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Research Interests

Trent's research focuses on population- and community-level interactions involving freshwater and marine fishes. The objective of his research program is to develop a greater understanding of the role of biotic and abiotic factors on the population ecology and biology of fishes and community structure of aquatic ecosystems in order to assist subsequent natural resource conservation and management efforts. Trent's current research is focused in three distinct areas: (1) ecology and biology of fish populations and communities in large river ecosystems; (2) population ecology and conservation of fishes in lake environments; and (3) impacts of human-induced perturbations on fish populations and aquatic communities. Examples of Trent's research in these particular areas are outlined below.

Ecology and Biology of Fish Populations and Communities in Large River Ecosystems

Large natural rivers are among the most biologically productive and diverse aquatic ecosystems. Fish communities are an integral component of these freshwater ecosystems as they perform vital fundamental services for maintaining ecosystem function and resilience and also support regionally and economically important fisheries. Because temperate freshwater ecosystems in North America are being depleted of species nearly as rapidly as tropical forests, it is imperative that we fully understand the fish populations that occupy these unique environments. Trent is currently working with state and federal management agencies to meet this particular need, focusing on whitefishes and Pacific salmonids in Alaska river systems.

Broad Whitefish.

Broad Whitefish

Little is known about broad whitefish in the Yukon River, a species that is highly migratory and is important for subsistence harvest. For this study, we have identified the following objectives: (1) examine the stock characteristics of broad whitefish in the middle Yukon River; (2) evaluate migration patterns and spawning run timing using radio telemetry; and (3) assess life history, particularly anadromous or amphidromous movement patterns, using otolith elemental analysis. Through this study, we will gain a better understanding of broad whitefish which will facilitate management efforts for this species in the Yukon River.

Bering Cisco.

Bering Cisco

Little is known about the life history of Bering cisco. However, Alaskan Native coastal villagers have historically relied heavily on this species for subsistence purposes. For this study, we will link traditional local knowledge of Bering cisco with scientific collections to better understand the life history of this species. Our study objectives include the following: (1) examine the stock characteristics and population dynamics of Bering cisco in the Yukon River Delta; and (2) assess life history, particularly anadromous or amphidromous movement patterns, using otolith elemental analysis. Through this study, we will gain a better understanding of Bering cisco which will facilitate management efforts for this species in the Yukon River.

Humpback Whitefish and Least Cisco

The Chatanika River supports personal-use spear fishery for humpback whitefish during their fall spawning migration. This system also supports a large spawning population of least cisco, which also are occassionally taken during the fall fishery. To assess the impact of the fishery on long-term population viability and to better understand the life history of these fishes, we have identified the following project objectives for these three species: (1) assess their stock characteristics and population dynamics; (2) evaluate the impact of varying levels of harvest-induced mortality; (3) characterize the stock attributes of harvest fish relative to the non-harvested population; (4) examine the summer-fall-winter movement patterns and spawning run timing; (5) characterize reproductive habitat attributes and spawning success; and (6) assess the reproductive biology of spawning fish. With the results that we gather during this study, we will be able to provide resource managers with critical information for better managing these populations of whitefish in the interior of Alaska.


Whitefishes support important subsistence fisheries in the Selawik and Kobuk river drainages (including the Selawik National Wildlife Refuge), with an annual harvest that exceeds all other fishes in the region. Given the importance of whitefish in the drainage, it is important to understand the life history, stock structure and dynamics, and habitat availability and use. Inconnu, a large, long-lived piscivorous whitefish, is one of the most important fishes harvested in the Selawik River drainage. Trends in spawning abundance, biological attributes, and spawning biology have been examined in the drainage. However, winter habitat use was not defined due to sampling constraints and telemetry restrictions. Because winter habitats can be limiting in Arctic waters, a better understanding of the distribution, movement patterns, and habitat requirements of inconnu is necessary in the Selawik and Kobuk river drainages. In particular, there is a need to understand the role of water depth, temperature, and salinity on habitat availability and use for this species. Recently, an application for the development of an ice road in this area has been approved; ice-road development requires water drawdowns to strengthen road integrity, which may negatively impact the availability and quality of winter habitat for inconnu. Climate-induced changes resulting from altered hydrological regimes may also impact habitat integrity during winter. Therefore, there is a need to better understand the winter habitat requirements, use, and availability for inconnu, an integral component of the subsistence harvest in the Selawik River drainage. To achieve this goal, the following objectives have been identified: (1) Identify the late fall and winter distribution of inconnu in the Selawik and Kobuk river drainages; and (2) assess the importance of water depth, temperature, and salinity as determinants of winter habitat use of inconnu in the Selawik and Kobuk river drainages.

Chinook Salmon

Chinook Salmon – Recruitment Modeling

Accurately forecasting spawner abundance and setting realistic escapement goals for Pacific salmonids is challenging given our poor understanding of environmental impacts on spawner-recruit relationships. We will examine the impact of environmental variability on abundance and survival estimates of Chinook salmon in the Kuskokwim River. Our specific study objectives are to: (1) describe potential environment-recruit relationships by incorporating environmental variables into a spawner-recruit model; and (2) identify deficiencies in environmental and life-history information needed for improvement of this model. These objectives will be met by using the Kuskokwim River Chinook salmon spawner-recruit model currently being developed through a project sponsored by the Arctic-Yukon-Kuskokwim Sustainable Salmon Initiative to assess the effects of various environmental conditions. The total suite of variables will be reduced through an exploratory phase, and formal selection procedures will be used for the remaining variables to identify the final best-fit model. By understanding the environment-recruit relationship and improving our ability to forecast abundance, this project will allow for the development of appropriate, science-based escapement goals and better strategies for the management of Chinook salmon in the Kuskokwim River drainage at sustainable levels.

Sockeye spawning.

