UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, Secretary
FISH AND WILDLIFE SERVICE Arnie J. Suomela. Commissioner
NATURAL HISTORY OF THE SANDBAR SHARK EULAMIA MILBERTI
By STEWART SPRINGER
FISHERY BULLETIN 178 From Fishery Bulletin of the Fish and Wildlife Service VOLUME 61
PUBLISHED BY U.S. FISH AND WILDLIFE SERVICE • WASHINGTON • 1960
PRINTED BY U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON, D.C.
For sale by the Superintendent of Documents, U.S. Government Prlntln~ Office, WashlnAton 25. D.C. Price 35 cents The series, Fishery Bulletin of the Fish and Wildlife Service, is cataloged as follows:
U. S. F·i8h and TV-ildlife 8el'l'i.ce. Fishery bulletin. v. 1- ·Washington, U. S. Govt. Print.. Off., 1881-19 v. in illus., maps (part fold.) 23-28 em. Some vols. issued in the congressional series as Senate or House documents. Bulletins composing v 47- also numbered 1- Title varies: v. 1--49, Bulletin. Vols. 1--49 issued by Bureau of Fisheries (called Fish Commission, v. 1-23)
1. Fisheries-V. S. 2. Fish-culture-V. S. I. Title.
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II CONTENTS Pall'e Introduction______1 ~omenclature______2 Populations of Eulam-ia milberti______3 Ecological and systematic relationships of the genus ElIlam-ia.______4 Specimens examined .______5 Field recognition ______6 Distribution of E'ltlamia milbertL ______10 General nature of distribution______10 Factors affecting distribution______12 Nursery grounds and distribution of young______13 Distribution off Atlantic coast of the United States and in eastern Gulf of ]dexico______14 Distribution in Bahamas and West Indies______16 Distribution in western Gulf of ]dexico and western Caribbean ______17 ~igration------______19 Eleproduction______20 Courtship and mating______20 Time of mating______21 Development of the embryo______22 Number of young in litter .______23 Length of young at birth______23 Abnormal embryos______25 Sex ratios______25 Growth and size at maturity______26 Food and feeding habits ______29 Abundance______32 Enemies ~____ 32 Summary______34 Literature cited______36
ill ABSTRACT
Populations of l'andbar sharks of the eastern and western parts of the Atlantic Ocean are defined and general problems of nomenclature, the ecology of large carcharhinid sharks, and field recognition of sandbar sharks are discussed. A more-detailed account of observat,ions on Eulumiu milberti, restrir.t,ed t,o the population of the western North Atlant,ir., is given, out.lining distribution of adults and young, migrations, development, and behavior, based on observations from the commerr.ial shark fishery which operat,ed from r.enters in the Southeastern States from 1935 to 1950 and supplemented by dat,a from reseal'r.h vessels operating after 1950. Comparisons wit,h other species in the area, lists of large species-of sharks taken at cel't,ain times off Salerno, Florida; Bimini, Bahamas; t,he mouth of the Missis sippi River, Louisiana; and the Caribbean coast of Nicaragua-Costa Rir.a, as well as disr.ussiollS of interspecies r.ompet,ition. are inr.luded.
IV NATURAL HISTORY OF THE SANDBAR SHARK, EULAMIA MILBERTI
By STEWART SPRINGER, Fishery Methods and Equipment Specialist BUREAU OF COMMERCIAL FISHERIES This account of the sandbar sha,rk, Eulamia SIUH'ks occupy a place in nature at the top of m;ilbe~l'tl (Miillerand Henle), is an attemptto bring the food chain. As predators they compete with together aU the significant information on one man, but it is by no means established that their kind of common and moderately large shark. predatory activities are always harmful. They Sharks have been studied because they are occa are a nuisance or are harmful to fishermen chiefly sionally dangerous to man, often a nuisance to because of the damage they do to nets or to fish fishermen and, in the past at least, have been that have been caught on setlines. In some locali valuable as a source for food, leather, vitamin A, ties, in England and Australia, for example, fish meal, and some specialty products. A rather sharks are utilized and are consequently of some comprehensive body of knowledge exists about value. In the United States, landings at present some of the smaller species, such as the compara are of no great importance. tively valuable soupfin shark of the coast of Sharks may be chUlgerous to man through at North America (Ripley, 1946) and the school tacks on swimmers and survivors of marine dis shark of Australia (Olsen, 1954), both species of asters, but Etdamia '1nilbe'l'ti is· not a species Galeol'h.i-nus, nnd the common spiny dogfish, implicated in well-documented records of attacks. Squaltl8 (Ford, 1921; Hickling, 1930; Temple There may be sevel'ltl reasons for this. E. mHbe1'ti man, 1944). Information on the natural history ordinarily stays away from beaches and does not of the larger species is fragmentary. This is to often feed at the surface. It usually seeks small be expected, because large species not only are prey. During the summer, when the female sand difficult to cntch and handle, but also are far bar sharks come inshore near the heavily popu ranging and require observation over a wide geo lated centers from New York southward along graphical area. the Atlantic coast to give birth to their young, The sharks, together with their relatives, the it is not t.heir habit to seek food. The large males skates, rays, and chimaeroids, form a class of do not come inshore. So the sandbar shark, while vertebrates that is sharply set off from the classes la,rge enough to be dangerous and perhaps the which contain the fishes, amphibinns, reptiles, most common of the larger sharks in shore waters birds, and mammals. The sharks and other mem southward from New York, is isolated by its bers of the class Chondrichthyes have cartilagi habits from encounters with man. Nevertheless, nous skeletons, and while elements of the shark the sandbar shark is potentially dangerous to man skeleton may become calcified, no true bone is and might become a more, serious danger with formed. This is the basis for the definition that minor shifts in the environmental situation. is generally used to distinguish the Chondrich The most annoying aspect of my work with thyes from the higher vertebrates. But there are sharks, prior to the publicat.ion in 1948 of the other differences in the chemistry and physiology first volume of Fishes of the 'Western North At that are very likely of great importnnce but are lantic on sharks by Dr. He.nry B. Bigelow and little understood. The evolutionary connections 'Villiam C. Schroeder, was that many western of the modern sha.J'ks and their allies with other Atlantic sharks could not be identified with con modern vertebrates are obscure and of great an fidence because of It scattered literature of vary tiquity. ing quality. It is appropriate that I acknowledge the importance of this excellent general work to NOTE.-Approved for publl~8tlon. October 27. 19118. Fisbery BulletIn 178. me, because without it I\nd without the encourage- 1 2 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE ment of its authors, I would not have attempted most any carcharhinid if applied liberally but preparation of t.his report. Dr. Richard H. to none if applied strictly, I regard Sq1talJu8 Backus of the Woods Hole Oceanographic Institu 1)lum,beu8 as It nomen nude'ln. tion, Dr. Giles W. Mead of the U.S. Fish and I am also unable to accept Nardo's description 'Vildlife Service, lwd Dr. Leonard P. Schultz of as specifically applicable to the sandbar shark the U.S. National Museum made many helpful based on the argument that t.he. sandbar shark is suggestions during the preparation of this report. the most common large carcharhinid of the Captain B. ,V. "Tinkler was especially helpful in Adriatic. keeping fishing logs and measurements of about A most extraordinary snarl has developed over 1,300 large sharks he took off the Bahama Banks the years in the determination of the scientific and off Nicaragua. Records obtained while I ,vas name to be applied to the sandbar shark. The employed by the Shark Industries Division of origin of t.his complication probably lies in the the Borden Company and while I was aboard the peculiarities of the distribution of species of exploratory fishing vessel Oregon of the Fish and carcharhinid sharks along the Atlantic coast of 'Wildlife Service comprise. the basic data used the United States. Mistakes in identification of here. Special assishtnce was given me also by the specimens have been frequent, probably because Lerner Marine La.boratory of the American Mu the descriptive accounts of the early authors were seum of Natural History, by permitting 2 months very brief and did not select truly diagnostic of field study at Bimini, Bahamas, in the summer features for emphasis. Systematists had too few of 1948. In all my work with sharks, I have been specimens ilnd too little datlt on distribution to given the most generous help by my associates in note that. segregation of the sexes and segregation commercial shark fishing and aboard exploratory of the adults and young characterized these fishing vesse.Is. sharks at some seasons. In the latitudes from New York to Chesapeake NOMENCLATURE Ba.y at depths within easy rench of collectors or This report is not int.ended to set.tle problems fishermen, two common large carcharhinid sharks of nomenc.lature and taxonomy, but. to be useful occur, the sandbar shark, E. m,ilbe1'ti (MUller and it is necessary t.o name the sharks under discus Henle), and the bull shark, Oa.1'charhimt8 leucas sion and t.o define the names used. My choice of (MUller and Henle). The sandbar sha.rk is rep a name for t.he sandblu' shark is Enlmnia, ndlbe'l'ti resented in this area by adult females and by the (MUller and Henle) 1841. Use of Eula1nia fol young of both s~xes, but ra.rely by adult. males in lows my partial revision of the carcharhinids the observable elements of the population. The (Springer, 1950). For the specific name milbe'l'fi bull shark is represented usually by adult males, I follow Bigelow and Schroeder (1948) who note but females and young are also present sporadi that, if it is finally proved t.hat the Mediterranean cally.2 form is ident.ical with t.he American, the name The ranges of the sandbar shark and the bull plum,beu8 Nardo 1827, must. be used for the com shark will be discussed later a·s well us the ap bined species in place of'rnilbe1·t-i. pa.rent competition between these species. An J disagree, however, with Fowler (1936), with t.he preceding stat.ement by Bigelow and Schroe effect of the occurrence of the two species to-
der, and with Tortonese (1951,1956) t.hat Nardo's • Large male Ct,rchm'hilil/o lellca8 were reported from the description is valid. The description by Nardo Chesapeake Bay area by Schwartz (1958) ; one was taken from the Patuxent River In 1957 and another at Flag Pond in the would apply to almost any cal'charhinid amI the summer of 1958. This Is apparently the first published report specific mention of the rounded snout 1 would of the sllecies from Chesapeake Bay. Specimens of large sharks came to the attention of Edgar H. Hollis. of thp. Mar~'land De apply better to some other carcharhinids than to partment of Tidewater Fisheries in 1957, because Chesapeake the sandbar shark. Because t.here is no type and fishermen regarded them as rarities. Photographs of the speci m",ns sent me b~' Mr. Hollis were sufficient to permit identifica because Nardo's descript.ion would apply to al- tion as C. lel/Ca8. Nichols (1918) and Nichols and Breder (1927) reported a. lel/Ca8 from the south shore of Long Island, 1 The total description and diagnosis of Sqrwl;'8 pll/ll1 bello h~' noting that these specimens were huge males. Attention Is Nardo, 1827. p. 35, Is as follows: "Speciel secllndae cOII\·p.nit called to this parenthetically because the appearance of adult exacte Sqllal. Glallell8. Hloc..1 color excil;pretur pt forma males at the perlpher~' or In the cooler parts of ranges of rostri quae in exemplarl nostro rotunda est." carcharhlnld sharks iM frequent. NATURAL HISTORY OF THE SANDBAR SHARK 3 gether, howe,ver, has been to foster confusion in thesis that is a. haza.rd to one attempting to fit a the nomenclature. There appears to have been real shark to a position in zoological classification. a tacit. assumption by some nat.uralists that sexual dimorphism accounted for differences in sandbar POPULATIONS OF EULAMIA MILBERTI sharks and bull sharks despit.e recognition of the Sandbar sharks, Eulmnia m.ilbe-rti, occur in exist.ence of both species. portions of the te~nperate and tropical Atlant.ic, Superficially, the sandbar sha,rk and the bull the Caribbean, t.he Gulf of Mexico, and the Medi shark resemble one anot.her but, as will be shown t.erranean. Our data in this st.udy primarily cover later, sandbar sharks can easily and positively be the population inhabiting t.he western North separated from bull sharks on t.he basis of several Atlantic, the Gulf of Mexico, and the east.ern anat.omical characteristics. Identification of Caribbean. Lat.er, the normal movements and specimens from t.he Middle Atlantic States, par distribut.ion of this population will be discussed. ticularly the Atlantic coast from Cape Cod to We need first to consider the relationships of the Chesapeake Bay, presents an added difficult.y be various populat.ions. In addition to the popula cause of t.he several very similar offshore species tion of the western North Atlantic two others which may be caught occasionally, but probably . may be roughly defined. One occurs along the rarely in inshore waters: Eulmnia. obsc/u'u (Le. coast. of South America from Trinidad east.ward Sueur), E. fa.leifo·r·mls (MUller and Henle), E. amI southward. The other is found along thl' ftorida'lla (Bigelow, Schroeder, and Springer), west coast. of Africa and is presumed to be con and E. allilna Springer. R.ecent. unpublished tjnuous with the st.ock entering. t.he Mediter records of the occurrence of E. 11lRberti young ranean. and of t.he occurrence of '(!al'ch.arM'I1US leucas The population occurring on the coast of South adults are rather numerous, and following publi America appears to be a minor one. The species c!ltion of t.he first. volume of Fishes of t.he W'est. has been reported and figured by R.ibiero (1923) ern North Atlantic (Bigelow and Schroeder, from the coast of Brazil. 1948) t.here appears to be lit.tle confusion of the 'While engaged in commercial shark fishing in two species. April and May 1949, I made shipboard examina Belaboring the point t.hat. descriptive accounts tions (Springer, 1949) of a series of sandbar of carcharhinids must. be det.ailed and selective to sharks from the north and east coasts of Trinidad have any meaning seems necessary t.o affect t.he and identified them in error as E. plu.m.belM. I int.renched misconcept.ions about. E. 11l.ilbertl t.hat. now believe that differences between the Trinidad can be derived from t.he literature. Fowler's specimens and typical '11l.ilbe1'fi from the Atlantic (1936) description of E. plttjnbe1ls (plum.beu.s = coast of t.he United States are insufficient to war 11l.ilber!i), which was based on American Middle rnnt. recognition of separate species, and that. the St.ates examples, alt.hough in a report on 'Vest conservative course, pending accumulation of new African marine fishes, is not. unique in confusing data, is to look upon the various Atlantic sandbar E. 11lRb&rti wit.h anot.her species,S but it is de sharks as representing a single species. At. the t.a.Hed enough to be especially vulnerable t.o criti Trinidad locations, adult males and fpmales as cism. Mon." elements of his description fit. the well as young of all sizes from 4 feet upward bull shark, (!aJ·eh.a.rhIn1ls leu
