Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—Unique genetic lineages of <em> Micropterus </em>species are increasingly recognized; however, little effort has been devoted to identifying their ecological relationships despite recognition of their conservation value by management agencies. Our study objectives were to determine young-of-year, first-summer survival, and examine overall channel-unit habitat use by the Neosho subspecies of Smallmouth Bass <em> Micropterus dolomieu velox </em>from two Ozark streams (Spring and Buffalo creeks). We completed snorkel surveys approximately every 2 weeks from June–September 2013. As anticipated, young-of-year mortality was high during the first 2 weeks of the sampling period (85% in Buffalo Creek and 99% in Spring Creek). Mortality stabilized by the end of July in both streams and was similar over subsequent 2-week periods (95% CI: 0.13%–2.38% and 0.72%–3.48%, in Spring Creek and Buffalo Creek, respectively). In Spring Creek, backwater habitats were unavailable, and young-of-year fish used both pool and run habitats throughout the study duration. However, we observed different habitat-use patterns in Buffalo Creek: young-of-year fish used pools and backwaters throughout the season, use of run habitats increased by late July, and increased use of backwater habitats followed an increase in late summer discharge. In general, there was substantial habitat use variability both within and between streams. Considering both stream reaches combined, young-of-year fish densities in riffle habitat were statistically lower than other channel units. We show that young-of-year Neosho Smallmouth Bass mortality is high during the first few weeks following swim up, and that backwater habitats may be important to early life stages under certain environmental conditions.

Diet and secondary production of some species of Hydropsyche larvae (Trichoptera: Hydropsychidae) in the tailwater affected by dam removal and the emptying of an impoundment

The diet of 4th and 5th instar larvae of filter-feeding trichopteran species [Hydropsyche contubernalis McLachlan, H. modesta Navás and H. pellucidula (Curtis)] that are dominant in the benthos in riffle habitats was analysed. Caddisflies were collected in a river section downstream of a dam. Samples were collected in 2 periods: S1—during the functioning of the dam reservoir, and S2—just after it was emptied (reservoir recovery). Gut contents were examined from the anterior part of the alimentary canal. Formless content, diatoms and other algae were considered as detritus. The diet of 4th instars mostly consisted of plant and animal detritus, with a small contribution of early stages of Chironomidae larvae. In contrast, 5th instars consumed larger chironomids in the subfamilies Orthocladiinae and Tanytarsini. When the reservoir was emptied, an increase in the contribution of invertebrates to the diet was observed – chironomid larvae, trichopterans and ostracods dominated. In spring they were Chironomidae (Cricotopus sp.), while in winter and summer Simuliidae. The most diversified diet was recorded in H. contubernalis and H. modesta in the summer of S2. Trichopteran secondary production in the investigated river section was similar in both study periods: 38.8 in S1 and 35.3 g dry mass m-2 year-1 in S2. In both study periods, the highest values of production were recorded in the stony riffle habitat, where H. contubernalis comprizeded 23.4% (S1) and 18.8% (S2) of total annual trichopteran production originating from all the investigated habitats.

Comparative Ecology of Two Sympatric Species of Dace (Rhinichthys) in the Fraser River System, British Columbia

Age, growth and food habits of leopard dace (Rhinichthys falcatus) in the lower Fraser River are described. Although recently emerged leopard dace and longnose dace (Rhinichthys cataractae) occur together in regions of slow or no current along the river margin, older longnose dace soon begin to occupy regions of higher water velocity. Yearling and older leopard dace remain predominantly in areas of little current. Laboratory experiments in a stream tank demonstrate a strong current preference in longnose dace fry, yearlings and adults. Leopard dace of comparable size show no preference for water current. The swimbladder volume of yearling and adult longnose dace is much lower than that of leopard dace, possibly an adaptation of the former species to occupation of riffle habitat. Temporary coexistence of the two closely related species in the same niche is discussed briefly.