Structural changes in gills of Lost River suckers exposed to elevated pH and ammonia concentrations

The Lost River sucker (Deltistes luxatus) is a federally listed, endangered fish that occurs primarily in Upper Klamath Lake-a hypereutrophic lake in southern Oregon, USA. A decline of the sucker population in the lake over the past few decades has been partly attributed to adverse water quality conditions, including elevated pH and ammonia concentrations that occur during summer cyanobacterial blooms. We quantitatively analyzed structural changes in gills of larval Lost River suckers after they were exposed to elevated pH and ammonia concentrations for 30 d. Exposure to pH as high as 10 caused no observed structural changes. However, lamellar thickness and O(2) diffusion distance increased significantly (P<0.05) at ammonia concentrations that did not significantly decrease survival, growth, whole-body ion concentrations, or swimming performance. Additionally, we qualitatively observed increases in the frequency of hyperplasic and hypertrophic mucous cells, tissue damage, epithelial lifting, and infiltration of white blood cells into paracellular lymphatic spaces at the highest sublethal ammonia concentration. These observed gill changes typically indicate compromised respiratory and ionoregulatory capacity, although such effects were not manifested in the assays we performed. Regardless, these structural gill changes appear to be a more sensitive indicator of exposure to elevated ammonia concentrations than are more traditional sublethal indices. Therefore, gill histopathology might be a relevant early-warning monitoring tool of the health of Lost River suckers in Upper Klamath Lake, and other species in similar eutrophic systems.     

Abundance,size, and feeding success of larval shortnose suckers and Lost River suckers from different habitats of the littoral zone of Upper Klamath Lake

We examined near-shore habitat use by larval shortnose and Lost River suckers in the lower Williamson River and Upper Klamath Lake of south-central Oregon. Emergent macrophytes Scirpus, Sparganium and Polygonum supported significantly more, larger, and better-fed larvae than submergent macrophytes, woody vegetation, or open water. Abundance, size, and gut fullness were similar for sucker larvae collected from different emergent macropytes. During the larval period, there was no evidence of density dependant effects or habitat shifts. Ranked catch per unit effort data indicated potential predators also were more likely to use emergent macrophytes, but ordination indicated larvae and potential predators were differentially distributed along a vegetation structure-water depth gradient with larvae in shallow vegetated areas. Between-habitat differences appeared to be due to larval sucker selection for, or better survival in, emergent macrophytes, rather than differential access or exclusion from other habitats. The importance of emergent macrophytes appears to be related to increased foraging success and reduced predation. Because larvae in emergent macrophytes have a size and gut fullness advantage, the amount of emergent habitat could affect early survival. However, interannual differences in recruitment to the adult population may or may not be dependent on larval dynamics. Our results suggest larval sucker access to emergent macrophytes may be necessary, but perhaps not sufficient, for promoting good year class formation.     

Development of a quantitative assay to measure expression of transforming growth factor β (TGF-β) in Lost River sucker (Deltistes luxatus) and shortnose sucker (Chasmistes brevirostris) and evaluation of potential pitfalls in use with field-collected samples

The Nature Conservancy is in the process of restoring the Williamson River Delta in an attempt to recreate important juvenile habitat for the endangered shortnose sucker Chasmistes brevirostris and the endangered Lost River sucker Deltistes luxatus. Measurement of TGF-β mRNA expression level was one of the indicators chosen to evaluate juvenile sucker health during the restoration process. TGF-β mRNA expression level has been correlated with disease status in several laboratory studies and TGF-β mRNA expression level has been used as a species-specific indicator of immune status in field-based fish health assessments. We describe here the identification of TGF-β and a possible splice variant from shortnose sucker and from Lost River sucker. The performance of a quantitative RT-PCR assay to measure TGF-β mRNA expression level was evaluated in field-collected spleen and kidney tissue samples. The quality of extracted RNA was higher in tissues harvested in September compared to July and higher in tissues harvested at lower temperature compared to higher temperature. In addition, the expression level of both TGF-β and 18S as assessed by qRT-PCR was higher in samples with higher quality RNA. TGF-β mRNA expression was lower in kidney than in spleen in both Lost River sucker and shortnose sucker.     

