Wednesday, 27 April 2016

Studying the phytoplankton with citizen science

The phytoplankton in the sea, and the plankton food web they support, underpin the rest of the marine food chain (seeThe importance of plankton). Living at the surface of the sea the plankton are particularly sensitive to changes in sea surface temperature, both directly through the effects of temperature upon their physiology, and indirectly through the effects of temperature upon the physics of the water column. As sea surface temperatures increase due to current global warming evidence is mounting that the phytoplankton are reacting to this change in their habitat, and this calls for more research to understand (see: What’s happening to the oceans’ phytoplankton?).
Phytoplankton: These microscopic cells begin the marine food chain. They are so numerous they account for 50% of photosynthesis on Earth.
One new project that is specifically designed to enable you to help add to our knowledge of the Oceans’ phytoplankton is the citizen science Secchi Disk study This study combines a 150 year-old piece of equipment invented by the Pope’s astronomer with modern smartphone technology to help collect data on the phytoplankton from oceans around the world. So, what is a Secchi Disk and how does the project work, and most importantly, how can you take part?
The Secchi Disk is a plain white, 30cm diameter disk attached to a tape measure and weighted from below. It is one of the simplest and oldest pieces of marine scientific equipment.
Firstly, just what is a Secchi Disk ? Long before modern navigational aids, when sailors just had a compass, the sun and the stars to rely upon, they knew that either the colour of the water or its clarity could provide information about their location, for example the Sargasso Sea is particularly clear while neighbouring waters are less so. To help sailors determine water clarity they would lower a white object, often a disk, over the side of the ship and watch it disappear from sight; the quicker it disappeared from sight the lower was the water clarity. Until 1865 this technique was relatively, informal. In 1865 Pope Pius IX tasked Alessandro Cialdi the commander of the Papal navy to determine the currents in the Mediterranean Sea. Cialdi asked the Pope’s Astronomer Pietro Angelo Secchi, to formalize the method of using a white disk to help determine the currents by measuring their changing clarity. A scientific paper on the currents in the Mediterranean sea was written and from then on the white disk became known as a Secchi Disk, and it has been used as a standard and simple way to measure water clarity ever since. Unchanged for decades, a Secchi Disk is a plain white disk 30 cm in diameter that is attached to a tape measure and weighted from below. When the disk is lowered into the water from the side of a boat the depth at which it just disappears from sight is noted and is called the Secchi Depth.
When lowered vertically into the water the depth below the surface at which the Secchi Disk disappears is called the Secchi Depth and this measures water clarity. In water over 25m deep and over 1km from shore, the main determinant of water clarity is the phytoplankton. 
Away from estuaries and coasts the main determinant of water clarity is the amount of phytoplankton in the water column. Consequently, marine biologists have used the Secchi Depth to measure phytoplankton since the Secchi Disk’s ‘invention’ in 1865. Now, with evidence to suggest the phytoplankton in the world’s oceans are changing due to climate change, and because of their important role in the marine food chain and the Earth’s carbon cycle, we need to know if, how and why they are changing. Even though we can now obtain remote estimates of phytoplankton from satellite measurements of ocean colour, in situ measurements are still fundamental and scientists still use Secchi Disks. However, there are simply too few scientists to survey the world's oceans as well as we would wish. This is where sailors, acting as citizen scientists, can help science by making and using a Secchi Disk. By collecting Secchi Depths from around the world, from now and into the indefinite future, any seafarer can help grow the database of Secchi Depth measurements to give a much bigger time series in terms of its temporal and spatial extent.
Dr Richard R Kirby created the citizen science Secchi Disk study in 2013 to enable any seafarer to help collect data to understand the affect of climate change on the phytoplankton.
So how can citizen scientists get involved ? Anyone who goes to sea can take part, whether you are a sailor with your own yacht, a crew-member, or are on a charter sailing holiday, or you are an angler, a diver or a fisherman. All you need is a Secchi Disk and the free Secchi app installed onto your smartphone or tablet. The Secchi app is available as a native app for iOS and Android phones and also as a Web app (Secchi Web) for Windows devices (Secchi Web also runs on iOS and Android). The Secchi Disk is a DIY element to the project. A Secchi disk can be made from any material, such as a white plastic bucket lid or a piece of plywood painted white. Offcuts of 3-5 mm white Foamex that you can often obtain from printers work very well. Attached to an inexpensive fibreglass tape measure with a weight hanging below, the Secchi Disk is lowered vertically into the seawater (you need to use sufficient weight to make the disk sink vertically, which will depend upon the disk material), and the Secchi Depth is noted. The quicker the Secchi Disk disappears from sight the smaller the Secchi Depth and the more phytoplankton there is in the water. Simple!

