Abstract — Daily and seasonal activ- 
ity rhythms, swimming speed, and 
modes of swimming were studied 
in a school of spring-spawned age- 
0 bluefish (Pomatomus saltatrix) for 
nine months in a 121-kL research 
aquarium. Temperature was lowered 
from 20° to 15°C, then returned to 
20°C to match the seasonal cycle. 
The fish grew from a mean 198 mm 
to 320 mm (n = 6 7). Bluefish swam 
faster and in a more organized school 
during day (overall mean 47 cm/s) 
than at night (31 cm/s). Swimming 
speed declined in fall as temperature 
declined and accelerated in spring in 
response to change in photoperiod. 
Besides powered swimming, blue- 
fish used a gliding- ups wimming 
mode, which has not been previously 
described for this species. To glide, 
a bluefish rolled onto its side, ceased 
body and tail beating, and coasted 
diagonally downward. Bluefish glided 
in all months of the study, usually 
in the dark, and most intensely in 
winter. Energy savings while the fish 
is gliding and upswimming may be as 
much as 20% of the energy used in 
powered swimming. Additional sav- 
ings accrue from increased lift due 
to the hydrofoil created by the hori- 
zontal body orientation and slightly 
concave shape. Energy-saving swim- 
ming would be advantageous during 
migration and overwintering. 
Manuscript submitted 27 February 2008. 
Manuscript accepted 1 August 2008. 
Fish. Bull. 107(1):1— 12 (2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Effects of seasonal change ©n activity rhythms 
and swimming behavior of age-0 bluefish 
( Pomatomus saltatrix ) and 
a description of gliding behavior 
Linda L. Stehlik 
Email address: Lmda.Stehlik@noaa.gov 
National Marine Fisheries Service, NOAA 
Northeast Fisheries Science Center 
James J. Howard Marine Sciences Laboratory 
74 Magruder Road 
Highlands, New Jersey 07732 
Bluefish ( Pomatomus saltatrix) are 
temperate-zone fish with seasonal 
cycles of activity that revolve around 
lengthy coastal migrations. Age-1 and 
older bluefish migrate northward from 
April through July along the conti- 
nental shelf of the United States from 
Florida to as far north as Maine. They 
spawn in southern and middle-Atlan- 
tic waters. These bluefish are collected 
on the shelf in spring at a tempera- 
ture range of 8-23°C, mainly 10-19°C 
(Shepherd and Packer, 2006). Spring- 
and summer-spawned cohorts of age- 
0 bluefish arrive in coastal waters 
and estuaries beginning in June and 
remain there throughout summer at 
temperatures of 14-25°C (Nyman and 
Conover, 1988; Able et ah, 2003). Age- 
0 fish reside in estuaries and coastal 
waters until late October, whereas 
older age classes remain until late 
November (Scharf et al., 2004; Shep- 
herd and Packer, 2006). Bluefish 
migrate southward along the Atlan- 
tic continental shelf from along the 
beaches to well offshore. Temperatures 
on the shelf where they are captured 
in fall are 10-27°C, mainly 17-25°C 
(Shepherd and Packer, 2006). Adults 
and the age-0 spring-spawned cohort 
spend winter on the outer continental 
shelf and slope from Virginia south to 
Florida (Shepherd and Packer, 2006; 
Shepherd et al., 2006). These lengthy 
migrations involve risks and are ener- 
getically costly. 
With increasing temperature, the 
rates of metabolic processes of ec- 
totherms increase (the bioenergetic 
response) (Fry, 1971; Brown et ah, 
2004). Within the thermal tolerance 
ranges of most fishes, as temperature 
increases, activity, food consumption, 
and growth increase (Beamish, 1978). 
Bluefish have a higher rate of increase 
in metabolism with temperature than 
their main competitors in the temper- 
ate zone, weakfish (Cynoscion regalis) 
and striped bass (Morone saxatilis) 
(Hartman and Brandt, 1995). The 
bioenergetic response in bluefish was 
observed experimentally in a school 
of 550-650 mm adults held in a 121- 
kL research aquarium under a sum- 
mer photoperiod (Olla and Studholme, 
1971). At 19.5°C, they swam at 40-60 
cm/s. As the temperature increased 
to 30°C over a month, their swim- 
ming speed increased to 80-100 cm/s. 
The high food consumption rates of 
bluefish rival those of tropical species 
(Juanes and Conover, 1994; Buckel et 
al., 1995). Increased food consump- 
tion at higher temperatures is accom- 
panied by increased growth rates in 
bluefish (Buckel et al., 1995; Hart- 
man and Brant, 1995). 
Diel activity cycles or rhythms in 
bluefish are known. Olla and Stud- 
holme (1972) examined effects of 
photoperiod upon the activity of six 
age-l+ bluefish in the aforementioned 
121-kL aquarium. The mean swim- 
ming speed of the school increased 
after transition to daylight, peaked 
at midday, and slowed in afternoon. 
In darkness, the school was more dis- 
persed, interfish distance increased, 
and speeds were more variable (Olla 
and Studholme, 1971, 1972). Less is 
known about seasonal rhythms in 
