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What the sources say

Great Hammerhead SharkSphyrna mokarran

Every figure, record and mechanism on the Great Hammerhead Shark profile was written from a source, and this is the working table behind it: 64 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

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Source
01

Florida Museum of Natural History, Discover Fishes

Sphyrna mokarran. Florida Museum of Natural History, Discover Fishes.

The page sayswired with electric sensors
The source sayshammerheads have small pores or “ampullae of Lorenzini”, distributed along the ventral surface of their head. The pores are gel-filled and serve as highly sensitive electrical receptors
The page saysWarm temperate and tropical coastal waters, coral reefs, and continental shelves worldwide
The source saysfound in coastal warm temperate and tropical waters within 40°N – 35°S latitude ... commonly in shallow coastal areas such as over continental shelves and lagoons
The page saysStingrays and other rays
The source saysknown to prefer stingrays and other batoids when available (Compagno et al., 2005)
The page saysbony fish
The source sayseats bony fishes and invertebrates, as well as other sharks and rays (Denham et al., 2007)
The page saysother sharks
The source sayseats bony fishes and invertebrates, as well as other sharks and rays (Denham et al., 2007)
The page saysAmpullae of Lorenzini, gel-filled pores under its head that sense the electrical signals of prey, even prey buried in sand
The source sayshammerheads have small pores or “ampullae of Lorenzini”, distributed along the ventral surface of their head. The pores are gel-filled and serve as highly sensitive electrical receptors that are used, among other things, to detect the electrical signals that are emitted by potential prey items – including those that are buried under the sand such as stingrays
The page saysThe Largest of the Hammerheads
The source saysThe great hammerhead is the largest of the hammerheads in the family Sphyrnidae
The page saysis the largest of the hammerhead sharks
The source saysThe great hammerhead is the largest of the hammerheads in the family Sphyrnidae
The page saysIt can reach a maximum length of 18 to 20 feet
The source saysThey can reach a maximum length of 18-20 feet (Compagno et al., 2005)
The page saysaverages over 500 pounds (230 kg)
The source saysthe great hammerhead averages over 500 pounds (230 kg)Note: The current Florida Museum page overrides ADW's older, heavier 350 to 500 kg range, which the page does not use
The page saysOne caught off Sarasota, Florida, weighed 991 pounds (450 kg)
The source saysThe world record great hammerhead was caught off Sarasota, Florida (US) weighing 991 pounds (450 kg)Note: The page states the individual's weight, not that it is still the world record: a current record needs a source dated after the latest catch, and the page is undated
The page saysGreat hammerheads are expected to live 20 to 30 years
The source saysExpected life span of the species is 20-30 years of age
The page saysfrom the Gulf of Mexico and the Caribbean to the Mediterranean, the Indo-Pacific and the Pacific coasts of Mexico and Peru
The source saysit ranges from North Carolina (US) south to Uruguay, including the Gulf of Mexico and Caribbean regions ... from Morocco to Senegal, including the Mediterranean Sea ... from the Ryukyu Islands to New Caledonia and French Polynesia. In the eastern Pacific it ranges from southern Baja, California (US) through Mexico, south to Peru
The page saysIt is often found in shallow water down to 80 meters, over continental shelves (the shallow seabed that borders the land) and in lagoons, but it also ranges far offshore as deep as 300 meters
The source saysThis large coastal/semi-oceanic shark is found far offshore to depths of 300m (Myers, 1999), but are commonly in shallow coastal areas such as over continental shelves and lagoons to depths of 80 mNote: The parenthesis defines 'continental shelf' in plain words; it states nothing about the shark
The page saysSome populations move toward cooler water each summer
The source saysThe great hammerhead migrates seasonally, with some populations moving poleward to cooler waters during the summer months
The page saysSensing Buried Prey
The source saysdetect the electrical signals that are emitted by potential prey items – including those that are buried under the sand such as stingrays
The page saysIts hammer-shaped head is called a cephalofoil
The source saysAnterior margin of cephalofoil straight and hammer-shaped
The page saysLike all sharks and rays, it has small gel-filled pores called ampullae of Lorenzini along the underside of its head
The source saysAs with all sharks and rays, hammerheads have small pores or “ampullae of Lorenzini”, distributed along the ventral surface of their head. The pores are gel-filled
The page saysThey work as highly sensitive electrical sensors, picking up the signals given off by prey, even a stingray buried under sand
The source saysserve as highly sensitive electrical receptors that are used, among other things, to detect the electrical signals that are emitted by potential prey items – including those that are buried under the sand such as stingrays
The page saysGreat hammerheads are known to prefer stingrays and other rays when they can find them
The source saysThey are known to prefer stingrays and other batoids when available (Compagno et al., 2005)Note: Batoids are the rays; 'when they can find them' is the source's 'when available'
The page saysGreat hammerheads also eat bony fish, squid and other sharks
The source sayseats bony fishes and invertebrates, as well as other sharks and rays (Denham et al., 2007)Note: Squid is ADW's (claim 'squid': 'invertebrates such as squid and octopus')
The page saysThe underside of its hammer-shaped head is dotted with ampullae of Lorenzini, small gel-filled pores that act as highly sensitive electrical receptors
The source sayshammerheads have small pores or “ampullae of Lorenzini”, distributed along the ventral surface of their head. The pores are gel-filled and serve as highly sensitive electrical receptors
The page saysAll sharks and rays have them
The source saysAs with all sharks and rays, hammerheads have small pores or “ampullae of Lorenzini”
The page saysThey pick up the electrical signals given off by prey, including stingrays buried under the sand
The source saysused, among other things, to detect the electrical signals that are emitted by potential prey items – including those that are buried under the sand such as stingrays
The page saysThe Florida Museum counts 17 unprovoked attacks on people by hammerheads of all species, none fatal
The source saysAccording to the International Shark Attack File, there have been 17 unprovoked attacks with no fatalities for all species of the genus SphyrnaNote: body; the sentence stats.dangerLevel: High rests on. The page is undated, so the count is attributed to the museum rather than stated as current (#218)
The page sayssays few can be pinned on this one because hammerheads are hard to tell apart
The source saysHowever, few of the attacks can be directly attributed to this species as it is generally difficult to distinguish among species of hammerheads involved in attacksNote: body; stats.dangerLevel