Estimates of daily mortality from a neascus trematode in age-0 shortnose sucker (Chasmistes brevirostris) and the potential impact of avian predation

Parasites may be an important component of early life mortality in fishes, but assigning part of total mortality to parasites is difficult. The Chapman-Robson mortality estimator is a robust and potentially valuable way to quantify the added mortality of parasites when age data are available. We used daily age data and the Chapman-Robson catch-curve procedure to estimate daily mortality for 15 years in juvenile age-0 shortnose suckers (Chasmistes brevirostris), and for 6 years, the daily mortality of fish with and without black spot infection, a trematode whose final host is a piscivorous bird. Infected fish always had higher mortality rates than uninfected fish, and for 3 years when those differences were significant, the added daily mortality for infected fish was 3.6–3.7 %. Based on the proportion infected each year, and for durations of 15–50 d, juvenile populations were 18.3–38.6 % lower than they would have been without black spot infections. There were no significant differences in growth between infected and uninfected fish in most years and little indication of a direct metabolic impact of infections. Thus, this added mortality, primarily in July and August, seemed unlikely to be an indirect result of infection and was most likely due to predation. The source of that predation is unknown but the parasite’s final hosts, piscivorous birds, seemed the most obvious candidate for this added mortality.     

Habitat use and population characteristics of potentially spawning shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820), blue sucker (Cycleptus elongatus (Lesueur, 1817), and associated species in the lower Wisconsin River, USA

The goal of this study was to compare the possible locations, timing, and characteristics of potentially spawning shovelnose sturgeon (Scaphirhynchus platorynchus), blue sucker (Cycleptus elongatus), and associated species during the spring of 2007–2015 in the 149‐km‐long lower Wisconsin River, Wisconsin, USA, a large, shallow, sand‐dominated Mississippi River tributary. A 5‐km index station of two pairs of rocky shoals surrounded by sandy areas was electrofished for shovelnose sturgeon and blue sucker in a standardized fashion a total of 40 times from late March through mid‐June, the presumed spawning period. On one date in 2008 and two dates in 2012, all rocky shoals and adjacent sandy areas in the lowermost 149 km of the river were also electrofished for both species. Shovelnose sturgeon and blue sucker appeared to spawn in the limited rocky areas of the river along with at least four other species: mooneye (Hiodon tergisus), quillback (Carpiodes cyprinus), smallmouth buffalo (Ictiobus bubalus), and shorthead redhorse (Moxostoma macrolepidotum), usually at depths of 0.8–2.0 m and surface velocities of 0.4–1.0 m/s. However, apparently spawning shovelnose sturgeon were found only on mid‐channel cobble and coarse gravel shoals within a single 7‐km segment that included the 5‐km index station, whereas apparently spawning blue suckers were encountered on these same shoals but also more widely throughout the river on eroding bluff shorelines of bedrock and boulder and on artificial boulder wing dams and shoreline rip‐rap. Both species showed evidence of homing to the same mid‐channel shoal complexes across years. Blue sucker tended to concentrate on the shoals earlier in the spring than shovelnose sturgeon, usually from late April through mid‐May at water temperatures of 8.0–15.5°C along with quillback and shorthead redhorse. In comparison, shovelnose sturgeon usually concentrated on the shoals from mid‐May through early June at 13.5–21.8°C along with mooneye and smallmouth buffalo. Based on recaptures of tagged fish, at least some shovelnose sturgeon and blue sucker returned to the shoals at one‐year intervals, although there was evidence that female blue sucker may have been more likely to return at two‐year intervals. Most shovelnose sturgeon could not be reliably sexed based on external characteristics. Spawning shovelnose sturgeon ranged from 487 to 788 mm fork length, 500–2400 g weight, and 5–20 years of age, whereas spawning blue sucker ranged from 495 to 822 mm total length, 900–5100 g weight, and 5–34 years of age, although age estimates were uncertain. Females were significantly larger than males for both species although there was overlap. Growth in length was negligible for tagged and recaptured presumably spawning shovelnose sturgeon and low (3.5 mm/y) for blue sucker, suggesting that nearly all growth may have occurred prior to maturity and that fish may have matured at a wide range of sizes.     

