Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Fisheries”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
USGS2022

Physiological and nutritional constraints on zooplankton productivity due to eutrophication and climate change predicted using a resource-based modeling approach

Emerging evidence suggests that zooplankton production is affected by physiological and nutritional constraints due to climate change and eutrophication, which in turn could have broad implications for food-web dynamics and fisheries production. In this study, we developed a resource-based zooplankton production dynamics model that causally links freshwater cladoceran and copepod daily production-to-biomass (P/B) ratios with water temperature, phytoplankton biomass and community composition, and zooplankton feeding selectivity. This model was used to evaluate constraints on zooplankton growth under four hypothetical scenarios: involving natural plankton community seasonal succession; lake fertilization to enhance fisheries production; eutrophication; and climatic warming. Our novel modeling approach predicts zooplankton production is strongly dependent on seasonal variation in resource availability and quality, which results in more complex zooplankton dynamics than predicted by simpler temperature dependent models. For mesotrophic and hypereutrophic lakes, our study suggests that the ultimate control over zooplankton P/B ratios shifts from physiological control during colder periods to strong resource control during warmer periods. Our resource-based model provided important insights into the nature of biophysical control of zooplankton under a changing climate that has crucial implications for food web energy transfer and fisheries production.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1998

DNA and allozyme markers provide concordant estimates of population differentiation: Analyses of U.S. and Canadian populations of Yukon River fall-run chum salmon ( Oncorhynchus keta )

Although the number of genetic markers available for fisheries research has steadily increased in recent years, there is limited information on their relative utility. In this study, we compared the performance of different "classes" of genetic markers (mitochondrial DNA (mtDNA), nuclear DNA (nDNA), and allozymes) in terms of estimating levels and partitioning of genetic variation and of the relative accuracy and precision in estimating population allocations to mixed-stock fisheries. Individuals from eight populations of fall-run chum salmon ( Oncorhynchus keta ) from the Yukon River in Alaska and Canada were assayed at 25 loci. Significant differences in mitochondrial haplotype and nuclear allele frequencies were observed among five drainages. Populations from the U.S.-Canada border region were not clearly distinguishable based on multilocus allele frequencies. Although estimates of total genetic diversities were higher for the DNA loci ( H t = 0.592 and h = 0.647 for nDNA and mtDNA, respectively) compared with protein allozymes ( H t = 0.250), estimates of the extent of population differentiation were highly concordant across marker classes (mean theta = 0.010, 0.011, and 0.016 for allozymes, nDNA, and mtDNA, respectively). Simulations of mixed-stock fisheries composed of varying contributions of U.S. and Canadian populations revealed a consistent bias for overallocation of Canadian stocks when expected Canadian contributions varied from 0 to 40%, due primarily to misallocations among genetically similar border populations. No single marker class is superior for differentiating populations of this species at the spatial scale examined.

Yukon River↗
USGS2006

AFS men and women differ most in their lifestyle choices

The American Fisheries Society sponsored a survey to examine the career development choices of men and women and how they might differ by gender. A random sample of 700 men and 700 women was selected from the AFS membership database. The survey was mailed out in October 2004 and 991 questionnaires were returned for an adjusted response rate of 71%. Some differences exist between men and women in the areas of interest development, education, and employment, but the substantive differences occur in lifestyle choices. Women with a fisheries career are less likely to be married than men, even when age is controlled for, and women who are married are more likely to have dual-career considerations than their male counterparts. Among respondents without dependents in their home during their professional career, twice as many women as men think having children will adversely affect their career. For those with dependents, more than twice as many women as men said they had to put their career "on hold" because of their dependents. While AFS members do not represent all members of the fisheries profession, their experiences shed substantial light on the lifestyle choices likely faced by most members of the profession.