Source
02

Animal Diversity Web, University of Michigan

Sphyrna mokarran (great hammerhead). Animal Diversity Web, University of Michigan.

The page sayscoral reefs
The source saysThese sharks inhabit both the pelagic and coastal regions in coral reefs, inland seas, lagoons, and bays in tropical and subtropical environments
The page sayssquid
The source saysinvertebrates such as squid and octopusNote: Florida Museum says only 'invertebrates'; ADW names squid. No disagreement between the two

Source
03

Piercy, Carlson & Passerotti 2010

Piercy, Carlson & Passerotti (2010). Age and growth of the great hammerhead shark, Sphyrna mokarran, in the north-western Atlantic Ocean and Gulf of Mexico. Marine and Freshwater Research.

The page saysA 2010 study aged 216 sharks from the Gulf of Mexico and the northwest Atlantic by counting yearly growth bands in their backbones, and the oldest was 44
The source saysage and growth estimates for the great hammerhead were determined from sharks (n = 216) ranging in size from 54- to 315-cm fork length (FL), captured in the Gulf of Mexico and north-western Atlantic Ocean ... Annual band pair deposition was confirmed ... Great hammerheads have one of the oldest reported ages for any elasmobranch (44 years) ... The present study is the first to provide vertebral ages for great hammerheadsNote: Vertebral ages = growth bands counted in the backbone. The 2010 comparison 'one of the oldest reported ages for any elasmobranch' was cut: it is a record dated 2010, and later shark ages exceed it

Source
04

Rigby et al. 2019

Rigby et al. (2019). Sphyrna mokarran. The IUCN Red List of Threatened Species 2019: e.T39386A2920499.

The page saysCritically Endangered
The source saysIUCN Red List category: Critically Endangered (CR)
The page saysThe great hammerhead is listed as Critically Endangered on the IUCN Red List
The source saysIUCN Red List category: Critically Endangered (CR)Note: Read through GBIF's current copy of the Red List

Source
05

Payne et al. 2016

Payne et al. (2016). Great hammerhead sharks swim on their side to reduce transport costs. Nature Communications.