Recent,small beginnings: genetic analysis suggests Catostomus rimiculus (Klamath smallscale sucker) in the Smith River,California, are introduced

Identification of introduced species can be important to understanding ecological systems and meeting conservation and management goals, but the process can be surprisingly challenging. The Klamath smallscale sucker Catostomus rimiculus seems likely to be native to the Smith River because the drainage separates two basins believed to be within the fish's native range, the Rogue and Klamath rivers. Further, C. rimiculus is broadly distributed in the Smith River, and the indigenous Dee-ni’ People of the Smith River have a unique word for sucker. Nonetheless, a historical survey of fishes that described C. rimiculus from the Rogue and Klamath rivers did not include C. rimiculus among the fishes of the Smith River. To determine whether the genetic structure of the Smith River C. rimiculus reflects expectations for a native sucker population, the authors of this study examined variation in microsatellite and mitochondrial genetic markers from the Smith River and surrounding drainages. The genetic analyses revealed a pattern consistent with extreme founder effects in Smith River C. rimiculus, as would be expected from a single introduction of six or fewer effective individuals. The sharing of a high-frequency haplotype between the Smith River and Klamath River that is not detected in the Rogue River suggests the Klamath River as the likely source for the introduction. The findings highlight that local-scale introductions can be easily overlooked because the newly established populations can appear to be parts of contiguous natural distributions.     

Genetic structure of a disjunct peripheral population of mountain sucker <Emphasis Type="Italic">Pantosteus jordani</Emphasis> in the Black Hills,South Dakota,USA

A peripheral population of mountain sucker, Pantosteus jordani, located in the Black Hills of South Dakota, USA, represents the eastern-most range of the species and is completely isolated from other populations. Over the last 50 years, mountain sucker populations have declined in the Black Hills, and now only occur in 40 % of the historic local range, with densities decreasing by more than 84 %.We used microsatellite DNA markers to estimate genetic diversity and to assess population structure across five streams where mountain suckers persist. We evaluated results in the context of recent ecological surveys to inform decisions about mountain sucker conservation. Significant allele frequency differences existed among sample streams (Global F_ST = 0.041) but there was no evidence of isolation by distance. Regionally, genetic effective size, N_e, was estimated to be at least 338 breeding individuals, but N_e within streams was expected to be less. Despite almost complete demographic isolation and reduced population size, there appears to be little evidence of inbreeding, but genetic drift and local isolation due to fragmentation probably best explains genetic structure in this peripheral mountain sucker population. Recommended strategies for population enhancement include restoration of stream connectivity and habitat improvement. Moreover, repatriation and assisted movement (i.e., gene flow) of fishes should maximize genetic diversity in stream fragments in the Black Hills region.     

Age determination, bomb-radiocarbon validation and growth of Atlantic halibut (Hippoglossus hippoglossus) from the Northwest Atlantic

