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At least 1,369 records · Page 76Linked to original sources
USGS1990

Hamdah ancient gold mines, Kingdom of Saudi Arabia

The Hamdah prospect is a 1.5-km 2 area that includes ancient mine workings 15 km southeast of Hamdah in the southern Arabian Shield. The workings cluster at a gently dipping thrust contact between serpentinite (above) and hornblende schist (below) exposed in a window within the serpentinite. Aplite sills intrude the contact, and gold concentrations occur just above or below it. The ancient mine dumps cover >100,000 m 2 of the prospect and are estimated to be 1.5 to 1.8 m thick. They contain nearly 181,000 metric tons of material at an average grade of 4.5 g/t gold, thus having an estimated total gold content of 831 kg, or 26,726 Troy oz. Almost 100 percent of the contained gold is recoverable by cyanide acid leaching. Eleven new diamond-drill holes were completed to supplement information from 12 drill holes completed during an earlier drilling program, in order to enable more detailed evaluation of the prospect. The drill holes are grouped in the northeast, southeast, southwest, and west quadrants of the prospect. In the northeast quadrant, where 9 drill holes intersect gold at shallow (<27 m) depths, the quadrant is calculated to contain nearly 242,300 metric tons of gold-bearing material. The calculations show: (1) 19,144 metric tons high-grade material grading 21.4 g/t Au at 5 g/t cutoff; (2) 39,884 metric tons of material grading 8.5 g/t Au at 5 g/t cutoff; (3) 71,617 metric tons of material grading 3.9 g/t Au at 1 g/t cutoff; and (4) 111,641 metric tons low-grade material grading 2.0 g/t Au at 1 g/t cutoff. Total gold content of this selected block is 1,251 kg gold, or 40,234 Troy oz. The mineralized zone in 1 the northeast quadrant is open to the northeast, east, and southeast. Drill data are insufficient in detail to allow grade or tonnage estimates for the southeast, southwest, and west quadrants of the prospect. Gold is concentrated in surface alluvium in the southeast and southwest of the prospect, in amounts that are of possible economic significance. Ground geophysical surveys (CEM and VJJ7) revealed the presence of electrical conductors at shallow depths, some of which correlate with possible disseminated sulfide minerals, and others with the thrust contact. It is recommended that the thickness of the dumps be more accurately determined, and that the gold leachability of bulk dump material be tested. Shallow reverse-circulation drilling is recommended on 25-m centers in the northeast quadrant, and diamond drilling is recommended elsewhere at the prospect. Geophysical surveys are required to help establish depths to the serpentinite/schist contact on the northeastern, southern, and western margins of the prospect. Detailed mapping should be undertaken at the prospect, and a mineral-belt type of mapping program should be completed over the larger Hamdah region.

Open-File Report↗
USGS2016

Montana StreamStats—A method for retrieving basin and streamflow characteristics in Montana: Chapter A in Montana StreamStats

The U.S. Geological Survey (USGS) provides streamflow characteristics and other related information needed by water-resource managers to protect people and property from floods, plan and manage water-resource activities, and protect water quality. Streamflow characteristics provided by the USGS, such as peak-flow and low-flow frequencies for streamflow-gaging stations, are frequently used by engineers, flood forecasters, land managers, biologists, and others to guide their everyday decisions. In addition to providing streamflow characteristics at streamflow-gaging stations, the USGS also develops regional regression equations and drainage area-adjustment methods for estimating streamflow characteristics at locations on ungaged streams. Regional regression equations can be complex and often require users to determine several basin characteristics, which are physical and climatic characteristics of the stream and its drainage basin. Obtaining these basin characteristics for streamflow-gaging stations and ungaged sites traditionally has been time consuming and subjective, and led to inconsistent results. StreamStats is a Web-based geographic information system application that was created by the USGS to provide users with access to an assortment of analytical tools that are useful for water-resource planning and management. StreamStats allows users to easily obtain streamflow and basin characteristics for USGS streamflow-gaging stations and user-selected locations on ungaged streams. The USGS, in cooperation with Montana Department of Transportation, Montana Department of Environmental Quality, and Montana Department of Natural Resources and Conservation, completed a study to develop a StreamStats application for Montana, compute streamflow characteristics at streamflow-gaging stations, and develop regional regression equations to estimate streamflow characteristics at ungaged sites. Chapter A of this Scientific Investigations Report describes the Montana StreamStats application and the datasets, streamflow-gaging stations, streamflow characteristics, and regression equations (as described fully in Chapters B through G of this report) that are used for development of the StreamStats application for Montana.

