Weekly Sea Discovery: Fish or Eel? The Mysterious Gunnels of Mayne Island

While turning over rocks and searching for hidden creatures along Mayne Island’s shores, you may see a long, slippery animal slide into a dark crevice. Your first guess might be that you’ve just seen an eel, with a long tapered body and round head, but these are in-fact gunnels! Gunnels are fish with bodies adapted to swimming and squeezing between rocks and crevices.  

A crescent gunnel (Pholis laeta) rests among some algae-covered rocks. The markings on its dorsal fin are somewhat crescent-shaped, hence their name. Photo: Kathleen Reed

Now you may be thinking, how are these fish alive when there is hardly any water around them? These quick-moving fish can survive in the intertidal zone by hiding under rocks and in moist areas like seaweed. But they have another trick up their slimy bodies: gunnels can breathe air! Adult gunnels feed on various crustaceans and molluscs, as well as the surrounding algae. They are found from the intertidal to the shallow waters below and are frequently spotted in eelgrass beds hiding among the blades like the bay pipefish.  

A small saddleback gunnel (Pholis ornata) blends in with the rocky substrate. Their patterning is slightly different from the crescent gunnel with more U and V shapes. Photo: Chris Wilson

A few common gunnel species found around Mayne Island and the Southern Gulf Islands are the saddleback gunnel, the penpoint gunnel and the crescent gunnel.  

A penpoint gunnel (Apodichthys flavidus) camouflages in the surrounding green seaweed. Photo: Jeanne Luce

The Penpoint Gunnel is easier to differentiate from the two other gunnel species with a single dark line running vertically through each of its eyes. Unlike the other two species, they lack detailed dorsal (back) patterns,. They can be various colours, like bright green or brown or red. With these different colours, they can camouflage in multiple layers of brown, red and green algae.  

Red-necked grebe eating a crescent gunnel. Drayton Harbor, Blaine, WA. Photo: Andrew A Reding

In the marine food-web, gunnels are part of the group known as forage fish, with other small fishes like the Pacific sand lance and herring. Various animals like sea birds, river otters and larger fishes, like adult salmon, prey on gunnels. These eel-like fish are an important link in the food web leading up to Southern resident killer whales.  

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