Once the Secchi Depth is determined, you use your smartphone and the free Secchi app to obtain the GPS location and to enter the Secchi depth - a network connection isn’t required for this. The Secchi App will store the data on the phone and the Secchi Disk project receives the data as soon as network connectivity is regained. Anyone can follow the data collected on the project map. The aim of the project is to chart the seasonal and annual changes of the phytoplankton from now and into the future. It is a long-term project that carries on indefinitely. Seafarers may measure the Secchi depth at the same place regularly, or occasionally, or they may take measurements from different places as they travel. The more sailors that take part the better the coverage of the oceans, and the more remarkable and useful the citizen science Secchi Depth database will become.

I’ll now reveal my vested interest in this blog since I am the leader of the Secchi Disk project. Often, we look back and wish we had already started monitoring something about the natural world - if only we had started measuring 'x' some years ago. In terms of the phytoplankton there really is no time like the present to start growing the Secchi Depth database and this is why I created the Secchi App and this citizen science project. Since its launch in 2013 the project has gone from strength to strength. Already it is the world’s largest marine citizen science study with data from every ocean. In 2014 there was a Secchi Disk 'first' when Jimmy Cornell’s grand-daughter Nera measured a Secchi depth from the Northwest Passage, which has only recently become navigable due to global warming. Whether sailing in coastal waters or cruising across oceans, families find the project particularly useful as an educational addition to being on the water. This year small boat fishermen joined the study, as they are fully aware of the importance of understanding the phytoplankton that underpins all fisheries.

So, if you go to sea, why not take part in this study to help improve our understanding of the oceans’ phytoplankton, or alternatively, share this blog, so that more citizen scientists can find out about the project.

You can find the Secchi Disk project at, on Facebook and on Twitter @secchiapp.

Dr Richard Kirby is a British plankton expert, scientist, author and speaker. Follow Richard @planktonpundit on Twitter. Richard’s book “Ocean Drifters, a secret world beneath the waves” is available on Amazon and as an iBook

Friday, 1 April 2016

Conserving the Falkland Islands' natural environment

Falklands Conservation is a non-governmental organisation working to protect the wildlife in the Falkland Islands for future generations. It undertakes practical conservation projects, surveys and scientific studies, conducts annual monitoring of seabird populations, rehabilitates oiled penguins, publishes guides and information on many aspects of the Falkland Islands environment, and involves islanders of all ages in its activities, including running a Watch Group for children. It relies on donations and public support to carry out its work.

The Annual Seabird Monitoring Programme 

The Falkland Islands support seabird populations that are of global importance both numerically, and in terms of conservation status. An estimated 72% of the global population of Black-browed Albatross breeds in the Islands which are also home to the majority of the world’s population of Southern Rockhopper Penguin, Gentoo Penguin and Southern Giant Petrel. The Southern Rockhopper Penguin is classified as 'Vulnerable' (IUCN Redlist), due to large decreases in its population over the last century. Whilst the Black-browed Albatross has recently made positive moves from 'Endangered' to 'Near Threatened', it shares this status with the Gentoo Penguin which moved from 'Least Concern' in the early 90s. The Southern Giant Petrel moved from 'Vulnerable' to 'Least Concern' in the early 2000s. 
Teaching a local volunteer how to ring young black-browed albatrosses on Steeple Jason in March 2015.
The changing fortunes of these important Falkland Islands species demonstrates how critical it is to monitor such populations, and, given the proportions of the global populations in the Islands, it is easy to understand how further changes in local populations could readily impact the global conservation status of these species, just as they have before. Falklands Conservation initiated the Falkland Islands Seabird Monitoring Programme (FISMP) in 1989/90. Since then, population monitoring has continued on an almost annual basis. 

Currently the FISMP monitors breeding population trends and breeding success in Gentoo Penguin, Southern Rockhopper Penguin, King Penguin, Black-browed Albatross, Southern Giant Petrel and Imperial Shag, visiting remote survey sites and islands by 4 x 4, plane and boat. Monitoring a range of species with differing ecologies has additional benefits as they also serve as indicators of potential change in other Falkland Islands seabird populations or oceanographic conditions.
Counting gentoo penguins for the Falkland Islands Seabird Monitoring Project.