Chinook Salmon – Growth Assessment

This project will validate the relationships between scale and otolith characteristics and juvenile growth trends and body size for both hatchery-reared and wild caught juvenile Chinook salmon. The results of this research will complement parallel studies on (1) using archived scale samples to develop a time series of freshwater growth in Yukon and Kuskokwim river Chinook salmon that will be used to assess the effects of freshwater growth on survival to the age of reproduction and (2) the effects of Ichthyophonous to provide insight into the importance of freshwater growth in determining inter-annual fluctuations in the returns of Arctic-Yukon-Kuskokwim (AYK) Chinook salmon stocks. The specific objective of this project is to validate the correlation between juvenile body size and growth and scale circulus and otolith daily growth ring width in Chinook salmon from the Y-K region in a controlled rearing experiment and from wild-caught fish.

Habitat Characterization and Enumeration of Juvenile Pacific Salmon

Ongoing climate change in Alaska has the potential alter the availability and quality of riverine habitats used by Pacific salmonids. As a result, there is a need to evaluate salmon escapement goals and consider the ecological needs of the watershed or the watersheds' potential carrying capacity. For this study, we will evaluate the quantity of salmon spawning and juvenile rearing habitat for a small coastal watershed (Kulukak River) within the Togiak National Wildlife Refuge in 2009 and 2010. The entire drainage will be photographed using an aircraft equipped with high resolution digital and forward looking infrared photography equipment. Ground control points and Ikonos satellite imagery will be used to georeference the produced images. A decision-based fusion technique will be used to produce a classified image which combines the best characteristics from the three image sources. Field habitat data will be used to develop a classification scheme based on the spectral image and the habitat's value as salmon adult spawning and juvenile rearing habitat. Adult salmon spawning locations and abundance will be determined using low-level helicopter surveys and GPS technology. Juvenile rearing habitat will be estimated to classify juvenile salmon rearing habitat types in selected stream reaches. An estimate of the quantity of total available salmon spawning and rearing habitat will be made for the entire watershed and estimates for varying water flow stage will be calculated using stream gage data. Juvenile rearing carrying capacity will be determined based on the estimate of available rearing habitat during periods of minimal winter flows levels. The number of spawning adult salmon required to produce the minimum number of juveniles of each species will be estimated using fecundity and survival estimates available from existing research literature and field sampling. Estimated minimum sustainable escapement will be compared to existing escapement goals and estimates for Chinook, coho and sockeye salmon.

Dolly Varden

Estimating growth or the physiological well-being of fish is a common component of fisheries research and management. Growth and condition estimates generated from traditional weight-length based approaches are generally less precise than laboratory based methods such as proximate analysis. However, the former method is often favored as it is non-lethal and less costly. Recent research suggests that bioelectrical impedance analysis (BIA) may produce growth and condition estimates rivaling those of proximate analysis largely without lengthy laboratory procedures. Because BIA is a relatively new technique to fisheries science, research regarding its applicability to different species and the development of standardized methods is warranted. A specific objective of this project is to determine the effectiveness of BIA to estimate proximate composition in Dolly Varden from the Barter Island area of the Ivishak River in the North Slope of Alaska using three different needle placement schemes: lateral, ventral, and combined. As a result, it is anticipated research and management efforts for Dolly Varden in Alaska will be improved by adding BIA to existing and future data collection activities.

Shovelnose Sturgeon

The collapse of sturgeon caviar (i.e., roe) fisheries in Europe and Asia, coupled with the imperiled status of many sturgeon species in North America, has raised concerns regarding the potential for overexploitation of shovelnose sturgeon in the Midwestern United States. Using data collected from exploited and unexploited populations of shovelnose sturgeon in the Wabash River, biological attributes (i.e., length, weight, and age) and population dynamics (i.e., growth, recruitment, and mortality) will be described and compared between these two stocks. These data, coupled with life history and population dynamics information from published studies, will be incorporated into an age-structured population model. Predictions without harvest will be compared to estimates of yield, size and age structure, reproductive potential, and recruitment derived from two minimum length limit scenarios (400 and 500 mm) simulated for the exploited shovelnose sturgeon stock in the Wabash River. Based on these results, recommendations will be provided to the Indiana and Illinois Departments of Natural Resources' Fisheries Division to ensure that a proactive approach is taken for shovelnose sturgeon management and conservation in the Wabash River.

Flathead Catfish.

Flathead Catfish

Flathead catfish have historically gathered little interest from recreational and commercial anglers in the northern United States, resulting in a lack of information regarding the population characteristics, movement patterns, habitat use, and home range of these stocks. The purpose of this study was to examine these characteristics of flathead catfish in the lower St. Joseph River, Michigan, to direct future management efforts and increase our knowledge of flathead catfish in the northern United States. To examine the biological attributes and stock dynamics of flathead catfish in this system, fish were collected from June through September 2002 and 2003 using stationary electrofishing. Fish density was estimated at 191 individuals/rkm (range, 92 to 309 fish/rkm) and annual survival ranged from 67 to 76%. Growth was greatest for fish less than two years of age and decreased among older age classes. The size and age structure of flathead catfish was dominated by fish less than 400-mm TL and four years of age, although individuals greater than 1,100-mm total length and up to age 17 were present in the population. Seasonal movement patterns, habitat use, and home range of flathead catfish were determined using ultrasonic telemetry from June 2002 through August 2003. Habitat use of flathead catfish was dominated by large woody debris and rip-rap at water depths less than 3 m during all seasons except winter, when fish utilized main-channel pool habitats associated with coarse substrates at a mean water depth of 4 m. Flow rates at fish locations were not significantly different among seasons. The seasonal movement distances and home range of flathead catfish were greatest during spring and fall months when fish transitioned between summer and winter habitats. These results suggested that the population characteristics of flathead catfish in this system are similar to those of other stocks throughout their geographic range, and that the rate of exploitation in this system is low. Further, seasonal differences exist in the movement patterns, habitat-use, and home range of flathead catfish, and that the availability of structure and main-channel pool habitats are important considerations in the management of this species.

Blue Sucker.

