Tranrncrlonr of the Amricmi Fhherlss Socisry 132392-397, 2003
8 Copyright by the American Fiahcrlo~Society 2003
NOTES
Critical Swimming Speed and Behavior of Juvenile Shovelnose
Sturgeon and Pallid Sturgeon
U.S. Army Engineer Waterways Experiment Station,
ER-A, 3909 Halls Ferry R o d ,
Vicksburg, Mississippi 39180, USA
Departrnenr of Biology,
Universlry of Missis~ippi,
Vniversify, Mississippi 38677, USA
-
Abstract.-The swimming performance of hatcheryreared. juvenile shovelnose sturgeon Scaphirhynchus
plarorynchus and pallld sturgeon S. albus was studied in
a laboratory swim tunnel at 20°C and 1O0C. The mean
30-min critical swimming speed was not significantly
different between species at either temperature (36.9 crd
s for shovelnose sturgeon and 35.9 cm/s for pallid uturgeon at 20°C. 19.4 cmls for shovelnose sturgeon and
15.0 c d s for pallid sturgeon at 10°C), Free swimming
(swimming without contact with the substrate) waa observed less than 18% of the time at speeds greater than
15 cmls. As speed increased, pallid sturgeon Swam gignificantly less in the water column at 20°C; however,
speed had no effect on percent free swimming among
shovelnose sturgeon at 20°C. The results of this utudy
Indicate thal, over the temperature and size range tested,
shovclnose sturgeon and pallid sturgcon probably do not
segregate in rivers due to different swimming or stationholding abilities
Shovelnose sturgeon Scaphirhynchus platorynchar and pallid sturgcon S. alhus are sympatric in
the main-stem Mississippi and Missouri rivers and
are: generally associated with flowing water htlbitats in or near the main channel (Bailey and Cross
1954). Adults of both species are known to use
relatively low-velocity areas astiociated with dike
fields, sand bars, and islands (Carlson et al. 1985;
Hurley ct al. 1987, 1999; Bramblett 1996; Curtis
ct al. 1997). Colleclions of young river sturgeons
(Scaphirhynchus spp.) in the wild are infrequent,
and young pallid sturgeon have only recently been
sampled. Juvenile (5.0-21.0 cm) shovelnose sturgeon and pallid sturgeon have been collected by
* Corresponding author: adamsr@siu.edu
Present address: Department of Zoology. Fisheries
and Illinois Aquaculture Centar, Southern Illinols University, Carbondale, Illinoiu 62901-6501, USA.
Received February 7, 2W1;accepted Septembar 9, 2002
bottom trawling on the sand flats of the Mississippi
River, primarily in main channel border areas
whcre velocities 20 cm above the b o t t ~ mranged
from 20 to 80 crnls; sand troughs were usually
present in general capture locations (M. Petersen
and D. Herzog, Missouri Department of Conservation-U.S. Oeological Survey Long-Term Resource Monitoring Program, personal communication). The extent of overlap in habitat use by
river sturgeons remains relatively unknown (particularly for the early life stages), but a potential
consequence of sharing habitat would be an interspecific competition for resources.
Fish occupying similar habitats partition resources along a trophic gradient or through differences in the temporal or spatial use of the habitat (Roes 1986). Closely related, sympatric species may segregate spatially in lotic environments
through limits in their ability to occupy increased
velocities (e.g., Peakc et al. 1997). While most
available information suggests that river sturgeons
at a given life stage occupy the same general habitats, in some field studics adult pallid sturgeon
were found to occupy faster currents and to be
more abundant in swift, channel habitats than
shovelnose sturgeon (Forbes and Richardson
1905; Carlson et al. 1985). However, the interpretation of adult and juvenile capture data is hindered
by uncertainty in identification, the difficulties associated with measuring the focal point velocity
of fish in large, turbid rivers, and thc differences
in fish body sizc. Also, river sturgeons can maintain station against curre,nt by activcly swimming
or by station-holding (Adams et al. 1997, 1999).
The relative abilitics of Ash to withstand and negotiate currents can be examined in laboratory
flumes where Ash are subjected to known velocities and behaviors readily observed.
