Abstract
The cost of locomotion is defined as the energetic cost of
transporting one unit of body mass one unit distance. Previous
experiments reported that the cost of locomotion in swimming fish
of sizes .OO1 to 1 kg follows a common trend: as body mass
increases, the cost of locomotion decreases. In this study, costs
of locomotion were calculated for sevengill sharks, Notorynchus
cepedianus, of weights 10.3 to 51 kg. The costs calculated
followed the trend previously reported. The sharks used in this
study represent the largest swimming fish for which the cost of
locomotion has been calculated and demonstrate that the cost of
locomotion trend holds for animals upward of 50 kg. Average
swimming velocities were also calculated in order to compare them
to a cost-optimization model based on the hypothesis that an
unmolested fish will swim at a velocity that requires the least
energy expenditure. In this study, swimming velocities varied from
.31 to .44 m smi over a total body length range of 1.34 to 2.21 m.
Ihese velocities are lower than those predicted by the cost¬
optimization model and those observed in two other shark species.
Introduction
An animal must move to compete for prey, to avoid predation,
and to migrate. Movement requires energy as the animals must
produce thrust, overcome drag, and maintain bouyancy (Alexander,
197781982). Since animals require movement for daily activities,
the amount of energy put into the transport of body mass is of
interest. Cost of locomotion was defined by Schmidt-Nielsen (1972)
as the amount of fuel (in cal) necessary to transport one unit of
body weight (in kg) over one unit of distance (one m). Schmidt¬
Nielsen (1984) and Beamish (1978) collated cost of locomotion data
for fish of sizes 1 to 1000 g and found that the cost of
locomotion decreases with increasing mass (Fig. 1). The largest
animal studied, however, weighed only 1000g. It was of interest,
therefore, to examine the cost of locomotion in larger fish.
The sevengill shark makes an ideal subject for such a study
for two reasons. First, individuals of this species can have a
mass in excess of 50 kg. This mass allows for a test of the
descending trend of Fig. 1 for an animal 50 times larger than the
largest shown. Only one other study of cost of locomotion in
sharks has been reported (Parsons 1990). The largest shark in that
study, a bonnethead shark, weighed only 8 kg. Secondly, the
sevengill shark is a ram ventilator. The shark must constantly
swim in order to circulate water over its gills and breathe.
Despite this ceaseless motion, a 51 kg captive sevengill shark
eats less than .8 kg of salmon a week (Gilbert Van Dykhuizen,
personal comment).
This paper also compares swimming velocity of the sevengill
shark to both theoretical predictions and other shark species.
Weihs' (1977) hypothesized that an unmolested fish will swim at a
yelocity that requires the least energy expenditure per unit
distance travelled (Fig. 2). Parsons (1990) reported swimming
velocities for bonnethead sharks and Weihs (1981) reported
swimming velocities for bull and sandbar sharks. In both of these
studies, the observed speeds matched Weihs' prediction. The
velocities for these three sharks are compared to the average
velocity of the sevengill sharks.
Materials and Methods
General
Six sevengill sharks, Notorynchus cepedianus, were used for
this study. The sharks were held at the Monterey Bay Aquarium,
Monterey, California. Sex, weight, and length data for each shark
are contained in Table 1. During the study, water temperature was
130c (+-10c).
Cost of Locomotion
Four pieces of information are necessary to compute an
animal's cost of locomotion: 1) the amount of fuel ingested, 2)
the resting metabolic rate, 3) the animal's mass, and 4) the
distance travelled. For this study, the amount of fuel ingested by
each animal was obtained from feeding records by averaging the
number of grams of salmon eaten by each individual during the five
months preceeding this study. Next, caloric intake was calculated
by first taking the caloric value of the ingested salmon. (2,170
cal q-i, Altman 1968). Second, the number of calories absorbed
from the food was estimated by multiplying the total caloric value
of the salmon by an estimated assimilation rate. Wetherbee (1988)
