Stehlik: Effects of season on activity rhythms and swimming behavior of Pomatomus saltatrix 
9 
of flatfishes and the large area of the pectoral fins of 
certain sharks generate enough lift to permit gliding 
without stalling (Weihs, 1973). Sharks and flatfishes, 
which have no swim bladders, are always negatively 
buoyant. The shortfin mako ( Isurus oxyrinchus ), great 
white shark ( Carcharodon carcharias), and blue shark 
(. Prionace glauca) use bouts of gliding and upswimming 
in undulatory patterns over tens of meters (Klimley et 
al., 2002). Tuna ( Thunnus spp.), billfish (Istiophoridae), 
and marine mammals glide while performing diving 
oscillations (Weihs, 1973; Klimley et al., 2002). 
Reports of gliding in teleosts are scarce, and such re- 
ports have mostly been based on observations of flatfish- 
es. American plaice ( Hippoglossoides platessoides ) used 
a glide-and-settle mode of swimming, gliding over 50 
m while avoiding simulated trawl gear (Winger et al., 
2004). Japanese flounder (Paralichthys olivaceus) used 
bouts of gliding and powered ascent in the field and in 
the laboratory (Kawabe et al., 2003, 2004). Ogilvy and 
DuBois (1982) stated that bluefish cannot glide, because 
the surface area of their pectoral fins is not enough to 
produce much lift, and if they stopped propelling them- 
selves, they would stall. However, bluefish do not stall 
because they turn onto their sides and increase their 
horizontal surface area. 
Energetics 
Force required by a fish to swim forward must overcome 
pressure drag in front of the fish, frictional drag from 
distortion of water flow over the body, and turbulence 
from the swimming movements themselves. The drag 
in powered swimming is related to the drag created 
by gliding by a ratio, k: (Weihs, 1973; Magnuson, 
1978), 
k = Fs/Fg, 
where Fs = the drag force of swimming; and 
Fg = the drag force of gliding. 
The ratio, k, varies between 1 and 4 (Weihs, 1973). In a 
scombriform lunate-tailed tuna, the kawakawa ( Euthyn - 
nus affinis), k has been estimated at 1.2 (Magnuson, 
1978). The streamlined body of the kawakawa generates 
relatively little drag during swimming; therefore gliding 
does not save it much energy. In contrast, a fish that uses 
anguilliform propulsion, such as a trout, dace, flatfish, 
or bluefish, may have a k of 3 to 4 (Weihs, 1973). A fish 
uses less energy or thrust during a cycle of gliding and 
upswimming than during horizontal powered swim- 
