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At least 631 records · Page 35Linked to original sources
USGS2016

Effects of turbidity on predation vulnerability of juvenile humpback chub to rainbow and brown trout

Predation on juvenile native fish by introduced rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta is considered a significant threat to the persistence of endangered humpback chub Gila cypha in the Colorado River in Grand Canyon. Diet studies of rainbow and brown trout in Glen and Grand canyons indicate that these species eat native fish, but impacts are difficult to assess because predation vulnerability is highly variable depending on the physical conditions under which the predation interactions take place. We conducted laboratory experiments to evaluate how short-term predation vulnerability of juvenile humpback chub changes in response to changes in turbidity. In overnight laboratory trials, we exposed hatchery-reared juvenile humpback chub and bonytail Gila elegans (a surrogate for humpback chub) to adult rainbow and brown trout at turbidities ranging from 0 to 1,000 formazin nephlometric units. We found that turbidity as low as 25 formazin nephlometric units significantly reduced predation vulnerability of bonytail to rainbow trout and led to a 36% mean increase in survival (24–60%, 95% CI) compared to trials conducted in clear water. Predation vulnerability of bonytail to brown trout at 25 formazin nephlometric units also decreased with increasing turbidity and resulted in a 25% increase in survival on average (17–32%, 95% CI). Understanding the effects of predation by trout on endangered humpback chub is important when evaluating management options aimed at preservation of native fishes in Grand Canyon National Park. This research suggests that relatively small changes in turbidity may be sufficient to alter predation dynamics of trout on humpback chub in the mainstem Colorado River and that turbidity manipulation may warrant further investigation as a fisheries management tool.

Journal of Fish and Wildlife Management↗
USGS2023

Cold-water corals of the world: Gulf of Mexico

The Gulf of Mexico is a semi-enclosed sea that borders the USA and Mexico and covers approximately 1.5 million square kilometers. The northern Gulf is topographically complex and is a rich source of oil and gas deposits, which has led to a great deal of research on benthic ecosystems from the coastal zone to the deep sea. While not fully explored, the distribution of cold seeps and deep corals in the northern Gulf is reasonably well described. The eastern Gulf has a moratorium on energy industry development and consequently less exploration and research has been conducted in this region; however, recent explorations have revealed deep scleractinian reefs on the west Florida slope and extensive octocoral gardens on the deep escarpment. The Gulf is a productive sea with lucrative fisheries in addition to oil and gas. Exploitation of natural resources and potential climate change impacts threaten vulnerable ecosystems in the Gulf, including those in the deep sea. This chapter describes the oceanography and geology of the Gulf of Mexico, presents the current state of the knowledge of cold-water coral distribution, physiology and ecology, and provides an assessment of the threats to these vulnerable ecosystems.

Book chapter↗
USGS2016

A resilience approach can improve anadromous fish restoration

Most anadromous fish populations remain at low levels or are in decline despite substantial investments in restoration. We explore whether a resilience perspective (i.e., a different paradigm for understanding populations, communities, and ecosystems) is a viable alternative framework for anadromous fish restoration. Many life history traits have allowed anadromous fish to thrive in unimpacted ecosystems but have become contemporary curses as anthropogenic effects increase. This contradiction creates a significant conservation challenge but also makes these fish excellent candidates for a resilience approach. A resilience approach recognizes the need to maintain life history, population, and habitat characteristics that increase the ability of a population to withstand and recover from multiple disturbances. To evaluate whether a resilience approach represents a viable strategy for anadromous fish restoration, we review four issues: (1) how resilience theory can inform anadromous fish restoration, (2) how a resilience-based approach is fundamentally different than extant anadromous fish restoration strategies, (3) ecological characteristics that historically benefited anadromous fish persistence, and (4) examples of how human impacts harm anadromous fish and how a resilience approach might produce more successful outcomes. We close by suggesting new research and restoration directions for implementation of a resilience-based approach.

