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. / Graduate / 0793 / 0329 / 0792 / mbeck@uvic.ca

Black Carp (Mylopharyngodon piceus) is an invasive fish species native to Asia that has become increasingly abundant within the Mississippi River Basin during the past decade. Originally introduced to control snails that are an intermediate host for trematode parasites of fishes in aquaculture ponds, Black Carp are now present in several rivers in the U.S. and represent a potential threat to threatened and endangered mussel populations. Black Carp have historically been classified as molluscivores; however, a recent study that examined gut contents of Black Carp collected from the Mississippi River Basin indicated that Black Carp are opportunistic consumers that prey upon a wide variety of invertebrates and are flexible in their feeding modes. Despite the potential for Black Carp to compete with native riverine fish species for invertebrate prey, only one published study has compared Black Carp trophic position with that of native fishes in a small portion of the Black Carp’s invaded range. Therefore, the objectives of this study were to assess trophic overlap between Black Carp and two fish species native to the Mississippi River Basin using isotopic niche analysis and gut contents analysis. Dorsal muscle tissue samples were collected from Black Carp, Freshwater Drum (Aplodinotus grunniens), and Blue Catfish (Ictalurus furcatus) and analyzed for δ13C and δ15N to assess each species’ isotopic niche. Freshwater Drum and Blue Catfish gut contents were also removed and analyzed and compared to published Black Carp stomach contents data. Gut contents analysis indicated differences in diet composition between Black Carp and the two native fish species. Chironomidae had the highest frequency of occurrence (67%) and percent of taxa by number (47%) for Freshwater Drum. Trichoptera had the highest frequency of occurrence (58%) and percent of taxa by number (30%) for Blue Catfish, and Gastropoda had the highest frequency of occurrence (16.5%) of any specific prey taxa for Black Carp. Black Carp showed low isotopic niche overlap (≤47%) with both native species when muscle tissue δ13C and δ15N data from all fish collection locations were combined and when assessment of isotopic niches was restricted to the subset of locations where all three species were collected. Isotopic niche overlap was also low (10-48%) between Black Carp and both native species when isotopic niches were compared at individual collection locations. Intraspecific isotopic niche overlap among fish collection locations was highly variable (0-69%) within each of the three species, highlighting the need to assess interspecific isotopic niche overlap by collection location. Broad isotopic niches exhibited by Black Carp in the Mississippi River and tributaries are indicative of substantial trophic diversity among individuals and use of multiple basal energy sources, consistent with a recently published study which found that Black Carp diet composition differed among individuals and that Black Carp consumed a variety of invertebrates, including non-benthic taxa.