552508 0-60--2 6 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE the British Museum of Natural History, although tive conversation by some of my friends who are specimens from the western Atlantic were pres ichthyologists. This view may easily develop ent. Tortonese noted (1938) that there are two from unsatisfactory attempts to make identifica sppcimens in the Musee di Trieste collected in tions with methods which are quite adequate and 1869 and 1871 and, after exa,mination of speci successful in application to teleosts but fal] short mens labeled milbe'l'ti from the western Atlantic when applied to sharks, and particularly to car in the Museum at Paris and the British Museum, charhinid sharks. E. 1nilbeTti, in waters off the he indicated (in 1951) that he regards 1nilbe1'ti United States, is readily defined and problems as a synonym of plU'lnbeus. concerning it are not complicated by the existencp. of geographic or environmental races or sub FIELD RECOGNITION species, insofar as the available evidence shows. Eulamia milbert'i is commonplace in appear This is apparently not true of some of the other lwce. It has neither unusual color markings nor ca.rcharhinids where separate populations may be spectaculal' stTuctural features. The length of defined on the basis of morphological differences the shark at maturity, 7 feet, makes the species shown in the analysis of adequate series from too large for the biological collector and too small different a,reas. to interest the journalist. It is necessary to The keys and descriptions given by Bigelow and search for distinguishing featUl'es (fig. 1). The Schroeder (Hl48) are adequate for the identifica opportunity for comparison of series under onli tion of the carcharhinid sharks of the western nary circumst-ances is negligible, and almost all North Atlantic excepting Eula1nia altil1UL, which identificat-ions of the larger sharks are necessarily was described (Springer, 1950) after publication made in t he field. The suggestion that many of of this work. Nevertheless, identifications need the presently recognized species of carcharhinid to be made carefully because of the general struc sharks are not in fact separable from one another tural similarity of the species which look alike on but should be regarded as unidentifiable parts of superficial examination. Sharks of the genus a species complex has been advanced in specula- Eulamia in the !aldfm'mis-sp1"in,qeri group are
FlOUR!;; l.-E/llQ1n?·a, millJel"li in un exhibition tank. TIl(' high, triangular first dorsal fin, nonfalcatE' pectoral fins, and rrlativrly hip;h srcond dorsal and anal fins, ncarly cqual to one anothcr in area, arc chantct('ristic of the species_ (Pho togl'llph courtesy of Marinc Studios, Marincland, St.. AUll;ustine, Fla.) NATURAL HISTORY OF THE SANDBAR SHARK 7 not well known and possibly are incompletely de the shllllower water E. lnilbe-di in the Straits of fined. Minor differences between Atlantic and Florida area and extends well into the nighttime Gulf of Mexico populations of E. obse'll,Ta need range of the night shark, HypQprio·n signa-tUB further study. There is no difficulty, however, in Poey. The geographical range of E. altima may distinguishing E. 1nllbeJ'ti from these species or be quite extensive, but it is unknown because from other species of sharks ordinarily found comparatively little fishing has been carried out within its geographical range. at the depths where this species might be expected The importance of determining the presence or to occur. Such fishing as has been done in mid absence of a middorsal ridge (a low ridge in the water and just beyond the edges of the Conti skin extending for all or a part of the distance nental Shelf by commercial shark fishermen indi between the first and second dorsal fins) for the cates that the species is relatively common. identification of carcharhinid sharks cannot be Probably many more E. altima would have overemphasized. This minor structural feature been taken by the commercial fishery were it not is certainly nonadaptive and its usefulness as an for the fact that in the Florida-Caribbean region indicator of probable relationships should be the liver oil of altima is characteristically lower great (see Springer, 1950: p. 1, and Backus, in vitamin-A content than is that of any of the Springer, and Arnold, 1956: p. 180, for discus other species of E'Ukunia or of H ypoprion in that sion). The first mention of this characteristic in area. published work was by Nichols and Breder In a large measure, the confusion in the nomen (1927), but correct identifications of the common clature of the Ia.rger American carcharhinids that large ground sharks of the east coast of the existed before the publication of the 1948 work United States were made by Nichols and by Rad by Bigelow and Schroeder would undoubtedly cliffe independently before 1916. have been avoided if descriptive literature had In one of the more valuable papers on sharks, included information on the presence or absence Radcliffe (1916) made the first general use of the of the middorsal ridge. A fine replica of a shark, structure of the dermal denticles to show differ which in the light of the better descriptions now ences in western North Atlantic carcharhinid available can easily be identified as Cal'chal'h:inu-s species; and his illustrations show clearly the le1tcaS (Mimer ~nd Henle), a species without. a distin~tive denticle type and arrangement which middorsal ridge, is shown in an illust.ration in an sets E. 'I1l.ilbert·i. off from other carcharhinids informative n,rt.icle (Rockwell, H116: p. 161) within its range, except. for the newly described under the caption Oa.1'cn..a1'hi11ll.tIJ obscu/ru8 (Eula E. al#ma. Both E. lIlHberti and E. altima differ n!-ia ObSC1bra.), a species with a middorsal ridge. from all other North American carcharhinid Determination of the presence or absence of the sharks in having nonimbricate denticles without ridge is sometimes difficult, particularly for mu strongly projecting points; however, the denticles seum specimens or for specimens that have been of E. altima are much smaller than those of exposed to the sun for a long period. Although E. lIlJlbeJ'ti. identifications can be made without reference to Commercial shark fishermen at Salerno and Key the ridge, they are likely to be difficult and use West, Fla., recognized althna as distinct from the of all of the available differentiating character sandbar shark and called it the bignose shark or istics is desirable. Knopp's shark before it. received a scientific The confusion of the sandbar shark with the name. The diagnosis given with the original de bull shark extends to the Pacific. References scription of E. altima. (Springer. 1950) should have frequently been made to the sandbar shark, be adequate for the determination of specimens Eula:m.ia 1n-ilberti, as occurring on the Pacific of all sizes. All of the known examples of E. coast of Panama. There is no evidence of this althna have been taken at depths of 50 to 150 and the species probably is not found there. Gar fathoms off Salerno. Florida, in the Straits of man's (191:l) synonymy of m.ilbert-i included Florida, in the northeastern Gulf of Mexico, and EulfUnia nic(lra{/ue'l/IJiil Gill and Bransford, the in the Dragon's Mouth between Trinidad and fresh-water bull shark. The two bull sharks, Venezueill. Its vertical range overlaps that of nical'ague'1lsis and leucas are so similar to one 8 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE another that their separation is doubtful. There Differences between ndults of E. altbna. and is a Pacific species so similar to nicaragnensis and m.ilberti are quite apparent in field examination lenca~ that commercial shark fishermen who fished when the two are seen side by side. The snout of on both coasts claimed they were una·ble to dis althna is longer and notably thicker dorsoven 'tinguish one from the other except by area of trally. Furthermore, the first dorsal fin in E. capture. I do not know the scientific name for altima looks quite different because it is not quite the form if it has a name, but whatever the so far forward as in E. 'mRbeJ'ti and is neither so species, it is like nicm·agu.l!'l18is or le1tca.s and not erect nor so high. The high and erect dorsal fin like mHbeJ'ti. Meek and Hildebrand seemingly of E. m./lbeJ'ti in a forward position (fig. 2) is a had difficulties with this one in Fishes of Panama reliable and adequate character for field recogni (1923), whe.rein they discuss a Pacific specieg tion of adults in the water, if the size. of the ('aJ'charh.inuB azw'e'll-8 (Gilbert and Starks) as a shark is taken into consideration. synonym of m.ilbeJ'ti. But Meek and Hildebrand Gill (1862) based his c.lassification of the car did not see a specimen from the area which they c.harhinid sharks almost entirely on the structure themselves could identify as m.ilberti and the of the tp.eth. His arrangement of genera was not significant sentence in their treatment states- satisfactory and it is apparent that short. descrip We certainly must regard the present arrangement as tions of shark teeth are inadequate and leq,d to tentative only. for more specimens must be compared confusion even though the number and form of before the true affinities of the specimens from the op the teeth show comparatively little variation posite coasts can be established. within species and are of considerable diagnostic. A paper by R.osenblatt and Baldwin (1958) on value. The persistenc.e of essentially similar some of the carcharhinids of the eastern Pacific shape and structure in the suc.cessively larger presents for the first time information on the teeth appearing in some· carcharhinid sharks as presence or absence of the middorsal ridge in they grow has been fairly well established by ob Pacific species. This is an impOitant contribution servation. In E. m:ilbeJ'ti, at least, this appears and includes more comprehensive descriptions to be true, although this is neither universal than have hitherto been available for sharks of among sha.rks nor adequately demonstrated for the eastern tropical Pacific. These authors find many speCIes. the separation of E-u.him-ia from Oarcnarldnu.s To obtain some verification of the extent of unacceptable for Pacific species. In support of variat.ion in the number of tooth rows in car this an unfortunate choice of illustrative argu charhinid sharks, I took advantage of a situation. ment is used. They say (!. altima, for example, requiring the preparation of several hundred has a definite dermal ridge but teeth which are as dean, dry shark jaws for a commercial order. I l1!trrow as those of any member of the smooth carefully identified the sha.rks and tagged the backed group (Springer, 1950). This is an error. jaws of a series of 110 E. 'fIz.ilbe-rti together with The teeth of althna in the upper jaw are similar aU other sharks appearing at the same time on in general shape to the teeth of the other species the dock at Salerno, Fla. All of the rnilberti and of Eulmnia. These authors logically ca.ll atten most of the other sharks were adults; sex was not tion to the ill-assOl:ted group left in the genus noted. After the jaws were clea,ned I c.ounted (!arcnaJ'M-nus by my 1950 revision. mentioning and recorded the number of tooth rows (table 1). wu.cas and ·velo.l! as examples. I am in complete To the extent tn:at this sample represents t.he agreement wit.h this but find no cogent argument population of m.ilbertl, the counts of rows of for the elimination of Eulmnla, since the species teeth indicate that variation is small in tha.t of E-ulOln-ia as restricted are remarkably similar species. to one another in all of their morphological f('a The shape and the relative position of the fins ttIres. The sharks allied to the genus C(u"chaJ' in carcharhinid sharks are reasonably useful Mn1l8 are far too widespread and numerous and characteristic.s for identification. Small differ there is far too little known about them for an ences in the size of fins or even in their positions, adequate study of thp. entire group. Additional however, are of comparatively little value because revisions of the group are needed. of differential growth and the diverse trends this NATURAL F.USTORY OF THE SANDBAR SHARK 9
FI: HI~ 2.-E/llamia wilbert?' turning in front of the camera at 1\1urinel:lJld, Fla. Note that the pectoral fins arc quite broad at their base., relatively pointed and not strongly concave on thoir trailing edges. \\"ith the exception of the caudal fin, all fins function as rudders or stabilizers and CHunot be used indeppudently for locomotion TIll' I)('ctornls provide lift to ofT~l't the lift of the asymmetrical caudal since without a forward lift· the shark would tl'nd to somersllult. The large stiff fius iu forwllrd positions reducl' thl' ability of this spccips to roll :lI\d twist but may be expected to increase the precision of it,s forwarrl swoops at creatures on tIlt' se:L bottom. (Photograph courtesy of Marine Studio.', Marineland, Fla.)
growth may take in dif:l'erent species. Data to Englewood, Fla., 2,210, 2,070, and 2,240 mm. long, sho,,, adequately the differential grmvth in car the pectoral fin lengths are 21.3, 21.5, and 21.0 charhinids are lacking. But one example will percent of the total length. Let us compare these suffice to show how unreliable proportional meas proportions with measurements of pectoral lin urements can be for comparisons between species leno'ths of the whitetip shark, P/CI'olam.i.ops ~ . in whieh speeimens of different sizes an 1 ages lon,qi.mmll/8 (Poe,)'). ~\ latc-l'ndJI'Yo \"hitet ip 5~() arc involved, and in which the growth patterns mm. long, takcn 1~5 miles off New Smyrna, Fht., of the species being conl])ared are unknown. ]n 11<1,-; a pectoral fin length 22.G percent of the tobi t.hree CXHlllples of yOllllg 1,,-'. 'II1ilb('l'ti, Ci8!). (iSO, length; :l yOllng whiletip ],020 mm. IOllg, taken and (i;3!) 111m. long, from the vicinity of "Tood. ofl' Tampico, ]\Jexico, has a pectoral fin 25.5 per Hole, Mass., the lengths of pectoral fins (meas cent of the total length; and an adult whitetip, ured on their outer margins or leading edges) 2.310 mm. long, from the central Caribbean, has are 16.2, ] 5.!), and 15.0 percent of n1e total length a pectoral fin 22.0 percent of the total length. of the sharks. In three adult rnilberti from off The figures indicate a proportionately longer 10 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
TABLE l.-Tooth-ro!O counts in carcharhinid sharks taken off Salerno, Fla., summer oj 1947
Number of specimens bavlng toothrow counts I of- Species ------1------EulamiaUppermilbertijaw_. (110 specimens):•• . .• .___ 3 37 55 11 4 •. _ Lower jaw_. •• .. .. __ .• • . __ 12 20 44 30 3 1 •_ E. jloTidana (48 speclmens): . . Upper Jaw ....• •• __ . • .------__ ._ ------._ ---- ..-_ 1 3 _ Lower Jaw •• •. • .. .•• . 1 1 29 11 3 I_ 6 13 23 4 E. ooBcuTa (39 specimens): Upper jaw ._•..• . -. -- . ._._ 3 15 12 7 2 Lower jaw__ • • -. ._ 1 3 15 10 8 1 1 CaTc:IlaThinuBUpper jaw.I,uras (24 specimens):. . .. .__ 2 5 15 1 1 • . _ Lower . .. . •. ._ . 18 3 3 .• _ C. limbatuBUpper jaw(31 specimens): .. . .__ 1 0 4 14 11 0 1 _ Lower jaw . . . . 1 25 5 . _ C. maculipinniBUpper jaw (13 specimens):._. . ._____ 1 1 2 4 3 2 Lower jaw . • ... . 2 1 9 1 _ GakocerdoUppercuoierjaw (21 specimens):._. .• .______4 3 12 2 . • __ Neg~~ t~~~~~t;~~;(~;~~~~~~~~;;~;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;; ::~: ::~: :;~: ::~: ::~: ;;;; ;;;; ;;;; ::~: ---. --~- ::~: ;;;; ;;;; ;;;; ;;;; ;;;;
I All counts made from cleaned jaws from which all membranous sheathing had been removed to permit accurate counts whether or not teeth of the functional row were missing.