Fisheries↗
USGS2017

It is the time for oceanic seabirds: Tracking year-round distribution of gadfly petrels across the Atlantic Ocean

Aim Anthropogenic activities alter and constrain the structure of marine ecosystems with implications for wide-ranging marine vertebrates. In spite of the environmental importance of vast oceanic ecosystems, most conservation efforts mainly focus on neritic areas. To identify relevant oceanic areas for conservation, we assessed the year-round spatial distribution and spatio-temporal overlap of eight truly oceanic seabird species of gadfly petrels ( Pterodroma spp.) inhabiting the Atlantic Ocean. Location Atlantic Ocean. Methods Using tracking data (mostly from geolocators), we examined year-round distributions, the timing of life-cycle events, and marine habitat overlap of eight gadfly petrel species that breed in the Atlantic Ocean. Results We compiled 125 year-round tracks. Movement strategies ranged from non-migratory to long-distance migrant species and from species sharing a common non-breeding area to species dispersing among multiple non-breeding sites. Gadfly petrels occurred throughout the Atlantic Ocean but tended to concentrate in subtropical regions. During the boreal summer, up to three species overlapped spatio-temporally over a large area around the Azores archipelago. During the austral summer, up to four species coincided in a core area in subtropical waters around Cape Verde, and three species shared habitat over two distinct areas off Brazil. The petrels used many national Exclusive Economic Zones, although they also exploited offshore international waters. Main conclusions Tracking movements of highly mobile vertebrates such as gadfly petrels can provide a powerful tool to evaluate and assess the potential need for and location of protected oceanic areas. As more multispecies, year-round data sets are collected from wide-ranging vertebrates, researchers and managers will have greater insight into the location of biodiversity hotspots. These can subsequently inform and guide marine spatial planning efforts that account for both conservation and sustainable use of resources such as commercial fisheries.

Diversity and Distributions↗
USGS2017

Engaging the user community for advancing societal applications of the Surface Water Ocean Topography mission

Scheduled for launch in 2021, the Surface Water and Ocean Topography (SWOT) mission will be a truly unique mission that will provide high-temporal-frequency maps of surface water extents and elevation variations of global water bodies (lakes/reservoirs, rivers, estuaries, oceans, and sea ice) at higher spatial resolution than is available with current technologies (Biancamaria et al. 2016; Alsdorf et al. 2007). The primary instrument on SWOT is based on a Ka-band radar interferometer (KaRIN), which uses radar interferometery technology. The satellite will fly two radar antennas at either end of a 10-m (33 ft) mast, allowing it to measure the elevation of the surface along a 120-km (75 mi)-wide swath below. The availability of high-frequency and high-resolution maps of elevations and extents for surface water bodies and oceans will present unique opportunities to address numerous societally relevant challenges around the globe (Srinivasan et al. 2015). These opportunities may include such diverse and far-ranging applications as fisheries management, flood inundation mapping/risk mitigation/forecasting, wildlife conservation, global data assimilation for improving forecast of ocean tides and weather, reservoir management, climate change impacts and adaptation, and river discharge estimation, among others. Although SWOT is a research mission and not scheduled for launch for another 4 years, there is a need to build engagement within the application community now and to explore how best to advance the societal relevance and benefits of the SWOT mission from concept to reality. The SWOT Applications Working Group organized a workshop on 5–6 April 2017 at the U.S. Geological Survey (USGS) headquarters in Reston, Virginia. The goal of the workshop was to understand and communicate how the applications community can use SWOT data to address problems of profound societal relevance.

