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USGS2006

Causes of mortality in California sea otters during periods of population growth and decline

Elevated mortality appears to be the main reason for both sluggish growth and periods of decline in the threatened California sea otter population . We assessed causes of mortality from salvage records of 3,105 beach-cast carcasses recovered from 1968 through 1999, contrasting two periods of growth with two periods of decline . Overall, an estimated 40%-60% of the deaths were not recovered and 70% of the recovered carcasses died from unknown causes . Nonetheless, several common patterns were evident in the salvage records during the periods of population decline . These included greater percentages of (1) prime age animals (3-10 yr), (2) carcasses killed by great white shark attacks, (3) carcasses recovered in spring and summer, and (4) carcasses for which the cause of death was unknown. Neither sex composition nor the proportion of carcasses dying of infectious disease varied consistently between periods of population increase and decline . The population decline from 1976 to 1984 was likely due to incidental mortality in a set-net fishery, and the decline from 1995 to 1999 may be related to a developing live-fish fishery. Long-term trends unrelated to periods of growth and decline included a decrease in per capita pup production and mass/length ratios of adult carcasses over the 31-yr study. The generally high proportion of deaths from infectious disease suggests that this factor has contributed to the chronically sluggish growth rate of the California sea otter population .

California↗

USGS2007

Use of the Delphi method in resolving complex water resources issues

The tri-state river basins, shared by Georgia, Alabama, and Florida, are being modeled by the U.S. Fish and Wildlife Service and the U.S. Army Corps of Engineers to help facilitate agreement in an acrimonious water dispute among these different state governments. Modeling of such basin reservoir operations requires parallel understanding of several river system components: hydropower production, flood control, municipal and industrial water use, navigation, and reservoir fisheries requirements. The Delphi method, using repetitive surveying of experts, was applied to determine fisheries' water and lake-level requirements on 25 reservoirs in these interstate basins. The Delphi technique allowed the needs and requirements of fish populations to be brought into the modeling effort on equal footing with other water supply and demand components. When the subject matter is concisely defined and limited, this technique can rapidly assess expert opinion on any natural resource issue, and even move expert opinion toward greater agreement.

Journal of the American Water Resources Associatio↗

USGS2017

Life history and status of Shortnose Sturgeon (Acipenser brevirostrum LeSueur, 1818)

Shortnose Sturgeon = SNS (Acipenser brevirostrum) is a small diadromous species with most populations living in large Atlantic coast rivers and estuaries of North America from New Brunswick, Canada, to GA, USA. There are no naturally landlocked populations, so all populations require access to fresh water and salt water to complete a natural life cycle. The species is amphidromous with use of fresh water and salt water (the estuary) varied across the species range, a pattern that may reflect whether freshwater or saltwater habitats provide optimal foraging and growth conditions. Migration is a dominant behavior during life history, beginning when fish are hatchling free embryos (southern SNS) or larvae (northeastern and far northern SNS). Migration continues by juveniles and nonspawning adult life stages on an individual time schedule with fish moving between natal river and estuary to forage or seek refuge, and by spawning adults migrating to and from riverine spawning grounds. Coastal movements by adults throughout the range (but particularly in the Gulf of Maine = GOM and among southern rivers) suggest widespread foraging, refuge use, and widespread colonization of new rivers. Colonization may also be occurring in the Potomac River, MD–VA–DC (midAtlantic region). Genetic studies (mtDNA and nDNA) identified distinct individual river populations of SNS, and recent rangewide nDNA studies identified five distinct evolutionary lineages of SNS in the USA: a northern metapopulation in GOM rivers; the Connecticut River; the Hudson River; a Delaware River–Chesapeake Bay metapopulation; and a large southern metapopulation (SC rivers to Altamaha River, GA). The Saint John River, NB, Canada, in the Bay of Fundy (north of the GOM), is the sixth distinct genetic lineage within SNS. Life history information from telemetry tracking supports the genetic information documenting extensive movement of adults among rivers within the three metapopulations. However, individual river populations with spawning adults are still the best basal unit for management and recovery planning. The focus on individual river populations should be complemented with attention to migratory processes and corridors that foster metapopulation level risks and benefits. The species may be extirpated at the center of the range, i.e., the midAtlantic region (Chesapeake Bay, MD–VA, and probably, NC), but large rivers in VA, including the James and Potomac rivers, need study. The largest SNS populations in GOM and northeastern rivers, like the Kennebec, Hudson, and Delaware rivers, typically have tens of thousands of adults. This contrasts with southern rivers, where rivers typically have much fewer (<2500) adults, except for the Altamaha River (>6000 adults). River damming in the 19th and 20th Centuries extirpated some populations, and also, created two dysfunctional segmented populations: the Connecticut River SNS in CT–MA and the SanteeCooper rivers–Lake Marion SNS in SC. The major anthropogenic impact on SNS in marine waters is fisheries bycatch. The major impacts that determine annual recruitment success occur in freshwater firstly, where adult spawning migrations and spawning are blocked or spawning success is affected by river regulation and secondly, where poor survival of early life stages is caused by river dredging, pollution, and unregulated impingement/entrainment in water withdrawal facilities. Climate warming has the potential to reduce abundance or eliminate SNS in many rivers, particularly in the South. In 1998, the National Marine Fisheries Service (NMFS) recommended management of 19 rivers as distinct population segments (DPSs) based on strong fidelity to natal rivers. A Biological Assessment completed in 2010 reaffirmed this approach. NMFS has not formally listed DPSs under the ESA and the species remains listed as endangered rangewide in the USA.

