̽��ֱ�� of Cambridge - fishing

Fish fed to farmed salmon should be part of our diet, too, study suggests

cg605 — Wed, 20 Mar 2024 16:10:00 +0000

Scientists found that farmed salmon production leads to an overall loss of essential dietary nutrients. They say that eating more wild ‘feed’ species directly could benefit our health while reducing aquaculture demand for finite marine resources.

Researchers analysed the flow of nutrients from the edible species of wild fish used as feed, to the farmed salmon they were fed to. They found a decrease in six out of nine nutrients in the salmon fillet – calcium, iodine, iron, omega-3, vitamin B12 and vitamin A, but increased levels of selenium and zinc.

Most wild ‘feed’ fish met dietary nutrient recommendations at smaller portion sizes than farmed Atlantic salmon, including omega-3 fatty acids which are known to reduce the risk of cardiovascular disease and stroke.

“What we’re seeing is that most species of wild fish used as feed have a similar or greater density and range of micronutrients than farmed salmon fillets,” said lead author, Dr David Willer, Zoology Department, ̽��ֱ�� of Cambridge.

“Whilst still enjoying eating salmon and supporting sustainable growth in the sector, people should consider eating a greater and wider variety of wild fish species like sardines, mackerel and anchovies, to get more essential nutrients straight to their plate.”

In the UK, 71% of adults have insufficient vitamin D in winter, and teenage girls and women often have deficiencies of iodine, selenium and iron. Yet while, 24% of adults ate salmon weekly, only 5.4% ate mackerel, 1% anchovies and just 0.4% herring.

“Making a few small changes to our diet around the type of fish that we eat can go a long way to changing some of these deficiencies and increasing the health of both our population and planet,” said Willer.

̽��ֱ��researchers found consuming one-third of current food-grade wild feed fish directly would be the most efficient way of maximising nutrients from the sea.

“Marine fisheries are important local and global food systems, but large catches are being diverted towards farm feeds. Prioritising nutritious seafood for people can help improve both diets and ocean sustainability,” said senior author Dr James Robinson, Lancaster ̽��ֱ��.

This approach could help address global nutrient deficiencies say the team of scientists from the ̽��ֱ�� of Cambridge, Lancaster ̽��ֱ��, ̽��ֱ�� of Stirling and the ̽��ֱ�� of Aberdeen.

̽��ֱ��study was published today in the journal, Nature Food.

̽��ֱ��scientists calculated the balance of nutrients in edible portions of whole wild fish, used within pelleted salmon feed in Norway, compared to the farmed salmon fillets.

They focused on nine nutrients that are essential in human diets and concentrated in seafood – iodine, calcium, iron, vitamin B12, vitamin A, omega-3 (EPA + DHA), vitamin D, zinc and selenium.

̽��ֱ��wild fish studied included Pacific and Peruvian anchoveta, and Atlantic herring, mackerel, sprat and blue whiting – which are all marketed and consumed as seafood.

They found that these six feed species contained a greater, or similar, concentration of nutrients as the farmed salmon fillets. Quantities of calcium were over five times higher in wild feed fish fillets than salmon fillets, iodine was four times higher, and iron, omega-3, vitamin B12, and vitamin A were over 1.5 times higher.

Wild feed species and salmon had comparable quantities of vitamin D.

Zinc and selenium were found to be higher in salmon than the wild feed species – the researchers say these extra quantities are due to other salmon feed ingredients and are a real mark of progress in the salmon sector.

“Farmed salmon is an excellent source of nutrition, and is one of the best converters of feed of any farmed animal, but for the industry to grow it needs to become better at retaining key nutrients that it is fed. This can be done through more strategic use of feed ingredients, including from fishery by-products and sustainably-sourced, industrial-grade fish such as sand eels”, said Dr Richard Newton of the Institute of Aquaculture, ̽��ֱ�� of Stirling, whose team also included Professor Dave Little, Dr Wesley Malcorps and Björn Kok.