Building Capacity for Habitat Restoration 

This Darwin Plus funded project trials the use of native plants for restoring eroded land on farms and nature reserves. Soil erosion from fire, climate change and grazing is a significant problem across the Falkland Islands and threatens important habitats including coastal tussac and its ecosystem with penguins and sea lions. There is currently no supply of native plant seed for landowners wishing to restore their land with native plants and this project aims to provide start up quantities of seed and growing information.
A variety of seeds collected.
To do this a Native Seed Growing Hub has been established, providing seeds for trials on a range of eroded soils across the Falklands. Fourteen native plant species have been tested and a number, including tussac grass and fuegian couch grass, have grown very successfully.
Assessing the habitat restoration plots.

Oiled Seabird Rehabilitation Facility 

The Oiled Seabird Rehabilitation Facility cares for oiled and injured seabirds, mostly penguins, which are brought in by the public to be cleaned of oil, and then rehabilitated until they are ready to be released.
First, vegetable oil is massaged into the feathers. This thins out the heavy crude oil. Then washing up liquid and water remove all trace of the oil.
This involves an intensive programme of washing, hand feeding and husbandry, conducted by staff and volunteers. This includes the generous donation of fish from local fishing companies. The facility was formally opened in March 2015, and is also providing capacity for the offshore oil industry’s Oil Spill Response Plans.
The penguins are given time to swim and preen, ensuring they are fully waterproof before they are released back into the wild.
The penguins are then taken to a remote beach to be released.

Watch Group 

Our efforts to build appreciation and understanding of wildlife and conservation continue through the Watch Group. The junior membership of Falklands Conservation has 55 members ranging in age from 8 years old to 15.
Looking at a sample aboard the expedition vessel Hans Hansson.
With the support of the Standard Chartered Bank, we are able to take children to many of the more remote parts of the Falklands, and to maintain a programme of activities throughout the year. These incorporate our main strategic focus; strengthening biosecurity and managing invasive species, terrestrial habitat restoration, and enhancing marine management.
Children explore rock pools during a camp to Elephant Beach Farm.
The children are educated and enthused about these topics through activities such as tussac planting, beach cleans, and exploring marine ecosystems through rock pooling and collaboration with the Shallow Marine Survey Group. Plans for the future are to incorporate an education centre into our new building.
A group takes a closer look at the pond life at Hawks Nest Pond, West Falkland.

Lower Plants Project 

The Lower Plants Project is a two year project surveying the bryophytes and lichens of the Falkland Islands undertaken and run by Falklands Conservation between 2014–2016. Funded by the UK Government through DEFRA (Department for Environment, Food and Rural Affairs) and the Darwin Initiative, this project was set to fill the ‘critical knowledge gap’ in bryophytes and lichens that was identified in the Falkland Islands Biodiversity Strategy 2008–2018, and to increase local awareness.
A workshop run to increase awareness of the different species.
The project is addressing this knowledge gap, and is providing data essential for effective conservation planning and enhancement of the ‘Important Plant Areas’ of the Islands. The main objective is to create an up to date species list for the three taxonomic groups we know as mosses, liverworts and lichens and to create a capacity and legacy for future research on this area of botany.
A selection of mosses, liverworts and lichens.
The legacy would be in the form of a laboratory, a herbarium, and an increased awareness among the public of the Falkland Islands regarding bryophytes and lichens. To date, the project has discovered 40 new moss records, 8 new liverwort records and 80 new lichen records for the Falklands, which include approximately 15 species new to science. 

If you would like to become a member of Falklands Conservation, adopt a penguin, or donate towards our Wildlife Rehabilitation Centre, the education centre for the Watch Group, or any other of our conservation activities, please visit, our Just Giving Site at or follow us on Twitter @FI_Conservation or Facebook

Monday, 8 February 2016

What’s happening to the oceans’ phytoplankton?

Research suggests that the oceans’ phytoplankton are declining in abundance in many places.
Global Biosphere September 1997 - August 1998 composite image showing the magnitude and distribution of global oceanic chlorophyll a and terrestrial primary production.

But first of all, what are phytoplankton, and secondly, why should we be interested in what’s happening to them?

