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At least 1,261 records · Page 70Linked to original sources
USGS2024

Existing evidence on the effects of climate variability and climate change on ungulates in North America: A systematic map

Background Climate is an important driver of ungulate life-histories, population dynamics, and migratory behaviors. Climate conditions can directly impact ungulates via changes in the costs of thermoregulation and locomotion, or indirectly, via changes in habitat and forage availability, predation, and species interactions. Many studies have documented the effects of climate variability and climate change on North America’s ungulates, recording impacts to population demographics, physiology, foraging behavior, migratory patterns, and more. However, ungulate responses are not uniform and vary by species and geography. Here, we present a systematic map describing the abundance and distribution of evidence on the effects of climate variability and climate change on native ungulates in North America. Methods We searched for all evidence documenting or projecting how climate variability and climate change affect the 15 ungulate species native to the U.S., Canada, Mexico, and Greenland. We searched Web of Science, Scopus, and the websites of 62 wildlife management agencies to identify relevant academic and grey literature. We screened English-language documents for inclusion at both the title and abstract and full-text levels. Data from all articles that passed full-text review were extracted and coded in a database. We identified knowledge clusters and gaps related to the species, locations, climate variables, and outcome variables measured in the literature. Review findings We identified a total of 674 relevant articles published from 1947 until September 2020. Caribou ( Rangifer tarandus ), elk ( Cervus canadensis ), and white-tailed deer ( Odocoileus virginianus ) were the most frequently studied species. Geographically, more research has been conducted in the western U.S. and western Canada, though a notable concentration of research is also located in the Great Lakes region. Nearly 75% more articles examined the effects of precipitation on ungulates compared to temperature, with variables related to snow being the most commonly measured climate variables. Most studies examined the effects of climate on ungulate population demographics, habitat and forage, and physiology and condition, with far fewer examining the effects on disturbances, migratory behavior, and seasonal range and corridor habitat. Conclusions The effects of climate change, and its interactions with stressors such as land-use change, predation, and disease, is of increasing concern to wildlife managers. With its broad scope, this systematic map can help ungulate managers identify relevant climate impacts and prepare for future changes to the populations they manage. Decisions regarding population control measures, supplemental feeding, translocation, and the application of habitat treatments are just some of the management decisions that can be informed by an improved understanding of climate impacts. This systematic map also identified several gaps in the literature that would benefit from additional research, including climate effects on ungulate migratory patterns, on species that are relatively understudied yet known to be sensitive to changes in climate, such as pronghorn ( Antilocapra americana ) and mountain goats ( Oreamnos americanus ), and on ungulates in the eastern U.S. and Mexico.

Environmental Evidence↗
USGS2024

Movement behavior in a dominant ungulate underlies successful adjustment to a rapidly changing landscape following megafire

Background Movement plays a key role in allowing animal species to adapt to sudden environmental shifts. Anthropogenic climate and land use change have accelerated the frequency of some of these extreme disturbances, including megafire. These megafires dramatically alter ecosystems and challenge the capacity of several species to adjust to a rapidly changing landscape. Ungulates and their movement behaviors play a central role in the ecosystem functions of fire-prone ecosystems around the world. Previous work has shown behavioral plasticity is an important mechanism underlying whether large ungulates are able to adjust to recent changes in their environments effectively. Ungulates may respond to the immediate effects of megafire by adjusting their movement and behavior, but how these responses persist or change over time following disturbance is poorly understood. Methods We examined how an ecologically dominant ungulate with strong site fidelity, Columbian black-tailed deer ( Odocoileus hemionus columbianus ), adjusted its movement and behavior in response to an altered landscape following a megafire. To do so, we collected GPS data from 21 individual female deer over the course of a year to compare changes in home range size over time and used resource selection functions (RSFs) and hidden Markov movement models (HMMs) to assess changes in behavior and habitat selection. Results We found compelling evidence of adaptive capacity across individual deer in response to megafire. Deer avoided exposed and severely burned areas that lack forage and could be riskier for predation immediately following megafire, but they later altered these behaviors to select areas that burned at higher severities, potentially to take advantage of enhanced forage. Conclusions These results suggest that despite their high site fidelity, deer can navigate altered landscapes to track rapid shifts in encounter risk with predators and resource availability. This successful adjustment of movement and behavior following extreme disturbance could help facilitate resilience at broader ecological scales.