Fisheries↗
USGS1947

Age and growth of the kiyi, Leucichthys kiyi Koelz, in Lake Michigan

Ages were determined and individual growth histories were calculated from the examination and measurement of the scales of 1,649 kiyis captured at seven localities in Lake Michigan in 1931 and 1932. The numbers of individuals employed for the investigation of other phases of the life history (such as length-frequency distributions, length-weight relationship, and sex ratio) varied according to the amount of data available or required. Age-group IV was dominant in the 1931 collections from Racine, Port Washington, and Kewaunee, Wisconsin, and age-group V dominated the 1932 samples from the Fox Islands and from three localities southward of Manistique, Michigan. A trend was noticeable toward an increase in average age from south to north. Among the explanations suggested for the observed differences in age composition were: Variation with latitude in the natural span of life; differences in fishing intensity; fluctuations in the strength of year classes (to account possibly for the shift in the dominant age group from 1931 to 1932). The oldest male kiyi belonged to the VII group and the oldest female was a member of the X group. The possible distorting effects of such factors as gear selection traceable to differences in the mesh sizes of nets fished in 1931 and 1932, selection by nets on the basis of the condition (K) of the fish, and local variations in fishing intensity and hence in the selective destruction of rapidly growing individuals in the fishery were held to be sufficiently great to render doubtful the significance of most of the observed local differences in growth rate. Kiyis from all samples were combined to determine the general growth in length. The growth in weight of the Fox Islands fish, however, was considered separately as these fish were consistently lighter than kiyis of corresponding length from other localities. The Lake Michigan kiyi grows slowly, with the females growing slightly more rapidly than the males. The grand average calculated lengths indicated, for example, that the females did not attain a total length of 10 inches until the fifth year of life or the males until the sixth. Similarly, the calculated weight of 4 ounces was not reached until the fifth or sixth year (with the actual time varying with sex and locality). The season's growth of the kiyi probably begins sometime in May and most or all of the growth is completed by the end of August. The calculated lengths of the age groups exhibited large discrepancies that differed from “Lee's phenomenon” as ordinarily observed in that the data for the later rather than the earlier years of life were affected most severely. Chief among the factors held responsible for these discrepancies were gear selection and the selective destruction of the more rapidly growing individuals in the fishery. Errors inherent in the (direct-proportion) method of computing growth from scale measurements were considered to have been unimportant. The Lake Michigan kiyi exhibits growth compensation–the tendency for the smaller of the young fish to have the more rapid growth in the later years of life. Comparisons with the average lengths and weights of the age groups of the Lake Ontario kiyi given by Pritchard (1931) indicated the Lake Michigan fish to be the larger at the earlier ages (age-groups II and III) and the smaller at the later ages (age-groups IV to VI). The length-frequency distributions of the age groups exhibited extensive overlap. As many as eight age groups were represented in a single centimeter interval of length. The length frequencies and average lengths of all fish collected, arranged according to the mesh sizes of the gill nets by which they were captured, revealed that the selective action of these nets in the taking of kiyis was much more obvious in the numbers of fish in the catch than in their average size. As an illustration, in 1930–1931, the 2 3/4-inch mesh nets took fish that were only 0.1 inch longer than those in 2 1/2-inch meshes but captured less than one fourth as many. Gill nets fished in northern Lake Michigan in 1932 captured kiyis that averaged 0.2 to 0.4 inch longer than those taken in the same meshes in southern Lake Michigan in 1930–1931. Because of the more slender form of kiyis from the northeastern island region of Lake Michigan, data on the general length weight relationship were compiled separately for fish of that area and for those of the great central basins of the lake. In both regions the weight increased to a power slightly greater than the cube of the length. Available information on condition indicated that the coefficient (K) was higher in August and early September than in May, June, and July. Condition declined from early September to October and early November–the latter period the time of most active spawning. Spawning itself was accompanied by an additional loss of about 12 per cent of the body weight of females and of somewhat less than 2 per cent of the weight of males. Analysis of the variations of K within a group that was homogeneous with respect to age, sex, maturity, and time of collection revealed that a net of a particular mesh size tends to take the heavier of the shorter fish and the lighter of the longer fish within its range of effectiveness. Among fish of the same length the values of K tended to increase with increase in the mesh size of the nets employed for their capture. Practically all fish in the samples were mature (only 11 immature in more than 6,000). These “immature” fish were probably “non-functional” since all of them approached or exceeded the average length of the mature kiyis. Females were strongly predominant in the collections at all seasons but were relatively more plentiful during the summer (90 per cent of the total) than during the spawning period (75 per cent). Possible factors contributing to this predominance of females and to the change in the sex ratio at the spawning season were discussed. A decrease in the relative abundance of males with increase in age appears to be characteristic of the kiyi. This decrease indicates a differential mortality of th sexes (greater relative destruction of males in the spawning period when they are unusually abundant or a greater natural mortality rate for the males). Current fishery regulations on mesh size and closed seasons afford the kiyi good protection but offer no guarantee against depletion from too intensive fishing.

