Hiu Super Langka Ditemukan, dan Dimakan…

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Nelayan dari Filipina ini pasti akan terperangah jika saja mereka sadar ikan yang mereka makan adalah species hiu yang amat sangat langka.

Biasa disebut sebagai Megamouth, sepanjang sejarahnya hiu super langka ini hanya pernah ditemukan sebanyak 41 kali. Salah satunya adalah yang sudah dimakan oleh nelayan itu.

Menurut media setempat, nelayan tersebut sebenarnya hendak mencari ikan sarden ketika kailnya memerangkap ikan berdimensi berat setengah ton dan panjang empat meter.

Juru bicara WWF mengatakan hiu itu dipotong-potong, kemudian dimasak dalam santan seperti kebiasaan penduduk lokal.

Sejauh ini hiu megamouth hanya berhasil ditemukan delapan ekor di perairan Filipina, sisanya adalah di Jepang, Brazil, Meksiko, Afrika Selatan, Australia, dan di perairan California.

berikut penemuan megamouth di seluruh dunia !!!

Photo/ID	Date	Location	Sex	TL (m)	M (kg) (CF)	PCL (m)	Comments and Reference In Mass column, CF = condition factor = M/TL^3
#1 holotype	15 Nov 1976	Oahu, Hawaii (21o 51' N, 157o 46'W)	M	4.460		3.091 69.3% TL	Adult male. Taylor, Compagno & Struskaker (1983).
#2	29 Nov 1984	California	M	4.490			Lavenberg and Seigel (1985).
#3	18 Aug 1988	Western Australia	M	5.150		3.430 66.6% TL	Mature male. Berra and Huchins (1990).
#4	23 Jan 1989	Hamamatsu, Shizuoka, Japan	M	~4			Nakaya (1989).
#5	June 1989	Yaizu, Shizuoka, Japan	F*	~4.9			Miya et al. (1992). *Most likely a female (John Morrissey)
#6	21 Oct 1990	California	M	4.9			Fitted with two ultrasonic transmitters and tracked for two days. Lavenberg (1991). Additinal photos by Tom Haight: #1; #6; #20.
#7	29 Nov 1994	Hakata Bay, Fukuoka, Japan (34o 40' N, 130o 50'E)	F	4.710		3.136 66.6% TL	First ever female (but see #5), immature. Castro et al. in Yano, Morrissey, Yabumoto, and Nakaya, eds. (1997).
#8	4 May 1995	Senegal	M	~1.8			Immature male. Séret (1995).
#9	18 Sep 1995	Brazil	M	1.9			Immature male. Amorim et al. (1995, AES abstract); F.Amorim, A.F., C.A. Arfelli, & J.I. Castro (2000).
#10	30 Apr 1997	Mikizaki, Owase City, Japan	F	5.44			150 m deep, Yano et al. (1999).
#11	20 Feb. 1998	Cagayan de Oro, Philippines	M	5.49			M. Amorim, A.F., C.A. Arfelli, & J.I. Castro (2000).
#12	23 Apr 1998	Osawe, Honshu, Japan	F	5.20			Amorim, A.F., C.A. Arfelli, & J.I. Castro (2000).
#13	30 Aug. 1998	Manado, North Sulawesi, Indonesia	F	~5.0			Observed being attacked by sperm whales (Pecchioni P. $ Benoldi C. 1999; Amorim, A.F., C.A. Arfelli, & J.I. Castro 2000).
#14	1 Oct. 1999	San Diego, California	F	5.18			On October 1, 1999, a megamouth shark (female, aprox. 17 ft) was caught in a drift gillnet and released alive in good condition. A National Marine Fisheries Service observer was aboard the commercial swordfish vessel, 30 miles west of San Diego, California. The observer was able to take four color photographs including one of the upper jaw (white lip) / lower jaw (dark spots on white chin) and others of the underside of body (no visible claspers). Water depth at this location is 190 fms. and water temperature was 67.2 F. This is the third (November 1984, October 1990) megamouth caught off Southern California in a drift gillnet targeting swordfish. Don.Petersen@noaa.gov
#15	19 Oct. 2001	California	M	~5.5 FL			On October 19, 2001, another Megamouth shark (male, approx. 18 ft. fork length) was caught in a drift gillnet and released alive in good condition. A U.S. National Marine Fisheries Service observer was aboard the commercial swordfish vessel, approx. 42 miles northwest of San Diego, California. The observer was able to collect a tissue biopsy and take many color photographs including one of the upper jaw with white lip and lower jaw with dark spots on a white chin. The observer also noted the presence of claspers. Water depth at this location is 460 fms. and the sea surface temperature was 65.8 F. This is the fourth (November 1984, October 1990, October 1999) Megamouth shark caught off Southern California in a drift gillnet targeting swordfish. If you are interested in seeing the photos, please go to the following web site: http://swr.nmfs.noaa.gov/mega15.htm Don Petersen
