Have Invasive Mysids (Mysis diluviana) Altered the Capacity of Osoyoos Lake, British Columbia to Produce Sockeye Salmon (Oncorhynchus nerka)?

Abstract

Background:During 2005-13, at Osoyoos Lake, British Columbia, we investigated trophic relationships among fry ofOncorhynchus nerkaWalbaum (Sockeye and kokanee), a suite of limnetic planktivores includingMysis diluviana, and their zooplankton prey.Objectives:Our goal was to quantify the impacts that a recently introduced population ofMysiswould have on density, growth and survival of resident age-0 Sockeye Salmon.Methods:Evidence ofMysisimpact was based on (a) simple correlation analysis between various biophysical performance measures and (b) production and bioenergetics models used to identify the strength of bottom-up (i.e. production-driven) and top-down (i.e.consumption-driven) processes.Results:This nine-year study indicated that the Osoyoos Lake food web was strongly influenced by external events These included: large annual variations in river discharge, an earthen dam failure and effluent input from an Okanagan River tributary, and highly variable recruitment ofO. nerkafry given out-of-basin factors (harvest, marine survival) controlling adult salmon returns. Surprisingly, large annual variations inO. nerkarecruitment (0.63 - 7.0 million fry), did not induce significant “top-down” associations in growth, survival or subsequent production among the macro-planktivores (pelagic fish andMysis) and their zooplankton prey. A single significant correlation (p ≤ 0.05) betweenO. nerkafry abundance and their von BertalanffyW∞parameter emerged from a set of 14 potential top-down associations tested. By contrast, we identified several strongly positive “bottom-up” effects in which survival ofO. nerkafry was significantly associated (p ≤ 0.01) with annual variations in total zooplankton biomass,Daphniabiomass andEpischurabiomass. Our results indicate thatMysisplayed a dual role in the Osoyoos Lake pelagic food web. As predators, they accounted for an average (June-October) of 64% of the total prey biomass consumed by fish andMysis. As prey,Mysiscontributed an average of 35% of the prey biomass consumed by fish. Consumption by fish andMysistogether accounted for daily losses of only 4.5% of non-mysid zooplankton biomass and 34% of daily zooplankton production.Conclusion:We conclude that in all years, combined prey consumption byMysisand fish was never high enough, acting alone, to reduce the availability of their potential zooplankton forage base. However, we also estimate that in the absence ofMysis,O. nerkafry could experience a 43% increase in their daily food intake and that fish andMysismight control their principal prey taxa when exogenous factors (e.g.annual discharge) induced major reductions in zooplankton biomass. Finally, althoughMysishas clearly altered the energy flow pathways from plankton to fish in the Osoyoos Lake food-web, mysids have not precluded rebuildingO. nerkaabundance to levels at or exceeding historic maxima.

Migration and survival of Okanagan River Sockeye Salmon Oncorhynchus nerka, 2012–2019

“…Recreational, tribal, and commercial harvest opportunities further complicate management of Okanagan Sockeye during summer months. An average of 19% of Okanagan Sockeye are harvested between Wells Dam (rkm 830) and spawning grounds each year, often when fish are congregated in large numbers at the thermal barrier [37]. Mortality of fish that evade capture compounds this issue: some fishery managers apply a 40-60% mortality rate for salmon released from commercial gillnets and 10% for salmon release from recreational fisheries, rates that increase with increasing water temperatures [57].…”

“…Vaseux Lake, located downstream of Skaha Lake, is relatively shallow and hosts large populations of Northern Pikeminnow Ptychocheilus oregonensis and Smallmouth Bass Micropterus dolomieu that likely influence juvenile survival. Cessation of migration or alternative life history patterns (i.e., non-migrants are perceived as mortality in mark-recapture modeling) once Skaha Lake smolts encounter the productive Osoyoos Lake is another possibility [37]. Finally, differences between hatchery-and wild-origin juvenile Okanagan Sockeye could explain differences in survival during the smolt emigration [35,56].…”

Metabarcoding of native and invasive species in stomach contents of Great Lakes fishes

“…Metabarcodinging analysis of the three native prey in predator scDNA contributes to understanding the Lake Michigan offshore food web and exhibited frequencies of occurrences similar to published conventional diet analyses [i.e., 22 , 37 , 69 ]. Outside the Great Lakes, the three native prey identified in scDNA are of conservation concern [ 72 , 73 , 76 , 77 ]. Sample site, predator species, and predator TL significantly influenced AIS and native prey occurrence patterns.…”

“…The three native species were selected as we expected them to be common diet items in both native and non-native predators [ 37 , 69 ] and because they are likely to interact with the target AIS directly or indirectly [ 70 , 71 ]. Additionally, these three native invertebrate species have been reported as invasive or as posing invasion risks outside the Great Lakes [ 72 , 73 ]. BLAST analyses against the custom databases were performed using the map reads to reference function in QIIME with default parameters, except having adjusted the minimum match value to 98% for reads from the universal primer set, and having set this value to 96% as a minimum match value for reads from any of the target AIS primer sets.…”

Age‐Structured Interactions among Reintroduced Sockeye Salmon, Resident Kokanee, Invasive Mysids, and their Zooplankton Prey in Skaha Lake, British Columbia

“…However, in 1916 construction of the McIntyre Dam near Oliver, British Columbia (Figure 1), virtually excluded Sockeye Salmon from Skaha Lake and the upper Okanagan basin. In addition, during 1964-1994 average escapement of Okanagan Sockeye Salmon spawning downstream of McIntyre Dam fell from 50,000 to 20,000 adults, and during 1994-2004 escapement declined further to <5,000 adults averaged over 3 years and <1,500 during 1 year (Hyatt and Rankin 1999;Hyatt et al 2018a).…”