Writing as a marine biologist nearing the end of a 50-year career, mainly spent in commercial bivalve aquaculture, I feel I should be well placed to give an overview of changes I have seen in my lifetime and some thoughts on the future possible direction of food production from the seas. Central to this will be finding a balanced resolution between sustaining marine habitats whilst hopefully producing more valuable food for humans.

It was Sir Alistair Hardy, no less, who first proposed the idea that humans have an aquatic ancestry. The implications of this for human nutrition, most notably a relatively large requirement for long-chain omega-3 fatty acids, a major component of the brain and nervous system, has been highlighted by proponents such as Professor Michael Crawford, who has pointed out that the only other species on the planet with such large brains, dolphins, are fish eaters. Our ability to synthesise long-chain fatty acids (notably EPA and DHA) from the short chain ones found in terrestrial plants and hence throughout the terrestrial food-chain is very limited. The only ready-made source of long-chain fatty acids is algae and the aquatic food chain sustained by them. In terms of the global human population this means the marine food chain.

Mussel aquaculture in the Spanish Rías Baixas developed locally using homegrown expertise, but was supported by marine science led by personalities such as Miguel Torre at the Instituto Oceanográfico in La Coruña, looking at the upwelling off the north-west coast coast, and Antonio Figueras Snr, who originally worked in a hut built on an inter-tidal rock at Vilanova de Arousa, now the site of the CIMA laboratory. Growth was impressive though the 1970s and 1980s, with the introduction of mechanisation in grading, thinning and re-encording the mussels on to vertical growing ropes. At its peak, with about 3,500 large (up to 20 m × 27 m) rafts in the four rias, concerns grew that this intensity of aquaculture was resulting in excessive deposition of sediment below the rafts with consequential reduction in biodiversity in the immediate area. Controls included strict limits on the number of rafts permitted and a limit on the length of the vertical ‘dropper’ ropes to 12 m, (some operators had started to use ropes up to 27 m deep). The industry has stabilised and is now rigorously controlled, especially for algal toxins, which are frequent in the very productive upwelling water. Old (top) and new (bottom) ‘bateas’ (rafts) from which mussel growing ropes are suspended. Images: Alejandro Guerra / CIMA. 

When I first entered marine biology, I was fortunate that my home town of Poole was the centre of not only a small oyster industry but also had a laboratory at the power station, run jointly with Southampton University. The team there was led by the late Alan Ansell, DSc, to whom the marine aquarium at the Scottish Association for Marine Science (SAMS) is now dedicated. Working at the laboratory as a summer vacation. student, it may come as a surprise to many to hear that we were culturing phytoplankton in large scale outdoor tanks, with the aeration enriched with CO2 from the power station flue gas. This was in 1962, long before global warming had been thought about. The phytoplankton was then fed to American hard clams (Mercenaria mercenaria) a non-native species which had been found in Southampton Water and the Solent and which had become an important ‘bonus’ fishery in the area.

When I studied biological oceanography at Southampton, much emphasis was placed on measurement of marine productivity, the topic of Professor John Raymont’s magnum opus Plankton and Productivity in the Oceans (1963). He had led a project during the Second World War to fertilise a Scottish sea loch with a view to increasing the harvest from inshore waters. Leading marine biologists, including F.S. Russell and C. M. Yonge in their classic book The Seas (1928), had pointed out that farming the sea for bivalves was the most productive way of producing food in terms of unit surface area. They quoted a report by the old Ministry of Agriculture and Fisheries (MAFF) showing that an acre of good mussel bed can produce much more food (10,000 lbs of mussel meat p.a.) than any system of terrestrial farming of animals. This is without any input of feedstock or chemicals. So from an early stage in my career I was able to culture phytoplankton, measure it in the sea by chlorophyll analysis, filtration and by counting using an inverted microscope. I was taught that harvesting from close to the bottom of the marine food chain by filter feeders was the most environmentally benign way of producing food, because there were no inputs other than the seed bivalves, oysters, mussels or clams, and that the size of the resource at such a low trophic level was so great that the impact of harvesting by humans would be negligible. A few years later, eutrophication from terrestrial inputs became a hot issue and we were able to show that, by removing biomass from the system we were effectively improving water quality in very inshore waters. Indeed mussels have since been used for precisely that purpose in Swedish waters.

