Shark Research - Whale Shark Genome Just As Big As The Human Genome!

Researchers at Emory University and the Georgia Aquarium have now completed their sequencing of the whale shark (Rhincodon typus) genome. This is the first time a nuclear genome of an elasmobranch has ever been sequenced.

The estimated genome size of the whale shark was 3.44 gigabases (Gb) which puts it on par with our own genome (Homo sapien) at 3.3Gb (1). One barrier to sequencing the genomes of cartilaginous fish is that their estimated genomes tend to be rather large; the genome of only one other cartilaginous fish, the elephant shark (Callorhinchus milii), has been sequenced and this was an attractive candidate for genome sequencing as its predicted genome was less than 1Gb (2). Genetic data for a bony fish, the rainbow trout (Oncorhynchus mykiss), is also available and at 1.9Gb this genome is smaller than that of the whale shark (3).

Using predictive software, the researchers estimated that the whale shark genome has 23,594 protein coding genes, which is very similar to the human genome which has 20,000-25,000 protein coding genes. As might be expected,the smaller genome of the elephant shark has only 18,872 protein coding genes.

Genomic studies like this are important as they not only help us understand more about how the underlying genetic code works to make an entire organism function, but they can also be used to deduce the evolutionary relationships between organisms with a greater degree of accuracy than morphological data. Genetic analysis of whale sharks has already proven that there is not just one global population of whale sharks - as was previously thought - but at least 2, genetically distinct populations.

Whilst this genome is just at the draft stage, the researchers hope to secure funding to continue their work and delve deeper into the genetic data of the whale shark in order to help us learn more about this ocean giant - so watch this space!

The draft genome is available at http://whaleshark.georgiaaquarium.org/.

Shark news - Shark Sanctuary Created in Madagascar!

The Government of Madagascar have created their first ever shark sanctuary in Antongil Bay, North West Madagascar. Covering 3,750km² of ocean, the Order has been put in place after lengthy consultation with fisheries, community fishermen, local authorities and NGOs and will protect this extremely rich area of biodiversity.

The area of the shark sanctuary. Image from Mongabay

The Order aims to empower village communities to manage their fishing activity, whilst ensuring that any exploitation of the fisheries resource is carried out sustainably and has three main objectives:

1) The preservation of the environment to ensure the sustainability of the ecosystem
2) The establishment of a sustainable fishing resource to improve the living standards of coastal populations in general and fishermen in particular, and
3) More equitable distribution of wealth created by fisheries by enhancing the part of the local population against the interests of the municipal economy, regionally and nationally

Whilst sustainable fishing is encouraged within the sanctuary, shark fishing has been entirely banned. 19 species of shark are found in Antongil Bay of which over a third are threatened with extinction.

The announcement was made jointly with the Wildlife Conservation Society (English) and the Ministry of Marine Resources and Fisheries Madagascar (French)

Shark Research - Fisheries analysis reveals high shark bycatch in longline fisheries

A recent paper published in Marine Policy has carried out the first analysis of global elasmobranch bycatch patterns in commercial fisheries.

Bycatch - where species other than the intended target species are caught in a fishery - is a global problem. Many of today's commercial fishing methods, such as trawling or long lining, have few ways to ensure that only the intended species is caught.

By examining current fisheries data, the researchers assessed the quantity of elasmobranch bycatch across 4 commercial fishing methods: longlines, trawlers, purse-seines and gillnets. Of these 4 fishing methods, they found that pelagic longlines are responsible for the largest amount of shark bycatch - in fact in some instances the quantity of sharks caught in pelagic longline fisheries may exceed the intended catch. The majority of the shark bycatch was made up of blue shark (Prinace glauca) which is classified as Near Threatened in the IUCN Red List.

Long line fishing is a type of commercial fishing whereby a main line is laid out with hooks hanging off the line at intervals. Whilst longlines are intended to catch a target species - such as swordfish - the baited hooks also attract other species such as seabirds, turtles, other fish and sharks. Worse still, if fishing gear is discarded at sea the equipment can continue to catch and kill marine life - something known as ghost fishing.

This paper does not draw conclusions about the direct threat to sharks from these high levels of bycatch, but instead emphasises that the large numbers of sharks unintentionally caught and discarded by the commercial fishing industry is concerning and more research is required to understand if it is sustainable. The authors also highlight a need to implement management plans for elasmobranchs on a global scale.

 

 

Shark News - Megamouth Shark washes up in the Philippines

It seems as though all rarely sighted shark species are keen to make an appearance at the moment with a megamouth shark (Megachasma pelagios) washing ashore in the Philippines. This species is so rarely sighted that it is classified as Data Deficient in the IUCN Red List.

The 4.6m, male specimen was stranded on Pio Duran, Albay. Interestingly, this site is just a stones throw from Donsol - a natural aggregation site for whale sharks (Rhincodon typus). Like the whale shark, the megamouth shark is a filter feeder and could possibly have been attracted to the area by an abundance of Euphausiid shrimp - an important component of the diet of both the whale shark and the megamouth shark. In 2009 another megamouth shark was reported from Donsol, suggesting that this area could be frequented by these sharks. Megamouth sharks have been found at depths ranging from 5m to 4,600m and they may follow the diel vertical migration patterns of the Euphausiid shrimp - spending time at depth during the day and returning to the surface at night. This could explain why the sharks are so infrequently sighted. 

Photo courtesy of Marine Wildlife Watch of the Philippines. Photo credit Rosalina Sariola

This shark is thought to be circumglobal but a large number of sightings have been from Japan, Taiwan and the Philippines. The specimen has been nicknamed "Toothless" and has been stored on ice by the Bureau of Fisheries and Aquatic Resources (BFAR), Bicol to await a necropsy.