The page saysSwimming on Its Side
The source saysGreat hammerhead sharks swim on their side to reduce transport costs
The page saysIt Swims on Its Side to Save Energy
The source saysGreat hammerhead sharks swim on their side to reduce transport costs
The page saysA wild great hammerhead tagged on the Great Barrier Reef spent about 90% of an 18-hour tracking period
The source saysthe shark tagged at the Great Barrier Reef spent ∼90% of the 18 h deployment period (which was from early evening till late morning) swimming on its side at absolute roll angles between 50° and 75°Note: Matches the body and FAQ 3. Two sharks were tagged; the abstract's 'up to 90%' is this one shark's figure
The page saystilted 50 to 75 degrees onto one side
The source saysswimming on its side at absolute roll angles between 50° and 75°
The page saysrolled 50 to 75 degrees onto one side
The source saysswimming on its side at absolute roll angles between 50° and 75°
The page saysAlmost all sharks get lift, the upward push that stops them sinking, from the pectoral fins on their sides
The source saysAlmost all sharks are negatively buoyant ... and use their pectoral fins to generate vertical hydrodynamic force that counteracts gravity
The page saysA great hammerhead's dorsal fin, on its back, is longer than those side fins, the opposite of every other shark measured
The source saysthe dorsal fin of a great hammerhead is longer than its pectoral fins; the opposite is true for all other sharks for which we have data
The page saysTilting lets the dorsal fin share the work of making lift
The source saysRolling on its side, a shark gradually transfers some of the lift from its pectoral fins to the dorsal finNote: Replaces 'instead of their pectoral fins': Fig. 2 has lift from 'the combination of the pectoral and dorsal fins at greater roll angles'
The page saysIts dorsal fin is longer than its pectoral fins, so tilting lets the dorsal fin help make lift
The source saysthe dorsal fin of a great hammerhead is longer than its pectoral fins ... Rolling to its side, a great hammerhead therefore increases the horizontal span of its lift-generating surfaces
The page saysIn wind tunnel tests on a model shark, tilting cut drag, the force that slows a swimmer down, by more than 10%
The source sayswe built a morphologically accurate model of a great hammerhead ... and conducted a series of experiments in a wind tunnel ... At the relevant range of lift coefficients, the reduction in drag is more than 10%
The page saysIn wind tunnel tests on a model shark, tilting cut drag by more than 10%
The source sayswe built a morphologically accurate model of a great hammerhead ... and conducted a series of experiments in a wind tunnel ... At the relevant range of lift coefficients, the reduction in drag is more than 10%
The page saysThe researchers estimate it uses about 8% less energy to cover the same distance
The source saysthe COT estimates are shown in Fig. 3c,d ... ∼8% less energy is used to travel a given distance when swimming rolled than when swimming upright
The page saysTo save energy
The source saysGreat hammerhead sharks swim on their side to reduce transport costs
The page saysswims tilted 50 to 75 degrees onto its side
The source saysswimming on its side at absolute roll angles between 50° and 75°Note: vibe.reason; replaces 'panoramic ocean resonance', a place word (#218)
The page saysa roll estimated to save about 8% of the energy of swimming upright
The source says∼8% less energy is used to travel a given distance when swimming rolled than when swimming uprightNote: vibe.reason; the 8% is the researchers' estimate from the model, hence 'estimated'

Source
06

Roemer, Gallagher & Hammerschlag 2016

Roemer, Gallagher & Hammerschlag (2016). Shallow water tidal flat use and associated specialized foraging behavior of the great hammerhead shark (Sphyrna mokarran). Marine and Freshwater Behaviour and Physiology.

The page saysused to pin stingrays to the seafloor
The source saysSpecialized prey handling behavior of a great hammerhead was first described in detail by Strong et al. (1990). During this observation, a great hammerhead (~3.0 m TL) utilized its ... cephalofoil to pin a southern stingray, Dasyatis americana to the substrate (termed ‘pin and pivot’). A similar behavior was observed by Chapman and Gruber (2002) of a single great hammerhead (~3.6 m) capturing and consuming a spotted eagle rayNote: Two described events (1990 stingray, 2002 eagle ray); the reviewer replaced 'built to pin', which claimed a design purpose no source gives
The page saysIn 1990, scientists first described in detail how one used its head to pin a southern stingray to the seafloor, a move called "pin and pivot."
The source saysSpecialized prey handling behavior of a great hammerhead was first described in detail by Strong et al. (1990). During this observation, a great hammerhead (~3.0 m TL) utilized its ... cephalofoil to pin a southern stingray, Dasyatis americana to the substrate (termed ‘pin and pivot’)
The page saysIn 1990, scientists first described in detail how one great hammerhead used its head to pin a southern stingray to the seafloor, a move called "pin and pivot."
The source saysSpecialized prey handling behavior of a great hammerhead was first described in detail by Strong et al. (1990). During this observation, a great hammerhead (~3.0 m TL) utilized its ... cephalofoil to pin a southern stingray, Dasyatis americana to the substrate (termed ‘pin and pivot’)
The page saysIn 2002, scientists reported a similar move by a great hammerhead catching and eating a spotted eagle ray
The source saysA similar behavior was observed by Chapman and Gruber (2002) of a single great hammerhead (~3.6 m) capturing and consuming a spotted eagle ray

