Aquatic faunal remains form a significant proportion of many Early to Mid-Holocene shell midden deposits. The range of species represented in each midden is variable, reflecting factors such as local microenvironments, resource selection by humans, and archaeological preservation. For example, at Ulva Cave 36 distinct taxa of shellfish have been identified (Pickard and Bonsall 2009); at Morton the shellfish assemblage was similarly diverse with 37 taxa recorded (Coles 1971). By contrast at An Corran, Skye, 14 genera were recovered from Early to Middle Holocene deposits (Pickard and Bonsall 2009) and at Sand, Applecross, only eight taxa were recorded (Milner 2009).
Fish are reported to be abundant at all sites. Unfortunately, detailed reports of the fish bone assemblages remain scarce. With the exception of Sand, Applecross (Parks and Barrett 2009) species diversity is generally limited, but this may reflect publication standards as much as prey specialization. Gadidae are recorded at all sites for which information is available, and saithe (Pollachius virens) dominates the ichthyofauna recovered from the Oronsay sites (Anderson 1895, 1898; Connock et al. 1993; Mellars and Payne 1971; Mellars and Wilkinson 1980).
Sea mammals were recorded at the Oronsay sites, Risga in Loch Sunart, and Sand, Applecross (Anderson 1898; Grigson and Mellars 1987; Lacaille 1954; Parks and Barrett 2009). Finds include the very large rorqual (Balaenoptera spp.), and several smaller species — seals (Phocidae) and dolphin or porpoise (Delphinus delphis/Phocaena phocaena).
Brachyurans, or true crabs, are present in most middens. Generally, where data are available, the presence of edible, swimming and green shore crab is reported (e.g. Anderson 1898; Coles 1971; Lacaille 1954). At Ulva Cave at least six species of crab were identified (Pickard and Bonsall 2008). Lobster (Homarus gammarus) was recorded at the Oronsay sites (Mellars and Payne 1971). Fine sieving of midden samples from Ulva Cave also led to the recovery of fragments of sea urchin (Echinoidea) tests (Pickard and Bonsall 2008).
Other resources foraged on the shore include aquatic algae, inferred from the presence of small shellfish that live on seaweed but would have little food or decorative value. The seaweeds may have been harvested as food, fuel, or for medicinal properties (e.g. Banga 2002; Turner and Clifton 2006). Such shellfish species were particularly abundant at Ulva Cave (Pickard and Bonsall 2009). This may indicate a particular emphasis on seaweed collection at this site, but more likely reflects the sampling strategy adopted (Pickard and Bonsall 2009).
A wide range of aquatic bird species were identified at Morton with sea birds such as razorbill (Alca torda), and cormorant (Phalacrocorax carbo), comprising a significant proportion of the assemblage; however the relative abundance of the remains was not quantified (Coles 1971). Similar diversity of bird species is recorded at Risga although a distinct range of seabirds, including the now extinct great auk (Pinguinus impennis), were documented (Lacaille 1954). The majority of the species represented are seabirds that nest on cliffs or inhabit inshore waters.