This is a video of a snake pipefish.
From British weekly The Observer:
Birds choke to death on migrant fish
Baffled scientists warn of a ‘catastrophic’ impact as snake pipefish flood into British waters
Britain’s sea birds are facing a deadly new threat from a population explosion of strange, seahorse-like creatures in our coastal waters. The snake pipefish, virtually unknown around the UK in 2002, has undergone a massive, baffling and dangerous expansion since then, scientists have discovered.
Divers report seeing hundreds on single dives, while dozens of pipefish – which can grow to more than 18 inches in length – have been found in the nests of puffins [see also here; and here], kittiwakes, terns and other sea birds.
The discovery has alarmed biologists because they have found that chicks are choking to death on the rigid, bony bodies of pipefish, while adults are feeding on them despite the fact they have very little nutritional value.
The implications for future generations of sea birds – already badly affected by depletion of Atlantic and North Sea fish stocks – are alarming, scientists warned at a meeting of the Zoological Society in London last week.
A monogamous pipefish has the same type of ovary as observed in monogamous seahorses: here.