Phytoplankton are microalgae that float, drifting in the seas’ sunlit surface. Although these microalgae are too small individually to be seen by your naked eye, collectively they are so numerous that they are the ocean’s main primary producers. Just like plants on land, the phytoplankton uses the energy in sunlight to combine carbon dioxide and water to produce sugar and oxygen in the process we call photosynthesis. To give you an idea of the significance of phytoplankton, it is interesting to compare them to the macroalgae – the seaweeds, with which most people will be more familiar. Collectively, the macroalgae, although much bigger, account for less than 5% of the total primary production in the sea each year. As primary producers the phytoplankton underpin the marine food chain and determine the abundance of other marine life, from the amount of fish in the sea to the number of polar bears on the Arctic ice (see: The importance of plankton).

The phytoplankton do more than underpin the marine food chain however, as they also play a central role in the global carbon cycle by influencing the atmospheric composition of the greenhouse gas carbon dioxide. Over hundreds of millions of years the burial of some of the organic carbon fixed by phytoplankton photosynthesis sequestered carbon in the sediments; some of this became the Earth’s oil and gas reserves. Likewise, over similar time-scales, the burial of inorganic carbon in the calcium carbonate remains of phytoplankton coccolithophores sequestered carbon in deposits we now know as chalk. It is changes in the rates of phytoplankton growth and carbon fixation that are thought to have played an important role as feedback mechanisms driving climate change during glacial / interglacial periods. For example, as global temperatures cooled as the Earth entered a glacial period, it is suggested that steeper temperature gradients would have developed between the poles and the equator strengthening winds, which are thought to have then blown nutrients from the land to the sea. This increase in nutrients could have acted as a fertiliser promoting phytoplankton growth leading to a greater drawdown of carbon dioxide and a further cooling of the atmosphere.

So, as you can see, the phytoplankton play an important role on Earth despite their diminutive size, which is why a paper published by 3 Canadian Scientists in Nature in 2010 ( and caused quite a stir. The authors of the Nature paper led by Daniel Boyce used a 100-year data set to see if phytoplankton had changed in their abundance in the sea. Their results suggested that the phytoplankton had reduced in abundance globally by 40% since 1950, or a decline of about 1% per year. They suggested that warming seas due to climate change might have led to increased stratification (layering) reducing the supply of nutrients to the surface from deeper waters; in essence, the supply of fertiliser to the surface promoting phytoplankton growth had reduced. The Canadian scientists study was controversial however. Other scientists thought they saw different results and the study was also criticised on the fact that it combined data on phytoplankton collected in very different ways. The earlier part of the data set used Secchi Depths as a measure of phytoplankton (more about Secchi Depths in a later blog) and the later part used measurements of chlorophyll abundance.

Fast forward to the last three months of 2015 and three new studies on phytoplankton abundance were published in quick succession. The first of these by Cecile Rousseau and Watson Gregg looked at satellite ocean colour and environmental data, and reported that diatoms had declined by more than 1 percent per year from 1998 to 2012 globally (the 15-year period the scientists studied) leading to changes in both phytoplankton abundance and community composition. Losses of diatoms were most significant in the North Pacific, the North Indian, and the Equatorial Indian oceans ( and The scientists’ study suggested that a likely cause was a shallowing of the mixed-layer by 1.8 meters (5.9 feet). The mixed-layer is the uppermost layer of ocean water and a shallowing would reduce the nutrients available for phytoplankton growth. Why the mixed layer shallowed is still uncertain. One possibility the scientists suggested is a change in wind.
A collection of diatoms ©Richard Kirby. About 50% of the primary production on Earth takes place in the oceans and diatoms are the most important photosynthetic eukaryotes accounting for about 40% of total marine primary production.

However, the second study, also published in October 2015, and led by Michael Behrenfeld ( suggested that there is an inherent error in the algorithm we use to convert satellite measures of ocean colour (an estimation of chlorophyll abundance) into phytoplankton biomass. Phytoplankton can alter the amount of chlorophyll in their cells depending upon light intensity and nutrients. As a result, the scientists suggested that contemporary relationships between chlorophyll changes derived from satellite measures of ocean colour, are not indicative of proportional changes in productivity; light-driven decreases in chlorophyll can be associated with constant or even increased photosynthesis. In other words, failing to take account of this feature introduces a source of error causing temporal anomalies in surface chlorophyll to over-represent associated changes in mixed-layer productivity.

