Species cannot be conserved in isolation as each species is part of a complex food web. Seabirds, puffins, guillemots, terns and kittiwakes breeding on cliffs and islands in the North Sea and the Irish Sea depend on sandeels to feed their chicks. Sandeels are rich in protein and fat and are the correct size for the chicks to swallow.
Since 1970, the success of seabird breeding around the British Isles had been increasing steadily, but by 2000 the trend had reversed. In the 1980s a decline, followed by a crash in population of sandeels in the seas around the Shetland isles, had a devastating impact on the breeding success of seabirds in the area. Seabird chicks were starving to death – puffins failed to rear any young, and Arctic terns and kittiwakes also reared very few chicks. Industrial fishing was thought to be the cause, and in 1989 a ban on sandeel fishing was enforced in the area.
Raising the temperature
Unfortunately, the downward trend in breeding success of seabirds in UK waters has continued. The continuing decline in sandeels has now been attributed to climate change.
Sandeels in UK waters are at the extreme south of their range. They feed on zooplankton (for example, larvae of crustaceans, molluscs and fish) who in turn feed on smaller zooplankton and also phytoplankton, tiny organisms that derive their energy from the sun by photosynthesis. With the temperature of the sea increasing, this may be affecting the phytoplankton adversely and, in turn, the zooplankton.
A decline in zooplankton would lead to a decline in sandeels and this would have a direct impact on the breeding success of seabirds. Seabirds breeding in northern areas would be especially vulnerable to declining sandeel populations as there are no alternative fish species that can be used to feed chicks.
A puffin feeding on sandeels
In 2009, the Royal Society for the Protection of Birds (RSPB) reported increased breeding success of seabirds in Scotland. This may have been a result of a boost in sandeel populations linked to lower sea temperatures following a cold winter. However, the increases need to be looked at in comparison to previous successful years. The RSPB reported 9,400 kittiwake nests at Fowlsheugh reserve in 2009, but this is dramatically lower than the 34,000 kittiwake nests reported 17 years earlier.
Adapting to change
The overall downward trend in seabirds’ breeding success reflects the effects of climate change in altering the environment of a species to such an extent that food becomes scarce or unavailable. Some species have the flexibility to adapt. Great tits breeding in the UK depend on the large numbers of caterpillars that emerge in early spring. Caterpillars provide essential high fat and protein food for the Great tit chicks.
A green caterpillar
A long-term study in Wytham Woods Oxfordshire, England has demonstrated that Great tits have adapted well to the earlier season of spring in northern Europe. The birds are now breeding two weeks earlier than they did 47 years ago and can take advantage of caterpillars that emerge earlier in the season.
How you can help
At national and global levels we all need to press for conservation of fish stocks. These are crucial for maintaining biodiversity, and ensuring the availability of fish to future generations.
If you would like more information on declining fish stocks and the welfare of UK seas, the Marine Conservation Society FISHONLINE website offers advice on ways people can contribute to the responsible management of fish.