#16	18 Jan 2002	East Indian Ocean (2o 17.9' S, 88o 12.7'E)	M	2.35	~120 (9.2)		Tuna purse seine, discarded (John Morrissey). One more composite jgp. All photos copyright Sopana Boonyapiwat. For more information see http://www.flmnh.ufl.edu/fish/Sharks/Megamouth/Mega16.htm
#17	20 Apr 2002	Natures Valley, Western Cape Province, South Africa (33o 59' S, 23o 34'E)	F	~4			On 20 April 2002, a large shark was stranded at Natures Valley (33o 59' S, 23o 34'E) in the Western Cape Province, South Africa. Initial reports suggested that it was a whale shark, but subsequent reports and digital photographs confirmed that it was a megamouth, Megachasma pelagios. Dr Vic Cockcroft of the Centre for Dolphin Studies collected it from the beach to ensure that it was not washed out to sea again. It is the first record of this species in South Africa and the Western Indian Ocean and is the 17th discovered world-wide since its discovery off Hawaii was announced in 1976. It was iced early the next morning and collected by Dr Malcolm Smale and Matt Dicken and brought back to the Port Elizabeth Museum. It was placed in a scientific freezer and frozen to -20o C. A preliminary examination showed that the animal, approximately 4m long and female was in reasonable condition, but the skin was scuffed and there was some damage to the fins. It will be examined, measured and dissected by Drs Malcolm Smale (Port Elizabeth Museum) & Leonard Compagno (South African Museum) in early May. Various samples, including tissues for DNA analyses will be saved for future research. Taxidermists will make a mould of the animal for educational displays in museums. Elasmo-L posting by M. Smale on 23 April 2002.
#18	06 Jan 2003	Philippines		~4.97			#18 was caught in Philippines . More info at http://www.sharkmans-world.com and http://www.flmnh.ufl.edu/fish/Sharks/Megamouth/mega.htm
#19	26 May 2003	California		6.1-7.6	~5000		#19 reportedly sighted in California. More info at http://www.SHARKMANS-WORLD.ORG and http://www.flmnh.ufl.edu/fish/Sharks/Megamouth/mega.htm
#20	03 Jul 2003	Hualien Province Taiwan	M	~2.5	~490? (31.4)		The shark was caught on July 4, 2003 in Hualien Province, Taiwan, 800 meters off the coast. It was about 2.5 meters long and allegedly weighed 490kg. Victor Lin identfied claspers in the original photo so it`s a male. Victor Lin translated a newspaper clipping about this mystery fish dated 4 July 2003. Po-Feng Lee received pictures from Mr. Lee about this megamouth shark landing in east Taiwan. Thanks.
#21	07 Aug 2003	Omaezaki, Sizuoka Japan	M	4.30			Omaezaki, Sizuoka Japan; 7-August-2003; 430 cm; Tokai University (taxidermy).
#22	08 Mar 2004 0700h	Off Peru /Equador Lat 02 deg 54.374' Long 81 deg 14.858'	M	4.20			Information from Miguel A. Romero sent to Otto Gadig on 26 March 2004: Captured in northern Peru near the border with Ecuador. May be the first record in the eastern South Pacific. Miguel is writing a note for the SSG website. (Add URL once it's up.)
#23	13 Mar 2004	Gapang Beach, northern tip of Sumatra, Indonsia	M	1.767	13.82 (2.50)	1.144 (64.7 %TL)	I think there can be no doubt anymore that the shark specimen that washed ashore here today on Gapang Beach, less than 30 meters away from our doorstep, literally, is the rare shark species Megachasma pelagios. Thanks for the attention so far, Ton Egbers. Additional morphometrics: Caudal length 62 cm, Pectorals 33 cm Additional photos: #243;. #244; #249; lumbalumba diving center for more info and pics. White, Fahmi, and Kurnaen (2004). A juvenile megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae) from Northern Sumatra, Indonesia. The Raffels Bulletin of Zoology 52(2): 603-607. (5MB PDF)