The third study published in November 2015 by lead author Sara Rivero-Calle ( and looked at the abundance of coccolithophores in the North Atlantic over the last 45 years. Coccolithophores are the phytoplankton that surround their cells with plates of calcium carbonate. These authors found that the relative abundance of coccolithophores had increased 10 times, or by an order of magnitude, during this 45-year period. During the same period the authors found that the relative abundance of other species such as diatoms, had declined in some places. To explain the increase in coccolithophores the authors suggested that they may be taking advantage of the extra carbon from carbon dioxide dissolved in seawater as a result of rising levels of atmospheric carbon dioxide. Interestingly, in the geological record, coccolithophores have been typically more abundant during Earth’s warm interglacial and high CO2 periods.

Now, at the beginning of 2016, a new paper titled “A reduction in marine primary productivity driven by rapid warming over the tropical Indian Ocean” has just been published in the Journal Geophysical Research Letters - In the paper led by author Matthew Koll Roxy from the Centre for Climate Change Research at the Indian Institute of Tropical Meteorology, data is presented demonstrating a decline in phytoplankton in the western Indian Ocean by up to 20% over the last 60 years. The western Indian Ocean shows the largest warming trend among the tropical oceans and the study’s authors found the downward trend in phytoplankton could be explained by a reduction in nutrients reaching the surface form deeper waters due to increased stratification of the water column.

So what’s happening to the ocean’s phytoplankton at a global scale? I’d say there is both mounting evidence that phytoplankton populations are changing globally and that we need to understand how we study them, and as a result we urgently need much more research. As I explained above, these tiny organisms are central to the marine food chain and the global carbon cycle and consequently, I’d argue, it is imperative to understand what is happening to help us appreciate the ramifications of climate change, not just in the oceans but also for our planet.

Dr Richard Kirby is a British plankton expert, scientist, author and speaker. Follow Richard @planktonpundit on Twitter. Richard’s book “Ocean Drifters, a secret world beneath the waves” is available on Amazon and as an iBook

Sunday, 13 December 2015

Mangroves, an invaluable ally against climate change

Mangroves are the rainforests by the sea, found at the boundary where land meets ocean. They serve a wide range of ecological functions, providing economically valuable products and services. Mangroves, once estimated to cover an area of over 36 million hectares, dominated large stretches of tropical coastline. However, due to ongoing development pressures, mangroves are degraded and their area substantially diminished relative to their historic range, less than 15 million hectares remain.

Mangrove forests are vital for healthy coastal ecosystems. The shallow inter-tidal reaches that characterize mangrove wetlands offer refuge and nursery grounds for juvenile fish, crabs, shrimps, and molluscs, and are prime nesting and migratory sites for hundreds of bird species. Additionally, manatees, crab-eating monkeys, monitor lizards, Bengal tigers, sea turtles and mudskipper fish utilize the mangrove wetlands.

Mangroves play a vital role in protecting sea grasses and coral reefs from sediments and pollution, filtering out heavy metals and halting shoreline erosion. Mangroves buffer against hurricane winds, storm surges and tsunamis, saving thousands of lives, while protecting infrastructure. Mangroves are also invaluable in combating climate change!

Mangroves, tidal marshes and seagrass beds remove massive amounts of carbon from the atmosphere and fix it in mangrove soils, where it can remain for millennia. Unlike terrestrial forests, marine wetlands are constantly building carbon pools, storing large amounts of so-called "blue carbon" in highly organic sediments, storing up to 5-times more carbon per unit area than tropical rainforests. Their carbon sequestration potential is significant in helping to reduce atmospheric carbon dioxide. Including the carbon stored in soils, mangrove forests store the most carbon per hectare of any other forest type.

Deforestation and land-use change currently account for 8-20% of global anthropogenic carbon dioxide (CO2) emissions, second only to fossil fuel combustion. Destruction of mangroves accounts for around 10% of emissions from deforestation globally, despite accounting for just 0.7% of tropical forest area. Moreover, if left undisturbed, the carbon storage by mangroves currently continues to expand through biological sequestration of CO2 and carbon burial. If current trends in conversion continue, however, much of the carbon stored in mangroves along with its future accumulation could be lost.