Atlantic halibut (Hippoglossus hippoglossus) is the largest and one of the most widely-ranging and commercially-valuable groundfish in the Atlantic Ocean. Although presumed to be long-lived, their age and growth has not been validated. Ages were estimated by counting growth increments from approximately 2400 thin-sectioned sagittal otoliths collected from the Scotian Shelf and southern Grand Banks off eastern Canada. The accuracy of age estimates made from otolith thin sections was validated using bomb-radiocarbon assays of 13 otolith cores whose year of formation ranged from 1949 to 1975, encompassing the timeframe of the global radiocarbon pulse. Known-age juvenile halibut from a culture facility were used to identify the approximate location of the first annulus. Growth rate for males and females was similar up to about 70 cm (~5 years), after which point male growth slowed, while female growth continued to an age of up to 38 years and a maximum observed size of 232 cm. Males grew to an observed maximum length of about 175 cm and a maximum age of 50 years. A comparison of age estimates for otoliths collected in a ‘historic’ time frame (1963 to 1974) with those from recent years (1997 to 2007) shows that growth rate has not changed appreciably between the two time periods. Small but significant growth differences were observed between the Scotian Shelf and southern Grand Banks for both sexes, while large differences in length at age were observed between halibut caught with longline compared to otter trawl due to differences in length-based gear selectivity. Age interpretations based on sectioned otoliths tended to be 10–15% different than those based on break and burn, although the age comparison was confounded by other variables and must be considered provisional. Atlantic halibut is a long-lived fish, living up to at least 50 years, an important consideration for the management of the fishery.     

Microsatellite markers for the June sucker (Chasmistes liorus mictus), Utah sucker (Catostomus ardens), and five other catostomid fishes of western North America

We developed and optimized five new microsatellite markers for the genetic management of the endangered June sucker. We report the cross‐amplification of these markers, and seven microsatellites previously developed for Klamath Basin suckers, in seven catostomid species of western North America. No linkage disequilibrium was detected between pairs of loci. Since most of these loci exhibited conserved priming sites, they may be useful for landscape‐scale studies of speciation and patterns of gene flow among multiple sucker lineages.     

Postglacial dispersal of longnose suckers, Catostomus catostomus, in the Mackenzie and Yukon Drainages

The role played by stream transfers and reversals in the postglacial dispersal of fish populations in the Yukon and Mackenzie River drainages of Canada was analysed using genetic and meristic data from longnose sucker (Catostomus catostomus Forrester) populations. The hypothesis the suckers dispersed from the Yukon River into the Mackenzie River via the Peel River was evaluated. Meristic data (gill rakers and lateral line scales) were uninformative for this analysis. Genetic affinity between the Yukon River and upper Peel River populations, and between Mackenzie and lower Peel River populations is suggested by transferrin allele frequencies. These affinities support the view that longnose suckers inhabiting the middle and upper regions of the Peel River are derived from Beringian and Mississippian ancestors, while suckers in the lower Peel are descended from Mississippian stock. Evidence for dispersal by way of the Eagle River was not found. Affinities of sucker populations in other river systems in the region are also described.     

Natural growth and diet of known‐age pallid sturgeon (Scaphirhynchus albus) early life stages in the upper Missouri River basin,Montana and North Dakota

Prior to anthropogenic modifications, the historic Missouri River provided ecological conditions suitable for reproduction, growth, and survival of pallid sturgeon Scaphirhynchus albus. However, little information is available to discern whether altered conditions in the contemporary Missouri River are suitable for feeding, growth and survival of endangered pallid sturgeon during the early life stages. In 2004 and 2007, nearly 600 000 pallid sturgeon free embryos and larvae were released in the upper Missouri River and survivors from these releases were collected during 2004–2010 to quantify natural growth rates and diet composition. Based on genetic analysis and known‐age at release (1–17 days post‐hatch, dph), age at capture (dph, years) could be determined for each survivor. Totals of 23 and 28 survivors from the 2004 and 2007 releases, respectively, were sampled. Growth of pallid sturgeon was rapid (1.91 mm day^?1) during the initial 13–48 dph, then slowed as fish approached maximum length (120–140 mm) towards the end of the first growing season. The diet of young‐of‐year pallid sturgeon was comprised of Diptera larvae, Diptera pupae, and Ephemeroptera nymphs. Growth of pallid sturgeon from ages 1–6 years was about 48.0 mm year^?1. This study provides the first assessment of natural growth and diet of young pallid sturgeon in the wild. Results depict pallid sturgeon growth trajectories that may be expected for naturally produced wild stocks under contemporary habitat conditions in the Missouri River and Yellowstone River.     

