*Excludes Observations that spanned multiple years
| Pre 1970 | 326 |
|---|---|
| 1970 | 56 |
| 1971 | 43 |
| 1972 | 77 |
| 1973 | 97 |
| 1974 | 157 |
| 1975 | 88 |
| 1976 | 67 |
| 1977 | 59 |
| 1978 | 68 |
| 1979 | 95 |
| 1980 | 117 |
| 1981 | 181 |
| 1982 | 191 |
| 1983 | 198 |
| 1984 | 212 |
| 1985 | 193 |
| 1986 | 256 |
| 1987 | 236 |
| 1988 | 241 |
| 1989 | 260 |
| 1990 | 451 |
| 1991 | 320 |
| 1992 | 379 |
| 1993 | 422 |
| 1994 | 370 |
| 1995 | 315 |
| 1996 | 345 |
| 1997 | 298 |
| 1998 | 351 |
| 1999 | 380 |
| 2000 | 366 |
| 2001 | 370 |
| 2002 | 388 |
| 2003 | 394 |
| 2004 | 435 |
| 2005 | 430 |
| 2006 | 455 |
| 2007 | 430 |
| 2008 | 460 |
| 2009 | 495 |
| 2010 | 549 |
| 2011 | 573 |
| 2012 | 609 |
| 2013 | 622 |
| 2014 | 607 |
| 2015 | 693 |
| 2016 | 566 |
| 2017 | 477 |
| 2018 | 462 |
| 2019 | 479 |
| 2020 | 565 |
| 2021 | 593 |
| 2022 | 358 |
| 2023 | 5 |
| 2024 | 21 |
| 2025 | 21 |
| Total | 18272 |