Article by Capt. Mark Sampson
Identifying Delmarva Sharks
Whether or not someone is actually happy about an encounter they have with a shark, most fishermen would probably at least like to know what kind it was that they had swimming around their boat, took their bait, or stole their fish. Even among the so-called "shark experts", proper identification can be challenging and sometimes impossible if certain details are not available. Since most shark encounters are very brief, knowing how the identification process works can help folks know what to look for in the few seconds they might have to gather clues that will help them or someone else figure out what they saw.
There are at least 14-species of sharks that might be encountered off Delmarva. No other family of fish off our coast can boast anywhere near that many members, which means that “learning your sharks” can be rather challenging for even experienced fishermen and why every year I get texts, emails, phone calls, and dockside visits from folks seeking help to identify a shark they either caught, saw, or sometimes just "heard about" from someone else who actually had the encounter. For me, it's always fun, and sometimes rather challenging, to try and put all the pieces of the puzzle together and make a reasonable identification. Naturally, good photos make the task easy, but very often the images anglers have don't show enough of the necessary details, thus requiring that other variables be considered that will help to accurately discern one species from another. Knowing where, when, and how it was caught can help, as well as a fairly accurate estimate of size and how it reacted on the line or around the boat. Even seemingly unimportant details such as the presence of parasites, remoraras, scars, and even the relative size of a male shark’s claspers can help differentiate one species from another.
Sometimes it’s easy!
There are some sharks that even novice anglers can look at and know exactly what species they are from what they look like on the outside, in other words - the "morphological" characteristics. The unique appearance of a hammerhead, a thresher, and a mako make them pretty easy to distinguish from other sharks. But most species are pretty generic; brownish-gray, rounded nose, with few (if any) special features that stand out and advertise what kind of shark they are. Duskies, sandbars, blacktips, spinners, blacknose, bignose, bulls, and sharpnose can be the trickiest species to accurately identify unless you know just what to look for.
First decide what it's not.
I was once asked to help identify a species from pictures of bite marks alone. Since no one actually saw the shark, I informed the fellow asking that the only way to be certain of what it was would be from a DNA test, but since that was clearly not happening the best I could do was look at the facts and come up with the most likely candidate. The bite occurred in the surf so we could rule out mako and blue shark. The bite was the typical crescent shape and the teeth marks were evenly spaced apart and all in a single curved line, so from that I ruled out sand tiger which, because of its teeth leaves a very ragged bite. The bite was 3 ½ inches across so it was a relatively small shark but one that had a serious set of sharp teeth, thus eliminating a small thresher, sharpnose, as well as smooth or spiny dogfish. It was early enough in the season that I would not have expected it to be one of the species that don't typically show up until our nearshore waters warm up more than they had at the time, so I was comfortable suggesting that it was not likely a spinner, blacktip, tiger, blacknose, or hammerhead. So through the process of elimination I was down to sandbar or dusky shark, and since sandbars are very common catches in the surf and duskies not as much, I concluded that it was most likely a sandbar shark. That's one way of doing it.
Look at the fins.
Since a big part of shark identification involves eliminating species from the list of potentials, and oftentimes all you'll have to go by is a poor quality photo you took, or what you can pull from your memory bank about what features you actually observed,one key feature to pay attention to would be the shape of the tail - does it have the super long upper lobe like a thresher, or more equal size top and bottom lobes like the white, mako, and basking sharks? Look at the dorsal fin - does it have a faint black tip like a spinner or blacktip, is it tall, dark, and somewhat pointed like a hammerhead, fairly large and gray like a sandbar, midsize and brown like a dusky, or is it brown and proportionately small compared to the size of the shark like a sand tiger? Is the dorsal set forward on the body like a sandbar or blacktip, midway back like a dusky or spinner, or way back like a sand tiger? Look also at the second dorsal fin (the smaller one that's closer to the tail), is it only a little smaller than the first dorsal like the sand tiger, smooth and spiny dogfish, or tiny like the white and mako sharks?
