Defra in Denial

over Tees

Seal Pup Deaths 

Photo by Keith Luke on Unsplash

Scott Hunter

29 November 2025

Tees Estuary seals were in the news more than usual this summer. Sadly, while in previous years press reports have celebrated their increase in numbers, this year it was to herald the remarkably high mortality rate among weaned pups. By September, this had reached 100%.

Media interest in the issue increased when a group of local MPs published an open letter to Defra asking for this to be investigated. We note that, to date, Defra’s response has not been published.

For those engaged in their welfare, the unusual degree of attention from the media on the seals’ plight was undoubtedly welcome, even if it was only because matters had reached a point of crisis. The question remains, however, whether the public attention garnered will lead to action that will bring about material improvements in seal survival rates in the future.

At present we see no cause for optimism on that score. Our recent attempts to obtain information from Defra have yielded nothing of substance (and the BBC fared little better than we did), and certainly no sign of commitment to take action on the contamination in the estuary that is alleged to be the underlying cause of the mortality.

Before examining Defra’s apparent indifference to that underlying cause, we put the facts in context, including some of the bits other media have ignored.

Seals and the Tees Estuary Seal Colony

There are two species of seal around the UK’s coast – grey seals (Halichoerus grypus)  which are abundant, and harbour seals (Phoca vitulina), which are much less so. While both species inhabit Seal Sands in the Tees Estuary, it is a breeding colony only for harbour seals, and so the current crisis affects only harbour seal pups. The nearest other harbour seal breeding colonies are in The Wash (Norfolk), to the South, and Tayside, to the North. Both of these are considerably larger than the Teesside colony.

For much of the twentieth century the Tees Estuary was too polluted to support a seal colony at all. Some began to return in the late 1980s, when monitoring was first undertaken by David Bellamy and associates.   In 1994, the Industry Nature Conservation Association (INCA) was set up to take over monitoring them, recording both the numbers of adults arriving in the Tees Estuary, and the number of pups born each year. Numbers remain stubbornly low.

 In 2022, INCA issued a press release (Record number of seals found on Teesside’s shores with new research underway to find out why) celebrating the fact that live births had risen to 36. By comparison, a report by the Marine Mammal Protected Areas Taskforce( MMPAT) in 2023 indicated that harbour seal births in The Wash were estimated to be 1140.

INCA reported 24 live births in 2024, but its report (Tees Seal Research report) does not give mortality statistics. This is due in part to the fact that strandings often occur further down the coast from the area monitored by INCA.  So, what lies behind this excessive mortality rate?

What the papers say

All press reports state that the seals are dying from a disease known as ‘mouth rot’, described in the Northern Echo as

“The condition, which affects newly weaned pups, leads to muzzle swelling, facial wounds, abscesses, and severe ulceration”

It is an ugly and disfiguring disease, (graphic images of the disease in this report from the BBC) resulting in an inability to feed. Weakened pups then strand on local beaches. If British Divers Marine Life Rescue (BDMLR) is contacted in these circumstances, the stranded pups will be collected and taken to a vet. However, all of the pups transported to Clifton Lodge Vets in Hartlepool this year were either already dead, or so unwell that they had to be euthanised (reported in Hartlepool Mail). As there is no dedicated seal rescue facility in this area, others are transported to a Veterinary practice in Northumberland. That involves a long journey by road to a facility which is itself not a dedicated seal rescue centre.

Press reports, like the Hartlepool Mail, omit one important detail, however, which is that mouth rot is not unique to Tees Estuary Seals. When we approached BDMLR, we were told that mouth rot is affecting pups in other seal colonies, with the largest number of cases being found in The Wash, in North Norfolk (as might be expected given the size of the colony).

When we asked BDMLR if the mortality rate in The Wash was similar to that in the Tees Estuary, they were not able to provide us with the information. We then approached The New Horizon Centre at Teesside University which, in partnership with BDMLR, is currently undertaking research into the cause of mouth rot. But they were also unable to provide us with that information. The only clue that the same crisis is not underway in The Wash is that the MMPAT report makes no mention of excessive mortality there (we are grateful to Sue Wilson of Tara Seal Research for crunching the numbers available from BDLMR, from which she concludes that mortality in the colony in The Wash is around 2%).