Transactions of the American Fisheries Society↗
USGS1981

Forage species in lakes and reservoirs of the western United States

Fisheries management in the western United States has concentrated on salmonid species, particularly in streams. Forage‐fish management in lakes and reservoirs is not highly developed, and has emphasized introductions of both predators and prey. In coldwater lakes, kokanees Oncorhynchus nerka have been established widely as the principal forage for salmonids and often support a sport fishery themselves. Introductions of other forage organisms in coldwater lakes and reservoirs, notably the opossum shrimp Mysis relicta and redside shiner Richardsonius balteatus have had mixed results due in part to food competition with resident species. A variety of exotic predator and prey species have been introduced in coolwater and warmwater reservoirs. Results have varied greatly, and include establishment of successful sport fisheries, elimination of native fishes, failure of introduced predators or prey, and predation on stocked salmonids. Native forage species generally have been overlooked by management, although there appears to be a large potential for their utilization, particularly with coadapted salmonid species. Better screening procedures for exotic introductions and a concerted investigation of the ecological requirements of both native and introduced predator‐prey combinations are required for intelligent management of western lakes and reservoirs.

western United States↗
USGS1985

Stocking and hooking mortality of planted rainbow trout in Jocassee Reservoir, South Carolina

Attempts to establish a 'put-grow-and-take' fishery for rainbow trout (Salmo gairdneri) in Jocassee Reservoir, South Carolina failed despite plantings of 200,000 fish in 1972-1979 because few of the stocked fish survived to legal size. At the same time, a fishery for brown trout (Salmo trutta) was established successfully by planting far fewer fish. Experiments were conducted to determine if stress at stocking and injuries and stress associated with catch and release of fish by shoreline anglers were responsible for the poor survival of rainbow trout. Only 1 of the 606 rainbow trout stocked in floating wire cages anchored in the reservoir died during the first 3 days, and fewer rainbow trout than brown trout died as a result of catch-and-release fishing during the first 11 days after stocking. Thus, these factors were not responsible for the lack of success in establishing a rainbow trout fishery in this reservoir.

North American Journal of Fisheries Management↗
USGS1992

Fyke-net and gill-net size selectivities for yellow perch in Green Bay, Lake Michigan

We estimated a fyke‐net selectivity function for yellow perch Perca flavescens in Green Bay, Lake Michigan, by comparing length‐frequency distributions of yellow perch captured in fyke nets with different mesh sizes in 1986. Using a length—girth relationship for Green Bay yellow perch, we expressed selectivity as the ratio of girth ( G ) to effective mesh perimeter ( P ), which was 5–7% less than nominal mesh perimeter. Then, fitting an existing gill‐net selectivity function to the Green Bay yellow perch fishery, we found fyke‐net and gill‐net selectivities were similar, with similar G / P ratios, but fyke nets had smaller effective mesh perimeters and thus were more efficient at capturing smaller yellow perch for any given mesh size, The derived fyke‐net selectivity function can be used to determine mesh sizes that minimize the sublegal catch of yellow perch in this fishery and could be applied to entrapment gear in other yellow perch fisheries, given data on the length–girth relationships and effective mesh perimeters.