#24	19 Apr 2004	Tokyo Bay near Ichihara City	F	5.63	1215 (6.8)		A rare megamouth deep-sea shark is displayed after being discovered in Tokyo Bay near Ichihara City, in this handout photo released by the Natural History Museum and Institute, April 22, 2004. The shark measures 5.63 meters (18.47 feet) in length, 2,679 lbs in weight, and its mouth is 1.15 meters (3.77 feet) in diameter, which the museum says is the world's largest of its kind yet reported. Thanks to Alex Buttigieg for posting information
#25	23 Apr 2004	Off Ajiro, Shizuoka Japan	F	~4.9 5.5?	>1000?		Megamouth Shark #25 Caught Off Ajiro, Shizuoka Japan April 23, 2004 Sources of Information: Masami Furuta Toba Aquarium Newspaper article in Japanese mentions TL = 5.5 and 5.6 m and weight of "1", implying over 1 ton (V. Lin).
#26	4 Nov 2004 5 pm	Barangay Namocon, Tigbauan, Iloilo, Philippines	F	5.04	~1000 (7.8)		From David Greenfield #24 is now at SEAFDEC FishWorld, SEAFDEC Aquaculture Department,Tigbauan, Iloilo, Philippines. Stranded alive at Barangay Namocon, Tigbauan, Iloilo, Philippines at 4 PM and died at 10 PM. The Manila Bulletin Online has complete story. Additional photo and other details.
#27	23 Jan 2005	off Kiseicho Nishiki, Mie, Japan	F	5.28			Megamouth Shark #27 Captured In Purse Seine off Japan Sources of Information: Masami Furuta Toba Aquarium A megamouth shark was captured with a purse seine set off the coast of Kiseicho Nishiki, Mie, Japan. The purse seine was set at a depth of 200 meters around 5:00am on January 23, 2005. We received a phone call informing us of the possible catch of a megamouth shark. We went to the fishing port but by the time we arrived, the megamouth was already dead. This megamouth was a female with a body length of 528 centimeters. The megamouth was hoisted onto a truck with the assistance of a lift and was transported to the Toba Aquarium where it was placed in a freezer. In the near future, we will taxidermy this animal for display at the aquarium.
#28	30 Jan 2005	Cagayan de Oro City, Island Mindanao, Philippines	F?	4.17	~1000 (13.8)		Megamouth found dead in Cagayan de Oro BenCyrus G. Ellorin / MindaNews / 30 January 2005. Thanks to Alex Buttigieg for update. For details and photos click here.
#29	~ 25 Apr 2005	Hualien, Eastern Taiwan			580		First of four was caught about a week befor the second one on May 2, 2005.
#30	02 May 2005	Hualien, Eastern Taiwan			580		Second one was caught on May 2. All four were purchased by the same fish processor who said they were all the same species (pretty distinctive). The first two were both 580 kg each. They were sold for consumption.
#31	04 May 2005	Hualien, Eastern Taiwan	F	4.8 PCL?	689 (6.2)		Third one of four: This female megamouth shark was caught in Hualien, central eastern Taiwan. The carcass is now in the hands of Dr. Kwung-Tsao Shao at the Academia Sinica. The specimen was in excellent shape and on ice - never frozen. It wasn't out in the sun for more than minutes. It was caught about 2 am and was still alive. Died about an hour later. It was landed at port at about 9:30 am on May 4 (Taiwan time). Thanks for information and photos to Shih-Chu Yang and John Y. Wang and Victor Lin.
#32	05 May 2005	Hualien, Eastern Taiwan	F	5.7 PCL?	807 (4.4)		Fourth one of four: Was sold directly to Kwung-Tsao Shao (Academia Sinica) and was shipped to the Taipei Zoo for dissection (as was the thrid specimen).
#33	05 June 2005	Hualien, Eastern Taiwan	M	~3.5-4.0	400-500		The fishermen in Hualien got another megamouth...I guess it's #33? Because it was Sunday and the fishery office isn't open, length and weight were not taken at the dock buy according to the dealer the weight was 400~500kg and closer to 500kg. . I have asked the fisherman to save some vertebra and muscle tissue for me. There was an earthquake the day before, and this megamouth shows up. Just like last time. according to the dealer is 400~500kg and closer to 500kaccording to the dealer is 400~500kg. This shark was in bad shape when Victor Lin rushed to the dock two days after capture. The tail was broken when hung onto the boat. The first half was about 1.75 m and tail end about 178cm . The whole right upper jaw was gone. It probably "slipped" into the sea when they hooked the shark and broke the jaw.
