William G. Raschi and John A. Musick rn.~T'TD .!. r'T ,N.! ... The College of William and Mary. Gloucester Point .... M. MacDonald (Rutgers Univ.), M. Namack, J.
NASA Contractor Report 3963
NASA-CR-396319860013418
Hydrodynamic Aspects of Shark Scales
William G. Raschi and John A. Musick
rn.~T'TD .!. r'T
,N.!. '" 1_1 hOd?
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MARCH 1986
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LANGLEY RESEARCH CfNTE;F? LIBRARY, NASA
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NASA Contractor Report 3963
Hydrodynamic Aspects of Shark Scales
William G. Raschi Bucknell University Lewisburg, Pennsylvania John A. Musick Virginia Institute of Marine Science The College of William and Mary Gloucester Point, Virginia
Prepared for Langley Research Center under Contract NASl-16042
NI\S/\
National Aeronautics and Space Administration
Scientific and Technical Information Branch 1986
LIST OF FIGURES
Figure
Ti tle
Page
1
Scale measurements used in this study ........•...•....•..•••.•.•
2
Scanning electron micrographs of scales from Prionace glauca showing the presence of microrelief. ......•....•.••••••••
3
Scanning electron micrograph of the posterior margin
5
10
of
scales from Carcharhinus pl umbeus ..•. -. . . . . . • . . • . . .• . • • • • • • . • . • ••
14
4
Scale morphometries for ~. plumbeus.............................
16
5
Scanning electron micrograph of scales from Carcharhinus obscurus taken from the posterior ••••.••.•••.••••••••.••••• ~ •••.
20
6
Scale morphometries for C. obscurus •••...•.•.•.••••••••••••.••••
22
7
Scanning electron micrograph of the posterior margin of scales from Prionace glauca.....................................
25
8
Scale morphometries for~. glauca ••.••.•••••.•.•.••...•....•..••
28
9
Scanning electron micrograph of the posterior margin of scales from Carcharhinus signatus ••.•••••••.•••••••••••••••••...
31
10
Scale morphometries for C. signatus •..•.•.••...••••••••.•••.....
33
11
Scanning electron micrograph of the posterior margin of scales from Rhizoprionodon terraenovae ........••..•.•.•.•••••...
37
12
Scale morphometries for R. terraenovae ••••.•••.••••••.•.•••..••.
39
13
Scanning electron micrograph of the posterior margin of scales from Carcharhinus falciformis •••...•..••••••••••.•.•.....
43
14
Scale morphometries for C. falciformis ..••..••...••••.•••••..•..
45
15
Scanning electron micrographs of the posterior margin of scales from Carcharhinus leucas.................................
16
49
Scanning electron micrograph of a scale from Carcharhinus limbatus and Ginglymostoma cirratum .•••.••••....•.•••••...•.•... iii
52
LIST OF FIGURES (Continued)
Figure
Title
17
Scanning electron micrograph of the posterior margin of
Page
scales from Sphyrna mokarran and Isurus oxyrinchus •••..•••.•.••• 55 18
Scanning electron micrograph of the posterior margin of scales from Sphyrna lewini......................................
19
58
Scanning electron micrograph of the dorsal surface of scales from Mustelus canis......................................
61
20
Scale morphometrics for M. canis •••.•.•••••••.••••••••••••••••••
63
21
Scanning electron micrograph of the posterior margin of scales from Galeocerdo cuvieri ••••••••...•.•••..••••••••.•••••••
67
22
Scale morphometrics for G. cuvieri .••.•••••••••••••••••.••••...•
69
23
Scanning electron micrograph of scales from Odontaspis taurus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Q. taurus •••.••••••....•••••...••••••.•• 75
24
Scale morphometrics for
25
Lengths and widths of scale crowns as estimated from growth
. equa tJ.ons •.••••.••.••..•.•••••.•...•.•••.•••.•.•••.•..•.••••••.• 26
82
The relationship between keel spacings as measured from a variety of species and the length of the fish •.•.•.•••••••••.•••
28
79
Heights and spacings of keels on the scale crowns as estimated from growth equations ..•.•..••••••••.•.••••••..•.•.•••
27
72
90
The relationship between keel heights as measured from a variety of species and the length of the fish ••.••••..•.••••.•••
iv
93
LIST OF TABLES
Table
Title
Page
I
Summary of the material collected for scale examination.....
4
II
Occurrence of microrelief ...................................
12
III
Scale morphometrics for the additional species as listed in the text.................................................
IV
48
Summary of slopes of the growth characteristics from scales of the nine species of which adequate numbers of specimens are available............................................... 84
V
Reduction in the secondary and tertiary keel spacing and heights (expressed in percentages) as compared with primary
values......................................................
98
Collection data for the material examined ...................
108
Appendix
I
v
ACKNOWLEDGEMENTS Embarrassingly, and
the
this
study has taken nearly five years to complete
futility of trying to remember everyone who has helped collect
all of the material we've used becomes immediately apparent. The removal of
these skin samples was often an ancillary task, occassionally deemed
unduly
onerous (Mundy, 1981), and very often accomplished at the end of
rather long and tiring days. Be assured that those omitted here are done so completely accidentally. For
help
in the field, we'd like to again thank M.E. Anderson (Cal.
Acad. Sci.), J. Gourley, D. Koester (Eye and Ear Hospital of Pittsburg), M.
MacDonald
(Rutgers Univ.), M. Namack, J. Smith (NMFS, Beaufort) and
in particular, the invaluable help of J. (VIMS)
Colvocoresses (VIMS). P. Mason
provided ample technical assistance for the SEM preparations, as Baumgardner and J. Estep (Bucknell Univ.) in the preparation of
did
K.
the
manuscript.
Bucknell University provided additional facilities and
financial support.
vi
INTRODUCTION The
energetics
thrust the
and
drag.
seeming
of
fish
locomotion
depends
on a balance between
The interest stimulated by "Gray's Paradox", that is
lack of sufficient power to overcome many of the estimated
values of drag, has resulted in the delineation of a number of potential drag
reducing
variety
of
mechanisms
structural
(Walters,
1962)
and
increase
surface
(Webb,
mechanisms, scale
Elasmobranch
perform
function.
this
type
layer,
a
particular interest is a
as scombroid scale corselets
(Burdak,
and
thereby
1969; Bone, 1972), which boundary
alter
layer
placoid scales, or dermal denticles, may
Bone and Howarth (1966) have suggested that
of scale reduces drag by creating turbulence in the boundary
thereby
preventing
Weinstein
(1978)
arranged
v-shaped
reduction number
such
Of
ctenii
roughness
characteristics. such
1975).
in
the
have
its
shown
grooves turbulent
separation.
More
recently, Walsh and
that surfaces composed of longitudinally
can
significantly
bursting
reduce
drag
through a
activity. Placoid scales from a
of galeoid shark species exhibit this type of surface morphology
and may therefore represent a potential drag reduction mechanism. Following
its
eruption
through
the
epidermis,
a
typical scale
consists of three parts (Applegate, 1967). An expanded, plate-like crown lies narrow scale
above neck into
the
surface of the skin and is attached by a somewhat more
or pedicel to a rectangular or stellate base anchoring the the
integument. The crown normally exhibits a large medial
ridge or keel which runs longitudinally along the midline and is flanked along
either
side by one or more lateral keels (Compagno, 1979). These
I
keels
often
lateral
extend
cusps.
the
This
posterior margin of the crown into medial and
general
arrangement
is
found
in
many
widely
separated phylogenetic groups (White, 1937). comparison
A
of
theoretical,
grooved
difficult
obtain
to
reasons. from
Although
various
Radcliffe, and
from
specimen,
including
not
inclination 1970)
and
as by
existing
drawings.
only
Walsh
and
literature
for
of
the
Weinstein
is
a number of
1948~
Castro, 19831
In
addition,
a
great deal of
their
general
shape (Applegate,
1967~
Sayles and Hershkowitz, 1937) but also the
1928~
of the crown to the body surface (Chernyshov and
well. a
Finally,
all
synchronomorial
living species of galeoids are
scale type (Compagno, 1973) whose
shape often change dramatically through replacement (Garrick, 1917~
Radcliffe,
this
study
from
a
examine
these
Daniel,
1979~
of
1960;
by
that
found between scales from different locations on a single
characterized size
the
proposed
with
1916), it is often difficult to determine their actual sbapes
is
Zayets,
from
dimensions
several authors have presented representative scales
variation
angle
surface
crown
shark species (Bigelow and Schroeder,
dimensions
Compagno,
various
then,
variety what
Raschi, et al.,
1982~
Reif, 1974). The aims of
are to compare the surface structure of scale crowns of
shark
changes
species may
occur
replacement.