Journal of Applied Ichthyology↗

USGS2019

Satellite tracking of gulls and genomic characterization of fecal bacteria reveals environmentally mediated acquisition and dispersal of antimicrobial resistant Escherichia coli on the Kenai Peninsula, Alaska

Gulls (Larus spp.) have frequently been reported to carry Escherichia coli exhibiting antimicrobial resistance (AMR E. coli); however, the pathways governing the acquisition and dispersal of such bacteria are not well-described. We equipped 17 landfill-foraging gulls with satellite transmitters and collected gull fecal samples longitudinally from four locations on the Kenai Peninsula, Alaska to assess: 1) gull attendance and transitions between sites, 2) spatiotemporal prevalence of fecally-shed AMR E. coli, and 3) genomic relatedness of AMR E. coli isolates among sites. We also sampled Pacific salmon (Oncorhynchus spp.) harvested as part of personal-use dipnet fisheries at two sites to assess potential contamination with AMR E. coli. Among our study sites, marked gulls most commonly occupied the lower Kenai River (61% of site locations) followed by the Soldotna landfill (11%), lower Kasilof River (5%), and upper Kenai River (<1%). Gulls primarily moved between the Soldotna landfill and the lower Kenai River (94% of transitions among sites), which were also the two locations with the highest prevalence of AMR E. coli. There was relatively high spatial and temporal variability in AMR E. coli prevalence in gull feces and there was no evidence of contamination on salmon harvested in personal-use fisheries. We identified E. coli sequence types and AMR genes of clinical importance, with some isolates possessing genes associated with resistance to as many as eight antibiotic classes. Our findings suggest that gulls acquire AMR E. coli at habitats with anthropogenic inputs and subsequent movements may represent pathways through which AMR is dispersed.

Alaska↗

USGS2015

Strontium isotopes delineate fine-scale natal origins and migration histories of Pacific salmon

Highly migratory organisms present major challenges to conservation efforts. This is especially true for exploited anadromous fish species, which exhibit long-range dispersals from natal sites, complex population structures, and extensive mixing of distinct populations during exploitation. By tracing the migratory histories of individual Chinook salmon caught in fisheries using strontium isotopes, we determined the relative production of natal habitats at fine spatial scales and different life histories. Although strontium isotopes have been widely used in provenance research, we present a new robust framework to simultaneously assess natal sources and migrations of individuals within fishery harvests through time. Our results pave the way for investigating how fine-scale habitat production and life histories of salmon respond to perturbations—providing crucial insights for conservation.