Blue Sucker

The blue sucker has historically been a species of special concern in Indiana and throughout much of its native distribution.  Species from the sucker family (Catastomidae), in general, are important for many reasons.  While not a sport fish, they provide an important forage base for game fishes.  In addition, several species are considered to be indicator species and are only present in systems with good water quality.  However, there remains more unknown about the blue sucker than is known.  For example, the age structure of populations of this species remains unclear because aging structures and procedures have not been standardized.  Further, there is little information available on population dynamics, stock structure, habitat use, or movement patterns in large riverine ecosystems.  For this research, we will examine these attributes of blue sucker populations in the upper Wabash River, Indiana. 


Little information exists on the stock characteristics and dynamics of longnose gar and shortnose gar. We examined the size and age structure, mortality, growth, and condition of both species from the Wabash River, Indiana-Illinois, from June through August 2006. Longnose gar ranged from 492 to 1,224 mm in total length (TL) and from 250 to 5,600 g in wet weight (WW), while shortnose gar ranged from 498 to 776 mm in TL and from 350 to 1,900 g in WW Longnose gar and shortnose gar ranged in age from 2 to16 and 2 to12 years, respectively. Total annual mortality ranged from 13 to 17% for longnose gar and from 25 to 29% for shortnose gar. Annual growth in length was most rapid through age 6 for longnose gar (range, 18 to 100 mm/yr) and age 4 for shortnose gar (range, 9 to 48 mm/yr). Variation in relative condition of longnose gar and shortnose gar was heterscedastic over the size range of fish collected, but there was no significant relationship between relative condition and total length. This information on gar stock structure is useful for fisheries biologists responsible for managing the Wabash River and maintaining a diverse and healthy fish assemblage in this system.


Lampreys have experienced wide-spread declines in population abundance on a global scale primarily as a result of anthropogenic disturbances.  However, the conservation of native lampreys has not been a fisheries management priority in North America.  Even though these ancestral fishes share many of the same habitats as salmonids in freshwater ecosystems, native lampreys as a group have received little management or research attention.  This paucity of information limits the development of management and conservation plans for lamprey species in Alaska, which is particularly problematic given ongoing changes and reductions in aquatic habitat availability due to climate change.  Lampreys support important subsistence and commercial fisheries in the lower Yukon River, with the impacts of these fisheries on the long-term sustainability of lamprey populations unknown.  Further, the role of lampreys in freshwater and marine ecosystems, both as predator and prey, remain largely unknown.  As a result, there is a clear need to develop a better understanding of lamprey species in Alaska.  For this research, we propose to determine the species assemblage of larval lampreys that utilize the Chena and Chatanika rivers within the Yukon River drainage located in the interior of Alaska.  Currently, it is believed that two lamprey species reside in these systems, the Arctic lamprey and the Alaskan brook lamprey.  However, a quantitative evaluation of these species has not taken place in interior of Alaska rivers.  To further increase our understanding of lampreys in the Chena and Chatanika rivers, we will also examine the distribution and abundance of each lamprey species.  In addition, we will also assess the biology, ecology, and life history of each larval lamprey species in each system by quantifying the size and age structure, trophic (i.e., feeding) ecology, and micro-scale habitat requirements in the Chena and Chatanika rivers.  The objectives of this study include the following: (1) determine the species composition of larval lampreys using morphological and meristic characteristics; (2) identify lamprey species using genetic baseline information from collections targeting adult, spawning-phase and larval lamprey aggregations; (3) examine the distribution, relative abundance, and density of larval lampreys; (4) assess the size and age structure, trophic ecology, and habitat requirements of larval lampreys; and (5) Examine temporal trends and variability in growth of larval lampreys.  With this information, our understanding of the distribution, abundance, and life history of larval lampreys in interior of Alaska rivers will be increased significantly, thereby allowing for the development of appropriate and science-based management and conservation decisions. 

Population Ecology and Conservation of Fishes in Lake Environments

Throughout the Great Lakes, many native fish species are imperiled due to habitat degradation, overexploitation, and/or the introduction of exotic organisms.  To further complicate matters, little is known about the population dynamics, stock structure, and habitat requirements for many of these fishes.  As a consequence, restoration of native species complexes and subsequent management efforts cannot proceed until more is known regarding basic population-level processes associated with these species. 

Lake Sturgeon

Characterization of Early Life History Stages

In the Green Bay basin, an insufficient understanding of lake sturgeon early life history and loss of important nursery habitats has been identified as a critical impediment to successful rehabilitation of this species.  Because each life stage has unique resource requirements, identifying and preserving critical microhabitats which provide sufficient prey resources and a suitable physico-chemical environment will be important determinants of successful recruitment.  This study examined linkages among population abundance and structure, distribution, and movement and usage patterns of larval, juvenile, and subadult lake sturgeon relative to the availability of physical habitat, chemical environmental factors, and benthic macroinvertebrate prey in the lower Peshtigo River and the immediate, nearshore waters of Green Bay.  Sampling results from this project will also be used to establish a quantitative sampling protocol for standardizing assessment surveys of early life stages of lake sturgeon in Great Lakes waters.  Age-0 lake sturgeon (mean fork length = 239 mm [range, 223 to 249 mm];  mean weight = 83 g [range, 74 to 90 g] were captured from September through October 2002 in the lower section of the Peshtigo River, Wisconsin, using wading surveys with dip nets, haul seines, backpack electrofishing, snorkeling, set lines, bottom trawls, gill nets, and fyke nets.  All fish were measured and weighed, and water quality parameters (i.e. water temperature, dissolved oxygen, pH, and conductivity), water depth, and river velocity were measured at each collection location.  Radio transmitters were attached to juvenile lake sturgeon larger than 75 g in weight, and were tracked at least twice each day.  At each capture site, a bottom dredge sample was also collected.  Dominant substrate types were visually estimated and a sample was preserved for later analysis of macroinvertebrate assemblage.  Quantitative analysis of habitat types within the Peshtigo River was conducted using dredge samples collected at three points perpendicular to river flow at 50-m intervals.  All juvenile lake sturgeon were captured over sand substrates, with particle size ranging from 1.99 to 0.12 mm in diameter, in depths less than 1.0-m, velocities greater than 0.66 m/s, and temperatures ranging from 14.5 to 23.8˚C.  Eight of thirteen juvenile lake sturgeon were collected over substrate containing macroinvertebrates.  Those with transmitters (N = 4) did not leave their capture site until water temperatures within the river declined to 12°C, when the fish moved downstream and into Green Bay within a two- to three-day period.  Catch-per-unit-effort (CPUE) was highest with the day seining (CPUE = 2.02 fish/h), followed by day wading surveys and night seining (CPUE = 0.86 and 0.80 fish/h, respectively).  No age-0 sturgeon were captured with bottom trawls, set lines, or fyke nets.  We recommend the use of day seining or day wading surveys in rivers similar to the Peshtigo River (i.e., shallow and low turbidity) for capturing age-0 lake sturgeon.

