Influence of river discharge on grass carp occupancy dynamics in south‐eastern Iowa rivers

Despite the longstanding presence of grass carp Ctenopharyngodon idella in the Upper Mississippi River (UMR) watershed, information regarding their populations remains largely unknown, in part because capture is difficult. Occupancy models are a popular wildlife assessment tool to account for imperfect detections but have been slow to be adopted in fisheries. Herein, we used occupancy modelling to evaluate the influence of two environmental covariates (river discharge and water temperature) on grass carp occupancy, extinction, colonization, and detection at nine sites within south‐eastern Iowa rivers from April to October 2014 and 2015. Grass carp were detected at least once at all but one site. The most parsimonious model indicated that grass carp colonization probability increased from 0.15 to 0.67 with increases in river discharge. In contrast, occupancy (0.20), extinction (0.29), and detection (0.50) probabilities were temporally constant. Models indicated that water temperatures did not influence grass carp extinction or colonization probabilities relative to river discharge. Cumulative grass carp detection probability approached 1.0, whereas conditional occupancy estimates were less than 0.1 when using five or more sampling transects. The use of a robust design occupancy model allowed us to estimate site occupancy rates of grass carp corrected for imperfect detections, while demonstrating the importance of river discharge for site colonization. These results can be used to assess the distribution of a cryptic fish while helping to guide grass carp sampling and removal efforts

Trout and salmon movements in two Idaho streams as related to temperature, food, stream flow, cover, and population density

Many juvenile salmon and trout migrated from the Lemhi River drainage each fallwinter-spring period. Seaward migration of anadromous trout and salmon normally occurred inthe spring but pre-smolt anadromous and non-anadromous fishes also left the stream usuallybeginning in the fall. I compared data on temperature, food abundance, stream flow, cover andpopulation density with movements and conducted field and laboratory tests to determinereasons for the two types of movements.Smolts of the anadromous species migrated for an obvious reason but none of the factors Iexamined appeared to \u27stimulate or release\u27 their seaward migration. Movement frequentlycoincided with changes in water temperature and stream flow, but I could not establish aconsistent causal relationship and concluded that photoperiod and perhaps growth must initiatethe physiological and behavioural changes associated with seaward migration.Non-anadromous and pre-smolt anadromous species emigrated from the streams for differentreasons than the smolts. I postulated that fish found the stream environment unsuitable duringthe winter. Stream temperature declined in the fall as fish began moving from the streams but Icould not induce more fish to stay in test troughs with 12 C water versus troughs with 0-10 Cwater. Fish emigrated before abundance of drift insects declined in winter. Emigration occurred inspite of the relatively stable flows in both streams. Population density modified the basic migrationpattern by regulating the number and percentage of fish that emigrated and to a limited extenttime of emigration.Movements of non-smolt trout and salmon correlated best with the amount of cover provided bylarge rubble substrate. Subyearling trout emigrated from Big Springs Creek which contained norubble substrate but remained in the Lemhi River which did. In both field and laboratory testsmore fish remained in troughs or stream sections with large rubble substrate than in troughs orsections with gravel substrate. Trout and salmon in many Idaho streams enter the substrate whenstream temperatures declined to 4-6 C. A suitable substrate providing adequate intersticesappears necessary or the fish leave

Influence of fishway placement on fallback of adult salmon at the Bonneville Dam on the Columbia River

Using radiotelemetry, we observed and quantified the behavior of upstream migrating adult Chinook salmon Oncorhynchus tshawytscha and sockeye salmon O. nerka exiting the Bradford Island fishway at the Bonneville Dam on the Columbia River in 1997 and 1998. Nearly all of the fish that exited the fishway migrated upstream along the Bradford Island shoreline. Those fish that took the route nearest to the spillway were most likely to fall back over the spillway. From 14.5% to 21.3% of the fish tracked along the Bradford Island shore fell back over the spillway of the dam. The combined effects of spill, water temperature, and Secchi disk visibility were associated with route patterns and fallback behavior during each year. High spill was significantly and positively correlated with fallback behavior for Chinook salmon in 1998. Most of the fish we tracked that fell back reascended the fishway and migrated upstream (greater than or equal to95% in 1997; greater than or equal to70% in 1998). We suggest that modifying the configuration of this fishway\u27s exit would decrease the proportion of fish that fall back, perhaps reduce the risk of injury and fatigue, and improve the precision of counts of fish migrating upstrea

