Scott A. Bonar

Relationship between Fish Size and Upper Thermal Tolerance

Abstract Using critical thermal maximum (CTMax) tests, we examined the relationship between upper temperature tolerances and fish size (fry–adult or subadult lengths) of rainbow trout Oncorhynchus mykiss (41–200-mm TL), Apache trout O. gilae apache (40–220-mm TL), largemouth bass Micropterus salmoides (72–266-mm TL), Nile tilapia Oreochromis niloticus (35–206-mm TL), channel catfish Ictalurus punctatus (62–264xa0mm-TL), and Rio Grande cutthroat trout O. clarkii virginalis (36–181-mm TL). Rainbow trout and Apache trout were acclimated at 18°C, Rio Grande cutthroat trout were acclimated at 14°C, and Nile tilapia, largemouth bass, and channel catfish were acclimated at 25°C, all for 14 d. Critical thermal maximum temperatures were estimated and data were analyzed using simple linear regression. There was no significant relationship (P > 0.05) between thermal tolerance and length for Nile tilapia (P = 0.33), channel catfish (P = 0.55), rainbow trout (P = 0.76), or largemouth bass (P = 0.93) for the length range...

Effects of Flooding on Abundance of Native and Nonnative Fishes Downstream from a Small Impoundment

Abstract Flooding can benefit native fishes in southwestern streams by disproportionately displacing nonnative fishes. We examined how the presence of an upstream impoundment affected this relationship in lower Sonoita Creek, Arizona. Nonnative species not found in the reservoir decreased in abundance in lower Sonoita Creek after flooding. The catch and relative abundance of some nonnative species found in both the reservoir and the creek increased in lower Sonoita Creek after flooding. Movement of nonnative fishes out of the reservoir via the spillway during periods of high water probably contributes to the persistence and abundance of these species downstream. Both preventing nonnative fishes from escaping reservoirs and the release of flushing flows would aid conservation of native southwestern fishes downstream.

Upper Temperature Tolerance of Loach Minnow under Acute, Chronic, and Fluctuating Thermal Regimes

Abstract We used four methods to estimate the upper lethal temperature of loach minnow Rhinichthys cobitis: The lethal thermal method (LTM), chronic lethal method (CLM), acclimated chronic exposure (ACE) method with static temperatures, and ACE method with diel temperature fluctuations. The upper lethal temperature of this species ranged between 32°C and 38°C, depending on the method and exposure time; however, temperatures as low as 28°C resulted in slowed growth compared with the control groups. In LTM trials, we increased temperatures 0.3°C/min and death occurred at 36.8 ± 0.2°C (mean ± SE) for fish (37–49 mm total length) acclimated to 30°C and at 36.4 ± 0.07°C for fish acclimated to 25°C. In CLM trials, temperatures were increased more slowly (1°C/d), allowing fish to acclimate. Mean temperature at death was 33.4 ± 0.1°C for fish 25–35 mm and 32.9 ± 0.4°C for fish 45–50 mm. In the ACE experiment with static temperatures, we exposed fish for 30 d to four constant temperatures. No fish (20–40 mm) survi...

Effects of Introduced Fishes on Wild Juvenile Coho Salmon in Three Shallow Pacific Northwest Lakes

Abstract Declines in Pacific salmon Oncorhynchus spp. have been blamed on hydropower, overfishing, ocean conditions, and land use practices; however, less is known about the impacts of introduced fish. Most of the hundreds of lakes and ponds in the Pacific Northwest contain introduced fishes, and many of these water bodies are also important for salmon production, especially of coho salmon O. kisutch. Over 2 years, we examined the predation impacts of 10 common introduced fishes (brown bullhead Ameiurus nebulosus, black crappie Pomoxis nigromaculatus, bluegill Lepomis macrochirus, golden shiner Notemigonus crysoleucas, green sunfish L. cyanellus, largemouth bass Micropterus salmoides, pumpkinseed L. gibbosus, rainbow trout O. mykiss, warmouth L. gulosus, and yellow perch Perca flavescens) and two native fishes (cutthroat trout O. clarkii and prickly sculpin Cottus asper) on wild juvenile coho salmon in three shallow Pacific Northwest lakes, all located in different watersheds. Of these species, largemouth...

Growth, condition, diet, and consumption rates of northern pike in three Arizona reservoirs

Abstract Northern pike (Esox lucius L.) introductions are controversial in the western United States due to suspected impacts they might have on established sport fisheries and potential illegal introductions. Three Arizona reservoirs, Parker Canyon Lake, Upper Lake Mary and Long Lake were sampled to examine the diet, consumption dynamics, and growth of northern pike. Northern pike diets varied by season and reservoir. In Parker Canyon Lake, diets were dominated by rainbow trout in winter and spring and bluegill and green sunfish in the fall. In Long Lake the northern pike ate crayfish in spring and early summer and switched to young of the year common carp in summer and fall. Black crappie, golden shiners, and crayfish were the major prey in Upper Lake Mary during spring, but they switched to stocked rainbow trout in the fall. Northern pike growth was in the high range of growth reported throughout the United States. Estimated northern pike specific consumption rate (scr) of rainbow trout (g/g/d × 10−6) was greatest in Upper Lake Mary (scr = 329.1 ± 23.7 g/g/d × 10−6) where stocked fingerling (<120 mm total length [TL]) rainbow trout were most vulnerable to these predators, compared to larger (>280 mm TL) rainbow trout stocked in Long Lake (scr = 1.4 ± 0.1 g/g/d × 10−6) and Parker Canyon Lake (scr = 287.2 ± 15.1 g/g/d × 10−6) where catchable-sized rainbow trout were stocked. Managers should consider the cost-benefits of stocking fish >200 mm TL in lakes containing northern pike.