2
with the above model as well as to to
these
scales
during
their
METHODS AND MATERIALS A
total
(Table
of 129 skin samples from 15 species of sharks was examined
I).
The
sportfishing clubs)
or
Institute
majority
tournaments through
the
of
the
fish
(Virginia longline
were
obtained
from
either
Beach and Charleston Shark fishing surveys
conducted
by
the Virginia
of Marine Science (VIMS) during the summers of 1981 and 1982.
Additional
material
was also collected from a variety of other sources
including the R/V Columbus Iselin cruise CI-7803, Taute Bros. (Marathon, Pflueger
Fla. ),
Marine
sportfishermen.
Collection
and
are
longitudes
fishing the
not
tournaments
Institut
Taxidermy data
and
a
number
of
individual
is presented in Appendix I. Latitudes
available
for
those
specimens collected at
in Charleston, S.C.; for specimen #64 on loan from
Fondamental
d'Afrique
Noire
and
for
the two aquarium
specimens, #82 and 83. Nomenclature follows Robins et ale (1980). Skin the
patches,
measuring 25-50 sq. cm, were removed from just below
anterior margin of the first dorsal fin. Subsamples were washed and
placed
in
a concentrated solution of sodium hypochlorite to remove the
scales
while
examination. distilled sample
the
Individual
water
were
remainder
and
then
of
the
scales
were
sample washed
was in
frozen several
for
future
rinses
of
air dried. Approximately fifteen scales from each
mounted
on
an
aluminum
SEM
stub and coated with
gold-palladium by vacuum evaporation. Four
sets
of
measurements
were made on five separate scales from
each
stub (figure 1). Initially, the length and width of each crown was
taken
from directly above its surface (0-20 degree tilt). Secondly, the
3
Table I.
Summary of the material collected for scale examination. Number of individuals examined
Size range (total length in cm)
Carcharhinus falciformis
5
103-268
Carcharhinus leucas
4
169-278
Carcharhinus limbatus
5
148-173
Carcharhinus obscurus
17
86-334
Carcharhinus p1umbeus
30
59-216
Carcharhinus signatus
8
76-222
12
156-404
Species
Galeocerdo cuvieri Ginglymostoma cirratum
2
72-77
Isurus oxyrinchus
3
132-182
----
10
37-127
Odontaspis taurus
9
165-247
13
34-348
Rhizoprionodon terraenovae
7
40-106
Sphyrna lewini
3
54-225
Muste1us canis
Prionace glauca
1 129
Sphyrna mokarran
4
252
Fig. 1. as follows:
Scale measurements used in this study.
Abbreviations are
"A", crown widths; "B", crown length; "C", primary inter...
keel distance; "D", primary keel height; 1°, 2°, 3° are the primary, secondary, and tertiary keels.
(Redrawn by J. Estep)
5
inter-keel
distance,
or
spacing,
was
measured
between the peaks of
adjacent
keels. These were taken from a posterior aspect with the crown
surface
tilted between 30 and 50 degrees. The bilaterally averaged pair
of
spacings
lateral,
or
Similarly, adjacent values. was on
between secondary
the
medial,
keels,
or
is
primary
designated
keel, and the adjacent as
the
primary value.
that pair of distances between the secondary keels and their lateral,
or
tertiary
keels,
are
considered
the secondary
Similar nomenclature is used for each subsequent pair. The mean
then calculated for all the averaged values for each of these pairs a
crown.
Finally, the heights of the ridges were measured with the
crown
tilted
so
degrees and
tilt).
compared
each
crown
from
the
Pairs of the secondary and tertiary keels were averaged with the primary ridge. A mean value for all the keels on
was CRT
magnifications scale
as to provide a view parallel with its surface (70-90
also screen between
calculated. All measurements were taken directly to 180
the
nearest five microns, with specimens at
and
200
X. The actual angle to which
was tilted depended on both the angle at which the crown sat
a on
the
scale
the
stub. In addition to the above measurements, the number of keels on
each
scale was counted and a photograph of one scale from each specimen
taken body
base as well as on variations of the seating of the scale on
for future reference. The regressions of all these measurements on lengths
for each species follows Snedecor and Cochran (1967) with
significance set at the 99% level.
7
RESULTS Scale Types Three this
different morphological types of scales were distinguished in
study.
crown
The first (figure 3) is characterized by a relatively thin
exhibiting a single, prominent primary keel and a variable number
of lateral, often smaller, keels. The anterior margin is normally evenly rounded found
with on
all
oxyrinchus, and
the
similarly
Prionace glauca, Rhizoprionodon terraenovae, Sphyrna lewini
thin pairs
lanceolate
shape,
of
posterior
Mustelus
the
The second morphological type (figure 19) exhibits a
crown
successive
pointed
either emarginate or smooth. This type is
specimens in the genus Carcharhinus as well as on Isurus
mokarran.
S.
species
posterior
canis
in
with
media~
a
lateral
pair of primary keels flanked by
keels. It has a typically blade-like, or
with a broadly rounded anterior margin and a sharply margin. this
This study,
type but
is
found
only on specimens of
appears to be typical of all the
in the genus Mustelus (Bigelow and Schroeder, 1948), except for
South American M. dorsalis (Bigelow and Schroeder, 1940). The third ( figure
type
correspondingly thicker very
is
21) heavy
characterized
base.
The
scale
by
a
necks
very
thick
crown
and
are disproportionately
and tend to be somewhat reduced in height. The crown exhibits a
prominent
primary
keel with a somewhat smaller pair of secondary
keels. The margins are evenly rounded with the absence of any noticeable cusps.
This
type
of
scale is found on Galeocerdo cuvieri, Odontaspis
taurus and Ginglymostoma cirratum.
8
Microrelief In
addition
examined
In
this
microrelief pockets
to
the normal ridges, approximately 50% of the scales study
also
exhibit
additional
microrelief.
This
is typically arranged in the form of hexagonal or octagonal
(figure
2),
often becoming compressed along the scale margin.
The
surface area covered by microrelief, when present, varies from only
the
anterior
II).
c.
margin
to
the entire dorsal surface of the scale (Table
It is found in varying degrees on all specimens of signatus,
mokarran;
on ~.
obscurus,
By
only
a
glauca,
R.
terraenovae,
specimens
of
C.
P.
few
leucas,
falciformis,
s.
lewini, S.
C. limbatus, C.
plumbeus; and is completely absent from all specimens of G.
!.
cuvieri,
canis,
M.