Ridgeback or not?
A feature that is very helpful to know is whether or not the shark has an "interdorsal ridge" which is a prominent crease in the skin running down the middle of the back between the first and second dorsal fins. Species of "ridgeback" sharks that are common off Delmarva include duskies, sandbars, tigers, and dogfish. Since none of the other prominent species off our coast have the ridge, observing the "presence" or "absence" of it allows one to immediately eliminate a number of sharks from consideration. It can be particularly helpful to know that of our local "generic" species - the spinner, blacktip, bull, sharpnose, and blacknose DO NOT have the ridge and neither do makos, hammerheads, sand tigers, blues, or threshers.
Where was it?
When asked to help identify a shark, the first thing I want to know is where it was caught or observed. Was it in the back bay, the surf, or how many miles offshore? Any shark can be anywhere at any time; We once hooked a 500 pound mako 5-miles from the inlet, caught a sand tiger 26-miles offshore, and had a huge tiger come up to the boat less than ½-mile out. If you know even a little about these species you're probably aware that those were very surprising encounters for those locations. Sure, it occasionally happens that sharks show up in places where they shouldn't be, but when someone tells me that they've caught a species in a place that's out of its "normal zone" I'm probably going to start off being a bit skeptical about their identification.
Frequency of catch (common or not?)
There's nothing to stop at lemon bonnethead, nurse, porbeagle, whitetip, or great hammerhead from visiting Delmarva waters, but since the chances of encountering one is so remote, you don't want to immediately jump to the assumption that you've caught or seen something that shouldn't be here. Then again, just like other fish, shark species will sometimes expand their range into areas they haven't been before. A bunch of years ago we tagged a blacknose shark off Ocean City. When I reported it to the tagging people they questioned my identification saying that they've never had a blacknose reported above North Carolina. When they saw the photo I sent them they were surprised that it was indeed a blacknose. Since then we've been catching about 6-12 blacknose every season. Another time someone told me they thought they had caught a small bull shark in the back bay. I was very skeptical of it being a bull and assumed they had caught a small sandbar shark which are somewhat common in our bay waters. However, even though the photos were not the best, from what I could see of the shark I couldn't rule out the strong likelihood that they had indeed caught a small bull shark! By the way, bulls are still a very rare catch off Delmarva but in recent years they've been showing up with a little more frequency.
Check out those claspers!
The male sex organs of a shark are two finger-like appendages between the pelvic fins. Males have em, females don't - simple science the people seem to be losing track of these days. Before a male shark becomes sexually mature the claspers are short (barely projecting beyond the back of the pelvic fins) and very flexible. As a shark becomes sexually mature its claspers calcify and become rigid and grow longer so that they project well beyond the pelvic fins. Since most species don't mature for many years and have reached a proportionately large size, the length of the claspers can give a clue as to whether or not you're looking at a small species or one that grows quite large. For instance, say you have a 4-foot shark with big claspers indicating a mature shark. If it's only 4-feet long and already sexually mature then it's not likely going to grow a whole lot more and, therefore, not going to be a dusky, sandbar, spinner, sand tiger or other large species of shark. It could, however, be a sharpnose, blacktip, blacknose, or dogfish. Conversely, if it's 4-feet long and its claspers indicate that it's still immature, then it won't be one of the smaller species of sharks.
Seasons
Knowing when a shark was caught can help with identification. If someone was to tell me that they caught a 3-foot shark in January I'd probably start by assuming that it was a spiny dogfish because that's one of the few small species of sharks we have around here when the water is cold. I'm always highly suspect that someone made a wrong identification when they tell me they encountered a certain species of shark in a month when that type is not usually found off our coast. However, just like where they should and shouldn't "be", sharks don't always stay in the water that's in a temperature range we think they prefer. So the "right" time of year is just a guideline not a rule.
