The UK’s marine environments are under more pressure than ever before. From the plastic pollution littering our beaches to the damage done by discarded fishing gear and intensive or sometimes illegal fishing practices. It is imperative to gain a better understanding and awareness of these issues and the action required to protect the seas we all love and depend on.
The team Andy has assembled includes divers, marine biologists and underwater videographers with the aim of assessing the marine environments along the West coast of the UK and to support the vital work of specific projects with the goal of protecting these habitats for future generations.
In February 2016 I was in Hong Kong looking into the shark fin trade, it was a couple of days before the Chinese New Year and there were fins everywhere, to suit all types of consumer. You could buy them in general food stores, pharmacies and fishing villages. You could buy small ones in plastic bags, multi-packs or single large ones with festive red bows tied around them.
I have written before about the origins of shark fin soup, however it is worth re-capping slightly: The cartilage in the fins is usually shredded and used primarily to provide texture and thickening to shark fin soup, a traditional Chinese soup or broth dating back to the Song Dynasty (960-1279). The dish is considered a luxury item embodying notions of hospitality, status and good fortune.
The origin of the dish can be traced to the Emperor Taizu of the Northern Song, who reigned from 960-976. It is said that he established shark fin soup to showcase his power, wealth and generosity. The dish’s popularity increased during the Ming Dynasty (1368-1644) as a result of an admiral of the imperial navy; Zheng He, who commanded expeditionary voyages around Asia and East Africa from 1405-1433, bringing back fins that fishermen had discarded. From this point onwards shark fin soup became an established dish and by the time of the Qing Dynasty (1644-1912) was in high demand.
It is not surprising that the popularity of a dish embodying such aristocracy and elitism declined once the Chinese Communist Party came to power in 1949. However, by the late 1980’s China had undergone far-reaching market-economy reforms which led to a rapidly expanding upper and middle class, who were eager to showcase their new-found wealth; shark fin soup once again became a way of doing so. Considering that the price per bowl can range from just HK$5 (45p) to an incredible HK$2000 (£180) depending on the type, style and preparation of the shark fin served, the dish is a viable option for a large number of people.
For fishermen operating within the global fin trade circumstances are different although all are motivated by a form of economic or socio-economic gain. Some large scale longlining operators see shark landings as a way to optimise their catch throughout the seasons, whereas with smaller-scale fisheries it is usually the prospect of short-term gain that initially entices them in. The price paid for the fins is higher than for their normal catch, yet they are paid relatively little when compared to the money made higher up the chain by the fin traders.
Hong Kong is an important trade hub and consumer of shark fins from shark fishermen operating globally. The main threat to shark populations remains overfishing, however the dried fin trade is undeniably a key driver of shark fishing, adding pressure to specific species and/or populations that are already at risk of extinction.
By using molecular genetics, the identification of shark species is possible even after fins have been removed. These techniques are the most reliable way to determine which species are the most heavily traded. However although this is useful, the species ID only gives us so much, for example some species specific populations are more at risk than others, for example globally the Porbeagle shark is classified as ‘Vulnerable’ by the IUCN (International Union for the Conservation of Nature), and yet the North East Atlantic population is ‘Critically Endangered’.
Thankfully a new scientific study has just been published by Fields et al. in the journal ‘Animal Conservation’ which has the potential to revolutionize our understanding of global shark trade dynamics and provide critical information required to effectively implement shark ﬁsheries management and trade restrictions.
In their study the authors investigate the trade of the scalloped hammerhead, of which there is a mounting concern about their sustainability with an increased effort to assess their global status and establish management measures. Globally the species is listed as ‘Critically Endangered’ by the IUCN and in 2013 was listed on Appendix II of CITES (Convention on International Trade in Endangered Species). The latter requires permits issued by the exporting country certifying that products were legally and sustainably taken from the wild and traceable throughout the supply chain.
However as the study points out, there have been seizures of illegal scalloped hammerhead products at the border in Hong Kong and retail market surveys have provided evidence of substantial non-compliance in the early implementation of CITES for scalloped hammerheads and other listed species. Although globally listed as ‘Critically Endangered’, there is variation in the status of individual scalloped hammerhead populations. Molecular analyses has revealed signiﬁcant global stock structure, with at least nine distinct regional populations described across the literature.
Therefore scalloped hammerhead shark populations thus experience different ﬁshing pressures and extinction risk based on the region in which they are found, making it important to know the sources of scalloped hammerhead products in fin trade and consumption locations such as Hong Kong. Fisheries management can then be prioritized further upstream in the supply chain.
In order to determine which populations of a species is being exploited by a fishery, the study uses a method known as GSI (‘genetic stock identification’). This technique is based on the use of genetic markers that differentiate populations. Samples of fin trimmings (smaller, cheaper off-cuts from the fin trade) were taken from an unknown mixture of shark populations and then compared to a comprehensive genetic database of all populations of that species. This method is possible because scalloped hammerheads have been the subject of a comprehensive analysis of global population structure and a previous study provided proof-of-concept that GSI was possible for this species.
The results for this study by Fields et al found that the majority of scalloped hammerhead fin trimmings (61.4%) came from the Eastern Paciﬁc population where this species is listed as ‘Endangered’. Overall six of the nine scalloped hammerhead populations were found in the fin samples, clearly indicating a near global sourcing of scalloped hammerhead ﬁns in the Hong Kong market.
The authors point out that many coastal sharks exhibit population structures similar to scalloped hammerheads and therefore similar databases and GSI workﬂows could be applied to these species if investments in global phylogeographic studies and trade surveys are undertaken. Such an investment would greatly advance species and stock-speciﬁc management for sharks, which are urgently needed worldwide.