Mangroves are among the most threatened and rapidly disappearing natural environments worldwide, with a much higher rate of loss than other tropical rainforests. One of the greatest threats to mangroves today is the rapacious shrimp aquaculture industry, which has caused massive mangrove losses in Asia and Latin America. With the current 0.7% rate of loss, most of the world’s mangroves may disappear by the end of this century. Conversion for agriculture or aquaculture, results in massive emissions of greenhouse gases into the atmosphere, as mangroves change from a sink for carbon to a massive source. This greatly exacerbates the problems of global warming.

Restoring mangrove forests would deliver significant benefits in reducing net greenhouse gas emissions, improving food security and livelihoods of coastal communities, increasing resilience in the face of sea level rise and extreme weather events, and improving habitat for many vulnerable species along extremely biodiverse tropical coastlines.

Alfredo Quarto is the Executive Director and co-founder of the Mangrove Action Project. You can follow Alfredo on Twitter @mangroveap. For more information visit MAP’s website

Saturday, 5 December 2015

Fishing for deadly ghost gear

Ghost Fishing’ is what fishing gear does when it has been lost, dumped or abandoned. Imagine a fishing net that gets snagged on a reef or a wreck and gets detached from the fishing vessel. Nets, longlines, fish traps or any man-made contraptions designed to catch fish or marine organisms are considered capable of ghost fishing when unattended, and without anyone profiting from the catches, they are affecting already depleted commercial fish stocks. Caught fish die and in turn attract scavengers which will get caught in that same net, thus creating a vicious circle.
Ghost fishing longline survey Croatia

Lost fishing gear, or so-called ‘ghost gear’ is one of the greatest killers in the oceans. Literally hundreds of kilometres of nets and lines get lost every year and due to the nature of the materials used to produce these types of gear, they can and will keep fishing for multiple decades, possibly even centuries.
Ghost fishing net survey Croatia

Divers are all too familiar with this phenomenon, especially in well-fished areas. As founders of the Ghost Fishing Foundation we were confronted with ghost gear while diving the many wrecks in the Dutch North Sea. In 2009 we were part of a local team of divers who started to clean those wrecks. After some years of local efforts it was time to broaden the horizon and get in touch with like-minded groups all over the world. And so the Ghost Fishing Foundation was born.
Ghost fishing net survey Croatia

The Ghost Fishing Foundation has been collaborating worldwide with various local groups of divers and salvage companies to remove lost fishing gear. With projects in Netherlands, Belgium, Germany, Croatia, United Kingdom and the United States we work on existing projects, set up new ones and document these through visual media, informing a wide audience and raising social awareness. We exchange solutions and best practices by maintaining a steady stream of information through social media, and a website that offers extensive information and possibilities for interaction.

Ghost fishing net recovery Croatia
The Ghost Fishing Foundation recently launched unique collaborations with several well-known organisations like Healthy Seas Initiative, World Animal Protection and Greenpeace and they are part of the Global Ghost Gear Initiative (GGGI). The GGGI aims to improve the health of marine ecosystems, protect marine animals, and safeguard human health and livelihoods. GGGI was launched in September 2015 and is the first initiative dedicated to tackling the problem of ghost gear on a global scale. The GGGI’s strength lies in the diversity of its participants including the fishing industry, the private sector, academia, governments, intergovernmental and non-governmental organisations.

If you would like to know more about ghost fishing gear visit or their social media channels on Facebook, Instagram and Twitter.

Pascal van Erp is the founder and chairman of the Ghost Fishing Foundation. You can follow Pascal at @suberp on Twitter.

Saturday, 28 November 2015

Bluefin tuna: a new perspective in the NE Atlantic

 In 2013, Angus Campbell caught a 515lb Atlantic bluefin tuna with a rod and reel off the Isle of Harris, the Outer Hebrides. Although this wasn’t out of the realms of possibility, this had never been done before in Scotland. In 2014, Dr. Francis Neat (Marine Scotland Science) initiated a scientific program on bluefin tuna in Scotland with the aim of finding out three things: 1) how long bluefin resided in Scottish waters, 2) where they went, when they left, and 3) what stock the fish belonged to. That year we successfully tagged three bluefin with miniPAT tags from Wildlife Computers. Although the project was a success, the results from our work were far from conclusive. We’re now in the process of starting a collaborative study with Stanford University, to contribute knowledge on this enigmatic species to the bigger picture of bluefin in the northeast Atlantic.