California↗
USGS2009

White phosphorus at Eagle River Flats, Alaska: A case history of waterfowl mortality

White phosphorus has a limited distribution in the environment because it only occurs where it has been directly used by humans. It is not transported aerially for any distance and, due to its density, has a limited ability to disperse through water. Therefore, it is not a contaminant of broad-scale concern. However, where it does occur, it can cause substantial mortality or critically injure populations of waterfowl. This chronic harm includes impaired liver and kidney functioning, decreased respiratory efficiency, increased susceptibility to predation, loss of body mass, general weakening and malaise, and curtailment of reproductive functioning. Lethal effects occur around 3---4 mg/kg or approximately 3-6 ingested particles; sublethal effects can occur with ingestion of as little as a single particle. The impact of P4 on waterfowl populations nesting around ERF has never been estimated. Even if direct mortality on ERF could be estimated accurately in ducks, the delayed toxicity of P4 in swans (and presumably other species that use small grit size) and the potential for swans to fly away after ingesting a lethal dose of P4 could greatly underestimate the overall mortality. Inhibition of laying, reduced fertility and hatchability, and teratogenesis in hens ingesting even a small amount of P4 could potentially have, an effect on populations greater than that exhibited by direct mortality. Predators such as bald eagles and gulls are also at risk due to the toxicity of pelletized, dissolved, and assimilated P4 in prey organisms. Although the U.S. Army stopped using P4 in wetlands in 1993 and remediation efforts have been underway since 1995, waterfowl mortality is expected to continue for several more years. Because Eagle River Flats is only one of several sites where P4 has been found in wetland conditions, further biological investigation is warranted at these other sites.

Book chapter↗
USGS2025

Not all who meander are lost: Migrating sea lamprey follow river thalwegs to facilitate safe and efficient passage upstream

Efficient navigation is crucial for the reproductive success of many migratory species, often driven by competing pressures to conserve energy and reduce predation risk. Little is known about how non-homing species achieve this balance. We show that sea lamprey ( Petromyzon marinus ), an ancient extant vertebrate, uses persistent patterns in hydro-geomorphology to quickly and efficiently navigate through complex ecosystems. Hydrodynamic flow models coupled with bathymetric mapping and fine-scale acoustic telemetry revealed movement paths that tracked thalweg scour channels, which are often the deepest and fastest-flowing sections of a river. These paths allow rapid and efficient upstream migration and suggest the existence of a bathymetric highway system. Near-substrate swimming along this path resulted in a median of 5.8% energy savings while also promoting improved safety from nocturnally active predators. We hypothesize sea lampreys use hydrostatic pressure-guided rheotaxis to achieve this navigation. It is likely this tactic relies on sensory information from the animal's primitive lateral line and perhaps the inner ear. Insights from this study can be used to redesign conservation practices to achieve improved control where the animal is invasive and improved fish passage within its native range.

Michigan↗
USGS2011

Comparative phylogeography of a coevolved community: Concerted population expansions in Joshua trees and four Yucca moths

Comparative phylogeographic studies have had mixed success in identifying common phylogeographic patterns among co-distributed organisms. Whereas some have found broadly similar patterns across a diverse array of taxa, others have found that the histories of different species are more idiosyncratic than congruent. The variation in the results of comparative phylogeographic studies could indicate that the extent to which sympatrically-distributed organisms share common biogeographic histories varies depending on the strength and specificity of ecological interactions between them. To test this hypothesis, we examined demographic and phylogeographic patterns in a highly specialized, coevolved community - Joshua trees (Yucca brevifolia) and their associated yucca moths. This tightly-integrated, mutually interdependent community is known to have experienced significant range changes at the end of the last glacial period, so there is a strong a priori expectation that these organisms will show common signatures of demographic and distributional changes over time. Using a database of >5000 GPS records for Joshua trees, and multi-locus DNA sequence data from the Joshua tree and four species of yucca moth, we combined paleaodistribution modeling with coalescent-based analyses of demographic and phylgeographic history. We extensively evaluated the power of our methods to infer past population size and distributional changes by evaluating the effect of different inference procedures on our results, comparing our palaeodistribution models to Pleistocene-aged packrat midden records, and simulating DNA sequence data under a variety of alternative demographic histories. Together the results indicate that these organisms have shared a common history of population expansion, and that these expansions were broadly coincident in time. However, contrary to our expectations, none of our analyses indicated significant range or population size reductions at the end of the last glacial period, and the inferred demographic changes substantially predate Holocene climate changes.

