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NEWSLETTER 05/2013 14. May 2013

Please acknowledge use of the database in your publications, and cite: 

Pollerspöck, J. 2013, Bibliography database of living/fossil sharks, rays and chimaeras (Chondrichtyes: Elasmobranchii, Holocephali),, World Wide Web electronic publication, Version 2013


New images at shark-references:

Many thanks to the following persons for the permission to use their images:


Missing papers:

Many thanks to all friends of shark-references, who send me some missing papers last month!

Shark-References would kindly like to ask you for your contribution to this project.

Please support and send missing papers (not listed papers or papers without the infosymbol) to





EEA Conference 2013

The Shark Trust is delighted to be hosting the 17th European Elasmobranch Association (EEA) conference in Plymouth this November. Plymouth is a centre of marine excellence and the Trust is pleased to announce the conference will be hosted in association with the Marine Institute of Plymouth University and the National Marine Aquarium.

for more information please visit:


The OCS Conference Organising Committee would like to extend an invitation to attend the

4th Oceania Chondrichthyan Society Conference

to be held at

Royal on the Park 
Brisbane, Australia


19th-20th September 2013

for more information please visit:


News from shark-references and partner:

A review of the fossil Echinorhinidae (species descriptions, distribution)

Distribution of fossil Echinorhinidae


Echinorhinus australis
Echinorhinus blakei
Echinorhinus caspius
Echinorhinus eyrensis
Echinorhinus kelleyi
Echinorhinus lapaoi
Echinorhinus pfauntschi
Echinorhinus pollerspoecki
Echinorhinus pozzii
Echinorhinus priscus
Echinorhinus richiardii
Echinorhinus schoenfeldi
Echinorhinus sp
Echinorhinus weltoni
Gibbechinorhinus lewyi
Orthechinorhinus pfeili
Paraechinorhinus riepli
Pseudoechinorhinus mackinnoni

Just finished:

A review of the fossil Chlamydoselachidae (species descriptions, distribution)

Distribution of fossil Chlamydoselachidae


Proteothrinax baumgartneri

Please send your images of fossil Echinorhinidae and Chlamydoselachidae to shark-references and inform me about new findings!

New described species/Taxonomic News:



HODNETT, J.-P.M. & ELLIOTT, D.K. & OLSON, T.J. 2013 A new basal hybodont (Chondrichthyes, Hybodontiformes) from the Middle Permian (Roadian) Kaibab Formation, of northern Arizona. New Mexico Museum of Natural History and Science, Bulletin, 60: 103-108

New genus: Diablodontus
New species: Diablodontus michaeledmundi
Abstract: The teeth of a new basal hybodont shark are described from the Middle Permian (Roadian) Kaibab Formation of northern Arizona. Diablodontus michaeledmundi gen. et sp. nov. represents the only known nondurophagous (crushing toothed) hybodont from the marine Middle Permian. Dental morphology suggests a close relationship between D. michaeledmundi gen. et sp. nov. and the Pennsylvanian and early Permian “Maiseyodus,” both of which belong to an indeterminate family of hybodontid hybodonts that was ancestral to the Hybodus clade. D. michaeledmundi gen. et sp. nov. could have inhabited a littoral habitat and had an ecomorphotype similar to extant hound sharks (Triakidae). 


New Paper

Recent Papers:

AKHILESH, K.V. & WHITE, W.T. & BINEESH, K.K. & GANGA, U. & PILLAI, N.G.K. 2013Biological observations on the bristly catshark Bythaelurus hispidus from deep waters off the south-west coast of India. Journal of Fish Biology, 82 (5): 1582-1591
AVENDAÑO-ALVAREZ, J. & PÉREZ-ESPAÑA, H. & SALAS-MONREAL, D. & GARCÍA-RODRÍGUEZ, E. 2013 Captures and Diet of Three Sharks Species in the Veracruz Reef System. Open Journal of Marine Science, 3 (2): 66-73
BRUNNSCHWEILER, J.M. & BARNETT, A. 2013 Opportunistic Visitors: Long-Term Behavioural Response of Bull Sharks to Food Provisioning in Fiji. PLoS ONE, 8 (3): e58522
CAMUS, A.C. & BERLINER, A.L. & CLAUSS, T.M. & HATCHER, N. &  MARANCIK, D.P. 2013 Serratia marcescens associated ampullary system infection and septicaemia in a bonnethead shark, Sphyrna tiburo (L.). Journal of Fish Diseases, in press
CAMUS, A.C. & SOTO, E. & BERLINER, A.L. & CLAUSS, T.M. & SANCHEZ, S. 2013Epitheliocystis hyperinfection in captive spotted eagle rays Aetobatus narinari associated with a novel Chlamydiales 16S rDNA signature sequence. Diseases of Aquatic Organisms, 104 (1): 13-21
CHAPMAN, D.D. & WINTNER, S.P. & ABERCROMBIE, D.L. & ASHE, J. & BERNARD, A.M. & SHIVJI, M.S. & FELDHEIM, K.A. 2013 The behavioural and genetic mating system of the sand tiger shark, Carcharias taurus, an intrauterine cannibal. Biology Letters, 9 (3): 20130003
CHAPPLE, T.K. & BOTSFORD, L.W. 2013 A Comparison of Linear Demographic Models and Fraction of Lifetime Egg Production for Assessing Sustainability in Sharks.Conservation Biology, in press
CHEN, X. & AI, W.M. & YE, L. & WANG, X.H. & LIN, C.W. & YANG, S.Y. 2013 The complete mitochondrial genome of the grey bamboo shark (Chiloscyllium griseum) (Orectolobiformes: Hemiscylliidae): genomic characterization and phylogenetic application. Acta Oceanologica Sinica, 32 (4): 59-65
COLL, M. & NAVARRO, J. & PALOMERA, I. 2013 Ecological role, fishing impact, and management options for the recovery of a Mediterranean endemic skate by means of food web models. Biological Conservation, 157: 108-120
CORCORAN, M.J. & WETHERBEE, B.M. & SHIVJI, M.S. & POTENSKI, M.D. & CHAPMAN, D.D. & HARVEY, G.M. 2013 Supplemental Feeding for Ecotourism Reverses Diel Activity and Alters Movement Patterns and Spatial Distribution of the Southern Stingray, Dasyatis americana. PLoS ONE, 8 (3): e59235
DICKEN, M.L. & BOOTH, A.J. 2013 Surveys of white sharks (Carcharodon carcharias) off bathing beaches in Algoa Bay, South Africa. Marine and Freshwater Research, in press
FERRARI, L.D. & KOTAS, J.E. 2013 Hook selectivity as a mitigating measure in the catches of the stingray Pteroplatytrygon violacea (Elasmobranchii, Dasyatidae) (Bonaparte, 1832). Journal of Applied Ichthyology, in press
FOFANDI, M.D. & ZALA, M. & KOYA, M. 2013 Observations on selected biological aspects of the spadenose shark (Scoliodon laticaudus Müller & Henle, 1838), landed along Saurashtra coast. Indian Journal of Fisheries, 60 (1): 51-54 
GILLIS, J.A. & MODRELL, M.S. & BAKER, C.V.H. 2013 Developmental evidence for serial homology of the vertebrate jaw and gill arch skeleton. Nature Communications, 4: 1436
HUVENEERS, C. & ROGERS, P.J. & SEMMENS, J.M. & BECKMANN, C. & KOCK, A.A. & PAGE, B. & GOLDSWORTHY, S.D. 2013 Effects of an Electric Field on White Sharks: In Situ Testing of an Electric Deterrent. PLoS ONE, 8 (5): e62730
ISHIMURA, G. & BAILEY, M. 2013 The market value of freshness: observations from the swordfish and blue shark longline fishery. Fisheries Science, 79 (3): 547-553
IZZO, C. & DREW, E.B. 2013 Analysis of body shape for differentiating among species of rajids. Journal of Fish Biology, 82 (5): 1632-1640
KADRI, H. & MAROUANI, S. & BRADAI, M.N. & BOUAÏN, A. 2013 Age, growth and reproductive biology of the rough skate, Raja radula (Chondrichthyes: Rajidae), off the Gulf of Gabes (southern Tunisia, central Mediterranean). Marine and Freshwater Research, in press
KIM, S.H. & SHIMADA, K. & RIGSBY, C.K. 2013 Anatomy and evolution of heterocercal tail in lamniform sharks. Anatomical Record, 296 (3): 433-442 