Alaska↗

USGS2021

Historic coregonine habitat use and assessment of larval nursery locations in Lake Erie

Coregonine fishes (Coregonus spp.) are important components of Great Lake food webs and support lucrative commercial and recreational fisheries. Due to a combination of several factors including habitat loss, over-exploitation, and introduction of exotic species, the distribution and abundance of coregonines have been reduced. Examples of these declines are evident in Lake Erie where cisco (C. artedi) have been nearly extirpated, and lake whitefish (C. clupeaformis), while still abundant, are declining. To identify key habitat locations of coregonines in Lake Erie, we conducted a literature review of historical spawning, nursery, and adult habitat sites where coregonines have been observed. We used these sites as a reference for larval sampling at six locations across the southern shore of Lake Erie during spring 2017. Paired bongo samplers were used to collect larvae, and average densities were calculated for comparison across sites. Larval coregonine (46 visually identified as lake whitefish; 8 classified as coregonines) densities were highest at Huron, OH (0.880/1,000 m3 ± 1.61), followed by Sandusky, OH (0.426/1,000 m3 ± 1.05), Dunkirk, NY (0.208/1,000 m3 ± 0.703), Fairport, OH (0.185/1,000 m3 ± 0.680), Erie, PA (0.120/1,000 m3 ± 0.532), and Conneaut, OH (0.1196/1,000 m3 ± 0.528). Using contemporary sampling data coupled with historical spawning locations, we identified sites that are currently being used as nursery locations by lake whitefish. By validating the contemporary use of historic spawning and nursery sites, this study identifies locations where habitat protection and restoration or future stocking of coregonids could be conducted in Lake Erie in efforts to recover populations and improve fishery production.

Lake Erie↗

USGS2012

Repeat surveys of spawning cisco (Coregonus artedi) in western Lake Superior: Timing, distribution and composition of spawning stocks

Acoustic (AC) and midwater trawl (MT) surveys of spawning cisco ( Coregonus artedi ) in Lake Superior have been combined with commercial yield to estimate exploitation. To time surveys properly, it is important to understand when adults typically arrive at spawning grounds and how numbers change as the spawning season progresses. We conducted repeat autumn surveys during nighttime hours at coastal sites where commercial roe fisheries occur. Spawner densities increased significantly from October to mid-November, but differences measured at sites sampled from mid- to late-November were comparatively small. Spawners occupied the upper 20–30 m of the water column during mid-November before utilizing a wider range of depths by late-November. We compared repeat AC densities to temporal trends of catch-per-unit-effort (CPUE) in suspended commercial gillnets and found good agreement within sites. Because different gillnet mesh sizes were used in each roe fishery. CPUE and AC density were poorly correlated among sites. We recommend that future surveys be conducted between mid- and late-November, and that MT gear be used to measure cisco densities in the uppermost 10 m of the water column where AC estimates may be conservative. Given the short temporal window for assessing spawner density, we believe both AC-MT and gillnet surveys will be needed to ensure that harvest of different stocks is kept at a sustainable level.

Lake Superior↗

USGS2024

Seasonal mortality of Wild Atlantic Menhaden (Brevoortia tyrannus) is caused by a virulent clone of Vibrio (Listonella) anguillarum; Implications for biosecurity along the Atlantic Coastal United States