PLoS ONE↗
USGS2012

Ontogenetic and among-individual variation in foraging strategies of northeast Pacific white sharks based on stable isotope analysis

There is growing evidence for individuality in dietary preferences and foraging behaviors within populations of various species. This is especially important for apex predators, since they can potentially have wide dietary niches and a large impact on trophic dynamics within ecosystems. We evaluate the diet of an apex predator, the white shark ( Carcharodon carcharias ), by measuring the stable carbon and nitrogen isotope composition of vertebral growth bands to create lifetime records for 15 individuals from California. Isotopic variations in white shark diets can reflect within-region differences among prey (most importantly related to trophic level), as well as differences in baseline values among the regions in which sharks forage, and both prey and habitat preferences may shift with age. The magnitude of isotopic variation among sharks in our study (>5‰ for both elements) is too great to be explained solely by geographic differences, and so must reflect differences in prey choice that may vary with sex, size, age and location. Ontogenetic patterns in δ 15 N values vary considerably among individuals, and one third of the population fit each of these descriptions: 1) δ 15 N values increased throughout life, 2) δ 15 N values increased to a plateau at ~5 years of age, and 3) δ 15 N values remained roughly constant values throughout life. Isotopic data for the population span more than one trophic level, and we offer a qualitative evaluation of diet using shark-specific collagen discrimination factors estimated from a 3+ year captive feeding experiment (Δ 13 C shark-diet and Δ 15 N shark-diet equal 4.2‰ and 2.5‰, respectively). We assess the degree of individuality with a proportional similarity index that distinguishes specialists and generalists. The isotopic variance is partitioned among differences between-individual (48%), within-individuals (40%), and by calendar year of sub-adulthood (12%). Our data reveal substantial ontogenetic and individual dietary variation within a white shark population.

PLoS ONE↗
USGS2015

Influence of habitat and intrinsic characteristics on survival of neonatal pronghorn

Increased understanding of the influence of habitat (e.g., composition, patch size) and intrinsic (e.g., age, birth mass) factors on survival of neonatal pronghorn ( Antilocapra americana ) is a prerequisite to successful management programs, particularly as they relate to population dynamics and the role of population models in adaptive species management. Nevertheless, few studies have presented empirical data quantifying the influence of habitat variables on survival of neonatal pronghorn. During 2002–2005, we captured and radiocollared 116 neonates across two sites in western South Dakota. We documented 31 deaths during our study, of which coyote ( Canis latrans ) predation ( n = 15) was the leading cause of mortality. We used known fate analysis in Program MARK to investigate the influence of intrinsic and habitat variables on neonatal survival. We generated a priori models that we grouped into habitat and intrinsic effects. The highest-ranking model indicated that neonate mortality was best explained by site, percent grassland, and open water habitat; 90-day survival (0.80; 90% CI = 0.71–0.88) declined 23% when grassland and water increased from 80.1 to 92.3% and 0.36 to 0.40%, respectively, across 50% natal home ranges. Further, our results indicated that grassland patch size and shrub density were important predictors of neonate survival; neonate survival declined 17% when shrub density declined from 5.0 to 2.5 patches per 100 ha. Excluding the site covariates, intrinsic factors (i.e., sex, age, birth mass, year, parturition date) were not important predictors of survival of neonatal pronghorns. Further, neonatal survival may depend on available land cover and interspersion of habitats. We have demonstrated that maintaining minimum and maximum thresholds for habitat factors (e.g., percentages of grassland and open water patches, density of shrub patches) throughout natal home ranges will in turn, ensure relatively high (>0.50) neonatal survival rates, especially as they relate to coyote predation. Thus, landscape level variables (particularly percentages of open water, grassland habitats, and shrub density) should be incorporated into the development or implementation of pronghorn management plans across sagebrush steppe communities of the western Dakotas, and potentially elsewhere within the geographic range of pronghorn.

