Short-Beaked Common Dolphins at Risk from Climate Change and PCBs
Rising sea temperatures and persistent chemical pollution are contributing to the growing number of dolphin deaths in UK waters, according to a new study published in Communications Biology. The research, led by the Zoological Society of London (ZSL), reveals a strong link between environmental stressors and the spread of infectious diseases in short-beaked common dolphins (Delphinus delphis), a sentinel species for marine health.
Climate Change and Ocean Pollution: A Deadly Combination
Marine scientists have long warned that both climate change and chemical pollution are major threats to ocean biodiversity. This study is one of the first to show how these two stressors act together, increasing the risk of disease-related mortality in marine mammals.
Key findings reveal that:
- Higher sea surface temperatures (SSTs) disrupt marine ecosystems and promote the spread of harmful pathogens.
- Polychlorinated biphenyls (PCBs)—toxic industrial chemicals banned in Europe in the 1980s—continue to accumulate in marine mammals’ fatty tissues, impairing immunity and reproduction.
How PCBs and Warming Seas Impact Dolphin Health
Despite being banned decades ago, PCBs still enter marine ecosystems through:
- Industrial runoff
- Dredging
- Inadequate waste disposal
- Atmospheric deposition
PCBs build up in dolphin blubber, weakening their immune systems and making them more vulnerable to infections. This is particularly concerning as ocean temperatures continue to rise due to climate change, altering prey availability and habitat use.
Study Overview: 30 Years of Data on Dolphin Strandings in the UK
The researchers analyzed data from 836 short-beaked common dolphins stranded along UK coasts between 1990 and 2020. A smaller group of 153 dolphins was selected for toxicological testing to determine PCB concentrations in their blubber.
Using logistic regression models, the team examined the relationship between infectious disease mortality and two key environmental factors:
- Monthly mean sea surface temperature
- PCB concentrations in dolphin blubber
They also considered variables like age, sex, body condition, and location.
Shocking Results: Increased Mortality Risk with Every Degree of Warming
The study revealed:
- A 14% increase in disease-related death risk for every 1°C rise in sea temperature
- A 1.6% higher risk for every 1 mg/kg increase in PCB concentration
- A PCB threshold of 22 mg/kg lipid, above which disease risk significantly increases
Although PCB levels showed a slight decline over the decades, adult males still had concentrations above the critical threshold. Meanwhile, sea surface temperatures in northern UK waters have continued to rise.
Why This Matters: A Wake-Up Call for Marine Conservation
This study sends a clear message: climate change and pollution are acting together to threaten marine life, and action must be taken before it’s too late.
Key takeaways:
- No interaction was found between sea temperature and PCB levels, but both are independent and significant contributors to dolphin mortality.
- Similar risks may be affecting other marine megafauna and even commercially valuable species like tuna or cod.
- The findings highlight the need for global conservation efforts that address both climate change and chemical pollution together—not separately.
Final Thoughts: What’s Next for UK Marine Wildlife?
Without immediate international action to limit warming and reduce environmental contaminants, dolphin populations—and the health of our oceans—may continue to decline. Identifying species-specific toxicity thresholds, like the 22 mg/kg lipid benchmark in dolphins, gives policymakers and conservationists a powerful tool to monitor and mitigate future threats.
Reference:
Williams, R. S. et al. (2025). Sea temperature and pollution are associated with infectious disease mortality in short-beaked common dolphins. Communications Biology. DOI: 10.1038/s42003-025-07858-7