Feeding and Habitat Preferences of Non-Native Smallmouth Bass (Micropterus dolomieui) in Lakes Throughout British Columbia




Beck, Martina

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Characterization of smallmouth bass (Micropterus dolomieu) interaction with native species assemblages, especially salmonids, in lakes throughout BC is prerequisite to identification of high-risk systems warranting on-going monitoring. Therefore this project addresses the following issues: How does smallmouth bass (SMB) trophic profile overlap with native species and does it vary across time and space? Schoener’s index of dietary overlap was not significant between SMB and rainbow trout (Oncorhynchus mykiss; α=0.406, 0.257), or cutthroat trout (Oncorhynchus clarkia; α=0.145, 0.29). Prey fish levels (Ei =35.4%) and the total energetic density (14.91±4.74J/g) of the cutthroat trout diet from Weston Lake (SMB free) were significantly higher compared to the diet of cutthroat trout from Cusheon Lake (Ei =3.3% and 7.69±1.93J/g) where non-native SMB have been introduced. Within the Vancouver Island study lakes, gut-content analysis revealed available signal crayfish serve as an important prey resource in the SMB diet (Ei =34%). What capacity do SMB have to take advantage of seasonal pulses of forage? SMB displayed the ability to rapidly (within 24hrs.) alter their diet and consumption levels (4.7 times higher) to maximize on pulses of rainbow trout fry following a stocking event. SMB did not spatially overlap with spring peaks in salmonid fry runs in the Okanagan lakes, as water temperature remained around the 10°C threshold when SMB are not yet active. Kokanee (Oncorhynchus nerka) fry did however make up Ei =83% of the yellow perch (Perca flavescens) diet. SMB are thriving in locations suspected to be on the limit for their environmental suitability through increased size at age for SMB in the Cariboo region in order to adapt to a longer (by 62 days) winter starvation period. SMB are a generalist predator able to adapt and thrive in very different systems; high vs. low productivity, few or many fish species, crayfish or no crayfish. The likely impacts of this in BC could include shifts in the diet of other fish species and increased costs associated with only stocking larger catchable sized trout in lakes containing non-native SMB. Policy recommendations based on our findings are that SMB introductions into systems that have rainbow/cutthroat trout are likely to cause the highest impacts on our native fisheries in BC if the systems are; highly productive, contain a high diversity of small bodied fish and invertebrate species, lack signal crayfish and large lakes with predominant littoral zones and complex shorelines.



smallmouth bass, freshwater fish, non-native, trophic overlap, British Columbia