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)

How well do marine protected areas truly protect highly migratory sharks?

The designation of an area of ocean as a marine protected area will be a cause of celebration for most conservationists; restricting fishing activity within a certain area takes pressure off fish stocks and benefits the ecosystem. However, many marine protected areas (MPAs) are created with a certain goal - often to protect coral reefs or specific resident species. Highly migratory species such as sharks would only benefit from the protection an MPA offers when they are residing within the MPA zone. A team of researchers at University of Miami have been investigating how much time 3 key shark species spend within the MPA designated zones around Florida and the Bahamas in order to ascertain the true level of protection these species enjoy.

Over the course of 4 years the researchers satellite tagged tiger (Galeocerdo cuvier), bull (Carcharhinus leucas) and great hammerhead (Sphyrna mokarran) sharks within the study area. The study area contained a mixture of national parks, economic exclusion zones (EEZ) and a national marine sanctuary which included a no-take zone. In addition to this, shark harvesting has been entirely prohibited in the Bahamas since 2011, when a shark sanctuary was created. Within Florida state waters it is not permitted to take tiger, great hammerhead, scalloped hammerhead (Sphyrna lewini) or smooth hammerhead (Sphyrna zygaena) sharks and the maximum catch for all other shark species is one shark per person per day. This study also included parts of the US EEZ which has more relaxed laws than Florida state waters and allows up to 36 large sharks per boat per day to be removed.    

The researchers discovered that none of the core habitat use by the bull sharks tagged in this study overlapped with any of the areas which would have afforded them complete protection. For the great hammerhead, 27% of their core habitat range fell within protected, no-take regions and for tiger sharks it was 34.74%. These figures show that, despite there being several regions where shark fishing is completely prohibited around Florida and the Bahamas, the sharks are not staying within those regions. However, the researchers did discover that these shark species spent quite a bit of time within the U.S. EEZ and if the same protection which is afforded sharks in the waters around Florida state were extended to include U.S. federal waters then the practical level of shark protection would increase.

Owing to the fact that bull sharks are classified as Near Threatened in the IUCN Red List, tiger sharks as Threatened and great hammerheads as Endangered these species require immediate and urgent implementation of regulations which will afford them complete protection from fishing. Studies such as this can be used to inform policy makers and prove that extended protection zones are mandatory if the future of these species is to be assured.  

Graham, F., Rynne, P., Estevanez, M., Luo, J., Ault, J. and Hammerschlag, N. (2016) Use of marine protected areas and exclusive economic zones in the subtropical western North Atlantic Ocean by large highly mobile sharks http://onlinelibrary.wiley.com/doi/10.1111/ddi.12425/full

Can a Marine Protected Area truly ever be protected?

Whilst it is estimated that over 3% of the worlds oceans have been designated as Marine Protected Areas (MPAs), enforcement of the regulations within these areas is often difficult. This is owing primarily to the expense and logistics of patrolling large areas of ocean as well as the low probability of arrest leading to prosecution.

One area which has a rich abundance of marine wildlife is Cocos Island National Park (CINP). CINP is an offshore, no-take marine protected area of nearly 2,000 square kilometres located off the coast of Costa Rica. Despite having been afforded National Park status and being a world heritage site, CINP suffers from illegal fishing being carried out in its waters.

The resources currently offered by the Costa Rican Government to patrol the park and deter fishing infringements are not proving adequate to prevent illegal fishing in the region. Hoping to be able to suggest ways to improve the efficiency of the patrols, a group of researchers analysed the last 5 years worth of patrol data to try and ascertain where efforts could be best applied.

During the last 5 years the patrol boats recorded a total of 300 fishing infringements with 34,500 hooks set and 2,000 fish caught. The overwhelming majority of the catch (66%) was made up of yellowfin tuna (Thunnus albacares), but sharks comprised 25% of the total recorded catch - predominantly the silky shark (Carcharhinus falciformis). Shark finning has been reported from CINP and declines in the abundance of sharks within the park have been reported.

The researchers reported that policing the park is confounded even further by the conflict of interest within the fisheries authority: most of the board members are representatives of the fishing industry. In addition to this the poachers do not seem to feel the threat of prosecution: the probability of arrest is very low, the probability of conviction practically non-existent and fleeing poaching vessels have commonly been observed flinging insults back at the patrol boats via the radio.

It may seem as though all of this paints a rather bleak picture for our wildlife (and our sharks!) However the researchers aims were to increase efficiencies amongst the patrol boats to help the wardens make the best use of the limited resources available to them. The analysis conducted by the team revealed that poaching was highest during the first quarter of the lunar phase and the third quarter of the year; the likelihood is that the reduced light conditions during the new moon brought predators closer to the surface and were also favourable conditions to carry out illegal fishing owing to the reduced risk of detection. Time of year also appeared to be a significant factor influencing fishing activity. The researchers therefore suggested aligning the majority of the patrol times to coincide with these peak periods of poaching.

