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The preferred salinities of five Pacific salmon species were studied. Each species was shown to undergo a temporal sequence of preference changes. The sequence began with a preference for fresh water then changed in the direction of increasing seawater concentration, the terminal pattern indicating a preference for water of open ocean concentration. This preference sequence was shown to parallel closely the horizontal salinity gradients typical of estuaries through which juvenile salmon pass on their seaward migration. On the basis of this evidence the following orientation mechanism was postulated: that juvenile salmon are able to use estuarine salinity gradients as one of the directive cues in their seaward migration. Further study of this orientation mechanism showed that the initial part of the preference sequence develops unaffected by seawater exposure. By contrast the latter part of the sequence (corresponding to seaward end of the estuary) was found to depend on a period of exposure to seawater otherwise a regression to a premigratory freshwater preference took place. The sensory stimuli leading to the salinity preference response were shown to depend on a complex interaction of naturally occuring sea salts. Experimentally the simplest salt mixture which would elicit a normal response consisted of two cations (Na⁺ and Ca⁺⁺) and one anion (Cl¯). It was shown further that taste or the common chemical sense was the primary sensory modality underlying the response and that juvenile salmon have an ability approaching absolute salinity discrimination. Speculation concerning the evolution of the salinity preference orientation mechanism was presented. Published evidence favours the view that migratory salmonids evolved from nonmigratory forms with limited osmoregulatory abilities. On this basis it was proposed that originally the ability to orient with respect to seawater concentration was of direct survival value to the stenohaline ancestral salmonid. Later, as diadromous movements expanded along with euryhalinity, salinity preference became integrated into a temporal sequence of changes and thereby an orientation device useful for migration. / Science, Faculty of / Zoology, Department of / Graduate

The seasonal salinity preference of four species of Pacific salmon was examined. Each species showed a strong preference for hypertonic seawater during the normal period of migration. Pink fry (Oncorhynchus gorbuscha) and coho yearlings (O. kisutch) lost this preference during the summer in contrast to Chum fry (O. keta) and sockeye yearlings (O. nerka). Three other types of behaviour showed seasonal changes consistent with a transitory "migration disposition". A preference for hypertonic seawater was associated with high levels of activity, strong schooling tendencies and depressed aggressive behaviour. Subsequent seasonal changes showed a marked increase in aggressive behaviour accompanied by decreased levels of activity and group behaviour. A long daily photoperiod (16 hours) prolonged the behaviour complex associated with seaward migration. A short daily photoperiod (8 hours) delayed but did not totally inhibit the development of a hypertonic salinity preference and associated behaviour. The preference of chum salmon fry for a series of seawater concentration indicated an all-or-none type response. A consistently strong preference was shown for seawater hypertonic to plasma chloride levels as reported in the literature. No preference was shown for hypotonic seawater. A series of experiments in which the composition of an artificial seawater was altered indicated that under natural conditions the expression of a preference for salt water probably depends on the concentration of sodium chloride. The swiftness of the response (chum and sockeye) indicated stimulation of a peripheral salinity receptor. Coho underyearlings injected with mammalian somatatropin showed an increased although not statistically significant preference for hypertonic sea water. Both activity and aggressive behaviour were depressed in comparison to control fish. / Science, Faculty of / Zoology, Department of / Graduate

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Conditioning experiments demonstrated a significant, repeatable and reversable capacity for groups of yearling sockeye salmon (Oncorhvnchus nerka) to discriminate between perpendicular planes of linearly polarized light. Polarized light was also shown to influence orientation behavior when compared with orientation under unpolarized light. A limited number of fish orientated at a common angle (between 22.5 and 45 to the right of) with respect to the plane of polarization. Possible analysers of polarized light are discussed. / Science, Faculty of / Zoology, Department of / Graduate