393
NOTES
--
The performance and behavior of river sturgeons have been examined in laboratory swim tunnels. Fifteen-minute critical swimming speeds
were de~erminedfor a limited number of wildcaught, adult shovelnose sturgeon that ranged in
size from 57 to 69 cm fork length (Adams et al.
1997). Swimming endurance curves have been
constructed for hatchery-reared juvenile pallid
sturgeon (13.0-20.5 cm fork length) at 20°C (Adams el al. 1999). Sturgeons in both studies, if allowed, could maintain station without actively
swimming by using the pectoral fins to generate
negative lift in a manner similar to that of other
benthic fishes (Matthews 1985; Facey and Grossman 1990; Arnold et al. 1991; Webb ct al. 1996).
In addition to station-holding, two swimming
methods ware observed in the laboratory flumes:
(1) substrate skimming, where the ventral body
surface is. in contact with the tunnel bottom, but
propulsion continues to be generated by body and
caudal An undulation, and (2) free swimming,
where swimming occurs within the water column
but without contact with the substrate. In previous
studies, river sturgeons were found to swim mostly
by substrate skimming, but the percent of time free
swimming tended to increase at low and extremely
high flows (speeds). Wherem frae swimming at
low speeds was typically steady in the middle of
the water column, free swimming at high speeds
was characterized by frantic activity and an apparent searching for vclocity refugia (Adams et al.
1999).
Previous laboratory studies provide measures of
active swimming ability md swimming behaviors
of shovelnose and pallid sturgeon, but direct cornparisons between the species are hampered by differences in body size, ontogeny, and source (river
versus hatchery). Given the ecological and economic importance of river sturgeons and the many
alterations to their native habitat (Keenlyne 1997),
it is imperative to understand the habitat use patterns of the two species, particularly during their
early life stages. Here, we studied rolative swimming performance in the laboratory to provide information on one factor potentially influencing
spatial habitat use by young river sturgeons. Critical swimming speed and the swimming behaviors
of hatchery-reared juvenile shovelnosc sturgeon
and pallid sturgeon of a similar size were compired at two temperatures (20°C and 10°C). These
water temperatures were within the range experienced by juvenile river sturgeon, representing a
moderately high and low value (D. Hcrzog, personal communication).
Methods
'
Fish were propagated at Gavins Point National
Fish Hatchery (Yankon, South Dakota) on approximately 1 July 1997. Parcntal shovelnose sturgeon and pallid sturgeon broodstock were from the
Yellowstone River and the confluence of the Yellowstone and Missouri rivers, respectively. Morphometric and genetic analyses indicated the
broodstock did not contain hybrid individuals
(Herb Bollig, Gavins Point National Fish Hatchery, personal communication). Approximately 70
juvenile pallid sturgeon arrived at the U.S. Army
Corps of Engineers Waterways Experiment Station
(Vicksburg, Mississippi) on 2 December 1997, and
swimming endurance over a range of velocities
was studied (Adams ct al. 1999); however, 30 d
elapsed prior to the present study. Six juvenile
shovelnose sturgeon arrived on 7 January 1998 and
were allowed 10 d to recover from transport and
handling prior to acclimation to 20°C. From the
original 70 pallid sturgeon, we chose 12 individuals equal in fiize to the six shovelnose sturgeon
for use in the present study.
Six shovelnose sturgeon and 12 pallid sturgeon
were held in two separate, 300-L Living Streams
model 510 (Frigid Units, Tolodo, Ohio). A higher
number of pallid sturgeon werc acclimated because extra fish were available to ensure a minimum sample size of six. The fish were acclimated
28 d to 20°C and tested over s period of 2 weeks.
After lowering the water temperature 1.5"CId to
10°C, the fish were acclimated 35 d before testing.
The water temperature was maintained within 1°C,
and fish were held on a 12 h light: 12 h dark cycle
throughout the study. Dissolved oxygen (8.16 2
1.31 mg/L [mean + SD]), pH (7.1-7.8). and conductivity (243.0 ? 34.0 pmhoslcm) were monitored regularly and remained similar for both holding tanks. Fish readily accepted Number 4 Silver
Cup Salmon Crumbles (Nelson and Sons, Inc.,
Murray, Utah), and werc fed once daily.