#34	26 Jan 2006	Off Bayawan coast, ~100 km south of Dmaguete City, Central Visayas, Philippines island of Negros		~5	~1000		Hundreds of residents of Bayawan City in southern Oriental Negros woke up yesterday to the sight of the biggest fish they ever saw following the accidental capture by fishermen of a rare five-meter megamouth shark. The shark, which was estimated to weigh one ton, was found by fishermen struggling to free itself from a net just off the Bayawan coast, some 100 kilometers south of Dumaguete City. Thanks to Alex Buttigieg for information and BenCyrus G. Ellorin for correction on location.
#35	12 Mar 2006	Macajalar Bay in Northern Mindanao, Philippines	F	2.26	60-80 (5.2-6.9)		BenCyrus G. Ellorin: I have checked with our counterpart in the Bureau of Fisheries and Aquatic Resources and was informed that Megamouth 35 is confirmed. Was dead when i was braught ashore after being entangled ina fisherman's gill net. We are still verifying the other one, it was caught? some 100kilometers from here in Medina town in Gingoog Bay where whale sharks are known to inhabit. Thanks to Alex Buttigieg for additonal information.
#36	23 March 2006	Off China Sea		4.7	650 (6.3)		Thanks to Victor Lin for photo and information.
#37	2 May 2006	Sagami Bay, Yugawara.(Kanagawa prefecture) Japan	F	5.7			It was caught by a fixed shore net on May 2nd, 2006. in Sagami Bay, Yugawara.(Kanagawa prefecture). It was alive when it was found in the net, and NHK's camera crew shot a film of it. Then it was pulled up but it was already dead. It was measured at 5.7m. Meg 37 was a female and is going to be displayed at the Keikyu Aburatsubo marine park ( in Kanagawa) Japan. Thanks to Alex Buttigieg for information and photo.
#38	16 Nov 2006	Tortugas Bay, West Coast of Baja California, Mexico	F	2.149	27 (2.7)		Megamouth # 37 was caught in a commercial shark gill net in the waters near Tortugas Bay, off the west coast of the peninsula of Baja California, México. The specimen was a juvenile female with a total length of 214.9 cm. After the specimen is preserved, it will be on public exhibit in the Regional Fisheries Center of Ensenada prior to possibly moving it to the Natural History Museum in Mexico City. (Text from http://www.flmnh.ufl.edu/fish/sharks/megamouth/mega37.html)
#39	July 2007	off Japan		~4	450 (7.0)		I just found news about a megamouth shark caught off Japan. Attached is photo of a 4m, 450kg megamouth caught off Japan in July, 2007. Victor Lin, personal communication.
#40	around 30 June 2008	off Taiwan	?	?	~200		The only information I was able to collect for this megamouth is its weight and capture date (200 kg+; around June 30). No length, sex, photo, nor other data. The fisherman (dealer) who reported it to me was the same one who bought the #33 megamouth, so I believe it to be authentic. Victor Lin personal communication.
#41	10 July 2008	off East Taiwan	?	5.0-5.5?	870 (7.0-5.2)		There was another megamouth caught off East Taiwan on July 10. This one was big, claimed to be 9 m in the news ( more likely 5.0~5.5m judging from the picture) and it was actually weighed at 870kg. Victor Lin personal communication.
#42	30 March 2009	Eastern Coast of Burioas Island in Donsol, Sorsogon province, central Philippines	?	4.0	500 (7.8)		Rare shark caught in Donsol--WWF MANILA, Philippines— (UPDATE) A rare shark was caught along the eastern coast of Burias Isle in Donsol by fishermen trawling for mackerel on March 30, officials from the World Wide Fund (WWF) for Nature said. Thanks to Alex Buttigieg for URL. Another account. Thanks to Bob Lea for URL.