South Dakota↗
USGS2018

Prey fish returned to Forster’s tern colonies suggest spatial and temporal differences in fish composition and availability

Predators sample the available prey community when foraging; thus, changes in the environment may be reflected by changes in predator diet and foraging preferences. We examined Forster’s tern ( Sterna forsteri ) prey species over an 11-year period by sampling approximately 10,000 prey fish returned to 17 breeding colonies in south San Francisco Bay, California. We compared the species composition among repeatedly-sampled colonies (≥ 4 years), using both relative species abundance and the composition of total dry mass by species. Overall, the relative abundances of prey species at seven repeatedly-sampled tern colonies were more different than would be expected by chance, with the most notable differences in relative abundance observed between geographically distant colonies. In general, Mississippi silverside ( Menidia audens ) and topsmelt silverside ( Atherinops affinis ) comprised 42% of individuals and 40% of dry fish mass over the study period. Three-spined stickleback ( Gasterosteus aculeatus ) comprised the next largest proportion of prey species by individuals (19%) but not by dry mass (6%). Five additional species each contributed ≥ 4% of total individuals collected over the study period: yellowfin goby ( Acanthogobius flavimanus ; 10%), longjaw mudsucker ( Gillichthys mirabilis ; 8%), Pacific herring ( Clupea pallasii ; 6%), northern anchovy ( Engraulis mordax ; 4%), and staghorn sculpin ( Leptocottus armatus ; 4%). At some colonies, the relative abundance and biomass of specific prey species changed over time. In general, the abundance and dry mass of silversides increased, whereas the abundance and dry mass of three-spined stickleback and longjaw mudsucker decreased. As central place foragers, Forster’s terns are limited in the distance they forage; thus, changes in the prey species returned to Forster’s tern colonies suggest that the relative availability of some fish species in the environment has changed, possibly in response to alteration of the available habitat.

California↗
USGS2025

Neonicotinoid exposure causes behavioral impairment and delayed mortality of the federally threatened American burying beetle, Nicrophorus americanus

Among the most immediate drivers of American burying beetle ( Nicrophorus americanus Olivier) declines, nontarget toxicity to pesticides is poorly understood. Acute, episodic exposure to neonicotinoid insecticides at environmentally relevant concentrations is linked to negative impacts on beneficial terrestrial insect taxa. Beyond mortality, behavioral indicators of toxicity are often better suited to assess sublethal effects of residual concentrations in the environment. First, Nicrophorus spp. congeners were used to generate and identify a low-dose exposure rate (lethal dose 10%; LD10) from an acute, 24-hour exposure and the concentration-series was confirmed by LC–MS/MS. Next, we evaluated the effects of single and repeated low-dose (LD10 = 58.9 ng/beetle) imidacloprid exposure on N . americanus behavior (10 minutes post-dose) and mortality (10 days post-dose). Behavior parameters were analyzed using EthoVision-XT. Control N . americanus were significantly less mobile, demonstrating death-feigning, an anti-predator behavior. Single LD10 dosed N . americanus were hyperactive, traveling over 4 times farther (total distance; p = 0.03) and faster (mean velocity; p = 0.02) than controls. Single and repeated LD10 dosed N . americanus extended their wings without taking flight and flipped on their backs. All control N . americanus survived 10 days post-dose; single LD10 and repeated LD10 exhibited 30% and 50% mortality, respectively. A single LD10 exposure event was sufficient to significantly elicit greater movement and high predation risk behaviors, whereas repeated LD10 exposure did not worsen behavioral impairment but increased mortality over time. Collectively, generalized linear mixed effects models indicated that distance traveled, velocity, and extended wings were significant predictors of mortality. Recently reclassified, the federally threatened N . americanus may be at greater risk to insecticide exposure than previously thought and vulnerable to episodic, low-dose neonicotinoid exposure.