A 100-L, Blazka-type swim tunnel (Baamish
1978) was used to measure sturgeon swimming
ability. The tunnel was constructed of Plexiglas
and had a working section 39 cm long and 15 cm
in diameter. TWOflow filters within the inner tube
reduced turbulence and promoted rectilinear flow.
Water velocities were calibrated with a MarshMcBirney flowrncter and ranged from 5 to 70 c d
9. During trials, black plastic shoats placed over
the working section prevented disturbance of the
fish. Temperature was controlled with a Remcor
liquid circulator (Glendale Heights, Illinois).
ADAMS ET AL.
394
Prior to testing, individual fish were fasted 36
h to achieve a postabsorptive state, thercby limiting the energy allocated to digestion and food
absorption. The sturgeon were transported approximately 6 m to the swim tunnel in a waterfilled cylinder and allowed a I-h habituation period, during which tunnel velocity was increased
from 5 to 10 cmls after 30 min. Following tunnel
habituation, the fish were subjected to a stepwise,
increasing velocity test (Brett 1964) to determine
30-min critical swimming ~peeds.Beginning at 15
cm/s, if a fish swam for 30 min and successfully
completed the bout, the speed was increased to 20
cmls. A stepwise increase in spced of 5 cmls every
30 min continued until the fish fatigued. Fatigued
fish could no longer maintain position against watcr current without bracing against the downstream
retaining screen and would not respond to mechanical stimulation (gentle prodding of the caudal
fin with a small, wooden paddle). Because fish
fatigued before the completion of a bout, the following formula was used to calculate critical
swimming speed (Brett 1964):
u,,
= u,
+ (u,) (W.
where u, is the highest velocity at which the fish
swam the prescribed time period, u, is the velocity
increment (5 cmls), t , is the time thc fish swam at
the fatigue velocity, and tz is the prescribed time
pcriod (30 min). Since fiturgeon occupied less than
10% of the cross-sectional area of the swim tunnel,
speeds were not corrected for a solid blocking offect (Wcbb 1975). Fork length, standard Icngth,
total length, caudal filament length, and mass werc
recorded at the completion of a test. Wcisel (1978)
reported that the ctiudal filament of shovclnose
sturgeon contained lateral line structures, and he
hypothesized that the filament helpod the fish orjent to current. Therefore, caudal filament lengths
may have indirectly affected (perhaps by influencing habituation or orientation in the swim tunnel) critical swimming speeds.
In addition to measuring swimming speeds, we
noted the behavior of both species in response to
increased velocity. During previous observations
in laboratory flumes (Adams et a]. 1997, 1999),
adult shovelnose sturgeon and juvenile pallid sturgeon exhibited an affinity for the tunnel bottom
and could maintain station against water velocity
by station-holding, Because our goal was to compare active swimming ability and not station-holding ability, fish that held station without body or
caudal fin undulation at speeds greater than 15 crn/
s were encouraged to swim (either skimming or
free swimming) by a gentle prodding of the caudal
fin. The total time spent swimming frec of any
contact with the tunnel bottom (free swimming)
was recorded during each velocity increment with
a stopwatch.
Thc critical swimming speeds and swimming
behaviors of shovelnose sturgcon and pallid sturgeon were measured at 20°C and 10°C. Some individuals of both species would not swim in the
tunnel (nonperformers) and were not included in
the analyses. Given the limited availability of
shovelnose sturgeon (six fish), individuals of tach
species were tested at both 20°Cand 10°C. Becausc
fish were retested, we detemincd if physical conditioning or habituation to the tunnel affected our
results. Three pallid sturgeon (not used in the experiments) were tested on three occasions: day 1,
day 14, and day 21 at 20°C.These data were analyzed using repeated-measures analysis of variance (ANOVA). Fixed-effects ANOVA and analysis of covariance (ANCOVA) were used to test
for differences in critical swimming speed between
species at each water temperature. The amount of
time fish swam free of the tunnel bottom was expressed as the percent of total time swam pcr
speed. Arcsine-transformed values of percent frec
swimming (Zar 1984) werc used in repeatdmeasures ANOVA to identify species and speed
effects, spced being the within-subjects factor. All
data met the assumptions of normality (chi-square
test) and homogeneity of variances (Levene's test).