This is particularly poignant, considering the news that broke just a few days ago about the record 26-tonne seizure of illegal shark fins by Hong Kong customs officials, in consignments from Ecuador worth an estimated HK $8.6 million (US $2.4 million). Consisting of predominantly Thresher and Silky shark species, with an estimated excess of 38,000 sharks killed. Add this to the other nine shark fin smuggling consignments that have already been seized by customs over the past 4 months, then that’s 67 tonnes so far this year. How many more have slipped through unnoticed? How long can shark populations sustain these pressures?
Reference: Fields et al 2020. DNA Zip-coding: identifying the source populations supplying the international trade of a critically endangered coastal shark. Animal Conservation. https://doi.org/10.1111/acv.12585
The newly discovered Pliotrema kajae and Pliotrema annae six-gill saw sharks, were discovered during research investigating small-scale fisheries operating off the coasts of Madagascar and Zanzibar. The discovery of these two new sharks highlights how little we still know about life in the ocean and the impact we are having on it.
Biofluorescence is essentially the ability of an organism, to absorb electromagnetic wavelengths from the visible light spectrum by fluorescent compounds, and the subsequent emission of this at a lower energy level.
A Basking Shark feeding on plankton. Photo Credit Richard Aspinall
The Basking Shark (Cetorhinus maximus) can reach lengths of up to 12m and is the largest shark in British waters and the second largest in the world after the Whale Shark. Both are plankton feeders, and it is the plankton rich water (primarily along the West Coast) during the spring and summer months which results in these giants visiting our shores.
Despite the basking shark belonging to the same family, as the great white shark (Lamniformes) it is in a genus of its own: Cetorhinidae. Of course being a plankton eater can make it rather more elusive than a great white and baiting it in is out of the question! However understanding more about how basking sharks feed and their prey certainly helps when trying to locate them in the Ocean. Dr Dave Sims and his team at the Plymouth Marine Laboratory have undertaken a substantial amount of work in this area;
Originally it was thought that basking sharks were indiscriminate filter feeders, engulfing whatever was suspended in front of them. However, Sims et al have shown that sharks elect to feed in waters which contain higher concentrations of their preferred prey species which happen to be planktonic shrimp. It is not known for certain how sharks actually locate high concentrations of these shrimp but there are currently a couple of theories. One theory is that sharks are capable of detecting the odour of dimethyl sulphide (DMS) emitted by phytoplankton when it is being grazed on by zooplankton. The second theory is that the sharks can detect activity of their prey using their electroreceptors known as Ampullae of Lorenzini.
Basking sharks feed at varying depths in the water column exploiting optimal food sources (deep sea shrimp have been found in their stomach contents). Sims et al reported that sharks do not feed when the plankton concentration is less than 1 gram of plankton per cubic meter of water, presumably because it is energetically not worthwhile. The higher the plankton concentration, the longer the sharks feed. When the plankton reach concentrations of 3 grams of per cubic meter of water the sharks will feed for up to two and a half times longer than when it’s at 1 gram. When they find a good place to feed they adopt a zigzag swimming pattern, this behaviour is termed “area restricted searching” or ARS. A preference for feeding occurs at current fronts where two water masses of different temperature meet. When the sea is calm less mixing occurs and the water stratifies into different layers, typically warmer on top, cooler below. This may result in the plankton experiencing low nutrient levels. Therefore plankton levels are higher where waters of different temperatures mix, such as at a thermal front. These fronts can be seen as almost slick lengths of still water and can be very useful for spotting sharks near the surface, these fronts can also collect quantities of debris such as jellyfish and seaweed which can make their identification even more obvious.
Basking sharks feed by a method known as obligate ram filter-feeding (Whale Sharks feed by a different technique known as suction feeding). They cruise along when feeding (typically around 1.9 miles per hour), with their mouth wide open, allowing the plankton rich water to pass through the gill slits where it is filtered out by gill rakers, near the rakers are cells which secrete large quantities of mucous when the shark closes its mouth (usually after 30-60 seconds), the rakers collapse squeezing the plankton mucous mixture into the mouth so it can be swallowed.
Many thanks to Richard Aspinall for the use of his images in this post.
References and Further Reading
Sims D.W. (1999) Threshold foraging behaviour of basking sharks on zooplankton: life on an energetic knife-edge? Proc. R.Soc.Lond. B.266:1437-1443.
Sims D.W.(2000) Filter-feeding and cruising speeds of basking sharks compared to optimal models: they filter-feed slower than predicted for their size. Jour. Exp. Mar. Biol. Ecol. 249: 65-76.
Sims D.W., Fox A.M. and Merret D.A. (1997) Basking shark occurrence off south-west England in relation to zooplankton abundance. J.Fish.Biol 51: 436-440.
Sims D.W. and Merret D.A. (1997) Determination of zooplankton characteristics in the presence of surface feeding basking sharks Cetorhinus maximus. Mar. Ecol. Prog. Ser. 158: 297-302.
Sims D.W. and Reid P.C. (2002) Congruent trends in long-term zooplankton decline in the north-east Atlantic and basking shark (Cetorhinus maximus) fishery catches off west Ireland. Fish. Oceanogr. 11:1: 59-63.
Sims D.W., Southall E.J., Richardson A.J., Reid P.C. and Metcalf J.D. (2003) Seasonal movements and behaviour of basking sharks from archival tagging: no evidence of winter hibernation. Mar.Ecol.Prog.Ser 248: 187-196.
Sims D.W., Southall E.J., Quayle V.A. and Fox A.M. (2000) Annual social behaviour of basking sharks associated with coastal front areas. Proc.R. Soc. Lond B. 267: 1897-1904.
Sims D.W and Quayle V.A. (1998) Selective foraging behaviour of basking sharks on zooplankton on a small scale front. Nature: 393: 460-464.