Family Megachasmidae

Family Megachasmidae1st specimen found in 1976 off Oahu, HI

Castro book written 1982, taxonomy not yet assigned

although little known about biology, still high profile species

Family Megachasmidae37 total recorded sightings

Family Megachasmidae#6 caught in drift net off Dana Point, CAonly one tracked and photographed alive

Taxonomycurrent taxonomy: (has been debated since discovered)

Order Lamniformes (Mackerel sharks) Family Megachasmidae (Megamouth shark)

Megachasma pelagios

mega= great chasma= cavepelagios= of the sea

probably most ancestral lamniform

MorphologyCharacteristics shared with order:

2 spineless dorsal fins, anal fin

cylindrical body with a short snout

lack nasoral groove and barbells (Order Orectolobiformes)

small spiracle behind eye

mouth extends behind eye

MorphologyCharacteristics shared with order:

MorphologyDistinguishing characteristics:large terminal mouth (not ventral)*

~ 50 rows of tiny, hooked teeth, 3 rows functional

large gill rakers

white “upper lip”- feeding? conspecific detection?

dark spots on lower jaw

no pigment cells on ventral side

soft body, poorly calcified skeleton, soft, loose skin,and soft fins

MorphologyCharacteristics shared with order:

Morphologywhite “upper lip”

MorphologySize: TL > 500cm

smallest recorded:190cm (male), #9, Brazil

MorphologySize: TL > 500cm

largest recorded:570cm (female), #37, Japan

MorphologySize: TL > 500cm

largest recorded:570cm (female), #37, Japan

largest reported:~ 700cm!!

Habitat and Distributiondetails unknown

oceanic, coastal and offshorecontinental shelf: 5-40moffshore: caught in very deep water, 8-166m

probably worldwide in tropics and subtropics, most specimens from w. Pacific

Habitat and Distribution

Behavioronly 2 observations to provide behavior information

#6 (CA), #13 (Indonesia)

probably low mobility due to soft body and fins

probably undergo vertical migrations following foodshark #6 tracked for 2 days

deep depths during day

midwater/shallow at night

Reproductionsize at maturity unknown

males: #2 (449cm TL) and 6 (494cm TL)- mature females: #7 immature at 471cm TL

#12 mature at 544cm (only mature female)

right ovary had a large number of eggs

Reproductionprobably viviparous and oophagous

ovary structure similar to other lamniforms

probably mate in fall off coast of SoCal (October/November)males #2,6- claspers suggested recent mating activity

male #6- wounds on jaw similar to other shark species’ mating wounds

Prey/Feeding Habits1 of 3 of the largest, filter feeding sharks

stomach contents: primary prey euphasiid shrimp (krill) some also with copepods and jellyfish

details of feeding mechanism unknown

filter feeding probably evolved independently from others (morphological differences)

more likely evolved from ancestral Odontaspididae

Prey/Feeding Habits

Prey/Feeding Habits

Predators and Parasitessperm whales- seen attacking shark #13 (Indonesia)

orcas also seen attacking white shark at Farallon Isl. (CA) within the same year

new info on shark/whale relationships?

cookie cutter shark- scars on almost every specimen

other parasites- similar to other sharks; copepods, cestodes

Population statusHuman importance:

None

too rare to be harvested

Conservation:Data Deficient on IUCN Redlist

Population statusHuman importance:

None

too rare to be harvested

Conservation:Data Deficient on IUCN Redlist

Literature Cited and Selected WorksCastro, J. 1983. The sharks of North American waters. Texas A&M Univ. Press, College Station. 180p.

Compagno, L.J.V. 2000. Megachasma pelagios. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 14 October 2007. Compagno, L., M. Dando, and S. Fowler. 2005. Sharks of the world. Princeton University Press, Princeton, NJ. 368p. Ito, H., M. Yoshimoto, and H. Somiya. 1999. External brain form and cranial nerves of the

megamouth shark, Megachasma pelagios. Copeia 1999(1): 210-213.

Martins, C. and C. Knickle. 2006. Megamouth shark. Florida Museum Natural History, Icthyology Department. University of Florida. < http://www.flmnh.ufl.edu/fish/>. Downloaded on 14 October 2007.

Nelson, D.R., J.N. McKibben, W.R. Strong, Jr., C.G. Lowe, J.A. Sisneros, D.M. Schroeder, and R.J. Lavenberg. 1996. An acoustic tracking of a megamouth shark, Megachasma pelagios: a crepuscular vertical migratory. Env. Biol. Fishes 49: 389-399.

Shimada, K. 2007. Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae). J.

Vert. Paleontology 27(2): 512-516.