Atlantic menhaden are a highly migratory marine species in the Eastern United States that suffer from seasonal chronic mortality. Affected fish show neurologic signs referred to as spinning disease, including circling at the surface and erratic corkscrew swimming before death. We investigated three similar menhaden mortality events consistent with spinning disease in coastal New Jersey and New York between 2020 and 2021 to understand the cause. A unique strain of Vibrio (Listonella) anguillarum (serogroup O3) was detected regularly in high loads, particularly in the brains of moribund fish, by both metagenomics and bacterial isolation. The most common histopathological changes in moribund fish were hemorrhagic meningitis, encephalitis, pyknosis, and karyorrhexis of hematopoietic tissues in the kidney and spleen. Whole genome sequencing of isolates from moribund fish representing a wide spatial and temporal range showed that they were nearly identical clones, suggesting it to be a pathogenic strain circulating in the population. Though V. anguillarum is believed to be the main pathogen associated with spinning disease and mortality, Yersinia ruckeri (serotype O1) was isolated from smaller numbers of fish. Considering the highly migratory nature of Atlantic menhaden throughout the eastern United States and their use as bait for other fisheries, these findings identify potential biosecurity challenges that should be considered in Atlantic salmon aquaculture, fisheries, and emerging marine aquaculture in the region.

Transboundary and Emerging Diseases↗

USGS2009

Managing Pacific salmon escapements: The gaps between theory and reality

There are myriad challenges to estimating intrinsic production capacity for Pacific salmon populations that are heavily exploited and/or suffering from habitat alteration. Likewise, it is difficult to determine whether perceived decreases in production are due to harvest, habitat, or hatchery influences, natural variation, or some combination of all four. There are dramatic gaps between the true nature of the salmon spawner/recruit relationship and the theoretical basis for describing and understanding the relationship. Importantly, there are also extensive practical difficulties associated with gathering and interpreting accurate escapement and run-size information and applying it to population management. Paradoxically, certain aspects of salmon management may well be contributing to losses in abundance and biodiversity, including harvesting salmon in mixed population fisheries, grouping populations into management units subject to a common harvest rate, and fully exploiting all available hatchery fish at the expense of wild fish escapements. Information on U.S. Pacific salmon escapement goal-setting methods, escapement data collection methods and estimation types, and the degree to which stocks are subjected to mixed stock fisheries was summarized and categorized for 1,025 known management units consisting of 9,430 known populations. Using criteria developed in this study, only 1% of U.S. escapement goals are by methods rated as excellent. Escapement goals for 16% of management units were rated as good. Over 60% of escapement goals have been set by methods rated as either fair or poor and 22% of management units have no escapement goals at all. Of the 9,430 populations for which any information was available, 6,614 (70%) had sufficient information to categorize the method by which escapement data are collected. Of those, data collection methods were rated as excellent for 1%, good for 1%, fair for 2%, and poor for 52%. Escapement estimates are not made for 44% of populations. Escapement estimation type (quality of the data resulting from survey methods) was rated as excellent for <1%, good for 30%, fair for 3%, poor for 22%, and nonexistent for 45%. Numerous recommendations for improvements in escapement mangement are made in this chapter. In general, improvements are needed on theoretical escapement management techniques, escapement goal setting methods, and escapement and run size data quality. There is also a need to change managers' and harvesters' expectations to coincide with the natural variation and uncertainty in the abundance of salmon populations. All the recommendations are aimed at optimizing the number of spawners-healthy escapements ensure salmon sustainability by providing eggs for future production, nutrients to the system, and genetic diversity.

Book chapter↗

USGS2018

Reexamining the frequency range of hearing in silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp

Silver ( Hypophthalmichthys molitrix ) and bighead ( H . nobilis ) carp (collectively bigheaded carp) are invasive fish that threaten aquatic ecosystems in the upper Midwest United States and the Laurentian Great Lakes. Controlling bigheaded carp is a priority of fisheries managers and one area of focus involves developing acoustic deterrents to prevent upstream migration. For an acoustic deterrent to be effective however, the hearing ability of bigheaded carp must be characterized. A previous study showed that bigheaded carp detected sound up to 3 kHz but this range is narrower than what has been reported for other ostariophysans. Therefore, silver and bighead carp frequency detection was evaluated in response to 100 Hz to 9 kHz using auditory evoked potentials (AEPs). AEPs were recorded from 100 Hz to 5 kHz. The lowest thresholds were at 500 Hz for both species (silver carp threshold: 80.6 ± 3.29 dB re 1 μPa SPL rms , bighead carp threshold: 90.5 ± 5.75 dB re 1 μPa SPL rms ; mean ± SD). These results provide fisheries managers with better insight on effective acoustic stimuli for deterrent systems, however, to fully determine bigheaded carp hearing abilities, these results need to be compared with behavioral assessments.

