Year Annual Number 1970 0 1971 0 1972 0 1973 0 1974 0 1975 0 1976 0 1977 0 1978 0 1979 0 1980 0 1981 0 1982 0 1983 0 1984 0 1985 0 1986 0 1987 0 1988 0 1989 0 1990 64 1991 0 1992 0 1993 6 1994 11 1995 5 1996 0 1997 0 1998 3 1999 18 2000 0 2001 6 2002 22 2003 15 2004 2 2005 2 2006 11 2007 18 2008 5