Experiments to test the effectiveness of low-frequency, high-intensity sound in excluding alewife, Alosa pseudoharengus, from an experimental net structure were conducted on Lake Ontario near Pickering, Ont. Sound was generated by modified seismic devices called pneumatic poppers. The number of alewife entering the experimental structure was reduced by 71–99% when the poppers were operating. Sonar evidence from one test suggested that another species which was not caught in the collection nets was less influenced by the acoustic deterrent. The results suggest that low-frequency, high-intensity sound may be effective in reducing losses of adult alewife at water intakes.
Laboratory and field tests were conducted to determine the effectiveness of filtered mercury vapour lights in attracting fish with possible utilization in a fish conserving scheme a t a n electrical generating station. I n laboratory tests, alewife demonstrated a n attraction to the mercury vapour light which was associated with an increase in swimming activity. This response was maintained over a 48-hour period. When the filtered mercury vapour lights were utilized in association with a fish pump in the Nanticoke Generating Station forebay, juvenile gizzard shad and smelt were attracted to the pump area. Although there was variation with time of day, tubidity andlighting array; the results suggested that the number of fish passing through the pump increased when the mercury vapour lights alone or when the mercury lights in association with a white strobe light were employed.
Herring gull broods were artificially increased to four and five chicks while others were reduced to one chick. The growth rates of chicks and chick weights at fledging were similar among all control and experimental broods. The experimentally increased brood sizes had a slightly higher fledging success than control broods, and the fledging success of one-chick experimental broods was higher than that of one-chick control broods. Thus, chick survival was not reduced in larger brood sizes and the number of young fledged per pair of adults increased with brood size. Further. chicks in large broods were at no weight (or viability) disadvantage despite the presence of a larger number of brood mates. We conclude that food was not limiting either the growth rate or fledging success of chicks from broods larger than the modal clutch size, and suggest that parents used local, abundant, artificial food sources in addition to their natural food supply.
The distribution of common tern (Sterna hirundo) nests relative to vegetation and objects (rocks and sticks) was studied on the Eastern Headland of the Toronto Outer Harbour in 1977. The vegetative cover in one study plot ranged from 0–10% to 91–100%, with a mean of 16%. In that plot the vegetative cover near nests ranged from 0–10% to 81–90%, with a mean of 44%. In the second study plot where plants were widely scattered, the great majority of the nests were situated next to plants or objects. Possible advantages and disadvantages of this behaviour are briefly discussed.
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