Bulletin of the American Meteorological Society↗
USGS2008

Effectiveness of piscicides for controlling round gobies (Neogobius melanostomus)

Round gobies (Neogobius melanostomus) were introduced to the Great Lakes presumably as a result of ballast water releases from seagoing freighters returning from European water bodies. These unwelcome fish have become established in the Great Lakes region and are expanding their range to suitable portions of other interior drainage basins including the Mississippi River traversing the central United States and the Trent-Severn waterway spanning south-central Ontario. If the invasion continues, use of chemical toxicants as a control measure may be necessary. Toxicity tests of the currently registered piscicides antimycin, rotenone, 3-trifluoromethyl-4-nitrophenol (TFM), and Bayluscide?? were conducted with three fish species native to the Great Lakes and round gobies collected from the Illinois Waterway. Tests indicated that round gobies are sensitive to all of the piscicides, however, the level of sensitivity is similar to that of the native fish species tested. Therefore, currently registered piscicides have limited potential to selectively remove round gobies. Bottom-release formulations of Bayluscide?? and antimycin were also evaluated as control agents for the normally bottom-dwelling round goby. Avoidance behavior tests demonstrated that the round goby did not react to the presence of either chemical. Therefore, the bottom-release formulations may have some application for the selective removal of round gobies, and may be one of the few tools presently available to fishery managers to help limit the range expansion of this invasive fish.

Journal of Great Lakes Research↗
USGS2003

Recommendations for assessing sea lamprey damages: toward optimizing the control program in the Great Lakes

The Great Lakes sea lamprey (Petromyzon marinus) control program currently allocates stream treatments to optimize the number of juvenile sea lampreys killed for a given level of control. Although the economic benefits derived from control appear to outweigh the dollars spent on control efforts, optimizing the number of sea lampreys killed will not necessarily optimize the economic benefits provided by the fish communities. These benefits include both non-consumptive and fishery values. We emphasize that the biological damages caused by each juvenile sea lamprey will vary, as will the economic value associated with each host that is killed. We consider issues related to assessing damages due to sea lampreys, taking into account effects on the fish community and fisheries, so as to improve the sea lamprey control program. We recommend a consolidation of information regarding the valuation of benefits, better understanding of variation in host-parasite interactions among the Great Lakes, and integration of the control program with other fisheries management objectives and activities. Adoption of these recommendations should promote lake trout rehabilitation in the Great Lakes, healthy fish communities and prudent use of limited fishery management resources.

Journal of Great Lakes Research↗
USGS2022

The impacts of mangrove range expansion on wetland ecosystem services in the southeastern United States: Current understanding, knowledge gaps, and emerging research needs

Climate change is transforming ecosystems and affecting ecosystem goods and services. Along the Gulf of Mexico and Atlantic coasts of the southeastern United States, the frequency and intensity of extreme freeze events greatly influences whether coastal wetlands are dominated by freeze-sensitive woody plants (mangrove forests) or freeze-tolerant grass-like plants (salt marshes). In response to warming winters, mangroves have been expanding and displacing salt marshes at varying degrees of severity in parts of north Florida, Louisiana, and Texas. As winter warming accelerates, mangrove range expansion is expected to increasingly modify wetland ecosystem structure and function. Because there are differences in the ecological and societal benefits that salt marshes and mangroves provide, coastal environmental managers are challenged to anticipate effects of mangrove expansion on critical wetland ecosystem services, including those related to carbon sequestration, wildlife habitat, storm protection, erosion reduction, water purification, fisheries support, and recreation. Mangrove range expansion may also affect wetland stability in the face of extreme climatic events and rising sea levels. Here, we review current understanding of the effects of mangrove range expansion and displacement of salt marshes on wetland ecosystem services in the southeastern United States. We also identify critical knowledge gaps and emerging research needs regarding the ecological and societal implications of salt marsh displacement by expanding mangrove forests. One consistent theme throughout our review is that there are ecological trade-offs for consideration by coastal managers. Mangrove expansion and marsh displacement can produce beneficial changes in some ecosystem services, while simultaneously producing detrimental changes in other services. Thus, there can be local-scale differences in perceptions of the impacts of mangrove expansion into salt marshes. For very specific local reasons, some individuals may see mangrove expansion as a positive change to be embraced, while others may see mangrove expansion as a negative change to be constrained.

