A further investigation of the homing behaviour of the intertidal cottid, Oligocottus maculosus Girard

The purposes of this study were to find the causes of the variability previously observed in the homing behaviour of Oligocottus maqulosus Girard and to attempt to clarify the mechanisms by which the fish homes; in particular whether olfaction is the major sensory mechanism involved. The study was conducted at 12 sites on the southwest coast of Vancouver Island, British Columbia. Variability in homing behaviour and morphological characters between fish in different tidepool and inlet areas, as well as age, year-class and length differences in homing behaviour in one tidepool area were examined. Consideration of the sensory mechanisms involved in homing behaviour included: interactions between resident and introduced fish, the nature of movement between the transplant and home pools, detection of chemosensory clues, the use of the paired fins to detect touch and/or chemosensory clues and in greatest detail, the roles of vision and olfaction in homing behaviour. Prior to investigating age and year-class differences, a method of age determination using otoliths was developed and compared with results from vertebrae and length-freguency analysis. At any one time there are three major age groups in the population with decreasing numbers of age 3 and 4 fish. Age-length relationships differed between areas. Differences were found in homing behaviour between areas, which could be related to wave action (turbulence) and the topographical irregularity (roughness) of the terrain. With decreasing turbulence and increasing regularity of the terrain, fidelity is shown to an increasing number of pools or a wider area and, in tidepool areas, increasing percentages of fish show homing behaviour. However, the fish which do home in turbulent rough areas show highest percentages returning to the home pool. In inlets, little homing behaviour is expressed. With decreasing turbulence and increasing regularity of the terrain, decreasing numbers of fish remain in the transplant area. These findings can be related to the reduced high tide activity of O. maculosus in turbulent areas shown by Green (1971b,c). No consistent differences, which could be related to exposure or homing behaviour, were found in the meristic and morphometric characters of O. maculosus in different areas. Investigation of cirri on O. maculosus in different areas showed that there is a variable increase in the number of cirri, on all parts of the body, with length and age. There are differences in these relationships between areas but they do not seem to be related directly to exposure. Year-class differences in cirri numbers are not apparent. The function of the cirri could not be determined. Age related differences in homing behaviour are apparent, although year-class differences are not. Examination of the age differences in homing behaviour by smaller size-classes than one year age groups showed that there is an improvement in the percentage successfully homing with length up to about 5 cm. Homing is best expressed in fish between 5 and 7 cm (age 2) and after this size there is a decrease in the percentage successfully homing. The percentage of homing fish returning to the home pool appears to be about equal for all size classes. There is a decline in the percentage remaining in the transplant area with length except in the largest size classes of fish. Juvenile fish (about 2.3 to 2.7 cm) which have moved into lower tidepools from the high tidepools in which they settle, show extensive movement between tidepools and appear to begin showing evidence of home range fidelity and homing behaviour at about 3 cm. It is suggested that during this period of extensive movement, the area is in some way "learned" and "memorized". Investigation of the sensory mechanisms involved in homing behaviour did not produce any evidence to show that pool density or "space", behavioural interactions, touch or taste clues detected by the paired fins or taste receptors located elsewhere on the body are involved in homing. Some evidence was found to suggest that movement between the transplant and home pool is directed. Vision and olfaction appear to be involved in homing, a combination of blindness and anosmia being the most effective in reducing homing success to low levels. Both senses are essential to the successful homing of juvenile fish but vision and subsequently olfaction become unnecessary in older fish. It is suggested that adult fish are unable to home unless one of these senses is available. Because of the difficulties of appreciating how either olfaction or vision can be used over any distance in the turbulent intertidal, it is suggested that olfactory and visual, and perhaps other clues from particular pools are used to home and that the fish moves from "pool" to "pool" to home. However, neither conspicuous visual landmarks nor olfactory clues emanating from the home pool were shown to be recognized by O. maculosus. The data from this and a related study (Khoo, 1971) suggest that the relative importance of sensory mechanisms may differ both in the development of homing behaviour and between areas.Science, Faculty ofZoology, Department ofGraduat