---
title: "What the sources say about the Scalloped Hammerhead | AnimalTracks.wiki"
description: "48 claims from the Scalloped Hammerhead profile, each beside the words of the source that backs it."
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---

# What the sources say about the Scalloped Hammerhead (*Sphyrna lewini*)

> 48 claims from the Scalloped Hammerhead profile, each beside the words of the source that backs it. A "..." marks a cut in a quote and [brackets] an insertion.

Profile: [Scalloped Hammerhead](https://animaltracks.wiki/animals/scalloped-hammerhead/)

## Scalloped Hammerhead Shark. NOAA Fisheries.

https://www.fisheries.noaa.gov/species/scalloped-hammerhead-shark

| The page says | The source says |
| :--- | :--- |
| Warm temperate and tropical coastal seas worldwide | found in coastal warm temperate and tropical seas worldwide |
| A scalloped hammerhead can weigh up to 335 pounds, grow up to 11 feet long and live up to 30 years, according to NOAA Fisheries | Weight Up to 335 pounds Length Up to 11 feet Lifespan Up to 30 years (note: NOAA Fisheries is the current institution page; ADW's older account gives a 31.5-year-old individual and 4.3 m, Florida Museum 'thought to be over 30 years') |
| It lives in warm temperate and tropical coastal seas worldwide: the western Atlantic from New Jersey to Brazil, the eastern Atlantic from the Mediterranean to Namibia, the Indian Ocean from South Africa and the Red Sea to Myanmar, and the Pacific from Japan to New Caledonia and from southern California to Ecuador | found in coastal warm temperate and tropical seas worldwide. In the western Atlantic Ocean, the scalloped hammerhead range extends from the northeast coast of the United States (from New Jersey to Florida) to Brazil ... In the eastern Atlantic, it can be found from the Mediterranean to Namibia. Populations in the Indian Ocean are found in the following locations: South Africa and the Red Sea to Pakistan, India, and Myanmar, and in the western Pacific, the scalloped hammerhead can be found from Japan and China to New Caledonia ... Distribution in the eastern Pacific Ocean extends from the coast of southern California (U.S.), including the Gulf of California, to Ecuador (note: quote trimmed before the source's trailing 'and possibly Peru,' which this claim does not assert) |
| NOAA Fisheries says the species is threatened by commercial fishing, mainly for the fin trade | They are threatened by commercial fishing, mainly for the shark fin trade |
| Fishing, mostly for fins. NOAA Fisheries says scalloped hammerheads are threatened by commercial fishing, mainly for the shark fin trade. | They are threatened by commercial fishing, mainly for the shark fin trade |

## Sphyrna lewini. Florida Museum of Natural History, Discover Fishes.

https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/sphyrna-lewini/

| The page says | The source says |
| :--- | :--- |
| Sardines, reef fish, squid, octopus, crustaceans, smaller sharks and stingrays | Common prey: small schooling fish such as sardines, conger eels, many reef fish species, squid, octopus, crustaceans as well as smaller elasmobranchs such as blacktip reef sharks, angelsharks and stingrays (note: 'reef fish' is the source's 'many reef fish species') |
| hunted at night | Scalloped hammerheads spend most of the day closer inshore, moving offshore to hunt at night |
| Sardines, many kinds of reef fish, squid, octopus and crustaceans are on the menu, along with smaller sharks and rays | Common prey: small schooling fish such as sardines, conger eels, many reef fish species, squid, octopus, crustaceans as well as smaller elasmobranchs such as blacktip reef sharks, angelsharks and stingrays |
| Stingrays seem to be a favorite, at a price: hammerhead sharks are often found with up to 50 or more stingray spines in their mouths and guts | Up to 50 or more stingray spines are often found in the mouth and digestive systems of hammerhead sharks, a price to pay for a favorite meal |
| Gathering in large groups also makes them easier to catch in large numbers on longlines, bottom nets and trawls, which has wiped out populations in some areas | This species tendency to aggregate in large groups making capture in large numbers on longlines, bottom nets and trawls even easier. This has led to complete die off of populations in certain areas |
| Because the species gathers in large groups, it is easier to catch in large numbers on longlines, bottom nets and trawls, which has wiped out populations in some areas. | This species tendency to aggregate in large groups making capture in large numbers on longlines, bottom nets and trawls even easier. This has led to complete die off of populations in certain areas (note: 'Because' carries the source's own 'tendency to aggregate in large groups making capture ... even easier') |
| dangerLevel: Medium | Hammerheads are considered potentially dangerous sharks. According to the International Shark Attack File, there have been 17 unprovoked attacks for the genus Sphyrna , though none were fatal. (note: stats.dangerLevel, 'Can injure, but rarely seriously': genus-wide attacks, none fatal; ADW: 'no confirmed attacks on humans by this species') |