~.
oxyrinchus,~.
dividing
designated
all
of
cirratum and O. taurus. the
scales
into
two artificial groups; one
as completely covered, with microrelief covering between 75%
and 100% of the crown surface (figure 2, 18) and the other designated as only
partially
(figure
5a,
19),
microrelief within
covered, it
becomes
development
each
species
with
microrelief apparent
reflects
the
covering
that relative
the
from
25% to 50%
relative degree of
size
of the specimen
(compare with Appendix I). In those species which
contain specimens exhibiting both complete and partial covering, such as C.
falciformis,~.
obscurus,
~.
plumbeus, P. glauca and
~.
terraenovae,
only the smallest individuals have completely covered scales while those from
larger
several
species
exhibited devoid
specimens
of
tend to be only partially covered. Furthermore,
examined, such as
~.
leucas,
~.
limbatus and
~.
canis,
only partially covered scales in addition to those completely any
microrelief; whereas none contained only specimens with
9
Fig. 2.
Scanning electron micrographs of scales from Prionace
glauca showing the presence of microrelief. (a) From a 34 cm TL male (specimen no. 106) at 190 X magnification, (b) From a 46 cm TL female (specimen no. 109) at 520 X magnification.
10
Table II.
Occurrence of microrelief Specimen number Complete
c.
fa1ciformis
1-3
Partial 4, 5 6
C. 1eucas
c.
limbatus
c.
obscurus
15-17, 19
c.
p1umbeus
32-40
c.
signatus
62-64, 67-69
13, 14 18, 20-23, 25-31 41 65, 66 87-96
M. canis P. glauca
106-115
116-118
R. terraenovae
119-121
122-125
S. 1ewini
126
127, 128
S. mokarran
129
12
completely covered scales. Both pieces of evidence strongly suggest that microrelief
is more prevalent on smaller scales from smaller specimens,
decreasing
in
significance
relative
of
degree
microrelief
on
larger
replacement
scales.
The
will be further discussed in a subsequent
report. The
dimensions
intraspecific
of
variation
the and
scale will
crowns
exhibit
considerable
be used to characterize scales from
each individual species.
Species Descriptions C. plumbeus
The
greatest
ontogenetic cm 83%
of
1948) The
scale
intervals
and
most
reliable
picture
of
postpartum,
total
total lengths of 59 to 216 cm. This accounts for
size range of between 56 cm (Bigelow and Schroeder,
249 cm (Garrick, 1982) previously recorded for this species.
scale
generally
the
development. Scales were removed from specimens at 5
between
the
of scales were examined from this species and
provide
therefore
may
number
crown
is moderately thick with very prominent ridges. It is
ovoid in shape, with broadly rounded margins and a relatively
short pedicel (figure 3). The size
width
range
replacement an
estimated
of
the
studied
crown is greater than the length throughout the
(figure
4).
widths increase ontogenetically with
at a rate of 3.02 microns/cm (r crown
width
= 0.93**).
This rate yields
of from 150 microns to 703 microns over the
total size range. Actual measurements range from 170 microns (specimen # 37)
to
785
microns
(specimen
#
61).
13
Crown
lengths
also increase
Fig. 3.
Scanning electron micrograph of the posterior margin
of
scales from Carcharhinus plumbeus. (a) From a 88 em TL female (specimen no. 37), (b) From a 188 cm TL female (specimen no. 57).
14
Fig. 4.
Scale morphometrics for
£.
resents the average of five measurements.
plumbeus.
Each data point rep-
Spacings and heights are
average values for all the keels on each crown.
Line equations are
calculated from the total number of individual measurements.
The
equation describing the increase in the number of keels is based on only those specimens larger than 110 cm TL (specimen no. 42-61).
16
.... -..... -- --
600
.... --- -
_
.....
.....
500
ya-189!5 . +3.02X
I-'
"
400
•
a
o
a
o
•
a
Il:
•
a
z
(.)
~
SCALE SCALE TOTAL TOTAL
....
/0 0
..
/' ~.
~--6'.~
•••• /0
. /0 6~
•
WIDTH LENGTH INTER-KEEL KEEL HEIGHT
•
o
./.
300
200
. //
. /.Y ../. ·0· /
...
....
TL (em)
(J)
•
,.-
NUMBER OF KEELS
•
(p
~
0
0
o
0
0
,./".......... 0
/0 0
0
Y--26 .08 .. 2.34 X
o
0
Carcharhinus plumbeus
0
o~v
~- ~
o
ct
ya 48.156 .. 0.30 X
•
••
•
_.a-a-----_--ro;----..-.--·----..---------- - - --
100
_ • • _ . _ . _ . _ . _ . _. ._. _ _ _. .
40
60
80
100
120
~
~. y I9.16+ 0.08X ... .--.-.~••-~ .6 Aa
_
• 140
TOTAL LENGTH (em)
.......
160
180
200
ontogenetically corresponding the
total
at
a
rate of 2.34 microns/em (r
estimated
size
range
range.
=
0.91**), yielding a
of from 105 microns to 533 microns over
Actual
measurements
range
from
125 microns
(specimen # 32, 37) to 625 microns (specimen # 61). Smaller prominent number TL
ridges,
c.
of
whereas
plumbeus
on
exhibit scales with only three
fish longer than 120 to 140 em TL, that
increases with the replacement scales at a rate of 0.03 keels/em 6.32**).
(t
crown 53,
specimens
The averaged, total inter-keel distance on a single
ranges from 55 microns (specimen # 38) to 125 microns (specimen # 56,
61).
These
of
0.30
microns/cm-rL(t
rate
spacings
of
from
spacing values also increase ontogenetically at a
65
16.62**).
microns
to
This rate yields estimated
120 microns. The primary inter-keel
distance varies from 55 microns (specimen # 38) to 150 microns (specimen #
61),
while the average secondary inter-keel distances are between 75
microns
to
183 microns. This corresponds to a decrease of between 6.1%
and 31.0% (average
=
18.6%) from the primary.
Keel heights tend to remain relatively constant, with an increase in the
average
height
=
microns/em TL (t (specimen
#
37,
all
keels
on
a
single
crown of only 0.08
7.74**). Total averaged heights range from 18 microns 41)
to
only
52 24
microns (specimen # 46), while predicted
values
range
range.
The primary keel is normally from 20 microns (specimen # 32, 34,
37,
from
for
microns to 38 microns over the total size
38, 39, 41) to 70 microns (specimen # 53) high. The secondary keels
exhibit an average reduction in height from that of the primary by 10.9% (ranging
from
an
increase
of
33%
to
a
decrease of 40%), with the
bilaterally averaged measurements ranging between 18 microns (specimen #
18
32,
41)
and
greater 75%),
55
microns
reduction with
of
values
(specimen # 53). Tertiary keels show a still
45.7%
ranging
from the primary keel (ranging from 7% to between
microns (specimen # 43) and 43
5
microns (specimen # 61)
c.
obscurus This
et
species
aI,
1973)
examined
to
from
generally
is larger than a
maximum
over
smaller.
~.
of
plumbeus, ranging from 69 em (Bass, 363
em (Garrick, 1982). Scales were
84% of this range. By comparison, these scales are Their
crowns
appear much thinner and less heavily
sculptured (figure 5). The anterior margin is broadly rounded while that of the posterior is always emarginate. Scales
are
approximately 22)
to
500
wider
190
cm
than
long
only
on
specimens
smaller
than
(figure 6), ranging from 180 microns (specimen #
microns
(specimen
#
31).
These
values
increase
ontogenetically
at a rate of 0.66 microns/em TL (r = 0.85**), result.ing
in
smaller
a
somewhat
microns. scales
Similarly, at
a
rate
the of
estimated length
range
of
from
229 microns to 418
of the crown increases on replacement
0.99 microns/em TL (r
=
0.87**). Actual lengths
measured between 170 microns (specimen # 22) and 560 microns (specimen # 31)
as compared with the projected estimated values of from 188 microns
to 472 microns. The
number
of ridges range from 3 on smaller specimens to 7 on the
larger. This number increases at a rate of 0.01 keels/em TL which is not significantly
different from 0 (t
=
2.21). The average total inter-keel
distance increases with body length at a rate of 0.05 microns/em TL (t
19
=
Fig. 5.
