Lutcavage and Kraus: Feasibility of photographic assessment of Thunnus thynnus 



501 



projected images. Considering that we could enumer- 

 ate only an undefined portion of the entire school, 

 this source of error was considered negligible. 



Species identification of small tunas by aerial ob- 

 servers can be difficult (Morgan, 1992), but the like- 

 lihood that spotters would mistake other species for 

 giant or large-medium bluefin tuna targeted in this 

 New England fishery is very slight. Commercially 

 valuable schools of yellowfin tuna are rare north of 

 Nantucket Shoals (Mather, 1962; Roffer, 1987), and 



experienced fish spotters would be unlikely to mis- 

 take targeted bluefin tuna for the smaller yellowfin 

 tuna. 



Marine mammals aggregate in groups of sizes com- 

 parable to that of giant bluefin tuna schools. Spot- 

 ters have reported that they can easily distinguish 

 giant and large-medium bluefin tuna from small 

 marine mammals by body shape, tail orientation, and 

 color, but identification is primarily made from swim- 

 ming postures and frequency of dorsal flexure. 