Montana↗
USGS1985

Hydrogeology of the Cross Bar Ranch well-field area and projected impact of pumping, Pasco County, Florida

The hydrogeology and development of a groundwater flow model are described for a 121-square-mile area in Pasco County, Florida. The hydrogeologic framework consists of the surficial aquifer--a thin blanket of sand--and the underlying carbonates of the upper Floridian aquifer. The aquifers are separated by a leaky sand and clay confining unit. The Cross Bar Ranch well field occupies 13 square miles and contains 17 production wells averaging about 700 feet deep and tapping the upper Florida aquifer. Procedures to calibrate, test sensitivity to input parameters, and validate the model 's accuracy are described. Pumping at 30 million gallons per day should result in 5 feet of decline in the water table of the surficial aquifer over an 8-square-mile area and in the potentiometric surface of the Upper Florida aquifer over a 15-square-mile area. Under the 45-million-per-day maximum permitted rate, drawdown should be 5 feet or more in the water table and potentiometric surface over areas of 16 and 28 square miles, respectively. At the center of pumping, water levels could decline 15 to 25 feet. The surficial aquifer could possibly be completely dewatered in a small area of the well field when pumping is at the maximum rate.

Florida↗
USGS2003

Monitoring in the nearshore: A process for making reasoned decisions

Over the past several years, a conceptual framework for the GEM nearshore monitoring program has been developed through a series of workshops. However, details of the proposed monitoring program, e.g. what to sample, where to sample, when to sample and at how many sites, have yet to be determined. In FY 03 we were funded under Project 03687 to outline a process whereby specific alternatives to monitoring are developed and presented to the EVOS Trustee Council for consideration. As part of this process, two key elements are required before reasoned decisions can be made. These are: 1) a comprehensive historical perspective of locations and types of past studies conducted in the nearshore marine communities within Gulf of Alaska, and 2) estimates of costs for each element of a proposed monitoring program. We have developed a GIS database that details available information from past studies of selected nearshore habitats and species in the Gulf of Alaska and provide a visual means of selecting sites based (in part) on the locations for which historical data of interest are available. We also provide cost estimates for specific monitoring plan alternatives and outline several alternative plans that can be accomplished within reasonable budgetary constraints. The products that we will provide are: 1) A GIS database and maps showing the location and types of information available from the nearshore in the Gulf of Alaska; 2) A list of several specific monitoring alternatives that can be conducted within reasonable budgetary constraints; and 3) Cost estimates for proposed tasks to be conducted as part of the nearshore program. Because data compilation and management will not be completed until late in FY03 we are requesting support for close-out of this project in FY 04.

Report↗
USGS2021

Method for compiling temporally and spatially aggregated data on hydraulic fracturing—Treatments and wells

This report provides a step-by-step method for compiling hydraulic fracturing data in the United States from the IHS Markit, 2019, U.S. Well History and Production Relational Database. Data on hydraulically fractured wells include their location (geologic province, State, county), well type (oil or gas), orientation (directional, horizontal, or vertical), spud date, completion date and the hydraulic fracturing treatments, treatment fluids types, treatment fluid volumes, additive types, agent types (“proppants”), and proppant amounts injected. This method also describes how to associate each unique well with the hydraulic fracturing treatments to provide an indication of the total amount of all treatment fluids injected into a well for hydraulic fracturing and the volume of each individual treatment fluid type injected.

