Seahorse numbers around Britain increasing
February 18th, 2008It may come as a surprise to most people that there are any seahorses at all in British coastal waters, and more surprising still that numbers appear to be increasing.
Seahorse experts met in London this month to discuss the apparent population surge in seahorses and their close relative, the pipefish.
The reasons for this increase, described as “rapid and dramatic” is not yet clear and a number of theories have been put forward including a natural population boom or warmer waters.
As with any shift in population, it is also having a knock-on effect upon other species, including sea birds.
They say although there have been changes in water temperature in the North Sea since around 1988, the large numbers of snake pipefish have only appeared in the last four or five years - putting a global warming theory in doubt.
“There is no doubt that numbers of snake pipefish have increased. In the last few years they are just everywhere,” said Professor Mike P Harris of CEH.
“Although climate change may well have had an effect, the jury is, we think, still out on this matter.”
Cindy van Damme of the Netherlands’ Wageningen IMARES - the Institute for Marine Resources and Ecosystem Studies, believes she may be nearer an answer.
She says recent shifts in ocean currents have led to a change in the composition of plankton - it has shrunk.
“Plankton is the major food item of pipefish and sea horses. The mouth opening of this group of fishes restricts the prey size they can handle. We think this mechanism explains the huge increase of snake pipefish. Hence this outbreak may very well last for only a limited number of years.”
However long it lasts, it is impacting startlingly upon pipefish predators - which include everything from mackerel, dolphins, otters and sharks to seabirds.
Although they are eaten by birds such as gannets, kittiwakes and puffins, their spiny, ‘armoured’ forms, like seahorses make them difficult for young birds to swallow and digest - some young birds even choke to death on them.
Pipefish form a distinct family with seahorses (syngnathids) and as the name would suggest, look like straight-bodied seahorses with tiny mouths.
Numbers of the snake pipefish, once rarely seen in northern British waters, now often end up in the region’s trawler nets in vast numbers, say scientists.
Once associated with deep northern waters, they have even been found recently further south by fishermen in the Thames Estuary.
A European team led by the Centre for Ecology & Hydrology (CEH) says that the numbers of snake pipefish in British waters has increased more than one hundredfold since 2003.
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