Biological hazards on the rise

Siri Elise Dybdal

At the end of last year, thousands of tiny mauve stinger jellyfish squeezed through protective nets at Loch Duart’s fish farm in Loch Maddy in the Western Isles. The jellyfish invasion wiped out 300,000 salmon, worth approximately £1m. It followed an incident in 2013 where 20,000 salmon were killed by a similar invasion at Marine Harvest’s Clare Island site in Ireland. It was the same species of jellyfish that decimated Northern Ireland's only salmon farm in 2007, when more than 100,000 fish, worth around £1m, were destroyed at a site near Glenarm Bay. However, the biggest loss in recent years occurred in 2002, when thousands of solmaris jellyfish killed a million salmon in farms in the Western Isles. Fish valued at around £3m were destroyed in sea lochs at Leurbost, Gravir and Loch Erisort off Lewis. There have been several well-publicised incidents where blooms of jellyfish in northern Europe have caused damage to aquaculture operations. In addition to mass mortalities, chronic exposure has been linked to the development of gill pathologies, increased stress and reduced feeding in salmon. Warmer water temperatures are one of the main factors that have increased the presence of jellyfish. These have also spurred on harmful algal blooms (HAB), which can have a significant impact on salmon, as they irritate gills and compromise or kill the fish. Gill disease has been responsible for large-scale mass mortalities as well as poor growth and performance in farmed salmon.

Record year for jellyfish A report by The Marine Conservation Society (MCS) and the University of Exeter took stock of where and when jellyfish occur in UK seas. The survey is the largest of its kind in the UK and has been attracting a growing number of jellyfish sightings, with 2013 proving a record year, when 1,133 reports were received. 2014 was also turning out to be good for jellyfish, with over 500 reports already received by mid-July, only halfway through summer months when most records are received. Dr Peter Richardson, Biodiversity Programme Manager at MCS, confirms that there has been a rise in jellyfish in UK waters, but says there is a lack evidence as to why. “There are some regional increases, including the Irish Sea and parts of the North Sea – but globally the jury is out about global increases and their link to anthropogenic factors. Some consider what we are seeing now to be a part of a natural twenty year boom/bust cycle,” he says. “I think we are seeing increases in jellyfish abundance in recent years around the UK. Whether it is natural or not I don’t know.” Whether jellyfish increases are natural or linked to human activities, jelly blooms can have a devastating impact. Given the economic consequences, it is something the industry cannot afford to ignore. “They have shut down power stations, wiped out fish farms and closed down tourist beaches so I would suggest that fish farms should be prepared for the potential impacts of hazardous jellyfish blooms such as the recent Pelagia noctiluca events,” Dr Richardson emphasises, referring to the recent mauve stinger attacks. Through sampling, it has been uncovered that mauve stingers are widely distributed in warmer waters in the Northeast Atlantic. Mauve stingers "bloom" when they move into waters where there is plentiful food, and the Northeast Atlantic has bountiful supplies of plankton and young fish. They are also thought to breed more quickly in warmer waters and the seas off the British coast have warmed by up to 1°C since 2002.

A risk “There are papers that claim that the frequency in bloom is due to climate change, but there are few historical records to back this up,” says Dr Clive Fox, principal investigator in fisheries and plankton ecology at the Scottish Association for Marine Science (SAMS). He says this is due to lack of sampling. “We can’t say for definite. What I can say is that the feeling is that it is a risk, but data from 10 years is not long enough.” According to Dr Fox there are various ongoing projects attempting to spot jellyfish blooms from satellites. However, the weather in Scotland is often cloudy, which is an obstacle when using this method. “There is another project looking at using remotely operated aircraft,” he says, and explains that this is basically a smaller scale drone. “It is still only at the research stage, but has the potential to spot blooms under the clouds,” he points out. Currently, he says, the aquaculture industry’s response to blooms is to put a tarpaulin or a ring of bubbles around the farm. “The bubble curtains just break the jellyfish up, but the stinging cells would still be active,” says Dr Fox, who admits there is currently “nothing very obvious” that can be done. The situation is further complicated by the fact that there is relatively poor understanding of the different species and the ecology of jellyfish in relation to conditions triggering blooms and outbreaks. He says more research is needed and believes being able to monitor the incursion might help mitigate the challenges.

