Dover Sole

The Dover sole (Microstomus pacificus) is a right-eyed flatfish in the family Pleuronectidae found along the Pacific coast of North America. Despite its name, it is unrelated to the true soles of Europe and is instead a flounder relative, distinguished by an especially thick, slimy mucus coating on its skin. It ranges from Baja California north to the Bering Sea, typically inhabiting deeper continental shelf and slope waters than many other regional flatfish. Dover sole support a long-standing commercial fishery on the U.S. and Canadian Pacific coasts and are considered a well-studied, generally stable component of West Coast groundfish assemblages.

Dover sole are recognized by their elongated shape and distinctively slimy skin.

• Body: elongated, oval, moderately flattened
• Eyes: both on the right side
• Coloration: uniform dull brown to grayish upper side, pale cream to white underside, without strong markings
• Skin: covered in a thick, slippery mucus layer, unusually pronounced compared to other flatfish
• Mouth: small and slightly asymmetrical
• Size: typically 30-45 cm The thick slime coat and drab, unmarked coloration help separate it from similarly shaped Pacific flatfish such as rex sole or petrale sole, which have firmer, less mucous skin.

Dover sole inhabit soft mud and sand bottoms of the continental shelf and slope in the northeastern Pacific, occurring from shallow coastal waters down to depths exceeding 1,000 m, with adults concentrated on the deeper slope. They range from northern Baja California, Mexico, north along the U.S. West Coast to British Columbia and into the Gulf of Alaska and Bering Sea. Cold, deep offshore waters are their preferred adult habitat, while juveniles tend to occupy shallower nearshore areas before gradually moving into deeper water as they grow. Their broad depth range makes them one of the more deep-dwelling common flatfish of the region.

Dover sole are bottom-dwelling predators that rest partly buried in soft sediment, feeding on polychaete worms, small crustaceans, and other invertebrates detected along the seafloor. They undertake depth-related migrations through life, with juveniles in shallower nursery grounds gradually shifting to deeper slope habitats as adults, and further seasonal movements linked to spawning. Spawning occurs offshore in deeper water, with females producing large numbers of pelagic eggs that drift before larvae settle to the bottom. They are not strongly schooling, more often found individually or loosely aggregated on the seafloor, and their heavy mucus coat is thought to offer protection against parasites and abrasion in their deep, soft-sediment environment.