Assessment of Remnant Population Status

There is a fundamental and critical lack of knowledge regarding the size, status, and stock characteristics of most remnant populations of lake sturgeon currently inhabiting the Lake Michigan basin.  As a result, this lack of understanding has hindered efforts to rehabilitate lake sturgeon throughout the watershed, a commitment identified in existing rehabilitation and management plans for this species.   To address this need, a basin-wide study has been implemented that will involve cooperative research efforts among three natural resources management agencies (U.S. Fish and Wildlife Service, Wisconsin and Michigan Departments of Natural Resources) and four public universities (Purdue, Michigan State, and Michigan Technological Universities, and the University of Georgia) to comprehensively assess and characterize the most significant remnant lake sturgeon stocks that persist and spawn in tributaries of Lake Michigan and Green Bay.  Specifically, the Purdue University component of this study will examine population abundance and reproductive success of spawning adults, and describe spawner habitat use and availability of spawning and resident lake sturgeon in the St. Joseph and Kalamazoo Rivers, tributaries in southeastern Lake Michigan.

Potential for Habitat Rehabilitation in Lake Michigan Tributaries

Lake sturgeon Acipenser fulvescens were historically one of the most numerous fish species in the main basin of Lake Michigan and Green Bay.  Throughout the Great Lakes, lake sturgeon abundance declined dramatically during the 1800s, with populations reduced to remnant levels by the early 1900s.  Factors attributed to these declines include water pollution, physical habitat alterations, impediments to migration, and commercial overexploitation.  Although improvements in water quality and harvest reductions have allowed for some recovery, limited availability of staging, spawning, and nursery habitats in historically important tributaries remains an impediment to rehabilitation.  Many of the rivers that presently support or historically supported lake sturgeon populations have been altered by the construction of hydropower dams, changes in land-use practices, and other anthropogenic impacts.  As a result, the extent to which these factors continue to limit habitat availability, and consequently recovery efforts, remains unknown.  Enhancement or rehabilitation of degraded habitats, including the addition of proper substrates, creation of backwater areas, maintenance of adequate and natural stream flows, removal of barriers, and installation of fish-passage structures, will be necessary to restore lake sturgeon tributaries throughout the Lake Michigan watershed.  Assessment of past and present habitat availability is necessary, and replacement, enhancement, or renewed accessibility to habitats will be essential for successful restoration.  Therefore, habitat enhancement or rehabilitation must be a priority for tributaries of Green Bay in order to allow for the long-term sustainability and recovery of lake sturgeon.  Specific objectives of this research include: (1) assessment and quantification of lake sturgeon spawning, nursery, and adult habitats currently available and potentially available above existing barriers; (2) examination of spatial (i.e., longitudinal) relationships of lake sturgeon habitats below and above existing barriers; and (3) development of a decision tool for prioritizing Green Bay tributaries, identifying appropriate rehabilitation strategies, and directing future enhancement or restoration of important habitats or habitat features for lake sturgeon populations.

Effects of Mortality Sources on Population Viability

Lampricide applications in streams containing swim-up larvae and small juvenile lake sturgeon Acipenser fulvescens may negatively impact recruitment, rehabilitation, and sustained viability of this species in the Great Lakes.  As a result, a no observable effect (i.e., no mortality) treatment protocol has been implemented in streams supporting lake sturgeon.  However, the overall effectiveness of lampricide treatments may be diminished because greater numbers of parasitic-phase sea lampreys Petromyzon marinus may be produced from tributaries through inefficient or failed lampricide treatments.  We used a stage-structured, life-history model to examine the impacts of lampricide applications and sea lamprey parasitism on the population viability of lake sturgeon in the Laurentian Great Lakes basin.  Population abundance, the number of age-1 recruits, and reproductive potential of lake sturgeon exhibited relative percentage decreases with increasing mortality of age-0 juvenile fish (range, 0 to 100%) as a result of lampricide applications at four-year treatment intervals.  When larval sea lamprey mortality (range, 100 to 0%) following lampricide treatments was incrementally decreased, lake sturgeon mortality from increased sea lamprey parasitism for both the low and high mortality simulation scenarios resulted in relative percentage decreases in population abundance, the number of age-1 recruits, and reproductive potential from baseline conditions.  Incremental increases in sea lamprey-induced lake sturgeon mortality (range, 0 to 22%) as estimated from wounding rate data resulted in relative percentage decreases in population abundance, the number of age-1 recruits, and reproductive potential from baseline conditions.  Based on the results of our model simulations, mortality agents, such as sea lamprey parasitism, that influence subadult and adult lake sturgeon have a greater impact on the long-term population viability of this species than mortality factors that affect early life stages (i.e., lampricide applications).  As a result, we do not recommend that lampricide-application strategies for the control of larval sea lamprey populations in tributaries containing lake sturgeon continue to follow the no effect protocol in order to allow for the long-term rehabilitation and management for this species. 