PLoS ONE↗

USGS2018

Before-after, control-impact analysis of evidence for the impacts of water level on Walleye, Northern Pike and Yellow Perch in lakes of the Rainy-Namakan complex (MN, USA and ON, CA)

Water level (WL) fluctuations in lakes influence many aspects of ecosystem processes. Concern about the potential impact of WL fluctuations on fisheries was one of the factors that motivated the decision in 2000 to alter the management of WL in the Rainy-Namakan reservoir complex (on the border between the U.S. state of Minnesota and the Canadian province of Ontario). We used a Before-After, Control-Impact (BACI) framework to identify potential impacts of the change in WL management to Walleye, Northern Pike and Yellow Perch catch per unit effort (CPUE). The CPUE of these species from 1990±1999 and from 2005±2014 were compared in four impact lakes (Lake Kabetogama, Namakan Lake, Rainy Lake and Sand Point Lake) and two control lakes (Lake of the Woods and Lake Vermilion) using a simple Bayesian model. Changes in fish CPUE in the impact lakes were often similar to changes that occurred in at least one control lake. The only change that was not similar to changes in control lakes was an increase of Yellow Perch in Lake Kabetogama. The two control lakes often differed substantially from each other, such that if only one had been available our conclusions about the role of WL management on fisheries would be very different. In general, identifying cause-and-effect relationships in observational field data is very difficult, and the BACI analysis used here does not specify a causative mechanism, so co-occurring environmental and management changes may obscure the effect of WL management.

Minnesota, Ontario↗

USGS2020

Describing historical habitat use of a native fish-Cisco (Coregonus artedi)-In Lake Michigan between 1930 and 1932

With the global-scale loss of biodiversity, current restoration programs have been often required as part of conservation plans for species richness and ecosystem integrity. The restoration of pelagic-oriented cisco ( Coregonus artedi ) has been an interest of Lake Michigan managers because it may increase the diversity and resilience of the fish assemblages and conserve the integrity of the ecosystems in a changing environment. To inform restoration, we described historical habitat use of cisco by analyzing a unique fishery-independent dataset collected in 1930–1932 by the U.S. Bureau of Fisheries’ first research vessel Fulmar and a commercial catch dataset reported by the State of Michigan in the same period, both based on gear fished on the bottom. Our results confirmed that the two major embayments, Green Bay and Grand Traverse Bay, were important habitats for cisco and suggest that cisco could complete the entire lifecycle within either of the Bays as there was no lack of summer feeding and fall spawning habitats. Seasonally, our results showed that cisco stayed in nearshore waters in spring, migrated to offshore waters in summer, and then migrated back to nearshore waters in fall for spawning. The results also suggest that in summer, most ciscoes were in waters with bottom depths of 20–70 m, but the highest cisco density occurred in waters with a bottom depth around 40 m. We highlight the importance of embayment habitats to cisco restoration and the seasonal migration pattern of cisco identified in this study, which suggests that a restored cisco population can diversify the food web by occupying different habitats from the exotic fishes that now dominate the pelagic waters of Lake Michigan.

Lake Michigan↗

USGS2020

Effects of tidally varying river flow on entrainment of juvenile salmon into Sutter and Steamboat Sloughs