“It was interesting to see that we’re effectively wasting around 80% of the calcium and iodine from the feed fish – especially when we consider that women and teenage girls are often not getting enough of these nutrients”.

Willer said “These numbers have been underacknowledged by the aquaculture industry’s standard model of quoting Fish In Fish Out (FIFO) ratios rather than looking at nutrients.

̽��ֱ��researchers would like to see a nutrient retention metric adopted by the fishing and aquaculture industries. They believe that if combined with the current FIFO ratio, the industry could become more efficient, and reduce the burden on fish stocks that also provide seafood. ̽��ֱ��team are building a standardised and robust vehicle for integrating the nutrient retention metric into industry practice.

“We’d like to see the industry expand but not at a cost to our oceans,” said Willer.

“We’d also like to see a greater variety of affordable, convenient and appealing products made of wild ‘feed’ fish and fish and salmon by-products for direct human consumption.”

̽��ֱ��research was funded by the Scottish Government’s Rural and Environmental Science and Analytical Services Division (RESAS), a Royal Society ̽��ֱ�� Research Fellowship, a Leverhulme Trust Early Career Fellowship a Henslow Fellowship at Murray Edwards College and the ̽��ֱ�� of Cambridge.

Reference: D. Willer et al. Wild fish consumption can balance nutrient retention in farmed fish Nature Food DOI: 10.1038/s43016-024-00932-z

̽��ֱ��public are being encouraged to eat more wild fish, such as mackerel, anchovies and herring, which are often used within farmed salmon feeds. These oily fish contain essential nutrients including calcium, B12 and omega-3 but some are lost from our diets when we just eat the salmon fillet.

Making a few small changes to our diet around the type of fish that we eat can go a long way to changing some of these deficiencies and increasing the health of both our population and planet

Dr David Willer, Zoology Department

Joff Lee / ̽��ֱ��Image Bank / Getty

Mackerel with potato salad

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A treasure trove of unseen writing by Ted Hughes and Seamus Heaney reveals a vital creative friendship

ta385 — Sat, 14 Nov 2020 06:00:00 +0000

A unique archive acquired by Pembroke College Cambridge transforms our understanding of the two poets, showing how they drew career-defining inspiration from a little known friendship circle, and a shared passion for Ireland, water and fishing, spanning five decades.

Man v fish in the Amazon rainforest

amb206 — Fri, 11 Nov 2016 08:00:00 +0000

Hunting brings us close to our prey but the blood of a dying animal, spilling on to our hands, reminds us of our own mortality. Trapping, the use of technology to entice and capture, distances us from the act of killing. But, in their making and their function, traps connect our minds and bodies to the animals we pursue.

Each year, the Enawenê-nawê, an indigenous community in the Amazon, construct monumental fishing dams to harvest migrating fish vital to their diet. Social anthropologist Dr Chloe Nahum-Claudel carried out her PhD fieldwork with this community, learning a dialect spoken by fewer than 1,000 people. She spent six weeks living alongside a group of 12 men as they constructed a dam.

She says: “I’m interested in the relationship between people’s practical economic lives and how they see the universe. My research with the Enawenê-nawê suggests that their dams are much more than a means to obtain food. ̽��ֱ��process shapes their minds, bodies and relationships with one another, with their prey, and with spirits and ancestors. My research was timely because these technologies are threatened by the construction of hydroelectric dams in many of the Amazon’s tributaries.”

̽��ֱ��process of making traps became a particular focus for Nahum-Claudel when, as she explains, she realised that we touch on our own vulnerability every time we catch another living creature and subject it to our wishes. She recently convened a conference to consider trap-making and how these activities can be used to approach the relationship between humans and other species.

“To trap an animal you have to be very knowledgeable about its habits, its preferences and its weaknesses, and then you have to put all this knowledge into the making of an effective trap, and the placement and disguise of your equipment. That’s why traps offer an interesting way to approach practical encounters between ourselves and other species,” she says.