pectoral fin in adults than in young for E. 7nil the size range of adults within the known seg b&r#, but an entirely different condition in P. ments of the population falls within limits which lo-ngimanus. are narrow enough to facilitate field identifica The sandbar sharks available to me were re tion by process of elimination. Thus, an adult markably uniform in general appearance and in Eula·m.ia more thttll 92 inches in tota.} length is those features that I could measure, count, or probably not -m.llbe1·ti, and adult males less than compare. In an attempt to learn something from 70 inches or adult. females less than 72 inches in morphometrics, a considerable number of 7nilbe1'ti total length are unknown. and other species were mea.sured carefully and in detail. However, the principal value that I de DISTRIBUTION OF EULAMIA MILBERTI rived from this excessively laborious task was in General nature of distribution the deliberate examination of specimens enforced The distribution of EulQlrnia milberti is diffi by measurement of detail and in the notes madl:' cult to treat adequately bec~use, even though to accompany t.he measurements. The exercise further discussions will be limited to the popuht served also to impress upon me the difficulties tion of the weste.rn North A.tlantie, the distribu attending att.empts to get adequate series to show tion patterns are extremely complex. The adults growth patterns among some of the species of segregate by sex and to some degree have differ large sharks which are not only migratory but ent vertical ranges. The nursery areas occupied probably short lived. by the very young sharks are free of adults ex A characteristic of great import.ance for field cept when the females come inshore to give birth recognition of specimens of carcharhinid sharks to their young. is the tot.al length of the specimen considered in The migratory patterns of young and adults connection with its sex and maturity (fig. 3). differ greatly. Finally there is a well-defined The mammalogists and ornithologists have long principal range oceupied by at least nine-t.enths considered total length important in identifica of the western North Athmtie population and an tion because mammals and birds have determi accessory rnnge of uncertnin importance. It is nate growth patterns. As will be shown later. quite possible that the populntion occupying the E. 'I1tilbertl has growth characteristics which re accessory range is not self-sust.aining and exist.s sult in adults of predictable size. Furthermore, only beeause there is continuous but quite acci- NATURAL HISTORY OF THE SAND'BAR SHARK 11
Carcharias taurus ...... 1IIIIIIIII1IIIIIIB1II!IIIIl1llllliill15 Ga/eocerdo cuvier .... ?~ ~~~::::: ~ ~~~~~~~~~~78
Negaprion brevirostris : ~ ~ ~ ~ ~ :::~ ~ ..... :::: : ~ ~: ~ : ~ ~ :.~i~6 .., ~ Aprionodon isodon ....••••.••••••:lIlIIII2o Carcharhinus ·/imbatus* ~:::~ ~ .. .; -- ...... &i!iJii Carcharhinus maculipinnis ...... _12
Carcharhinus /eucas :::•••••• ~:::: :~:::::::: •• :: ~ .~142
Eu/amia milberti ····················-.n5 ••••••• .. .•••••••••• .1IIIIIII!lIIIII899 Eu/amia altima ··:;.·.·.·.:~.·.:~.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.~15 Eu/amia f/oridana .. '?:: ~ ::::::: ~ ':::: .~34
Eu/amia obscura ~ ~ •••••••••••• ~ •••••• :::•••••••••••••••••••••••• ~ ~ ~ •• ~150
Sphyrna sp.** ~ ~ ~ ... -. -. ~ ~ ~ ~ ~ ...-.-. -. -. -... ~ ... -. ~ -. -. -. ~ -. -. -. -. -. ~l!3i!6 ilMil!la!lil!l!l!!ili!!ilJ!}@!aESl1i!&l1i!O\i\i&i&52
IIIIIII o 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190
_ =. siZE! range of embryos ~ = size of adults
FIGURE 3.-Comparative sizes of adults and young of common large sharks found within the geographical range of E. milberti. The figures at the right indicate the number of specimens in the sample used to determine size range. The size ranges for embryos are estimates based on maximum observed lengths of embryos and minimun lengths of free swimming young observed in Florida collections. (* Size range in Florida-Antillean specimens. Western Gulf of Mexico and Central American coast specimens are smaller and produce smaller young. The western stock may prove to be distinct nnd if so should take the name Carcharhinus natator Meek and Hildebrand. ** The great hammerhead of the West Indian region, following Bigelow and Schroeder (1948). The nomenclature is now unsettled. The name Sphyrna tudes is not available for the great hammerhead and probably should be replaced by Sphyrna mokarran (Ruppell)')
dental recruitment from the principal population. the coast of the Carolinas around the tip of Within the expected vertical and geographical Florida to the gulf coast of Florida as far north range of the species are some areas which appear as Tarpon Springs. It occurs uncommonly in the to be avoided. It is well to mention again that western part of the Gulf of Mexico and along the the sandbar shark, like other large sharks, is not continental shores southward to Costa Riea. It prevented by well-defined barriers from wander is a casual visitor on the northern coast of Cuba ing out of its normal range. and the western edges of the Bahama Banks. Its The limits of distribution are therefore not vertical range is from the shC'reline out to H35 sharply defined. Following the traditional pat fathoms. It. enters bay mouths but is not found tern in descriptions of distribution it may be said in fresh waters. that the sandbar shark, as represented by the The principal source of information on the western North Atla.ntie population, is eommon distribution of the sandbar shark c.omes from the. in summer off the Atlantic coast from Cape Cod C0Jl1lUe.l"C.i111 shark fishery. Atlant.ic coast shark to "Vest Palm Beach, Fla., and in winter from fishermen used bottolU setlines more often than 12 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE any other genr. Each unit of gear consisted of It where they have escaped the attention of natu main line of chain or wire rope a half-mile or ralists. On June 11, 1954, the first E. '1TIilbe'1'ti more in length. This was set on the bottom: known from waters beyond the Continental Shelf anchored at both ends with the anchors rigged was taken on a tuna longline hook at USFWS with buoys so that the lines could be retrieved. Oregon station 1099, 85 miles off the coast of Short, branch lines made of chain, each with a Texas where the depth was approximately 600 baited hook, were spaced at intervals of 20 to 40 fathoms. Since the hook was set to fish at about feet along the central part of the main line. The 30 fathoms, this shark, an adult male, was cruis typical unit had 100 hooks. Floating lines and ing in midwater. Throughout. the second half of tmchored gill nets were also used occasionally 1954, all of 1955, and the first part of 1956, long in the fishery. line fishing was cn.rried on in the offshore waters Positive information from the shark fishery on of the Gulf of Mexico by the M/V OregO'n and a the distribution of E. m.ilberti is quite volumi few commercial vessels. Large numbers of sharks nous and detailed. Systems of payments to fish were talten, ehiefly spec.ies known to be partly or ermen required detailed records involving iden entirely pelagic. No addit.ional mHbati were tification and measurement of all sharks landed taken until early February 1955, when a CODl by vessels of the principal fishing company. Al mercial vessel eaught two adult females about 50 together, records of landings of more than miles off the nort.hern edge of t.he Campeche 100,000 milberti during a period of 15 years have Bank where dept.hs were est.imated to be more been pxamined. than 1,000 -fathoms. These sharks were caught Information on the absence of E. 11IHberti from on longlines with hooks fishing not more than specific areas has been difficult to assemble, but 50 fathoms deep. These three captures, outside here also the records of the shark fishery supply the princ.ipal I'ange, appe.ar to have little signifi most of the data. The species was first reported cance in the general picture of t.he distribution in the Florida area from correctly identified of E-ulam-ia mRbel'ti. spe.cimens after the eommercial shark fishery Factors affecting distribution bega.n (Springer, 1938), so the earlier scientifie It may be assumed that water temperature and literature has been useless in the establish salinity are import.ant in limiting the distribution ment of the ra.nge of the spedes in the Florida of the sandbar shark and that there are other area southward. Offshore records, from areas factors clen.rly influencing the movements and where water depths a,re more than 500 fltt,homs, distribution of the species. The reaction of sand· are exclusively from catehes made, on tuna. bar sharks to ocean currents, the availability of longlines used by the explortttory fishing vessel food, the reln.tion between the growth rate or the Oregon (for descriptions of this gear see reproduetive pattern and the migratory move Bullis, 1955, and Captiva, 1955). Some informa ments, all appear to be important in forcing the tion on the distribution of the young was obtained species into a part.icular range. No data are from otter-trawl eatehes made by the exploratory available, however, to show the relative st.rengths fishing vessel. Dela·ware off the coast of North of these conditions as determinant.s of the range Carolina. Additional scattered records were of the sandbar shark. picked up from accidental catches made by com The facts, from superficial examination at least, mercial and sport fishermen who used various do not support t.he thesis that competition with types of gear, from catches made by collectors other species is a powerful influence in the selec fishing for aquarium specimens, and from biolo tion of a partieular range. Young E1l1mnla, m.il gists who captured specimens incidental to other bel'tl, for example, apparently cannot long sur eolleeting activities. vive wlwre large (!al'f'hul'ldnU8 leu.cas in propor The area of greatest uncertainty is in the off tion to mHbedi arc relatively nbundant.. The shore and midwater range. Reeent marine ex presence of largE:' numbers of large C. le'Ucas in ploration has sho"'n that substantial populations the vicinity of the mout.h of the Missi~Bippi Riwl' of large sharks, fishes, and invertebrates live in seemingly does not. deter gravid female milbert-i subsurface waters beyond the Continental Shelf from moving into the area to give birth to young. NATURAL HISTORY OF THE SANDBAR SHARK 13 Whatever the particular reason or reasons may m.ilbe1,ti with nearly full-term embryos off the be, the general absence of young 'l1l-ilbe'rti. in the Texas coast (Henry Hildebrand, 1954), and a Gulf of Mexico shows that conditions are un specimen 747 mm. (nearly 30 inches) from the favorable for them. Circumstantial evidence Texas coast (Bigelow an~ Schroeder, 1948). suggests that interspecies competition is respon It is probable that gravid females wandering sible, because large O. le.ucas eat young milberti. away from the principal range of the species give No explanation is apparent for the common birth to young along the Mexican and Central occurrence of E. 11'liilberti along the continental American coast, but no records of the capture of shor~s and its absence from most of the West yqung in this area. have been found. Shark fish Indian shallow waters except that the species ing on a small scale has been carried out over seems to have preferences for certain types of most of this area and catches have been examined bottom. E. ,milbe-r# is ordinarily not common in at various points from the mouth of the Rio areas of coral reefs or where the bottom is rough. Grande River to Costa Rica; but excepting the Since it is chiefly a bottom-dwelling species, it is Gulf of Campeche, no young 'l1Iilbe'rt-i appeared. not surprising that it would exhibit preference The female EuJawlt m,ilbe1·ti, which move into for one type of bottom over another. In its the principal nursery areas to give birth to their migratory passages around the southern tip of young, do not remain there long and do not feed Florida and the Florida Keys, however, there actively while there. This may explain the appears to be active avoidance of the fringing scarcity of records of captures of adult E. mil reef. Here the migrating adults leave the rela be'rti along the Atlantic coast. Great South Bay, tively shallow areas they inhabit on both the east Long Island, is one of the nursery areas of E'. and west coasts of Florida and temporarily enter 'l1l,ilberti and accounts of the appearance of fe and feed in much deeper water. males in the bay and birth of the young are given Nursery Arounds and distribution of young by Thorne (1916). Additional mention of the The principal nursery grounds of the western appearance of E. milberti in the Great South North Atlantic population of E1tlamia milberti Bay area is made by Nichols (1918), who notes lie in. relatively shallow water alon,g the Atlantic that the interesting fact about them is that the coast of the United States from Long Island to adults of the two sexes of the same species are Cape Canaveral, Fla. This range may be ex almost never taken together near Long Island. tended slightly at its northern end to the south Here the adult females are E. milberti and the side of Cape Cod in favorable years but the adult males are CarcharMntUJ l.eu·CaB. southern limit is more definitely fixed. Not one Records of young sharks from Chesapeake Bay young mRberti has been taken south of Cape show that E. m.flbe-rti gives birth to young in the Canaveral, around the tip of Florida, or in the bay in summer. William Massmann, of the Vir eastern Gulf of Mexico. On the east coast of ginia Fisheries Laboratory, has kindly given me Florida, south of Cape Canaveral, a few sexually (in correspondence) records of E. milbert-i from immature 1nilbert-i of almost adult size have been the lower Chesapeake Bay. He says- taken; but in this area adult milberti are com Although young of this species are probably the most abundant shark In the Bay In summer, I would not say mon. A great quantity and variety of fishing that It is numerous. • •• It Is commonly caught by effort has been concentrated south of Cape anglers and probably rather generally distributed In the Canaveral on the Florida coast. The total ab lower Bay. I have not seen an adult In the Bay or any sence of young milberti here is remarkable in Individual more than three and a half feet long.. view of the somewhat indefinite range limits of After a comparatively brief period in shallow the adults. water or in the mouths of bays, perhaps at the A secondary nursery range apparently lies in beginning of cool weather, young m.ilberti appear the northwestern pa.rt of the Gulf of Mexico. It to move offshore. The only area from which is indicated only by the capture of a few females young 1nllbe1'ti are known in the winter season with near full-term embryos near the mouth of lies off the coasts of the Carolinas at depths out the Mississippi River, the capture of a large to 75 fathoms. 1152li08 Q.