LI, Z. & WANG, B. & CHI, C. & GONG, Y. & LUO, H. & DING, G. 2013 Influence of average molecular weight on antioxidant and functional properties of cartilage collagen hydrolysates from Sphyrna lewini, Dasyatis akjei and Raja porosa. Food Research International, 51 (1): 283-293
MCMEANS, B.C. & ARTS, M.T. & LYDERSEN, C. & KOVACS, K.M. & HOP, H. & FALK-PETERSEN, S. & FISK, A.T. 2013 The role of Greenland sharks (Somniosus microcephalus) in an Arctic ecosystem: assessed via stable isotopes and fatty acids.Marine Biology, 160 (5): 1223-1238
MELO PALMEIRA, C.A. & DA SILVA RODRIGUES-FILHO, L.F. & DE LUNA SALES, J.B. & VALLINOTO, M. & SCHNEIDER, H. & SAMPAIO, I. 2013 Commercialization of a critically endangered species (large tooth sawfish, Pristis perotteti) in fish markets of northern Brazil: authenticity by DNA analysis. Food Control, in Press
MERLY, L. & SMITH, S.L. 2013 Collagen type II, alpha 1 protein: A bioactive component of shark cartilage. International Immunopharmacology, 15 (2): 309-315
MOTTA, F.S. & CALTABELLOTTA, F.P. & NAMORA, R.C. & GADIG, O.B.F. 2013Length-weight relationships of sharks caught by artisanal fisheries from southeastern Brazil. Journal of Applied Ichthyology, in press
MOUTOPOULOS, D.K. & RAMFOS, A. & MOUKA, A. & KATSELIS, G. 2013 Length-Weight Relations of 34 Fish Species Caught by Small-Scale Fishery in Korinthiakos Gulf (Central Greece). Acta Ichthyologica et Piscatoria, 43 (1): 57-64
MULL, C.G. & LYONS, K. & BLASIUS, M.E. & WINKLER, C. & O’SULLIVAN, J.B. & LOWE, C.G. 2013 Evidence of Maternal Offloading of Organic Contaminants in White Sharks (Carcharodon carcharias). PLoS ONE, 8 (4): e62886
NIETO-NAVARRO, J.T. & ZETINA-REJÓN, M. & ARREGUÍN-SÁNCHEZ, F. & PALACIOS-SALGADO, D.S. & JORDÁN, F. 2013 Changes in fish bycatch during the shrimp fishing season along the eastern coast of the mouth of the Gulf of California.Journal of Applied Ichthyology, 29 (3): 610–616
O'SHEA, O.R. & THUMS, M. & VAN KEULEN, M. & KEMPSTER, R.M. & MEEKAN, M.G. 2013 Dietary partitioning by five sympatric species of stingray (Dasyatidae) on coral reefsJournal of Fish Biology, in press
PAIBOONLEESKUL, K. & ROMRATANAPUN, S. & THAPANAND-CHAIDEE, T. 2013Ageing of shortspine spurdog in the Andaman Sea of Thailand. Maejo International Journal of Science and Technology, 7 (Special Issue): 14-21
ROBINSON, L. & SAUER, W.H.H. 2013 A first description of the artisanal shark fishery in northern Madagascar: implications for management. African Journal of Marine Science, 35 (1): 9-15
ROMANOV, E.V. & BACH, P. & REBIK, S.T. & LE TURC, A. & SERET, B. 2013 First pelagic record of the velvet dogfish Zameus squamulosus (Günther, 1877) (Squaliformes) from the southwestern Indian Ocean and some notes on its regional distribution.Zoosystema, 35 (1): 11-23
SEGURA, A.M. & MILESSI, A.C. & VÖGLER, R. & GALVAN-MAGAÑA, F. & MUGGEO, V. 2013 The determination of maturity stages in male elasmobranchs (Chondrichthyes) using a segmented regression of clasper length on total length. Canadian Journal of Fisheries and Aquatic Sciences, in press
SEMBA, Y. & YOKAWA, K. & MATSUNAGA, H. & SHONO, H. 2013 Distribution and trend in abundance of the porbeagle (Lamna nasus) in the southern hemisphere. Marine and Freshwater Research, in press
SWINSBURG, W.A. 2013 Survival of the blacktip shark, Carcharhinus limbatus. Open Access Master’s Theses. Paper 14 
TAYLOR, J.K.D. & MANDELMAN, J.W. & MCLELLAN, W.A. & MOORE, M.J. & SKOMAL, G.B. & ROTSTEIN, D.S. & KRAUS, S.D. 2013 Shark predation on North Atlantic right whales (Eubalaena glacialis) in the southeastern United States calving ground. Marine Mammal Science, 29 (1): 204–212 
UDYAWER, V. & CHIN, A. & KNIP, D.M. & SIMPFENDORFER, C.A. & HEUPEL, M.R. 2013 Variable response of coastal sharks to severe tropical storms: environmental cues and changes in space use. Marine Ecology Progress Series, 480: 171-183
YOKOTA, L. & GOITEIN, R. & GIANETI, M.D. & LESSA, R. T.P. 2013 Diet and feeding strategy of smooth butterfly ray Gymnura micrura in northeastern Brazil. Journal of Applied Ichthyology, in press