“I also realised that this was a neglected field of research. There’s been a lot written about hunting – and trapping is one method of catching prey. But unlike hunting, trapping doesn’t have to be fatal; ornithologists studying bird migrations have to trap birds and camera-traps are used to monitor tigers in India. I was interested in bringing people together to see if there were overlaps in the practice of trapping in such diverse contexts.”

Nahum-Claudel’s conference paper, which will form the first chapter of her forthcoming book, describes the Enawenê-nawê’s fishing technology and how it shapes them. ̽��ֱ��Enawenê-nawê are pescatarians who employ a variety of fishing techniques depending on the seasonal opportunities.

̽��ֱ��most impressive and unusual of these technologies are fishing dams built to coincide with the downstream migration of shoal-living fish, which spawn in the flooded forest during the rainy season. Each year teams of fishermen leave their large village while the fish are busy feasting and spawning and set to work building dams to trap the fish as they try to return downstream, once the river levels start to fall.

These dams are two-part technologies. In the first week or so, the men make a weir across the river using timber, bark and lianas from the surrounding forest. Men float the logs downriver and then dive into the fast flowing water to anchor them in the river bed. Frail, elder men later make nets to catch jumping fish. Ideally, the weir closes off the entire river so that not one fish can escape.

Once the weir is complete, the team turn their attention to making 100 or so man-sized traps which are crafted from cylinders of bark and basketry woven from the ribs of palm fronds. ̽��ֱ��special bark cylinders, which are said to resemble men’s thorax are prised off of tree trunks like waist coats, and must not snap. ̽��ֱ��completed trap is man-sized and phallic-looking.

In her paper, Nahum-Claudel explains that the activities of weir-building and trap-making demand different kinds of effort and imply contrasting kinds of sociability for the community. As the men construct the weir, moving vigorously between the forest and the water, they liken themselves to the creator deity who built the first dam as he made the world. Like him, they are masters of the boundary between land and water, which, as fisher people, is the crucial one in their universe.

She says: “What I mean by mastery is clear in the expression men use to describe the fish’s demise. They say that the fish ‘drown in the traps’. Men create the conditions in which the fish drown in their own watery dominion and, what’s more, the fish bring about their downfall by entering the traps out of their own curiosity and desire. When the men make traps, the seated handiwork makes them more contemplative. As anyone who does craftwork knows, the activity of making something with your hands encourages a mood of reflection and brings about identification with the object crafted.”

While weir-building is physically demanding and highly organised, tending the traps is more restful and is described by the Enawenê-nawê themselves as ‘lying down to rest’. Camped downstream of the dam, the men may be physically absent but their thoughts and actions are understood to have an impact on their traps’ ability to capture fish – precisely because the trap never loses its bond with the man who has crafted it.

“ ̽��ֱ��men live for the traps, devoting themselves to animating them so that they will catch plenty of fish,” says Nahum-Claudel. “They whisper to their traps and utter magical incantations. Sweet-smelling leaves are rubbed on the mouths of the traps to make them enticing to the fish. ̽��ֱ��team self-consciously strives to create a joyful atmosphere which the traps ‘desire’. There is much sexual banter – it’s locker-room talk all the time – and I was constantly reminded that I should not be grumpy, argumentative or stingy so as not to sour the mood.”

These practices seem to be about ensuring the traps’ efficacy and protecting the men themselves. Both of these aspects are thought of in terms of fertility. ̽��ֱ��traps are said to enter the weir ‘like a penis penetrating for the first time’ and the fish are seduced into entering their fragrant openings. As soon as they set the traps in place, the fishermen say that they become like virgins who have had sex for the first time.

“It is as if the traps were their own penises,” Nahum-Claudel says, “because their insertion thrusts men into the same state of vulnerability as teenage boys experience after they have had sex for their first time and their partner bleeds”. Through sex, men become open to the blood of women and they must exercise care in what they eat and in the activities they undertake when their wives menstruate or give birth. ̽��ֱ��first time this happens to a teenage boy, the restrictions to his activity and diet are strict – he lies down to rest and fast in his hammock for several days.