Assessing water quality suitability for shortnose sturgeon in the Roanoke River,North Carolina,USA with an in situ bioassay approach

The aim of this study was to determine the suitability of water quality in the Roanoke River of North Carolina for supporting shortnose sturgeon Acipenser brevirostrum, an endangered species in the United States. Fathead minnows Pimephales promelas were also evaluated alongside the sturgeon as a comparative species to measure potential differences in fish survival, growth, contaminant accumulation, and histopathology in a 28‐day in situ toxicity test. Captively propagated juvenile shortnose sturgeon (total length 49 ± 8 mm, mean ± SD) and fathead minnows (total length 39 ± 3 mm, mean ± SD) were used in the test and their outcomes were compared to simultaneous measurements of water quality (temperature, dissolved oxygen, pH, conductivity, total ammonia nitrogen, hardness, alkalinity, turbidity) and contaminant chemistry (metals, polycyclic aromatic hydrocarbons, organochlorine pesticides, current use pesticides, polychlorinated biphenyls) in river water and sediment. In the in situ test, there were three non‐riverine control sites and eight riverine test sites with three replicate cages (25 × 15‐cm (OD) clear plexiglass with 200‐μm tear‐resistant Nitex^® screen over each end) of 20 shortnose sturgeon per cage at each site. There was a single cage of fathead minnows also deployed at each site alongside the sturgeon cages. Survival of caged shortnose sturgeon among the riverine sites averaged 9% (range 1.7–25%) on day 22 of the 28‐day study, whereas sturgeon survival at the non‐riverine control sites averaged 64% (range 33–98%). In contrast to sturgeon, only one riverine deployed fathead minnow died (average 99.4% survival) over the 28‐day test period and none of the control fathead minnows died. Although chemical analyses revealed the presence of retene (7‐isopropyl‐1‐methylphenanthrene), a pulp and paper mill derived compound with known dioxin‐like toxicity to early life stages of fish, in significant quantities in the water (251–603 ng L^?1) and sediment (up to 5000 ng g^?1 dry weight) at several river sites, no correlation was detected of adverse water quality conditions or measured contaminant concentrations to the poor survival of sturgeon among riverine test sites. Histopathology analysis determined that the mortality of the river deployed shortnose sturgeon was likely due to liver and kidney lesions from an unknown agent(s). Given the poor survival of shortnose sturgeon (9%) and high survival of fathead minnows (99.4%) at the riverine test sites, our study indicates that conditions in the Roanoke River are incongruous with the needs of juvenile shortnose sturgeon and that fathead minnows, commonly used standard toxicity test organisms, do not adequately predict the sensitivity of shortnose sturgeon. Therefore, additional research is needed to help identify specific limiting factors and management actions for the enhancement and recovery of this imperiled fish species.     

Riverscape genetics identifies speckled dace (<Emphasis Type="Italic">Rhinichthys osculus</Emphasis>) cryptic diversity in the Klamath–Trinity Basin

Cataloging biodiversity is of great importance given that habitat destruction has dramatically increased extinction rates. While the presence of cryptic species poses challenges for biodiversity assessment, molecular analysis has proven useful in uncovering this hidden diversity. Using nuclear microsatellite markers and mitochondrial DNA we investigated the genetic structure of Klamath speckled dace (Rhinichthys osculus klamathensis), a subspecies endemic to the Klamath–Trinity basin. Analysis of 25 sample sites within the basin uncovered cryptic diversity including three distinct genetic groups: (1) a group that is widely distributed throughout the Klamath River mainstem and its tributaries, (2) a group distributed in the Trinity River, the largest tributary to the Klamath River, and (3) a group identified above a 10 m waterfall in Jenny Creek, a small tributary to the Klamath River. All groups were resolved as divergent in nuclear microsatellite analysis and exhibited levels of divergence in mitochondrial DNA that were comparable to those observed among recognized Rhinichthys species. No physical barriers currently separate the Klamath and Trinity groups and the precise mechanism that generated and maintains the groups as distinct despite contact and hybridization is unknown. The present study highlights the importance of incorporating molecular analysis into biodiversity research to uncover cryptic diversity. We recommend that future biodiversity inventories recognize three genetically distinct groups of speckled dace in the Klamath–Trinity Basin.     