Host-Size Selection and Lethality of Sea Lamprey on Lake Sturgeon

The use of the no observable effect (i.e., no mortality) lampricide treatment protocol to protect lake sturgeon Acipenser fulvescens populations might also increase production of sea lampreys Petromyzon marinus and, consequently, parasitism on lake sturgeon. However, no studies have examined the influence of sea lamprey parasitism on lake sturgeon survival.  Because previous model simulations indicate that sea lamprey attacks on adult lake sturgeon adversely affect long-term population viability, understanding is needed of the relations among wounding rate, wound type, and host survival to ensure that sea lamprey control strategies optimize lake sturgeon rehabilitation in the Great Lakes.  For this study, we will examine the following objectives: (1) compare the short- and long-term survival of three size groups of lake sturgeon after a single sea lamprey attack; (2) determine the rate of wound healing and scar retention of lake sturgeon hosts following sea lamprey attacks; (3) develop a classification system for the categorization of sea lamprey marks on lake sturgeon.  For this experiment, we will use three size classes of lake sturgeon (N = 25 fish per size class; 125 lake sturgeon for this study are currently at Purdue University): (1) small (400 to 599 mm fork length); (2) medium (600 to 799 mm); and (3) large (800 to 999 mm). Each lake sturgeon will be weighed, individually placed in a holding tank with a single, pre-weighed sea lamprey, and the time and location of attachment will be recorded for each pairing. Following detachment, both fish will be re-weighed and the wound type on each lake sturgeon will be classified according to standard criteria. Surviving lake sturgeon will be transferred to recovery tanks at the same temperature as the test tanks to determine delayed mortality during a 14- to 21-d recovery period. Any mortality during this period will be further classified into fish that died from sea lamprey attack or secondary infection. Survivors will be held an additional 60+ days at 10oC to determine the rate of wound healing and scar retention. The number of live and dead lake sturgeon will be examined by size class, and location and duration of sea lamprey attachment. Dead lake sturgeon will also be assessed based on the source and timing of mortality. Sea lamprey data will be examined by weight gain, and location and duration of attachment.

Lake Sturgeon

Mortality and Recruitment Mechanisms of Lake Sturgeon Early Life Stages

Identification of the factors that regulate fish populations has been a major goal of fisheries research because variable survival among early life stages determines overall viability of the species.  Because each life stage has unique requirements, identification and quantification of egg, larval, and juvenile losses is required to understand the criteria for successful survival and recruitment to subsequent life stages.  However, the extent to which mortality mechanisms impact lake sturgeon early life stages and limit recovery efforts remain unknown.  For rehabilitation to be successful, an understanding of the relationship among mortality and recruitment factors acting on lake sturgeon populations is necessary.  For this study, we will examine the following objectives: (1) estimate egg density, production of larvae during the drift period, and the abundance of age-0 juvenile lake sturgeon prior to river emigration in the lower Peshtigo River; (2) identify and quantify the mechanisms of mortality during each lake sturgeon life stage; (3) determine if predation on age-0 life stages is dependent upon lake sturgeon body size; and (4) assess how mortality sources influence recruitment dynamics, year-class strength, and population viability of lake sturgeon.  Lake sturgeon egg density will be estimated using substrate mats (May 2006 and 2007).  To examine predation on eggs and yolk-sac larvae, we will use in-situ exclosures constructed of plastic boxes filled with coarse substrates.  To estimate relative abundance and production of lake sturgeon swim-up larvae, fish will be collected using drift nets set below the Peshtigo River spawning area (May and June 2006 and 2007).  Relative and absolute abundance of juveniles will be estimated from fish collected and marked or tagged following wading capture surveys (June - November 2006 and 2007).  Fish predators will be collected using gill nets and electrofishing (May - November 2006 and 2007).  This research will directly increase our understanding of the mechanisms directing recruitment dynamics of lake sturgeon in the Lake Michigan basin and help to identify mortality sources that may negatively impact ongoing and future recovery efforts for this species throughout the Great Lakes basin.

Lake Herring

Lake Herring

Since declining in the 1960s, lake herring Coregonus artedi populations have remained suppressed throughout Lake Superior, and only one strong year class (1998) has occurred over the past decade.  During this time, lake herring populations in Lake Superior have also exhibited high recruitment variability.  To improve our understanding of the mechanisms which influence year-class strength, we conducted a 225-d laboratory experiment to evaluate the effects of body size, condition, energy stores, and food ration on overwinter survival of age-0 lake herring.  Small (total-length range, 60 to 85 mm) and large (total-length range, 85 to 110 mm) fish were maintained under thermal and photoperiod regimes that mimicked those in Lake Superior from October through May. Fish in each size class were maintained at two feeding treatments: Artemia ad libitum or no food.  Mortality of large lake herring (fed, 3.8%; starved, 20.1%) was significantly less than those of small fish (fed, 11.7%; starved, 32.0%) within feeding treatments. Body condition and crude lipid content declined over the experiment for all fish; however, index values were significantly greater for large and small fed fish than large and small starved individuals. Final crude protein and gross energy content was also significantly greater in large fed lake herring (17.6% and 1,966 cal/g, respectively) followed by small fed (17.1% and 1,497 cal/g, respectively), large starved (15.4% and 1,125 cal/g, respectively), and small starved (13.2% and 799 cal/g, respectively) fish.  Individuals that survived the winter period had significantly greater energy stores than fish that died during the study. These results suggest that depletion of energy stores contributes to greater winter mortality of small fish, and may partially explain the recruitment variability that has been observed for lake herring in Lake Superior.