When the traps enter the weir the team of fishermen act in a very similar way, they fast and they say that they are now ‘lying down to rest’. This suggests that men are open to the blood of the fish caught in the traps – traps which are connected to their own bodies – just as they are open to the blood of women. Nahum-Claudel suggest that the dam fishing endeavour is about mitigating the risks involved in shedding blood while, at the same time, using the channel that exists between traps and men to promote the traps’ fertility. A theme that crops up repeatedly in Enawenê-nawê mythology is that the tables can easily turn and predator can become prey.

“Traps are all about hubris,” says Nahum-Claudel, “men build a deadly dam and drown fish in their own dominion. This activity is playing God, but everything about the men’s behaviour suggests that they are acutely aware of how risky this is, that it could – like a tragic play – end in their own downfall. What they stress as they trap the fish is not their Deity-like mastery but rather the subjection it implies. This feeling fits with the experiences of hunters and fishermen around the world. ̽��ֱ��proximity of life and death brings into focus human vulnerability so that hunting is rarely a question of unalloyed heroism. Enawenê-nawê dam fishing takes this to extremes because it is based on a monumental technology and entails intensive subjective and social involvement by the fishermen.”

Inset images from top: men harvest fish from their traps at Olowina River’s dam; the traps are ready to be inserted into the upriver face of a dam at Maxikywina River; a man dives down to pull up his trap from its position near the river bed. All photos: Chloe Nahum-Claudel, 2009. Nahum-Claudel's book is now available.

̽��ֱ��Enawenê-nawê people of the Amazon rainforest make beautifully engineered fishing dams. Living alongside this indigenous community, Dr Chloe Nahum-Claudel observed how the act of trapping fish shapes their minds, bodies and relationships. ̽��ֱ��proximity of life and death brings human vulnerability sharply into focus.

̽��ֱ��men live for the traps, devoting themselves to animating them so that they will catch plenty of fish.

Chloe Nahum-Claudel

Enawenê-nawê men check basket and bark traps for fish before reinserting them into the weir’s upriver face

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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What limpets can tell us about life on Mesolithic Oronsay

amb206 — Wed, 19 Aug 2015 08:00:00 +0000

Scroll to the end of the article to listen to the podcast.

For well over 100 years, archaeologists have been working in the windswept environment of the Isle of Oronsay on the west coast of Scotland to discover more about the people who lived on this tiny patch of land as long as 6,000 years ago – and how they exploited the natural environment around them.

Oronsay is remarkable for its stark beauty and its role as a habitat for wildlife. ̽��ֱ��island is also known for its five shell middens. Heaps of ‘kitchen waste’, they were left by people living at a period known as the Mesolithic. Also found are evidence of structures and hearths used for boiling and cooking food gathered from sea and shore. These too date from the Mesolithic.

Archaeologists have identified bones and shells from at least 30 species of marine life in the debris of these ancient rubbish heaps which, by virtue of their remoteness, lay undisturbed for so long under a thick covering of sand. Easily the most abundant of the molluscs to be found in the debris of the middens is the humble limpet.

Limpets can be found clinging to rocks all around the coast of Britain. Resembling the stereotype of a Chinese hat, the shell of the mollusc is conical but with ridges running from its outside edge to the peak. Inside, the soft body of the limpet is as vulnerable as a Dalek without its armour.

In the tough history of the Scottish islands, limpets were eaten mainly at periods when other foods were scarce. Today they are used by fishermen as bait and feature on the menus of only the most adventurous free food enthusiasts.

Archaeologist Sir Paul Mellars, emeritus professor of Prehistory and Human Evolution at Cambridge, first visited Oronsay in the mid-1970s. Over the course of five field seasons, often working in driving rain and at the mercy of Scottish midges, Mellars and colleagues excavated samples of shell material from all five middens on the island.

Using Radiocarbon dating, a technique that transformed the chronologies of human prehistory, archaeologists were able to show that the middens belong to the final stage of the Mesolithic period. This finding pointed to an intensive and relatively short-lived exploitation of the island by Mesolithic communities around the fourth millennium BC.