Open-File Report↗
USGS2014

Fisheries research and monitoring activities of the Lake Erie Biological Station, 2013

In 2013, the U.S. Geological Survey’s Lake Erie Biological Station successfully completed large vessel surveys in all three of Lake Erie’s basins. Lake Erie Biological Station’s primary vessel surveys included the Western Basin Forage Fish Assessment and East Harbor Forage Fish Assessment as well as contributing to the cooperative multi-agency Central Basin Hydroacoustics Assessment and the Eastern Basin Coldwater Community Assessment (see Forage Task Group and Coldwater Task Group reports, respectively). Further large vessel sampling included individual research data collection as well as assisting with University (e.g., University of Toledo) and agency (e.g., USFWS, USEPA) large vessel sampling needs. Our 2013 vessel operations began on April 4th and concluded on November 21 with a total of 77 large vessel sampling days (83 total days). During this time, crews of the R/V Muskie and R/V Bowfin deployed 174 trawls covering 147 km of lake-bottom, over 13 km of gillnet, collected hydroacoustic data that extended over 250 km of the central and eastern basins, and approximately 180 collective zooplankton, benthos, and water samples. 2013 was the first complete sampling year using the R/V Muskie. Technologies available on the new platform provided opportunities for LEBS to improve data sampling methods and results. An investment was made in mensuration gear for the trawls. This gear is attached to the trawl’s headrope, footrope, and wings; thus, allowing measurement of the area swept and conversion of catches to densities. Another improvement included real-time output of water parameter sonde profiles (e.g., temperature, dissolved oxygen). The ability to view profile data on a tablet allowed quick identification of thermoclines as well as the presence (or absence) of hypoxia. Minor modifications were made to survey designs relative to last year (see 2013 report), and thus, collection of long-term data from the R/V Muskie has commenced. One minor change was that we are now indexing yellow perch maturation data during our fall trawl surveys in response to a request from the Lake Erie Yellow Perch Task Group. Within the following sections, we describe results from our 2013 sampling efforts in Lake Erie.

Report↗
USGS1987

Documentation of computer program VS2D to solve the equations of fluid flow in variably saturated porous media

This report documents FORTRAN computer code for solving problems involving variably saturated single-phase flow in porous media. The flow equation is written with total hydraulic potential as the dependent variable, which allows straightforward treatment of both saturated and unsaturated conditions. The spatial derivatives in the flow equation are approximated by central differences, and time derivatives are approximated either by a fully implicit backward or by a centered-difference scheme. Nonlinear conductance and storage terms may be linearized using either an explicit method or an implicit Newton-Raphson method. Relative hydraulic conductivity is evaluated at cell boundaries by using either full upstream weighting, the arithmetic mean, or the geometric mean of values from adjacent cells. Nonlinear boundary conditions treated by the code include infiltration, evaporation, and seepage faces. Extraction by plant roots that is caused by atmospheric demand is included as a nonlinear sink term. These nonlinear boundary and sink terms are linearized implicitly. The code has been verified for several one-dimensional linear problems for which analytical solutions exist and against two nonlinear problems that have been simulated with other numerical models. A complete listing of data-entry requirements and data entry and results for three example problems are provided. (USGS)

Water-Resources Investigations Report↗
USGS2025

Black abalone surveys at Naval Base Ventura County, San Nicolas Island, California—2022 annual report

The U.S. Geological Survey monitors a suite of intertidal black abalone ( Haliotis cracherodii ) sites at San Nicolas Island, California, in cooperation with the U.S. Navy, which owns the island. The nine rocky intertidal sites were established in 1980 to study the potential effect of translocated southern sea otters ( Enhydra lutris nereis ) on the intertidal black abalone population at San Nicolas Island. The sites were monitored, typically annually or biennially, from 1981 to 1997. Monitoring resumed in 2001 and has been completed annually thereafter. Since 2018, the monitoring has been carried out by the U.S. Geological Survey Western Ecological Research Center. The study sites became particularly important from a management perspective after a virulent disease decimated black abalone populations throughout southern California beginning in the mid-1980s. The disease, withering syndrome, was first observed on San Nicolas Island in 1992, and during the next few years, withering syndrome reduced the black abalone population on San Nicolas Island by more than 99 percent. The black abalone was subsequently listed as endangered under the Endangered Species Act in 2009. The subject of this report is the 2022 survey of the sites and the status of the measured population of black abalone in comparison to long-term patterns (based on data collected since 1981) at San Nicolas Island. Between the years 2000 and 2022, the total monitored black abalone population on the island has grown from roughly 200 to more than 2,000, approximately a ten-fold increase following the disease-related decline. Since it was first consistently measured in 2005, the distance between adjacent black abalone has decreased substantially from approximately 50 centimeters to less than 15 centimeters, indicating that black abalone are sufficiently close together at several of the sites to reproduce successfully. The total black abalone count in 2022 was 2,156, which was 7.9 percent lower than the total count in 2020 but 6.6 percent higher than in 2021. There were increases and decreases among the sites and transects within each site in 2022, but six of the nine sites had higher counts than in the previous year. The 2022 count is one of the highest since 1993, second only to the 2020 count. In 2022, the annual recruitment rate, defined as the percentage of measured black abalone with a shell length of 3 centimeters or less, was the second highest recorded, only slightly less than in 2017.