Wisconsin↗
USGS2005

An empirical model for estimating annual consumption by freshwater fish populations

Population consumption is an important process linking predator populations to their prey resources. Simple tools are needed to enable fisheries managers to estimate population consumption. We assembled 74 individual estimates of annual consumption by freshwater fish populations and their mean annual population size, 41 of which also included estimates of mean annual biomass. The data set included 14 freshwater fish species from 10 different bodies of water. From this data set we developed two simple linear regression models predicting annual population consumption. Log-transformed population size explained 94% of the variation in log-transformed annual population consumption. Log-transformed biomass explained 98% of the variation in log-transformed annual population consumption. We quantified the accuracy of our regressions and three alternative consumption models as the mean percent difference from observed (bioenergetics-derived) estimates in a test data set. Predictions from our population-size regression matched observed consumption estimates poorly (mean percent difference = 222%). Predictions from our biomass regression matched observed consumption reasonably well (mean percent difference = 24%). The biomass regression was superior to an alternative model, similar in complexity, and comparable to two alternative models that were more complex and difficult to apply. Our biomass regression model, log10(consumption) = 0.5442 + 0.9962??log10(biomass), will be a useful tool for fishery managers, enabling them to make reasonably accurate annual population consumption predictions from mean annual biomass estimates. ?? Copyright by the American Fisheries Society 2005.

North American Journal of Fisheries Management↗
USGS2006

Comparing historical catch rates of American shad in multifilament and monofilament nets: A step toward setting restoration targets for Virginia stocks

Recreational and commercial harvest of American shad Alosa sapidissima in the Virginia waters of the Chesapeake Bay and its tributaries has been prohibited since 1994. The Atlantic States Marine Fisheries Commission Shad and River Herring Management Plan requires that Virginia develop restoration targets for its shad populations, but estimates of their sizes are not available and there is little information about historic population levels. Thus, establishing restoration targets based on population size is problematic. A current spawning stock monitoring program yields catch rate information that can be compared with historic catch rate information recorded in commercial fishery logbooks from the 1950s and the 1980s. However, multifilament gill nets were used in the 1950s and monofilament nets were used in the 1980s (as well as in the current monitoring program). A Latin square design was employed to test the differences in relative fishing power of the two gear types over 2 years of seasonal sampling on the York River, Virginia. Estimates are that the monofilament nets are roughly twice as efficient as the multifilament nets. Reported catch rates in the 1950s and 1980s are roughly equivalent. However, when adjustments are made for the differences in fishing gear, catch rates for the 1950s are twice as high as those during the 1980s. These results provide valuable information for setting restoration targets for Virginia stocks of American shad. ?? Copyright by the American Fisheries Society 2006.

North American Journal of Fisheries Management↗
USGS2006

Comparison of native and introduced flathead catfish populations in Alabama and Georgia: Growth, mortality, and management

We compared growth of flathead catfish Pylodictis olivaris from two native populations in Alabama (Coosa and Tallapoosa rivers) and two introduced populations in Georgia (Ocmulgee and Satilla rivers). We also compared mortality rates and potential outcomes of various management regimes (minimum length limits [MLLs]) among the populations. Total length-log10(age) regression slopes for introduced fish were higher than those for native fish, and von Bertalanffy growth coefficients (K) were greater for introduced fish (Ocmulgee: 0.195; Satilla: 0.201) than for native individuals (Coosa: 0.057; Tallapoosa: 0.059). Therefore, introduced flathead catfish grew more rapidly than those in their native range. Mortality (instantaneous mortality rate, Z) was higher in the Satilla River population (Z = -0.602) than in the Ocmulgee River (Z = -0.227) and Coosa River (Z = -0.156) populations. However, fish in the Satilla River population had been introduced for only 10 years and presumably did not reach their theoretical maximum age, potentially biasing the mortality estimate for that population. Simulation of management regimes in Fishery Analyses and Simulation Tools software predicted that maximum biomass of flathead catfish in the Ocmulgee (1,668 kg) and Satilla (1,137 kg) rivers was substantially larger than that in the Coosa (873 kg) and Tallapoosa (768 kg) populations. However, increased exploitation rates in the Ocmulgee and Satilla River populations resulted in dramatic declines in overall biomass, especially at lower MLLs (254 and 356 mm, respectively). Therefore, in systems where introduced flathead catfish represent an important recreational fishery but have dramatically reduced the abundance of native fishes through predation, minimal protection is recommended. We contend that rapid growth of introduced flathead catfish has major implications for their management and the conservation of native fishes. ?? Copyright by the American Fisheries Society 2006.