Scanning electron micrograph of scales from Carcharhinus
obscurus taken from the posterior, (a) From a 127 cm TL male (specimen no. 23), (b) From a 334 cm Tl female
(s~ecimen
20
no. 31).
Fig. 6.
Scale morphometrics for
£.
obscurus.
represents the average of five measurements.
Each data point
Spacings and heights are
average values for all the keels on each crown.
Line equations are
calculated from the total number of individual measurements.
22
...
~
~
600
•. . •
•
y- 4.08.0.01)(
NUMBER OF KEELS
500
90
120
150
180
210
240 270
o
aoo aao
TL (em)
C/)
z
N W
400
o o
• • SCALE o • SCALE • • TOTAL A • TOTAL
Y-1I9.99+0.99X
WIDTH LENGTH INTER-KEEL KEEL HEIGHT
0:: ~
300
••
•!~ ~.,.--.
i
___ 0."- .-----------o ----->'
0
a::
o • SCALE • • SCALE • a TOTAL • • TOTAL
•
Y=2.33+ O.OOX
300
330
360
390
(em)
ya-179.33 + 2.36 X
LENGTH WIDTH INTER - KEEL KEEL HEIGHT
o
o
600
y a 36.23+ 1.73X
o
0
:t
o
400
Galeocerdo cuvierl
. . . -.-...-- • o
•
~-~:.----
•
ya 22.31 + 0.63 X
.-~-~----
200
• ya2.14 +0.25X
o 150
180
210
240
270
300
330
360
390
TOTAL LENGTH (em)
.
~
.......... ----,----------------.-------~----
~
species. Scale
crowns
increasing (and
at
at
from
1
to
3
ridges,
a rate of 0.02 keels/cm TL (t
primary)
scales
exhibit
keel
a
=
with
values slowly
4.818**). Averaged total
spacings on a single crown increase on replacement
rate of 0.63 microns/cm TL (t
=
9.405**), ranging from 63
microns (specimen # 70) to 275 microns (specimen # 81). Estimated values range
between 51 microns and 489 microns over the published size range.
Similarly, increase
averaged
total
keel
heights
on
an individual crown
ontogenetically at a rate of 0.25 microns/cm TL (t
=
6.349**),
from 35 microns (specimen # 70) to 153 microns (specimen # 81).
ranging This
the
yields estimated values of between 14 microns and 187 microns over
the
published
#
(specimen averaged microns from
size 73)
range.
190 microns (specimen # 81) while the bilaterally
to
secondary
Primary keel heights range from 75 microns
keels
from 5 microns (specimen # 70) to 135
range
(specimen # 81). This amounts to an average reduction in height
the
particular specimens
primary
keel
interest
of
is
from 28.9% to 94.7% (average of 77.9%). Of
the striking change in general shape in larger
(as in specimen # 81) to one with proportionately much larger
and prominent ridges.
Odontaspis taurus Scales those
of
from this species (figure 23) are similar in many aspects to G.
proportionately generally
cuvieri. larger
limited
disproportionately
They
are
generally very large and heavy, with
bases. Keels also tend to be very large and are
to
three
larger
and
in
number,
with
the
primary
being
the secondary ridges confluent with the
71
Fig. 23.
Scanning electron micrograph of scales from Odontaspis
taurus, (a) Dorsal view of a scale from a 210 em TL female (specimen no. 100), (b) Apical view from a scale from a 235 cm TL male (specimen no. 104).
72
lateral
margins
narrow
of
the
crowns. Skin samples were removed from a very
portion (37.6%) of this species' published size range of between
100 cm (Castro, 1982) and 318 cm (Bigelow and Schroeder, 1948). Scale
crowns
are
generally
wider than long (figure 24) on fish
smaller than between 210 cm and 220 cm TL. Individual crown widths range from
340
microns
increasing 0.38**). 541
with
This
microns
#
(specimen body
length
97) at
a
to
565
rate
microns (specimen # 99),
of
0.84 microns/cm TL (r
=
rate results in estimated values between 358 microns and over the published size range. Crown lengths range between
265 microns (specimen # 97) and 615 microns (specimen # 103), increasing ontogenetically lengths
vary
at a rate of 2.72 microns/cm TL (r from
146
= 0.69**).
Estimated
microns to 739 microns over the published size
range. Crowns rate
of
exhibit 0.02
average
from 1 to 3 ridges, increasing ontogenetically at a
keels/cm
distance
of
TL
from
=
(t 130
3.279**). These keels are located an
microns (specimen # 97) to 225 microns
(specimen # 104) apart. These spacings increase on replacement scales at a
rate
of
estimated
0.59 value
microns/cm of
TL
between
(t
106
= 3.709**),
microns
and
a rate which yields an 235
microns
over the
published size range. Average keel heights for all the keels on a single crown
also increase with body length at a rate of 0.53 microns/cm TL (t
2.755**), (specimen values
of
#
ranging
from
32
microns
(specimen # 98) to 160 microns
99). Similarly, this rate yields a wide range of estimated from 15 microns to 130 microns over the published size range
for this species. Primary keel heights vary between 50 microns (specimen
#
100) and 160 microns (specimen # 99). Secondary keels are between 29%
74
Fig. 24.
Scale morphometrics for
sents the average of five measurements.
£.
taurus.
Each data point repre-
The spacings and heights are
average values for all of the keels on each crown.
Line equations are
calculated from the total number of individual measurements. are the same as in other graphs.
75
Symbols
6
600
C/)
yaS.SI-0.02X
4
2
500
NUMBER OF KEELS
•
• •• 170
-
190
-.
400
z o a:: o
~
ISO
200 TL
210
• • • • 220
230
Y·-126.27 + 2.72 X
o
i"
0
•
240
e-------::
0
(em)
• y. Z73.87 + 0.84 X
Odontasp/s taurus
300
Y·47.79 + 0.S9X
200
------------------------.---------------------.----.--A
100
___ 160
A
__--------A------------------~----------A-----------~A
170
180
190
200
210
TOTAL LENGTH (em)
A
A
Y·-3S.06 + 0.!S3X
220
230
240
and
91%
shorter
(average
of
56.9%)
than the primaries, with values
between 8 microns (specimen # 98) and 68 microns (specimen # 103). Finally, available
the
two
for
specimens
study
of
Ginglymostma
possessed
scales
cirratum which were
which
exhibited
many
characteristics similar to those of both G. cuvieri and O. taurus. These scales
(figure
conspicuous
16b)
cusps.
were
generally
Individual
crown
broadly lengths
rounded range
and
free
of
from 455 microns
(specimen
# 83) to 675 microns (specimen # 82), with average values for
the
five
scales from each specimen between 539 microns (specimen # 83)
and
599
380
microns
range and
microns (specimen # 82). Similarly, crown widths range between
of 566
part
(specimen
microns (specimen # 82). While distinct keels are for the most
elevations.
there
Distances
are
distinguishable
between
these
ridges
ridges range
or from
longitudinal 115 microns
# 83) to 220 microns (specimen # 82), with average values for
(specimen
specimen
heights
83) and 690 microns (specimen # 82) with the
for each specimen between 531 microns (specimen # 82)
values
absent,
each
#
between
175
microns
and 197 microns. Similarly, ridge
range from 18 microns (specimen # 83) to 42 microns (specimen #
82), with total averaged values between 26 microns and 39 microns. These values to
less
1982),
however, are from specimens only 70 to 80 em long, which amounts than and
may
1/4
of the total'length of 425 cm of the adult (Castro,
therefore
only
be considered as an indication of the
typical scale morphology from the juveniles of this species.
77
DISCUSSION Previous studies of the squamation on pelagic galeoids by Reif and Dinkelacker (1982) provide scale keel spacing values for eleven species which closely agree with the average values obtained in this study.