California↗
USGS1990

Synthesis of soil-plant correspondence data from twelve wetland studies throughout the United States

This report synthesizes the information collected for the U.S. Fish and Wildlife Service in a series of 12 studies designed to describe the relation between soils and vegetation in wetlands located in 11 States throughout the United States. Results of the study demonstrated almost complete agreement between hydric soils and hydrophytic vegetation. However, agreement between nonhydric soils and nonhydric vegetation was not as high because most nonhydric soils lay adjacent to the wetland boundary. There was some evidence that various vegetation layers describe the hydrophytic nature of the vegetation differently than others. Herbaceous species seem to reflect current hydrologic conditions while trees may reflect past hydrologic conditions. Wetland indicator categories for some plants listed in the Fish and Wildlife Service national list of plant species that occur in wetlands may need to be reevaluated as additional data become available. Similarly, soils listed in the Soil Conservation Service hydric soils of the United States list should always be verified in the field prior to assigning them to a hydric category. While wetland hydrology is the critical factor determining wetlands, the use of soils and vegetation are frequently adequate for designating wetland conditions.

Report↗
USGS1996

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1994 through September 1996

This report describes the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data presented are from January 1994 through September 1996, with a focus on data from July through September 1996 (third quarter of 1996). A complete database of ground-water withdrawals and chloride-concentration records since 1985 is maintained by the U.S. Geological Survey. Total rainfall for the period July through September 1996 was 8.94 inches, which is 60 percent less than the mean rainfall of 22.23 inches for the period July through September. July and August are part of the annual dry season, while September is the start of the annual wet season. Ground-water withdrawal during July through September 1996 averaged 1,038,300 gallons per day. Withdrawal for the same 3 months in 1995 averaged 888,500 gallons per day. Ground-water withdrawals have steadily increased since about April 1995. At the end of September 1996, the chloride concentration of water from the elevated tanks at Cantonment and Air Operations were 68 and 150 milligrams per liter, respectively. The chloride concentration from all five production areas increased throughout the third quarter of 1996, and started the upward trend in about April 1995. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations also increased throughout the third quarter of 1996, with the largest increases from water in the deepest monitoring wells. Chloride concentrations have not been at this level since the dry season of 1994. A fuel-pipeline leak at Air Operations in May 1991 decreased total islandwide withdrawals by 15 percent. This lost pumping capacity is being offset by increased pumpage at Cantonment. Six wells do not contribute to the water supply because they are being used to hydraulically divert fuel migration away from water-supply wells by a program of ground-water withdrawal and injection.

Open-File Report↗
USGS1996

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1994 through June 1996

This report describes the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data presented are from January 1994 through June 1996, with a focus on data from April through June 1996 (second quarter of 1996). A complete database of ground-water withdrawals and chloride-concentration records since 1985 is maintained by the U.S. Geological Survey. Cumulative rainfall for April through June 1996 was 22.64 inches, which is 12 percent more than the mean cumulative rainfall of 20.21 inches for April through June. The period April through June is part of the annual dry season. Ground-water withdrawal during April through June 1996 averaged 1,048,000 gallons per day. Withdrawal for the same 3 months in 1995 averaged 833,700 gallons per day. Withdrawal patterns during the second quarter of 1996 did not change significantly since 1991, with the Cantonment and Air Operations areas supplying about 99 percent of total islandwide pumpage. At the end of June 1996, the chloride concentration of water from the elevated tanks at Cantonment and Air Operations were 52 and 80 milligrams per liter, respectively. The chloride data from all five production areas showed no significant upward or downward trends throughout the second quarter of 1996. Potable levels of chloride concentrations have been maintained by adjusting individual pumping rates, and also because of the absence of long-term droughts. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations also showed no significant trends throughout the second quarter of 1996. Chloride concentrations have been about the same since the last quarter of 1995. A fuel-pipeline leak at Air Operations in May 1991 decreased total islandwide withdrawals by 15 percent. This lost pumping capacity is being offset by increased pumpage at Cantonment. Six wells do not contribute to the water supply because they are being used to hydraulically divert fuel migration away from water-supply wells by a program of ground-water withdrawal and injection.