Lake Whitefish

Lake Whitefish

Lake whitefish Coregonus clupeaformis historically supported an important commercial fishery in the Great Lakes. In Lake Michigan, this species formed the basis of the commercial fishery since the 1970s, with peak harvest occurring in the early 1990s. However, annual yield, length- and weight-at-age, and body condition of lake whitefish have all declined dramatically since this time. These declines have been largely attributed to the invasion of zebra mussel Dreissena polymorpha, which appears to have contributed to the lake-wide decrease and disappearance of the benthic amphipod Diporeia, the primary prey of whitefish. Egg lipid and caloric content, size-at-hatching, and subsequent growth and survival are known to be positively related for lake whitefish. Therefore, declines in Diporeia, a prey source with a higher energy content and essential omega-3 fatty-acid (FA) concentrations than many other prey types, may adversely impact recruitment because females are likely to produce smaller eggs with lower quality. Consequently, lake whitefish will hatch at smaller sizes, predisposed to essential fatty-acid deficiency, which may translate to lower first-year survival due to limited feeding opportunities and greater predation mortality. Because fall body size is strongly coupled to summer growth, smaller age-0 fish typically accumulate less energy reserves prior to the end of the growing season, more rapidly exhaust these stores over the winter, and are more likely to suffer mortality during this period. This research will contribute to our understanding of trophic food-web impacts on recruitment dynamics of lake whitefish in Lake Michigan and provide critical information necessary for improving fishery yield forecasts. The primary objective of this project is to determine the role and relationship of body size, condition, and proximate composition (i.e., lipid, protein, carbohydrate, caloric, water, and ash content; fatty-acid composition) on the first-year growth and survival of juvenile whitefish through the first winter of life. An additional objective of this study will be to determine the proximate composition of juvenile whitefish prey. Given the nature and magnitude of the alterations in trophic food-web structure that have taken place in Lake Michigan following the invasion of zebra mussels and the decline in Diporeia, it is imperative that we develop a better understanding of how these changes are affecting the dynamics and health of fish populations, particularly those with significant economic and ecological importance as whitefish. This research will directly contribute to our understanding of the mechanisms directing recruitment dynamics of whitefish in Lake Michigan and help to identify indices of fish health that federal, state, and tribal natural resource management agencies can use to monitor first-year growth, survival, and natural mortality of juvenile whitefish.


The Copper River drainage supports numerous burbot populations that have provided for up to 30% of the reported statewide harvest for this species, which occurs primarily within the larger lakes.   Due to concerns of over-harvests in the mid 1980s, a stock assessment program was initiated by the Alaska Department of Fish and Game (ADFG) aimed at monitoring population sizes to ensure acceptable levels of exploitation.  In 2007, a cooperative study between Wrangell St. Elias National Park and Preser, the Office of Subsistence Management, and ADFG was initiated to estimate population sizes for burbot within Tanada and Copper lakes, for which there were no previous studies.  Burbot abundances are typically estimated using mark-recapture experiments.  Throughout the 1990s, ADFG used multi-year sampling and the Jolly-Seber model to estimate burbot abundances. These studies typically took a minimum of five years to gain maximum precision for the estimates. Recently, as with Tanada and Copper lakes, within season two-event mark-recapture experiments have been used to estimate burbot abundances. This technique is typically far less expensive than the multi-year Jolly-Seber method and under most conditions, renders a more precise abundance estimate which is not lagged a year like the Jolly-Seber method.  This project proposes to describe the vertical movements of burbot within Tanada and Copper lakes relative to time, depth, and temperature to better understand their life history and independently assess the assumptions of the mark-recapture experiment.

Northern Pike

Historically, the Tolovana River drainage and Minto Flats northern pike population in Alaska has supported a major proportion of the recreational fishing effort for northern pike in Lower Tanana Management Area.  The Minto Flats northern pike population is jointly managed under both sport and subsistence fishery management plans, which stipulate that the total exploitation rate in both fisheries combined cannot exceed 20 percent annually.  Harvest of northern pike is estimated annually in the subsistence fishery through permit holder reporting requirements and in the recreational fishery through a statewide mail-out harvest survey.  Abundance of catchable sized fish (> 450 mm FL) is estimated periodically (every 3 to 5 years) for a study area centered around Minto Lakes using mark-recapture methods.  Abundance estimates obtained from the study area serve as an "index" for population size for the entire Minto Flats wetland complex.  Any improvements to the design or analysis of the mark-recapture experiments will provide ADFG better population data for managing these important sport and subsistence fisheries.  A detailed examination of movements and activity of radio-tagged northern pike present in the Minto Flats study area during a mark-recapture experiment has yet to be conducted.  Such information could provide valuable insights regarding the probability of capture of individuals present during the experiment, provide a means to test the assumption of population closure, and could help direct more efficient sampling efforts.

Impacts of Human-Induced Perturbations on Fish Populations and Aquatic Communities

While the ecology and management of riparian zones has been well studied in the American southwest and Pacific Coast of North America, the same cannot be said of the eastern corn-belt region or boreal mixed-wood forests.  Although unharvested forest strips are often left along permanent streams to protect riparian habitat, the width of these reserves is typically inadequate to mitigate the effects of surrounding land-use practices.  Because riparian zones provide important habitat features for aquatic organisms, understanding how human encroachment of riparian areas influences the structure and function of aquatic communities is an important undertaking.  Further, developing an understanding of how the intentional introductions of non-native fishes can disrupt energy flow, trophic dynamics, and biotic interactions is also critical for understanding aquatic community structure and function.  Finally, understanding indirect and direct anthropogenic impacts on aquatic organisms, particular their population structure and function, is important for the development of conservation management strategies.  Trent's current research projects include: (1) assessing the population structure of eastern hellbenders in the Blue River, Indiana; and (2) effectiveness of deepwater release devices in reducing mortality of deepwater rockfish due to angling-induced barotrauma.

Agriculture-Dominated Streams of the Upper Wabash River

Using the National Water-Quality Assessment (NAQWA) developed by the U.S. Geological Survey, we conducted an examination of the physical (i.e., in-stream and riparian habitat, channel conditions, and hydrology), chemical (i.e., dissolved gases, ions, and nutrients), and ecological (i.e., fish, benthic macroinvertebrates, and algal communities) components as part of an integrated assessment to determine the status and trends in water quality of wadeable lotic systems within the upper Wabash River basin.  By developing an understanding of the major natural and anthropogenic factors that affect observed water-quality conditions and trends in this drainage, we will be able to provide private landowners and natural resource planning agencies with the information necessary to not only effectively manage aquatic ecosystems, but to develop and implement land-use strategies that are consistent with sound stewardship practices across terrestrial-aquatic boundaries.  This implementation framework will be enhanced by the development of an empirical relationship among habitat availability, water quality, and biological condition at regional and local scales that will allow for the development and use of an integrated ecosystem model to forecast changes in environmental conditions given alternative approaches for maintenance or rehabilitation efforts within the upper Wabash River basin.  Specific study objectives of this project include: (1) development of relationships among fish community structure, benthic macroinvertebrate community structure, algal community structure, physical habitat complexity, and water chemistry under varying environmental gradients; (2) examination of local natural and human land-use patterns and practices on the relationship between biological, physical, and chemical components of the aquatic ecosystem; (3) determination of the influence of regional and segment characteristics and dynamics of the basin on the relationship between biological, physical, and chemical components of the aquatic ecosystem; and (4) development of a framework for bioassessment that integrates metric data collected on biological, physical, and chemical components in upper Wabash River tributaries.

