Most freshwater fishes have short pelagic early life stages. Lake Michigan presents an interesting scenario for yellow perch (Perca flavescens), a species with a long pelagic larval stage that may not be well adapted to lakes with an expansive pelagic environment and extensive offshore transport. We investigated the possibility that early life stages of yellow perch were transported well offshore from their nearshore spawning grounds and explored whether food resources were more or less favorable offshore. To determine the extent to which pelagic age-0 yellow perch moved offshore, we sampled at multiple scales ranging from local (< 2 km) to across the lake (>120 km). Evidence of offshore movement by larvae occurred at each scale.Yellow perch larvae were quickly transported offshore from nearshore spawning sites and remained in the offshore pelagia to sizes of at least 30 mm. Zooplankton density was greater offshore than nearshore, suggesting that pelagic age-0 yellow perch find improved food resources offshore than at their nearshore spawning sites. Currents operating at oceanographic scales likely influenced the offshore movement of pelagic age-0 yellow perch in Lake Michigan.These currents, coupled with prey availability for pelagic age-0 individuals, may influence the recruitment success of this species.
We investigated the predator‐prey interactions of two pelagic species, landlocked Atlantic salmon Salmo salar and rainbow smelt Osmerus mordax, in a large‐lake ecosystem. Our goal was to determine the overlap of habitats selected, based on profiles of temperature and dissolved oxygen (DO). We used hydroacoustics to ascertain the seasonal habitat selection of rainbow smelt and gill nets to sample Atlantic salmon in the Inland Sea of Lake Champlain, Vermont. We identified patterns of smelt habitat selection by overlaying the acoustically determined vertical distributions of smelt onto profiles of water temperature and DO. To verify species composition of acoustical targets, we performed midwater trawls using a stepped‐oblique method and found that rainbow smelt constituted 99.5% of trawl catches. Trawl catches and acoustic fish density were correlated, indicating that acoustic targets represented trawled fish. Atlantic salmon habitat selection was estimated from temperature and DO profiles taken at gill nets that caught salmon. Data for Atlantic salmon and rainbow smelt demonstrated extensive spatial overlap in habitat selection during the three sampling seasons. Our results provide greater insight into the predator‐prey interactions of these species as mediated by environmental factors. Because Atlantic salmon are stocked, this insight into the predator‐prey interactions may assist managers in effectively regulating stocking numbers.
Timing of hatch in fish populations can be critical for first‐year survival and, therefore, year‐class strength and subsequent species interactions. We compared hatch timing, growth rates, and subsequent mortality of age‐0 Rainbow Smelt Osmerus mordax and Alewife Alosa pseudoharengus, two common open‐water fish species of northern North America. In our study site, Lake Champlain, Rainbow Smelt hatched (beginning May 26) almost a month earlier than Alewives (June 20). Abundance in the sampling area was highest in July for age‐0 Rainbow Smelt and August for age‐0 Alewives. Late‐hatching individuals of both species grew faster than those hatching earlier (0.6 mm/d versus 0.4 for Rainbow Smelt; 0.7 mm/d versus 0.6 for Alewives). Mean mortality rate during the first 45 d of life was 3.4%/d for age‐0 Rainbow Smelt and was 5.5%/d for age‐0 Alewives. Alewife mortality rates did not differ with hatch timing but daily mortality rates of Rainbow Smelt were highest for early‐hatching fish. Cannibalism is probably the primary mortality source for age‐0 Rainbow Smelt in this lake. Therefore, hatching earlier may not be advantageous because the overlap of adult and age‐0 Rainbow Smelt is highest earlier in the season. However, Alewives, first documented in Lake Champlain in 2003, may increase the mortality of age‐0 Rainbow Smelt in the summer, which should favor selection for earlier hatching.
Received October 16, 2015; accepted January 12, 2016 Published online April 27, 2016
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