DNA identification reveals threatened species being overfished in Brazil

New research has revealed an alarmingly high level of trade of endangered shark species in northern Brazil.

As one of the top seven global consumers of shark meat in the world the shark fishing industry in Brazil is of commercial significance yet data on shark fisheries remains scarce. Official statistics on shark fishing are derived from data provided by commercial fishing vessels, however globally a significant artisanal fishing industry is thriving which, if added to official records, would contribute up to an additional 50% of total landings.

In addition to hosting the largest continuous mangrove forest in the world, Brazil's north coast is a shark conservation hotspot and supports nineteen shark species. This region is also an important fishing ground.

Whilst some sharks are protected under Brazilian law, specimens are commonly landed finned and headless at Brazilian ports. The lack of morphological features makes species identification and subsequent law enforcement problematic. A recent study published in Nature's Scientific Reports utilised DNA-based techniques to identify sharks collected from some of the most important fishing ports in northern Brazil to determine which species were being caught.

Of the 427 shark specimens analysed 82 (19.14%) were listed as either Critically Endangered, Endangered or Vulnerable in the IUCN Red List. A further 125 (29.18%) were in the Near Threatened category. Seventeen species in total were identified with the Caribbean sharpnose shark (Rhizoprionodon porosus) making up the majority of the sample size. The species in the most threatened categories were the great hammerhead (Sphyrna mokarran) (Endangered), the scalloped hammerhead (Sphyrna lewini) (Endangered), the smalleye hammerhead (Sphyrna tudes) (Vulnerable) and the daggernose shark (Isogomphodon oxyrhynchus) (Critically endangered). Of these species the daggernose shark is of critical concern owing to its conservation status and the fact that this shark occupies a restricted range around northern Brazil making it particularly vulnerable to exploitation and the risk of extinction.

The results produced here should rightly be cause for alarm; for shark fishing to have been occurring in a location of significant shark biodiversity and without sufficient protection measures in place will have had an impact on shark populations. Despite efforts from the Brazilian government to pass legislation that protects the local fauna the reality is that lack of resources and inadequate monitoring have rendered official protection obsolete. With such a large proportion of specimens captured being classified in a category of threat the authors recommend urgent implementation of more effective monitoring and measures to reduce shark bycatch.

Where is the largest shark biomass in the world?

Cocos Island National Park and the Chagos Marine Reserve might be considered to be contenders for the largest fish biomass on the planet, but a new location has been found to have an even larger biomass and it consists almost entirely of sharks!

The islands of Darwin and Wolf in the Galapagos have recently received full protection from fishing from the Ecuadorian Government (see The Shark Post: New marine sanctuary in the Galapagos will protect a variety of fish species). This change was partly driven by the conclusion that these islands support a large amount of shark species; now publishing in the journal Peerj a team of researchers have presented their evidence that Darwin and Wolf support the largest biomass of sharks reported to date. 

Using underwater cameras to conduct stereo-video surveys the researchers recorded and measured the fish around Darwin and Wolf islands. This data was then used to convert length measurements to biomass and the fish were classified as apex predators, lower level carnivores, planktivores and herbivores.

Primarily consisting of the scalloped hammerhead (Sphyrna lewini) (48.0%), the Galapagos shark (Carcharhinus galapagensis) (19.4%) and the blacktip shark (Carcharhinus limbatus) (5.1%), the shark biomass made up almost 73% of the total fish biomass at these 2 sites. Interestingly the majority of the fish observed were found in the south-east section of both islands; the researchers hypothesised that this might be owing to the unique currents which flow through these islands or possibly the south eastern part of these islands are used as a cleaning station or a location for nightly foraging excursions. 

Sharks are incredibly important to the Galapagos and to Ecuador; not only do sharks help regulate the ecosystem as apex predators but an individual shark in the Galapagos has been estimated to be worth USD$360,000 per year through tourism, whilst a fisherman may receive a one off payment of USD$158 for the same dead shark.  

Whilst veteran divers have reported larger abundances of sharks at Darwin and Wolf 30 years ago, there exists a real lack of long term studies in the area to quantify these observations. Owing to the fact that these islands are home to the last true coral reef in the Galapagos Marine Reserve, are important waypoints for whale shark migrations in the region and have now been proven to support the largest shark biomass ever recorded it is important that studies such as this continue in order to ensure ongoing protection of this biologically significant region.   