Size
Someone once told me about a 25-foot white shark they had swimming around their boat. When I told them that, from what I understood, the largest white shark recorded was 20-feet long they continued to insist the one they saw was 25. Since they had no photos I had to assume that they were either grossly exaggerating the length of the shark or it was more likely a basking shark which do occasionally show up off our coast and are sometimes confused for large whites. Knowing the size of a shark can be very important to identification. Obviously, some species just don't get as big as others. But as fishermen do tend to exaggerate a little (or a lot) you have to be careful using their estimate as a reliable clue for identification.
Study your sharks!
Obviously, in order to weave all these clues together into an accurate identification of a particular shark it’s helpful to have at least some knowledge of the morphological characteristics, life history, biology, and habits of more than just a couple species that frequent our home waters. The following list highlights a few key aspects of each species that can help with identification. And if you need a little extra assistance, please feel free to visit my BigSharks.com website where you can get my contact info and also find a link to my modernsharking YouTube channel that has a lot of our shark identification videos.
Shortfin Mako
Isurus oxyrinchus
Mid May- Mid June
1- Open ocean species that’s rarely taken closer than 20-offshore.
2- Very large eyes that appear totally black as if the entire eyeball is a large pupil.
3- Large gill openings that are proportionately larger than those found on most other sharks.
4- Deep blue back, silvery sides, snow-white belly, and firm, sleek, muscular physique.
5- Base of the tail is very wide but flat.
6- “Lunate” tail - top and bottom lobes are much more similar in length than that of other sharks.
7- Teeth are visible even with the mouth shut.
8- Teeth are long, thin, and NOT serrated like most other sharks.
9- NO Interdorsal ridge.
Longfin Mako
Isurus paucus
1- Very uncommon catch.
2- Pectoral fins are very long and project back behind the trailing edge of the dorsal fin.
3- Deep dark blue (almost black) back to a dark gray on the sides and then a white underside.
4- Underside of the snout and lower jaw is dark gray to black.
5- NO Interdorsal ridge.
White (Great White)
Carcharodon carcharias
April – December
1- From surf-line to beyond Continental Shelf.
2- Large jaws with “toothy” appearance.
3- Teeth are triangular and serrated although in young individuals the teeth will not be as triangular.
4- Unlike the pretty blue/silver of a mako, the white shark's color is brown/gray on the back turning to gray/white on the sides and belly.
5- “Lunate” tail - top and bottom lobes are much more similar in length than that of other sharks.
6- NO Interdorsal ridge.
Blue - Prionace glauca
May – November
(mostly May & June)
1- Open ocean species that’s rarely taken closer than 20-miles offshore.
2- Very dark blue back transitioning to a lighter blue on the sides and eventually changing to a snow-white belly.
3- Long pectoral fins.
4- Very thin and “snaky” in appearance.
5- Short triangular teeth that hook slightly to the side.
6- NO Interdorsal ridge.
Common Thresher
Alopias vulpinus
May – October
1- Most common species of thresher taken off Delmarva
2- From surf-line to edge of Continental shelf.
3- Deep blue and purple back, silver sides and white belly.
4- The top lobe of the thresher’s tail is as long as the entire body of the fish itself.
5- Small mouth and very small triangular teeth.
6- NO Interdorsal ridge.
Bigeye Thresher
Alopias superciliosus
1- Very uncommon catch.
2- 1st dorsal fin set very far back.
3- Deep helmet-like groves makes a “V” shape over top of head and gills.
4- Large eyes angled upward.
6- NO Interdorsal ridge.
Spinner
Carcharhinus brevipinna
Late June - September
1- Grayish bronze in color with a white belly.
2- Adults will usually display a Z-shaped swath of white and gray on each side. Snout appears less rounded than that of the dusky, sandbar, and bull.
3- Prominent black tip on the “anal fin” (last fin on the underside of the shark before tail).
4- Total length of about nine-feet.
5- NO Interdorsal ridge.
Blacktip
Carcharhinus limbatus
June – October
1- From surf-line out 60-miles.