Using spatial, seasonal, and diel drift patterns of larval Lost River suckers Deltistes luxatus (Cypriniformes: Catostomidae) and shortnose suckers Chasmistes brevirostris (Cypriniformes: Catostomidae) to help identify a site for a water withdrawal structure on the Williamson River, Oregon

A small irrigation diversion dam near Chiloquin, Oregon, was removed and replaced with a pump station to improve fish passage for Lost River suckers (Deltistes luxatus) and shortnose suckers (Chasmistes brevirostris) entering the Sprague River on their spawning migrations. During the developmental phase of the pump station, a need was identified to better understand the larval drift characteristics of these endangered catostomids in order to reduce entrainment into the irrigation system. The spatial, seasonal, and diel distribution of drifting larvae was measured during the 2004 spawning season at two proposed sites on the Williamson River where the pump station could be located. Larval drift for both species coincided with the irrigation season making them subject to entrainment into the irrigation system. Drift occurred almost exclusively at night with larvae entering the drift at sunset and exiting the drift at sunrise. Nighttime larval densities were concentrated near the surface and at midchannel at both sites. Densities were generally greater on the side of mid-channel with greater flow. During early morning sampling we detected a general shift in larval drift from surface to subsurface drift. We also observed an increase in larval densities towards the shore opposite from the proposed pump station at the upper site whereas larval densities remained high at midchannel at the lower site. During daytime sampling, the few larvae that were collected were distributed throughout the water column at both pump sites. This study found that larvae drifting during all time periods were generally distributed further across the cross section, deeper in the water column, and closer to where the proposed water withdrawal structure would be built at the downstream site when compared to the upstream site. Recommendations were provided to locate the withdrawal facility at the upstream site and operate it in a manner such that larval entrainment would likely be minimized.     

Infection by a black spot-causing species of Uvulifer and associated opercular alterations in fishes from a high-desert stream in Wyoming

Black spot is a common disease syndrome of freshwater fishes. This study provides information on the rank of density of the black spot agent and opercular bone alterations associated with at least one digenean, Uvulifer sp., infecting native and non-native catostomids and cyprinids of the Upper Colorado River Basin. We evaluated the density rank of pigmented metacercariae and associated alterations in the operculum of the bluehead sucker Catostomus discobolus, flannelmouth sucker C. latipinnis, white sucker C. commersoni, catostomid hybrids, roundtail chub Gila robusta, and creek chub Semotilus atromaculatus, sampled from Muddy Creek, Wyoming, USA in 2003 or 2004. All fish species contained individuals that exhibited gross signs of the black spot agent. Bluehead and flannelmouth suckers had 100% prevalence of infection. Although the other suckers and chubs contained encysted metacercariae in at least one individual, the presence of pigmented metacercariae was not apparent (i.e. based on gross observations) in many individuals. Catostomids had higher densities of metacercariae than cyprinids, as shown by frequency distributions of density ranks. Opercular holes (i.e. holes that completely penetrated the opercle and were in direct association with the pigment associated metacercariae) and pockets (depressions on the external surface of the opercle associated with metacercariae) were abundant among catostomids but rare among cyprinids.     