Salinas de León P, Acuña-Marrero D, Rastoin E, Friedlander AM, Donovan MK, Sala E. (2016) Largest global shark biomass found in the northern Galápagos Islands of Darwin and Wolf. PeerJ Preprints 4:e1872v1 https://doi.org/10.7287/peerj.preprints.1872v1

Huge quantities of sharks and rays being caught by fisheries in Tunisia

The Gulf of Gabes lies on the east coast of Tunisia and supports many small scale fisheries. Here artisanal fisheries commonly set trammel nets to catch shrimp (Melicertus kerathurus) from May to August each year. Now a team of researchers has been researching the impact of these fisheries on the local shark and ray populations.

The scientists, based at Institut National des Sciences et Technologies de la Mer in Tunisia, spent 3 months recording the number of elasmobranchs caught in fishing nets of the artisanal shrimp fisheries in the Gulf of Gabes. They took note of species, sex and total length (or disc width in rays).

In total 926 elasmobranchs were caught during this 3 month period; the overwhelming majority of the sharks and rays caught was made up by the common smooth-hound (Mustelus mustelus) but six other species (blackspotted smooth-hound (Mustelus punctuatus), common stingray (Dasyatis pastinaca), marbled stingray (D. marmorata), common torpedo ray (Torpedo torpedo), sandbar shark (Carcharhinus plumbeus) and spinner shark (C. brevipinna)) were also retrieved. Despite the fact that the sheer numbers of elasmobranchs caught in 3 months is fairly jaw dropping, what's really shocking about the results is that all of the captured sharks were either neonates or juveniles.

Removing immature specimens from a population can have huge implications for conservation owing to the fact that the organisms in question have not had the opportunity to reproduce. This is especially true for sharks who tend to have slow growth, low fecundity and long reproductive cycles making it difficult for most species to recover their stocks once depleted. The results here led the researchers to believe that the Gulf of Gabes might be an important nursery area for several species of elasmobranch.

Whilst large commercial fisheries are barred from many marine protected areas, small scale artisan fisheries are often permitted to operate. Recently there has been more attention paid to the impact of these smaller fisheries with the result that some marine protected areas are prohibiting all fishing activity within their waters (see The Shark Post: New marine sanctuary in the Galapagos will protect a variety of shark species).

Studies such as this are critically important as they provide scientists with the evidence to convince policy makers that key areas need protecting either by closing fisheries or creating a marine protected area. Considering that one of the above species is listed as Near Threatened in the IUCN Red List and two as Vulnerable (including the most commonly caught common smooth-hound), protecting elasmobranchs in this region should be of high importance.

Saidi, B., Enajjar, S. and Bradai, M. N. (2016), Elasmobranch captures in shrimps trammel net fishery off the Gulf of Gabès (Southern Tunisia, Mediterranean Sea). Journal of Applied Ichthyology. DOI: http://dx.doi.org/10.1111/jai.13061

Tiger shark distribution is larger than we thought

Despite having a circumglobular distribution, the tiger shark (Galeocerdo cuvier) has heretofore been considered a coastal species, sticking close to the continental shelf. However, a recent assessment of populations of G. cuvier in the Atlantic Ocean has revealed that this species is more widespread than first thought.

Publishing their work in the Journal of Fish Biology, a team of researchers have been utilising at-sea observers on board pelagic longline fishing vessels to document tiger shark sightings. From 1992 to 2013, 2,764 tiger sharks were reported and whilst a great deal of these observations were from coastal regions, 86.4% of the data occurred outside the existing geographic range of this species as proposed by the IUCN Red List. The observations change the current view of the distribution of G. cuvier, showing that this species is present in the open ocean, as well as along the continental shelf and the researchers propose that the distribution of G. cuvier should be amended to show that this shark is present throughout the Atlantic.

Interestingly the data also showed consistent sightings of G. cuvier along the equator which were not matched further North, suggesting that tiger sharks in the Atlantic could be utilising the North and South Equatorial Currents and the North Equatorial Counter Current to move across the Atlantic.  