Half-Log Introductions into Agriculture-Dominated Streams

One of the greatest factors limiting fish productivity in stable, low-gradient, headwater streams is the amount of in-stream cover provided by course woody debris.  In order to compensate for this lack of structure, managers often add woody materials into the stream channel to increase cover complexity and overall productivity.  In addition to providing valuable habitat features, the placement of woody debris within streams can create pools, increase the retention of sediment and organic materials, stabilize the physical streambed, and create unique channel morphologies.  A design typically used by managers in small stream systems is half-log habitat enhancement structures.  Half-logs attract juvenile and adult fish by providing overhead cover where it did not previously exist or may have existed but has been since removed. These structures can also provide an additional forage site for fish through the macroinvertebrates and periphyton that colonize them.  Half-logs (N = 108) were added to headwater streams (N = 9) of the upper Wabash River basin, Indiana, in July 2003.  Each stream contained three paired control and treatment reaches.  Treatment sites had added to them four half-logs each, while control sites were spaced a minimum of 100 m upstream and left unaltered.  Study sites (25 m in length) were sampled once monthly through October 2003 and April through September 2004 using backpack electrofishing employing a three-pass depletion method.  After manipulation, fish abundance was higher at treatment than control sites (mean = 652 and 493 fish, respectively).  Similarly, both catch-per-unit-effort (fish/hr) and biomass (g/m²) were higher at treatment sites (mean = 194.65 and 177.96; 4.25 and 2.85, respectively).  Species richness and the relative abundance of structure oriented species were also higher in manipulated reaches (mean = 7.11 and 6.81; 24.06 % and 21.94 %, respectively).  Our results suggest that sites which received half-log additions supported higher fish abundance, biomass, and diversity.  It is important to note the adverse effects of a 50-year flooding event that occurred during the week following half-log installation, which could have affected the significance of our first year results.  These structures are being evaluated as a possible management tool for use in these systems where a lack of naturally occurring large woody debris is a limiting factor for fish and macroinvertebrate production. 

Boreal Forest Streams in Northern Ontario

The use of riparian buffer zones to mitigate the effects of logging on fish populations in temperate forest streams is well understood and documented.  The characteristics and dynamics of large woody debris (LWD), an important component of fish habitat and a strong influence on stream morphology, is also poorly understood in these systems.  Many studies have demonstrated that large woody debris in forest streams can play a critical role in organic matter retention, channel configuration, pool formation, and habitat creation.  However, there have been no studies to date that have examined LWD dynamics in North American boreal forests.  In this study, the characteristics and importance of LWD were assessed in 16 boreal shield streams of mixedwood forests in northern Ontario. Three of the streams were in or near recent clearcuts, with the remainder in areas that have not been recently disturbed. The inputs, characteristics, and function of LWD in these boreal streams differed considerably from the typical patterns of LWD dynamics in other regions and forest types. The average frequency (11.6 · 100m-1), mean diameter (16.7 cm), and mean volume (1.1 m3 · 100m-1) of LWD in these streams were substantially less than reported from other areas. These smaller sizes reflect the typical forest stand characteristics in these boreal mixedwoods, where tree age and size distributions are truncated by natural disturbance. Averaged across sites, the primary input sources were natural mortality (24%) and windthrow (15%), although windthrow was shown to be highly variable and mostly associated with nearby clearcut logging. At the three sites near clearcuts, windthrow contributed 34-62% of LWD in streams. In study reaches where active beaver colonies were observed, beaver-felled trees accounted for up to 47% of LWD inputs. The average frequency of debris dams (2.4 · 100m-1) was less than those reported from studies in other areas and was positively correlated with stream substrata roughness. The influence of LWD on pool formation and channel morphology in these streams was negligible. Less than 15% of the pools in these streams were wood influenced. Most wood pieces appeared to be ineffective as pool-forming agents because of their relatively small size and instability, and because most streams across this region were dominated by boulder and rocky substrates. In these disturbance-driven boreal shield forests, it appears that most trees do not live long enough or grow to sufficient size to contribute functional LWD to impact stream morphology and pool formation.

Western Mosquitofish

Impacts of Western Mosquitofish

The western mosquitofish Gambusia affinis is the most widely distributed larvivorous fish used for mosquito control on a global scale.  Given the current outbreak of the mosquito-borne disease West Nile Virus in the United States, the introduction of this fish species into lentic and lotic systems as a mosquito-control agent has increased significantly over the past several years.  Because mosquitofish have been known to displace native fishes, reduce amphibian populations, and alter trophic food-web structure in aquatic ecosystems, there is much concern over the potential impacts that may result from increased stocking of this species in inland freshwater systems.  For this research, we propose to evaluate the potential impact of western mosquitofish on native fishes and amphibians in Indiana waters.  To facilitate this evaluation, we will also collect the same information on native Indiana killifishes (i.e., banded killifish Fundulus diaphanus, blackstripe topminnow F. notatus, northern starhead topminnow F. dispar, and northern studfish F. catenatus) in order to determine the relationship among trophically similar species.  In addition, we will also use laboratory microcosm and pond mesocosm experiments to examine the biotic interactions between western mosquitofish and native Indiana killifishes and determine whether western mosquitofish could impact early life stages of native amphibian species.  Specific study objectives include: (1) evaluation of the food habits, diet overlap, and prey selection of western mosquitofish and native killifishes in Indiana waters; (2) examination of the extent and magnitude of biotic interactions between western mosquitofish and native Indiana killifishes; and (3) determination of the extent and magnitude of predation by western mosquitofish on early life stages of native amphibians.