Working with industry partners The Crown Estate-funded project “Jellyfish monitoring in western Scottish waters in relation to aquaculture activities – establishment and testing of protocols for a monitoring network” by Clive Fox, Keith Davidson and Christine Beveridge from SAMS, was set up to evaluate the feasibility of establishing a monitoring program. It started in January 2012 and ran until June 2014. A previous project had already considered methods for monitoring the larger “true” jellyfish (scyphomedusae), but identified that many problems at farms would probably be caused by smaller hydromedusae in the water column. These species cannot be detected remotely and collection of plankton samples remains the only available method for monitoring their presence and abundance. The present project was set up to investigate whether a more comprehensive monitoring system could be established across the west coast. Working with industry partners, the project has established a baseline of the species occurring from the Clyde to the north of Skye over a period of two years. The project also produced an internet-based reporting system, which could provide the industry with a platform for collating data across multiple sites. It would be much more likely that patterns for jellyfish bloom occurrence would emerge if data across the whole west of Scotland could be analysed as a whole – as opposed to each company having access only to its own records. The project also trained farm staff in the collection of plankton samples and in identifying jellyfish, as well as preparing a sampling manual to guide monitoring. However, one significant issue which has emerged from the training workshops, is that farm staff felt they would be unlikely to find the time to analyse plankton samples for medusa themselves.

Algal blooms Another biological challenge the industry has faced in recent years is the threat posed by harmful algal blooms (HABs). Algal blooms are naturally occurring phenomena, but in recent decades there appears to have been an increase in their frequency and intensity and they are reported to be occurring over a wider geographical area. HABs can have a significant impact on salmon gill health, even though only 40 or so species are believed to produce potent toxins. Other species can cause physical damage, such as those containing barbs that can lodge among gill tissues. Blooms of these species can cause a great deal of financial damage to the industry.

Supporting research Jamie Smith, technical executive at the Scottish Salmon Producers’ Organisation (SSPO), says algal blooms are problematic because they use up the oxygen in the water as well as irritating the gills of salmon – either compromising the health of the fish or killing them. Such blooms often appear in connection with bad water quality. In Scotland, both visual inspection and monitoring are used to control the situation. Some companies subscribe to a service that provides satellite images showing the presence and movement of harmful algal blooms, giving them a chance to take mitigating action. “Farms also monitor and have plankton control most days,” Smith says. He says warmer waters have been increasing the frequency of incidents in recent times and predicts blooms could become more recurrent in the future. As a result of this threat, he says there is currently a lot of active research ongoing in the field. The industry is also supporting (financially and in kind) multi-million pound research projects on the subject. Amongst other things, SSPO members participate in the EU-funded AQUA-USERS project, which provides observation data that can indicate environmental events such as HABs. The key purpose of the project is to develop an application that brings together satellite information on water quality and temperature with in-situ observations, as well as relevant weather forecasts and ocean data, in order to predict when these environmental challenges will appear. To address the challenges, Scottish salmon farmers are implementing the latest husbandry techniques underpinned by the standards of production laid out in the Code of Good Practice for Scottish Finfish Aquaculture (CoGP), Smith says. These include the gathering and exchange of information and adopting innovative techniques.

On farm practice “The challenge depends on the size and type of jellyfish – the larger ones can be pushed up against the nets, restricting the flow of water, which means the fish do not receive enough oxygen. The smaller jellyfish, which can pass through the mesh of the nets, can clog the gills and again restrict the flow of oxygen to the salmon or they can have a toxic effect on the gills. Thankfully this is a rare event,” says Smith. “In the worst cases you can see the marks where fish have been stung along their flanks,” says Steve Bracken, business development manager for Marine Harvest Scotland. According to Bracken, daily water quality monitoring takes place on Marine Harvest’s farms to check for the presence of algae and the smaller jellyfish. Remote sensing is also used, but needs to be developed further as a method for early warning. Compressed air systems are used to flush the jellyfish away from the nets by creating an upwelling water movement, he says. Communication and cooperation “The dynamic marine environment alongside the effects of global climate change provides challenges for Scotland’s salmon farmers,” the SSPO says. “In 2014, there were anecdotal reports that water temperatures around the coast of Scotland were higher than expected, which had knock-on effects on the water quality. These changes to water temperature and quality can result in algal blooms, plankton and jellyfish swarms, which all present challenges for fish health.” Scottish salmon farmers have improved communication and co-operation amongst groups of farms across large areas. The sector also welcomes collaboration from outside the industry. “The Scottish salmon farming industry is open to cross-sector collaborations that have the potential to improve detection, recording and interpretation of environmental data, or may reduce the impact from these naturally occurring events,” Smith reflects. In the future, the SSPO says key points will be the ongoing commitment to research, subscribing to satellite images to predict the occurrence of HABs, and the continued exchange of information across the industry.