Movements of planted and wild trout in an Idaho river system

During 1959-61, 10,000 catchable-sized, hatchery-reared, rainbow trout were jawtaggedand released in the upper Salmon River, Idaho, and 2,247, 619, and 539 wild cutthroattrout, Dolly Varden, and rainbow trout, respectively, were caught on hook and line, tagged, andreleased in the Middle Fork of the Salmon River. More than 1,500 of the tagged, hatchery-reared,rainbow trout were recovered after being in the stream up to 1 year. Of those recovered the sameseason as released, more than 90 percent were taken within 2 miles of the release site. Ninetypercent of those recovered after having been in the river over winter were taken within 5 miles ofthe release site. Of 253 tagged wild cutthroat trout recovered, 64 were recovered in releaseareas, and 189 were recaptured one or more miles from their release sites (average for the latter,about 19 miles). Of 95 tagged wild Dolly Varden recovered, 27 were recovered in the releaseareas, and 68 were recovered one or more miles from release sites (average for the latter, 22.2miles). Twenty-seven tagged wild rainbow or steelhead trout were recovered; 14 in release areas, and 13 downstream from the release sites. Only 25.3 percent of the cutthroat trout and 28.4percent of the Dolly Varden were recovered within 1 mile of release sites

A review of literature related to movements of adult salmon and steelhead past dams and through reservoirs in the lower Snake River

A synthesis of published and unpublished literature on the upstream migration of adultsalmon and steelhead (Oncorhynchus mykiss), with particular reference to passage throughreservoirs and over dams, was prepared as part of an evaluation of fish passage through thelower Snake River. Most of the information on adult migrations in the Snake and Columbia riverswas collected on Chinook salmon (O. tshawytscha) and steelhead. The amount of flow,temperature and turbidity of the water, and partial barriers are natural factors that affect the rateof migration and survival of upstream migants. Human-caused alterations in flow, temperatures,and turbidities through the construction of dams and creation of reservoirs may be beneficial ordetrimental to migrants, depending on the amount of change from natural and the fishes\u27 ability toadapt. Dams and reservoirs placed in the migration path of adult salmon and steelhead usuallycreate unique passage problems because the structures and discharges differ and the stocks offish involved change from one section of the river to the next

Modelling submerged fluvial substrates with structure‐from‐motion photogrammetry

Natural sediment regimes of fluvial systems are variable and important to the biological and physical structures of rivers, yet watershed degradation has led to increased fine sediments entering and aggrading in rivers. As a result, quantifying substrate composition is important for targeting and monitoring restoration. Conventional methods for assessing substrate composition (e.g., pebble counts) can be time‐consuming and biased. We examined the use of the photogrammetric technique, structure‐from‐motion (SfM), as an alternative method by measuring streambed roughness. We expanded its application to submerged substrates in an artificial streambed to assess if roughness could predict pebble count substrate size percentiles across a range of manipulated levels of fine sediment aggradation. We then assessed the use of SfM in a free‐flowing river streambed. Results from the artificial streambed with coarse substrates (≤31% added fine sediment) revealed that repeated SfM models of the same streambed had a high degree of similarity (mean difference = 1 mm) and a strong relationship between SfM‐derived roughness and pebble counts (r2 \u3e .95). This relationship was weaker (r2 \u3c .66) and violated regression variance assumptions when substrates had up to 47% (55.7 kg) fines added, possibly due to SfM characterizing details not captured by pebble counts. In the natural streambed, there was a strong relationship between percentiles from the SfM model roughness and pebble count diameter (r2 = .96). SfM appears to be an efficient and appropriate alternative to direct substrate measurements across a broad range of streambed substrate compositions and thus a useful tool to model streambed morphology