Individual measurements for
glauca and
i.
while those of
£.
obscurus,
l.
oxyrinchus,
f.
lewini fall within the range obtained in this study,
£.
falciformis are only slightly larger than those
obtained here. A comparison of crown morphooetrics projected over the total size range for each species shows considerable intraspecific similarity (figure 25).
In the majority of species, crown lengths range from
approximately 100 microns on juveniles to nearly 500 microns on the largest adults, while crown widths exhibit a somewhat narrower range of from 125 microns on juveniles to a maximum of 425 microns on adults.
Crowns of similar size were observed on smaller species, such
as Rhizoprionodon terraenovae, as well as the much larger species, such as Carcharhinus obscurus.
Even the greatly elongated crowns of
the scales froo Mustelus canis exhibit comparable widths and only slightly greater lengths.
In contrast however, a few species possess
scales with noticeably larger crowns.
Carcharhinus plumbeus, for
example, possesses crowns with maximum widths up to 703 microns and lengths up to 533 microns.
Moreover, much larger dimensions are found
on both Odontaspis taurus and Galeocerdo cuvieri.
The largest
individuals of this last species, for example, would appear to possess scales whose crowns are somewhat longer than 1300 microns and wider than 1500 microns.
A few of the additional species, such as
78
Fig. 25. equations.
Lengths and widths of scale crowns as estimated from growth
Only those species are included for which sufficient data was
available for such calculations.
79
ex:>
--
LENGTH
0
II
II
.400
1000
100
200
fl. ~II"'." 0.11111'11. C. plll", ••II.
---200
MICRONS
M. ~II"'.
c.•••~II'U. WIDTH
If
,'.lItI.
c. ."".,••
c. ,.,.".,"". If. ,." •••••••
100
1000
1400
laoo
Carcharhinus leucas and Ginglymostoma cirratum, also appear to possess scales with significantly larger crowns. The
overall
interspecific between 100
similarity
adjacent
microns
probably
in
C.
(figure
also
26).
exhibit
The
a
great
average
deal
of
maximum distance
keels on a crown normally lies between 50 microns and most
species.
However,
C.
plumbeus,
~.
glauca and
leucas, possess scales with slightly larger spacings while
o.
those from
dimensions
keel
taurus, G. cuvieri, and probably
~.
cirratum, exhibit much
larger values. For example, the maximum spacing is more than 200 microns on
scales
average
keel
species, Isurus
o.
from
heights
with
and
and
remain
estimated
oxyrinchus
cuvieri
taurus
and
nearly 500 microns on G. cuvieri. The
less
maximum Sphyrna
probably
C.
than 50 microns in the majority of heights even as low as 10 microns in
lewini.
leucas,
Again
possess
however,
crowns
o.
whose
taurus, G. keels
are
significantly higher, up to four times so in Galeocerdo. The rates at which crown lengths and widths increase hO\\'ever, show a great
deal of interspecific variation (Table IV). Lengths of successive
replacement scales increase at rates between 0.50 microns/cm body length (C.
falciformis)
and
2.34 microns/em
(0.
taurus);
may
not
glauca.
Similarly,
replacement 0.39
or
scales
microns/cm
(P.
the
~.
plumbeus) or 2.72 microns/em
increase at all, as in the case of Prionace
rates
at
,"hich
the crown widths increase on
are also variable. Widths may increase as slowly as glauca)
and
0.66 microns/cm (C. obscurus) or as
rapidly as 3.02 microns/cm (C. plumbeus). Scales protective
on
the
majority
of
galeoid
species
perform
either
a
or hydrodynamic function (Reif, 1982). In either case, most,
81
Fig. 26.
Heights and spacings of keels on the scale crowns as esti-
mated from growth equations.
Only those species are included for which
sufficient data was available for such calculations.
82
SNO~~IW
ooz
o
001
001
I/UllfJ 'W
I
I
./UI.ltJJlfJ/"J '3
I
I
_IIAOUOII.l.l., '1/
I
.nJnfJ.qo ·3
lH913H
.'NIIU6/. ·3 DfJnllll (:I
I
.m,qUln/d '3
I
"n.lnlJl '0 !.I.,Atul '9
ooz
002
OOg
I 9NI~\fcJS
I
I
I
II III
-
(Y')
co
Table IV. Summary of slopes of the growth characteristics from scales of the nine species for which adequate numbers of specimens are available.
Species are arranged in order of
increasing rates of keel spacings. Species
Length
Width
Spacing
Height
C. signatus
0.57
1.16
-0.09
0.00
R. terraenovae
1.13
2.28
0.00
0.00
M. canis
2.06
2.30
0.00
0.,00
C. fa1ciforrnis
0.50
0.77
0.00
0.03
C. obscurus
0.99
0.66
0.05
0.03
P. glauca
0.00
0.39
0.06
0.03
C. p1urnbeus
2.34
3.02
0.30
0.08
o.
2.72
0.84
0.59
0.53
1. 73
2.36
0.63
0.25
taurus
G. cuvieri
84
if
not
all, of the external surface of the fish's body must be covered
despite
an
growth.
This requires that the ratio of the area of the skin covered by
scales
increasing
with
the
individual's
surface area which results from continuous body
total
area
of
skin remains constant throughout the
ontogeny (Reif, 1980). The amount of area covered by scale
crowns results from a combination of an increase in the number of scales with of
the increase in the size of the individual croWD. The wide variety scale
growth
rates observed in this study reflects the interaction
between these two processes. A The
sharp dichotomy exists in growth rates of the keel morphometrics.
majority
keel
spacings,
distance
of
microns/cm
Similarly, signatus, in
C.
species ranging
in
from
an
to
actual
the
decrease
in
the inter-keel
very slow rate of from 0.05 to 0.06
C. obscurus and P. glauca. Several species, including
falciformis
C.
the R.
exhibit extremely slow rates of increase for
signatus
C.
terraenovae,
as
of
keels
and M. canis, exhibit no increase at all.
remain
either ~.
terraenovae and
falciformis,~.
~.
at
a
constant height, as in C.
canis, or increase only very slightly,
obscurus and P. glauca. In a second group of
species however, inter-keel distances increase very rapidly; at rates up to
0.60
microns/cm,
Moreover, rates
between
cuvieri. these
the
Only
two
on
scales
from
both
O. taurus and G. cuvieri.
heights of these keels increase on replacement scales at 0.25
microns/cm plumbeus
C.
groups,
with
on O. taurus and 0.53 microns/cm on G.
occupies
keel
an intermediate position between
spacings
increasing
at a rate of 0.30
microns/cm and heights at a rate of 0.08 microns/cm. In
summary,
these
scales appear divided into two morphometrically
85
distinct
groups.
increase
in
The
size
approximately
425
majority
at
a
wide
of species exhibit scales whose crowns variety
of rates to a maximum width of
microns and a length of 500 microns. Ridges on these
crowns remain a nearly constant 50 microns high throughout each species' size
range
largely
characteristic of both the first and second morphological type·s
described possess
earlier
reaching
group.
microns from and
in
this report. A second group of species, however,
a much thicker, heavier scale. Crowns on these scales grow very
rapidly, first
and are normally located 100 microns apart. Such crowns are
widths and lengths nearly twice that of the
The keels on these scales are set further apart, from 235 taurus)
(0.
160
maximum
to 490 microns
~.
cuvieri), and are much higher, ~.
cuvieri). Both heights
replacement
scales. These species
microns (0. taurus) to 187 microns
spacings
increase
largely
comprise
exhibit
intermediate
plumbeus,
C.
growth rates
the
rapidly third
on
morphological
values
for
keel
group.
spacings
Only a few species G.
cirratum,
C.
leucas and P. glauca), keel height (C. leucas) or general
1£.
plumbeus).