The team also discovered that illegal fishing is focused around a seamount within the park and by zoning this region the park boundary could be more obvious and manageable. Along with this the rangers should be looking to invest in better technology to detect poachers and should also be trained in environmental and marine law - all of which would require a not insignificant monetary investment.

This research goes to show that shark finning - and illegal poaching in general - is not limited to the open ocean, away from the eyes of the law. Preventing these activities from happening requires a greater set of efforts than simply designating an area to be a national park. Protection of the park needs to be enforced and the attitudes of governments changed to encourage them to provide resource to support this protection.

Arias, A., Pressey, R., Jones, R., Alvarez-Romero, J. and Cinner, J (2016) Optimizing enforcement and compliance in offshore marine protected areas: a case study from Cocos Island, Costa Rica http://dx.doi.org/10.1017/S0030605314000337

What happens when conserving an Endangered species impacts a fishery worth A$1 million?

Conservation efforts in many parts of the world are often impacted by money. This is not a reference to the usual lack of funding for the average not-for-profit - although that is an important side note - but the often lucrative reasons for why a species has fallen into decline in the first place. With rhino horn worth more than gold and a bowl of shark fin soup selling for up to HK$2000 there is a price on the heads of wildlife so high that it can offer some convincing reasons to some parties against supporting conservation efforts.

Financial implications of lost business are also of concern to the fisheries industry. Whilst sustainable fishing is, of course, important to the fishing industry as it translates to continued employment, closing a fishery to protect a non-target species can lead to socio-economic conflict between conservationists and fishers if the fishery in question also contains a valuable target species.

This is what happened in 2012 with the release of a management strategy for the upper slope dogfish in Australia. One species of upper slope dogfish - Harrissons Dogfish (Centrophorus harrissoni) - is classified as Endangered in the IUCN Red List and uses Taupo seamount off New South Wales as a refuge. The management strategy released in 2012 proposed a higher level of protection for Taupo seamount which would officially close it to all fishing activity, therefore protecting this vulnerable species.

The road to this proposed closure had been a long winded process; Harrisson's Dogfish was first nominated for listing under the Environment Protection and Biodiversity Conservation Act in 2005. Taupo seamount was then sampled and subsequently identified as a refuge for Harrissons Dogfish in 2009 and subsequently the seamount was closed to commercial fishing activity under the advice of the Australian Fisheries Management Authority (AFMA) in 2010.  

The closure of the fishery in this instance caused controversy as the seamount chain in question contributes 25% of the annual total allowable catch of Blue-Eye Travally (Hyperoglyphe antarctica). This is a fishery which has a total value of A$1million and so the closure would have had a significant impact on the lives of the fishers and the Australian economy. 

In 2015 the original closure and planned upgrading of the seamount to Marine National Park status was revised (AFMA Ecological Risk management 2015) to allow commercial line fishing around Taupo seamount. Whilst this may initially seem like a step backwards, the revision was undertaken with a view that the fishery could be compartmentalised to allow fishers to maintain their catch of Blue-Eye Trevally whilst not impacting the Endangered Harrissons Dogfish.

Harrissons Dogfish is a diel vertical migrator - the shark spends daylight hours at depths of >550m and ascends at night-time to feed on micronekton. Researchers at CSIRO and Australian Museum hypothesised that the seamount could potentially be open to line fishing above 550m; this would allow fishers to catch Blue-Eye Travally during the day but should not have any impact on the Harrissons Dogfish stocks.

The researchers carried out their own fishing effort around the seamounts, deploying fishing lines both during the day and at night as well as into the Mid (280-550m) Zone and Deep (550-830m) Zone. The results showed that catches of Harrissons Dogfish were avoided when fishing for Blue-Eye Travally at depths of 280-550m during the daytime, using standard commercial power handline. Whilst surveying the area, the researchers also discovered that the range inhabited by Harrissons Dogfish was much wider than previously thought.

These results were used to inform policy makers when finalising the management plan for Harrissons Dogfish. Whilst the zoning category of the Taupo seamount was relaxed to allow commercial handline fishing activities, the zoning category of the Derwent Hunter Seamount was increased and the Queensland and Britannia seamounts were included in the Commonwealth Marine Reserves network owing to the new evidence of Harrisons Dogfish in these regions.

The declassification of Taupo seamount from Marine National Park to Habitat Protection Zone is never a step in the right direction as far as any conservationist is concerned. However strict regulations are in place: the fishery is subject to 100% monitoring and if any vessels interact with more than 3 Harrissons Dogfish they will lose their rights to fish in the region for 12 months. In addition to this the removal of Harrissons Dogfish has been entirely prohibited.