Recent Papers - Abstracts:

BALABAN, J.B. & SUMMERS, A.P. & WILGA, C.A.D. 2013 Mechanical Properties of a Shark Jaw Support Structure. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E9
BEDORE, C.N. & MCCOMB, D.M. & FRANK, T.F. & HUETER, R.E. & KAJIURA, S.M. 2013 Effects of temperature and anesthesia on visual temporal resolution in elasmobranch fishes. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E12
BLEVINS, E.L. 2013 Structure-function relationships in the pectoral fin of freshwater stingray Potamotrygon orbignyi. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E18
CAVE, E.J. & GUNN, T. & BEDORE, C. & KAJIURA, S. & KERSTETTER, D. 2013 Sexual dimorphism in the dentition of pelagic stingrays, Pteroplatytrygon violacea. Abstract-Poster Integrative and Comparative Biology, 53 (Suppl. 1): E260
CRISWELL, K.E. & FINARELLI, J.A. & FRIEDMAN, M. & GARWOOD, R. & COATES, M. 2013 Deltoptychius: investigating the roots of the chimaeroid cranial condition. AbstractIntegrative and Comparative Biology, 53 (Suppl. 1): E43
DEPEW, M.J. & COMPAGNUCCI, C. & FISH, J. & DEBIAIS, M. & COOLON, M. & BERTOCCHINI, F. & CASANE, D. & MAZAN, S. 2013 Pattern and Polarity in the Development and Evolution of the Gnathostome Jaw: Both Conservation and Heterotopy in the Branchial Arches of the Shark, Scyliorhinus canicula. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E51
FISH, F.E. & NEAL, D. & FONTANELLA, J.E. & DINENNO, N. & GABLER, M.K. 2013Flow patterns associated with swimming motions of benthic and pelagic batoids as visualized with DPIV. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E69
GABLER, M.K. & FISH, F.E. & BENESKI, J.T. & MULVANY, S. & MOORED, K.W. 2013The hydrodynamics of ground effect in relation to the head shape of the spotted eagle ray. Abstract-Poster Integrative and Comparative Biology, 53 (Suppl. 1): E286
GARDINER, J.M. & ATEMA, J. & HUETER, R.E. & MOTTA, P.J. 2013 Sensory switching in sharks: the role of multimodal stimuli in prey tracking and capture. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E74
HUBER, D.R. & NOAKER, D.E. & STINSON, C.M. & TATE, E.E. & ANDERSON, P.A. & BERZINS, I.K. 2013 Etiology of spinal deformities in captive sandtiger sharks Carcharias taurus. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E97
KOLPAS, A. & FISH, F.E. & MEADE, A. & DUDAS, M.A. & MOORED, K.W. 2013Mathematical analysis of three-dimensional open water maneuverability by mantas (Manta birostris). Abstract-Poster Integrative and Comparative Biology, 53 (Suppl. 1): E312
LASH, J.L. & SHERMAN, R. L. 2013 A Preliminary Comparative Study of Vascular Corrosion Casts of the Spiral Intestine of Select Acipenseriformes and Elasmobranchs. Abstract-Poster Integrative and Comparative Biology, 53 (Suppl. 1): E315
MARSHALL, H.M. & BRILL, R. & BUSHNELL, P. & SKOMAL, G. & BERNAL, D. 2013Comparison of fishing-induced stress response and post-release mortality between sandbar (Carcharhinus plumbeus) and dusky (Carcharhinus obscurus) sharks. AbstractIntegrative and Comparative Biology, 53 (Suppl. 1): E137
NOWINOWSKI, I. & BALABAN, J. & WILGA, C. 2013 Shape Changes in the Hyoid Arch of Four Shark Species. Abstract-Poster Integrative and Comparative Biology, 53 (Suppl. 1): E344
PAIG-TRAN, E.W.M. & SUMMERS, A.P. 2013 A filtration mechanism for large vertebrate suspension feeders: fluid flow and filter anatomy in the devil rays (Mantas and Mobulas). Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E160
PORTER, M.E. & DIAZ, C. & LONG, J.H. 2013 Extracellular matrix dominates the mechanical properties of shark vertebral columns in bending. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E170
RAMSAY, J.B. & WILGA, C.D. 2013 Preorbitalis and quadratomandibularis function during feeding in little skates, Leucoraja erinacea. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E175
RYGG, A.D. & COX, J.P.L. & ABEL, R. & WEBB, A.G. & SMITH, N.B. & CRAVEN, B.A. 2013 The Hydrodynamics of Olfaction in the Hammerhead Shark (Sphyrna tudes). Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E187
SICILIANO, A.M. & PORTER, M.E. & KAJIURA, S.M. 2013 Are you positive? Discrimination between poles of electric fields by elasmobranch fishes. AbstractIntegrative and Comparative Biology, 53 (Suppl. 1): E198
SODA, K.J. & SLICE, D.E. & NAYLOR, G.J.P. 2013 The use of geometric morphometrics and artificial neural networks to identify teeth to species in requiem sharks (Carcharhinus sp.). Abstract-Poster Integrative and Comparative Biology, 53 (Suppl. 1): E372
WEBB, J.F. & GILLIS, J.A. 2013 Lateral Line Morphogenesis in Chondrichthyan vs. Osteichthyan Fishes: New Perspectives on an Old Problem. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E223
WEN, L. & LAUDER, G. & WEAVER, J.C. & KOVAC, M. & WOOD, R.J. 2013Hydrodynamics of Self-propelling Flexible Synthetic Shark Skin Membranes. AbstractIntegrative and Comparative Biology, 53 (Suppl. 1): E223
WILGA, C. & SAKAI, S. 2013 Strain in the Hyomandibular Cartilage of Elasmobranchs. Abstract Integrative and Comparative Biology, 53 (Suppl. 1): E225