## Sphyrna lewini (scalloped hammerhead shark). Animal Diversity Web, University of Michigan.

https://animaldiversity.org/accounts/Sphyrna_lewini/

| The page says | The source says |
| :--- | :--- |
| near continental and island shelves, seamounts, reefs and drop-offs | scalloped hammerheads can also be found near continental and island shelves ... At dawn, they move from their offshore hunting grounds to island shelves, seamounts, and enclosed bays and estuaries. During the day they migrate to drop-off zones and reefs |
| A wide, notched head | Scalloped hammerheads have a small but prominent notch in the center of their characteristically-shaped head |
| with electroreceptors on its underside | these special electroreceptors are located on the underside of the snout |
| Hunting at night, a scalloped hammerhead uses a "smash and grab" technique: it accelerates toward prey and either swallows it whole or disables it with a bite | Scalloped hammerheads actively forage for food during the night, using a “smash and grab” feeding technique. They accelerate towards prey and either swallow it whole, or disable prey by biting it |
| By day, scalloped hammerheads move to drop-off zones and reefs | At dawn, they move from their offshore hunting grounds to island shelves, seamounts, and enclosed bays and estuaries. During the day they migrate to drop-off zones and reefs |
| where most females gather in all-female schools with the larger, more mature females in the center | most females are found in sexually segregated schools with larger, more mature females in the center (note: 'all-female' glosses 'sexually segregated') |
| Adult males join schools almost exclusively to find a mate | Adult males almost exclusively enter schools when in search of a mate |
| At dusk the sharks head back offshore to hunt | At dusk the sharks return to offshore pelagic areas and actively search for food |
| Most females travel in all-female schools, with the larger, more mature females in the center, while adult males join schools almost exclusively to find a mate. | most females are found in sexually segregated schools with larger, more mature females in the center ... Adult males almost exclusively enter schools when in search of a mate (note: 'all-female' glosses 'sexually segregated') |
| tags: electroreception | they have special sensory organs called Ampullae of Lorenzini; these special electroreceptors are located on the underside of the snout and "hammer", and aid in the detection of buried prey |

## Kajiura & Holland (2002). Electroreception in juvenile scalloped hammerhead and sandbar sharks. Journal of Experimental Biology.