Data were analyzed with Statistica 4.2 (Statistica
1994), and significance of differences determined
(P < 0.05).
No evidence of training or habituation was observed in individual pallid sturgeon that were tested repeatedly. Mcan 30-min critical swimming
speeds (34.1 ? 22.6 cmls; 36.2 ? 1.13 c d s ; 30.0
? 10.71 cmls) were not significantly different over
time (one-way, repeated-measures ANOVA; F2,,
= 0.794; P = 0.513). Theae data suggest that previous exposure to the swim tunncl was not a confounding variable in pallid sturgeon.
The fork length and mass of shovelnose sturgeon and pallid sturgeon did not differ uignificantly (Student's t-test; all P 0.20) at either water temperature (Table I). After accounting - for
body length, no relationship between filament
length and critical swimming spced was detected.
The caudal filament was partially severed on two
fish during transport to and positioning in the swim
-
NOTES
Shovelnwe Skuroeon
TOLE 1.-Morphomebics and 3 0 4 1 1 critical swimming speeds (at 20T and 10°C) of shovelnone sturgeon
and pallid sturgeon used in experlrnants. Values represant
means, with standard deviations in pmntheaes.
Shovalnosc
sturgeon
Vnriabla
rn
Pallld Bturpaon
Pallid
sturgmn
2WC
6
Sample aim
Fork length (cm)
Standard length (cm)
Caudd filament length (cm)
MUB k)
C r l d d nwimming apeod (cuds)
19.47 (0.73)
17.98 (0.75)
5.10 (2.62)
25.13 (4.09)
36.98 (3.49)
1O.C
Sample size
Fork length (crn)
Standard length (cm)
Caudal filament length (cm)
MP~B
el
Crldcal ~wlmmlngs p e d (cmls)
4
20.W (1.29)
19.43 (1.31)
2.48 (2.79)
33.86 (7.79)
19.48 (4.35)
tunnel. These fish exhibited erratic behavior in the
tunnel that resulted in reduced relative swimming
performance. These Ash were considered nonpcrformers and were not included in the analyses.
The critical swimming spttds of six shovelnofie
sturgeon and eight pallid sturgeon at 20°C were
compared using ANCOVA with mass as the significant covariate ( F , , , , = 9.04; P = 0.011), The
assumption of parallelism was met, as the interaction of mass and species was not significant
(F
= 0.11; P = 0.751). Shovelnose sturgeon
mass-adjusted, mean critical swimming speed
(36.98 3.49 cmh) was not significantly different
from that of pallid sturgcon (35.93 + 3.29 c d s )
at 20°C (one-way ANCOVA; F,,, = 0.49; P =
0.496; Table 1). At 1O0C, the critical swimming
speeds of four shovelnose sturgeon and six pallid
sturgeon were analyzed using ANOVA, since neither length nor mass were significant covariates of
swim specd. No statistical difference was detected
(one-way ANOVA; F , , , = 3.64; P = 0.093) between the mean critical swimming speed of shovelnose sturgeon (19.48 t 4.35 crnls) and pallid
sturgeon (15.05 + 3.06 crn/s) at 10°C (Table 1).
Sturgeons spent the majority of bouts skimming
(swimming with some degree of contact with the
tunnel bottom). but free swimming was also observed in both species. Considering only speeds
of 15-30 cm/s (to avoid missing cells in the analysis), we did not see an overall species or speed
effect on the percent free swimming at 20°C; however, the interaction of species and speed Was significant (repeated-measures ANOVA; F,,,, = 4.69;
P = 0.007). warranting an investigation of simple
,,,,
+
,
Swimming Speed (cmls)
FIUURE1.-Mean ( + 2 SEE) percent free swimming
(untrtmaformed) versus swimming speed for shovalnose
sturgeon and pallid sturgeon at 1 0 T and 20°C. Samplc
sizes arc given above error bars.
main effects. Though swim speed had no effect on
percent free swimming in shovelnose sturgeon at
20°C (repeated-measures ANOVA; F,,,, = 1.47;
P = 0.2631, the percent Frte swimming in pallid
sturgeon changed significantly with increasing
swim speed at 20°C (one-way, repeated-measures
ANOVA; F,,,, = 4.17; P = 0.018). Pallid sturgeon
swam in the watcr column significantly more at
15 cmls than at 25 and 30 c d s (Student-NewmanKeuls test; Figyre 1). At 1O0C, there was no significant effect of species or speed on percent free
swimming (Figure 1 ).
