*Excludes Observations that spanned multiple years
| Pre 1970 | 185 |
|---|---|
| 1970 | 50 |
| 1971 | 29 |
| 1972 | 56 |
| 1973 | 77 |
| 1974 | 108 |
| 1975 | 50 |
| 1976 | 44 |
| 1977 | 54 |
| 1978 | 59 |
| 1979 | 81 |
| 1980 | 96 |
| 1981 | 161 |
| 1982 | 165 |
| 1983 | 155 |
| 1984 | 177 |
| 1985 | 164 |
| 1986 | 191 |
| 1987 | 174 |
| 1988 | 198 |
| 1989 | 226 |
| 1990 | 277 |
| 1991 | 207 |
| 1992 | 269 |
| 1993 | 270 |
| 1994 | 233 |
| 1995 | 220 |
| 1996 | 260 |
| 1997 | 229 |
| 1998 | 218 |
| 1999 | 246 |
| 2000 | 248 |
| 2001 | 269 |
| 2002 | 288 |
| 2003 | 278 |
| 2004 | 348 |
| 2005 | 290 |
| 2006 | 314 |
| 2007 | 323 |
| 2008 | 350 |
| 2009 | 407 |
| 2010 | 406 |
| 2011 | 412 |
| 2012 | 541 |
| 2013 | 566 |
| 2014 | 513 |
| 2015 | 515 |
| 2016 | 459 |
| 2017 | 375 |
| 2018 | 365 |
| 2019 | 395 |
| 2020 | 590 |
| 2021 | 497 |
| 2022 | 335 |
| 2023 | 3 |
| 2024 | 11 |
| 2025 | 7 |
| Total | 14034 |