. The Canadian field-naturalist. 1971 Kott: American Brook Lampreys in Ontario 237 of May for brook lamprey and in June for sea lamprey. Since ammocoetes of both species have similar requirements, a two week differ- ence in spawning time could have a significant effect in reducing competition between the species. Smith, et al. (1968) found that the brook lamprey hatches two weeks after eggs are fertilized, so that as sea lamprey are just starting to spawn, youg brook lamprey have already hatched. If both species have the same growth rate, in beds containing amocoetes of both species, brook lam
. The Canadian field-naturalist. 1971 Kott: American Brook Lampreys in Ontario 237 of May for brook lamprey and in June for sea lamprey. Since ammocoetes of both species have similar requirements, a two week differ- ence in spawning time could have a significant effect in reducing competition between the species. Smith, et al. (1968) found that the brook lamprey hatches two weeks after eggs are fertilized, so that as sea lamprey are just starting to spawn, youg brook lamprey have already hatched. If both species have the same growth rate, in beds containing amocoetes of both species, brook lamprey would be larger in size. Competition for food would be reduced if the larger ammocoetes select a larger food particle size. The difference in spawning times could be largely temperature dependent. Piavis (1961) found that °C was the optimum tempera- ture for the hatching of sea lamprey eggs. At this temperature 78% of the eggs developed to the prolarval stage. Using the data of Smith, et al (1968) one can calculate at 23% pro- larval development from eggs of brook lamprey at Vladykov (1949) found that 17X was the optimum temperature for spawning in brook lamprey. McCauley (1963) has shown that the optimum range for hatching of sea lamprey eggs is very narrow. If this is true for lampreys in general, a 2^ lower optimum for the brook lamprey would necessitate an earlier spawning time to ensure a maximum spawning success. Samples were available from the beginning, the peak, and the end of the spawning move- ments. Although the sex ratio may change as the spawning run progresses, with females being more frequent towards the end of the run, no significant change in this ratio occurred in the population investigated. In this brook lamprey spawning population, as in spawning populations of other species of lampreys, males predominate (Applegate, 1950; Wigley, 1959; Hardisty, 1960; Purvis, 1970). In ammocoete populations, Hardisty found that the sex ratio was approxima
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