In addition to this is the frustration expressed by the Hartlepool vets (to the Hartlepool Mail and others) that they consider mouth rot to be a treatable condition, yet the seals here are dying. So, whatever is happening in the Tees is materially different from what is happening in The Wash. Which is what prompted the MPs’ letter to Defra, and which is exercising at least one of the seal monitoring groups, Tara Seal Research.

Tara Seal Research

Some of the press reports contain comment from veteran researcher, Sue Wilson, of Tara Seal Research (and previously of David Bellamy Associates), who provides crucial additional information. Her testimony is that seals stranding on Teesside Beaches are found to be below their birth weight, indicating that they may have been already unwell before contracting mouth rot. Independent research undertaken by Tara indicates that the blubber of these seal pups contains high levels of Polychlorinated Biphenyls, or PCBs, chemicals which are known to be harmful to aquatic life in general and to apex predators like seals in particular. Unlike BDMLR and Teesside University, however, Tara is not in receipt of Defra funding and so their ability to commission further testing is severely limited.

Questions arising are, what are PCBs? Where did they come from? How do they get into the seal blubber? What does this tell us about the marine ecosystem in the Tees Estuary? And, what is Defra’s doing about it?

Effect of Polychlorinated Biphenyls on Aquatic Life

Polychlorinated Biphenyls are non-soluble fluids once used for a variety of industrial purposes. They were banned in the UK in 1977. Nearly half a century later, they are still present in the marine ecosystem (according to research by OSPAR (here) which oversees marine conservation in the North East Atlantic and whose protocols are (notionally) adhered to by the UK). OSPAR classifies PCBs as Persistent Organic Pollutants (POPs).

“Polychlorinated biphenyls (PCBs) are human-made chemical compounds that were banned in the mid-1980s owing to concerns about their toxicity, persistence, and potential to bioaccumulate in the environment…

“PCBs do not break down easily in the environment and are not readily metabolised by humans or animals. PCBs accumulate in marine animals , with greater concentrations found at higher trophic levels. PCB compounds are toxic to animals and humans, causing reproductive and developmental problems, damage to the immune system, interference with hormones, and can also cause cancer.” (OSPAR).

‘Trophic levels’ refers to the place of a plant or animal in the food chain. Seals are apex predators and have no natural enemies. Apex predators are the highest trophic level.

When David Bellamy and his team first visited the Tees Estuary in the late 1980s they found “… Cod and Flounder, Plaice and Sole. In late summer Sprats come to the estuary followed by the predatory mackerel (The Tees/The Living River). Apart from mackerel, these form the Tees Estuary seals’ diet. As for the fish themselves, their diet is made up of smaller fish and crustaceans, like crab and shrimp. The crustaceans are filter feeders that sift the sediment in search of plankton, the lowest trophic level, which have absorbed the PCBs.

OSPAR states “PCBs … are not readily metabolized by humans or animals”, that is to say, they remain in the body and are not generally excreted. PCBs, in addition to being non-soluble are also lipophilic, that is to say they are absorbed into fatty tissue.

So, when fish predate crustaceans, the PCBs accumulate in their bodies, and the accumulation increases again when seals consume affected fish, as shown in this infographic:

Source: https://northeastfc.uk/doku.php?id=pcbs_and_harbour_seal_pups

Therefore, the higher up the food chain a species is, the greater the bio-accumulation, and therefore the greater the health risk. While seals cannot readily excrete PCBs, adult females transfer them to their young through their milk. So, Tees seal pups begin life by consuming relatively high levels of PCBs, and their subsequent failure to thrive follows from this. In addition, the high levels of PCBs in adult females is also known to result in elevated rates of aborted foetuses, hence, possibly, the low birth rate in the Tees Estuary as compared to colonies elsewhere.

 History of PCB Manufacture

Most PCBs worldwide were manufactured by US corporation, Monsanto from 1930 until 1977/8, when they were banned both in the UK and the US (other countries followed suit over the following decade). In the UK, Monsanto operated a single PCB manufacturing plant, in Newport, in South Wales. Monsanto’s record of environmental damage is appalling, with large quantities of waste material being dumped in disused quarries in the Newport area over decades. Given that PCBs are as much a danger to humans as to other species, this constitutes a major health hazard there.

