Sharks always are objects of interest, not only to fishermen and mariners but to seaside visitors generally, because of their evil appearance, their ferocity, the large size to which some of them grow, the destruction they wreak on fishermen's nets and lines as well as on the smaller fishes on which they prey, and because of the bad reputation certain kinds have earned as maneaters.
The Gulf of Maine is not particularly rich in sharks (very poor indeed compared with our southern coasts), for while the number of species actually recorded there is considerable (indeed any high-seas shark might stray thither) the little spiny dogfish alone is numerous in the sense in which this term is applied to the various commercial fishes. And only two of the larger species, [page 16] the mackerel shark (Lamna nasus), and the blue shark (Prionace glauca), occur with us in numbers sufficient for one to be fairly sure of seeing them during a summer's boating off the coast north of Cape Cod.
With the larger sharks generally so scarce (the mackerel shark is harmless to anything larger than the fishes on which it feeds, and the blue shark is also harmless, although better armed), the danger of attacks on bathers is negligible in our Gulf. Indeed, not a single well-authenticated instance of the sort is on record for the past 80 years for the coast north of Cape Cod, though the beaches are crowded every summer with vacationists. But as long as the white shark or man-eater (Carcharodon carchartas) does stray occasionally into the Gulf (p. 26), it is always remotely possible that we may be horrified some summer by the news of tragedies such as occurred on the New Jersey coast in July 1916, when several persons were killed or injured, presumably by a small shark of this species that was captured nearby a few days later, and near Mattapoisset, on Buzzards Bay, Mass., on July 25, 1936, when a swimmer was fatally injured by a shark, species not determined.
All Gulf of Maine sharks give birth to young that are not only practically adult in structure but of relatively large size at birth, and there is a placental connection between mother and embryo in some, but not in others. Still other sharks lay eggs; this is true of the chain dogfish (Scyliorhinus retifer, p. 34), which is common out on the continental shelf from the offing of Cape Cod, southward, and of its immediate relatives; also of the heterodontids or Port Jackson sharks which are not represented in the Atlantic.
There is so little market for sharks in Gulf of Maine ports (attempts to introduce the dogfish as a food fish having failed so far) that the amounts landed in Maine and Massachusetts were only about 240,000 pounds in 1947, and about 309,500 pounds in 1949; they interest fishermen chiefly as nuisances because of the damage they do to nets and other gear, except that mackerel sharks are marketable.
It is possible to identify all the sharks so far known from the Gulf (and this includes all that are likely to occur there except strays) by the sizes and relative locations of the fins, and by such tooth characters as may be seen at a glance at the open mouth or easily felt with the finger (after the shark is dead!).
We have attempted in the following descriptions of the several species to include only such features as will tell what shark is at hand; for more minute particulars we refer the reader to our account of the sharks of the western North Atlantic (p. 2).
|KEY TO GULF OF MAINE SHARKS|
|1.||There is an anal fin||2|
|There is no anal fin||16|
|2.||Head greatly expanded sidewise, at level of eyes, in hammer- or shovel-form||3|
|Head of ordinary shape, with rounded or pointed snout||4|
|3.||Outline of front of head only slightly concave opposite nostrils if at all so; grooves (if any) from nostrils shorter than horizontal diameter of eyes; free tip of second dorsal fin is not longer than forward margin of the fin; rear margin of anal fin is only weakly concave; teeth near outer corners of mouth are rounded, without sharp cusps.||—||Shovel head, p. 44|
|Outline of front of head is deeply indented opposite each nostril; grooves from nostrils are more than twice as long as horizontal diameter of eye; free tip of second dorsal fin is considerably longer than front margin of the fin; rear margin of anal fin deeply concave; teeth near corners of mouth are like those near center of mouth, with sharp cusps||—||Hammerhead, p. 45|
|4.||Caudal peduncle (root of tail) is not widely expanded sidewise as a lateral keel on either side; upper lobe of caudal fin is much longer than lower lobe||8|
|Caudal peduncle is widely expanded sidewise as a lateral keel on either side; lower lobe of caudal fin is nearly as long as upper lobe, suggesting the caudal fin of a mackerel or swordfish||5|
|5.||Gill openings very large, the first pair nearly meeting below the throat; teeth tiny, many hundred in number; gill arches with numerous horny gill rakers directed inward-rearward||—||Basking shark, p. 28|
|Gill openings, confined to sides of head; teeth large, few in number; gill arches do not have horny gill rakers||6|
|6.||Upper teeth broadly triangular, with serrate edges; anal fin is entirely behind second dorsal fin||—||White shark, maneater, p. 25|
|Upper teeth with smooth-edged cusp, with or without a denticle on either side, at the base; anal fin is not entirely behind second dorsal fin||7|
|7.||First two teeth from center in each jaw are similar to the succeeding teeth; origin of first dorsal fin is over or in front of inner corner of pectoral fin when latter is laid back; forward part of caudal fin has a small secondary lateral keel on each side, below the primary keel formed by the lateral expansion of the caudal peduncle.||—||Mackerel shark, p. 20|
