Geology topics

D.G. Simpkins

Publications and source records attributed to D.G. Simpkins.

8 recordsLinked to original sources

USGS2019

Growth of hatchery‐reared chinook salmon in Lakes Michigan and Huron exhibits limited spatial variation but Is temporally linked to alewife abundance

Chinook Salmon Oncorhynchus tshawytscha were introduced into Lakes Michigan and Huron in the 1960s to diversify recreational fisheries and reduce overabundant, nonnative Alewife Alosa pseudoharengus. Alewife remain the primary prey of Chinook Salmon but have experienced substantial declines in abundance due to reduced food resources and salmonine predation pressure. The movements of Chinook Salmon have been linked to the density and spatial distribution of Alewife, but spatial patterns in Chinook Salmon growth have not been well documented and the temporal relationship between growth and Alewife density has not been evaluated during the current period of low Alewife abundance. We evaluated spatial and temporal variation in growth of Chinook Salmon in Lake Michigan and the U.S. waters of Lake Huron and explored linkages with Alewife density. Von Bertalanffy growth parameters were generally similar for recaptured coded‐wire‐tagged Chinook Salmon from different stocking locations and different recovery locations. Only a few small differences among stocking and recovery regions were evident, with regions divided into two subtly different groups with shared growth parameters. The small regional differences may be attributable to unique habitat and/or stocking characteristics of specific regions. In Lake Michigan average Chinook Salmon length at age also varied across years and was tightly coupled with annual lakewide densities of age‐1 and older Alewife, suggesting that Chinook Salmon growth from 2012 to 2016 was constrained by Alewife density. Our findings are consistent with evidence of lakewide movements associated with foraging and support continued management of Chinook Salmon in Lake Michigan as a single population. Furthermore, similar growth in Chinook Salmon from Lakes Michigan and Huron corroborates evidence that Chinook Salmon move from U.S. waters of Lake Huron to Lake Michigan to feed and reinforces the recent decision to include most fish stocked in northwestern Lake Huron in the Lake Michigan population when managing for predator–prey balance.

Lake Michigan, Lake Huron↗

USGS2011

Identifying structural elements needed for development of a predictive life-history model for pallid and shovelnose sturgeons

Intensive management of the Missouri and Mississippi Rivers has resulted in dramatic changes to the river systems and their biota. These changes have been implicated in the decline of the pallid sturgeon ( Scaphirhynchus albus ), which has been listed as a United States federal endangered species. The sympatric shovelnose sturgeon ( S. platorynchus ) is more common and widespread but has also been in decline. The decline of pallid sturgeon is considered symptomatic of poor reproductive success and low or no recruitment. In order to organize information about these species and provide a basis for future development of a predictive model to help guide recovery efforts, we present an expert-vetted, conceptual life-history framework that incorporates the factors that affect reproduction, growth, and survival of shovelnose and pallid sturgeons.

Alabama, Arkansas, Colorado, Georgia, Illinois, In↗

USGS2004

Constraints of body size and swimming velocity on the ability of juvenile rainbow trout to endure periods without food

The hypothesis that body size and swimming velocity affect proximate body composition, wet mass and size-selective mortality of fasted fish was evaluated using small (107 mm mean total length, LT) and medium (168 mm mean LT) juvenile rainbow trout Oncorhynchus mykiss that were sedentary or swimming (c. 1 or 2 body lengths-1) and fasted for 147 days. The initial amount of energy reserves in the bodies of fish varied with L T. Initially having less lipid mass and relatively higher mass-specific metabolic rates caused small rainbow trout that were sedentary to die of starvation sooner and more frequently than medium-length fish that were sedentary. Swimming at 2 body length s-1 slightly increased the rate of lipid catabolism relative to 1 body length s-1, but did not increase the occurrence of mortality among medium fish. Death from starvation occurred when fish had <3.2% lipid remaining in their bodies. Juvenile rainbow trout endured long periods without food, but their ability to resist death from starvation was limited by their length and initial lipid reserves. ?? 2004 The Fisheries Society of the British Isles.

Journal of Fish Biology↗

USGS2004

Factors affecting swimming performance of fasted rainbow trout with implications of exhaustive exercise on overwinter mortality

We evaluated the effects of body size, water temperature, and sustained swimming activity on swimming performance and the effects of exhaustive exercise on mortality of fasted juvenile rainbow trout. Fasting caused swimming performance to decline more rapidly for small fish than large fish, and warmer water temperatures and sustained swimming activity further decreased swimming performance. Exhaustive exercise increased mortality among fasted fish. Our observations suggest that juvenile rainbow trout with little or no food intake during winter can swim for long periods of time with little effect on mortality, but swimming to exhaustion can enhance mortality, especially among the smallest juveniles.