-..6O-3 14 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Distribution oft Atlantic coast of the United States and rather rare in Chesapeake Bay although more in eastern Gulf of Mexico common than nny other shark except the spiny Th~ northern limit of th,e range of the sandbar dogfish. Radcliffe (1916) st.ates t.hat t.he species shark is easily established.. ': There are no reliable appears to be rare in the Beaufort, North Caro records of its capture from the Gulf of Maine lina, region. However, it was regarded as com (Bigelow and Schroeder, 1953), but SO~lt.h of mon in bays on t.he ocean side of Long Island Cape Cod it has been taken frequently but Irregu from mid-june to mid-September, by Nichols and larly at. Woods Hole, Mass. Numerous records Breder (1927). of the spec.ies along the Atlant.ic coast of the The apparent scarcity of adtilt E. milberti United States are summarized by Bigelow and noted by Hildebrand and Schroeder and by Rad Schroeder (1948). Sandbnr sharks may be said cliffe is' easily explained. It is possible that E. to be common in summer along the Atlantic coast mHbe.·rti ente~s the mouths of bays t.o give bh·th of the United St.ates from Long Island to the tip to young more frequently than records suggest. of Florida and in winter n.Iong the waters of the Fema.Ie Carcha:rhIn:u.s le.1wa.s and Negapri(rn b·re·"i Continental Shelf off the Carolinas southward to rostris move inshore and stop feeding for a short the southern tip of Floridn, in water of moderate period at t.he time of the birth of their youug, ~est depths in the Florida. Straits and along the and immediately aft.er the young are born t~e coast of Florida northward to Tarpon Sprmgs females move into comparatively de.epe.r water. or the Middle Grounds (the rough bottom area This may be a common habit among carchar south of Cnpe San Blas, Fla.). This area is the hinids al~d certainly a very use.fnl one to provide principal known range, but the species hilS also for survival of the species. The Long Island been taken in small numbers from the northern re.cords are to a large extent based on harpooned and western Gulf of Mexico, the western borders specimens, and adult females should probably not of the Bahnma Bank, the northern coast of Cuba, c~~st be. expected to be easily availahle. t.o capture on and the Caribbean of Nicaragua and nort,h baited hooks in areas where the young are born. ern Costa Rica (fig. 4). The best fishing depth for adult E. 'milberti The hypothesis is advanced here that the sand from the Carolinas south to Miami was found by bar sharks of the eastern and southern sides of the commercial shark fishermen to be 15 "to 30 the Gulf Stream in the Straits of Florida are fathoms. On this stretch of coast. it was rarely casunl visitors to those areas and that the stock if ever tilken beyond 50 bthoms on bottom set of the northern and western parts of the Gulf of lines and made up less than 5 percent of the catch Mexico is a breeding stock which is not self on floatlines set beyond the 100~fathom curve. sustaining, but is recruited in part from migra Sout.hward from Miami, m./lberti was rare tory adtilts moving to the northern and western among the. keys, in HawkChannel, or along t.he parts of t.he Gulf by mistake or through error in shallower portions of the reefs south of tl.le orientation and navigat.ion during the regular Florida Keys. In the. winter, a few appeared III wint.er migration of the principal stock. catches made in the Northwest Ship Chmmel but., TIlP- sandbnr sluu'k has been taken frol11 the in general, the,se waters were le,ft toother species. shnllows a.Iong beaches out. to a depth of about The sandbar sha,rks, however, were the common 135 fathoms. The young have been t.aken most. est sharks on the bottom be,yOIi.d the fringing reef often in shallow waters to depths of about. 5 to out t.o depths of 50 fathoms an,d made up sub 25 fathoms in summer, but in wint.er- they move stantial portions of catches out. to 100 fathoms. offshore t.o warmer wnt.er and depths ns great. as They wel~ appreciably nwre numerous in catches 75 fathoms off the Ca.rolinn const.. off the lower kevs where currents were not so The sandbar shnrk is known only from the strong. NOl1.hw;rd from the keys along t.he west shallower part, of the Continentn.I Shelf in the Florida coast as far as Tampa, E. m1lbe.rti was wnrmer months in the extreme northern part of found t.o be most abundant. in depths of less tha~ its range. Probably the adults are more common 30 fnt,11onls. . .. ";, .." off beaches Hum in major bays or inlets. Hilde Shark-fishing vessels operated out ·of Salerno, brand and Schroeder (19~S) found the SpeCleg Fla., almost e,very day that weather permitted NATURAL mSTORY OF THE SANDBAR SHARK 15
NORT. AMERICA
... PRIMARY WINTER RANGE OF ADULTS
IILF till IEIICD
o····~.. .".•'. '",.' C , •I I IE'. SE , , • .. •
FIGURE 4.-Geographical distribution of the western North Atlantic population of the sandbar shark, Eulamia milberti. from 1936 to 1950, except for parts of 1939 and Jupiter Light. Some details of these landings, 1940 when activities were suspended due to over showing catch per unit of effort, were reported in production. These vessels landed .their catches an earlier publication (Springer, .1951). These daily at Salerno where the sharks were identified, data show that at Salerno the highest average measured, and recorded. Cate-hes included in the rate of catch of E. mHbe'rt-i occurred annually in Salerno landings were made from Bethel Shoal, the month of Februa.ry and the lowest average north of Fort Pierce, Fla., to the offings of rate of catch in September. These data concern 16 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE only adult 'lldlberti and the comparatively few aa:na from thevicinity of St. Croix and St. Thomas sexually immature m.ilbertl of adult size occur in the Virgin Islands. Mather's fishing operations ring with the adults. rovered the depth range in which E. m.-ilbe·"ti On the west coast of Florida, shark-fishing would be expeet.ed if its geographical range ex vessels caught no E. m.ilbert·i at all from May tends through the West Indies and if the absence through November and reported their largest of milbert-i follows the usual pattern in the West catches from January through March in each of Indies. several years for which data are available. At Key "Vest, Fla., high catch rates were ob TABLE 2.-Sharks taken by commercial.fishing I.essels in the Salerno-Fort Pierce area (Bethel Shoal to Jupiter Light) tained for mHbe'l'tl from deepwater sets made in and landed at Salerno, Fla., in May and June 1945-46 the winter and early spring but catches at other [I to 3 vessels; only sh...ks with hide length of55 in. or more included; ftshing seasons were poor. depths from 18 to 40 fathoms~ High catch rates of adult E. mHbe'rti were ob Number of sharks tained by shark-fishing vessels off the Carolinas Species in September, and from 1946 to 1949 one or two 1945 1946 of the' more able shark-fishing vessels followed Eulamla mllbtTtI (MiilIer and Henle), sandbar shark_ _ 1,515 987 the fishing for adult m.ilberti southward, arriving Sph/ITua sp.,' hammerheads .______323 268 Elliamia ob8cuTa (LeSueur), dusky sh...k______269 94 off Salerno in January or February. Eulamia (lOT/dana silky sh...k .______(Bigelow, Schroeder, and Springer), 220 191 Scouting by shark-fishing vessels showed that GalroctTdo cuvitT (LeSueur), tiger sh...k______lIS 64 CaTchaTh/uusltllcas (Muller and Henle), bull shark____ 61 41 some adult milberti were present in each month Net/apTian bTeviro'/T/s (Poe.y), lemon shark______20 19 CarrhaThi-llus sp.,' blacktips______3 16 of the year along the Atlantic coast between the Ginglgmos/oma ciTTa/um cOmeliu), nurse shark_ _ 2 6 CaTchaTodon raTrhaTias (Linnaeus), great white shark__ 2 5 l,uTlII OIg,/nehus Raflnesque, mako ._____ 0 2 latitudes of Charleston, South Carolina, and Unidentified ._____ 120 2 Miami, Florida. Although E. milbedi was the principal species sought in this area, other species I 3 species; station records do not distinguish kind. '2 species; station records do not distinguish kind. contributed variously to the value of the total catch. Table 2 shows the comparative availa That the Gulf Stream is not itself a barrier to bility of large sharks to the kinds of fishing gear E. mHbe:l'tl is apparent from the occasional cap employed in the Salerno area in the late spring. tures along the Bahama Banks and off the north Distribution in Bahamas and West Indies ern coast of Cuba. It is possible t.hat large nUlll E. mllberti is common only on the western side bel'S of migratory sha.rks may wander away from of the. Gulf 8tre.am. On the eastern side of the normal migratory routes at t.imes when unusual stream, it is replaced by E. falelformJs as the condit.ions prevail. Cert.ainly a few 1nilbe-l'tl common inshore EU}(J.,mi.a. The wandering of crosg the stream. milbe-rtl into the Antillean area may be quite From May 18, 1948, to July 8, 1948, I under limited. There are no records of "111iilberti. east took a program of e.xpe.rimental shark fishing ward through the West Indies nor from the along the western edge of the Bahama Bank from southern shores of Cuba. A shark fishing opera Riding Rock nortllwRl'd. Fishing operations tion o~ ·the eastern part of the Bahama, Bank in were carried out from a base a.t. the Lerner Ma the period from 1947 to 1949 did not take mll rine Laboratory of the American Museum of be-rtC .. Nat.ura:l History at Bimini, using a fishing vessel and gear provided by t.he Shark Industries Divi .'. E. falc-ifol'mis was reported by Evermann and sion of the Borden Co. Fishing was carried on Marsh (1902) from. Puerto Rico; by Be.ebe and chiefly by bottom setJines at. dept.hs from 10 to Tee Va.n (1928) from Port-au-Prince Bay, Haiti; 200 fathoms, but some, float.ing lines were used t.o by Nichols (1929) from Puerto Rico; and by assure coIled-ion of as wide a variety of sharks as Backus (1957) from open sea situations east of possible. Sets included some made at various the Gulf Stream. None of these authors noted levels along the ext.remely precipitous slope of the the presence of E. m,ilbe-rti. bank, which drops off abruptly from about. 20 Frank Mather III has told me in correspond fathoms down to the floor of t.he Gulf Stream ence of the capture of E. fakifo-rmi~ and E. flo-ri- channel where depths are more than 150 fathoms. NATURAL HISTORY OF THE SANDBAR SHARK'" 17 During the entire fishing period along the Ba at Snlerno. This is a, poor fishing spot, however, hama Banks only 14 E. mHbel'ti were caught in so the commercial vessels rarely caught springel'i. the lot of 447 sharks. Of t·he tot.al, 197 were Distribution in western Gulf of Mexico and western reef sharks, Eulmnia sp1,tngel'i (BigelO\y and Caribbean Schroeder) . Posit.ive knowledge of the distribution of E'u,{anl-ia 'lnilbe'l't'i in the western part of the Gulf TABLE 3.-Sharks taken in, exploratory fishing from the Dusky along edges of northwestern Bahama Banks, of Mexico and along the Caribbean coast of Cen May 18 to July 8, 19J,.8 tral America is based on records of 8 gravid fe males off the. Mississippi River delta, 1 gra,vid Number of sharks taken in- female and 1 young male from t.he coast of Texas, Species Bimini Walker 1 adult male and 2 adult females from the south area Key (20-200 0\)-100 central part of the Gulf of Mexico over deep fathoms) fathoms) wat.er, and 51 adult.s from the Caribbean c,oast of
Enlamia ,prlngeri (Bigelow and Schroeder),reef shark_ 10 187 Nicaragua and Costa Rica. Ga~ocerdo cuvl" (I.eSueur), tiger shark •_ 60 13 Eulamia ob,cura (LeSueur" dusky shark •_ 46 5 From the mouth of the Mississippi River east Ntgaprion brtpirostri8 (Poe)-), lemon shark •_ 2 18 Eulamia altima Springer, I,ignose shark. _ 17 2 ward and southward around the Gulf to the Fulamia florldana
I Antillean form. the tip of Florida to the Carolinas. I visited aU • Nomenclatorial status of this species not determined. of these stations frequently and sometimes par During the same season of the year in which t.icipated in fishing operations. The presence of the exploratory fishing was done, a great. number milbel'ti in appreciable quantity would almost of sharks were landed across the Gulf Stream at certainly have been noted in catches from the sta Salerno, Fla., about. 80 miles from t.he northern tions at Panama City and Carrabelle, Fla., had end of our Bahama fishing area. But more than specimens been taken. half of t.hem were E. 1'nilbert-i, and no E. falci It is not possible to present a meaningful ac fo-rmi,s was landed. Results of the Bahama fish count of the sandbar shark, Eu,z
TABLE 5.-Embryos of F.ulamia milberti, by size group and month, from females collected off th~ southeast coast of Florida between Fort Pierce and Tor/ugas, 1946-49
Number of litters Averagc litter length
______I._J_Ul__y_~~I~~~~~ Ma~~~~ I inch and under______5 7 . _ 2inches______5 _ 3 inches______4 • _ 4 inches______6 • _ 5 inches______1 1 , _ ~ :~~g~~::::::::::::::::::::::: ------~- 8inches______:::::::::: ::::::::::2:::::::::: 2 :::::::::: :::::::::: :::::::::: :::::::::: :::::::::: :::::::::: :::::::::: ::::::::::_ 9 inches______I • _ 10Inc)les______I _ 11 Inches______1 _ 12Inches______I I . • •_ 13Inches______I • _ 14lnches______2 3 _ 15Inches______2 1 27 _ 16Inches______I I 1 11 _ 17Inches______6 I • _ 18Inches______7 4 I . _ l\linches______4 6 3 1 •_ 20 Inches______3 1 • _ 21Inches .____ 1 _
22IIlches . ':.. . 5 _~ ~ __ . ~ _
~ :~~~:~:::::::::::::::::::::: :::::::::: :::::::::: :::::::::: :::::::::: :::::::::: :::::::::: :::::::::: ::::::::::1 ~ ------~- ~ 1