In order to compare these measurements with a hypothetical model for drag
reduction,
each
species. The little information presently available can be divided
roughly
it
is first necessary to consider swimming speeds for
into two categories. Burst speeds, such as those which might be
used in capturing highly mobile prey or in escaping predators, have been estimated
at
522
cm/sec for
s.
brevirostris
leucas and at 244 cm/sec for the lemon
shark,
Negaprion
cm/sec
have been recorded for Carcharhinus (Prionace) glauca (Nikolsky,
1978).
Secondly,
a
limited
(Gero,
number
86
1952).
Values as large as 1000
of measurements are available for
voluntary, or sustained, speeds.
Beamish (1978) estimated sustained
speeds of between 18 and 202 cm/sec for
£.
leucas based on Thorson's
(1971) tagging studies while Heard and Ripley (1951) have reported similar speeds of 43 cm/sec for the soupfin shark (Galeorhinus zyopterus); both being based on longer-term
~igrational
studies.
Specific shorter-term observations of cruising speeds have been reported for
f.
leucas of 56 to 83 cm/sec and for
£.
plumbeus of 60 to
67 cm/sec (Weihs, et al., 1981) from an aquarium study. Due to the very limited number of actual measurements, it is necessary to rely only on estimates for the majority of other species. Weihs (1977) proposed the use of the following equation to predict voluntary swimming speeds: U = 0.503 L 0.43 where U is the voluntary swimming speed and L is the body length. This equation closely approximates those values previously reported for both
£.
plumbeus and
£.
leucas.
Similarly, Wardle (1975)
proposed the following equation to predict maximum burst speeds: U
= AL/2T
where A is the stride length, based on Bainbridge's (1958) estimate of forward motion of from 60% to 80% of both length (L), (60% was used in the present study) and T is muscle contraction time (estimated to be about 0.08 S for fish of about 2 m in length, using Wardle's 1975 curves).
While this equation has only been verified with teleost
87
data, it appears to provide a sufficient estimate for elasmobranchs. Therefore for example, estimated swimming speeds for a specimen of
£.
leucas between 1.5 and 2.0 neters long should lie between voluntary swinmling speeds of 53 cm/sec to 60 em/sec and burst swimnling speeds of 900 em/sec to 1200 em/sec, values close to those previously reported from the literature. It is now possible to evaluate the keel morphometrics" exhibited by each species in terms of potential drag reduction.
The actual
measurements, expressed in metric terms, can be expressed in terms of law of the Wall coordinates through the following two equations (Walsh and Weinstein, 1978): h+
= hu/v (C /2) 1/2 s + = su/v (C /2) 1/2 f
f
. where h + and s + are heights and spacing in terms of law of the Wall coordinates, hand s are heights and spacing in em, u is the free stream velocity (here expressed in swimming speeds), v is the kinematic viscosity of sea water and C is skin friction. f
This later
term can be calculated from the following equation: C
f
=
.074 R- 1/ 5
where R is the Reynold's number: defined above.
R
= Lu/v; L, u, and v having been
The major limitation on these equat ions lies in the
paucity of information on specific swimming speeds.
88
Throughout their ontogeny, all of the species examined in this study (with
the
cuvieri)
possible possess
optimal
value
swimming
exception
scales
of
speeds
16
of
with
(in
(figure
the
ridge
law
of
27).
very
largest
spacings
specimens ofG.
less than the proposed
the Wall coordinates) at voluntary
Moreover,
a
number
of
these species
maintain keel spacings which approximate the optimal value projected for burst
swimming
£.
limbatus, and
S.
speeds. This is particularly true in
£.
obscurus,
mokarran.
In
£.
falciformis,
£.
signatus, Isurus oxyrinchus, Sphyrna lewini,
contrast,
the ridge spacings on the scales from
Galeocerdo cuvieri, Odontaspis taurus and Ginglymostoma cirratus rapidly increase ontogenetically to values well above this optimal level. Similar heights
trends
are
also
observed
in a comparison of actual keel
to the corresponding theoretical optimal values (figure 28). At
voluntary
swimming
maintain optimal
scales value
speeds, all of the species which were examined here
whose of
8
keels (again
are
noticably smaller than the proposed
expressed in terms of the law of the Wall
coordinates). Moreover, keel heights closely approach the optimal values predicted cuvieri,
for ~.
cirratum and
Lastly, scale
levels.
additional
relief
relative
burst swimming speeds in all of these species, except G.
is
dimensions
taurus.
insight
available
closeness Whereas
2.
of
both
into
through
the hydrodynamic significance of interspecific
comparisons of the
keel morphometrics to these theoretical optimal C.
falciformis
and
C.
signatus maintain keel
suprisingly close to those predicted for burst values, quite
89
Figure 27.
Scale ridge spacing compared to predicted optimal
dimensions for sustained (A - A') and burst (B - B') swimming speeds as a function of fish length.
Species are as follows:
(1) Galeocerdo cuvieri, (2) Odontaspis taurus, (3) Carcharhinus plumbeus, (4) Prionace glaucs, (5) Carcharhinus obscurus, (6) Carcharhinus signatus, (7) Carcharhinus falciformis.
90
morphometrics intermediate deviation burst
observed
is
opposite
the
for
C.
these
scale
swimming
G.
obscurus,
between
in
on
C.
two
topography
speeds
may
cuvieri
and
O.
taurus.
plumbeus
and
P.
glauca
extremes. from
be
The
explanation
Scale appear
for this
optimal conditions predicted for
partially
found through interspecific
comparisons of swimming speeds. In
conclusion,
study drag
exhibit
a
reduction
falciformis, mokarran, optimal
keel
majority
the
signatus, C. limbatus,
values
exhibit
between
values. While the majority of the species, including C.
possess
O.
keel morphometrics of species examined in this
wide range of values with respect to proposed optimal
C.
species,
the
scales
!.
oxyrinchus,
~.
lewini and S.
whose keel heights and spacings approach the
predicted for burst swimming speeds, at least two other
taurus and G. cuvieri, appear not to follow this trend and
of
heights
and
spacings
well
above
such levels over the
their size range. Such differences may reflect the balance
thicker,
thinner,
narrower scales adaptive for protection functions and
more
specifically
sculptured
scales
adaptive for drag
reduction.
The
presence
of
either
scale
type
should, in part, reflect the
overall
speeds of each species. While this assumption is again hampered
by
absence of actual measurements, generalizations can be inferred
from and
the
natural history information such as that found in works by Bigelow Schroeder
others.
Of
suggesting
(1948), Castro (1982), Clark and von Schmidtt (1965) and
those
species which possess scales with keel morphometrics
optimal drag reduction capabilities, there is ample evidence
92
Figure 28.
Scale ridge height compared to predicted optimal dimensions for
sustained (A - A') and burst (B - B') swimming speeds as a function of fish length.
Species are as follows:
(1) Galeocerdo cuvieri, (2)
Odontaspis taurus, (3) Carcharhinus plumbeus, (4) Prionace glauca, (5) Carcharhinus obscurus, (6) Carcharhinus signatus, (7) Carcharhinus falciformis.
93
A
--
--
250
--
--
---
A'
200 en
c: 0
~
u
-E
~
+=:>
150
.&:.
at
CI)
100
:::I:
50
4
_ _ _ __ __ __ 6 8~~~~==~~======~~~~---------------=~5=
--===~.-,-....;;;;-;;...=:...:=-=
- - - - - - - - - - - - - - - - - - - - - - - - - - __ J __ _
~
8'
o
1.5
2.0
2.5
Total Length (m)
3.0
to
indicate
generally
high swimming speeds. Carcharhinus signatus, C.
falciformis
and
I.
al.,
and
Strasburg,
1982;
adaptations predator
which
in
variously
oxyrinchus are epipelagic (Castro, 1983; Raschi et
are
1958)
and exhibit a variety of structural
necessary for the increased speed required by a
such an environment, including a conical or pointed snout,
reduced
fins
and,
in
the last species, a lunate tail with
lateral keels on the caudal peduncle. Furthermore, the prey consummed by including
sharks,
these
falciformis
(Bane,
exocoetids
for
and
sharks
other
1966),
C.
swimmers
whose
addition,
both
and
small
tuna
(Thunnus)
for
C.
squid
and
a variety of teleosts including
signatus (Raschi, et al., 1982) and swordfish, tuna for
I. oxyrinchus (Randall, 1963), are fast, active
capture
!.
squid
would
require
oxyrinchus and
E.
higher
swimming
speeds.