Survival of Apache Trout Eggs and Alevins under Static and Fluctuating Temperature Regimes

Abstract Increased stream temperatures due to global climate change, livestock grazing, removal of riparian cover, reduction of stream flow, and urbanization will have important implications for fishes worldwide. Information exists that describes the effects of elevated water temperatures on fish eggs, but less information is available on the effects of fluctuating water temperatures on egg survival, especially those of threatened and endangered species. We tested the posthatch survival of eyed eggs and alevins of Apache Trout Oncorhynchus gilae apache, a threatened salmonid, in static temperatures of 15, 18, 21, 24, and 27°C, and also in treatments with diel fluctuations of ±3°C around those temperatures. The LT50 for posthatch survival of Apache Trout eyed eggs and alevins was 17.1°C for static temperatures treatments and 17.9°C for the midpoints of ±3°C fluctuating temperature treatments. There was no significant difference in survival between static temperatures and fluctuating temperatures that share...

Upper Thermal Tolerances of Rio Grande Cutthroat Trout under Constant and Fluctuating Temperatures

Abstract The Rio Grande Cutthroat Trout Oncorhynchus clarkii virginalis is the southernmost subspecies of Cutthroat Trout, and as with the other subspecies, stream temperature regulates growth, reproductive success, distribution, and survival. An understanding of the upper thermal tolerance of Rio Grande Cutthroat Trout is important for developing water temperature standards and for assessing suitable habitat for reintroduction and management. Hatch success of Rio Grande Cutthroat Trout eggs was determined under static temperatures. The thermal requirements of fry and juveniles were also assessed under static and fluctuating temperature regimes using the acclimated chronic exposure method. Egg hatch success was 46–70% from 6°C to 16°C but declined significantly at 18°C and 20°C. Maximum growth of fry that were fed to satiation occurred at 15.3°C. The 30-d ultimate upper incipient lethal temperature (UUILT) was 22.6°C for fry and 21.7°C for juveniles. Survival during fluctuating temperature experiments was...

Captive breeding of endangered Yaqui topminnow and Yaqui chub for recovery purposes.

Abstract Yaqui topminnow Poeciliopsis occidentalis sonoriensis and Yaqui chub Gila purpurea, two federally endangered fishes from the Rio Yaqui basin (Arizona, USA, and Sonora, Mexico), were propagated by various methods. Propagation of Yaqui topminnow was attempted in aquaria and wading pools; the greatest number of offspring was produced in 556-L, plastic wading pools. We added substrate, artificial plants, and a vertical mesh barrier to create refuge for offspring. Fish were stocked when water was 19°C; after 1 month, when water temperatures exceeded 21°C, Yaqui topminnow started to produce young continuously. On average, 7.4 offspring/d were captured from four pools collectively. Yaqui chub were propagated in 189-L, glass aquaria. We manipulated photoperiod, diet, and substrate to induce spawning of Yaqui chub, but success was only achieved after the water was chilled to 17°C for 30 d and then adjusted to 21°C over 14 d. After the water was maintained at 21°C for 3 d, we covered the bottom of each aqu...

Captive Breeding of Endangered Mohave Tui Chub

Abstract The endangered Mohave tui chub Gila bicolor mohavensis, which occurs only in three populations in southern California, has not been previously spawned in captivity. Captive breeding of imperiled fishes can be important to conserve biodiversity and aid in native fish conservation efforts by reducing the collection of wild fish for translocations, providing individuals for experimental studies, and ensuring species survival. To spawn Mohave tui chub, we lowered water temperature to 10°C, held this temperature constant for 30 d, and then warmed the tank at a rate of 1°C per day to reach ambient air temperature (20–22°C). We used a photoperiod of 10 h light : 14 h dark and adjusted the photoperiod to 14 h light : 10 h dark when the tank reached 15°C. These photoperiod and water temperature regimes were designed to simulate Mojave Desert springtime conditions. Artificial plants were provided as spawning substrate. Three spawning events produced over 1,700 larval fish. Fish not subjected to this photop...

Comparing Efficiency of American Fisheries Society Standard Snorkeling Techniques to Environmental DNA Sampling Techniques

AbstractAnalysis of environmental DNA (eDNA) is an emerging technique used to detect aquatic species through water sampling and the extraction of biological material for amplification. Our study compared the efficacy of eDNA methodology to American Fisheries Society (AFS) standard snorkeling surveys with regard to detecting the presence of rare fish species. Knowing which method is more efficient at detecting target species will help managers to determine the best way to sample when both traditional sampling methods and eDNA sampling are available. Our study site included three Navajo Nation streams that contained Navajo Nation Genetic Subunit Bluehead Suckers Catostomus discobolus and Zuni Bluehead Suckers C. discobolus yarrowi. We first divided the entire wetted area of streams into consecutive 100-m reaches and then systematically selected 10 reaches/stream for snorkel and eDNA surveys. Surface water samples were taken in 10-m sections within each 100-m reach, while fish presence was noted via snorkeli...