145 |
| 2020 | 107 |
| 2021 | 89 |
| 2022 | 112 |
| 2023 | 77 |
| 2024 | 108 |
| 2025 | 46 |
| 2026 | 15 |
| Total | 5485 |