reported assimilation rates of 622 to 834 in the lemon shark at
25°C and these values are used here. Finally, resting metabolic
costs were subtracted. Brett and Blackburn (1978) reported resting
metabolic rates for elasmobranchs in general of 97 to 269 cal kg-i
h-l at 150C, Scharold (198981990) and Bushnell (1982) reported
metabolic rates within this range for the leopard and lemon
sharks. Adjusting these values to 130C using a o 2.3 produced a
resting metabolic range of 82 to 228 cal kgri hri. Each shark was
weighed during the study. Distance travelled was measured as
follows, A blueprint of the tank where the sharks were held was
obtained and visual reference points such as anemones and rocks
were marked on the blueprint. Each shark was observed for one hour
sessions and its position in the tank was recorded on the
blueprint every ten seconds. Each shark was watched for three
sessions during daylight hours and one session at night. he
beginning of the daytime sessions varied from 1000 to 1800 and the
nighttime session took place at 0000.
Swimming Velocity
From the collected distance data, an average swimming
velocity was calculated and compared with Weihs' (1977) cost¬
optimization model.
Results
Cost of Locomotion
The cost of locomotion, calculated using different
combinations of assimilation rates and resting metabolic rates,
are shown in Fig. 3. Most of the values generated from the
possible combination of assimilation and resting metabolic rate
cluster around the regression line obtained for other fish.
However some combinations, such as the lowest assimilation rate
(624) and the highest resting metabolic rate (269 cal kg-i h-i),
generate a cost of locomotion as low as O cal gri kmi. This cost
is obviously too low since an animal cannot move its body mass
without any energy expenditure. These zero results occur when the
assimilation estimate is too low, the resting metabolic rate
estimate is too high, or a combination of both. These points
illustrate the problem of defining a resting metabolic rate for an
animal that is in constant motion.
Swimming Velocity
The swimming velocities found in this study are lower than
the optimal velocities predicted by Weihs (Table 1 and Fig. 2).
Discussion
Cost of Locomotion
The total cost of locomotion estimates made here were
slightly higher than the cost of locomotion predicted from the
general trend for swimming organisms (Fig.4), but when possible
resting rates are subtracted to yield net costs, the values
cluster around the predicted result (Fig. 3). However, since
assimilation rate and resting metabolic rate estimates were drawn
from other shark species, these results must be viewed with
caution. In conclusion, the results of this study support the cost
of locomotion regression found for other fish (Figs. 1 and 3) and
show that this relation correctly predicts the cost of transport
for sharks weighing upward of 50 kg. This explains the somewhat
surprising fact that a 50 kg shark can survive on less than 1 ko
of food per week.
Swimming Velocity
Ihis study found swimming velocities of .31 to .44 m s-i for
sharks of lengths 1.34 to 2.21 m (Table 1). Weihs (1981) reported
a swimming velocity of .62 to .72 m smi for bull and sandbar
sharks of lengths 2.0 to 2.3 m, and Parsons (1990) reported
swimming speeds of .29 to .67 m s-* for bonnethead sharks of
lengths .34 to .95 m. Both of these studies however were done at
25"C and, more importantly, measured these speeds over a fixed,
relatively short, and straight section of the tank. This study, on
the other hand, averages data from both the straight sections of
the tank and the sections where the sharks had to turn to
negotiate the walls. It was very clear from my observations that
the sharks swam fastest during the straight sections of the tank.
Since periods of wall negotiation were included in the calculation
of the average speed, it may explain why the speeds observed in
this study are lower than speeds of other species and lower than
Weihs' predicted velocities (Fig. 2). The curved portions of the
tank simply may prohibit the sharks from travelling at the optimal
velocity that Weins predicts.
Literature Cited:
Alexander, R. McNeill and G. Goldspink (1977). Mechanics and
energetics of animal locomotion. John Wiley & Sons, New York.
Alexander, R. McNeill (1982). Locomotion of animals. Blackie & Son
