Description and common attributes
Sea Mither is a spirit of summer days that quells the turbulent sea waters around the northern isles of Scotland. Shetland islanders, particularly fishermen, seek her protection from the Devil. Control of the seas is maintained by Teran, the spirit of winter, until Sea Mither arrives around the time of the vernal equinox in mid-March. Both spirits are invisible to humans. Teran is her arch-enemy and the pair fight bitterly, often for weeks as she tries to gain control. Their arguments cause gale-force winds and heavy tumultuous seas as she tries to wrest control from him. Teran's screeches are carried by the howling gales as the two spirits try to oust each other. The period of the spring combat between the pair is termed the "Vore tullye" or the "spring struggle". Eventually Sea Mither overcomes Teran, relegating him to the depths of the ocean; inclement summer weather is caused by Teran's attempts to escape.
During summer months the Sea Mither also keeps the demonic nuckelavee creature confined, and undertakes benevolent labours: she empowers aquatic creatures with the ability to reproduce; warms and calms the seas; and instils a softer song-like quality to the gentle summer breeze. According to folklorist and Orkney resident Walter Traill Dennison, during Sea Mither's reign in summer the conditions reported by islanders may have "tempted one to believe that the Orkney archipelago had become the islands of the blessed." But the continual work she undertakes to keep everything calm and the strain of maintaining control over Teran gradually tires her.
As autumn approaches, Teran takes advantage of Sea Mither's exhaustion to break free, and conflict between the two starts again. The power struggles cause the weather to change with darkening skies and howling winds. This time, Teran triumphs in the conflict termed the "Gore vellye".[lower-alpha 1] Control of the ocean and weather is returned to Teran and Sea Mither is forced to leave. Teran possesses a malevolent grip on the seas, creating turbulent storms, freezing the seas, and causing aquatic creatures to refrain from reproducing; the status of the nuckelavee's activity is unknown during Teran's reign. No details are given as to where she spends the winter, but during the storms caused by Teran the fishermen were consoled that Sea Mither would return refreshed and powerful in the spring, to again oust Teran from his grip over the seas.