Find grammatical error in this sentence

0 Some fish use their sense of smell as a guide 01b00when return to 01font00their 02font00spawning site.02b0-

0 Some fish use their sense of smell as a guide 01b00when return01font00ing02font00 to 01font00the/their02font00 spawning site.02b00 0-

0 Is there any matter at "their sense" ? Should it be "their 01b00senses02b00" ?0-

0I would use the singular unless the sense of smell of a tuna, say, is different than the sense of smell of a salmon. 02br
02br
00It's like the equally befuddling "The girls raised their right hand(s)" - does each girl have one right hand or more than one right hand? 0-

0 No, that part is fine. 0-