This data could have implications for the conservation and management of this species as it could indicate that there is a larger biomass of tiger sharks than previously thought, or that tiger sharks in the open ocean are more vulnerable to fishing pressure owing to the fact that it was not previously confirmed that this species was present in the open ocean. Either way this data fills yet another gap in our existing knowledge of this Near Threatened species.

Domingo, A., Coelho, R., Cortes, E., Garcia-Cortes, B., Mas, F., Mejuto, J., Miller, P., Ramos-Cartelle, A., Santos, M. N. and Yokawa, K. (2016), Is the tiger shark Galeocerdo cuvier a coastal species? Expanding its distribution range in the Atlantic Ocean using at-sea observer data. J Fish Biol, 88: 1223–1228. doi:10.1111/jfb.12887

The worlds first ever shark sanctuary: has it been effective?

Palau attracted international attention in 2009 when the island nation created the first ever shark sanctuary. Created in response to the rapid depletion of sharks in the region, all commercial shark fishing has been banned within the sanctuary, which covers an area of approximately 600,000 sq km.

However, despite all the best intentions, enforcement of these restrictions is incredibly tough - especially for a small island nation such as Palau. Not only is the area in question a very large area to patrol, many of the reefs which attract sharks are located far away from the main populace, making constant visibility of shark fishing activity around these reefs troublesome. These factors mean that any type of enforcement requires a great deal of time and money.

In order to ascertain if the shark sanctuary has been having any benefit to the local shark populations, a team of researchers have conducted surveys on a selection of reefs within the shark sanctuary. During the course of the surveys estimates of shark density based on sightings were calculated and observations of derelict fishing gear were recorded to try and ascertain any potential level of illegal fishing activity.  

The researchers found that areas with higher densities of derelict fishing gear (longlines and nets) had lower densities of sharks. They also discovered that grey reef sharks (Carcharhinus amblyrhyncos) observed close to reefs from the main island group were larger and occurred in higher densities than those from the southwest islands - a group of isolated islands occurring in the south of the country. A smaller total body length measurement and a lower density of sharks could be indicative of fishing pressure on the shark population; the fact that these attributes were observed on the most remote reefs could allude to the fact that illegal fishing is more commonly being practised away from the principal islands. In addition to the above, local rangers had reported seeing unauthorised fishing of sharks and the researchers did observe a shark caught in derelict fishing gear.    

These observations suggest that illegal fishing activity has not been entirely eradicated from the shark sanctuary and could potentially be having an impact on the shark populations in the more remote areas of the sanctuary. However it should be noted that the surveys took place only 4 years after the shark sanctuary was created and owing to the slow recovery rate of sharks the results reported here may reflect the historic state before fishing pressure was relieved from the shark populations within the sanctuary.

The Shark Post has been writing a lot about the effectiveness of marine protected areas (MPAs) recently (see The Shark Post: How well do marine protected areas truly protect highly migratory sharks? and The Shark Post: Can a Marine Protected Area truly ever be protected?) and more research is coming to light to show that the creation of a marine protected area is just one half of the battle; the real uphill struggle is enforcing the laws which have been laid down.

Vianna, G. M. S., Meekan, M. G., Ruppert, J. L. W., Bornovski, T. H. and Meeuwig, J. J. (2016) Indicators of fishing mortality on reef-shark populations in the world’s first shark sanctuary: the need for surveillance and enforcement.

The Ecological Role of Sharks On Coral Reefs Is Not As Straightforward As First Thought

The term "apex predator" is frequently applied when talking about sharks regardless of the species being discussed. However, a team of researchers based in Australia have been reviewing the trophic positioning of reef sharks and it seems as though not all shark species can be considered to be apex predators in their habitat.

It may seem rather obvious when you stop to consider it; after all the vast spectrum of shark species stretches from definite apex predators such as the great white (Carcharodon carcharias) to species which surely must occupy a lower level in the food web such as the epaulette shark (Hemiscyllium ocellatum). However, the authors suggest that owing to the deficiency of data on shark dietary habits, early researchers lumped all sharks together into a single "apex predator" class.   