North American Journal of Fisheries Management↗
USGS2008

Physiological response of some economically important freshwater salmonids to catch-and-release fishing

Catch-and-release fishing regulations are widely used by fishery resource managers to maintain both the quantity and quality of sport fish populations. We evaluated blood chemistry disturbances in wild brook trout Salvelinus fontinalis, brown trout Salmo trutta, cutthroat trout Oncorhynchus clarkii, and Arctic grayling Thymallus arcticus that had been hooked and played for 1-5 min in waters of the intermountain western United States. A hatchery stock of brown trout was included for comparison. To assess time needed for recovery, additional test groups were played for 5 min and then released into net-pens, where they were held for up to 72 h. The osmoregulatory and metabolic disturbances associated with catch-and-release fishing under the conditions we tested were minimal and judged to be well within normal physiological tolerance limits. In fish that were held for recovery, the blood chemistry alterations that did occur appeared to be related to stress from confinement in the net-pens. Our results confirm the results of previous studies, showing that prerelease air exposure and handling cause more physiological stress than does either hooking per se or playing time. Fishery managers must be aware of the differences in the perceptions, attitudes, and values of different societal groups, some of which feel that catch-and-release fishing should be banned because it is cruel to the animals. On the basis of brain anatomy, it seems highly unlikely that fish experience pain in the same manner as humans experience it, because fish lack a neocortex, the brain structure that enables the sensation of pain in higher vertebrates. However, independent of the neurobiological argument, our results indicate that under conditions similar to those tested, fish subjected to catch and release are neither suffering nor particularly stressed. Improved education programs about the relatively benign physiological effects of catch-and-release fishing as a fishery management practice would be beneficial to anglers and the nonfishing public alike.

North American Journal of Fisheries Management↗
USGS2020

Applications of deep convolutional neural networks to predict length, circumference, and weight from mostly dewatered images of fish

Simple biometric data of fish aid fishery management tasks such as monitoring the structure of fish populations and regulating recreational harvest. While these data are foundational to fishery research and management, the collection of length and weight data through physical handling of the fish is challenging as it is time consuming for personnel and can be stressful for the fish. Recent advances in imaging technology and machine learning now offer alternatives for capturing biometric data. To investigate the potential of deep convolutional neural networks to predict biometric data, several regressors were trained and evaluated on data stemming from the FishL™ Recognition System and manual measurements of length, girth, and weight. The dataset consisted of 694 fish from 22 different species common to Laurentian Great Lakes. Even with such a diverse dataset and variety of presentations by the fish, the regressors proved to be robust and achieved competitive mean percent errors in the range of 5.5 to 7.6% for length and girth on an evaluation dataset. Potential applications of this work could increase the efficiency and accuracy of routine survey work by fishery professionals and provide a means for longer‐term automated collection of fish biometric data.