Global Change Biology↗
USGS2013

The quality of our Nation’s waters--Ecological health in the Nation's streams, 1993-2005

This report summarizes a national assessment of the ecological health of streams done by the U.S. Geological Survey's (USGS) National Water-Quality Assessment Program (NAWQA). Healthy functioning stream ecosystems provide society with many benefits, including water purification, flood control, nutrient recycling, waste decomposition, fisheries, and aesthetics. The value to society of many of these benefits is substantial; for example, sportfishing in the United States generates an estimated annual economic output of $125 billion, including more than 1 million jobs (National Research Council, 2005; American Sportfishing Association, 2008). Continued monitoring and assessment of the Nation’s streams is needed to support informed decisions that will safeguard this important natural and economic resource. The quality of streams and rivers is often assessed with measures of the chemical or physical properties of water. However, a more comprehensive perspective is obtained if resident biological communities are also assessed. Guidelines to protect human health and aquatic life have been established for specific physical and chemical properties of water and have become useful yardsticks with which to assess water quality. Biological communities provide additional crucial information because they live within streams for weeks to years and therefore integrate through time the effects of changes to their chemical or physical environment. In addition, biological communities are a direct measure of stream health—an indicator of the ability of a stream to support aquatic life. Thus, the condition of biological communities, integrated with key physical and chemical properties, provides a comprehensive assessment of stream health.

conterminous United States↗
USGS2025

Population dynamics of White Sturgeon in the upper Snake River, Idaho: Evaluation of management options for a harvest fishery

Objective Understanding how fish populations will respond to management actions is critical for making effective management ­decisions. This study provides important information regarding population demographics for a nonnative, hatchery-implemented population of White Sturgeon Acipenser transmontanus . We investigated the population dynamics of White Sturgeon in the upper Snake River, Idaho, and developed an age-structured population model to evaluate potential stocking and harvest scenarios (e.g., length limits and annual quotas). Methods White Sturgeon were sampled from June to October 2022 and from June to August 2023 using angling (i.e., rod and reel) and setlines from a 260-km-long section of the Snake River. Capture histories from 261 known-age White Sturgeon informed age and growth analysis and an evaluation of movement trends. A closed-population capture–recapture model and an estimate of setline-specific catchability were used to estimate the total abundance of White Sturgeon in the upper Snake River. Apparent survival for the population was estimated using a Cormack–Jolly–Seber model. Finally, a population model was parameterized using information on the population dynamics of White Sturgeon in the upper Snake River. The model was used to estimate the effects of varying stocking rates and harvest scenarios (i.e., harvest slot of 76–122 cm fork length [FL] and annual quotas of 0–25 White Sturgeon harvested) on the population. Results In total, 340 individual White Sturgeon were captured throughout the study area, with 181 recapture events. Individuals varied in FL from 54 to 205 cm, and the mean relative weight for captures was 105.2 (SD = 14.4), suggesting relatively high body condition. Age varied from 2 to 25 years, and White Sturgeon moved an average of 8.1 km (SD = 23.5) downstream from stocking locations. Estimated abundance of White Sturgeon in the tailwaters of American Falls Dam was 428 fish (95% CI = 403–463). That abundance estimate was used to inform a total abundance estimate of 887 White Sturgeon (95% CI = 835–960) in the study area. Apparent annual survival was 0.79 (95% CI = 0.64–0.89). A stocking rate of 285 age-2 White Sturgeon/year was necessary to maintain current abundance. For every five fish harvested (harvest slot = 76–122 cm FL) per year, estimated abundance decreased by about 2.2% over 20 years. Conclusions Our research identified fast growth of White Sturgeon relative to other populations and relatively high mortality for a White Sturgeon population without exploitation. Also, like other studies evaluating harvest, a population model was used to illustrate the effect of varying rate functions on a fishery. The age-structured population model suggested that a harvest fishery is possible while still meeting management goals for the upper Snake River White Sturgeon fishery.