Atlantic bluefin tuna post-release off the Isle of Harris, Scotland exhibiting miniPAT

Bluefin tuna are commercially important, highly migratory apex predators, split into three geographically distinct species: Atlantic, Southern and Pacific bluefin tuna. Demand for these fish has skyrocketed over the last few decades in line with the rise of the Japanese sushi-sashimi market, in which bluefin is the most highly prized delicacy. The majority of bluefin caught is flash frozen and shipped to Japan for auction, with single fish fetching exorbitant amounts of money: in 2013 a fish weighting 489lbs sold for $1.76m. Although this figure was especially high, fish regularly sell for tens of thousands of dollars.

Graph showing price of inaugural bluefin tuna sold at the Tsuiji fish market, Japan

Atlantic bluefin tuna are comprised of at least two genetically distinct stocks, designated by their spawning region: the eastern stock in the Mediterranean and the western stock in the Gulf of Mexico. Fish from both stocks make seasonal migrations from warm low-latitude waters to highly productive foraging grounds at higher latitudes [1]; although not all fish do this, and whether bluefin migrate or not is related to maturity and body size, with larger fish ranging further. Despite being genetically distinct, migratory fish mix extensively outside of their spawning areas and fish from the western stock can be found in the eastern Atlantic and vice versa [2]. As a result of prolonged overfishing on both sides of the Atlantic, the western and eastern stocks were reduced to 17% and 33% respectively, of 1950’s spawning stock biomass by 2008 [3]. This caused the bluefin regulatory body, ICCAT (the International Commission for the Conservation of Atlantic Tunas) to introduce stock rebuilding programs, ultimately resulting in slashed catch quotas.

Atlantic bluefin tuna, south Donegal, Ireland 2015
The extent of bluefin distribution is limited by temperature, despite their advanced thermoregulatory capacity. Recent reports of bluefin in the Greenland strait (2010), the establishment of small-scale fisheries off Iceland and Norway (2014), increased sightings off Ireland and Scotland (2012-13-14), fish caught off Wales (2015) and even sightings off Cornwall, England (2015) suggests bluefin have repatriated highly productive northern latitudes in significant numbers in recent years. This simple fact would lead us to believe that something has changed; what that ‘something’ is, is cryptic.

Map showing UK and Ireland Atlantic bluefin tuna sightings 2013-15

We are exploring three possible causes for these recent changes; 1) a warming ocean climate, allowing tuna to exploit areas previously too cold, 2) the forage prey are now ranging further north and in greater abundance than previously believed, e.g. mackerel, or 3) a recovery of the eastern bluefin stock, as has been heralded by ICCAT; this would result in a more significant cohort of larger, more migratory fish. These hypotheses are not mutually exclusive and may all be acting in concert. Consequently, this is just the beginning of tuna research in the UK and Ireland.

Atlantic bluefin tuna feeding on sprat off Donegal, Ireland 2015

Our work would certainly not be possible without the efforts of a number of recreational fishermen, acting responsibly on a catch-and-release basis. This form of fishing represents a hugely sustainable way of gaining revenue from bluefin tuna. A report looking into further developing the existing bluefin recreational fishery in Canada’s Atlantic provinces, estimated that 1 tonne of bluefin quota allocated to a live-release fishery could yield up to $100,000; 6 times that of a capture fishery, whilst having minimal effect on the stock [4]. If the eastern Atlantic bluefin stock has bounced back, such fisheries may have a place in the UK and Ireland, and one of the key project aims of our work in Scotland is to advise as to whether or not this would be a possibility. Well managed catch-and-release fisheries represent a way of providing much needed revenue to often remote coastal communities, whilst also supporting vital scientific research on apex predators and maintaining good fish stocks.

1: Walli, A. et al. PLOS One, 4(7): e6151. (2009) doi: 10.1371/journal.pone.0006151
2: Block, B. et al. Nature, 434: 1121-1127. (2005) doi: 10.1038/nature03463
3: Taylor, N. et al. PLOS One, 6(12): e27693. (2011) doi: 10.1371/journal.pone.0027693

Tom Horton is a marine biologist, wildlife guide and photographer specialising in the spatial ecology of marine megavertebrates around the UK & Ireland. His current work involves basking sharks, ocean sunfish and Atlantic bluefin tuna. You can follow Tom and check out his work and pictures on Twitter @profhorts.