Open-File Report↗
USGS1996

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1994 through March 1996

This report describes the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data presented are from January 1994 through March 1996, with a focus on data from January through March 1996 (first quarter of 1996). A complete database of ground-water withdrawals and chloride-concentration records since 1985 is maintained by the U.S. Geological Survey. Cumulative rainfall for January through March 1996 was about 30 inches, which is 9 percent less than the mean cumulative rainfall of about 33 inches for January through March. The period January through February is the end of the annual wet season, while March marks the start of the annual dry season. Ground-water withdrawal during January through March 1996 averaged 970,300 gallons per day. Withdrawal for the same 3 months in 1995 averaged 894,600 gallons per day. With- drawal patterns during the first quarter of 1996 did not change significantly since 1991, with the Cantonment and Air Operations areas supplying about 99 percent of total islandwide pumpage. At the end of March 1996, the chloride concentration of water from the elevated tanks at Cantonment and Air Operations were 47 and 80 milligrams per liter, respectively. The chloride data from all five production areas showed no significant upward or downward trends throughout the first quarter of 1996. Potable levels of chloride concentrations have been maintained by adjusting individual pumping rates, and also because of the absence of long-term droughts. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations also showed no significant trends throughout the first quarter of 1996. Chloride concentrations have been about the same since the last quarter of 1995. A fuel-pipeline leak at Air Operations in May 1991 decreased total islandwide withdrawals by 15 percent. This lost pumping capacity is being offset by increased pumpage at Cantonment. Six wells do not contribute to the water supply because they are being used to hydraulically divert fuel migration away from water-supply wells by a program of ground-water withdrawal and injection.

Open-File Report↗
USGS2015

Water data to answer urgent water policy questions: Monitoring design, available data and filling data gaps for determining the effectiveness of agricultural management practices for reducing tributary nutrient loads to Lake Erie -- Addendum describing new, expanded, and planned monitoring sites

This Addendum describes new, expanded, and planned water monitoring sites in the Lake Erie drainage basin that were initiated subsequent to the preparation of Betanzo et al. (2015), the primary report with which this Addendum is associated. In addition to the new water monitoring sites, new programs have been initiated that focus on expansion of agricultural management practices to reduce nutrient transport to Lake Erie and facilitate data sharing between researchers involved with agricultural management and water-quality monitoring. This Addendum evaluates the applicability of these new monitoring sites and programs for answering the case-study policy question explored in Betanzo et al. (2015), “How effective are agricultural management practices at reducing nutrients from nonpoint sources at the watershed scale in the Lake Erie drainage basin?” The water monitoring data needs for answering the case-study policy question identified in Table 18 of Betanzo et al. (2015) were used to identify relevant monitoring sites in this Addendum, specifically focusing on total phosphorus (TP), dissolved reactive phosphorus (DRP)1 , and streamflow data (the complete list of parameters needed appears in Table 3 of Betanzo et al. (2015)). The new information summarized in this Addendum consists of water monitoring and agricultural management activities conducted by agencies and organizations whose data were compiled in the nutrient data set described in Betanzo et al. (2015), and programs identified in public news releases. Although this information is considered to be comprehensive and complete as of February 2015, there may be other new or planned water monitoring programs, of which we are not aware, that are not included here.

Indiana, Michigan, New York, Ohio, Pennsylvania↗
USGS2024

Structured science syntheses to inform decision making on Federal public lands

The U.S. Geological Survey, Bureau of Land Management, and U.S. Fish and Wildlife Service partnered to develop a new type of science product: the structured science synthesis. Structured science syntheses are peer-reviewed reports that synthesize science information about a priority resource management issue on public lands. Structured science syntheses are developed explicitly to facilitate the application of science to decision making. Key characteristics of structured science syntheses include that they are coproduced with resource managers, developed using clear, repeatable methods and designed for ease of use. The syntheses include different types of science information needed for analyses completed under the National Environmental Policy Act.