THE MEGAMOUTH

The Megamouth shark is one of the greatest fish discoveries to have emerged in the 20^th Century – a fish that grows to at least 5 ½ m (18 ft) going undiscovered until 1976! Moreover, this first discovery was pure accident! Some 26 miles (42 km) northwest of the Hawaiian island of Oahu in November 1976, the 4 ½ m (14 ½ ft) adult male Megamouth became entangled in a parachute sea anchor of the US Navy vessel AFB-14. It then took eight years and 14 days for the second specimen -- a similar sized male -- to become trammelled in a swordfish gillnet off Santa Catalina, South West California. We now know of 35 confirmed individuals of this enigmatic shark worldwide: 15 males, 17 females and the remaining three of undetermined sex (although one of these – caught in Suruga-Wan Bay during June 1989 – was probably a female). There are also a further two credible but unsubstantiated sightings of Megachasma, both off Dana Point in California (one in October 1990 and the other in May 2003). The most recent capture came from Sagami Bay in Japan's Kanagawa prefecture in May 2006, when a 5.7m (18.7 ft) female became entangled in a fixed shore net.

The largest specimen on record so far is the May 2006 capture from Japan. Prior to the latest discovery, the title for largest Megamouth was tied between numbers 11 and 15. Specimen 11 was caught in the Philippines during February 1998, while individual 15 became entangled in a drift-gill net about 42 miles (67 km) northwest of San Diego, California in October 2001. Both individuals measured almost 5 ½ m (18ft). Conversely, the smallest specimen hitherto recorded was found recently, washed up on a beach in Sumatra, Indonesia during March 2004 (photos of which adorn this page). On the afternoon of 13^th March 2004, Syukur stumbled across an unusual fish lying in shallow water on the Gapang Beach, close to his house. Realizing that this was something special, Syukur and his friend, Ton Egbers, collected the recently dead shark, placed it on a concrete slab and took some photographs. It was not long before the discovery of the World’s 20^th Megamouth shark began causing a stir – not only was it the 20^th, it was arguably the smallest ever recorded, a male measuring only 1.77m (5 ¾ ft)*. Prior to this, the smallest specimen was a 1.8m (6ft) individual of unknown sex caught at Dakar in Senegal (North West Africa) in May 1995. However, the Senegal specimen was discarded before any photos or tissue samples were taken – Egbers and a friend (Rama) had the presence of mind to pack and freeze their find, which is now awaiting a new home in a suitable museum.

Despite the first discovery having been made in 1976, the first paper describing and officially classifying this new shark did not make it into the scientific literature until July 1983 (in the Proceeding of the California Academy of Sciences) – a gap of almost seven years from discovery to description! According to ReefQuest Director Aidan Martin, the paper’s publication in 1983 was only spurred by a practical joke played on the principle author (Leighton Taylor) by two of his colleagues! Anyway, the paper made it into print, with co-author and elasmobranch taxonomy guru Professor Leonard Compagno, currently at the South African Museum, erecting a new family and genus within the Lamniform (Mackerel shark) order.

Compagno considered that the differences in Megamouth’s teeth and skull morphology (form), when compared to the other lamnoids (Great White, Mako, Thresher, Basking shark etc.), were sufficiently different to warrant placement in its own family, the Megachasmidae. Compagno called this mysterious creature Megachasma pelagios that, roughly translated, means “the great open-mouthed shark of the open sea”. However, there was some debate as to whether the distinctions Compagno had used to separate the Megamouth from other extant (living) lamnoids were sufficient to justify placing it in its own family. The primary objection to Compagno’s proposed phylogeny came from Dr. John Maisey, a palaeontologist at the American Museum of Natural History in New York. In a short paper to the journal Copeia in 1985, Maisey suggested that – based on five lines of morphological evidence – Compagno’s decision to place the Megamouth in its own family was unjustified.

Maisey considered that Megachasma was actually a sister taxon of the Basking shark (Cetorhinus maximus) -- in other words, the Megamouth and Basking sharks were more closely related to each other than any of the other mackerel sharks -- and, as such, should be placed in the Cetorhinidae family. Compagno repudiated this, counter-arguing each of Maisey’s lines of evidence in a 1990 paper. In this paper (published as part of the NOAA Technical Report, Elasmobranchs as Living Resources), Compagno concluded that the Megamouth was the sister-group of the Alopiidae (Thresher sharks), Cetorhinidae and Lamnidae (the family containing the Makos, Porbeagle, Salmon and Great White sharks). Compagno also reported that, based on the jaw mechanism and morphology, this shark probably uses pharyngeal suction (i.e. it expands its throat, causing a vacuum that sucks hapless prey into its mouth) to capture prey, rather than the active (swimming) filter-feeding seen in the Whale and Basking sharks. Compagno noted that the teeth of the Megamouth are similar to that of Megascyliorhinus (an extinct Collared Carpet shark – family Parascyllidae), while its skull bares similarities to Squalicorax (an extinct Lamnoid shark, sometimes referred to as a “Crow Shark” because of its habit of scavenging). However, these similarities are, on their own, insufficient to do little more than speculate on the possible fossil relatives of Megachasma.