HODNETT, J.-P.M. & ELLIOTT, D.K. & OLSON, T.J. 2013 A new basal hybodont (Chondrichthyes, Hybodontiformes) from the Middle Permian (Roadian) Kaibab Formation, of northern Arizona. New Mexico Museum of Natural History and Science, Bulletin, 60: 103-108
ITANO, W.M. 2013 Abnormal serration rows on a tooth of the Pennsylvanian Chondrichthyan Edestus. New Mexico Museum of Natural History and Science, Bulletin, 60: 139-142



New Understanding of Rare White Shark Movement Around Hawai'i

Apr. 18, 2013 — A study just published in theJournal of Marine Biology sheds new light on the relatively rare but occasionally recorded presence of white sharks in waters surrounding the Hawaiian Islands, and suggests a new method to help distinguish between white sharks and close relatives, such as mako sharks. The paper, titled "Occurrence of White Sharks in Hawaiian Waters," was written by Kevin Weng of the University of Hawai'i at Mānoa's School of Ocean and Earth Science and Technology (SOEST) and Randy Honebrink of the Hawai'i DLNR Division of Aquatic Resources (DAR).

According to William Aila, chairperson of the State of Hawai'i Department of Land and Natural Resources, "This study is valuable in that it provides a better understanding of the biology and behavior of white sharks, which is very useful for management purposes. White sharks were caught by pre-contact Hawaiians, and their teeth used in weapons and other implements. But in many ways they continue to mystify us today."
Satellite tracking studies have previously shown that Hawai'i's white sharks are migrants from population centers off California and Mexico. A relatively small proportion of those West Coast sharks migrate all the way to Hawai'i, which is why they are so rarely seen.
The authors reviewed all available sources of information relating to white sharks in Hawai'i, including newspaper accounts of shark attacks, shark control program catch records, photos and videos from various sources, and satellite tracking data. Only data that could be confirmed as pertaining to white sharks was included in the analysis. In cases where information was insufficient for positive species identification, the sightings were eliminated.
According to Dr. Weng, "We learned that white sharks occur in Hawai'i across a broader part of the annual cycle than previously thought -- we recorded observations from every month except November. This is important for our understanding of white shark life history and population."
Since all records of white sharks in Hawaiian waters are of individuals larger than 3.3 meters (10.8 feet), and no juveniles have ever been reported, there is no evidence of white sharks being residents or pupping there.
Scientists have learned a great deal about the migratory patterns of white sharks in the Eastern Pacific since the advent of satellite tracking, but important questions remain. "Our satellite tracking studies have been conducted in places where we can get very close to the animals -- seal colonies -- but this means that we may be sampling a subset of the population, and thus obtaining biased results," said Weng. "It is possible that there are individuals that do not aggregate around seal colonies."
"Male and female white sharks have different migration patterns," explained Weng. "Males have been recorded in Hawai'i from December through June, but females have been observed here all year round." Female white shark visits to Hawai'i may be related to a two-year reproductive cycle, in which they return to coastal aggregation sites off California and Mexico on alternating years. That leaves them with more time to spend in Hawai'i, where warmer water temperatures may speed up fetal development. Our results are consistent with a very recent paper by Domeier and Nasby-Lucas in the journalAnimal Biotelemetry.