Limited, Bishopbriggs, Glasgow.
Altman, Philip L. and Dorthy S. Dittmer (ed.) (1968). Metabolism.
Biological Handbooks, Bethesda, Maryland, p. 13.
Brett, J.R. and J.M. Blackburn (1978). Metabolic rate and energy
expenditure of the spiny dogfish, Squalus acanthias. J. Fish Res
Board Can 35: 816-821.
Bushnell, P.G. (1982). Respiratory and circulatory adjustments to
exercise in the lemon shark, Negaprion brevirostris. Master
Thesis, University of Miami, Florida. 90pp.
Parsons, G.R. (1990). Metabolism and swimming efficiency of the
bonnethead shark, Sphyrna tiburo. Marine Biology 104: 363-367.
Scharold, Jill, N. Chin Lai, William R. Lowell, and Jeffrey B.
Graham (1989). Metabolic rate, heart rate, and tailbeat frequency
during sustained swimming in the leopard shark, Triakis
semifasciata. Exp. Biol. 48: 223-230.
Scharold, Jill and Samuel H. Gruber (1990). Telemetered heart rate
as a measure of metabolic rate in the lemon shark, Negaprion
brevirostris. Unpublished paper.
Schmidt-Nielsen, Knut (1972). Locomotion: energy cost of swimming,
flying, and running. Science, New York 177: 222-228.
Schmidt-Nielsen, Knut (1984). Scaling: why is animal size so
important. Cambridge University Press, New York.
Weihs, Daniel (1977). Effects of size on sustained swimming speeds
of aquatic animals. In: Pedley, T.J. (ed.) Scale effects in animal
locomotion. Academic Press, New York, p.333-338.
Weihs, Daniel, Raymond S. Keyes and David M. Stalls (1981).
Voluntary swimming speeds of two species of large carcharhinid
sharks. Copeia 1981: 219-222.
Wetherbee, Bradley M. (1988). Absorption efficiency of the
juvenile lemon shark, Negaprion brevirostris, at varying rates of
energy intake. Unpublished Masters Thesis. University of Miami,
Florida. 78pp.
Van Dykhuizen, Gilbert (1990). Senior Oquarist, Monterey Bay
Aquarium. Telephone: (408) 648-4810.
Table 1. General data on the sevengill sharks
Weight
Shark
Sex
Total Body
(kg)
Length (m)
Male
51.0
29.1
Male
1.83
31.4
Female
1.74
Female
1.50
13.2
Female
1.47
14.5
1.34
Female
10.3
Avg. Swimming
Velocity ms- (STD)
.40 (0.03)
40 (o.02
.44 (0.01)
33 (0.01)
.33 (0.01)
.31 (0.01)
Table 2. Caloric intake and total cost of locomotion with
different estimated assimilation rates
Total
TOTAL COST OF LOCOMOTION (cal kg-i m-*)
Shark
caloric
using 837
using 627
intake
estimated
estimated
cals (STD)
assimilation
assimilation
rate
rate
2.66 (1.91)
.0812
.1087
2.18 (1.62)
.1558
.1164
4.70 (2.03)
2788
2083
1.30 (1.07)
.2449
1829
1.66 (0.90)
.2888
2158
.3333
1.27 (O.89)
.2490
Table 3. Net cost of locomotion using different combinations of
estimated assimilation rates and resting metabolic rates
ET COST OF LOCOMOTION (cal kg-i m-i)
Shark
etimated
assimilation rate:
837
627
627
82
228
resting met. rate:
82
228
-i h-1)
(al k
.0511
.0236
.0590
.0984
2274
.1589
.1366
.O661
.1765
.1145
.0556
o2
.2193
.0963
.1462
2589
1274
.0430
.1746
Figure Legend:
Fig. 1: The regression for cost of locomotion for swimming animals
The equation, y - 1.416w-o., relates the cost of locomotion
y in cal gri km' to the weight of the animal w in g. Note that
weight is expressed g. All other figures express the weight in kg.
Fig. 2: The optimal swimming velocities predicted by Weins (1981)
Weihs derived an equation which relates optimum velocity to
total length: Ua = 0.45641°. where Up is optimum velocity in m
sri and L is total length in m. The average swimming velocities
found for each of the sharks in this study are also shown in this
figure.
Fig. 3: Cost of locomotion using combinations of estimated
assimilation rates and resting metabolic rates
The line in this figure is the regression from Figure 1. When
weight w is measured in kg and cost of locomotion y is measured in
cal kgr' mi, the equation of this line becomes y - O.252w-o..
Fig. 4: Total cost of locomotion compared to predicted net cost
This diagram shows the relationship between estimated total
costs, using assimilation rates of 624 to 834, and predicted net
costs.
Energy expenditure, cal q km
—5

/3
0.8
0.4
0.2 +
1.0
Figure 2.

2.0
1.5
Length (m)
2.5
o.
5
01-
Figure 3.

Sumbol estimated
estimated resting
assimilation metabolic rate
rate
cal/(kg t)
83X
228
0
337
82
228
628
628
82

100
10
Weight (kg)
0
Figure 4.

337 estimated assimilation rate
a 627 estimated assimilation rate
100
Weight (kg)