Table 5 shows the length distribution by Hildebrand and Schroeder (1928) report six months of emhryos of E. m.il.be'l'fi from off south E. milbe1'ti. in their colle.ction from Chesapea,ke east.ern Floridn. It is possihle that some of the Bay 17%, to 25% inches long. Presumably these variation in length of embryos neal' full term is were not embryos. Records furnished by William due to inclusion in the sample of measurements H. Massmann (in correspondence) for young from females of widely differing geographical Chesapeake Bay mllbedl include specimens from origin, for example northern Florida and Chesa, 21% to 28 inches that were taken in 10 collections peake Bay. from June 7 to October 7. Massmann'8 series is At Salerno, Fla., 5- to 10-mm. sandbar shark not large enough to establish progressively larger embryos were found commonly in July and Au size with later dates. gnst bnt no large embryos were seen during Some young E. m.ilbeJ'ti may be born prema these months. In.Jnne only a few among the turely at lengths of less than 20 inches either be large numbers of adult. female Eo -m.ilbe1't-i landed cause of crowding, in large litters, or extraordi at the Salerno dock contained embryos and the nary activity on the part of the mother. Cap few that were found were 24 inches long. Since hIres of very small young in otter trawls, for no free-swimming young were taken at Salerno example, might result from the entry of the or around southern Florida, est.imation of the mot.her into the. net followed by a successful size at birth in this area depends entirely on struggle to escape. This could bring about pre determination of the maximum length of em mature birth of one or more young which might hryos. R.ecords of young E. m.llbeJ'li. from Cape be left in the net. Ca.nnvern.l, about 60 miles north of Salerno, north-· Nichols and. BredeI' (1927) note that females wa.rd are common. Twenty-four-inch embryos ca.rrying young were taken in Great South Bay, from south Florida. were found to be most C01U Long Island, from .June 22 to August 5. Also mon in May but substantial numbers were seen in they state, when relea.sed the young were about April, and one set of 24-inch embryos wn..s taken 22 inches long and weighed 2% pounds. One of from a female collected off l\farquesas Island in a.bout 3 feet seen in Sandy Hook Bay as early as the Lower Florida Keys in Marph. Eight adult June 9 may have been of the preceding year. In female sandbar sharks were tnken on July 2, near September 1924, five young ranged from 24% to the mouth of the Mississippi River. Of these, 26 inches in total length. Bigelow and Schroeder five contained 24-inch embryos and one had 25 (1948) summarized the indications of size at inch embryos. Two had evidently ghoen. birth to birth from various Atlantic. coast records ·north young just before they were caught. of Florida in approximately the same way. It is NATURAL HISTORY OF THE SANDBAR SHARK 25 reasonable to expect that E. ndlbe1# at birth lllay of the capture of 26 males and 25 females otT the be somewhat smaller in the northern part of its Cttribbenn coasts of Nicaragua, and Costa Rica range than in the southern pttrt and that the in the fall. growth mte in eooler waters is slower. Data on the sex ratio in young E. m-ilbe1# is Abnormal embryos limited to a series of 203 young from 26 to 50 In the l:tte spring of Hl42 I collected at Salerno, inches long collected by otter trawl in February Fla., a series of Enla-nda m.ilbel'ti embryos of 1958 otT North Carolina. There were 91 males both sexes and near full term which were a,p and 112 females in this collection. parently perfect exeept for having the eyes on Florida shark fishery records of carcharhinids the lower side of the snout, almost in contact other thnn those of the genus E'Illmnia show local with one another and just posterior to the nos segregation by sex and size but in no other car trils, and having no trace of a,n opening in the charhinid nor in the IUlI1unerheads is there any skin for the mouth, although the jaw eartilages denr indicntion from available records from were apparently normal. The speeimens were Florida of great imbalance in the sex mtios of preserved in formalin but dried out during the adults. following years and were discnrded. Again ill TI~e unavailabilit.y of male m.:ilbe·rti to baited 1946 similar embryos were collected, and about hooks during the mating season may explain in half a barrel were preserved; but all were, lost ill part. t.he smaller number of males in the landings. a hurricane which destroyed a dock building. However. because Florida commercial sluu,l\: fish No abnormal young were found in the rela ing after IH46 wa·s carried on out to dept.hs tively large series of litters examined in 1948 and grent.er than t.he maximum knowll depth range of I hud no late.r opportunity to see substantial the species, and because the males brought the femal~s. numbers of E. milbel'ti embryos. All litter mates fishermen a higher price t.han the it is exhibited the same abnormal condition and were certain that there was no intentional selection of remarkably uniform structurally.' A very rough femnles. The fishermen believed that the schools estimate of the frequency of occurrence is one set of males, if found, were easier to catch in htrge of abnormal young in 500 to 1,000 sets of ap numbers. Females were far more abundant than parently normal pups. mnles in the deeper water catches made off the Florida Keys in the lat.e fall and early spring, SEX RATIOS and n much greater abunda.nce of females chnr It. was the general observation that landings acterized the wint.er catches on the west coast of adult Euhun';((, mRberti at Salerno were in the of Florida. ratio of 5 females to 1 male.. A simila.r sex l'lttio It has already been shown t.hat. approximately was estimated for Salerno landings of E. obscu:ra equal numbers of male nnd female mllboofi nre and for Bahama landings of adult E. spl'in!!el'i. horn. The evidence that there are subst.antially A disproportionately large number of female E. more females than males in the adult population florida-1w, were landed at Salerno' but the records is very strong, if our information adequately do not furnish an adequate basis for an estimate. covers the geographical range of the. species. Al An insufficient numbe.r of E. altiJ1/'(~ or E. spring though it is quite possible that segments of the e/'j, were recorded for estimate. Murphy and adult population have been entirely overlooked Nichols (1916). say that the commonest large in the otTshore and midwater depths in the north sharks in the waters about New York are the ern part of its range, the short.age of ma.Ies in the ground sharks (0a'rcnar'ldlJl.uJ5), and also that population around southern Florida is remark males of these fishes are mrelyseen but toward able. midsummer many' of the females eMer our bays There is some indirect evidence nlso of n short where they give birth. to their young. They age of males in the breeding population. If the further state that the commonest ground shark' femnles bear pups in alternate years. 50 percent is Oal'cnm·h.imf.s mHbe·rtl.; The Ol)ly record sug of the adult females would be expected t.o be gesting equality in the number of adults of the gravid in winter. I have previously reported sexes of E. m.-ilbedi is Captain 'Vinkler's I'ecord (Springer, 1940) that. only about. 17 percent of the 26 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE lldult females taken in winter off Englewood, on cient handicap to prevent E. mHberti from being the west CO:1st of :Florida, were gravid. I saw one of the commoner sharks. large numbers of E. milbel't{ in 1942 and again from 1946 through 1949 at Salerno, and my notes GROWTH AND SIZE AT MATURITY include seyernl estimates of the proportion of In Florida catches. adult male Eulmnia m.il gravid to nongruvid lIclult females seen on the berN average 4.2 inches shorter than the avemge dock. For the late-wint.er :ll1d early sprillg ndnlt femille nnd weigh 32 ponnds less than the periods, it was estimated that substantially less average nongravid adult female. The smaller t.han a third of the females were currying pups. size of the adult male. is characteristic of all of In my sample of iW9 adult females taken for the western North Atlantic carcharhinids al length-frequency data, approximately' 18 percent though the size of males and females at birth is were grnyid. approximately the same. For about 20 years I Three interest.ing, if theoretical, explanat.ions maintained n close watch on landings of one are suggest.ed to account for the apparent differ or more commercial vessels and saw no m.ilbe'l'ti ences in the number of male,s and females in females longer than 9:3 inches and no males longer m.ilbertl and in other Eulamia. than 89 inches among the thousands that were The mating pnttern appears to be particularly exnminec1. dangerous to the male,s, since mating oc('.urs when The smallest sexually mature male in the ma the females nre in a. feeding cycle while the males terial exnmined wns 71 inches and the smallest are not. That is~ during court.ship males may nip sexually mntnre female was 72 inches in total or slash to :,;ome extent but. do not take l:wge length. SexlHlI maturity in the male is easily bites. The fema.les have no such inhibitions ex nnd positively determined because enlnrgement of cept at. the time the young are bol'l1, and fatal the t.est.es to functionnl size is immediately fol accidents to males may be frequent during court lowed by the nppearance of a ring of calcium at ship. However, if this expla,nution is to be ac the surface of the major clasper cartilage. This ceptable, some further speeulatiOll is needed to ring is easily seen in cross section but since it.s suggest why aaleo('t~}'do with a similar mating effect. is to stiffen the segments of the clasper, pattern is not represented in the adult population seet,ioning is unnecessary for positive determina by a preponderance of fema.les. tions. Determinat.ion of sexual maturity in fe Geiser (1924) summarized a. variety of reports ma.le speeime.ns whel'e the specimens we,ee 11on on the higher death rate for males in some mam gravid or had no courtship scars wa·s made by mals, fishes, and invertebrates, and suggests that examination of the OVIUY and -the oviducts. The there' is a genetic bn·sis for this in certain cases females were regarded ~s sexually iinmature if where the possession of two sex chromosomes by none of the eggs in the ovary had begun to incrense the females * .., * ensures a greater longevity of in size and if the oviducts were· smaller in diame ter than is chal'actel'istic of the fully contracted the female by "canceling out" possible mutations oviducts in females following parturition. It in the. x-chromosome. especially associated lethals. may be noted in table 6 that, while nt len:o;t ~ while in the ma.le there is no such "cance.ling femllle mRbel'ti were. mature at a length of 72 out:' inches, 5 immature females of greater length were The third explanation is that the males occupy collected. Obviously the length at. which the fe wider geographical and vertical ranges than the males may hecome sexually mature. varie.s more females. remain in the cooler parts of the ranges, thnn 4: inches. and exhibit a grenter tendency to wander t.han The left skew of the length-frequency polygons the fema.les. Thus, greater numbers of males shown in figure 5 may he the result. of a,ny of se.\' than females are lost to the breeding populntion eral varin,bles including the length nt whieh by wandering and death in unfnvorable environ mat.urity is re.aehed.· ments. A t.otal of 51?, adult sandbar shnrks was select '\Vhntever the explanation for the unequal sex ed from southeastern Florida. entches for meas ratio, the smaller number of: males is not a suffi- urement of total length and for comparison of NATURAL HISTORY OF THE SANDBAR SHARK 27 recorded or none were recorded. Selection was 901------=:------__ affected by the scarcit.y of males. The compara tively large sample of fall females at Salerno had 801----~------_+----t------~ to be me.asured to get. any catches that included d. = ---- mnJes which rarely appeared there at tlutt sea·son. ~r=- 701-----'------,f-----1~----- In the sample t.aken from the lower east coast of :Florida, 10 shM'ks, 5 males and 5 females, were 601------·----+------ Ul were e.xcluded from the calculations of mean ~'" 501------+------+------/ lengt.hs· of adults, but the sizes together with the ill dates of capture ai'e given in footnotes to table 6, IL o 401------1------\----__1 which shows the mean length of the sample lots. II: \oJm By its migratory movements and its restriction ~ z 301------I~...:.,,::_------___\---__I to limited nursery areas, the North American population of E. m.ilbeJ'ti appea.rs to be subject " \ \ 201------,1--/------'\------\,..--__1 to constant mixing. It does not seem reasonable \ to expect a rigid segregation by area of origin of \ , thos~ mRlJeJ'ti mating off southern Florida. This 10 I------::.,:..,,...... ------~:__------\-__I may be one factor in the apparent homogeneity of the population. n M ~ ~ ~ ~ ~ ~ ~ ~ In some of the other carcharhinids, environ lOTAL LENGTH IN INCHES mental or racial factors appear to affect the size FIGURE 5.-Length-frequency polygons for adult male and at which the species becomes mature. For ex female Eulamia milberti from southern Florida. amplE'. t.he avera.ge size of the bull shark, 00.1' length frequency wit.h the length frequencies (:h(r.J'hInu.~ 7eneas, from the vicinity of Trinidad of 76 shark-s from off Fort Myers on the west· is appreciably less than t.he average size of adult.s coast. of Florida, and of 51 sharks from the Carib of the. same species from the Gulf of Mexico. bean coast of southern Nicaragua and nort.hern Important difference.s in the size at. maturity as Costa Rica (table 6). To reduce bias, all sharks well as the size at birth se.parate t.he Texas and of all species in any catch were measured and southern Florida populations of the little black- TABLE 5.-.Mean length, number measured, and length range of adult Eulamia milberti, by sex, area, and season of collection [.Lengths ill inches; length range in samples in parentheses) January-March April-June July-September October-December Combined data Area Number Mean Number Mean Number Mean Nnmber Mean Number Mean in lengt.h in length in length in length in length sample sample sample sample sample ------MALES: Sout.heastern Florida , _ 78.1 36 78.4 5 78.8 5 78.8 114 78.7 (71-891 (72--861 (7fHl2) (73-82) (7\-89) Southwestern Florida (from 2 schoolsl- _ 79.0 . -- _ (73-841 Nicaragua-Costa Rlca .. _ 16 79.9 10 75.0 26 78.4 (72--89) 171-841 (7J-8\l1 FEMALES: Sont.heastern Florlda.______III 82.8 63 82.9 1)4 83.0 161 82.9 399 82.9 Gravid· (72-91) (76-92) <74-91)• (73-90)_ (72-921 71 83.:1 173-881 Gravid (from I school>. _ .';9 82.8 _ (75-88)83.8 _ Nongmvid (from I school>' _. _ 48 83.3 (75-871 -- _ Southwestcm Florida: Nongravid _ 47 m~Jo) Nicaragua-Cost.a Rica: Nongravid______7 82.6 18 83.9 25 83.5 (78-88) (76-90) (76-90) I 5 immatnre males were collected wit.h t.his sample bnt exduded from tabulation and from calculations of mean length: I specimen 64 inches long collected in March, 2 specimens each 66 inches long collected In Augnst, 1specimen 59 inches long collected in October, and I speCimen 6S inehes long rolle.cted in November. • 5 Immature females were collected with this sample but excluded frolll tabnlation and from calculation of mean lengths: 1 specimen 72 Inches long collected in January, I specimen 76 Inches long collected in April, I specimen 73 inches long colle·cted in July, and :l specimens collected in October of which 1 was 75 inches long and the other 76 inches. • From preceding collections. 28 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE tip shark;, O"arcnadl.lnus limbatus, but whether weighed 94, 115, and 1~2 pounds, while e.ight 83 different'species, subspecies, or races are involved inch females weighed 12g, 127, 141, 14~, 146. 148, remains to be determined. 161, and 162 pounds, and six 7S-inch females In the last week of February 1958, I was able weighed 102, 1:36, 147, 147, 1M, and 164 pounds. to get evidence that the edge of the Continental 'Veights of livers, other viscera, fins, and eviscer She.lf off the Carolinas is indeed an important ated carcasses were obtained, but unfortnnately wintering ground for immature milbel'ti. A whe.n t.hese. weights were recorded they were tied se.ries of 25 tows with a modified Number 41 otter in solely with the totnl we.ight of each shark. trawl made by the Bureau of Commercial Fish Analysis of the figures gives some indication that eries exploratory vessel De1'«(·lNtl'e while I was liver weights in female E. m.ilbf1'tl contributed aboard took 203 immature m.ilbel'ti between the disproportionately to total weights. Livers of offings of Cape Hatteras and Cape Lookout. In males weighed from 7 to 14 pounds and livers of one tow in 52 fathoms, 197 '/n.ilb&l'ti from 27 to 43 females from 7.25 to 31 i)OlUlds. The a,verage inches long were taken and in three other tows at weight of 40 livers from females was 18.5 pounds. depths of about 50 fathoms 4 m.ilbel'fi were It. would he convenient and would fit most. of picked up. Tows made at. ot.her depths from ~o t.he facts to assume that the growth of Eulamia t.o 250 fathoms failed to eat.eh mRbel'ti. The m.ilbe'l'fi. is very rapid, but. there. is merely pre water t.emperature at the bot.tom at. t.his time. was sumptive evidence for this. It is hy no means the about. 