But PCBs were never manufactured on Teesside, and while there are reports of PCBs being illegally dumped in landfill in other parts of the country, no such reports have originated in this region. Yet a 2000 PhD thesis (J. Reed, 2000, POLYCHLORINATED BIPHENYLS IN MARINE SEDIMENTS AND DREDGED MATERIAL AROUND ENGLAND AND WALES) identifies the Tees Estuary as a PCB hot spot and the ongoing seal mortality indicates that this remains the case.

Disposal of PCBs, Past and Present

The fact that PCBs are persistent in the environment, does not mean that they are indestructible. They can be destroyed by incineration and the Health and Safety Executive (HSE) now requires that they are incinerated in premises specially licensed for this purpose. So, the proper disposal of PCBs now appears to be in hand (although there are caveats). In the past, on the other hand, they were dumped in landfill or directly into watercourses. Over time, leachate from contaminated material on land has found its way into the marine environment, which is now host to about 30%  of all the PCBs ever manufactured (P. Ngoubeyou et al., 2022).

Whose Responsibility is it Anyway?

Ultimate responsibility for environmental protection both of land and sea falls to the Department of the Environment, Fisheries and Rural Affairs (Defra), and its various partner agencies. PCBs entered the marine environment as liquids, heavier than water, that were deposited on river and estuary beds where they adsorbed to silt and sediment layers there. In the case of the Tees, such are the tidal conditions, that the Estuary requires frequent dredging in order to maintain the shipping lane.

One Defra agency, the Marine Management Organisation (MMO, is responsible for issuing dredging licences. Those applying to undertake dredging are obliged to obtain and analyse sediment samples. These are then tabulated and submitted to the MMO, which determines whether the dredge material can be deposited at sea, or, if it is deemed too toxic, to be deposited safely on land.

The sites where dredge material is disposed of at sea are monitored by the Centre for Environment, Fisheries and Aquaculture Science (Cefas). Cefas is also a Defra partner agency. The Environment Agency is another partner. It monitors water quality, and both it and Cefas monitor aquatic life.

In other words, when it comes to knowledge of the overall health of the marine environment, Defra holds all the cards. But seals also play a crucial role in assessment of that environment. Thus, a recent research report by the University of St Andrews: 

“The UK hosts approximately 40% of the world’s grey seals and 30% of the eastern Atlantic subspecies of harbour seal. These species are used by the UK and European governments as indicators of marine environmental health.”

In other words, the seal pup deaths in the Tees Estuary are evidence of a much larger problem in local marine environment.

Defra in Denial

Each time we have written to Defra about PCB contamination we have received a statement in response. Each time the statement has been wholly irrelevant to the matter in hand, as none have ever mentioned PCBs. Thus:

“Seal deaths can sadly occur for many reasons, including storm surges, food shortages, trauma, predation or disease outbreaks such as ‘mouth rot’.”

We replied that we had asked specifically about PCBs and were told that the agency had nothing further to add. When we sent a ‘right of reply’ email, detailing the criticism we intended to make of Defra’s inaction over PCBs, we received the following:

“We are saddened to hear of the seal deaths and are already engaging with scientists and wildlife experts to tackle this disease. 
“Defra-funded research has identified the cause of mouth rot to be a new calicivirus, and we are now funding further research to develop testing to diagnose and help manage the virus.” 
“We remind the public not to approach dead or sick seals, but to report it to wildlife authorities.”

So, in the quotable statements the name polychlorinated biphenyls does not appear at all.  But along with them, some background information stating that there is no evidence that mouth rot is caused by PCBs.  This is equally unhelpful.  As far as we know, no one has suggested that PCBs are a cause of mouth rot.  Certainly not us.

Defra is engaged in ‘tackling this disease’. If, by engaging with scientists they discover the virus that causes mouth rot, enabling a more tailored treatment to be developed, then that will be of benefit to certain harbour seal populations, but not including the one in the Tees Estuary.