Comparison of electrofishing and trammel netting variability for sampling native fishes

The variability in size structure and relative abundance (CPUE; number of fish ≥200 mm total length, L_T, collected per hour of electrofishing or trammel netting) of three native Colorado River fishes, the endangered humpback chub Gila cypha, flannelmouth sucker Catostomus latipinnus and bluehead sucker Catostomus discobolus, collected from electrofishing and trammel nets was assessed to determine which gear was most appropriate to detect trends in relative abundance of adult fishes. Coefficient of variation (CV) of CPUE ranged from 210 to 566 for electrofishing and 128 to 575 for trammel netting, depending on season, diel period and species. Mean CV was lowest for trammel nets for humpback chub (P = 0·004) and tended to be lower for flannelmouth sucker (P = 0·12), regardless of season or diel period. Only one bluehead sucker >200 mm was collected with electrofishing. Electrofishing and trammel netting CPUE were not related for humpback chub (r = ?0·32, P = 0·43) or flannelmouth sucker (r = ?0·27, P = 0·46) in samples from the same date, location and hour set. Electrofishing collected a higher proportion of smaller (<200 mm L_T) humpback chub (P < 0·001), flannelmouth suckers (P < 0·001) and bluehead suckers (P < 0·001) than trammel netting, suggesting that conclusions derived from one gear may not be the same as from the other gear. This is probably because these gears fished different habitats, which are occupied by different fish life stages. To detect a 25% change in CPUE at a power of 0·9, at least 473 trammel net sets or 1918 electrofishing samples would be needed in this 8 km reach. This unattainable amount of samples for both trammel netting and electrofishing indicates that detecting annual changes in CPUE may not be practical and analysis of long‐term data or stock assessment models using mark‐recapture methods may be needed to assess trends in abundance of Colorado River native fishes, and probably other rare fishes as well.     

Effects of prey density on growth and survival of white sucker,Catostomus commersoni,and pumpkinseed,Lepomis gibbosus,larvae

Synopsis Growth and survival of white sucker and pumpkinseed larvae were examined in the laboratory in relation to prey density. Mortality of both species was greatest during the transition from endogenous to exogenous nutrition. Mortality prior to yolk absorption was substantial for white suckers and was not related to prey density whereas, pumpkinseed mortality during the same period was low. After yolk absorption, however, pumpkinseed suffered considerably higher mortality rates than white sucker larvae and, in both species, mortality and growth were directly related to prey density. The minimum prey density supporting 10% survival of pumpkinseed larvae was estimated at 0.16 plankters ml^-1 whereas, for white suckers it was 0.15 plankters ml^-1. Significant growth of both white sucker and pumpkinseed larvae, however, occurred only at prey densities higher than 0.25 plankters ml^-1. We suggest that since egg size and yolk reserve are greater in sucker larvae, suckers are better adapted to survive short term declines in prey abundance during the transition to exogenous feeding than pumpkinseed larvae. The reproductive strategies of each species seems to reflect this, with suckers spawning over a short time interval, but producing young with large yolk. Pumpkinseed, in contrast, spawn intermittently over an extended period but produce young with relatively small volk reserves.     

Growth chronologies of white sucker, Catostomuscommersoni, and lake trout, Salvelinusnamaycush: a comparison among lakes and between trophic levels

A growth chronology index was used to determine whether changes in ecosystem structure and function in lakes could be associated with fish growth histories. Growth chronologies were compared for white suckers, Catostomus commersoni, from Little Moose (oligotrophic), Oneida (eutrophic), and Cayuga (mesotrophic) lakes (New York) from opercular bone growth increments, and for lake trout, Salvelinus namaycush, from Little Moose Lake using otolith growth. The longevity of these species allowed the development of chronologies from 17 to 33 years in length using only contemporary collections. We used these chronologies to examine whether fish growth histories could be used as an index for ecosystem-scale changes. Specifically, we examined whether zebra mussel, Dreissena polymorpha, invasion in Oneida and Cayuga lakes in the early 1990s, and treatment of sewage effluent from dwellings around Little Moose Lake beginning during the late 1980s could be detected in white sucker and lake trout growth chronologies. White sucker growth in Oneida and Cayuga Lakes did not differ before and after zebra mussel invasions. Neither white sucker nor lake trout growth chronologies from Little Moose Lake reflect changes in growth expected with reduced productivity levels associated with improved sewage treatment. Growth chronologies of these two species did not detect the ecosystem-scale changes that occurred in the study lakes.     