Fact Sheet↗
USGS2011

Comparative mobility of sulfonamides and bromide tracer in three soils

In animal agriculture, sulfonamides are one of the routinely used groups of antimicrobials for therapeutic and sub-therapeutic purposes. It is observed that, the animals when administered the antimicrobials, often do not completely metabolize them; and excrete the partially metabolized forms into the environment. Due to the continued use of antimicrobials and disposal of untreated waste, widespread occurrence of partially metabolized antimicrobials in aquatic and terrestrial environments has been reported in various scientific journals. In this research, the mobility of two sulfonamides - sulfamethazine (SMN), sulfathiazole (STZ) and a conservative bromide tracer was investigated in three soils collected from regions in the United States with large number of concentrated animal-feed operations. Results of a series of column studies indicate that the mobility of these two sulfonamides was dependent on pH, soil charge density, and contact time. At low pH and high charge density, substantial retention of sulfonamides was observed in all three soils investigated, due to the increased fraction of cationic and neutral forms of the sulfonamides. Conversely, enhanced mobility was observed at high pH, where the sulfonamides are predominantly in the anionic form. The results indicate that when both SMN and STZ are predominantly in anionic forms, their mobility approximates the mobility of a conservative bromide tracer. This observation is consistent for the mobility of both SMN and STZ individually, and also in the presence of several other antimicrobials in all three soils investigated. Higher contact time indicates lower mobility due to increased interaction with soil material.

Journal of Environmental Management↗
USGS2001

Long-term monitoring of creep rate along the Hayward fault and evidence for a lasting creep response to 1989 Loma Prieta earthquake

We present results from over 30 yr of precise surveys of creep along the Hayward fault. Along most of the fault, spatial variability in long-term creep rates is well determined by these data and can help constrain 3D-models of the depth of the creeping zone. However, creep at the south end of the fault stopped completely for more than 6 years after the M7 1989 Loma Prieta Earthquake (LPEQ), perhaps delayed by stress drop imposed by this event. With a decade of detailed data before LPEQ and a decade after it, we report that creep response to that event does indeed indicate the expected deficit in creep.

Geophysical Research Letters↗
USGS1997

History of Fire and Fire Impacts at Tonto National Monument, Arizona

A study of the history of fire and fire impacts on desert plants of Tonto National Monument was made in 1990-1991 by the author. Four major fires and several minor ones have occurred on the monument since 1942, all lightning caused. Twenty photo stations set up after the 1964 Schultz Fire were found and replicate photos made at the rebar-marked sites. Photographic documentation of the impacts of several fires made comparison of vegetation changes over time possible. Five monitoring plots were established in March and April 1990, representing a variety of vegetation associations in burned and unburned areas. An inventory of plants of the monument was completed in 1964 by Burgess (1965) prior to the first major fire. Comparisons of change across the 26-year span were made during this study. The effects of fire?in some areas multiple fires?were determined and reported on.

Technical Report↗
USGS1946

The whitefish fishery of Lakes Huron and Michigan with special reference to the deep-trap-net fishery

This study of the whitefish fishery of Lakes Huron and Michigan includes: (1) a review of the available statistics of production, 1879-1942; (2) a detailed analysis of the annual fluctuations in the production and abundance of whitefish and in the intensity of the whitefish fishery in the State of Michigan waters of the lakes, 1929-1942, with special reference to the effects of fishing with deep trap nets; (3) an account of the bathymetric distribution and vertical movements of whitefish and certain other species; and (4) a report of field observations made in 1931 and 1932, as related particularly to the destruction of undersized whitefish by pound nets and deep trap nets. The main body of the manuscript and appendices A, B, and C, completed in March 1942, contain statistics through the year 1939. Since that time, records for the years 1940-1942 have become available. Because these additional data did not alter any of the conclusions of the manuscript but actually strengthened them, it was not deemed justifiable to expend the considerable amount of time and money that would be required to revise the study. The 1940-1942 records are therefore presented in appendix D. From a relatively high production in the earlier years of the period, 1879 to 1942, the yield of whitefish declined to a lower level about which the catch fluctuated until the late 1920's and early 1930's when a general increase in production occurred. This recent increase was higher and the subsequent decline more severe in the Michigan waters of Lake Huron than in other areas.

Lake Huron, Lake Michigan↗