In
limbatus, exhibit jumping behavior
(Garrick and Schultz, 1963; Springer, 1963). Finally, the two species of hammerheads
examined,
morphologies reduction. argument
matching This
as
particularly
a fast
lewini
those
and S. mokarran, possess scales with
leading
to
the
proposed
optimal
drag
is particularly interesting in light of the occasional
presented
functions
S.
that
the
hydroplaning and
lateral device
expansion for
what
of the sphyrnid head many consider to be a
agile group of sharks (see arguments in Budker,
1971). In
contrast,
sluggish.
both
Odontaspis
waters.
Whereas
teleost
and
its
G.
cuvieri
and
o.
taurus
probably are more
taurus normally is found in very shallow, coastal stomach
elasmobranch
contents
fish,
include a wide variety of both
it also feeds on a variety of benthic
invertebrates and carrion (unpublished VIMS longline data). This species
95
tends
to be very heavy bodied, with relatively large fins. Furthermore,
O. taurus has been observed swallowing air and remaining motionless near
the
bottom
(Bass
considered
a
(Randall, hunger
sluggish
(Castro,
species,
1982).
however,
observation consists
that
of
often swimming somewhat indifferently
certainly
Overall
as
the
suggested bird
swimming by
fraction
speeds
Dodrill in
may
and
this
be
less
Gilmore's
than (1978)
species' diet actually
dead or moribund individuals. Galeocerdo cuvieri occurs in
oceanic
and
Ballard, 1972). Galeocerdo cuvieri must also be
1963), although it may become quite active when stimulated by
estimated
both
and
and
shallower
coastal
waters.
While
stomach contents
include a wide variety of more active teleosts, elasmobranchs
even cetaceans, a significant fraction of its diet includes garbage (Gudger,
carrion
and
invertebrates
and
sea
1949),
1948, turtles.
as
well
as
slower
benthic
Like the previous species, it also is
relatively heavy-bodied. Additional examples of this trend can be found in those species with intermediate of
£.
scale
characteristics. The more heavily sculptured scales
leucas, for example, reflect both its relatively sluggish behavior
(Randall, species
1963) often
plumbeus
is
as
well
entering also
as its shallower, benthic distribution, this shallow
estuaries
and
rivers.
Carcharhinus
generally slower swimming, as suggested by the large
numbers of crustacea and mollusks in its diet, and its normal habitat of shallow, which
waters. In contrast, it sibling species,
£.
obscurus,
is semipelagic and seems to include a larger proportion of active
teleosts much
coastal
less
in
its diet, appears to be a more active species and exhibits heavily
sculptured scales. Finally, P. glauca appears to be
96
something 1958)
of
and
an
exception.
physically
is
This species is truly pelagic (Strasburg,
very streamlined, with long pectoral fins, a
long, pointed snout and a relatively thin body, all suggesting that this species
is
cephalopods example the
a
very active swimmer. Furthermore, it frequently feeds on
(Clarke
Tricas,
scales
and
1979).
should
Stevens,
1974)
and faster teleosts (see for
Therefore, it might be expected that ridges on
be somewhat lower and more closely spaced than they
actually are on the larger individuals. The
values
average
reported
values.
morphometrics Furthermore, values
in
which
keel
scales
heights allow
might
more
role
and and
both keel heights and spacings are
then,
has a range of values for the keel
function
lateral
over
a
wider
range
of speeds.
values
(Table
V)
might
Comparing Tables IV and V, those species whose
the most rapid growth rates, such as ~.
~.
falciformis,
~.
glauca, also exhibit the greatest reduction in lateral
spacings
therefore,
function in a
for those species with significant rates of increase
morphometrics. exhibit
obscurus
scale
for
the reduction in the heights and spacings from the primary
through
compensatory
Each
here
for
when compared with the primary values. This will some
portion
of
the
scale
to
exhibit
more
appropriate values even while the overall dimensions increase rapidly. In in
conclusion, it appears that the majority of the species examined
this
scales at
with
dimensions which should promote significant drag reduction
estimated burst speeds. Different scale morphologies in the last two
species such
study, with the exceptions of O.taurus and G. cuvieri, possess
as
may
be
associated
protection.
with adaptations other than hydrodynamics,
The remaining species (C. leucas, C. obscurus, C.
97
Table
v.
Reduction in the secondary and tertiary keel spacing and
heights (expressed in percentages) as compared with primary values.
These
values are rounded to the nearest whole percentage and represent the average and range (in parentheses). Keel Spacing
Species 2
0
c.
p1umbeus
19 (6-31)
c.
signatus
20 (7-37)
Keel Height 3
0
46 (35-59)
2
0
3
0
11 (+33-40)
46 (7-75)
17 (0-36)
43 (25-61)
18 (17-40)
48 (25-80)
21 (0-50)
51 (25-75)
R. terraenovae
22 (14-32)
c.
fa1ciformis
24 (9-39)
c.
obscurus
30 (13-45)
33
58
P. glauca
39 (34-43)
20 (21-54)
83 (81-85)
M. canis
18 (0-42)
36 (13-71)
61 (43-82)
32 (23-41)
25 (8-39)
o. taurus
57 (29-91)
G. cuvieri
78 (29-95)
98
plumbeus, scale
G.
cirratum and P. glauca) vary in the agreement of observed
dimensions to predicted optimal values. This variability probably
reflects
the
differences
in
overall
behavioral differences.
99
swimming
speeds
suggested
by
FUTURE STUDIES While are
the data presented here strongly suggests that placoid scales
capable
shark
species,
enhance scale
this
providing several
picture.
morphologies
values. from
of
While
natural
The
drag reduction for a number of
lines
of
research
could greatly
most troublesome point in evaluating these from
the paucity of reliable swimming speed
was circumvented to some extent through inferences
history information, an understanding of overall swimming
budgets,
speed
additional
arose
this
significant
measured
for
extended
periods
of
time,
would
be
invaluable. Such work is now possible using radio telemetry in the field (for
example,
feasible types
of
for
see
Sciarrotta and Nelson, 1977) and would certainly be
most
of the species included in this report. "Flowmeter"
equipment
could
potentially provide actual speeds, avoiding
many of the problems inherent in long term tagging studies. Secondly, extremes
in
material
for
oxyrinchus
an
examination
swimming
speeds
of
additional
should
species characterized by
be highly recommended. While the
an evaluation of a more complete series of scales from I.
and
c.
limbatus has recently become available, the inclusion
of additional "fast" species, in particular many of the lamnids would be particularly sedentary
interesting.
species,
Similarly,
more
scales
from
additional
such as the orectolobids, would provide information
on non-drag related scales. Finally, hydrodynamics
a
reevaluation may
be
of
the
fossil record, in light of scale
particularly fruitful (Schaeffer, 1967). While a
large amount of information is currently available regarding the overall
100
shape
of
individual
measurements Many
of
required
these
scales,
from
scales for
fossil
species,
the
adequate
hydrodynamic comparisons are still lacking.
such
as
those
found on members of the genus
Orodus, appear appropriately shaped and arranged (Zangerl, 1968) despite their cyclomorial nature and may provide a suitable starting point.