Nebraska, Oklahoma↗
USGS2022

Influence of anthropogenic subsidies on movements of common ravens

Anthropogenic subsidies can benefit populations of generalist predators such as common ravens (ravens; Corvus corax ), which in turn may depress populations of many types of species at lower-trophic levels, including desert tortoises (Gopherus agassizii ) or greater sage-grouse (Centrocercus urophasianus). Management of subsidized ravens often has targeted local breeding populations that are presumed to affect species of concern and ignored “urban” populations of ravens. However, little is known about how ravens move, especially in response to the presence of anthropogenic subsidies. Therefore, subsidized ravens from distant populations that are not managed may influence local prey. To better understand this issue, we deployed global positioning system – global system for mobile communications transmitters to track movements of 19 ravens from September to December 2020 relative to 2 land cover types that provide subsidies: developed areas and cultivated crops. On average, ravens moved 41.5 km (±30.5) per day, although daily movement distances ranged from 0.13– 206.1 km. Raven movement among cover types during the non-breeding season varied widely, with 100% of individuals each using land cover types that provide subsidy and other types at least once in the season. On 100% of days ravens used areas that did not provide subsidy, on 86.7% of days they used developed areas, and on 20.5% of days they used cultivated crops. Although on some days a raven would stay exclusively in areas that did not provide subsidy, there were no days in which a single raven ever stayed exclusively in developed or cultivated crops. Ravens moved shorter distances on days when they used subsidies more frequently. Further, time spent in developed areas and cultivated crops increased when ravens roosted closer to them, although this effect was greater for developed areas than for cultivated crops. Individual ravens were not associated exclusively with either of the subsidy-providing landscapes we considered, but instead all birds used both subsidized and other landscapes. Our research suggests that management of ravens during the non-breeding season and possibly during the breeding season, intended to reduce risk of predation on desert tortoises, will be most effective if conducted on a broad scale because of distances the birds travel and the lack of separation between putative “urban” and “natural” populations of ravens.

California↗
USGS2012

Time-specific patterns of nest survival for ducks and passerines breeding in North Dakota

In many bird species, survival can vary with the age of the nest, with the date a nest was initiated, or among years within the same nesting area. A literature review showed that patterns of survival vary in relation to nest age and date and are often contradictory. Inconsistencies could be a result of temporal variation in the environment or life-history differences among species. We examined patterns of nest survival in relation to nest age, date, and year for several duck and passerine species nesting at a single location in North Dakota during 1998–2003. We predicted that if environment shaped nest survival patterns, then temporal patterns in survival might be similar among three species of upland nesting ducks, and also among three species of grassland passerines nesting at the same site. We expected that survival patterns would differ between ducks and passerines because of relatively disparate life histories and differences in predators that prey on their nests. Nest survival was rarely constant among years, seasonally, or with age of the nest for species that we studied. As predicted, the pattern of survival was similar among duck species, driven mainly by differences in nest survival associated with nest initiation date. The pattern of survival also was similar among passerine species, but nest survival was more influenced by nest age than by date. Our findings suggest that some but not all variation in temporal patterns of nest survival in grassland birds reported in the literature can be explained on the basis of temporal environmental variation. Because patterns of survival were dissimilar among ducks and passerines, it is likely that mechanisms such as predation or brood parasitism have variable influences on productivity of ducks and passerines nesting in the same area. Our results indicate that biologists and managers should not assume that temporal environmental variations, especially factors that affect nest survival, act similarly on all grassland birds.

North Dakota↗
USGS2012

Adaptive breeding habitat selection: Is it for the birds?

The question of why animals choose particular habitats has important implications for understanding behavioral evolution and distribution of organisms in the wild and for delineating between habitats of different quality for conservation and management. Habitats chosen by animals can influence fitness outcomes via the costs (e.g., predation risk) and benefits (e.g., food availability) of habitat use. Habitat preferences should therefore be under selection to favor those that confer fitness advantages (Clark and Shutler 1999). Indeed, prevailing theory suggests that the habitat preferences of animals should be adaptive, such that fitness is higher in preferred habitats (Hildén 1965, Southwood 1977, Martin 1998). However, studies have often identified apparent mismatches between observed habitat preferences and fitness outcomes across a wide variety of taxa (Valladares and Lawton 1991, Mayhew 1997, Kolbe and Janzen 2002, Arlt and Pärt 2007, Mägi et al. 2009). Certainly, one limitation of studies may be that assessment of “fitness” is typically constrained to fitness surrogates such as nest success rather than lifetime reproductive success or classic Fisherian fitness (Endler 1986). Nevertheless, important habitat choices such as nest sites influence the probability that temporarily sedentary, dependent young are discovered by enemies such as predators and parasites. We therefore expect, on average, to see congruence between evolved habitat preferences and relevant components of fitness (e.g., nest success). Here, we (1) review the prevalence of apparent mismatches between avian breeding-habitat preferences and fitness outcomes using nest-site selection as a focus; (2) describe several potential mechanisms for such mismatches, including anthropogenic, methodological, and ecological–evolutionary; and (3) suggest a framework for understanding the contexts in which habitat preferences represent adaptive decisions, with a primary focus on ecological information theory. We largely focus on habitat selection as a behavioral process at the scale of individuals (e.g., Robertson and Hutto 2006), rather than at the scale of population-level patterns (Fretwell and Lucas 1970, Morris 2003, Johnson 2007). However, these two scales cannot be wholly divorced from one another, as we will discuss.