64° F. in 50 fathoms, but temperatures were only view that could be reasonably advanced and ltppre.c,iably eooler, ltbtmt [.7 0 F., in both 80 it would be especially weak for milbedi for fathoms and 80 fathoms. which the immature part of the popultltion is not It is suggested that the 197 young m.ilbedi well known. Nevertheless, on the basis of little taken in February 19[,8, we·re young of the year, real evidence I suggest that it is probable that born in the summer or early fall of 1957, and that growth from birth to mat.llrity ta.kes about 2 yeltrS, their average length of 34 inches represented occltsionally 1 yenr, rarely 3 years. growth from birth of about 12 inches in approxi The length uniformity indicat.ed in table 3 for mately 7 months. However, if it is correct that both male and female adult m.flberti from differ all of these young we.re born in 1957, some. may ent seasons would be. expected from a species with have grown as little as 5 inches and some more determinate growth. Predictable adult size in than 20 inches. Such an irregular growth pat relatively narrow ra.nges nlso characterizes other tern would help to explain some other facts of species of Eu,l{tm.ia. Negapl'io'n, and perhaps Om' the m:ilbel'fi. life history, for example, the sea chaJ'M/I:Ils. On the other hand, it is presumed sonal differences in the vitamin-A potency of that some individuals of Pl'iorwce and Pterola:nd adults taken by the shark fishery. ops continue growing after maturity to reach In .January and February 1945, I obtained two nbnormally large sizes. Records of Galeoce'l'do boatloads of sharks from O. E. Holley, an expert more than 14 feet long are not uncommon in the shark fisherman at Fort Myers, Fla. Of the 133 literature and some of these records apparently sharks brought in, 73 were adult E. mHberti and nre relinble and I accept them as such. Never none of the female E. m.ilbel'ti were gravid. The theless, I hnve seen more than a thousand large 27 males in the sample ranged from 74 to 84 Ga.leocerdo from the Florida-'West Indian region inches in total length (average, 79 inches) and and have metls1U'ed all of the excel>tionally large weighed from 94 to 130 pounds (average, 113.7 ones that I have seen. None were found to exceed pounds) . The 46 females ranged from 72 to 90 14 feet in total lengt.h. Great. increa.se beyond inches in length (average, 82.3 inches) nud the usual adult size hns been noted, howewr, for weighed from 102 to 184 pounds (average, 145.1 8phy1'Wf sp.. the great. hammerhead. In my pounds). The specimens were weighed and metlS sample of 52 adult females, 5 were much larger ured about 36 hours afte.r capture and the stom than would be expected. If, as indicated by my achs of all of the sharks were empty or nearly sample. the' nsual size for adult female grent empty. 'Veight among sharks of the same length hammerheads is 10 to 12 feet, the attainment. of \Taried considerably. Thus, three 7S-inch males approximately 15 feet by 10 percent. of the lot NATURAL HISTORY OF THE SANDBAR SHARK 29 preeludes description of the growth as determi resulted from t.he sharks being taken in ltll area nate, ·at. least for t.he great hammerhead. One . of localized upwelling that had stunned large individlHlI, measured but not included in the numbers of fish a·nd bottom invertebrates. Very sample, was 18 feet long. Although t.he continua few instances were. noted in which shark remnins tion of growth after maturity as a peculiarity of were found in 1II./lDertl stomachs and no evidence the female apparently does not. obtain in E. m:il was found that 'l1IHbedi commonly fed on large 7/e1'1i. it is evidently the pattern in some species turtles, porpoises, birds, ships' glubage, or sur of Spnyrna., in Ptero7amIops, and occasionally in face material recognized by the inclusion of (;a7eoce·l'do. Sargassum weed or t.ypical surface-dwelling forms. FOOD AND FEEDING HABITS Some indication of the probable food prefer Examination of stomachs of Eu7amla mHbedi ences of E. m:ilbel'ti can be found in the experi as a source of information on the food of the ences of eomme.l,cial fishermen. It. was demon species has been disllppointing. Compnl'ison of strated to the satisfaction of Florida shark fisher t.he feeding habits of E. mHbe"l'fi wit.h the feeding men that there were somewhnt different require habits of other ctlrcharhinid species of the ments for bait depending on what species was Florida region, however, has proved to be more sought.. It was also found that the increased cost illuminating. Various bits of evidence show that of very fresh bait. or bait. frozen when fresh, was E. mHbertl is a discriminat.ing feeder: that it is a fully justified by the improved catches. All of bottom feeder; that it feeds on small bottom fish the carcharhinid species of the Florida area, even and invertebrates rather than t.he larger ones; those frequent.ly feeding on garbage, apparently that it. prefers fresh fish t.o stale or decomposed prefer fresh bait. The bllit. most. universttlly ac fish; that it prefers fish to porpoise meat or to eepted by all species was fresh fish and E. ?nU the flesh of domestic animals; and that its feed Dei'tl rarely was taken on a.ny other bait.. Some ing is remal'kably successful in comparison with species. not.ably E'lilamia 008C1(.1'« and Gal.eoce1'do, some of its Ia.rger eal'eharhinid relatives. took cut. porpoise readily, and one species, Oa1' A very large proportion of the sharks in eom cha.rnimlB 7e·/l.cas, occasionally preferred pieces of mereiallandings were found to have empty stom fresh shark. Cut bait was found to be very much achs. An obvious explanation for this is that better than the entire fish of any species. Prob most of the sharks were examinee] after the. pas ably the diffusion of juices from cut bait was sage of several hours wlien small and readily greater than from fish in the rounel. digestible meals would presumably have been In t.he Salerno, Fla., area the best catches were eompletely hydrolized. Observations and exami obt.nined by sets made in the late afternoon with nat.ions of stomachs of sharks of many speeies pieknp of the lines stnrting the following morn has led me t.o the opinion t.hat the larger species ing as soon as there was sufficient. light to locate find food less oft.en than the small ones, and t.hat the buoys. The freshness of the bait may have through no cJlOice of their own, large sharks have had some bearing on t.he applll'ent. better fishing empty stomachs more oft.en than not. at dusk and during the early part of the night. In the st.omachs of Enlamla. m:ilbe'l'ti a few fish Catches made during the early morning nnd remains, usually not identifiable as to species, throughout the day were not infrequent, how eephalopods. and crust.ncean remains were found ever. and it seems probable t.hat the early part from time. to time. Goatfishes (Mullidae), snake of the night is m~rely a period of increased feed eels (Ophichthyidae). sea robins (Triglidae), and ing activity for E:u}:a:lIlia lIIHbel'tl. cusk eels (Ophidiidae). wel'e among the t.ypes It is the common habit of many species of most. commonly found. A eoJIect.ion of 16i m./l sharks, ineJuding Eulwnia m1ne/,ti, to nudge or oerti, all with fish, octopns, or crabs in t.heir hit. objects with theIr noses. I am convinced stomachs was reported in an earlier publicat.ion that. they do this to test t.he object for ·juices. (~pringt'r, 1946). There were unusual cireum The edible qualit.ies of the object are thus deter mined by the shark through sensory crypts which stances about this catch,. however. which sun'(l"est00 that the large amount of food in t.he stomachs are widely dispersed over the skin of the hE-ad 30 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE and body. These organs, whieh perform a fune supply of food regularly. Galeocerdo au-lIfer, tion eorresponding to taste, have been described· Oarchm'kinlls l-ellca~, and Eu..lam;ja obsC1./-m, all in detail by BudkeI' (1938). Under ordinary spedes more than twiee as heavy as milbe'rt-i, drcumstances the testing procedure is routine for frequently have livers 25 pereent or more of the objects which are not moving or which are not total weight of the fish. On the other hand, they part of a series of similar-appearing objeets, one often have very small livers, as low as 3 pe.rcent of whieh has already proved edible. The pro of the total weight. The inferenee is reasonable cedure may be omitted if there is eompetition for that the larger spedes have greater difficulties food. finding food, or more precisely, may have to wait It seems improbable that the sensory erypts longer between meals. This inference from liver of the head function in any othe.r way than as weight also is eonsistent with the observation gustatory organs. To find suitable food or to that the foods of the larger species are frequently find an area having food in it, Eulmnia tnilbe'l'fi of a less digestible type and may be taken as a as well -as many other species depends on olfac kind of desperation measure and certainly not as tory organs. Experiments by Parker and Shel a first choice. Galeoc.e-rdo, for example, fre don (1913) with llIuJJtelu8 CI1:1l.iJJ probably outline quently fills its stomach with large horseshoe the general pattern of beha.vior of the eachar erabs, huge horse conchs complete with shell, hinids in their search for food. or even old shoes and tin eans. Careharhinid sharks in general are opportun Bee-ause of eommercial interest in the vitamin ists in feeding and necessarily so. Without spe A eontent of shark-liver oils that existed for a cial techniques, developed in some spedes but not lllunber of years, a large amount of data is to to my knowledge in E1tlam1a -mH.,berti, sharks be found in the literature on the subject. Also are relatively ineffective at catching uninjured available to me are data on the oil and vita fish in open wnter or even at finding such slow min-A content of livers of E. m:ilbe-l'ti taken at moving objects as crabs. The shark's ability to Salerno. Some determinations for Salerno spe exist on a regimen of feast and famine, imposed cies were given in an earlier publieation by its ineptness in eatehing food at will, is prob (Springer and Fre.nch. 1944). Better methods of ably made possible through its unique digestive estimation of the vitamin-A eoneent-ration in liver and fnt-storage organs. A general outline of the oils eame into general use later. but these did not processes of digestion and fat storage by sharks appreciably alter the general trends observed. is beyond the scope of this report. It is pertinent The tendency in each species to an inerease in to point out that their digestion is rapid and the vitamin-A coneentration, or poteney, of the thorough, and that the shark's liver with its high liver oil with the inerease in size of that species perce.ntage of oil is a good index of its meta has been noted by many workers (Pugsley, 1939; bolie well-being. The larger, fatter livers are Broeklesby, 1941; Templeman, 1944; Ripley and found in sharks in good condition while small Bolomey, 1946, et c.atera). The liver-oil vitamin livers with little oil are' frequently found in A potency varies considerably. Eaeh species and sharks having severe injuries, sharks in obviously locality produces sharks having potencies that are poor conditiqn, or in t.he males at the end of the approximately predictable. Characteristically, mating season. in most. speeies the males produce oil of some The liy~n:_ of adult E." milberti typically re·l)l'e what higher vitamin-A poteney than that of t.he sents beh~eEm 10 and Hi percent of Ow animal's females, but they often have less oil in their total weight, rarely more than 18 percent and livers. rarely less than 6 percent. The proportional An hypothesis whieh has general support is weight of the liver in a.dult E. mRbe-di males is again advanced here that within a given species lower than in f~males, but the liver weight of the and loeality, the. total amount of vitamin A in species is remarkably· uniform in comparison with the liver of a shark is roughly proportional t.o larger species of carcharhinids within its geo the llge of the shark. Thus, the older the shark graphical range. This is strong evidence that the greater is the total amount of vitamin A E. -milberti is suecefisful in getting an adequate in its liver. The rate of increase in vitamin A NATURAL HISTORY OF THE SANDBAR SHARK 31 may rise sharply as the shark becomes sexually vitamin-A potency from data assembled by the mature but this does not affect the general trend shark fishery is as follows: in the total amount of vitamin A stored. Fluc Extremely low potencies-Gulf ()f Me.xico; low tuations in the amounts of oil stored in the liver potencies-northern Bahamas and shallow-water may normally accompany such events as young areas of the 1Vest Indies; intermediate potencies bearing, nutting, .and periods of poor feeding, -Carolina COltst, east coast of Florida, and COlLst and these fluctuations apparently affect potency, of Cuba; high potencies-southern Caribbean, but the total amount of vitamin A is subject to coast of Costa. Rica to the Guiana coasts. To fluctuation to n lesser degree. It. has been shown a limited extent this classification is useful to for Ga.leOJ·hlnus zyoptel'1.IS of the Pacific coast trace probable origins of elements of migratory (Ripley und Bolomey, 1946) that the total stocks. Potency differences among liver oils taken amount of vitamin A in the largest males and from single adult specimens of Eula'lnia '1nilbe'l'ti largest females does not greatly differ. were in the range from about 2,500 to 25,000 Livers of Squalus 8uddeyi of the Pacific coast .I.U./gm. One exception' was noted in that one have. a higher average vitamin-A pote.ncy than assay (the only one available) on mixed E. mil livers of Squ,a1118 (UJanthios of the Atllmtic. The berN livers from the coast of Nicaragua-Costa two species are morphologically so similar thnt Rica was substantially higher, about 38,000 I.U./ taxonomists have had doubts about their sepa.ra gm. tion. Concerning the differences in liver oil po If E. mHbertl from the coast of Nicaragua tency, Templeman (1944) has the. following com Costa Rica returned regularly to the species' At ment: lantic population center from Florida northward, Whether the greater length of the mature Squa~us some among the hundreds of livers of mllbel'ti 8I1CJ..,Ui reflects a greater age or a greater growth rate h\ken at Salerno, and assayed separately should than those of Squallts aca.nthias is not known, but this have had potencies greater than 38,000 I.U./gm. greater size is possibly partly responsible for the higher None had such a high potency. vltamin-A value of its liver oll. The average potency of oil from livers of Eu The greater vitamin-A content of shark livers la:1nia 11lHberti was found to be substantially does not ulways occur in the larger individuals lower from the southwest coast of Florida than in a given species. For example, my own meas from the southeast coast although the extremes urements and assays show that O. lencas off th~ in jndividual potencies were about the same. mouth of the Mississippi River average appre Since both stocks have a common origin from the ciably longer and heavier than O. lcu.cas taken Atlantic coast north of Cape Canaveral we might off the mouth of the Orinoco River; but the liver assume. that the difference in a.verages results oil potency of the species from the vicinity of from either the lower age of the. adult rnilberti