History Repeats Itself

There is something in Defra’s handling of this crisis that is oddly, and worryingly, reminiscent of its handling of a previous one in this region. When thousands of crustaceans died in the Estuary and beyond in the autumn of 2021, Defra diagnosed the cause as a Harmful Algal Bloom (HAB) that had been present in coastal waters during the month prior to the sudden die-off. Inshore fishermen and others, meanwhile, were suspicious that this was, in fact, the result of a pollution incident and commissioned a group of scientists to investigate. These scientists concluded that the cause may have been contamination with the chemical pyridine.

Evidence Examined by an ‘Independent Panel’

There was a stand-off. Defra stopped actively investigating the die-off, and doubled down on its claim that this was the result of a naturally occurring HAB. The fishermen remained equally insistent that this was a pollution incident, and the matter ended up before the Environment, Fisheries and Rural Affairs Committee in the House of Commons in October 2022. The outcome of that hearing was that an independent panel of experts – the Crustacean Mortality Expert Panel (CMEP) - was appointed to examine the available evidence put forward by each side, but, as we reported in November 2022, the panel was warned at the outset not to give too much credence to pyridine contamination.

The panel got to work examining the evidence over a four-week period in late 2022/early 2023 (the report is here). Their conclusions were at once startling and predictable. Predictably, they found it highly unlikely that pyridine was the cause. Less predictably, they found that it was also unlikely that HAB was the cause. What was startling was that the panel came up with another explanation that they considered to be as likely as not that the cause was an unknown pathogen (basically, it’s 50/50). This seems to have been conjured out of thin air and not based on any of the evidence presented to the panel.

Defra ‘protests too much’

Defra has been in no hurry to hunt down this unknown pathogen. As far as we are aware, no research has been commissioned into. Meanwhile at least two further reports (discussed by us here and here) subsequent years have sought to reassert that pyridine was absolutely, definitely not the cause.

The independent panel report was widely ridiculed when first published, yet it succeeded in effectively bringing an end to debate over the issue. While others have moved on, Defra and selected members of the independent panel have not.

At the time of the die-off we accused of Defra of shielding the powers behind the Tees Freeport project as if that was the ultimate motivation for denying that the die-off could have been a pollution incident. In the wake of the seal mortality, it now appears that the motivation in stonewalling any suggestion of chemical contamination in the marine environment may be to shield Defra itself.

PCBs can be hard to find

“… knowledge of the emission sources of PCBs, transport pathways, and sites of contamination and biomagnification is of great benefit to scientists and researchers, as well as many regulatory organizations.” (P. Ngoubeyou et al., 2022)

Assisting Defra in its denial of the PCB issue, sadly, is the marine environment itself. It turns out that these contaminants are easier to find in marine mammals than they are in marine sediments. 

The Tees has the unenviable reputation of being the most polluted watercourse in the UK. Recent capital projects, however, have provided us with extensive information of the different contaminants in the estuary bed. The largest of these was the South Bank Quay project. As large quantities of sediment were to be removed, a wide area was tested to determine the levels of contamination it contained. Below is an official list of some of the contaminants that are tested for and the levels , measured in parts per million, at which they become critical:

Source: Marine Management Organisation

So, one class of PCBs (sum of 25 congeners), is critical at 0.2 parts per million where ‘action level 2’ is the point at which the relevant government agencies acknowledge that something needs to be done about the contamination.

And below is an excerpt from sediment analysis of one section of the estuary. BH34 is borehole 34, a site which was found to be so heavily contaminated that the Marine Management Organisation (which licences dredging) refused permission for the sediment in its vicinity to be disposed of at sea. The top row of the table shows the individual PCBs tested for. Other than borehole 34, however, PCBs are found only in negligible quantities and often below the level of detection (<LOD). This appears to be the case across most of the area from which samples were taken.

Source: Marine Management Organisation

Yet PCBs were once extensively used in industry and casually discarded into the environment. They would have been used particularly in most of the heavy industry around the Tees Estuary.  It is therefore remarkable that the extensive sediment sampling that was undertaken in advance of constructing the South Bank Quay should reveal so little of it.   So where are the point sources of contamination?

This issue will be considered in detail in our second report, along with further examination as to why Defra may be so shy about acknowledging the problem of PCB contamination.