|First two teeth from center in each jaw are noticeably more slender and more flexuous than the succeeding teeth; origin of first dorsal fin is behind inner corner of pectoral fin when latter is laid back; forward part of caudal fin does not have a secondary longitudinal keel||—||Sharp-nosed mackerel shark, mako, p. 23|
|8.||Upper lobe of caudal fin is nearly or quite as long as head and body combined||—||Thresher, p. 32|
|Upper lobe of caudal is less than one-half as long as head body combined||9|
|9.||Second dorsal fin is nearly as high vertically as first dorsal fin||10|
|Second dorsal fin is less than one-half as high vertically as first dorsal fin||12|
|10.||First dorsal fin is wholly or mostly forward of the origin of the pelvic fins||11|
|First dorsal fin is wholly posterior to bases of pelvic fins||—||Chain dogfish, p. 34|
|11.||Teeth high, narrow, sharp pointed, not in mosaic arrangement; snout conical; fifth gill openings well in front of pectoral fins||—||Sand shark, p. 18|
|Teeth small, low, rounded, in mosaic arrangement; snout flat, broadly rounded in front; fifth gill openings are behind origins of pectoral fins||—||Smooth dogfish, p. 34|
|12.||Origin of first dorsal fin far behind inner corner of pectoral fin; upper surface brilliant blue in life.||—||Blue shark, p. 39|
|Origin of first dorsal fin is over or anterior to inner corners of pectorals; ground color of upper surface is gray, brownish or dusky in life, not bright blue||13|
|13.||Length of snout in front of mouth is not more than one-half as great as breadth of mouth; upper jaw has a furrow on either side extending from outer corner forward past level of eye; caudal peduncle with a low longitudinal keel on either side; upper and lower teeth are of shapes shown in figure 11; their margins coarsely serrate.||—||Tiger shark, p. 37|
|Length of snout in front of mouth is more than two-thirds as great as breadth of mouth; furrows on upper jaw, if any, do not extend forward-inward as far as level of eye; caudal peduncle without longitudinal ridges; teeth are not of shape shown in figure 11, their margins either only very finely serrate or smooth||14|
|14.||Outer corners of mouth have a short "labial furrow" extending inward-forward along each jaw; teeth are alike in the two jaws, directed sharply outward, margins of upper teeth smooth, as well as those of lower teeth.||—||Sharp-nosed shark, p. 40|
|Outer corners of mouth have no labial furrow on lower jaw and upper labial furrow is so short as to be hardly noticeable; teeth directed only moderately outward, their margins only finely serrate; lowers noticeably more slender than uppers||15|
|15.||Origin of first dorsal fin is about over inner corner of pectoral when latter is laid back; vertical height of first dorsal fin is less than distance from eye to first gill opening||—||Dusky shark, p. 41|
|Origin of first dorsal is about over axil (armpit) of pectoral, its vertical height (after birth) is at least as great as distance from eye to third gill opening||—||Brown shark, p. 43|
|16.||Trunk much flattened dorso-ventrally; eyes on top of head; front margins of pectorals overlap the gill openings.||—||Angel shark,[Note]|
|Trunk subcylindrical; eyes on side of head; front margins of pectorals do not overlap the gill openings||17|
|17.||Each dorsal fin is preceded by a stout and conspicuous spine||19|
|Dorsal fin-spines either lacking, or are so nearly concealed in the skin that their presence can be detected by touch only||20|
|18.||Upper teeth with 5 erect cusps; lower teeth with only one cusp, the successive cusps directed outward, forming a nearly continuous horizontal cutting edge all along the jaw||—||Etmopterus princeps, p. 47|
|Upper and lower teeth are alike in shape||19|
|19.||Upper teeth quadrangular as well as lower teeth, with one cusp directed outward, forming a nearly continuous horizontal cutting edge along each jaw||—||Spiny dogfish, p. 47|
|Upper and also lower teeth each have 3 to 5 erect, triangular cusps||—||Black dogfish, p. 51|
|20.||First dorsal fin well in advance of pelvic fins; upper teeth noticeably different in shape from lower teeth||21|
|First dorsal fin stands over posterior part of bases of pelvic fins; upper are teeth similar to lower teeth in shape.||—||Bramble shark, p. 56|
|21.||Lower teeth erect, triangular, their edges serrate||—||Dalatias licha, p. 55|
|Lower teeth quadrate, the cusp directed outward, forming a nearly continuous horizontal cutting edge; their outer margins deeply notched, the edges smooth||22|
|22.||Dermal denticles rounded, overlapping, scale-like, entirely concealing the skin (fig. 20); each dorsal fin is preceded by a short spine, embedded nearly to its tip in the skin, but recognizable by touch||—||Portuguese shark, p. 52|
|Dermal denticles conical, only moderately close set, the skin visible between them; dorsal fine not preceded by spines||—||Greenland shark, p. 53|
[Note] Not yet known from the Gulf of Maine though reported from Martha's Vineyard.
 In 1830 (an event often quoted) one Joseph Blaney, fishing from a small boat in Massachusetts Bay off Swampscott, Mass., was attacked by some fish that was seen to overset and sink his boat and, presumably, devoured him, for neighboring fishermen who hastened to his rescue found no trace of him. Whether his attacker was a large shark or a killer whale is an open question.
 Murphy and Nichols (Brooklyn Mus. Quart., vol. 3, 1916, No. 4, pp. 145-160) give a detailed account of this occurrence.
 See Gudger (Amer. Midland Natural., vol. 44, 1950, p. 714) for clinical details of this case.