reaching the west coast of Florida or a lower the Mississippi River mouth is extremely low, rate of vitamin-A accumulation due to the period while that of the C. leucas from the vicinity of spe.nt in the Gulf of Mexico, or from bot.h of the Orinoco is high. These differences are quite these. great and reasonably constant. Adult male O. The liver-oil. potency of the eight adult female leucas from the Orinoco area have liver-oil po E. m.ilberfi from the mouth of the Mississippi tencies above 50,000 I.U./gm. (international units River was higher and the total vitamin A from per gram uncorrected for irrelevant absorption), these sharks was about the amount to be ex while adult males from the Mississippi area gen pected from similar sharks. taken on the east erally have liver-oil potencies of 1,000 to 5,000 eoast. of Florida. This poteney would be ex I.U'/gm. Variation in liver-oil potency by area pected only if these sharks originate outside of is perhaps greater in O. l.eueos than in most shark the Gulf of Mexico. species of the northwestern Atlantic, but the vari To the extent t.hat data on vitamin-A potency ation is appreciable in all species. determinations have any validity for the deter A rough classification by regions of part of the mination of age or the areas of origin of migra northwestern Atlantic on the basis of shark-liver tory stocks, they support. the general conclusions 32 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE that E. lIlilb('rti does not live to a great age and mHbn'fl, chiefly because of the greater area of that those individuals migrating a great distance their habitats. to the coast of Nicaragua-Costa Rica do not re It is generally recognized that marine animal turn.. populations are unstable and are subject to re ma.rlmble changes in total numbers and occasional ABUNDANCE shifts in geographical range. !3uch changes may, The inshore range of the sandbar shark has of course, occur in the Atlantic population of made this species readily available to the shark E. mHbertl. fishery. This was particularly noticeable tit Sa A concentration of E. m.llberti appeared for a lerno, where the range is restricted by a narrow few cla.ys in the late spring or early summer of ing of the Continental Shelf and where special 1935 off Dog Keys Pass on t.he coast of Missis conditions of current and temperature tend to sippi. These sharks were not only out of their produce a narrow path inshore for the south normal range but. behaved in a way that is not bound migrants. Approximately 58 percent of normal for mHbel'ti or perhaps for any shark. t.he sharks landed by the fishery at Salerno be They struck at anyt.hing thrown into the water, tween 1938 and 1946 were sandbar sharks. Al fought one another over pieces of charcoal, fought though present throughout tlle year, they were so vigorously that some were killed and eaten comparnt.ively more frequent in Salerno catches by others of the school. Sharks frequently fol from December through July as shown by rec low shrimp boats such as we were using at the ords of the catch per unit of effort (Springer, t.ime, and churn the surface of the water after 1951). Except for winter fishing on the south scrap fish thrown overboard; but the intensi.ty west. coast of Florida which produced 11 fe.w of this attack by out-of-range mHberti was much hundred E. m:ilberti each winte.r, few sandbar stronger than any shark action I have seen since. sharks were ta.ken in the Gulf of Mexico. Alt.hough no great fluctuations were noted in It is estimated that during the period 1935 t.o the general abundance of E. m.ilberti during the 1950 from 5,000 to 15,000 sandbar sharks were period from 1935 to 1950, its competitor, the bull taken yearly from the entire range of the fishery shark O. leuNl8, appeared once to go through a and th:;lt these were nearly all adults with an major but temporary shift in abundance. In avera.ge weight of about 130 pounds. The. yearly 1n37 so many bull sharks were caught off Salerno catch might be estimated, therefore, as between that catches exceeded the demand. The· company 650,000 and 1,950,000 pounds, a small qmmt.ity buying shark livers and oil was forced to delay compared with yearly landings by the commer pa.yme.nts to fishermen for a period of several cial fishery of many species of bony fishes. Dur months. This was not merely a matter of eco ing the years that the shark fishery operated, it nomic adjustment to be settled by a reduc.tion in was prosecuted vigorously, and, alt.hough there price but the supply of tanks and drums for was no evidence that fishing pressure reduced the storage of liver oil was exhausted and a court stock of sandbar sharks, it was found that the injunction was finally issued to stop all shark catch per unit of effort was reduced by concen landings because shark carcasses were accumulat trating too much gear in one area. Efforts to ing along the shores. This was the only known expand production were successful chiefly by ex appearance of bull sharks in large numbers on t.ension of the arel1 of fishing into the ranges of the east coast of Florida. It seems likely that other species of sharks. A fluctuation in abnnd persistence of great. numbers of bull sharks, es Il.l1Ce with a· low in every third year was found in pecially north of Cape Canavera.l, would have the catch per uni.t of effort. at Salerno (Springer, adversely ltffected the population of E. m.i7berti. 19!11). Although data are lacking to support such a ENEMIES contention except observations at sea, it. is esti The principal predators on sharks are other mated that several other species of E'll.lmn:ia, par shnrks of larger size. 'Vherever concent.rations ticularly E. {loridana, occur in substantially of mixed sizes occur predation by the larger greater species-mass around Florida than does E. sharks on the. smaller ones is normal. The con- NATURAL HISTORY OF THE SANDBAR SHARK 33 centration of sharks occurring near the mouth of Tiger sharks, perhaps for reasons of poor speed the Mississippi River in the summer months may and maneuverability associated with their smaller be as great as anywhere in the world. Some idea, and lighter weight fins, catch young sharks less of the predation that may occur is furnished by frequently than do bull sharks. Furthermore, the results of' one line of 180 shark hooks set on tiger sharks are primarily nocturnal in forayl:i the night of July 22, 1947, off Pass a rOutre, La. llltO inshore waters and at such times newborn This line caught 68 large sharks, whole and Ull or small sharks retreat to shoaler water. On the damaged, but 40 of the hooks had only the other hand, bull sharks are not exclusively noc heads of large sharks and 12 more had only turnal and they are more frequent in relatively the heads of small sharks. Almost all of the shallow water. Stomach contents show that they larger sharks on the line contained small sharks are regularly predatory on small species such as or llieces of large ones. One tiger shark, Gltl,f?Q Careha.l'hInus aCl'o-noht-8, C. porosus, 8colioilon ee-rdo, had swallowed a medium-sized bull shark terra.-'1l-lH'ae, and Apl'io-nodo'n i.sodon. The bull which in turn had a major portion of a somewhat shRrk also is the only species in the range of smaller blacktip in its stomach. The blacktip, E. milbe'rti with a preference for shark as a however, had driven the head of a M'!l~~teln8 ea'ni.s bait. a.bout 4 feet long up the leader so it. would be There is strong circumstantial evidence, derived reasonable to assume that the large, tiger shark from an examination of the geographical ranges was the fourtll shark to be taken in that one and nursery-ground preferences of the varioul:i night Oli one hook. The bottom conditions. species of Eulam.ia, that the bull shark is the depths, and temperatures where this line was set most important predator on young sharks and appeared to be similar to conditions on lnllbf?'1,ti actually restricts the distribution of mHberti. The nursery grounds but predation would presumably life history of the bull shark is similar to that eliminate young mllbe'r# in the area. of species of Eulmnia, but the bull shark is al Full-grown sandbar sharks probably are rarely ways found in shallow water and its nursery subject to successful shark attack by other spe grounds are in bays or estuaries, even in brackish cies. The tiger shark (Galeoeel'do) , dusky shark and fresh water. The nursery range of the bull (E-ulcunia oOs("l.(,m) , and bull shark (CarcharMnu.s shark is shoaler and less saline than the- nursery le-ucas) , have all been found occasionally with mnge of n~llb&rti, but adult bull sharks inhabit pieces of full-grown sandbar sha.rk in their'stom the depth and salinity range normal to nursery achs, but the sandbar sharks may have been on grounds of milberti. Young bull sharks remain shark lines when. attacked. Perhaps none of in estuarine waters during t.he' early growing these species are able to catch adult sandbar season, and since the females do, not eat at the sharks under ordinary circumstances. Great time the young are born and gen~rally move out white sharks, (!a'1'charodo'n C(il'cnarias. have been of the very shallow water inllnecliately after the found with adult milbedi in their stomachs and birth of the young, the young hull sharks are it is probable that the great white shark could protected to some degree from predation by the catch them. The white shark is not common large members of their own species. enough, however, to be an important factor in Bull sharks occur from Long Island southward predation. At Salerno~ captures were about 27 and are migratory but t.heir centers of abundance great white sharks per 190,000 of--all species. are in the GuIf of Mexico and soutlnva;rct par All carcharhinids more -than 6 feet long may ticularly nea,r the mouths of large rivers. Along occasionally eat young E. n1iilberti, but circum the Atlantic coast north of Florida, hull sharks stances of seasonal and geographical distribution are not common. but m,ay be subject in t.his area keep most species from preying on them. There to great. fluctuation in abundance. Bull sharks nre two notable exceptions: the tiger shark and are ext.remely common around the mouths of the the bull shark. These sharks feed on young Mississippi and Orinoco Rivers and between these sharks or on small species regularly, and both points along the inshore, Continental Shelf. There lllay be found at times within the known range is pract.ically no information about their occur of young m.ilbel'ti. rence in the West Indies. 34 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE No Euhunia except milbel'ti is known to Ill\,ve tor solutions. .Juices from shark stomachs that nursery grounds within the geographical and conta.ined huge amounts of shark flesh in obvi habitat range of the bull shark. The nursery ously decomposing condition were found to be ranges of E. althna. and E. obsc·/tra are well off substantia.lly above pH 8.0, whereas juices from shore. in deeper water, E. jlOl-idana nursei'y shark stomachs conta.ining fish, tm'tles, birds, or grounds are on offshore banks where bull sharks small amounts of fresh shark were estimated at do not go, and bull sharks are uncommon at pH 4.0 or below. It is not dear whether ex least, or normully absent around reefs which are eessively large meals of decomposed shark flesh nursery grounds for spl'ingeri. The sugges produce any result more serious than delayed tion is advanced he.re that predation by the bull digestion. shark is the chief reason, and perhaps the oniy I have not seen evidence that internal parasites reason, for the scarcity of E. milberti in the Gulf ever greatly damage E-u.la.·mJ((, mRberti. Round of Mexico and sout.hward in continental waters. worms in the st.omach, roundworllls and adult The comparatively few bull sharks of the Atlan tapeworms in the scroll-type intestine, and cope tic coast may be presumed to act as a eheck on pods on the gills and external surfaces were the numbers of young E. 11I.ilberti, but withoilt commonly seen. In comparison with other large disastrous effects for that species. Florida sharks,mRbeJ'fi seemed to he the least Some interesting eomplications are associated troubled by parasites. Occasionally, sharks taken with predation of large sharks upon smaller ones. from lines apparently set in areas of extraordin Evidently all carcharhinid sharks will eat other nry abundance of II small isopod were 'found t.o sharks sometimes if not regularly. However, it have a large proportion of the viscera eaten away is a shark fisherman's axiom that sharks left on by swarms of the isopoch" which had entered tll(' the line to spoil will burn out the fishing grounds body cavity by way of the soft parts around and make it necessary to move away 5 miles or the a·1lUS. It has been assumed that. these iso so to eontinue fishing. A rationale has been pods attack successfully only after the sharks partly outlined in an earlier publication die on the lines or at least have been restrirt.ed (Springer, 1954) covering experiments with 1111(.8 in movement.. Similar isopods attack living small tellfs in tanks. Feeding of lI/1fstelus was entirely fishes and man (Springer, 1957) and it seems inhibited in the presence of shark flesh that had quite possible that. they may a'!so attack living been allowed to stand at room temperature for sharks. If they successfully attack living sharks 4 days. they may be one of the principal enemies of Presumably sharks have no difficulty digesting sharks in temperate and tropical waters of shal shark flesh provided it is fresh. Although sharks low and modernte depth. I have seen evidence appear to be able to digest the partially decolll of their work on shark catches made off South posed flesh of other vertebrates, their digestive Carolina, Florida, Louisia.na., Cuba, and sout.hern processes are slowe,d or stopped completely when California. they sWil.Ilow large quantities of decomposing SUMMARY sharks or rays. The overlapping geographical and habitat The flesh of sha.rks becomes strongly alkalh1e ranges and superficial resemblance of E'ulmnht during decomposition. The continuous liberation m.ilbedi, the sandbar shark. and (Ym'chal'hinU8 of amlllonia through action of enzymes produced leu.ca.