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Fishery Bulletin 107(1 ) 
ming over the same distance (Weihs, 1973; Webb, 1978). 
The smallest possible glide angle produces the greatest 
energy benefits. A fish having k = 3, that achieves a glide 
angle a of 11°, and uses the most advantageous upswim 
angle /3 of 37° saves 49% of the energy needed for a 
straight swim over the same distance, although it covers 
the distance in 12% more time (Weihs, 1973). 
If k = 3 for a bluefish and the glide and ascent angles 
are those measured in this study, namely, a - 18° and 
/3 = 12°, a bluefish would save 20% of the energy it 
would use to actively swim the same horizontal dis- 
tance. In January 1996, 14% of the bluefish in the 
aquarium were gliding at once, and if one multiplies 
by two to include the ascending fish that were unseen, 
more than one-quarter of the school was using this 
energy-saving mode at one time. 
The function of gliding in migration has been studied 
outside the phylum of fishes. Some birds, particularly 
raptors, minimize the use of powered flight in migra- 
tion by soaring upward on a rising heated air current 
and then gliding as far as possible to the next thermal 
current (Kerlinger, 1989). While soaring, birds flatten 
and extend their wings to increase their surface area. 
While gliding, they partially fold their wings to adjust 
their wing area and foil shape, to control the angle and 
speed of descent. Energy used in the soar and glide 
mode of flight for a hypothetical raptor, depending on 
its weight and wing area, is 10-40% of the energy 
used in powered flight. A broad-winged hawk (Buteo 
platypterus) in migration, given atmospheric conditions 
that produce consistent thermal currents, can fly 8 hr/d 
and travel 320 km/d with only occasional wing flapping 
(Kerlinger, 1989). 
If a bluefish is turned onto its side, its tail shape is 
similar to that of the most energy-efficient tail shape 
of birds that glide. The most efficient lift-to-drag ratio 
is produced with a forked tail, the outermost feath- 
ers of which are twice the length of the innermost, 
and by a 120° angle when the tail is spread (Thomas, 
1997). In juvenile bluefish, the ratio of the lengths of 
the outer to inner caudal fin rays (measured from a 
straight line across the narrowest part of the caudal 
peduncle) is about 2:1. The angle of the fork, however, 
is 65-80°. 
Migration capability and swimming speed 
When one compares information from bluefish tagging 
data with information on swimming capability ascer- 
tained in the laboratory, one concludes that migration 
is not a continuous activity. Recently, bluefish migra- 
tion data from years of tagging studies along the U.S. 
eastern coast were summarized, and recoveries were 
grouped by season and distance (Shepherd et al., 2006). 
Among the southward-traveling bluefish, one group 
had a relatively short migratory path (about 600 km), 
having been tagged in the middle-Atlantic region and 
recaptured off North Carolina. Longer movements 
(up to 2000 km) were made by another group of fish 
tagged in the northern region (New England through 
New York Bight) and recaptured from the Carolinas 
south to Florida. The speeds calculated from the tag 
recoveries from fish at large for 2-3 mo, averaged 
5.9 km/d (Shepherd et al., 2006), which are much 
less than speeds observed in laboratory studies. In 
the research aquarium, spring-spawned age-0 fish, in 
the late fall, including all hours of day and night and 
periods of gliding, averaged 33.6 cm/s (29 km/d). They 
would be able to travel the 600 km from the New York 
Bight to just south of Cape Hatteras, where age-0 fish 
overwinter, in 22 d. Older fish (500-550 mm) swim at 
sustained speeds up to 60 cm/s (52 km/d) (Olla et al., 
1970) and could travel 2000 km in a minimum of 31 
days. Age-2 + bluefish are the only fish captured regu- 
larly on Georges Bank and northward, and therefore 
would travel the farthest (Shepherd and Packer, 2006). 
Although a few tagged bluefish have attained speeds 
>20 km/d and one has attained >48 km/d (Shepherd 
et al., 2006), they are in the minority. Bluefish may 
not migrate directly, but intermittently. Their paths 
include detours, feeding stops, and searches for toler- 
able water conditions. 
Little has been published on northward migration 
routes of bluefish. The timing of these migrations can 
be inferred from ichthyoplankton collections. From 
these, it is known that bluefish spawn in southeast U.S. 
continental shelf waters from March through May and 
continue to spawn in northeast U.S. continental shelf 
waters through August (Hare and Cowen, 1996; Berrien 
and Sibunka, 1999). Eggs from the spring spawning 
are entrained in currents off the southeast U.S. outer 
continental shelf waters and in the Gulf Stream (Ken- 
dall and Walford, 1979; Hare and Cowen, 1996). These 
currents travel northward at 50-100 cm/s (Hare and 
Cowen, 1996; Hare et al., 2002), and perhaps the blue- 
fish themselves use them to migrate. Energy-conserving 
behavior would be extremely valuable to bluefish when 
they must migrate and produce eggs and sperm at the 
same time. 
Overwintering 
Bluefish are intolerant of cold, as is evident from their 
distribution range and from laboratory studies. A blue- 
fish transferred from water 19.5°C to 10°C loses equi- 
librium and motor control, sinks, and soon dies (Olla et 
al., 1985). Gradual acclimation however allows them to 
endure longer. In North Carolina, age-0 bluefish sur- 
vived for weeks in outdoor enclosures as temperatures 
declined gradually to 10°C, but a rapid temperature 
decline to 6°C killed many (Slater et al., 2007). The 
majority of bluefish, from age-0 spring-spawned to adults 
<45 cm, winter from south of Cape Hatteras, NC, to 
Florida (Shepherd et al., 2006; Morley et al., 2007), 
where surface waters do not decline below 15°C. Large 
adults, particularly >45 cm, also winter on the outer con- 
tinental shelf and slope off Virginia and North Carolina 
(Shepherd et al., 2006). On the shelf-slope edge in that 
area, winter bottom temperatures vary among years 
from 10°C to >12°C (Bigelow, 1933). Age-0 bluefish can 