The definition of an apex predator is an animal which occupies the top of a food chain, has no natural predators of its own and maintains the health of the habitat it resides in by exerting an influence over the species below. The researchers looked specifically at reef associated shark species and found that most of the species they focused on functioned more as mesopredators than apex predators. For example, the grey reef shark (Carcharhinus amblyrhincos), whilst occupying the highest trophic level in it's habitat, is vulnerable to being preyed upon by opportunistic apex predators such as the tiger shark (Galeocerdo cuvier). In addition to this, mesopredators such as the grey reef shark may be jointly occupying the top trophic level with large predatory teleost fish, further evidencing their removal from "apex predator" status. In contrast, a large pelagic apex shark such as the tiger shark will migrate between open ocean and reef and their trophic role may vary across habitats. However on the reef these sharks exert a high degree of influence over the associated community, have no natural predators and take a wide variety of prey items thus fulfilling all the requirements of being apex predators.     

So what is the value of sharks on a reef if they are not all fulfilling apex roles which would exert influence over the community? The researchers suggested a broad range of functions for sharks on reefs. For example the small home ranges of some of the mesopredatory sharks contribute to nutrient cycling between pelagic and reef habitats. Both apex and mesopelagic sharks will remove sick and weak individuals from coral reef habitats and potentially suppress the spread of disease by keeping population numbers in check. It has also been suggested that certain mesopredatory reef associated sharks may be able to keep invasive species such as lionfish in check. In addition to this, the presence of sharks has significant economic value: the researchers cite the shark sanctuary in Micronesia which was created to protect the local shark species owing to the socio-economic benefits of shark diving in the region. Despite being a "shark sanctuary", many fish and coral species will also enjoy the benefits of this marine protected area. 

This review is really rather interesting as it gives us all pause for thought regarding the diversity of shark species in our oceans and the fact that despite often being viewed as fearsome predators, some sharks will end up as prey for larger predators. The authors also raise a variety of questions on how sharks interact with coral reef communities and their influence on the reef system, laying the foundation for future research.

The original paper is published in trends in Ecology and Evolution. DOI: http://dx.doi.org/10.1016/j.tree.2016.02.014 

New marine sanctuary in the Galapagos will protect a variety of shark species

The Galapagos Islands are known globally as a rich area of biodiversity and the islands themselves have enjoyed 97% percent protection since they were declared a national park in 1959. However, despite the creation of a marine reserve in 1998 to protect the waters around the islands, some fishing has been permitted and less than 1% of these waters has complete protection.

Despite the fact that the marine park is closed to trawls and other high impact, commercial fishing activities, the artisanal fishing is still having an impact on populations of large predators. Owing to high demand, populations of key species are being depleted to unsustainable levels. In addition to this not all landings made within the marine reserve are declared, making the true numbers of species caught difficult to ascertain.

This is about to change however as on Monday the Ecuadorian President Rafael Correa Delgado announced a new marine sanctuary for The Galapagos. This new sanctuary will lie between Wolf and Darwin Islands and will cover a region of more than 15,000 square miles; unlike the current marine reserve, the new sanctuary will be completely off limits to any fishing activity.

The new marine sanctuary will mean that 33% of the waters around the Galapagos now enjoy complete protection from fishing. Happily it is predominantly sharks which have driven this change; the Galapagos Islands have been cited as having the greatest abundance of sharks in the world and the official announcement from the Ministry of Environment stated that the sanctuary had been created with the idea of protecting endangered species such as hammerhead sharks. Of course it is not just sharks that will benefit, the coral reef and fish in the marine protected area will also thrive under the new no-take policy.

Whilst declaring a marine sanctuary is only one part of the battle (see The Shark Post: Can a Marine Protected Area truly ever be protected?), this protection could not have come soon enough as many of the shark species which inhabit these waters are under threat; the scalloped hammerhead (Sphyrna lewinin) is listed as Endangered in the IUCN Red List, whilst the Whitetip Reef Shark (Triaenodon obesus) and the Galapagos Shark (Carcharhinus galapagensis) are listed listed as Near Threatened. These species will all benefit from this new no-take area.

On his Twitter account, the Environmental Minister Daniel Ortega Pachero (@dvortega) said that the new marine sanctuary is a moral obligation to the Galapagos, Ecuador and the world. Very true words as the benefits of protecting areas of rich biodiversity like The Galapagos will indeed be felt throughout the world.

Sources: Ministerio de Ambiente
National Geographic
Elucidating fishing effects in a large-predator dominated system: The case of Darwin and Wolf Islands (Galápagos)