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

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 global strategy to protect sharks and rays released

Working together, several of the most influential conservation organisations have published a new global strategy to conserve sharks and rays. The report, published in January 2016, is a partnership of IUCN Species Survival Commission (SSC) Shark Specialist Group (SSG), Shark Advocates International, The Shark Trust, TRAFFIC, Wildlife Conservation Society (WCS) and World Wide Fund for Nature (WWF) and is the product of an intensive 18 month planning process.

The primary goal of the global strategy is to halt the decline of shark and ray populations globally and to improve the conservation status of the worlds shark and ray species. This main goal will be driven by three further goals which are to have been achieved by 2025:

"2025 Sustainable Fisheries Goal: Fisheries driven overexploitation and waste of sharks and rays are substantially reduced through increased adoption and implementation of sound, science-based fisheries management measures in at least 40 priority countries and in Areas Beyond National Jurisdiction (ABNJ)"

"2025 Responsible Trade Goal: Effective trade controls are in place to ensure international trade in sharks and rays, and the products derived from them, is legal, sustainable and traceable."

"2025 Responsible Consumption Goal: The demand for (largely unsustainable) shark and ray meat, fins, squalene, manta and devil ray gill plates, and freshwater stingrays is significantly reduced in the most important global markets, while markets increasingly demand that any shark and ray products are sustainably produced and traceable."

This global management strategy comes at a critical time for the worlds sharks and rays. Not only are populations being exponentially reduced by the practise of shark finning, but unsustainable fishing practices mean that shark populations are being depleted at a faster rate than they can restock. in addition to this a general paucity of data on global shark populations and fisheries means many species are hard to assess and thus protect. Whilst 181 of the 1,038 known shark and ray species are listed in one of the three threatened categories in the IUCN Red List, almost half of the total number are listed as Data Deficient, meaning that we do not yet have enough information on the particular species in order to make an assessment of its conservation status.

Urgent attention will be given to the most threatened species first which includes the sawfishes, angel sharks, guitarfishes and wedgefishes; these families all contain species which have been classified as Critically Endangered or Endangered by the IUCN Red List.

Implementation of this global strategy will require extensive engagement with the public and governments in the primary target countries as well as continued research to bridge the gaps in current data. However, ambitious as this strategy is it is entirely necessary if shark and ray populations are to be protected; more heartening perhaps is the commitment that these large conservation organisation have promised towards protecting the worlds sharks and rays by releasing this strategy.

Bräutigam, A., Callow, M., Campbell, I.R., Camhi, M.D., Cornish, A.S., Dulvy, N.K., Fordham, S.V., Fowler, S.L., Hood, A.R., McClennen, C., Reuter, E.L., Sant, G., Simpfendorfer, C.A. and Welch, D.J. (2015). Global Priorities for Conserving Sharks and Rays: A 2015–2025 Strategy.

Shark Research - Insights into mortality of whale sharks in Atlantic and Indian Ocean tuna fisheries

A recent research article in Biological Conservation has examined mortality rates of whale sharks (Rhincodon typus) as a result of the European tuna purse seine fisheries in the Atlantic Ocean and Indian Ocean.

Tuna often associate with large marine species such as dolphins and whale sharks; tuna fishermen sometimes rely on sightings of these species to indicate the presence of large schools of tuna. Once tuna have been sighted, a net is set to encircle the shoal and the bottom of the net is drawn together, like a purse, to trap the fish. Owing to the fact that there are often large marine fauna close by, these animals can also become trapped along with the tuna.

This study used log book data and observer data to assess the number of whale sharks sighted, caught and killed in purse seine nets in the Atlantic Ocean and the Indian Ocean. The biggest incidence of whale shark mortality occurred in certain hotspots where whale sharks overlapped with the purse seine fishers. Overall the incidence of whale shark mortality in the Atlantic and Indian Oceans was relatively low - from 1995 to 2011, 2 whale sharks were reported to have died out of 186 encircled by the nets. In recent times, the purse seine fisheries have implemented new strategies for ensuring the survival of whale sharks caught in nets, such as the cutting of the net to allow the shark to escape.

This data is in stark contrast to whale shark mortality in the Pacific Ocean provided by the Western and Central Pacific Fisheries Commission (WCPFC). Between 2007-2009, 56 whale sharks died in purse seine nets - the most common reason cited was that the fishermen were not aware of the presence of the shark in the net before mortality occurred. As a result of this, the WCPFC has banned the setting of nets around whale sharks since the beginning of 2014.

Additionally, both the Indian Ocean Tuna Commission (IOTC) and the WCPFC have admitted that accurate data on the number of whale sharks encircled and killed by purse seine fisheries is difficult to obtain. The data for this study relied on the accurate reporting of whale shark mortality by purse seine skippers and observers - which only cover 10% of the European fleet.

More analysis of the tuna purse seine fishery and better observer coverage is needed in order to obtain a better picture of the mortality of large pelagics in the tuna purse seine industry.

Shark Research - Researchers in Brazil find new techniques to improve the survival rate of tiger sharks caught in longline fisheries

Researchers in Brazil have used tagging methods to study the mortality and behaviour of juvenile tiger sharks (Galeocerdo cuvier) after they had been caught and released from bottom longline fishing gear.

The researchers tagged 21 tiger sharks caught in longlines during the course of the experiment. The sharks were hooked by the jaw using circle hooks as oppose to J-hooks - a method which has been previously proven to improve survival rates post-release. After the sharks were released, their movements were monitored via satellite. Most of the sharks caught were released in good health and none of the individuals died within 30 days of release, indicating that this species could be robust enough to successfully survive catch and release from longline circle hooks when caught as bycatch. This could be particularly important in this region of Brazil owing to the fact that all the sharks caught in this study were juveniles and therefore had no opportunity to reproduce. The authors also noted that the fishing pressure on the local shark population in this region was particularly high as artisanal fishermen in neighbouring waters fishing with gillnets and reported a much higher mortality rate for tiger sharks than reported from this study using longline circle hooks.

Interestingly, the researchers also discovered that tiger sharks released after capture tended to move into deeper water and did not return to the same area where they were captured for a considerable time. This suggests that these catch and release methods could be employed to successfully relocate problem tiger sharks in the area - a strategy which would be preferable to culling.

Other studies have predicted that tiger sharks are a keystone species in many ecosystems, and the removal of this apex predator would cause a great deal of disturbance in the ecosystems they are associated with. Therefore effective management strategies to minimise the impact of the fishing industry on tiger sharks are essential.  

Sharks, along with other marine animals, are often caught unintentionally by the fishing industry as bycatch and estimates suggest that the bulk of this is ascribed to longline fisheries. The fact that tiger sharks could survive catch and release - at least if circle hooks are used for the capture - could be used to facilitate the effective management of longline fisheries with regards to shark conservation.

André S. Afonso, Fábio H.V. Hazin, Post-release survival and behavior and exposure to fisheries in juvenile tiger sharks, Galeocerdo cuvier, from the South Atlantic, Journal of Experimental Marine Biology and Ecology, Volume 454, May 2014, Pages 55-62
Link to the paper

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