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1991-12-01
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The hypothesis that salmonine catches in Lake Ontario are greater at thermal fronts in spring and early summer was tested in 1990 by comparing catches in non-frontal water and three types of fronts (thermal bar, 4 °C; spring thermocline, 6-8 °C; thermal break, ? 9 °C). A thermal front in the spring on Lake Ontario is a rapid temperature cline across the surface of the lake (in this study defined as ? 0.15 °C/min at the standard 3.2 - 4.8 km/h trolling speed) parallel to shore that extends obliquely from the surface toward shore and the bottom. Surface temperature was recorded every 2 min during 45 hours of fishing. Only
20% of the time was spent fishing in thermal fronts where 35% of the 88 strikes occurred. Catch per unit effort (CPUE) for salmonines at thermal fronts was significantly greater than non-frontal CPUE on each of the 11 sampling dates (P < 0.001). Catches were better in thermal breaks (P < 0.002), spring thermocline (P < 0.01) and thermal bar (P < 0.05) than in non-frontal waters. The data support the hypothesis that there is a relationship between salmonine susceptibility to capture and thermal fronts. Relative to non-frontal water, coho salmon (Oncorhynchus kisutch) CPUE was greater in the spring thermocline (P < 0.01); rainbow/steelhead trout CPUE was greater in thermal breaks (P < 0.05), spring thermocline (P < 0.05) and thermal bar (P < 0.002). It appears that anglers can effectively catch specific salmonine species by fishing specific thermal structures. These results likely are applicable to other pelagic habitats utilized by salmonines.