Year Annual Number 1970 0 1971 0 1972 0 1973 0 1974 0 1975 0 1976 0 1977 10 1978 0 1979 0 1980 15 1981 0 1982 33 1983 0 1984 10 1985 22 1986 0 1987 0 1988 0 1989 36 1990 0 1991 0 1992 0 1993 0 1994 0 1995 0 1996 0 1997 3 1998 0 1999 0 2000 0 2001 13 2002 0 2003 0 2004 4 2005 2 2006 0 2007 0 2008 3