2- Grayish bronze in color with a white belly.
3- Adults will usually display a conspicuous Z-shaped swath of white and gray on each side.
Snout appears less rounded than that of the dusky, sandbar, and bull.
4- Total length is rarely over 6-feet.
5- “Husky in the shoulder area.
6- Lacks any black marking on the “anal fin” (last fin on the underside of the shark before tail).
6- Black-tips on fins might fade as the shark matures and sometimes are not evident at all.
7- Dermal denticles are often sloughing off around the base of the dorsal fin and on the back leaving an appearance of scarring and a loose-sand-like feel to the touch.
8- NO Interdorsal ridge.
Spinner or Blacktip?
A profile view of the two sharks will show that a spinner’s head from the tip of the nose to the back of it’s mouth is very sleek and almost looks as though it was squashed down to make it more streamlined.
The first dorsal fin on a spinner is farther back on the body than on a blacktip.
Spinners have black-tips on all fins including the bottom lobe of the tail AND on the “anal fin” which is the last fin on the underside of the shark before its tail. Blacktips lack the black tip on the anal fin.
Atlantic Sharpnose
Rhizoprionodon terraenovae
1- July through September.
2- Nearshore waters.
3- Small species of less than four feet and weigh under 15-pounds, most 5-10 pounds.
4- Distinctive white splotchy dots across their bronze back and sides.
5- Obvious white fringe along the trailing edge of the pectoral fins.
6- Teeth angle to the sides of the jaw.
7- Almost all will be male.
8- NO Interdorsal ridge
Tiger
Geleocerdo cuvier
June – October
1- May be taken from 3-14 feet long (TL)
(20-pounds to over 1000-pounds).
2- Mostly from 15-miles out to beyond the Continental Shelf but occasionally much closer to shore.
3- Stripe-like markings, that tend to fade in older animals.
4- Huge head and shoulder area followed by a sharply tapering back-half.
5- Very thick and coarse skin.
6- Thin layer slime over much of the skin.
7- Very wide head and body that tapers aggressively to the tail.
8- Top lobe of tail tapers to very thin tip.
9- Exceptionally large jaw with unique serrated teeth that hook sharply to the sides.
10- Interdorsal ridge.
Dusky
Carcharhinus obscurus
June – October
1- Surf-line out to beyond the Continental Shelf.
2- Most are taken within 10-miles of coast.
3- Grow to 12-feet but most taken are under 5-feet.
4- Gray/brown back, white belly.
5- Front of dorsal fin behind pectoral fins.
6- Skin is very slick (actually slimy) when felt from head to tail but very coarse from tail to head.
7- Rounded nose.
8- Serrated & triangular teeth on top, with thin straight teeth on bottom.
9- Usually exhibit clusters of little round pea-size scars from the first dorsal fin to tail.
10- Often confused with the sandbar shark.
11- Very common catch from boats and in the surf.
12- Interdorsal ridge.
Sandbar
Carcharhinus plumbeus
May - October
1- Surf-line to edge of Continental Shelf.
2- Sandbars will vary in color from bronze/gray to mostly gray.
3- Will grow to 7-feet (TL) but many caught under 2-5 feet (TL).
4- Large dorsal and pectoral fins.
5- Front of dorsal fin over pectoral fin.
6- Serrated & triangular teeth on top, with thin straight teeth on bottom.
7- Very common catch from boats and in the surf.
8- Interdorsal ridge.
Dusky or Sandbar?
The most definitive trait that distinguishes duskies from sandbars is the location of the first dorsal fin. On a sandbar shark if you were to draw a line from where the front edge of the dorsal fin connects to the body straight down the side of the shark to the belly, it would hit about the middle of the pectoral fin. Do the same to a dusky shark and the line would miss or just barely touch the very back edge of the pectoral fin. Also, a sandbar’s first dorsal fin is proportionately much larger than that on a dusky, and a sandbar typically has a greater girth up in the shoulder area.