Survival of juvenile salmonids in the Sacramento–San Joaquin Delta (Delta) varies by migration route, and thus the proportion of fish that use each route affects overall survival through the Delta. Understanding factors that drive routing at channel junctions along the Sacramento River is therefore critical to devising management strategies that maximize survival. Here, we examine entrainment of acoustically tagged juvenile Chinook Salmon into Sutter and Steamboat sloughs from the Sacramento River. Because these sloughs divert fish away from the downstream entrances of the Delta Cross Channel and Georgiana Slough (where fish access the low-survival region of the interior Delta), management actions to increase fish entrainment into Sutter and Steamboat sloughs are being investigated to increase through-Delta survival. Previous studies suggest that fish generally “go with the flow”—as net flow into a divergence increases, the proportion of fish that enter that divergence correspondingly increases. However, complex tidal hydrodynamics at sub-daily time-scales may be decoupled from net flow. Therefore, we modeled routing of acoustic tagged juvenile salmon as a function of tidally varying hydrodynamic data, which was collected using temporary gaging stations deployed between March and May of 2014. Our results indicate that discharge, the proportion of flow that entered the slough, and the rate of change of flow were good predictors of an individual’s probability of being entrained. In addition, interactions between discharge and the proportion of flow revealed a non-linear relationship between flow and entrainment probability. We found that the highest proportions of fish are likely to be entrained into Steamboat Slough and Sutter Slough on the ascending and descending limbs of the tidal cycle, when flow changes from positive to negative. Our findings characterize how patterns of entrainment vary with tidal flow fluctuations, providing information critical for understanding the potential effect of management actions (e.g., fish guidance structures) to modify routing probabilities at this location. Main Content View Larger 1 Sponsored by the Delta Science Program and the UC Davis Muir Institute ABSTRACT Survival of juvenile salmonids in the Sacramento–San Joaquin Delta (Delta) varies by migration route, and thus the proportion of fish that use each route affects overall survival through the Delta. Understanding factors that drive routing at channel junctions along the Sacramento River is therefore critical to devising management strategies that maximize survival. Here, we examine entrainment of acoustically tagged juvenile Chinook Salmon into Sutter and Steamboat sloughs from the Sacramento River. Because these sloughs divert fish away from the downstream entrances of the Delta Cross Channel and Georgiana Slough (where fish access SFEWS Volume 19 | Issue 2 | Article 4 https://doi.org/10.15447/sfews.2021v19iss2art4 * Corresponding author: rperry@usgs.gov 1 Western Fisheries Research Center US Geological Survey Cook, WA 98605 USA 2 California Water Science Center US Geological Survey Sacramento, CA 95819 USA 3 Current address: Mid-Columbia Fish and Wildlife Conservation Office Yakima Basin Program US Fish and Wildlife Service Yakima, WA 98903 USA the low-survival region of the interior Delta), management actions to increase fish entrainment into Sutter and Steamboat sloughs are being investigated to increase through-Delta survival. Previous studies suggest that fish generally “go with the flow”—as net flow into a divergence increases, the proportion of fish that enter that divergence correspondingly increases. However, complex tidal hydrodynamics at sub-daily time-scales may be decoupled from net flow. Therefore, we modeled routing of acoustic tagged juvenile salmon as a function of tidally varying hydrodynamic data, which was collected using temporary gaging stations deployed between March and May of 2014. Our results indicate that discharge, the proportion of flow that entered the slough, and the rate of change of flow were good predictors of an individual’s probability of being entrained. In addition, interactions between discharge and the proportion of flow revealed a non-linear relationship between flow and entrainment probability. We found that the highest proportions of fish are likely to be entrained into Steamboat Slough and Sutter Slough on the ascending and descending limbs of the tidal cycle, when flow changes from positive to