Journal of Freshwater Ecology↗

USGS2003

Interacting effects of water temperature and swimming activity on body composition and mortality of fasted juvenile rainbow trout

Abstract: We assessed changes in proximate body composition, wet mass, and the occurrence of mortality among sedentary and actively swimming (15 cm/s) juvenile rainbow trout (Oncorhynchus mykiss) (120-142 mm total length) that were held at 4.0, 7.5, or 15.0 ??C and fasted for 140 days. Warmer water temperatures and swimming activity accentuated declines in lipid mass, but they did not similarly affect lean mass and wet mass. Swimming fish conserved lean mass independent of water temperature. Because lean mass exceeded lipid mass, wet mass was not affected substantially by decreases in lipid mass. Consequently, wet mass did not accurately reflect the effects that water temperature and swimming activity had on mortality of fasted rainbow trout. Rather, lipid mass was more accurate in predicting death from starvation. Juvenile rainbow trout survived long periods without food, and fish that died of starvation appeared to have similar body composition. It appears that the ability of fish to endure periods without food depends on the degree to which lipid mass and lean mass can be utilized as energy sources.

Canadian Journal of Zoology↗

USGS2003

Physiological responses of juvenile rainbow trout to fasting and swimming activity: Effects on body composition and condition indices

The physiological traits that allow fish to survive periods of limited food resources are poorly understood. We assessed changes in proximate body composition, relative organ mass, blood metabolites, and relative weight (Wr) of sedentary and actively swimming (15 cm/s) juvenile rainbow trout (154-182 mm total length) over 147 d of fasting. Fasting caused measurable responses that were augmented when fish were swimming. Lipids and plasma triacylglycerides declined over time. Proteins were catabolized simultaneously with lipid reserves, but ammonia concentrations in plasma did not increase. The liver somatic index (LSI) did not change substantially over 105 d, suggesting that gluconeogenesis maintained blood glucose concentrations and hepatic glycogen reserves for a substantial period of fasting. The gut somatic index (GSI) and Wr declined linearly during fasting, but the LSI did not decline until after 105 d of fasting. Consequently, the use of different body condition indices could lead to different conclusions about the condition of juvenile rainbow trout. Swimming activity caused fish to have lower lipid and protein reserves than those of sedentary fish. No mortalities were observed among sedentary fish, but mortalities occurred among actively swimming fish after 97 d of fasting when 3.2% or less lipid remained in their bodies. Body condition indices did not account for differences in proximate body composition between sedentary and actively swimming fish and were relatively poor predictors of lipid content and risk of mortality. The probability of mortality was most accurately predicted by percent lipid content. Therefore, we suggest that fisheries scientists consider using percent lipid content when evaluating the physiological status and risk of mortality due to starvation among juvenile rainbow trout.

Transactions of the American Fisheries Society↗

USGS2003

Effect of swimming activity on relative weight and body composition of juvenile rainbow trout

Fisheries managers often assess body condition using relative weight (Wr) because it provides a comparative measure of fish plumpness among individuals and populations. However, it is not known whether the morphological information that Wr summarizes reflects physiological measures, such as relative lipid reserves, in rainbow trout Oncorhynchus mykiss. The purpose of this study was to determine whether swimming activity affects either the Wr or proximate body composition of juvenile (total length, 170-260 mm) rainbow trout. When rainbow trout from a hatchery were fed ad libitum for 147 d, inactive (no current) and active (15 cm/s current velocity) fish did not differ in Wr However, inactive rainbow trout maintained relatively constant lipid levels, whereas active fish declined in lipid content. Relative weight may provide a comparable measure of body form, but it is not an accurate index of lipid content between active and inactive rainbow trout fed an excess ration. For assessing the physiological condition of rainbow trout, measurement of proximate body composition appears to be more accurate than indices based on length and weight.

North American Journal of Fisheries Management↗

USGS2000

Drifting invertebrates, stomach contents, and body conditions of juvenile rainbow trout from fall through winter in a Wyoming tailwater

We investigated the availability of drifting invertebrates and the stomach contents and body conditions of stocked (hatchery) and naturally spawned (wild) juvenile (20-25 cm total length) rainbow trout from fall through winter in the Big Horn River downstream from Boysen Dam in Wyoming. When the density and biomass of drifting invertebrates declined with water temperature during the fall, stomach contents and body conditions substantially decreased among both wild and stocked fish. During the coldest portion of the winter, the density of small drifting invertebrates increased as did the body conditions of both wild and hatchery trout. We suggest that the perceived increase in body conditions during late winter was due to survival of fish with higher body conditions and not growth of fish from fall to late winter.

Transactions of the American Fisheries Society↗