The Auk↗
USGS2008

Effects of environmental factors on incubation patterns of Greater Sage-Grouse

Birds in which only one sex incubates the eggs are often faced with a direct conflict between foraging to meet metabolic needs and incubation. Knowledge of environmental and ecological factors that shape life-history strategies of incubation is limited. We used continuous videography to make precise measurements of female Greater Sage-Grouse ( Centrocercus urophasianus ) incubation constancy (percentage of time spent at the nest in a 24-hour period) and recess duration. We used an information-theoretic approach to evaluate incubation patterns in relation to grouse age, timing of incubation, raven abundance, microhabitat, weather, and food availability. Overall, sage-grouse females showed an incubation constancy of 96% and a distinctive bimodal distribution of brief incubation recesses that peaked at sunset and 30 min prior to sunrise. Grouse typically returned to their nests during low light conditions. Incubation constancy of yearlings was lower than that of adults, particularly in the later stages of incubation. Yearlings spent more time away from nests later in the morning and earlier in the evening compared to adults. Video images revealed that nearly all predation events by Common Ravens ( Corvus corax ), the most frequently recorded predator at sage-grouse nests, took place during mornings and evenings after sunrise and before sunset, respectively. These were the times of the day when sage-grouse typically returned from incubation recesses. Recess duration was negatively related to raven abundance. We found evidence that incubation constancy increased with greater visual obstruction, usually from vegetation, of nests. An understanding of how incubation patterns relate to environmental factors will help managers make decisions aimed at increasing productivity through successful incubation.

The Condor↗
USGS2022

Habitat-specific foraging by striped bass (Morone saxatilis) in the San Francisco Estuary, California: Implications for tidal restoration

Non-native predatory fish strongly impact aquatic communities, and their impacts can be exacerbated by anthropogenic habitat alterations. Loss of natural habitat and restoration actions reversing habitat loss can modify relationships between non-native predators and prey. Predicting how these relationships will change is often difficult because insufficient information exists on the habitat-specific feeding ecology of non-native predators. To address this information gap, we examined diets of non-native Striped Bass ( Morone saxatilis ; 63 to 671 mm standard length; estimated age 1-5 yrs) in the San Francisco Estuary during spring and summer in three habitat types – marsh, shoal, and channel – with the marsh habitat type serving as a model for ongoing and future restoration. Based on a prey-specific index of relative importance, Striped Bass diets were dominated by macroinvertebrates in spring and summer (amphipods in spring, decapods and isopods in summer). In spring, diets were relatively consistent across habitats. In summer, marsh diets were dominated by sphaeromatid isopods and shoal/channel diets by idoteid amphipods and decapods. Striped Bass consumed a variety of native and non-native fishes, primarily Prickly Sculpin ( Cottus asper ) and Gobiidae. The highest importance of fish prey was in the marsh in spring (~40% prey weight), and fish prey comprised less than 25% prey weight in all other season/habitat combinations. Linear discriminant analyses suggested that marsh foraging was prevalent in Striped Bass collected in other habitats, mostly due to the predominance of marsh-associated invertebrates found in the stomachs of individual Striped Bass collected outside of the marsh. Striped Bass diets differ across habitats, with marsh foraging important to Striped Bass regardless of collection location. This information can be used to forecast the potential utilization of restored habitats by this non-native piscivore.

California↗
USGS1957

Recent changes in the deep-water fish populations of Lake Michigan

The deep-water fish fauna of Lake Michigan consisted of lake trout (Salvelinus namaycush), burbot (Lota lota maculosa), seven species of chubs or deep-water ciscoes (Leucichthys spp.), and the deep-water sculpin (Myoxocephalus quadricornis). Other species occupied the deep-water zone but were not typically part of the fauna. Lake trout, burbot, and a well established commercial fishery held the chub population in somewhat of a balance until the sea lamprey (Petromyzon marinus) destroyed the lake trout and burbot. Released from predation, one species of chub (L. hoyi) increased until its abundance in 1955 was 347 percent of that in 1930–1933. It is the smallest and most slowly growing of the chubs in the lake. Other chubs were reduced in abundance (1954–1955 abundance only 37 percent of that of 1930–1932) by an increased fishing pressure and by sea lamprey predation which shifted to them when lake trout and burbot became practically extinct. Selective destruction of the large chubs reduced the average length by 1.5 and 2.2 inches in the northern and southern portions of the lake, respectively, and practically eliminated two largest species (L. johannae and L. nigripinnis). Chubs over 10 inches long made up 72 percent of the catches in 1930–1932, but only 21.5 percent in 1954–1955.