negative. Our findings characterize how patterns of entrainment vary with tidal flow fluctuations, providing information critical for understanding the potential effect of management RESEARCH Effects of Tidally Varying River Flow on Entrainment of Juvenile Salmon into Sutter and Steamboat Sloughs Jason G. Romine 1,3 , Russell W. Perry* 1 , Paul R. Stumpner 2 , Aaron R. Blake 2 , Jon R. Burau 2 2 VOLUME 19, ISSUE 2, ARTICLE 4 actions (e.g., fish guidance structures) to modify routing probabilities at this location. KEY WORDS Telemetry, juvenile salmon, migration routing, survival INTRODUCTION The Sacramento–San Joaquin River Delta (hereafter referred to as “the Delta”) is a complex series of channels and embayments in west central California of the United States. The Delta has undergone drastic transformation through construction of dikes, levees, reclaimed land, dredged canals and cuts, and water export projects (Nichols et al. 1986). The loss of habitat coupled with introduction of non-native piscivorous fishes has led to the decline of several salmonid stocks that utilize the Delta (Lindley 2009; National Marine Fisheries Service 2014). The physical complexity of the Delta poses significant challenges for understanding how juvenile salmon negotiate the complex channel network and survive in different migration routes. Yet such information is critical for understanding how water-management actions, such as operation of water diversions, influence survival of juvenile salmon. Through-Delta survival of juvenile Chinook Salmon that emigrate from the Sacramento River ranges from 10% to 80%, depending on river flow and migration route (Perry et al. 2018). The Delta can be broken down into four primary routes: (1) Sacramento River, (2) Steamboat and Sutter sloughs, (3) Georgiana Slough, and (4) Delta Cross Channel (DCC). Fish that remain in the Sacramento River consistently have the highest survival (Perry et al. 2010, 2013, 2018). However, fish that enter the interior Delta—the region to the south of the Sacramento River (Figure 1)—have the lowest survival among all routes and survive at less than half the rate of fish in the Sacramento River, likely as a result of longer migration times and exposure to non-native predators (Newman and Brandes 2010; Perry et al. 2018). On average, fish that migrate through Steamboat and Sutter sloughs exhibit survival similar to fish that remain in the Sacramento River at high flows but have lower survival at low flows (Perry et al. 2018). Because of differences in survival among migration routes, the proportion of fish that use each route affects the total survival of the population. Therefore, understanding the drivers behind fish routing in the Delta is imperative to inform management actions that help in the recovery of imperiled salmonid populations in the Central Valley. For example, Perry et al. (2013) found that total survival through the Delta could be increased by up to 7 percentage points by eliminating entrainment into Georgiana Slough and the DCC. These findings led to investigation of management actions to reduce entrainment into the DCC (Plumb et al. 2016) and Georgiana Slough (Perry et al. 2014). Both physical and non-physical barriers have been tested at the entrance to Georgiana Slough divergence (Perry et al. 2014; Romine et al. 2016). A non-physical barrier was able to reduce entrainment to the interior Delta through Georgiana Slough (Perry et al. 2014), but a floating fish-guidance structure reduced entrainment to a lesser extent (Romine et al. 2016). Research and engineering solutions to minimize entrainment have focused on the Georgiana Slough divergence, the DCC divergence, and the Old River divergence in the San Joaquin River (Buchanan et al. 2013; SJRG 2013). However, there has been little focus on understanding fish routing dynamics at other primary river junctions in the Delta, such as Sutter and Steamboat sloughs. Sutter and Steamboat sloughs diverge from the Sacramento about 10 km upstream from the DCC and Georgiana slough, and represent the first major junction that juvenile salmon encounter as they enter the Delta from the Sacramento River ( Figure 1 ). Because Sutter and Steamboat sloughs are upstream of the entrance to the interior Delta via the DCC and Georgiana Slough (Figure 1), juvenile salmon that enter Sutter and Steamboat sloughs avoid entrainment into the interior Delta where survival is low. Thus, management actions to increase entrainment could increase overall.