The taxonomy of this shark was finally subjected to molecular phylogenetics (using DNA to infer relatedness) with the discovery of the seventh specimen, a 4.71m (15 ½ ft) female found washed ashore in Hakata Bay, Japan in November 1994. The specimen was rushed to the Marine World complex in Fukuoka (Northwest Japan), where a host of scientists performed a painfully methodical dissection, collected tissue samples and then stuffed the carcass with blankets, sewed it up and put it on display. From this single specimen, a collection of 21 scientific and technical papers was spawned, published as a single volume (Biology of the Megamouth Shark, 1997) representing the most complete reference on the Megamouth to date. In this volume Dr. John Morrissey at Hofstra University in New York and two colleagues – Katherine Dunn (at Texas A & M University) and Francesco Mule (also at Hofstra) – used samples of skeletal muscle to uncover the taxonomic relationships of the Megamouth. Morrissey et al. found that, not only is Megachasma the most primitive living Lamniform, but it is also not the sister taxon of the Basking shark (rejecting Maisey’s hypothesis and supporting Compagno’s inference that filter-feeding had evolved independently in this shark). Subsequent genetic analysis on other specimens (most notably by Dr. Gavin Naylor) has corroborated Morrissey et al.’s findings, retaining the placement of the Megamouth in its own – monotypic – genus (Megachasma) and family (Megachasmidae).

An interesting paper from this anthology by Yutaka Itabashi at the Hokkaido University in Japan and two colleagues (Atsuko Yamaguchi at Tokyo University and Kazuhiro Nakaya at Hokkaido) looked at the composition of liver oil from this specimen, reporting that 90% of the lipids (fats and oils) were triacylglycerols (the form in which most fats are stored in the human body). This suggests that the shark is not a deep-sea species, but surface dweller. Successive papers have since revealed that this shark inhabits waters from the surface down to almost 170 m (about 560ft). A study by a seven-strong team of researchers, led by the late Donald Nelson, tracked Megamouth number 6 – a 4.94m (16ft) male that became tangled in a gillnet off Dana Point in California during October 1990 – along a 38 ½ mi (62 km) path for 50.5 hours (just over 2days) using acoustic transmitters. The biologists found that the shark spent the daytime at depths of between 120 and 166 m (394 – 545ft), migrating surface-ward to spend the nights in shallower water, between 12 and 25 m (39 – 82ft). The researchers calculated that the shark swam at an average speed of 1.5 to 2.1 km per hour (about 1 to 1 ½ mph), which fits reasonably well with swimming speeds calculated for other plankton feeders such as the Basking shark (Cetorhinus maximus) and Whale shark (Rhincodon typus), but is slower than the average reported for larger, predatory sharks such as the Great White (Carcharodon carcharias).

Based on the information returned by Nelson et al.’s transmitters, the researchers suggested that the shark’s movements (shallow at night and deeper during the day) may be related to the light intensity – the shark may be attempting to avoid conditions it deems too bright (from their data, this would be about 0.4 lux) – an idea referred to as the “Light Preferendum Model” (or “Isolume Hypothesis”). However, several attempts to reproduce the effects dictated by the Preferendum Hypothesis have failed, and studies by Professor Howard Roe (at Southampton Oceanography Centre in the UK) suggest that many species of zooplankton (tiny, floating animals) can’t attain sufficient speed to follow the rising and falling of this isolume in the water column. Ergo, it seems more likely that such migrations are the result of some other (or collection of) factor, probably food-related. Aidan Martin covers this idea in greater detail on his site and I would recommend a visit if you’re interested in learning more. Basically, Aidan considers that it is far more likely that the Megamouth’s nocturnal excursions into shallow water are related to the “Deep Scattering Layer” -- a surfeit of marine animals ranging from tiny zooplankton to fish and squid that migrate up and down in the water column en masse -- that moves surface-ward as night ensues and sinks back down to 1000 m (3000ft) or more at daybreak. Aidan explains that the movements observed by Nelson and his colleagues could be the Megamouth following as its food moves up and down in the water column.