Misidentification of similar looking sharks, such as makos, has been a recurring problem. A recent example was the sighting of a shortfin mako shark off Ka'ena Point, O'ahu, on Jan. 12, 2012. This sighting, captured on a video that "went viral," was reported around the world as a white shark by the news media, an error that continues to this day.
This study proposes a simple method to help distinguish between the two species based on the shape of the head. Mako sharks have a more acute head shape than white sharks. Since many sightings only obtain photographs of the head, this method should be helpful for situations with limited information and no specimen.

Journal Reference:
1.     Kevin Weng, Randy Honebrink. Occurrence of White Sharks (Carcharodon carcharias) in Hawaiian Waters.Journal of Marine Biology, 2013; 2013: 1 DOI:10.1155/2013/598745

This is a white shark in water near Guadalupe, Mexico, which is one of the source areas for sharks that visit Hawai'i. (Credit: Kevin Weng, UHM.)

Shark Embryos Devour Each Other in the Womb: Sibling Rivalry at its Finest

First Posted: May 01, 2013 09:24 AM EDT

Talk about sibling rivalry. Sand tiger shark embryos actually cannibalize their littermates while still in the womb. Now, new research reveals why sharks are such bad brothers. (Photo : Flickr/Brian Gratwicke )
Talk about sibling rivalry. Shark embryos actually cannibalize their littermates while still in the womb; the largest one eats all but one of its siblings. Now, new research reveals why sharks are such bad brothers.
In order to find out why this phenomenon occurs, researchers analyzed shark embryos found in sand tiger sharkswhich, despite their name and their in utero behavior, are a non-aggressive species. They are only known to attack humans when bothered first. In order to better understand these embryos, the scientists examined them at various stages of gestation. They discovered that the later the pregnancy is, the more likely the remaining shark embryos had just one father.
So what does that mean exactly? Before now, researchers weren't sure whether females mated with just one partner or with multiple partners. After a bit of DNA testing, researchers discovered that litters that possessed five to seven embryos had at least two fathers. It's possible that females mated with even more males, though; at the start of gestation, there can be as many as 12 littermates. It could be that the other littermates with different fathers had already been eaten.
The cannibalization itself is actually a useful strategy for the sharks. It allows the two remaining babies to grow large enough to be relatively unbothered by predators once they're actually born. What is more surprising, though, is the fact that the two sharks are usually full siblings as opposed to half siblings. This suggests that the largest embryo actually targets other embryos that are from other fathers.
"Basically, that loser father ultimately provided food for a rival male," said co-author Demian Chapman, a marine biologist at Stony Brook University, in an interview with LiveScience.
Currently, it's still a mystery as to what makes one father's embryos successful over another's. Yet the researchers do have some theories. It's possible that the embryos from the first male to fertilize the female simply get bigger first and devour their littermates.
The strategy could actually encourage females to select good mates. Since shark mating involves violent biting, this cannibalism may allow females to avoid resisting and being too picky about what males she mates with while still ensuring high-quality offspring.
The findings are published in the journal Biology Letters.
CHAPMAN, D.D. & WINTNER, S.P. & ABERCROMBIE, D.L. & ASHE, J. & BERNARD, A.M. & SHIVJI, M.S. & FELDHEIM, K.A. 2013 The behavioural and genetic mating system of the sand tiger shark, Carcharias taurus, an intrauterine cannibal. Biology Letters, 9 (3): 20130003