Sacramento–San Joaquin Delta↗

USGS1967

A closed recirculated sea-water system

Study of a virus disease in the chinook salmon (Oncorhynchus tshawytscha ) necessitated the use of a marine environment to study the long range effects of the disease and to complete the life cycle of its etiologic agent. A closed recirculated sea-water system was designed for use under experimental laboratory conditions so that controlled studies of the disease could be made. As others may wish to do marine environment studies in the laboratory, the design and operation of our system are presented. Other systems currently in use have been described by Chin (1959), DeWitt and Salo (1960), McCrimmon and Berst (1966), and the authors of collected papers edited by Clark and Clark (1964). Preparatory to the design and construction of the system in use in this laboratory, visits were made to marine systems in use at the University of Washington's College of Fisheries, Seattle, -washington, and Friday Harbor Laboratory, San Juan Island, Washington; the Washington State Department of Fisheries' Point whitney Shellfish Laboratory, Brinnon, Washington; Humboldt State College, Arcata, California; and the Steinhart Aquarium of the California Academy of Science, San Francisco, California.

Progressive Fish-Culturist↗

USGS1960

Collection and preservation of fish and other materials exposed to pesticides

The effects of pesticides on fish have become improtant to fish conservation since World War II, when DDT first came into common use. With the development of other potent insecticides and the increasing use of massive dosages in more recent years, the threat to fish and fish foods has increased. Fishery biologists have conducted some studies on the effects of insecticides, but it has been impossible for fishery science to keep pace with chemistry and agriculture.

Progressive Fish-Culturist↗

USGS1998

Isolation of Acholeplasma laidlawii from centrarchids in a Central Florida Lake

In 1991, the poor physical condition of largemouth bass Micropterus salmoides from Lake Harris, Florida, was associated with the decline of the lake's fishery. The swim bladders of emaciated bass had mild inflammation and ecchymotic hemorrhages. A mycoplasma-like organism isolated from swim bladders was initially believed to be the causative agent. The organism was later identified as Acholeplasma laidlawii by using a fluorescent antibody procedure and was demonstrated to be nonpathogenic. Parenteral injection of the organism into healthy largemouth bass fingerlings produced no signs of disease or difference in growth rate compared with control fish during a 16-month period. Field studies resulted in isolation of A. laidlawii from black crappies Pomoxis nigromaculatus , bluegills Lepomis macrochirus , and redear sunfish L. microlophus , but not from noncentrarchids in Lake Harris or from any fish species in a control fishery (Lake Holly, Florida). The absence of organisms in all emaciated bass, our inability to reproduce the disease, and isolation of the organism from seemingly healthy fish suggest this organism was not pathogenic.

Journal of Aquatic Animal Health↗

USGS2008

Large-scale marine ecosystem change and the conservation of marine mammals

Papers in this Special Feature stem from a symposium on large-scale ecosystem change and the conservation of marine mammals convened at the 86th Annual Meeting of the American Society of Mammalogists in June 2006. Major changes are occurring in multiple aspects of the marine environment at unprecedented rates, within the life spans of some individual marine mammals. Drivers of change include shifts in climate, acoustic pollution, disturbances to trophic structure, fisheries interactions, harmful algal blooms, and environmental contaminants. This Special Feature provides an in-depth examination of 3 issues that are particularly troublesome. The 1st article notes the huge spatial and temporal scales of change to which marine mammals are showing ecological responses, and how these species can function as sentinels of such change. The 2nd paper describes the serious problems arising from conflicts with fisheries, and the 3rd contribution reviews the growing issues associated with underwater noise. ?? 2008 American Society of Mammalogists.

Conference Paper↗

USGS2007

The relationship between circulating ecdysteroids and chela allometry in male tanner crabs: Evidence for a terminal molt in the genus Chionoecetes

Whether male Tanner crabs, Chionoecetes bairdi, undergo a terminal molt associated with a change in claw allometry has long been debated. We measured molting hormone levels in captured male C. bairdi to assess the potential for molting. We plotted a frequency histogram of chela height to carapace width ratios and found a bimodal distribution of crabs with a ratio of approximately 0.18 separating the two modes. Male crabs with a ratio less than 0.18 were classified as "small-clawed" (SC) while crabs with a ratio greater than 0.18 were classified as "large-clawed" (LC). Circulating molting hormones between SC and LC crabs were compared. Significantly lower ecdysteroid levels were found in LC crabs, indicating that this morphotype had negligible potential for molting. Circulating ecdysteroids were measured in SC males of different shell conditions (soft, new, old, and very old) and no significant differences were found. This research suggests that the molt to LC morphology is a terminal molt. The results from this study have important implications for fisheries management because sub-legal LC males will not recruit into the fishery and removal of larger males may have long term effects on population size structure.

Journal of Crustacean Biology↗