Modern visitors to Oronsay might well ask themselves why people would have chosen to live in such a far-flung environment, at least eight miles from the mainland. “As fishermen will tell you even today, the waters around Oronsay and the bigger island of Colonsay are rich in seafood. And the calcite-rich shell sand that covers much of the islands makes the land fertile enough to grow crops,” says Mellars.

“What’s so fascinating about the Oronsay middens is that they date from a time when people were on the point of moving from being hunter-gatherers, or hunter-fisher-gatherers, to farmers. These heaps of debris give us a glimpse of lives at a time of transition.”

Mellars’ early work focused on the range and relative importance of the different food resources as revealed by the contents of the middens. Debris from both fish and shellfish was evident. Analysis of these deposits showed that one species – saithe or coalfish – accounted for more than 90% of fish bones. Among molluscs, limpets greatly predominate over other molluscs such as whelks and periwinkles.

“It’s not hard to come up with plausible explanations for the preference for limpets, which are plentiful. They taste like bits of car tyre – but they are meatier, and more nutritious, than whelks and winkles. Furthermore, limpets are a lot easier to extract from their shells. These factors combine to make limpets a more energy efficient resource,” says Mellars.

̽��ֱ��shapes of limpet shells vary according to where they are found. Limpets inhabiting the lower parts of the tidal range are generally much flatter than those occupying the higher parts of the shore. Measurements of the height of limpet shells found in the middens revealed that they had been collected almost exclusively from the lower part of the tidal range – and chiefly from the very low tide situations exposed only during spring tides.

Mellars proposed two possible explanations. Firstly, limpets from low-tide zones are tenderer than others. Secondly, continuous harvesting of limpets may have led to an over-exploitation of more easily-accessible areas of the shore. With the disappearance of limpets from the upper levels, the human population sought foodstuffs close to the low tide line.

Advances in technology are now enabling Mellars to come up with answers to other key questions – especially the question of seasonal patterns of saithe fishing and harvesting. Although abundant around Oronsay and other islands in the summer, the fish migrate into deeper water late in the autumn. This means that communities relying on marine life would need to look elsewhere for sustenance during winter and spring.

In a collaboration between the Departments of Archaeology and Earth Sciences, limpet shells from the middens were embedded in resin and then cut in half to expose the calcite interiors. ̽��ֱ��oldest material deposited by the shell is at the pointed top while the shell deposited just before the limpets were harvested lies on the outermost edge.

Rebecca Vignols, an Earth Sciences student, used a computer-controlled microdrill to obtain tiny samples of calcite from points less than half a millimetre across in a closely-packed series at the edge of the shells. To get the full picture of seasonal change at the location the limpets lived, some limpets were drilled in a detailed series right to the top of the calcite in the shell. ̽��ֱ��ratio of light and heavy isotopes in water is affected by water temperatures, and the limpets build these changes into their shells as they grow.

̽��ֱ��oxygen isotope ratios in the shell samples were measured in the Department’s mass spectrometers. In this way, the water temperatures at the time the shells were harvested could be compared with the full seasonal temperature range at the site where they lived. This data reveals that limpets were harvested throughout the winter months. Limpets may have been consumed in combination with other seasonal foodstuffs such as hazel nuts.

̽��ֱ��five middens on Oronsay are located around I km apart from each other. All are close to the beach and face east, away from the worst of the Atlantic gales. “ ̽��ֱ��spacing of the middens seems to suggest that they were made by communities who moved along the shoreline. As they exhausted the supply of limpets in one half kilometre stretch of beach, they moved on to the next, perhaps making two runs per year in order to let the molluscs regenerate. You could almost describe it as a kind of farming,” says Mellars.

No pottery has been found in the middens but hundreds of ‘limpet scoops’ were retrieved. Some are simply finger-shaped pebbles from nearby beaches; others are made from deer horn. “Horn from at least two types of red deer was used. There have never been deer on Oronsay or Colonsay, which means that the horn may have come from Islay, Rum or Skye, and would have come by boat, suggesting a flourishing trade in this raw material for tool making,” says Mellars.

