Skeleton at Clashnessie
Anne Nicoll recently showed me a remarkable object she found whilst walking her dog on Clashnessie beach (NC0531) in February. It was the perfectly preserved skeleton of a small fish, just over 15cm long, with a tiny toothed mouth, large eye sockets and a long ‘tail’ with a small caudal fin at the end.
After looking at my seashore books, I was able to identify it as a fifteen-spined stickleback Spinachia spinachia, a marine relative of the more familiar three-spined stickleback Gasterosteus aculeatus (photo 1).
I took a quick photograph as a record (photo 2) and then showed it to David Haines who produced one of his detailed stacked images (photo 3). This enables one to see the delicately-ridged surface of the gill covers and count the 15 bones in front of the dorsal fin which supported the spines from which it gets its English name. The scientific name derives from the Latin spina, as also does that of the vegetable, which has spiny fruits.
Relationship with seagrass
Fifteen-spined sticklebacks are wholly marine, ‘largely confined to meadows of seagrass (Zostera spp.) and algae’, although they may be found ‘in rock pools after the tide has ebbed’. They are also ‘a small part of the diet of otters foraging in the marine environment’.
The association with seagrass is interesting since uprooted stems of this marine flowering plant are occasionally washed up on Clashnessie beach and others around Assynt. However, it has recently only been found in situ just off Drumbeg (NC1233).
Three-spined sticklebacks are more versatile, occurring in both freshwater and the sea. We once found one in a rockpool on the coast of Eilean Chrona (NC0633) and have also seen them in brackish pools at the mouth of the River Leireag (NC1431).
NBN has no records of the fifteen-spined stickleback from the coast of Assynt, the nearest being Eilean Port a’Choit in the Laxford estuary (NC2148) to the north and Tanera Beg in the Summer Isles (NB9607) to the south. So, a fascinating find.
Illustration from The Hamlyn Guide to the Seashores and Shallow Seas of Britain and Northern Europe (A.C. Campbell and James Nicholls, 1976). Quotes on biology from Fish Atlas of the Celtic Sea, North Sea and Baltic Sea (edited by H.J.L. Heesen et al., 2015).
Ian M. Evans