Marine conservation was very much in its infancy. For my doctorate study I monitored growth of hatchery-reared native oysters at a number of sites in Hampshire and Sussex. One of these was Pagham Harbour in West Sussex, which even in those days was a highly protected reserve. Nevertheless, I was given permission to include an experimental tray of native oysters there, though use of a boat was not permitted and the trial had to be accessed from the shore, a minor inconvenience. All the agencies I dealt with were highly supportive (Sea Fisheries Committees, MAFF and the old White Fish Authority (WFA)—now Seafish). In 1965 the first Pacific oysters (Crassostrea gigas) from Canada were brought into quarantine by MAFF at Conwy and semi-commercial quantities began to be provided by the WFA, which had set up a hatchery on the same site. So I was able to compare growth and mortality rates of both native and Pacific oysters. It became clear that it was the high natural mortality rate of the native oyster, rather than its slower growth rate, that was the key factor preventing its successful large scale cultivation. Since then, Pacific oysters have come to be regarded by many as an unwanted alien, even though they have greatly reduced fishing pressure on native oysters and in areas like the Thames estuary they frequently act as ‘cultch’ for juvenile native oysters, so aiding their recovery. A new book, Where Do Camels Belong? by Ken Thompson (Profile Books, 2014) considers the arbitrary nature of such decisions and should be read by all involved in this debate, as it is so central to the issue.

Morecambe Bay Oysters. We should celebrate the fact that a modern and environmentally benign form of oyster farming, from hatchery, through nursery stage and then to final on-growing to market size can still exist in Britain, given that it is an industry which all but disappeared fifty years ago. Images: Kelsey Thompson of Morecambe Bay Oysters.

An offer of work managing a hatchery for native oysters in Galicia, northern Spain took me into the world of fully commercial shellfish farming. It was here that I first witnessed large-scale shellfish farming, in the form of large mussel rafts in the Rías Baixas, of the Atlantic coast. That experience, though brief, was life changing. The fact that seafood was so much an everyday part of the diet of most Galicians and so important in the local economy was very different from all my previous experience.

Clearly any form of food production in the sea, either fishing wild stocks or growing fish or shellfish in aquaculture farms, will have environmental consequences of some degree. The aim should be to understand them and to manage them. That requires good marine experimental and observational science. A good example of such an approach is the long standing experimental closure of selected scallop beds around the Isle of Man.

The benign bureaucracy that existed previously has now become so complex that I would not feel capable of starting an aquaculture business today, however small. Indeed, the costs of having to deal with bureaucracy and the legal costs it could impose if any, even entirely innocent, error were made, would make it difficult to sleep peacefully at night, even if the business reached profitability. I have the greatest admiration for those few people who have succeeded in this (see above).

An area in which I have a particular interest is that of seagrass (Zostera) management, particularly because getting this wrong can have a very serious impact on shellfishing. Looking at the history of its decline from a fungal ‘wasting disease’ in the 1920s and 1930s, it is clear that inshore Zostera beds had survived over 50 years of extremely intensive oyster dredging during the massive boom in oyster fishery from about 1860 till the outbreak of the First World War. The decline of Zostera beds happened when oyster dredging was at a very low point. So the question arises whether Zostera beds in sedimentary estuaries may actually benefit from some disturbance. In a recent TV programme on Africa, Sir David Attenborough showed a seagrass bed being maintained precisely because it is cropped by sea turtles. On land we manage even highly protected grasslands by cropping. I do not believe we have sufficient evidence or experience of the best way of managing seagrass beds and some good experimental marine science is needed here.

The marine environment is dynamic and should be viewed as a mosaic in space and time. This means that marine conservation zones should be fluid, requiring constant monitoring and be susceptible to change or even to being rescinded as evidence of that changing mosaic emerges, not just immutable boundaries laid down for all time. The ‘iterative’ approach to their identification and nomination, as currently employed by the government, serves as a progressive approach towards the moving target of appropriate conservation zones, but it cannot simply cease with their designation. The sea will carry on changing.

Clive Askew (clive@bellhammer.myzen. co.uk) is a bivalve aquaculture consultant and former (retired) Fisheries Consultant to the Fishmongers’ Company.

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Clive Askew

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