Idaho↗
USGS2013

An evaluation of liquid ammonia (ammonium hydroxide) as a candidate piscicide

Eradication of populations of nonnative aquatic species for the purpose of reintroducing native fish is often difficult because very few effective tools are available for removing aquatic organisms. This creates the need to evaluate new chemicals that could be used as management tools for native fish conservation. Ammonia is a natural product of fish metabolism and is naturally present in the environment at low levels, yet is known to be toxic to most aquatic species. Our objective was to determine the feasibility of using liquid ammonia as a fisheries management tool by evaluating its effectiveness at killing undesirable aquatic species and its persistence in a pond environment. A suite of invasive aquatic species commonly found in the southwestern USA were introduced into two experimental outdoor ponds located at the Rocky Mountain Research Station in Flagstaff, Arizona. Each pond was treated with ammonium hydroxide (29%) at 38 ppm. This target concentration was chosen because previous studies using anhydrous ammonia reported incomplete fish kills in ponds at concentrations less than 30 ppm. Water quality was monitored for 49 d to determine how quickly the natural bacteria in the environment converted the ammonia to nitrate. Ammonia levels remained above 8 ppm for 24 and 18 d, respectively, in ponds 1 and 2. Nitrite levels in each pond began to rise approximately 14 d after dosing with ammonia and stayed above 5 ppm for an additional 21 d in pond 1 and 18 d in pond 2. After 49 d all water in both ponds was drained and no fish, crayfish, or tadpoles were found to have survived the treatment, but aquatic turtles remained alive and appeared unaffected. Liquid ammonia appears to be an effective tool for removing many problematic invasive aquatic species and may warrant further investigation as a piscicide.

North American Journal of Fisheries Management↗
USGS2010

Evaluation of methods for identifying spawning sites and habitat selection for alosines

Characterization of riverine spawning habitat is important for the management and restoration of anadromous alosines. We examined the relative effectiveness of oblique plankton tows and spawning pads for collecting the eggs of American shad Alosa sapidissima , hickory shad A. mediocris , and “river herring” (a collective term for alewife A. pseudoharengus and blueback herring A. aestivalis ) in the Roanoke River, North Carolina. Relatively nonadhesive American shad eggs were only collected by plankton tows, whereas semiadhesive hickory shad and river herring eggs were collected by both methods. Compared with spawning pads, oblique plankton tows had higher probabilities of collecting eggs and led to the identification of longer spawning periods. In assumed spawning areas, twice-weekly plankton sampling for 15 min throughout the spawning season had a 95% or greater probability of collecting at least one egg for all alosines; however, the probabilities were lower in areas with more limited spawning. Comparisons of plankton tows, spawning pads, and two other methods of identifying spawning habitat (direct observation of spawning and examination of female histology) suggested differences in effectiveness and efficiency. Riverwide information on spawning sites and timing for all alosines is most efficiently obtained by plankton sampling. Spawning pads and direct observations of spawning are the best ways to determine microhabitat selectivity for appropriate species, especially when spawning sites have previously been identified. Histological examination can help determine primary spawning sites but is most useful when information on reproductive biology and spawning periodicity is also desired. The target species, riverine habitat conditions, and research goals should be considered when selecting methods with which to evaluate alosine spawning habitat.

North American Journal of Fisheries Management↗
USGS2023

Spawning locations, movements, and potential for stock mixing of walleye in Green Bay, Lake Michigan

Effective fishery management in large systems relies on understanding how individual stocks contribute to a fishery over spatial and temporal scales. The current conceptual model for management of Walleye Sander vitreus in Green Bay designates Walleye in the northern and southern parts of the bay as distinct stocks, with little mixing between the northern and southern fisheries, and assumes that Walleye in both northern and southern Green Bay primarily spawn in tributaries as opposed to shoreline or offshore reef areas. We used acoustic telemetry to test this conceptual model for Walleye management in Green Bay. Telemetry indicated that the majority of Green Bay Walleye use tributaries for spawning. However, many individuals were assigned to open-water spawning locations during consecutive years in both northern (26%) and southern (21%) Green Bay, suggesting that open-water spawners may represent a larger proportion of the Walleye stocks than previously thought. Differential movement was observed between northern and southern portions of Green Bay, with 56% of Walleye tagged in northern Green Bay crossing receiver lines to move south compared to only 19% of Walleye tagged in southern Green Bay crossing receiver lines to move north. Walleye typically transitioned across these boundaries in summer and fall, suggesting that stock contributions to the fishery in each zone may differ seasonally. Differential movements of northern Green Bay Walleye may be influenced by broad-scale differences in habitat and prey availability, which are likely related to the differential effects of dreissenid mussel invasion in Green Bay. Our results suggest that adjustment of monitoring efforts to account for open-water spawners may provide a more complete picture of stock status. Additionally, more research examining potential food web effects of northern Green Bay Walleye moving into southern Green Bay may be needed to determine how these movements might influence other important species.