So when conservation conflicts with huge financial profit can there be a happy medium? This solution may be a way to keep everyone happy; however the truth of the matter is that the only way we will known is by ongoing monitoring and sampling in the region to see if the populations of Harrissons Dogfish truly are unaffected by the Blue-Eye Travally industry.

New species of shark discovered in Argentina!

Researchers from Buenos Aires have discovered an exciting array of fossilised selachian teeth, including a new species.

The fossilised teeth were collected from the Calafate Formation in Argentina and were discovered during the preparation of another fossil of a very large elasmosaurid plesiosaur. After conducting a thorough analysis of squaliform phylogeny and evolution, the authors were able to ascertain that some of the teeth discovered had never been described before and comprised a new species of the genus Protosqualus: Protosqualus argentinensis.  

Images of fossilised P. argentinensis teeth. Image courtesy of Sergio Bogan at Fundación de Historia Natural Félix de Azara Departamento de Ciencias Naturales y Antropología CEBBAD - Universidad Maimónides

The exciting news doesn't end there, however. Not only did the authors describe a new species, but this is also the first time any member of the genus Protosqualus has been discovered in South America. Previous examples of this genus have been noted from Russia, Australia and India and it has been suggested that this species would have had an anti-tropical distribution which is supported by the findings here.

The authors also discovered teeth belonging to the previously described Hexanchiform Notidanodon dentatus. Whilst today most Hexanchiform species are extinct, were it alive today Notidanodon dentatus would have a handful of living relatives in the cowsharks and frilled sharks. Interestingly previous examples of this extinct species have also been found in association with an elasmosaurid plesiosaur suggesting that this species may have been a scavenger opportunistically taking advantage of these marine reptiles.

Fossilised N. dentatus teeth. Image courtesy of Sergio Bogan at Fundación de Historia Natural Félix de Azara Departamento de Ciencias Naturales y Antropología CEBBAD - Universidad Maimónides

What's even more exciting (yes - there's more!) is the placement of these species. As noted in the paper, the Northern Patagonian fossil record is dominated by Lamniform (living species of which would include mackerel sharks like the Great White) and ray teeth, whilst the Southern Patagonia fossil record is comprised of cold water species suggesting that there was little species overlap in the late Cretaceous oceans around South America.

Whilst these species may be long extinct, piecing together their life history from the fossil record will help us to understand modern day sharks better and provides insight into how the prehistoric oceans may have looked.

Sergio Bogan, Federico L. Agnolin & Fernando E. Novas (2016) New selachian records from the Upper Cretaceous of southern Patagonia: paleobiogeographical implications and the description of a new taxon, Journal of Vertebrate Paleontology http://www.tandfonline.com/doi/full/10.1080/02724634.2016.1105235

All female Tiger Shark hangout found in the Bahamas

You might not expect to hear that ultrasounds are being given to pregnant tiger sharks (Galeocerdo cuvier), but that is exactly what happened in a recent research study carried out at Tiger Beach in the Bahamas. Tiger Beach is a popular shark diving destination owing to the large numbers of tiger sharks there. The area has warm, calm water and is relatively shallow leading the researchers to hypothesize that the sharks present in the region could be pregnant females taking advantage of the clement conditions. 

In order to test this assumption the team captured 65 tiger sharks; in order to assess whether these sharks were pregnant they carried out ultrasounds and tested levels of circulating sex steroid hormones in the sharks. Typically in a study of this nature, the most effective sampling techniques would result in killing the animal in question in order to assess pregnancy - not so beneficial when your end goal is to protect the species you are studying! Happily, the researchers in this study were able to successfully gather the required information using the non-lethal sampling techniques described above. 

Of the 65 tiger sharks captured, only 6 were male. Of the 59 females 19 had not yet reached maturity, 17 were mature, non-pregnant females and 23 were mature, pregnant females. These results suggest that Tiger Beach is a high-use site for female tiger sharks and may function not only as a secure site in which to give birth but also as a place for young female tiger sharks to reach maturity free of harassment from males.  

Knowing that Tiger Beach is an area favoured by pregnant female tiger sharks could have significant implications for the conservation of this species; the removal of pregnant females from a population can have dramatic effects on population size and thus this population should be afforded protection from fisheries. Whilst Tiger Beach is situated within the Bahamas Exclusive Economic Zone (EEZ) which is a shark sanctuary where all harvest of sharks is forbidden, tiger sharks can freely move out of the boundaries of the EEZ and may then be at risk from fisheries.   

The full article is Open Access and can be read at http://www.int-res.com/abstracts/ab/v24/n3/p175-184/.

Sulikowski JA, Wheeler CR, Gallagher AJ, Prohaska BK, Langan JA, Hammerschlag N (2016) Seasonal and life-stage variation in the reproductive ecology of a marine apex predator, the tiger shark Galeocerdo cuvier, at a protected female-dominated site. Aquat Biol 24:175-184