Dlscusslon
In a comparison of similar-sized fish, we found
no evidence that shovelnose sturgeon and pallid
sturgeon have different 30-min critical swimming
speeds. The critical swimming speeds for both
sturgeon species in the present study corresponded
well with the speed at which pallid sturgeon are
predicted to endure for 30 min at 20°C (Adam et
al. 1999). Thc two species may not differ in prolonged swimming ability, but the sustained and
burst swimming spccds of shovelnose sturgeon
have not been determined. The experimental design was limited in its ability to discern the strict
effects of tamperature on critical swimming s p e d
396
ADAMS
because temperature treatments could not be randomized. However, critical swimming speed decreased approximately 51-58% in both species
when acclimated from 20-10"C, indicating an
overall similar physiological response (within this
temperature range) as related to performance.
Both species demonstrated an affinity for the
Plexiglas bottom during laboratory tests. They
generally ~ w a mfrec of the tunnel bottom less than
18% of the time at specds greater than 15 c d s
(Figure 1). The remaining portion of bouts were
spent swimming with the body in contact with the
tunnel bottom (skimming). This type of swimming
behavior may allow the exploitation of slower currents present at the boundary layer in rivers, enhancing mobility in a physically challenging environment. At 2 0 ° C pallid sturgeon swam in the
water column significantly more at low speeds than
at faster speeds, but shovelnose sturgeon dcmonstrated no apparent trend with a change in velocity.
This difference in percent free swimming between
specics at 20°C is not easily explained. At 1OoC,
both species were active at low spccds, and generally swam more in the water column during tunnel habituation (5-10 cmfs) than at 20°C. All sturgcon could maintain station by remaining motionless at speeds equal to or less than 15 c n ~ l sand
were not stimulated to swim; therefore, swimming
activity at thesc specds was voliiional. Free swimming at these low swim specds was characterized
by steady swimming in the middle of the water
column, with occasional searches for lower velocity arcas. Our observation that fihovelnose sturgeon behaved differently at 20°C could b e due to
many factors (e.g., differcnces in thermal optima
or an artifact of acclimation) and requires further
study.
Thc critical swimming ~ p c c d sdetermined for
shovtlnose and pallid sturgeon are low relative to
most speeds reported for tcleosts. During active
swimming, the hetcrocorcal caudal fin of sturgeons
may not generate as much thrust as that of other
specics, and the presence of bony scutes increases
drag (Webb 1986). Poorer relative performance
also may b e due to the lower metabolic capacity
of sturgeons (Singer et al. 1990). Fish morphology
(a wide, flat rostrum; large pectoral fins; a flat ventral body surface; and bony scutes) and observations in the laboratory flumcs (Adams ct al. 1997)
suggest that river sturgeons can compensate for
low swimming performance by station-holding
and skimming. The degree to which river sturgeons, particularly juveniles, usc station-holding
and skimming in the wild is unknown. Though
ET AL.
additional studies are needed to describe habitat
use and the extent of overlap, shovelnose sturgeon
and pallid sturgeon probably do not segregate in
rivers based on different swimming or stationholding abilities within the temperature and size
range tested.
Acknowledgments
Sturgeon were spawned and reared by H. Bollig
at a a v i n s Point National Fish Hatchery, Yankton,
South Dakota, and provided to us by L. Lee at the
Upper Mississippi Science Center, Lacrosse, Wisconsin. Without their generosity. this study would
not have been possible. Sturgeon were maintained
under the authority of U S . Fish and Wildlife Permit SA 96-32. We txtcnd our appreciation to J.
Killgore, J. Hoover, and F? Kirk at m e Waterways
Experiment Station, Vicksburg, Mississippi, for
providing laboratory space and commenting on the
manuscript. The authors benefited frbm discusSheehan.
~ j o n swith D. Herzog, J. Hoover,' and
This study was funded by the Environmental Management and Restoration Research Program, U.S.
Army Corps of Engineers. Permission to publish
this information was granted by the Chief of Engineers.
*.
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