*Excludes Observations that spanned multiple years
| Pre 1970 | 176 |
|---|---|
| 1970 | 1 |
| 1971 | 7 |
| 1972 | 15 |
| 1973 | 3 |
| 1974 | 2 |
| 1975 | 1 |
| 1976 | 18 |
| 1977 | 24 |
| 1978 | 2 |
| 1979 | 12 |
| 1980 | 12 |
| 1981 | 31 |
| 1982 | 3 |
| 1983 | 16 |
| 1984 | 18 |
| 1985 | 30 |
| 1986 | 94 |
| 1987 | 56 |
| 1988 | 256 |
| 1989 | 43 |
| 1990 | 20 |
| 1991 | 272 |
| 1992 | 297 |
| 1993 | 527 |
| 1994 | 386 |
| 1995 | 402 |
| 1996 | 207 |
| 1997 | 191 |
| 1998 | 106 |
| 1999 | 130 |
| 2000 | 80 |
| 2001 | 198 |
| 2002 | 146 |
| 2003 | 162 |
| 2004 | 228 |
| 2005 | 231 |
| 2006 | 158 |
| 2007 | 227 |
| 2008 | 159 |
| 2009 | 177 |
| 2010 | 699 |
| 2011 | 238 |
| 2012 | 147 |
| 2013 | 193 |
| 2014 | 228 |
| 2015 | 496 |
| 2016 | 393 |
| 2017 | 370 |
| 2018 | 294 |
| 2019 | 425 |
| 2020 | 224 |
| 2021 | 237 |
| 2022 | 316 |
| 2023 | 323 |
| 2024 | 95 |
| 2025 | 46 |
| 2026 | 0 |
| Total | 9848 |