Color is not usually a good thing to use for identification because within a species the color of individual animals can vary a bit. But usually duskies tend to be more of a dark brown in color while sandbars will be gray or a gray/bronze. These color schemes tend to make the sandbar overall much lighter in color than the dusky.
On duskies, one can sometimes notice clusters of small pea size scars on the back. Most, but not all, duskies will exhibit these scars which are seldom seen on sandbar sharks. Finally, the skin is very different between the two species. A dusky is covered by minutely small and sharp overlapping dermal denticles and a thin layer of slime. Run a hand from head to tail down a dusky and it will feel slimy and very smooth, go the other way and it will be slimy but very rough. Do the same with a sandbar shark and it will feel coarse in either direction because the skin consists of blunt non-overlapping denticles and there is no slime.
Scalloped Hammerhead
Sphyrna lewini
June – October
1- Mostly 15-miles out to beyond Continental Shelf but small ones much closer to shore.
2- No longer a common catch as it was in past years.
3- Usually caught from 80-150 pounds though occasionally over 200.
4- Color can vary from olive to bronze/gray to all bronze.
5- Leading edge of the head has a depression or “scalloped-out” area directly in the center.
6- NO Interdorsal ridge.
Smooth Hammerhead
Sphyrna zygaena
June - October
1- Surf-line to beyond Continental Shelf.
2- Most common HH species taken off Delmarva.
3- Will grow to 13-feet (TL) but most caught will be under 6-feet (TL).
4- Weight range from less than 10-pounds to over 200. Usually 20-80 pounds.
5- Dark olive/gray color.
6- Often have a thin layer of black slime on skin.
7- Center of the head is “smooth” and not indented as in other hammerheads.
8- NO Interdorsal ridge.
Great Hammerhead
Sphyrna mokarran
June - November
1- Will grow to over 18-feet and can weigh over 1200-pounds.
2- Not a common HH off Delmarva.
3- Most likely to be taken beyond the edge of the Continental Shelf.
4- Head is straight, not curved back slightly like the other species of H-Head.
5- First dorsal fin of a great hammerhead is extra tall and the trailing edge of it curves back in a sickle-shape.
6- NO Interdorsal ridge.
Sand Tiger
Carcharias Taurus
June – October
1- Surf-line out to 15-miles.
2- Up to 10-feet (TL) rarely under 5-feet (TL)
3- Small eyes.
4- Rough brown/gray and blotchy skin.
5- Short fins, First and second dorsal fin similar in size.
6- Long thin teeth with small “cusplets” on either side.
7- Teeth can be seen even when its jaws are closed.
8- Very common catch from boats and in the surf.
9- NO Interdorsal ridge.
Spiny Dogfish
Squalus acanthias
October - May.
1- Will grow to about 4-foot but most are caught under three.
2- Brownish gray with a small white spots on the back and sides.
3- Very small but sharp teeth.
4- Rounded top lobe of tail.
5- One inch-long (or longer) spines in front of each of the two dorsal fins.
6- Interdorsal ridge (faint).
Smooth Dogfish
(Sand Shark)
Mustelus canis
May-November
1- From surf line out 20-miles
2- Will grow to about 5-feet but most are caught under 3-feet.
3- Small mouth with many very blunt teeth.
4- Oval shaped eyes.
5- Very common catch from boats and in the surf.
6- Interdorsal ridge.
Bull
Carcharinus leucas
June – October
1- Most likely to be caught in nearshore waters.
2- Lengths to 11-feet but usually under 8-feet.
3- Large mouth
4- Husky body (large girth)
5- Dorsal fin is relatively low and very triangular.
6- NO Interdorsal ridge.
7-Very uncommon catch.
Blacknose
Carcharinus acronotus
July-September
1- Uncommon catch.
2- Will grow to about 4-feet.
3- Black tip on snout is not always present
4- One of the few 4-foot sharks in this area that the males will be mature.
5- NO Interdorsal ridge. §
