expt_block  date        mussel_density  prey_eaten  carap_width  sex  parasite  
4           2012-07-19  2               0           13.2         ?    No        
4           2012-07-19  4               4           12.5         F    No        
4           2012-07-19  6               3           12.4         F    No        
4           2012-07-19  8               5           12.5         M    No        
4           2012-07-19  10              1           13.2         M    No        
4           2012-07-19  16              2           12.5         M    No        
4           2012-07-19  24              11          12.1         M    No        
4           2012-07-19  32              6           12.8         M    No        
4           2012-07-19  2               0           12.9         M    Yes       
4           2012-07-19  4               1           12.3         F    Yes       
4           2012-07-19  6               1           12.9         M    Yes       
4           2012-07-19  8               3           11.7         M    Yes       
4           2012-07-19  10              0           10.8         F    Yes       
4           2012-07-19  16              0           11.3         F    Yes       
4           2012-07-19  24              3           12           F    Yes       
4           2012-07-19  32              5           10.1         F    Yes