Illinois, Michigan, Ohio↗
USGS2011

Mitigating by-catch of diamondback terrapins in crab pots

Chronic by‐catch of diamondback terrapins ( Malaclemys terrapin ) in blue crab ( Callinectes sapidus ) pots is a concern for terrapin conservation along the United States Atlantic and Gulf of Mexico coasts. Despite the availability of by‐catch reduction devices (BRDs) for crab pots, adoption of BRDs has not been mandated and by‐catch of terrapins continues. We conducted experimental fishing studies in North Carolina's year‐round blue crab fishery from 2000 to 2004 to evaluate the ability of various BRDs to reduce terrapin by‐catch without a concomitant reduction in the catch of blue crabs. In 4,822 crab pot days fished, we recorded only 21 terrapin captures. Estimated capture rates were 0.003 terrapins/pot per day in hard crab experimental fishing and 0.008 terrapins/pot per day in peeler experimental fishing. All terrapin captures occurred from April to mid‐May within 321.4 m of the shoreline. Longer soak times produced more dead terrapins, with 4 live and 4 dead during hard crab experimental fishing and 11 live and 2 dead during peeler experimental fishing. The 4.0‐cm BRDs in fall and 4.5‐cm and 5.0‐cm BRDs in spring reduced the catch of legal‐sized male hard crabs by 26.6%, 21.2%, and 5.7%, respectively. Only the 5.0‐cm BRDs did not significantly affect the catch of legal‐sized hard male crabs. However, BRDs had no measurable effect on catch of target crabs in the peeler crab fishery. Our results identify 3 complementary and economically feasible tools for blue crab fishery managers to exclude terrapins from commercially fished crab pots in North Carolina: 1) gear modifications (e.g., BRDs); 2) distance‐to‐shore restrictions; and 3) time‐of‐year regulations. These measures combined could provide a reduction in terrapin by‐catch of up to 95% without a significant reduction in target crab catch.

North Carolina↗
USGS2022

Food web perspectives and methods for riverine fish conservation

Food web analyses offer useful insights into understanding how species interactions, trophic relationships, and energy flow underpin important demographic parameters of fish populations such as survival, growth, and reproduction. However, the vast amount of food web literature and the diversity of approaches can be a deterrent to fisheries practitioners engaged in on-the-ground research, monitoring, or restoration. Incorporation of food web perspectives into contemporary fisheries management and conservation is especially rare in riverine systems, where approaches often focus more on the influence of physical habitat and water temperature on fish populations. In this review, we first discuss the importance of food webs in the context of several common fisheries management issues, including assessing carrying capacity, evaluating the effects of habitat change, examining species introductions or extinctions, considering bioaccumulation of toxins, and predicting the effects of climate change and other anthropogenic stressors on riverine fishes. We then examine several relevant perspectives: basic food web description, metabolic models, trophic basis of production, mass-abundance network approaches, ecological stoichiometry, and mathematical modeling. Finally, we highlight several existing and emerging methodologies including diet and prey surveys, eDNA, stable isotopes, fatty acids, and community and network analysis. Although our emphasis and most examples are focused on salmonids in riverine environments, the concepts are easily generalizable to other freshwater fish taxa and ecosystems.

Wiley Interdisciplinary Reviews (WIREs): Water↗
USGS1988

Cooperative federal-state liming research on surface waters impacted by acidic deposition

In the eastern and north-central United States, lakes and streams with low acid neutralizing capacity are at risk from acidity. Resource management agencies are interested in developing mitigation strategies that protect or restore fisheries in these waters. Addition of limestone (calcium carbonate) to improve water quality and prevent episodic depressions of pH during precipitation events and spring runoff is one mitigation technique being used. The ecological changes that accompany such treatment of streams and lakes are being investigated in a cooperative program between the U.S. Fish and Wildlife Service and individual states. Streams in Massachusetts, West Virginia and Tennessee, and a lake in Minnesota are included in this 5-yr research program. Intensive monitoring during pre- and post-liming tracks a suite of physical, chemical and biological parameters that influence the re-establishment or maintenance of healthy fisheries. Supporting studies on liming being conducted at Adirondack lakes in New York focus on fisheries management. A model on the influence of liming on light attenuation and thermal stratification is also being developed. Management guidelines are to be generated from the program results.

Massachusetts, Minnesota, Tennessee, West Virginia↗
USGS1999

Effects of recent volcanic eruptions on aquatic habitat in the Drift River, Alaska, USA: Implications at other Cook Inlet region volcanoes