Little is known about the feeding behaviour or the chosen prey of the Megamouth shark. The only information we have is based on the analysis of stomach contents from freshly dead specimens – such data indicate that Megachasma feeds on euphausiid shrimp (krill), copepods (small, free-living, often parasitic crustaceans) and deepwater jellyfish (Atolla vanhoeffeni). The exact method by which the Megamouth catches its prey is also largely conjectural. In their tardy paper describing the first Megamouth specimen, Leighton Taylor, Leonard Compagno and Paul Struhsaker suggested that -- based on its soft, flabby body and fins, low-flow feeding apparatus and small gill openings -- this giant fish probably swims slowly through schools of krill with its mouth open and, every now and then, closes its mouth and contracts its pharynx (to concentrate the shrimp) before swallowing. Leighton et al. also considered that the silvery strip around the mouth of Megachasma may serve as a “light trap” to lure prey into its jaws (a surmise with which several other authors agreed). However, study of subsequent individuals has failed to prove the existence of any bioluminescent tissue or bacteria. This strip of skin is covered with guanine crystals (the same substance that give fish scales their shiny appearance), giving it a shiny hue that fades with preservation. The notion that this silvery strip acts as a light trap is still quite plausible, even though we now know that it is not bioluminescent.

The idea that the Megamouth “slowly swam through” aggregations of its prey -- as inferred by Taylor et al. on the basis of the aforementioned morphological characteristics (i.e. soft flabby body etc.) -- was supported by an analysis of the gill structure performed by Shin Oikawa at the Kyushu University and Takeshi Kanda at the Miyazaki University. Oikawa and Kanda compared the gills of the seventh Megamouth specimen to those of the Shortfin Mako shark (Isurus oxyrinchus), concluding that the larger and thicker gill filaments found in Megachasma compared to Isurus represented a larger water-to-blood barrier. This, coupled with the observation that Megamouth gills have a thick collagenous layer that further impedes oxygen uptake from the water, suggests that this shark has a low metabolism and supports Taylor et al.’s surmise that this shark is probably rather inactive.

One aspect of the Megamouth’s feeding biology that has become clear with the intensive study of specimen seven, is that this fish has fewer teeth than either the Whale or Basking sharks and displays an apparent sexual dimorphism in Megachasma dentition. In their paper for the Biology of the Megamouth Shark, Yoshitaka Yabumoto and his co-workers found that the female specimen they analysed had 83 rows of teeth in her upper jaw and 97 in her lower jaw, of which only three rows were functional. By comparison, the Basking shark may have well in excess of 100 rows of teeth and the Whale shark can have over 300 rows. Yabumoto et al. also note that, based on observations from previous specimens, females have more teeth than males – why this should be is still unclear.

Almost nothing is known about the reproduction of these mysterious sharks. Of the 20 specimens found to-date, two (individuals 2 and 6, both males) have displayed signs of recent or impending mating. Observations on the structure of the ovaries from female number seven by Jose Castro at the Mote Marine Laboratory in Florida and three co-workers suggest that this shark displays oviparity, as is found in other lamnoids (i.e. the first embryo to develop in each uteri feeds on the stream of eggs coming in from the oviduct). Indeed, in his 2001 revision of the Food & Agricultural Organization’s (FAO) Sharks of the World, Professor Leonard Compagno states that the Megamouth is “probably aplacental viviparous with uterine cannibalism or cannibal viviparity suspected in the form of oophagy” – in other words, the Megamouth young probably develop without a placenta, gaining their nourishment from eating either their developing siblings or (more likely) the stream of fertilized eggs entering the uterus.

Studies on the brain of the tenth Megamouth specimen -- the 5.44m (almost 18ft) mature female caught in a purse seine net at 23:40h on 30^th April 1997 about 12 miles (19 km) south of Mikizaki on the Central South Coast of Japan -- revealed a small brain set in the back of a very large brain cavity. Hironobu Ito, at the Nippon Medical School in Tokyo, and two colleagues found that the brain -- which weighed only 19.8g (0.7oz) and represented only 0.0019% of the body weight of this 1040kg (nearly 2300lbs) fish -- displayed similar features to the brains of the Frilled (Chlamydoselachus anguineus) and Seven-gilled sharks (Notorynchus cepedianus). In elasmobranchs (sharks, skates and rays), the cerebellum -- one of the major divisions of the brain that controls voluntary movement and body equilibrium -- is divided into an unpaired corpus cerebelli flanked by a pair of auricles, the top parts of which (called the pars medialis) receive vestibular signals (those involved with balance) while the bottom bits (the pars lateralis) get input from the lateral line. It seems that the auricles also receive information from the brainstem and damage to one auricle leads to the muscles on one side going into a state of partial contraction (referred to as tonus), causing the shark to swim in circles. Ito and his colleagues found that Megachasma had a small corpus cerebelli and large auricles, features shared with Chlamydoselachus and Notorynchus, both of which are considered “primitive” species. However, Ito et al. do point out that the aforementioned traits may be characteristic of the species’ relatively inactive feeding behaviour. The biologists also note that Megachasma has a well-developed telencephalon (end brain) and large olfactory bulbs, suggesting that this species has a proficient sense of smell. Oddly, Ito et al. failed to find any terminal nerves outside the brain, which (if they actually aren’t present, rather than having be destroyed by ice crystals) would make the Megamouth brain differ from that of other elasmobranchs and more closely resemble the brains seen in some bony fishes.