Wisconsin↗
USGS2020

Using video survey to examine the effect of habitat on gag grouper encounter

Gag is a reef fish that was declared overfished in the Gulf of Mexico (GOM) in 2009. Although Gag are no longer listed as overfished, fisheries managers are concerned that stocks may not be recovering. Our objective was to identify habitat characteristics important to Gag, and their effect on the probability of Gag occurrence. We obtained data from three separate fisheries-independent video surveys that sampled in the eastern GOM from 2010-2017: the National Atmospheric and Oceanic Administration (NOAA) Panama City, FL Office, the NOAA Southeast Area Monitoring and Assessment Program, and the Florida Fish and Wildlife Research Institute. We ran a separate mixed effects logistic regression for each survey, and used Akaike’s Information Criteria to determine the best fitting models. Some variables - percent rock coverage, vertical relief, latitude, and depth - were present in all confidence models. Depth did not have the same relationship with Gag across all surveys, suggesting that shallower habitats (<50 m) might be more suitable for juveniles, whereas deeper habitats (>50 m) might be more suitable for adults. Managers may be able to help Gag and encourage their recovery by using these data to establish or expand protected areas throughout shallower waters.

Florida↗
USGS2016

Identifying alternate pathways for climate change to impact inland recreational fishers

Fisheries and human dimensions literature suggests that climate change influences inland recreational fishers in North America through three major pathways. The most widely recognized pathway suggests that climate change impacts habitat and fish populations (e.g., water temperature impacting fish survival) and cascades to impact fishers. Climate change also impacts recreational fishers by influencing environmental conditions that directly affect fishers (e.g., increased temperatures in northern climates resulting in extended open water fishing seasons and increased fishing effort). The final pathway occurs from climate change mitigation and adaptation efforts (e.g., refined energy policies result in higher fuel costs, making distant trips more expensive). To address limitations of past research (e.g., assessing climate change impacts for only one pathway at a time and not accounting for climate variability, extreme weather events, or heterogeneity among fishers), we encourage researchers to refocus their efforts to understand and document climate change impacts to inland fishers.

Fisheries↗
USGS2022

Seasonal movements and spatial overlap of juvenile and adult lake sturgeon in Lake Champlain

The lake sturgeon Acipenser fulvescens is a large, long-lived, potamodromous species that is widely distributed throughout freshwater systems in the central part of North America. In this study, we used acoustic telemetry to examine seasonal distribution and movement patterns of endangered Lake Sturgeon in Lake Champlain, Vermont. Acoustic tags were implanted in 29 juvenile Lake Sturgeon (453–874 mm TL) and 19 adults (1,215–1,615 mm TL) from the Winooski River and nearby areas of Lake Champlain between 2015 and 2019; tags were detected with 23 passive acoustic receivers deployed in the river and delta area and an additional 34 receivers deployed throughout Lake Champlain. Home range analysis using a lattice-based density estimator indicated that juvenile home range sizes were the same as adult home range sizes in spring and summer but were statistically larger than adult home ranges in winter. Cumulative home range analysis showed that juvenile and adult home ranges overlapped in shallow (<10-m) water in the summer and fall. In winter and spring, cumulative home ranges from juveniles included deepwater sites (>25 m), while adults remained in shallow water near the mouth of their spawning river. Seven juveniles made long-range movements (18–34 km) during the winter and spring months, and 13 juveniles moved back into the lower section of their natal river after overwintering in Lake Champlain. This study is the first to directly compare adult and juvenile Lake Sturgeon distribution, home range size, movements, and habitat use in a large lake system and provides a baseline for further research on the movement ecology of Lake Sturgeon in Lake Champlain.