Numerous drainages supporting productive salmon habitat are surrounded by active volcanoes on the west side of Cook Inlet in south-central Alaska. Eruptions have caused massive quantities of flowing water and sediment to enter the river channels emanating from glaciers and snowfields on these volcanoes. Extensive damage to riparian and aquatic habitat has commonly resulted, and benthic macroinvertebrate and salmonid communities can be affected. Because of the economic importance of Alaska's fisheries, detrimental effects on salmonid habitat can have significant economic implications. The Drift River drains glaciers on the northern and eastern flanks of Redoubt Volcano: During and following eruptions in 1989-1990, severe physical disturbances to the habitat features of the river adversely affected the fishery. Frequent eruptions at other Cook Inlet region volcanoes exemplify the potential effects of volcanic activity on Alaska's important commercial, sport, and subsistence fisheries. Few studies have documented the recovery of aquatic habitat following volcanic eruptions. The eruptions of Redoubt Volcano in 1989-1990 offered an opportunity to examine the recovery of the macroinvertebrate community. Macroinvertebrate community composition and structure in the Drift River were similar in both undisturbed and recently disturbed sites. Additionally, macroinvertebrate samples from sites in nearby undisturbed streams were highly similar to those from some Drift River sites. This similarity and the agreement between the Drift River macroinvertebrate community composition and that predicted by a qualitative model of typical macroinvertebrate communities in glacier-fed rivers indicate that the Drift River macroinvertebrate community is recovering five years after the disturbances associated with the most recent eruptions of Redoubt Volcano.

Environmental Management↗
USGS2017

Evaluating stocking efficacy in an ecosystem undergoing oligotrophication

Oligotrophication has negatively affected fisheries production in many freshwater ecosystems and could conceivably reduce the efficacy of stockings used to enhance fisheries. In Lake Michigan, offshore oligotrophication has occurred since the 1970s, owing to reductions in total phosphorus (TP) inputs and nearshore sequestration of TP by nonindigenous dreissenid mussels. We evaluated simultaneous effects of stock enhancement and oligotrophication on salmonine species (Chinook salmon Oncorhynchus tshawytscha , lake trout Salvelinus namaycush , and steelhead O. mykiss ) that support valuable recreational fisheries. We employed a novel application of an Ecopath with Ecosim model by conducting a full factorial simulation experiment. Our design included multiple levels of salmonine stocking, consumption by invasive quagga mussels ( Dreissena bugensis ), and TP that were informed by manager interests. Under all levels of TP and quagga mussel consumption, our results showed that stock enhancement could still increase salmonine biomass, but positive responses were stronger for lake trout and steelhead than Chinook salmon. Simulations showed that quagga mussel consumption has deleterious effects on pelagic-oriented prey fishes and Chinook salmon, which feed almost exclusively on the pelagic-oriented alewife ( Alosa pseudoharengus ). In summary, results from our simulation experiment suggested that lake trout and steelhead are better suited to the current ecosystem than Chinook salmon, and therefore, stock enhancement provides the highest gains for these two species. Furthermore, simulated biomass of all recreational salmonine species increased with increasing TP, indicating the need for managers to consider how potential future oligotrophication will limit the carrying capacity of salmonine biomass in Lake Michigan

Lake Michigan↗
USGS2010

The areal extent of brown shrimp habitat suitability in Mobile Bay, Alabama, USA: Targeting vegetated habitat restoration

The availability of wetlands and shallow water habitats significantly influences Gulf of Mexico (GOM) penaeid shrimp fishery productivity. However, the GOM region has the highest rate of wetland loss in the USA. Protection and management of these vital GOM habitats are critical to sustainable shrimp fisheries. Brown shrimp (Farfantepenaeus aztecus) are a major component of GOM fisheries. We present an approach for estimating the areal extent of suitable habitat for post-larval and juvenile brown shrimp in Mobile Bay, Alabama, using an existing habitat suitability index model for the northern GOM calculated from probabilistic survey of water quality and sediment data, land cover data, and submerged aquatic vegetation coverages. This estuarine scale approach is intended to support targeted protection and restoration of these habitats. These analyses indicate that approximately 60% of the area of Mobile Bay is categorized as suitable to near optimal for post-larval and juvenile shrimp and 38% of the area is marginally to minimally suitable. We identify potential units within Mobile Bay for targeted restoration to improve habitat suitability. ?? 2010 Springer Science+Business Media B.V.

Environmental Monitoring and Assessment↗