Year,Mean_length_cm
1968,31.5562
1969,30.6449
1970,28.0588
1971,29.5831
1972,28.4373
1973,
1974,
1975,
1976,
1977,
1978,
1979,
1980,30.7045
1981,30.7565
1982,29.3282
1983,30.7517
1984,29.5934
1985,29.6151
1986,29.6759
1987,30.3044
1988,30.6395
1989,30.0150
1990,28.9813
1991,30.3233
1992,29.3902
1993,28.0919
1994,32.4338
1995,30.6520
1996,28.6208
1997,27.0820
1998,25.6704
1999,26.9448
2000,26.3874
2001,27.4443
2002,28.9448
2003,26.6438
2004,26.9265
2005,27.2136
2006,27.9326