101
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Mundy,
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1951. Poissons. Exped. Oceanogr. BeIge Eaux cotieres Afr. Sud
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in identifiying sharks. Copeia 1917: 25-28. Randall, J.E. 1963. Dangerous sharks of the western Atlantic. In: Sharks and Survival. P.W. Gilbert (ed.) D.C. Heath and Co. Boston, Mass. Raschi,
W., J.A. Musick and L.J.V. Compagno 1982. Hypoprion bigelowi, a
s~nonym
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Carcharhinus
signatus (Pisces: Carcharhinidae), with a
description of ontogenetic heterodonty in this species and
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T.C. and D.R. Nelson 1977. Diel behavior of the blue shark,
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107
and Orodus. Nobel
Appendix I.
Species
Carcharhinus falciformis
Collection data for the material examined
Specimen number
Total length (em)
103 111 115 189 268 169 201 215 278 148 150 157 167 173 86* 96 104 108
1 2
Carcharhinus leucas
Carcharhinus limbatus
3 4 5 6 7 8 9 10 11 12 13
Carcharhinus obscurus
Carcharhinus plumbeus
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 27 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
III
119 120 123 127 168 173 182 196 218 238 329 334 59 62 67 73 80 88 94 99 102 106 115 117 125 127
108
Sex
M M F F F F M M F M M M M M F F F F F F M F
M M F F M F F F F M F M
M F F M M M M F F F F
Latitude
Longitude
Not 37°03' 37°03' 37°03' Not 37°17' 37°17 ' Not Not 37°17'37°17' 36°54' 36°55 ' 37°17' 36°54' 36°55' 36°54' 37°00' 37°05' 36°55' 36°55 ' 36°54 ' 36°54' 37°00' 36°55' 37°00' 36°55 ' 37°00' Not 36°54 ' 36°54' 37°17' 37°17 ' 36°56 ' 37°05' 37°17' 37°05' 36°54' 37°05 ' 36°54' 37°05' 37°05' 37°05' 37°05' 36°54'
available 74°37' 74°37' 74°37' available 75°46' 75°46' available available 75°46 ' 75°46' 75°59' 75°42' 75°46' 75°59' 75°42' 75°59' 75°21' 75°55' 75°42' 75°42' 75°59' 75°59' 75°21' 75°42' 75°21' 73°42' 75°21 ' available 75°59' 75°59' 75°46 ' 75°46' 76°01' 76°08' 75°46' 75°55' 75°59' 76°08' 75°59' 76°08' 76°08' 75°55' 75°55' 75°59'
Species
Specimen number
Carcharhinus plumbeus (cont.imued)
46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76
Carcharhinus signatus
Galeocerdo cuvieri
77
Ginglymostoma cirratum Isurus oxyrinchus Mustelus canis
78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96
Total length (cm)
132 136 145 146 152 158 161 167 173 178 185 188 191 196 207 216 76 94 179 192 211 215 217 222 156 173 188 213 217 223 238 252 258 271 292 404 72
77 132 163 182 37 52 56 61 93 101 109 113 116 127
109
Sex
Latitude
F F
37°00 ' 37°05' 36°54' 36°55' 37°00' 36°55' 37°00' 37°00' 36°55' 37°00 ' 37°00 ' 36°55' 37°00' 36°55 ' 37°00' 37°05'
M F F F F
M F F F F F F F F
M F F
M M M M M M F F
M M F
M F F F F F F
M M F F
M M M F
M M F F F F
Longitude
75°21' 76°08' 75°59' 75°42' 75°21' 75°42' 75°21' 75°21' 75°42' 75°21' 75°21' 75°42' 75°21' 75°42' 75°21' 76°08'
Not available Not available Abidj an "Reine Pokon" 38°54'
73°25'
Not available Not available Not available 38°54' 37°03' 37°07' 36°55' 37°00' 37°03' 36°55' 37°03'
73°25' 74°37' 75°41' 75°42' 75°21' 74°37' 75°42' 74°37'
Not available 36°54' 37°00' 36°55' 36°54'
75°59' 75°21' 75°42' 75°59'
Aquarium specimen Aquarium specimen 37°03'
74°37'
Not available 37°03' 37°07' 36°54'
74°37' 75°41' 75°59'
Not available 37°17' 37°00' 37°00' 37°07' 37°07' 36°55' 37°07'
75°46' 75°21' 75°21' 75°41' 75°41' 75°42' 75°41'
Species
Odontaspis taurus
Prionace ga1uca
Rhizoprionodon terraenovae
Sphyma 1ewini Sphyma mokarran
Specimen number
Total length (cm)
97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129
165 194 204 210 224 229 231 235 247 34* 39* 42* 46* 165 181 190 202 214 228 248 287 348 40 83 98 95 97 101 106 54 221 225 252
*embryo
110
Sex
latitude
F
37°17' 37°17' 37°17' 37°05' 37°05' 37°05' 37°17' 37°00' 37°00'
M F F M M F M M M F F F M M M F M F M F F M M F F F F F F M M M
Longitude
75°46 ' 75°46 ' 75°46 I 76°08 ' 76°08' 76°08' 75° 46' 75°21 ' 75°21 ' Bermuda Bermuda Bermuda Bermuda
37°03' 37°03"' 37°03' 37°03' 37°03' 37°03' 37°03' 37°03' 37°03' Not Not 37°00' 37°05 ' 37°05' 37°05' 36°55 ' Not Not 37°00' Not
74°37' 74°37' 74°37' 74°37' 74°37' 74°37' 74°37' 74°37' 74°37' available available 75°21 ' 75°55' 75°55' 75°55' 75°42' available available 75°21 ' available
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1. Report No.
12. Government Accession No.
3. Recipient's Catalog No.
NASA CR-3963 4. Title and Subtitle
5. Report Date
March 1986 Hydrodynamic Aspects of Shark Scales
6. Performing Organization Code
7. Author(s)
8. Performing Organization Report No.
William G. Raschi and John A. Musick 10. Work Unit No.
9. Performing Organization Name and Address
Virginia Institute of Marine Science
I College of William and Mary
11. Contract or Grant No.
Gloucester Point, VA 23062
NASl-16042 13. Type of Report and Period Covered
12. Sponsorin" Agency Name and Address
National Aeronautics and Space Administration Washington, DC 20546
Contractor Report 1982-83 14. Sponsoring Agency Code
505-31-13
15. Supplementary Notes
Langley Technical Monitor: Michael J. Walsh William G. Raschi: Bucknell University, Lewisburg, Pennsylvania. John A. Musick: Virginia Institute of Marine Science, The College of William and Mary, Gloucester Point, Virginia. 16. Abstract
Ridge morphometries on placoid scales from 12 galeoid shark species were examined in order to evaluate their potential value for frictional drag reduction. The geometry of the shark scales is similar to longitudinal grooved surfaces (riblets) that have been previously shown to give 8 percent ski n-fri cti on reduction for turbul ent boundary 1ayers. The present study of the shark scales was undertaken to determine if the physical dimensions of the ridges on the shark scales are of the right magnitude to be used by the sharks for drag reduction based on the previous riblet work. The results indicate that the ridge heights and spacings are normally maintained between the predicted optimal values proposed for voluntary and burst swimming speeds throughout the individual's ontogeny. Moreover, the species which might be considered to be the "faster" possess smaller and more closely spaced ridges that based on the riblet work would suggest a greater frictional drag reduction value at the high swimming speeds, as compared to their more sluggish counterparts.
17. Key Words (Suggested by Authors(s))
Boundary layer Drag reduction
I
18. Distribution Statement
Unclassified - Unlimited Subject Category 34
19. Security Classif.(of this report)
Unclassified
/20. Security Classif.(of this page)
Unclassified
/21. No. of Pages 122. Price
116
A06
For sale by the National Technical Information Service, Springfield, Virginia 22161
NASA-Langley, 1986