Oronsay’s middens all date to a similar period late in the Mesolithic and are composed of layers of material assembled over some 300 years. ̽��ֱ��apparent ceasing of limpet harvesting, which had been a way of life for generations, marks a significant change in lifestyle. Narratives about the spread of farming have shifted radically over the years.

“There’s been huge debate about the arrival of farming in the British Isles. “When I was a young archaeologist, it was thought that farming spread up the Danube and came north as a result of colonisation. In the 1980s, it was trendy to argue that local people made the transition to farming independently or with the influence of occasional incomers,” says Mellars.

“ ̽��ֱ��consensus today, and the theory I support, is that the communities who lived on Oronsay and other islands interbred with incomers who didn’t wipe them out but introduced them to other ways of ensuring a supply of food during the lean winter months. Something a lot more palatable than limpets – such as mutton and beef!”

This research was funded jointly by the Leverhulme Trust and the McDonald Institute for Archaeological Research (Cambridge).

Next in the Cambridge Animal Alphabet, M is for a small creature that can cause a big nuisance but also tell us a lot about pollution in water.

Inset images: Oronsay (Guy Beauchamp); Limpets (Kim Freeman); Drawings of shell sampling (Rebecca Vignols); Oronsay landscape with cows (Carron Brown).

The Cambridge Animal Alphabet series celebrates Cambridge's connections with animals through literature, art, science and society. Here, L is for Limpet and what they can tell us about Mesolithic middens, seasonal changes in the Atlantic Ocean, and the lives of people living on the remote Isle of Oronsay 6,000 years ago.

These heaps of debris give us a glimpse of lives at a time of transition

Paul Mellars

Clinging on

Guy Beauchamp

Oronsay

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Trawling survives selling previously discarded fish

bjb42 — Tue, 03 Aug 2010 00:00:00 +0000

A paper published in the current issue of the journal Conservation Letters by researchers from the ̽��ֱ�� of Cambridge shows that the drivers for the use of this once discarded resource are twofold: declining shrimp stocks and profits, and the development of alternative markets, which include the rapidly growing poultry-feed industry.

Trawl fishing is a technique employed the world over in which a fishing vessel drags a gaping net along the ocean floor. Unfortunately, though trawlers target a limited number of species such as shrimp and some fish, trawl nets capture anything in their path and seriously damage the seafloor as well. It's been estimated that trawlers in the tropics capture an average of 10 kilos of bycatch for every kilo of shrimp.

When trawl fishing first began in South and Southeast Asia, trawlers discarded large quantities of bycatch. ̽��ֱ��lead author of the study, Aaron Savio Lobo from the Department of Zoology, says this is now changing, "Recently there has been a shift in this trend and an increase in the use of the previously discarded bycatch."

Several species of bycatch which were traditionally discarded are now being sold for local consumption. Additionally, there has been increased demand for 'trash fish' to feed the region's rapidly growing poultry industry, a consequence of the country's rising affluence.

̽��ֱ��Cambridge team's research demonstrates that even though the profits obtained from the original target catch have fallen almost to nothing, the development of new markets for bycatch now means that trawlers can continue fishing and still remain profitable.

Looking to the policy implications of the study, Lobo says: "If appropriate measures are not taken immediately to limit overfishing then the outcomes could be catastrophic for the ecosystem and result in the permanent loss of livelihoods for the fishers in the region."

Fishermen barely eking out a profit because of overfishing of their target stock, shrimp, are now surviving by selling their bycatch (the low-value fish also caught in the large, indiscriminate nets). Although good for the fishermen, scientists warn that the prolonged trawl fishing along certain areas will lead to an "ecological catastrophe" and the "permanent loss of livelihoods for fishers" as well as other individuals who work in the industry.

If appropriate measures are not taken immediately to limit overfishing then the outcomes could be catastrophic for the ecosystem and result in the permanent loss of livelihoods for the fishers in the region.

Aaron Savio Lobo

leinadsimpson from Flickr

trawl

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