Brill et al.: Horizontal and vertical movements of juvenile Thunnus thynnus 



163 



diffuse attenuation poefficienl. 490 nm ^^002 

 [comoos !e r^age A^^^^fi July 1998) ^ |B>>Bin 

 75.8 75 6 75 4 ,■. .  - 74 8 74.6 74 4 /4 ^' 74.0 



Figure 9 



Composite satellite images (17 June-lO July 1998) showing (A) chloro- 

 phyll-Q concentrations (mg/m') and (B) water clarity measured as the 

 diffuse attenuation coefficient (1/m, at an in vacuo wavelength of 490 

 nmi) and movements of the five juvenile bluefin tuna. Locations of juve- 

 nile bluefin tuna schools recorded during aerial surveys conducted in 

 1997 are shown by filled circles. (Lutcavage, M. 1998. Aerial survey 

 of school bluefin tuna off the Virginia Coast, July 1997. Report to the 

 National Marine Fisheries Service, cooperative agreement NA77fm0.533. 

 (Available from the author, Edgerton research Laboratory. New England 

 Aquarium, Central Wharf Boston, MA 02110].) are shown by filled cir- 

 cles. The edge of the continental shelf is indicated by the .50-, 100-. and 

 200-m isobath lines (Brill and Lutcavage, 2001). Figure reprinted with 

 permission of American Fisheries Society. 



Carey ( 1992) was one of the first to appreciate the impor- 

 tance of vertical thermal structuring and stated "Temper- 

 ature gradients of 15° to 20°C are not uncommon within 

 the depth ranges of pelagic fish. By moving a few hundred 

 meters vertically, an animal may encounter a greater tem- 

 perature change than it experiences seasonally or in mov- 



ing thousands of miles horizontally." As with bluefin tuna, 

 the vertical movements of yellowfin tuna and swordfish 

 also result in their experiencing vertical temperature gra- 

 dients orders of magnitude greater than horizontal tem- 

 perature gradients (Carey and Robison, 1981; Carey, 1990; 

 Holland et al., 1990; Cayre and Marsac, 1993). The inabil- 



