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UBC Theses and Dissertations

Field study of the distribution and behavior of Oligocottus maculosus Girard : a tidepool cottid of the northeast Pacific Ocean Green, John Marshall


The study was concerned first of all with the distribution pattern at low tide of Oligocottus maculosus Girard and other cottid fishes inhabiting tidepools on the west coast of Vancouver Island, B.C. Five species (O. maculosus, G. remensis, Clinocottus acuticeps, C. einbryum and C. globiceps) have their centers of distribution in the intertidal zone. Seven species (Hemilepidotus hernilepidotus, Artedius lateralis, A. fenestralis, Ascelichthys rhodorus, O. snyderi, Enophrys bison and Leptocottus armatus) inhabit tidepools but are most abundant in the subtidal zone. O. maculosus is the most abundant and widely distributed tide-pool cottid in the intertidal zone. Only three other species (C. acuticeps, C. embryum and C. globiceps) regularly inhabit tidepools above LLHW (lowest lower high water). The primary environmental factor correlated with the distribution of O. maculosus is exposure to wave action. In exposed transects this species is restricted to the upper intertidal zone, while in sheltered transects it inhabits tidepools throughout the intertidal zone. Observations show that O. maculosus responds to water turbulence by retreating to cover. It is concluded that to inhabit a given tidcpool O. maculosus must have a minimum period of low turbulent conditions. This species has 'capitalized' on the tidcpool habitat to invade the open coast environment. The study's second concern was to determine the fidelity of individual O. maculosus to the tidcpool in which they are found. O. maculosus shows fidelity to specific tidepools and will return to these pools when displaced from them. The results indicate that the navigational ability of O. maculosus is not solely dependent upon familiarity .with geographical features of the intertidal zone. It is suggested that homing behavior functions as a mechanism stabilizing the spatial distribution of this species. Thirdly, the study was concerned with determining what factors affect the field activity such as feeding and spawning of O. maculosus, and a comparison of its field activity to that under controlled conditions. In the natural habitat its activity is dependent primarily upon such factors as turbulence, temperature and light. Field observations on feeding behavior support Morris1 (I960) conclusion, drawn from physiological studies, that approximately the 16°C isotherm is the limiting environmental factor in the southward distribution of this species. Under constant conditions O. maculosus exhibits a tidal rhythm of locomotor activity. The characteristics of the rhythm indicate that it is entrained directly by the tide. Hydrostatic pressure is suggested as the possible synchronizer. The rhythm is not directly related to the field activity of O. maculosus. It is concluded that it represents the coupling of an avoidance or escape response to a biological clock. Such a mechanism would function with, and be partially responsible for, the homing behavior.

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