Transactions of the American Fisheries Society↗
USGS1964

Status of the deepwater cisco population of Lake Michigan

The species and size composition and the abundance of the cisco (Leucichthys spp.) population of Lake Michigan have undergone drastic changes since the sea lamprey became established in the 1940's. The changes were measured by the catches of gill nets of identical specifications fished at the same seasons, depths, and locations in 1930-32, 1954-55, and 1960-61. The two largest ciscoes (johannae and nigripinnis), exploited heavily in a highly selective fishery from the midnineteenth century to the early 1900's, were only sparsely represented in the catch in the 1930's and were absent from catches of the comparison surveys in 1954-55 and 1960-61. The species of intermediate size (alpenae, artedi, kiyi, reighardi, and zenithicus) constituted about two-thirds of the cisco stocks of the deepwater zone in the 1930's but declined to 23.9 and 6.4 percent in the 1950's and 1960's, respectively. Major causes of change were the increased fishing pressure and sea lamprey predation that accompanied the disappearance of the lake trout. The small, slow-growing cisco (hoyi) - the primary food of lake trout - which was not fished intensively, and was too small to suffer greatly from sea lamprey predation, increased from 31.0 percent of the catch in the 1930's to 76.1 percent in the 1950's and 93.6 percent in the 1960's. Consequences of the extreme imbalance of the cisco population have been a reduction in mean size of all species, extension of the range of the very abundant hoyi (formerly most abundant in moderately shallow areas) to almost all depths and sections of the lake, and possibly introgressive hybridization among the various species. The primary change in the fishery has been a shift from gill nets to more extensive use of trawls which can take the now abundant smaller fish.

Transactions of the American Fisheries Society↗
USGS1980

Effects of recreational river traffic on nest defense by longear sunfish

An underwater camera system was designed to record the behavior of male nest-guarding longear sunfish (Lepomis megalotus) during periods of boating activity. Boats traveling at slow speeds near nests usually drove males from their nests, increasing the likelihood of egg predation. Boats moving at higher speeds or further from nests caused little or no displacement of males, but increased turbidity and possible success of predators. Location of a nest near cover increased the male's ability to protect his nest during repeated surface disturbances.

Transactions of the American Fisheries Society↗
USGS2000

Shifts in depth distributions of alewives, rainbow smelt, and age-2 lake trout in southern Lake Ontario following establishment of Dreissenids

In the mid-1990s, biologists conducting assessments of fish stocks in Lake Ontario reported finding alewives Alosa pseudoharengus , rainbow smelt Osmerus mordax , and juvenile lake trout Salvelinus namaycush at greater depths than in the mid-1980s. To determine if depth distributions shifted coincident with the early 1990s colonization of Lake Ontario by exotic Dreissena mussels, we calculated mean depth of capture for each of the three species during trawl surveys conducted annually during 1978–1997 and examined the means for significant deviations from established patterns. We found that mean capture depth of alewives, rainbow smelt, and age-2 lake trout shifted deeper during the build up of the dreissenid population in Lake Ontario but that timing of the shift varied among seasons and species. Depth shifts occurred first for rainbow smelt and age-2 lake trout in June 1991. In 1992, alewives shifted deeper in June followed by age-2 lake trout in July–August. Finally, in 1993 and 1994, the distribution of lake trout and alewives shifted in April–May. Reasons why the three fishes moved to deeper water are not clear, but changes in distribution were not linked to temperature. Mean temperature of capture after the depth shift was significantly lower than before the depth shift except for alewives in April–May. Movement of alewives, rainbow smelt, and age-2 lake trout to colder, deeper water has the potential to alter growth and reproduction schedules by exposing the fish to different temperature regimes and to alter the food chain, increasing predation on Mysis relicta in deep water and decreasing alewife predation on lake trout fry over nearshore spawning grounds in spring.

Transactions of the American Fisheries Society↗