Source
07

Stanhope et al. 2023

Stanhope et al. (2023). Genomes of endangered great hammerhead and shortfin mako sharks reveal historic population declines and high levels of inbreeding in great hammerhead. iScience.

The page saysworldwide
The source saysIt has a worldwide distribution, found in coastal tropical and warm temperate seas
The page saysIt lives in warm coastal seas around the world
The source saysIt has a worldwide distribution, found in coastal tropical and warm temperate seas
The page saysmainly because it is fished heavily for its large fins
The source saysIts critically endangered status is primarily due to heavy fishing for its large fins, which are highly valued in the shark fin trade
The page saysIts global population is estimated to have fallen by more than 80% over the last three generations
The source saysglobal population reduction was recently estimated at >80% over the last 3 generationsNote: The genome paper cites this estimate (its ref 30, Sherley et al., the JARA Red List tool); it is not the study's own, so 'The same study estimated' was cut
The page saysA 2023 study read the genome, the full set of DNA,
The source saysHere, we present chromosome-level genome assemblies for the Critically Endangered great hammerheadNote: 2023 is the paper's publication year (iScience 26, 2023), as in the reference list
The page saysof one great hammerhead from the North Atlantic
The source saysThe North Atlantic population, from which our individual arose
The page saysIt had low genetic variety
The source saysThe great hammerhead exhibited low genetic variation
The page saysat the bottom of a broad list of fish species
The source saysGenome-wide heterozygosity estimates for white shark, whale shark, and hammerhead were at the bottom of those of a broad list of fish speciesNote: The source's 'below the majority of all but a selected few endangered species of mammals' is ambiguous, so the mammal comparison was cut
The page sayssigns of inbreeding (when parents are close relatives) as high as in some critically endangered animals
The source saysThe inbreeding coefficient for hammerhead (FROH >1Mbp) was almost 9%, comparable to or exceeding other examples of critically endangered taxa
The page saysmore sharks must be sampled before drawing firm conclusions about the whole species
The source saysHeterozygosity and ROH of the reference individual suggest low diversity and inbreeding even in this population; however, sampling additional individuals would be necessary before making any more definitive population- or species-level conclusions
The page saysCritically Endangered, mainly due to heavy fishing for its fins
The source sayschromosome-level genome assemblies for the Critically Endangered great hammerhead ... Its critically endangered status is primarily due to heavy fishing for its large fins, which are highly valued in the shark fin trade
The page saysA 2023 study of one great hammerhead's genome found low genetic variety
The source saysThe great hammerhead exhibited low genetic variationNote: 2023 is the paper's publication year; 'one great hammerhead' is the study's single reference individual (next claim)
The page saysand signs of inbreeding, though its authors say
The source saysHeterozygosity and ROH of the reference individual suggest low diversity and inbreeding even in this population; however, sampling additional individuals would be necessary

Source
08

Doan & Kajiura 2020

Doan & Kajiura (2020). Adult blacktip sharks (Carcharhinus limbatus) use shallow water as a refuge from great hammerheads (Sphyrna mokarran). Journal of Fish Biology.

The page saysDrone footage from southeast Florida shows adult blacktip sharks fleeing into shallow water when a great hammerhead comes after them
The source saysAerial drone footage of blacktip sharks, Carcharhinus limbatus, along the coast of southeast Florida, USA, shows adult blacktips fleeing to the shallow water adjacent to the beach when confronted with or chased by a predatory great hammerhead shark

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.