https://doi.org/10.1242/jeb.205.23.3609

| The page says | The source says |
| :--- | :--- |
| A wide head that seems to sense prey no better than a sandbar shark's, but searches a wider area and can pivot into sharp turns at high speed | oriented to dipole electric fields from the same maximum distance ... Scalloped hammerheads typically demonstrated a pivot orientation ... which enables the hammerheads to execute sharp turns at high speed ... the sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields, it does provide (1). a greater lateral search area (note: 'an ordinary shark' is the sandbar shark, the carcharhinid the study compared against) |
| It appears to sense a weak electric field no better than a sandbar shark does, but seems to give a wider search area and sharp turns at high speed | oriented to dipole electric fields from the same maximum distance (approximately 30 cm) ... which enables the hammerheads to execute sharp turns at high speed ... the sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields, it does provide (1). a greater lateral search area |
| A hammerhead's wide head is called a cephalofoil, and one idea was that it evolved to sharpen the shark's electric sense | The unique head morphology of sphyrnid sharks might have evolved to enhance electrosensory capabilities ... the edge of the cephalofoil closest to the dipole (note: the abstract uses 'sphyrnid head morphology' and 'cephalofoil' for the same structure; 'one idea was' keeps the source's 'might have evolved' hedge) |
| A 2002 study tested that by comparing juvenile scalloped hammerheads with sandbar sharks, which have no hammer, using a weak electric field like the one prey gives off | The 'enhanced electroreception' hypothesis was tested by comparing the behavioral responses of similarly sized carcharhinid and sphyrnid sharks to prey-simulating electric stimuli. Juvenile scalloped hammerhead sharks Sphyrna lewini and sandbar sharks Carcharhinus plumbeus oriented to dipole electric fields (note: published 2002 (J Exp Biol 205(23)); sandbar sharks are the carcharhinids, which lack the sphyrnid head) |
| Both species picked it up from the same maximum distance, about 30 centimeters: the wide head does not appear to make the shark's electric sense sharper | oriented to dipole electric fields from the same maximum distance (approximately 30 cm) ... the sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields |
| What it does seem to give is a wider search area, which may help the shark find prey, and better maneuverability | it does provide (1). a greater lateral search area, which may increase the probability of prey encounter, and (2). enhanced maneuverability, which may aid in prey capture |
| The hammerheads typically turned by holding the edge of the head nearest the target still and bending the body toward it, a sharp turn made at high speed | Scalloped hammerheads typically demonstrated a pivot orientation in which the edge of the cephalofoil closest to the dipole remained stationary while the shark bent its trunk to orient to the center of the dipole ... which enables the hammerheads to execute sharp turns at high speed (note: 'nearest the target' glosses 'closest to the dipole') |
| The wider-bodied sandbar sharks swam in a broader arc | By contrast, sandbars swam in a broader arc towards the center of the dipole ... The greater trunk width of the sandbar sharks |
| It doesn't appear to sharpen its electric sense. | the sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields |
| A 2002 study compared juvenile scalloped hammerheads with sandbar sharks, which have no hammer, and both species picked up a weak electric field from the same maximum distance, about 30 centimeters. | Juvenile scalloped hammerhead sharks Sphyrna lewini and sandbar sharks Carcharhinus plumbeus oriented to dipole electric fields from the same maximum distance (approximately 30 cm) (note: published 2002 (J Exp Biol 205(23))) |
| What the wide head does seem to give is a wider search area, which may help the shark find prey, and better maneuverability. | it does provide (1). a greater lateral search area, which may increase the probability of prey encounter, and (2). enhanced maneuverability, which may aid in prey capture |
| The hammerhead typically holds the edge of its head nearest the target still and bends its body toward it, turning sharply at high speed. | Scalloped hammerheads typically demonstrated a pivot orientation in which the edge of the cephalofoil closest to the dipole remained stationary while the shark bent its trunk to orient to the center of the dipole ... which enables the hammerheads to execute sharp turns at high speed (note: replaces the earlier 'pivoting onto prey faster than a narrow-headed shark': the abstract says sharp turns at high speed, and compares flexibility with sandbar sharks, not speed; 'nearest' glosses 'closest to the dipole') |
| The wider-bodied sandbar sharks swam in a broader arc. | By contrast, sandbars swam in a broader arc towards the center of the dipole ... The greater trunk width of the sandbar sharks |
| for a shark that searches a wider area with its broad head and can pivot into sharp turns at high speed | Scalloped hammerheads typically demonstrated a pivot orientation ... which enables the hammerheads to execute sharp turns at high speed ... it does provide (1). a greater lateral search area (note: vibe.reason) |

## Wells et al. (2018). Movement, Behavior, and Habitat Use of a Marine Apex Predator, the Scalloped Hammerhead. Frontiers in Marine Science.

https://doi.org/10.3389/fmars.2018.00321

| The page says | The source says |
| :--- | :--- |
| Studies have found them clustering around seafloor features such as seamounts, and a 2018 study listed possible reasons: better hunting, magnetic patterns in the seafloor, or simply that tagged sharks were tracked for only a short time | several studies have found that scalloped hammerheads have relatively small home ranges and display aggregative behaviors around bathymetric features, such as seamounts, potentially due to enhanced prey availability, geomagnetic associations from gradients in the seafloor, or simply short durations of tagged individuals (note: 'better hunting' paraphrases 'enhanced prey availability'; 'tracked for only a short time' paraphrases 'short durations of tagged individuals'; 'only a short time' is the source's 'short durations') |
| Their fins are highly valued too: estimates published in the 2000s put 1.3 to 2.7 million scalloped and smooth hammerheads through the Hong Kong fin trade each year | Scalloped hammerhead fins are highly valued in the shark fin trade (Abercrombie et al., 2005) with estimates ranging between 1.3 and 2.7 million scalloped and smooth hammerheads (S. zygaena) used in the Hong Kong fin trade annually (Clark et al., 2006 ; Camhi et al., 2009) (note: the estimates are cited to Clark et al. 2006 and Camhi et al. 2009, hence 'published in the 2000s') |
| As of 2018, scientists weren't sure. Several studies have found scalloped hammerheads clustering around seamounts and other seafloor features, and a 2018 study listed possible reasons: better hunting, magnetic patterns in the seafloor, or simply that tagged sharks were tracked for only a short time. | several studies have found that scalloped hammerheads have relatively small home ranges and display aggregative behaviors around bathymetric features, such as seamounts, potentially due to enhanced prey availability, geomagnetic associations from gradients in the seafloor, or simply short durations of tagged individuals (note: 'weren't sure' reflects 'potentially due to'; 'better hunting' paraphrases 'enhanced prey availability') |
| Their fins are highly valued, and estimates published in the 2000s put 1.3 to 2.7 million scalloped and smooth hammerheads through the Hong Kong fin trade each year. | Scalloped hammerhead fins are highly valued in the shark fin trade (Abercrombie et al., 2005) with estimates ranging between 1.3 and 2.7 million scalloped and smooth hammerheads (S. zygaena) used in the Hong Kong fin trade annually (Clark et al., 2006 ; Camhi et al., 2009) (note: the estimates are cited to Clark et al. 2006 and Camhi et al. 2009, hence 'published in the 2000s') |