~, the bull shark, ha.ve led to some, confu during the course of ordinnry putrefactive de sion and n tangled nomenclature. The recogni composition on the uren that normalIy occurs in tion of m.ilbeJ'ti of Muller and Henle as the spe shnrks (see Smith. HIS(1), seems effectively to cies name for the sandbar shark is based on the block, or at least to greatly retard, digesti0l1. opinion that plltlnbeu8 of Nardo is a nome'll The proteolytie enzymes of the shark's stomach '1I:lldf;~m,. are most active in an acid medium (Sprissler, The sandbar shark differs from the bun shark 1942). In my examinations of juices of shark in the structure and spacing of the derma'! denti stomachs in the field, estimates were made of the des, in having a ridge in the skin of the back hydrogen-ion concentration,. as shown by. indica- between the first and second dorsal fins, and in NATURAL HISTORY OF THE SANDBAR SHARK 35 the smaller size and less robust body form. The and are probably not self-sustaining wit.hout re sandbar shark swimming in the open sea or in cruit.ment from the main population by migra an exhibition tank may be distinguished readily tory wandering or failure of such orientation from the bull shark been-use of its comparatively mechanisms as the species may possess. more erect and higher first dorsal fin placed The primary nursery range lies in shallow slightly further forward, its some\vhat larger eye, coastal waters of less than 20 fathoms from its somewhat longer snout, and its genei'ally less Cape Cod, Mass., to Cape Canaveml, Fla.; and . robust body form. a secondary nursery range lies in the Gulf of Although the sandbar shark inhabits both the Mexico west of Mobile Bay and north of the eastern and western parts of the At..lunt.ic, this 28th pn,rallel. Newborn sandbar sharks are not report concerns only one popnlation of the spe-. lmown outside the general geographical limits of cies centered along the southeastern coast of the the nursery ranges, but the young sharks mov~ United States. offshore to deeper (and ,varmer) water during Species of the genus Etdmnla usually are sharks the winter. of the continental shelves, oceanic banks, and The species is migratory with annual move island terraces throughout their life cycles in ments of some segments of the population ex contrast to most species of Oa1·cha.J'1d'ntl-8, which tending at lenst 600 miles. Sandbar sharks in aTe typically shallow-water forms having their migratory pa.ssage around the southern tip of lHlrsery grounds in brackish or fresh-wllter estu Florida hold to dept.hs of 50 fathoms or more aries, river mouths, or along continental beaches, in apparent avoid:Ulce of coral reef a.reas. Their or in island lagoons. Eulmn-ia. m.ilberti occupies vertical distribution in the southern part of the the shoalest habitat range of the [) or 6 species of species' geographical range, however, is soml:" Eulmnia. of the Atlantic coast of North AmericlL what deeper t.han in the northern part, suggest and enters est.tllll'ies t.o some extent to give birt.h ing thermal influence in the selection of habit.at. to its young. Its habitat preference may thus There is reason to believe that femnJe sandbar be said to be. intermediate between that typical sharks are inhibited from feeding at the time of of Eulamia and t.hat typical of Oal'clW1'hi:nus. birt.h of the young and for a short time t.here The sllndbllr shark is clearly separable from all aft.er. Nursery grounds are away from the nor other species within it.s geographical range and mal range of the males thus giving additional exhibits little variation in form and in tooth protection to newborn young. Feeding appears to count. be inhibited in male sandbar sharks during peri The sandbar shark, Eula'lnia. 'I1l:ilbe1'tl~ is found ods of active courtship. in waters of suitable depth, southward from Cape Young of nearly uniform size, numbering from Cod a.long the Atlantic coast. It occurs in the 1 to 14 in each litter, are born in early summer Gulf of Mexico and along the Caribbean coast (probably also in late spring) off nort.hern Flori of Cent.ral America to Costa Rica. It. occurs da. The average number in a litter is 9 and casually off the northern coast of Cuba and along the modal number 10. The gest.ation period is the western edges of the Bn-hama Bank, but prin from 8 to 12 months' duration. with 9 months cipal elements of the population are confined to estimat.ed in the latitude of northern Florida. the western side. of the. Gulf Stream. Sandbar Both oviducts are functional, a single embryo de sharks occur as bottom dwellers out to depths of velops in each shell membr~ne. and a pseudopla 100 fatllOms (extreme record 135 fathoms) and centa with :t simple stalk (yolk-sac attachment) may occasionally move out in midwatel' to oceanic forms. situations. The principal part of t.he ra.nge of Lengt.h at. bil"th is approximately 24 to 25 adults, away from the nursery grounds, ha.s been inches in the latitude of nort.hern Florida but shown by commercial catches to be in depths of may be less in lligher latitudes. Young born 10 to 30 fnthoms. in the vicinity of Long Island, N. Y., have been The sandbar shark populations of the northern reported to be 22 to 23 inches long at birth, and nnd western parts of the Gulf of Mexico and the even smaller ·young hnve been reported from Caribbean coast of Central America are small Chesapeake Bay. 36 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Although approximately equal numbers of large shnrks, particularly by bull sharks, but malel!! and females are born, catches indicate a also to a lesser extent by tiger sharks, dusky much larger proportion of adult females than sharks, and full-grown slutrks of their own adult males except off the coast of Nicaragua,. species. Females produce young no oftener than every LITERATURE CITED other year, but since only about 18 percent of BACKUS, RICHARD H. the adult females taken in the fishery were found 1957. Notes on western North Atlantic sharks. to be gravid, this apparent low productivity may Copeia, No.3, pp. 246-248. be the ~esult of the low proportion of males in BACKUS, RICHARD H., STEWART SPRINGER, and EDGAR L. the adult population. ARNOLD, JR. In samples from Florida, adult males are from 1956. A contribution to the natural history of the white-tip shark, Pterolamiop8 longiman1t8 (Poey). 71 to 89 inches in total length and adult females Deep-Sea Research, vol. 3, pp. 178-188. .from 72 to 92 inches. Average weights of adults BEEBE, WILLIAM, and JOHN TEEVAN. in samples from southern Florida are ~or males, 1928. The fishes of Port au Prince Bay, Haiti. 114 pounds, and for nongravid females, 145 Zoologica, vol. 10, No.1, pp. 1-279. BIGELOW, HENRY B., and WILLIAM C. SCHROEDER. pounds. 1948. Sharks. 111 Fishes of the western North At The mean length and length-frequency dist,ri lantic. Memoir No.1, Sears :Foundat.ion Marine bution (size range) by sex in catches believed to Research, pt. 1, pp. 59-576. have been made from single large schools closely 1953. Fishes of the Gulf of Maine. U.S. Fish and a,pproximated the mean' length and size range by Wildlife Service, Fishery Bullet.in 74, vol. 53, pp. 1-577. spe~ies sex of all adults of the from southern BROCKLESBY, H. N. Florida. No appreciable difference was noted in 1941. The chemistry and technology of marine mean lengths a.nd size ranges of adults in sam animal oils with part.icular reference to those of ples ta.ken at various seasons on the east coast of Canada. Fisheries Research Board of Canada, Florida, the west coast of Florida, and the Carib Bull. 59, pp. 1-442. BUDKER, PAUL. bea.n coast of Nicara.gua and Costa Uica except 1938. Les c,ryptes sensorielles et les denticules cutan~s the constant difference of about 4.2 inches be des Plagiostomes. Annales de I'Inst,itut Oc~ano tween average lengths' of adult males and adult graphique, vol. 18, pp. 207-288, pI. 1. females. Differences in the average lengths of BULLIS, HARVEY R., JR. 1955. Preliminary report on exploratory longline gmvid and nongravicl females were small. fishing for tuna in the Gulf of Mexico and the The rate of growth is not known. Indirect Caribbean Sea. Commercial Fisheries Review, evidence indicates that it may be very rapid until vol. 17, No. 10, pp. 1-15. se.xual maturity is reached, after ·whic.h little. CADENAT, JOHN. growth occurs'. 1950. Rapport sur Ies Selaciens des cotes du Sen~gal et. plus specialement sur lea Requins. Bulletin de The sandbar shark feeds chiefly on small bot l'Institut franliais d'Afrique noire, vol. 12, pp. tom-dwelling fishes, mollusks, and crustaceans. 944-975. It. 'rarely swallows indigestible materials. Uni 195i. Notes d'ichtyologie ouest-africaine. XVII formly plump livers suggest that milbe1,ti has little Biologie. Regime alimentaire. Bulletin de I'Institut difficulty in meeting its requirements for food. franliais d'Afrique noire, vol. 19, ser. A, No.1, pp. 274-294. From commercial catches it is estimated that CAPTIVA, FRANCIS J. the population is small in species mass as com- 1955. Longline gear used in yellowfin t.una explora pared with many teleosts. . tion. Commercial Fisheries Review, vol. 17, No. 10, The only important predators on sharks are pp. 16--20. COWLES, RAYMOND B. other sharks and not necessarilv sharks of other 1945. Temperature induced st.erility and evolut.ion. species. Fuil-grown sandbar ~harlts, unless in Science, vol. 101, No. 2618, pp. 221-222. . jured or ca'ught on a shark liile, appear rarely EVP;RMANN, BARTON W., and MILLARD C. MARSH. to be eaten by other sharks. Young sandbtu' 1902. The fishes of Puerto Rico. Bulletin of the U.S. Fish Commission, vol. 20 (1900). pt.. 1, pp. sharks are especially vulnerable to attack by 51-350, pIs. 1-51. NATURAL HISTORY OF THE SANDBAR SHARK 37 FORD, E. NARDO, G. D. 1921. A contribution to our knowledge of the life 1827. Prodromus ObservaUonum et disquisitionum histories of dogfishes landed at Plymouth. Journal Adriaticae Ichthy010giae. Giornale fisica, chimica, of the Marine Biological Association of the United storia naturale, medicina ed arti, vol. 10, pp. Kingdom, New Series, vol. 12, No.3, pp. 468-505. 22-40. Pavia (1827). FOWLER, HENRY 'V. NICHOLS, JOHN TREADWELL. 1936. The marine fishes of west Africa. Bull. 1918. Ground sharks of Florida and elsewhere. A:merican Museum National History, vol. 70, pt. 1, [Abstract.] Copeia, No. 53, p. 13. pp. 1-605. 1929. The fishes of Puerto Rico and the Virgin GARMAN, SAMUEL. Islands. New York Academy of Science Survey, 1913. The Plagiostomia (sharks, skates, and rays). vol. 10, Pt. 2, pp. 161-295. Memoir Museum Comparative Zoology, vol. 36, NICHOLS, JOHN TREADWELL, and CHARLES M. BREDER, JR. pp. 1-518, pI. 1-77. 1927. The marine fishes of New York and southern GEISER, SAMUEL WOOD. New England. Zoologica, vol. 9, No.1, pp. 1-192. 1924. Differential death-rate of the sexes among OLSEN, A. M. animals, with a suggested explanation. Washington 1954. The biology, migration, and growth rate of l;.Tniversity Studies, Science Series, vol. 12, No.1, the school shark. Galeorhinu8 aU8trali8 (Macleay) pp.73-96. (Carcharhanidae) insouth-eastern Australian waters. GILL, THEODORE N. Australian Journal of Marine and Freshwater 1862. Analytical synopsis of the order Squall. Research, vol. 5, No.3, pp. 353-410. Annals Lyceum Natural History, New York, vol. 7, PARKER, G. H., and R. E. SHELDON. pp.367-408. 1913. The sense of smell in fishes. Bulletin of the HICKLING, C. F. U.S. Bureau of Fisheries, vol. 32, Doc. No. 775. 1930. A contribution towards the life-history of the pp.35-46. spur-dog. Journal of the Marine Biological Asso PUGSLEY, L. I. ciation of the United Kingdom, new series, vol. 16, 1939. Factors influencing the vitamin A and D po No.2, pp. 529-576. tency of grayfish liver oil, Sqlla.l1l8 8ucklii (Girard). HILDEBRAND, HENRY H. Journal of the Fisheries Research Board of Canada. 1954. Shrimp (Penaeu8 aztecu8 Ives) grounds in the vol. 4, No.5, pp. 405-408. western Gulf of Mexico. Publication of the RADCLIFFE, LEWIS. Institute of Marine Science University of Texas, 1916. The sharks and rays of Beaufort, North vol. 3, No.2, pp. 233-366. Carolina. Bulletin of the U.S. Bureau of Fisheries, HILDEBRAND, SAMUEL F., and WILLIAM C. SCHROEDER. vol. 34, Doc. No. 882, pp. 241-284, pIs. 38-49. 1928. Fishes of Chesapeake Bay. Bulletin of the RIBIERO, ALIPIO DE MIRANDA. U.S. Bureau of Fisheries, vol. 43, pt. I, pp. 1-366. 1923. Fauna Braziliense, Peixes, vol. 2. RIPLEY, WILLIAM ELLIS. LEIGH-SHARPE, W. HAROLD. 1946. The soupfin shark and the fishery. California 1920. The comparative morphology of the secondary Division of Fish and Game, Fish Bulletin 64, sexual characters of elasmobranch fj.shes. Memoir pp.6--37. 1. Journal of Morphology, vol. 34, No.2, pp. RIPLEY, WILLIAM ELLIS, and RENE A. BOLOMEY. 245-265. 1946. The relation of the biology of the soupfin 1921. Idem, Memoir II. Ibid., vol. 35, No.2, pp. shark to the liver yield of vitamin A. California 359-380. Division of Fish and Game, Fish Bulletin 64, 1924. Idem, Memoir VI. Ibid., vol. 39, No.2, pp. pp.39-72. 553-566. ROCKWELL, ROBIlRT H. MEEK, SETH E., ·and SAMUEL F. HILDEBRAND. 1916. Long Island sharks for the Museum. Brooklyn 1923. The marine fishes of Panama. Field Museum Museum Quart.erly, vol. 3, No.4, pp. 160-167. Natural History Publication No. 215, Zoological ROSENBI,ATT, RICHARD H., and WAYNE J. BALDWIN. Series, vol. 15, pt. I, pp. 1-330. 1958. A review of the eastern Pacific sharks of the MULLER, JOHANNES, and F. G. J. HENLE. genus CarcharhiJl.1t8, with a redescription of C. 1841. Systematische beschreibung del' plagiostomen. malapoen8i8 (Fowler) and California records of Berlin, pp. 3-200, pIs. 1-60. C. remotus (Dumeril). California Fish and Game, MURPHY, ROBERT CUSHMAN, and JOHN TREADWELL vol. 44, No.2, pp. 137-159. NICHOLS. SCHWARTZ, :F. J. 1916. The shark situation in the watNs about New 1958. The cub shark, Carcharhinl/8 lencas, taken at York. Brooklyn Museum Science Quarterly, vol. 3, Flag Pond, Chesapeake Bay, Maryland. Maryland No.4, pp. 145-160. . Tidewater News, vol. 14, No.4, pp. 14 and 16. 38 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE SMITH, HOMER W. SPRISSLER, G. PAUL. 1936. The retent.ion and physiological role of urea.in 1942. An investigation of the proteinase of the gas Ehlsmobranchii. Biological Reviews, vol. 11, tric mucosa of shark. Catholic University of Amer pp. 49-81. ica, Contributions from Biological Laboratory, No. SPRINGER, STEWART. 42, pp. 1-52. 1938. Notes on the sharks of Florida. Proceedings STRASBURG, DONALD W. of t.he Florida Academy of Science, vol. 3, pp. 9-41. 1958. Distribution, abundance, and habits of pelagic 1940. The sex ratio and seasonal distribution of sharks in the Central Pacific Ocean. U.S. Fish and some Florida sharks. Copeia, No.3, pp. 188-194. Wildlife Service, Fishery Bulletin 138, vol. 58, pp. 1946. A collection of fishes from the stomachs of 335-361. sharks taken off Salerno, Florida. Copeia, No.3, TEMPLEMAN, WILFRED. pp.174-175. 1944. The life-history of the spiny dogfish (Squallls 1949. An outline for a Trinidad shark fishery. Pro acanthias) and the vitamin A values of dogfish liver ceedings of the Gulf and Caribbean Fisheries Insti oil. Newfoundland Department of Natural Re tute, 2d annual session, pp. 17-26. sources Research BulleUn No. 15 (Fisheries), pp. 1950. A revision of Nort.ll American sharks allied to 1-102. the genus Carcha.rhin1ts. American Museum Novi THORNE, EDWIN. tat.es, No. 1451, pp. 1-13. 1916. Occurrence of ground sharks, Carcharhinus, in 1951. The effect of the availability of sharks on a Great South Bay. Copeia, No. 35, pp. 71-96. shark fishery. Proceedings of the Gulf and Carib TORTONESE, ENRICO. bean Fisheries Institute, 4th annual session, pp. 1938. Revisione degli Squali del Museo Civico di 140-145. Milano. Atti della Societa Italiana di Scienze 1954. Laboratory experiments with shark repel N aturali, vol. 77, pp. 283-318. lents. Proceedings of the Gulf and Caribbean 1951. Studi sui Plagiostomi V, U1teriori considerazi Fisheries Institute, 7th annual session, pp. 159-163. oni sulle specie Mediterranee dei generi Sphyrna e 1957.. Some observations on the behavior of schools Carcharhin1ts. Doriana, Supplemento agli Annali of fishes in the Gulf of Mexico and adjacent waters. del Museo Civico di Storia Naturale "G. Doria", Ecology, vol. 38, No. I, pp. 166-171. vol. I, No. 20, pp. 1-8. SPRINGER, STEWART, and PRICE M. FRENCH. 1956. Fauna d'Italia, vol. 2, Leptocardia, Ciclosto 1944. Vitamin A in shark liver oils. Industrial and mata, Selachii. Edizioni Calderini, Bologna, pp. Engineering Chemistry, vol. 36, p. 190. 1-332. o U.S. GOVERNMENT PRINTING OFFICE: IQbO 0 - 55Z50B