Vermont↗
USGS2024

It's about time: A multistate semicontinuous time mark–recapture model to evaluate seasonal survival and movement rates of juvenile Coho Salmon in a small coastal watershed

Objective Many mark–recapture models assume that releases and recaptures are discrete events, and researchers often aggregate continuous recapture data (e.g., passive integrated transponder [PIT] detections) into coarse temporal scales to satisfy this assumption. This temporal discretization could result in parameter biases by ignoring the individual heterogeneity in the time susceptible to mortality after recapture and the conditions experienced (e.g., temperature and predation risk) before and after recapture. Our objectives were to (1) estimate the amount of bias in survival and emigration rates due to different temporal discretization durations when recapture events occur continuously and (2) apply this semicontinuous model to estimate rates of early emigration and overwinter survival for Coho Salmon Oncorhynchus kisutch in a coastal California watershed. Methods We developed a semicontinuous time multistate mark–recapture model to separately estimated emigration and survival rates throughout the year. We used weekly time-varying occasions paired with discrete spatial states and conducted extensive simulation trials to explore potential model bias. We then applied the model to an existing 4-year dataset of Coho Salmon PIT tag detections. Result Our simulations indicated that that the amount of bias in survival and movement rates decreased as the temporal discretization duration decreased. The confidence interval of the bias estimates included zero with a duration of 8 days, indicating that this duration was sufficiently short to model movement and survival. Results from our Coho Salmon analysis suggest that overwinter survival rate ranged from 0.72 to 0.83, which is higher than previous estimates for Coho Salmon in this region. We estimate that a substantial proportion of smaller juveniles (0.21–0.28 annually) move to downstream nonnatal rearing habitats before the spring smolt migration. Conclusion Our semicontinuous modeling approach can be implemented relatively easily and used to analyze continuous detection data to accurately estimate survival and movement rates. Our analysis of Coho Salmon PIT tag detections implies that previous low estimates of apparent overwinter survival of Coho Salmon were partially due to high movement rates to alternative rearing locations. This contrasts with conclusions from the previous research that suggested that overwinter survival was a major limiting factor for population recovery and implies that species recovery may be improved by considering multiple emigration patterns in the design of future research, monitoring, and restoration projects.

California↗
USGS2003

Mark-recapture population estimates of parasitic sea lampreys ( Petromyzon marinus ) in Lake Huron

Metamorphosed sea lampreys ( Petromyzon marinus ) were collected and marked at two points in their life cycle. Recently metamorphosed juveniles were collected from streams, marked with coded wire tags, and returned to migrate to the Great Lakes. Juveniles already in the lakes and feeding on teleost hosts were obtained from incidental catches by sport or commercial fisheries. Sea lampreys in the Great Lakes spend only 1 feeding year as parasites, and marked animals were recaptured during the spawning runs. For one marked group in each of four parasitic cohorts (feeding years 1991 to 1994) and two marked groups in each of three cohorts (feeding years 1998 to 2000) we recovered from 1.1 to 10.2 percent of marked animals. The number of metamorphosed animals present in autumn before migration to Lake Huron was estimated for five cohorts, with estimates ranging from 639 to 803 thousand. The number of feeding, parasitic animals present in Lake Huron in mid summer was estimated for five cohorts, with estimates ranging from 515,000 to 2,342,000. The larger estimates later in the parasitic year suggested that animals collected and marked from sport or commercial fisheries did not survive at the same rate as unmarked animals. It is recommended that only estimates from recaptures of animals marked in the streams before migration be used until it can be established why survival of juveniles obtained from sport or commercial fisheries might be affected.

Journal of Great Lakes Research↗