Pipefish place seabirds at threat

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A dramatic increase in the number of exotic pipefish in UK waters is placing seabirds at threat, according to the results of a study due to be published in the journal Ibis.

Snake pipefish, Entelurus aequoreus, were previously an uncommon species in British waters, but have undergone a dramatic population explosion over the past five years.

According to the study by Michael Harris, Mark Newell, Francis Daunt, John Speakman and Sarah Wanless, the Snake pipefish is a low-nutrition fish species that is increasingly a common food item in British seabirds such as Black-legged kittiwakes (Rissa tridactyla) and European shags (Phalacrocorax aristotelis).

Decline in other prey fishesThe authors compared the mean energy content of the pipefish to other species such as Sprat (Sprattus sprattus) and Lesser sandeel (Ammodytes marinus) that typically constituted the prey of seabirds, and found the energy content of pipefish to be significantly lower.

They also found the mineral content of pipefish to be higher, meaning that the pipefish had more bone and less flesh.

Shag, Phalacrocorax aristotelis. MPF, Creative Commons.

Coupled with the decline in populations of some fish (e.g. lesser sandeels) that were previously the dietary staple of seabirds, this has led to the increasing occurrence of pipefish amongst the prey fish caught and eaten by seabirds.

The authors think it plausible that the increasing usage of pipefish as a food species by seabirds has led to several large breeding failures of seabirds in the UK in recent years.

Breeding failuresThis is because "revious work at several colonies has shown that seabirds breed most successfully when they can feed their chicks on high-lipid content fish such as sprat, herring and capelin and are generally less successful when they have to rely either on species of lower lipid (and hence energy) value or when for some reason these normal prey have lower than average energy value."

In addition to the low nutrient content of pipefish, their length and rigidity makes them very difficult to swallow for seabirds, apparently because of "...both the bony nature of the fish and the extreme difficulty (perhaps impossibility) of breaking the pipefish into swallowable lengths.

"Not surprisingly, smaller species of seabird have more severe problems with young apparently starving to death even when sitting on piles of uneaten pipefish. In extreme cases, young of the smallest species, such as terns, choke to death on pipefish stuck in their gullets."

For more information, see the paper: Harris, MP, M Newell, F Daunt, JR Speakman and S Wanless (2008) Snake pipefish Entelurus aequoreus are poor food for seabirds. Ibis doi:10.1111/j.1474-919X.2007.00780.x