Assessment of Eastern Hellbender Population Status

The eastern hellbender is a large, primitive species of aquatic salamander native to clear, cool streams and rivers of the eastern United States. Hellbenders are habitat specialists that are confined to highly oxygenated, swift-flowing waters with large rocky substrates for hiding and nesting and an abundance of prey species such as crayfish. Because population declines and physical abnormalities have been documented throughout much of the hellbender's range and likely have multiple causes, it is critical to understand the population status and health, life-history attributes, habitat availability and quality, and the incidence of reproductive and recruitment success in order to develop appropriate conservation and rehabilitation strategies for this species. For this research, we propose to initiate research on the Eastern hellbender to: 1) examine the life-history attributes, population status, movement patterns, habitat availability and use, and reproductive and recruitment success; 2) develop a stage-structured, life-history model to evaluate the long-term population viability of the Eastern hellbender in the Blue River and assess the impacts of various perturbation and rehabilitation scenarios on the population abundance, recruitment, and reproductive potential of this species; and 3) develop a suite of hypervariable microsatellite markers, assess levels of genetic variation and genetic structure at both local and regional scales, and identify genetic source populations for potential augmentations.

Yelloweye Rockfish (Sebastes ruberrimus) by Crappy Wildlife Photography.

Yelloweye Rockfish

Deepwater Rockfishes

Anglers fishing the marine waters of Alaska rely heavily on groundfish stocks, particularly Pacific halibutand nearshore rockfishes, for subsistence, recreation, and economic opportunity.
A recent study commissioned by Alaska Department of Fish and Game estimated the economic impact to coastal communities by guided saltwater anglers alone exceeded $176 million annually. Restrictions to the recreational halibut fishery are likely to increase effort and harvest of rockfish by charter operators. Depressed rockfish populations are slow to recover due to their long lifespan, delayed maturation, and low reproductive potential. Conservative and creative management solutions are warranted to minimize the risk of population declines in rockfish stocks. Demersal rockfish, particularly yelloweye, quillback, and copper rockfish, even when caught at relatively shallow depths of 30 m, may sustain injury due to barotrauma. Barotrauma is damage to tissue caused by expansion of gas in the air bladder and in other organs that occurs with pressure changes as fish are brought to the surface. Returning these fish to capture depth (pressure) as soon as possible appears to increase survival, but little is known about the long-term effects of barotrauma on released fish. Several deepwater release devices are now commercially available, but the benefit of these devices to demersal rockfish populations is not yet understood. If deepwater release devices are to be considered a viable tool for fishery management, a better understanding of their effect on fish is needed.

Rainbow Trout

Rainbow Trout

The Alaska Department of Fish and Game manages stocked waters in Interior Alaska for rainbow trout under three management categories: regional, conservative, and special.  The "special" approach manages for a high probability of an angler catching more than one fish at least 457-mm total length (TL), which is considered a trophy fishery.  There is a demand from the angling public for trophy-sized fish.  Better allocation of fish stocks is a necessity for meeting the needs and desire of anglers and to maintain healthy fish populations.  The goal of this project is to develop a model that predicts rainbow trout productivity in stocked lakes in interior Alaska.  The overall objective is to evaluate rainbow trout at maximum length at age and by condition factor in stocked lakes and to analyze abiotic and biotic variables of interior lakes.  To achieve this objective, lakes will be visited three times between May and September 2008 and 2009 to measure and weigh fish, and to measure lake temperature, pH, dissolved oxygen, total dissolved solids (TDS), conductivity, alkalinity, hardness, phosphorus, nitrogen, lake depth, lake surface area, shoreline development, turbidity (Secchi depth), lake elevation, chlorophyll a, macrophyte cover, and zooplankton.  An expected outcome from this project is a predictive model that can be used by researchers and managers for evaluating rainbow trout productivity in stocked lakes in the interior of Alaska.

Razor Clams

Razor Clams

Growth, survival, and recruitment rates of the Pacific razor clam, an important species targeted by sport and personal-use fisheries on the east side of Cook Inlet, Alaska, are in decline.  The need for fisheries managers to respond to these changes and protect stock sustainability is greater now than ever before.  This project aims to provide baseline data for future management decisions by examining variations in life-history patterns of razor clams in the region, including determining the timing of adult spawning, duration of the larval period, clam size at settlement, and improving the recognition of sequential annular growth and juvenile clams.  Using this life-history data, we will be able to produce age determination indices and develop stock-recruitment models to predict future population trends and help guide management decisions.

Chum Salmon fry

Chum Salmon

Chum salmon were one of the more abundant fish species captured in the Bering and southern and central Chukchi seas during the 2007 BASIS trawls.  We expect this to also be the case in the summer 2012 and 2013 expansion of these trawl efforts into the northern Chukchi Sea.  The Arctic EIS trawl survey will give us an opportunity to collect baseline data on chum salmon relative abundance and early life history in the Chukchi Sea.  Sea surface temperatures recorded during the 2007 BASIS survey show a warming trend from south to north, with the central Chukchi Sea (68 to70° N) being approximately 1-2°C warmer than the southern Chukchi Sea (66 to 68° N).  This relationship is also expected further north (Moss et al. 2009).  Further, Arctic sea ice was minimal during the 2007 survey.  Assuming that cooler sea surface temperatures and more extensive sea ice are observed during 2012 and 2013 summer trawls, growth rates of juvenile chum could be different from fish collected in 2007.  All chum salmon captured in this study will be counted, weighed, and a random subsample of approximately five fish per station (approximately 75-100 fish from each the northern and the southern Chukchi Sea regions) will be taken for removal of both sagittal otoliths.  Ratios of Sr/Ca as measured from otoliths will be used to determine the timing of ocean entry and daily otolith increment counts will be used to determine growth rates.  The timing of ocean entry and growth rates will be compared between the northern and southern sea as well as between our 2012 and 2013 samples and samples collected from the southern Chukchi Sea during the 2007 BASIS cruise.

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