The marked differences in response to water current, exhibited by juvenile rainbow trout migrating into Loon Lake from its outlet and inlet streams, were studied both in the field and in experimental laboratory apparatus. All available evidence argued against genetically discrete outlet and inlet stocks, each maintaining different innate responses to water current. Difference in water temperature between streams was shown, in field and laboratory experiments, to regulate direction of juvenile trout migration through action on behaviour associated with downstream movement, maintenance of position and upstream movement. In laboratory experiments with cool (5°, 10° C.) flowing water, recently emerged fry rarely made contact with the stream bottom in darkness and exhibited much more downstream movement than in warm (> 14°C.) water. In cool streams of the Loon Lake system (daily mean consistently < 13°C.) large numbers of recently emerged fry moved downstream in darkness. Laboratory experiments indicated that combination of cool water (10°C.) and long day length (sixteen hours) induced downstream movement of fingerlings. In the field, fingerlings moved downstream largely in late spring and summer in cool streams of the Loon Lake system. In laboratory experiments with warm (15°, 20°C.) flowing water, recently emerged fry made frequent contact with the stream bottom in darkness and exhibited much less downstream movement than in cool (10°C.) water. In the warm outlet stream (daily mean in summer usually > 15°C.) recently emerged fry maintained position in darkness. Laboratory experiments suggested that short day length (eight hours) may facilitate maintenance of position exhibited by fingerlings in streams during late autumn and winter. Upstream movement of fry tested in the field and laboratory was most pronounced in warm water (>14°C). Fingerlings subjected to rapid 5°C. increases in water temperature in an experimental stream exhibited an immediate increase in upstream movement. Upstream movement in summer of large fry and fingerlings occurred only in the warm outlet stream; daily periodicity of upstream movement was positively correlated with sharp rises in water temperature. Evidence examined from four other widely separated stream systems indicated an environmental control of migration in juvenile rainbow trout similar to that demonstrated in the Loon Lake stream system. Possible mechanisms and interaction of factors controlling migratory patterns between and within streams are discussed. Significance of the predominant role played by temperature is considered. / Science, Faculty of / Zoology, Department of / Graduate

Diurnal migration of adult peamouth chub was studied in Nicola lake. Results are taken from over two hundred gill net sets in 1959 during which time more than five thousand chub were netted. A migration surfaceward and shoreward occurred in evening and a reverse migration in morning. Diurnal migration was characteristic of the summer. Chub during winter had constant close association with the bottom at which time bottom organisms were the main food item. Onset of diurnal migration in summer was accompanied by increase in importance of plankton and chironomid pupae in the diet. Adults of all sizes and both sexes performed similar diurnal migrations but young-of-the-year chub showed the reverse migration, inhabiting shallow shore waters by day and dispersing to deep water by night. Inversion in behaviour occurred at about one year of age. Adult migration was unrelated to oxygen or temperature changes but timing of migration and depth distribution of chub was closely associated with light intensity, adults avoiding brightly illuminated areas. A diurnal change in diet accompanied the migration. In August food items changed from plankton during day to chironomid larvae and pupae in evening and night. Adaptive value of the migration is discussed in relation to physical and biotic characteristics of the environment. / Science, Faculty of / Zoology, Department of / Graduate

The hypothesis that emigration of individuals in excess of resource carrying capacity acts as a population regulatory mechanism was tested experimentally using the desert pupfish (Cyprinodon macularius). When emigration was prevented, four pupfish populations monitored from May 1982 to March 1984 were unable to regulate numbers to resources. Numbers increased to a mean peak size 1.4 times greater than four pools open to emigration, followed by high mortality, a decline in body condition, reduced recruitment, and stunting. The pattern of overpopulation was similar to that observed in fenced populations of rodents. In contrast, pupfish in open pools had lower numbers, higher recruitment, better condition and growth, and higher total production. Emigration patterns were similar in all four open pools. Population size, rate of increase, and temperature affected emigration rates. Nearly twice as many males than females emigrated. Emigrant pupfish usually had poorer condition factors than residents. Pupfish showed a rapid and uniform increase in emigration when resources were reduced. Nearly one-half (42.2 and 41.8%) of pupfish populations emigrated from two open pools wherein resources were suddenly reduced by 50%. Many fewer fish emigrated from undisturbed control pools (15.2 and 16.0%). The results suggest that residency-emigratory behavior of pupfish can reliably and precisely effect changes in numbers to be in consonance with resources. They support emigration as sufficient to regulate pupfish numbers to resources in open systems without the need for other factors or mechanisms.

No description available.

No description available.