 According to Fristrup and Harbison ( 2002 ) , sperm whales eyes afford good vision and sensitivity to light . They conjectured that sperm whales use vision to hunt squid , either by detecting silhouettes from below or by detecting bioluminescence . If sperm whales detect silhouettes , Fristrup and Harbison suggested that they hunt upside down , allowing them to use the forward parts of the ventral visual fields for binocular vision . 