Delineation of discrete population segments of shortnose sturgeon <Emphasis Type="Italic">Acipenser brevirostrum</Emphasis> based on mitochondrial DNA control region sequence analysis

Shortnose sturgeon Acipenser brevirostrum is federally listed as ‘‘an endangered species threatened with extinction’’ in the U.S. but its listing status is currently under review. As part of this process, the U.S. National Marine Fisheries Service will determine if shortnose sturgeon are divided into Distinct Population Segments (DPS) across its distribution. In this regard, we sought to determine if shortnose sturgeon occur in genetically “discrete population segments,” and if so, the boundaries of each. We used mitochondrial DNA (mtDNA) control region sequence analysis to assess the genetic discreteness of 14 of 19 river populations that were recommended as DPS in the 1998 Final Recovery Plan for Shortnose Sturgeon. Nine of the 14 proposed DPS proved significantly discrete (P < 0.05 after Bonferoni correction) from both of their bracketing populations, the exceptions being those in the Penobscot River, Chesapeake Bay, Cooper River, and Ogeechee River (our sample from the Cape Fear River was insufficient to statistically analyze). Haplotype frequencies in the newly “rediscovered” Penobscot River collection were almost identical to those in the proximal Kennebec River system. Genetic data in combination with tagging results suggest that shortnose sturgeon in the Penobscot River are probably migrants from the Kennebec. Likewise, shortnose sturgeon found today within the Chesapeake Bay appear to be migrants from the Delaware River. While haplotype frequencies in the remnant Santee River population in Lake Marion differed significantly from those in nearby Winyah Bay, they did not differ significantly from those in the Cooper River. This suggests that the Cooper River harbors descendants of the Santee River population that are unable to access their historical spawning locales. The Ogeechee River collection was not genetically distinct from that in the nearby Savannah River, suggesting that it may host descendants of hatchery-reared individuals of Savannah River ancestry. Our genetic results indicate that most, but not all, rivers with shortnose sturgeon host genetically discrete populations, constituting important information in the consideration of DPS designations. However, shortnose sturgeon migrations through coastal waters to proximal rivers and release of hatchery-reared fish may confound results from genetic studies such as ours and lead to the possible misidentification of discrete population segments.     

Assessment of juvenile coho salmon movement and behavior in relation to rehabilitation efforts in the Trinity River, California, using PIT tags and radiotelemetry

Coho salmon (Oncorhynchus kisutch) of the Southern Oregon/Northern California Coast (SONCC) Evolutionarily Significant Unit (ESU) is federally listed as a threatened species. The Trinity River Restoration Program (TRRP) is rehabilitating the Trinity River to restore coho salmon (coho) and other salmonid populations. In order to evaluate the program’s actions, several studies of movements and behavior of coho in the Trinity River were conducted from 2006 to 2009, including snorkel surveys and mark-recapture techniques based on Passive Integrated Transponder (PIT) tags, elastomer tags, and radio transmitters. Catch, recapture, and condition of natural sub-yearlings, along with site fidelity and emigration of hatchery-reared yearlings in rehabilitated and reference habitats, were studied. Location was important because coho were absent from the lower controlled and rehabilitated sites most of the time. However, rehabilitation did not have a significant effect on natural coho salmon at the site level. Apparent survival of radio-tagged, hatchery-reared yearling coho released downstream from Lewiston Dam was much lower in the first 10 km downstream from the release site than in other areas between Lewiston Dam and the Klamath River estuary. Estimated survival of yearling hatchery coho salmon per 100 km down to Blake’s Riffle was estimated at 64 % over the distance of the 239 km study area. Migration primarily occurred at night in the upper Trinity River; however, as yearlings moved through the lower Trinity River towards the Klamath River, estuary nocturnal migration became less. Apparent survival was generally lowest in areas upstream from the North Fork of the Trinity River.