## Jorgensen, Klimley & Muhlia-Melo (2009). Scalloped hammerhead shark Sphyrna lewini utilizes deep-water, hypoxic zone in the Gulf of California. Journal of Fish Biology.

https://doi.org/10.1111/j.1095-8649.2009.02230.x

| The page says | The source says |
| :--- | :--- |
| One shark tracked for 74 days was recorded diving into the Gulf of California's oxygen minimum layer, a deep band of water with extremely little oxygen, which expanded the range of depths the species was known to use | A hammerhead shark Sphyrna lewini tracked for 74 days revealed an expansion of the range of vertical distribution for the species to include the extreme hypoxic environment of the oxygen minimum layer in the Gulf of California (note: 'a deep band of water with extremely little oxygen' defines 'extreme hypoxic environment' for young readers; 'deep' is from the title's 'deep-water, hypoxic zone') |
| Deeper than scientists once knew. One scalloped hammerhead tracked for 74 days was recorded diving into the Gulf of California's oxygen minimum layer, a deep band of water with extremely little oxygen. | A hammerhead shark Sphyrna lewini tracked for 74 days revealed an expansion of the range of vertical distribution for the species to include the extreme hypoxic environment of the oxygen minimum layer in the Gulf of California (note: 'Deeper than scientists once knew' paraphrases 'revealed an expansion of the range of vertical distribution') |
| That track, published in 2009, expanded the range of depths the species was known to use. | revealed an expansion of the range of vertical distribution for the species (note: published 2009 (J Fish Biol 75)) |

## Quattro et al. (2013). Sphyrna gilberti sp. nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the western Atlantic Ocean. Zootaxa.

https://doi.org/10.11646/zootaxa.3702.2.5

| The page says | The source says |
| :--- | :--- |
| In 2013, scientists named a new hammerhead species, Sphyrna gilberti, from young sharks caught off South Carolina that had passed as scalloped hammerheads | Eighty juvenile hammerheads diagnosable as S. lewini were collected in the coastal waters of South Carolina from 2001–2003 using longline and gillnet gear (note: published 2013-08-26 (Zootaxa 3702(2)); the abstract: 'Sphyrna gilberti sp. nov. is described based on 54 specimens collected in the coastal waters of South Carolina') |
| In body shape and anatomy, the only difference the paper found was the number of vertebrae in front of the tail | Morphologically, S. gilberti sp. nov. is separable from S. lewini (Griffith & Smith 1834) only in the number of precaudal vertebrae (note: 'in front of the tail' glosses 'precaudal') |
| Nobody knew yet how far the new species ranged | Due to rarity of specimens and the highly migratory behavior of most sphyrnids, the range of S. gilberti sp. nov. is unknown |

## Rigby et al. (2019). Sphyrna lewini. The IUCN Red List of Threatened Species.

https://www.iucnredlist.org/species/39385/2918526

| The page says | The source says |
| :--- | :--- |
| the IUCN's 2019 assessment rates it Critically Endangered | Critically Endangered A2bd (note: read in Chrome 2026-09-17 on the assessment page (iucnredlist.org refuses scripts): 'Critically Endangered A2bd', DATE ASSESSED 08 November 2018, YEAR PUBLISHED 2019, no DOI; matches GBIF's copy of the category (CR), cached at node_modules/.cache/animaltracks/source-text/9980e4ff6d93e22e.txt. Expected hand check.) |
| The IUCN's 2019 assessment rates the species Critically Endangered. | Critically Endangered A2bd (note: read in Chrome 2026-09-17 on the assessment page (iucnredlist.org refuses scripts): 'Critically Endangered A2bd', DATE ASSESSED 08 November 2018, YEAR PUBLISHED 2019, no DOI; matches GBIF's copy of the category (CR), cached at node_modules/.cache/animaltracks/source-text/9980e4ff6d93e22e.txt. Expected hand check.) |