The 3rd Megamouth specimen washed ashore in Australia during 1998. Isistius scar circled.

Although our knowledge about this elusive -- yet quite probably cosmopolitan -- species has increased almost exponentially in the last six years, there are still a considerable number of questions that have yet to be answered. For example, we really don’t know how large Megamouths grow, how many pups they have, when they mate (although observations on mating scars and claspers of stranded specimens seem to point to October or November time), how long they live or even how widely distributed they are. There are also gaps in our knowledge of what the Megamouth eats (although as described above, we have a couple of ideas based on the stomach contents of stranded individuals) and, more intriguingly, whether anything eats it!

With regard to the question of predation on the Megamouth shark, there are a couple of lines of evidence that lead us to believe that this shark is not exempt from the dinner tables of others! The seventh specimen that was so well studied back in 1997 had some intriguing cookie-shaped bite marks on its belly. The navel-like scar was found on the underside of the shark, just in front to the cloaca (genital and waste-voiding opening), from which the flesh had not been entirely removed (i.e. the bite was incomplete). Japanese ichthyologists Ryoji Yamaguchi at Miyazaki University and Kazuhiro Nakaya at Hokkaido University analysed the wound and reported that it had been made by “some animal with sharp teeth”. Indeed, Yamaguchi and Nakaya concluded that this female Megamouth had been bitten by a small Cookiecutter Shark (Isistius brasiliensis). Isistius brasiliensis is one of three similar species placed in the Dalatiidae family (Sleeper sharks) and is a smallish shark – growing to a maximum of about 56cm (nearly 2ft) – that spends much of its days in deep waters (below 1000m / 3289ft), migrating up to the surface at night. Morphological study of this little shark found it to possess specialized suctorial lips and a strongly modified pharynx, allowing it to attach to its victim (much like a plunger), sink its impressive batch of razor sharp teeth in and rotate around its axis. The shark can apparently control the suction in its throat by moving its basihyal (the fish equivalent of a tongue) and, once it has cut a plug of flesh, it swims off (leaving a cookie-shaped cavity in its hapless victim). These scars are well known from other large marine species, including whales, tuna, wahoo (a large, fast moving game fish) and other sharks. Indeed, the third Megamouth specimen – a 5.15m (nearly 17ft) male that washed ashore near the Mandurah Estuary in Western Australia during August 1988 – showed signs of a meeting with a Cookiecutter shark; the individual had a small, crater-like, plug of tissue removed just above the gills on its right-hand side. Other papers in the Biology of the Megamouth Shark compendium report the presence of various copepods, protozoa and tapeworm parasites found in this individual.

The discovery of the 13^th Megamouth also brought with it a tantalizing glimpse of another possible predatory relationship: this time with whales. On the 30^th July 1998, a research vessel just offshore from the Island of Nain in Indonesia spotted a Megamouth – which they estimated to be about 5m (16 ½ ft) long – being harassed by a pod of three 10 to 12 m (33 – 39ft) Sperm Whales (Physeter macrocephalus). The whales swam away as the researcher’s boat approached and the Megamouth continued swimming normally. The scientists took some photos and noticed some relatively minor abrasions to the shark’s gills, although the shark didn’t seem in undue anguish. It is not known whether this was an interrupted act of predation by these whales -- which are known to eat Giant squid (Architeuthis), fish, octopus and elasmobranchs -- or whether it was the same sort of harassment that dolphins have been observed to perform on some sharks.

* The smallest Megamouth (nicknamed "Memo Jr.") has been sent to the Indonesian Research centre in Jakarta where it will be prepared for permanent display shortly.

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