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The movement and competitive behaviours of male coho salmon (Oncorhynchus kisutch) reproductive tactics Prince, Angela

Abstract

The prevailing view regarding the fitness, evolution and maintenance of male coho mating strategies has been based on pieces of data from different salmon species. Since there is no reason to suppose that all salmon species are the same, there is a need for a quantitative description of male coho salmon breeding behavior. The focus of this thesis is to provide a detailed ethological study of male coho spawning behavior with the objective of quantifying 1) patterns of movements, and 2) interactions among males of different reproductive tactics(alpha, satellite, jack), and breeding groups. Because models that address the evolution and maintanence of reproductive strategies require estimates of tactic fitness for comparison, a secondary objective was to use the quantitative data collected to speculate about costs of reproduction for alternative reproductive tactics. In total, 43 male coho were captured and radio tagged during the 1992 and 1993 spawning escapements in Kanaka Creek. Dominant hooknose males moved within a restricted stream segment (mean daily distance (m) moved 86.33 SE 12.55) accessing the females within the segment. Satellite hooknose males moved both frequently and extensively (mean daily distance (m) moved 661.94 SE 200.13), often entering different waterways during their breeding lifespan. Jack males were found to reside in a small segment of stream throughout their breeding lifespan (mean daily distance (m) moved 46.3 SE 40.3) and made use of a variety of refuges, including the nest itself, from which to 'sneak' fertilizations. Sixty-two breeding groups were identified, each having a anywhere from one to five male group members. Rates of aggressive interactions (mean interactions per 10 minutes) were found to differ significantly among males adopting different reproductive tactics (P < 0.001). Alpha males had the highest rate of aggressive interactions (15.2 SE 2.9 ) compared to alternative male behaviors (first satellite 4.7 SE 0.9, second satellite 5.7 SE 1.3, and jack 2.4 SE 0.9). Aggression levels were found to differ significantly among mating groups ( 0.01 > P > 0.025). Intermediate size groups had the lowest aggression level, 11.57 SE 3.81 int/10 min (2 males) and 13.49 SE 3.87 int/10 min (3 males). The highest level of competitive interactions occurred when only one male and one female were present (29.05 SE 12.50 int/10 min). Pairs of combatants explained the increasing rate of aggression with group size for groups containing more than one reproductive tactic (2 to 5 males)(0.75

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