Estimating exploitable stock biomass for the Maine green sea urchin (Strongylocentrotus droebachiensis) fishery using a spatial statistics approach

The objective of this study was to investigate the spatial patterns in green sea urchin (Strongylocentrotus droebachiensis) density off the coast of Maine, using data from a fishery-independent survey program, to estimate the exploitable biomass of this species. The dependence of sea urchin variables on the environment, the lack of stationarity, and the presence of discontinuities in the study area made intrinsic geostatistics inappropriate for the study; therefore, we used triangulated irregular networks (TINs) to characterize the large-scale patterns in sea urchin density. The resulting density surfaces were modified to include only areas of the appropriate substrate type and depth zone, and were used to calculate total biomass. Exploitable biomass was estimated by using two different sea urchin density threshold values, which made different assumptions about the fishing industry. We observed considerable spatial variability on both small and large scales, including large-scale patterns in sea urchin density related to depth and fishing pressure. We conclude that the TIN method provides a reasonable spatial approach for generating biomass estimates for a fishery unsuited to geostatistics, but we suggest further studies into uncertainty estimation and the selection of threshold density values

Population Dynamics and Spatial Analysis of the Maine Green Sea Urchin (Strongylocentrotus droebachiensis) fishery

Fisheries research on the green sea urchin in Maine has been limited despite its importance to the state\u27s fishing industry. The objective of this thesis was to generate critical information for the management and monitoring of the Maine green sea urchin fishery. In particular there are three main areas of interest: (1) an investigation of biological reference points; (2) spatial analysis and biomass estimation, and (3) the development of a simulation framework approach to determine an optimal sampling strategy for the fishery-independent survey program. Biological reference points are markers conlrnonly used to monitor and manage fisheries. For the Maine sea urchin fishery, no biological reference point had been estimated as a management target, which made it difficult to determine the status of the stock and develop appropriate management plans. The purpose of this study was to investigate if Fo., and Fmax are appropriate management targets for the Maine sea urchin fishery and how uncertainties associated with them affect their suitability as management targets. A Monte Carlo simulation approach was used with fishery-dependent data to estimate uncertainties in the biological reference points FOJ and Fmx. FO.~ was considered a more suitable as a management target than Fmx because it is precautionary, more robust to estimation uncertainty and usually well defined. Current fishing mortality was greater than Fo,, for all tested variations; in other words, the stock is overfished. Estimates of exploitable biomass and current exploitation rate are essential for determining the current status of the sea urchin stock. With the onset of a fisherindependent survey program, it became possible to conduct a stock assessment that incorporates spatial variability. The objective of this study was to investigate the largescale spatial patterns in sea urchin abundance to estimate the fishery\u27s exploitable biomass. Triangulated irregular networks (TINS) were used to characterize the largescale patterns in the fishery-independent density data by size category and depth. Exploitable biomass estimates were almost identical to estimates calculated using a length-structured fisheries population dynamics model on fisheries-dependent data, providing independent validation of the estimates. The 2001 pilot study for the fishery-independent survey program was extensive, time-consuming and costly, and needed to be optimized to ensure its feasibility as a longterm scientific survey. The high degree of spatial variability in sea urchin abundance, however, prevented us fiom using standard optimization techniques, such as traditional statistics or even geostatistics. Kernel estimation and computer simulations were combined to create a framework for survey optimization. Optimization must decrease sampling intensity, yet produce accurate realizations of the large-scale spatial structure and be compatible with the planned statistical analysis. Considering that the sea urchin data will continue to be analyzed by traditional and spatial statistics, we chose the original fishery-independent survey with a reduction to 10 locations per strata as the optimal strategy. The research presented in this thesis provides the DMR with essential information on the sea urchin stock, suggests new analysis techniques, and recommends a cost and time effective plan for collecting quality long-term fishery-independent data

Controls on anastomosis in lowland river systems: Towards process-based solutions to habitat conservation

Anastomosing rivers were historically common around the world before extensive agricultural and industrial development in river valleys. Few lowland anastomosing rivers remain in temperate zones, and the protection of these river-floodplain systems is an international conservation priority. However, the mechanisms that drive the creation and maintenance of multiple channels, i.e. anabranches, are not well understood, particularly for lowland rivers, making it challenging to identify effective management strategies. This study uses a novel multi-scale, process-based hydro-geomorphological approach to investigate the natural and anthropogenic controls on anastomosis in lowland river reaches. Using a wide range of data (hydrologic, cartographic, remote-sensing, historical), the study (i) quantifies changes in the planform of the River Narew, Poland over the last 100 years, (ii) documents changes in the natural and anthropogenic factors that could be driving the geomorphic change, and (iii) develops a conceptual model of the controls of anastomosis. The results show that 110 km of anabranches have been lost from the Narew National Park (6810 ha), a 42% reduction in total anabranch length since 1900. The rates of anabranch loss have increased as the number of pressures inhibiting anabranch creation and maintenance has multiplied. The cessation of localized water level and channel management (fishing dams, water mills and timber rafting), the loss of traditional floodplain activities (seasonal mowing) and infrastructure construction (embanked roads and an upstream dam) are contributing to low water levels and flows, the deposition of sediment at anabranch inlets, the encroachment of common reed (Phragmites australis), and the eventual loss of anabranches. By identifying the processes driving the loss of anabranches, this study provides transferable insights into the controls of anastomosis in lowland rivers and the management solutions needed to preserve the unique anastomosing river pattern and diverse wet grasslands that are central to the conservation value of lowland floodplains

Impacts of Unionization on Employment, Product Quality and Productivity: Regression Discontinuity Evidence From Nursing Homes

This paper studies the effects of nursing home unionization on numerous labor, establishment, and consumer outcomes using a regression discontinuity design. We find negative effects of unionization on staffing levels and no decline in care quality, suggesting positive labor productivity effects. Some evidence suggests that nursing homes in less competitive local product markets and those with lower union density at the time of election experienced stronger union employment effects. Unionization appears to raise wages for a given worker while also shifting the composition of the workforce away from higher-earning workers. By combining credible identification of union effects, a comprehensive set of outcomes over time with measures of market-level characteristics, this study generates some of the best evidence available on many controversial questions in the economics of unions. Furthermore, it generates evidence from the service sector, which has grown in importance and where evidence has been thin.

Linking temporal scales of suspended sediment transport in rivers: towards improving transferability of prediction

Purpose Suspended sediment (SS) transport in rivers is highly variable, making it challenging to develop predictive models that are applicable across timescales and rivers. Previous studies have identified catchment and hydro-meteorological variables controlling SS concentrations. However, due to the lack of long-term, high-frequency SS monitoring, it remains difficult to link SS transport dynamics during high-flow events with annual or decadal trends in SS transport. This study investigated how processes driving SS transport during high-flow events impact SS transport dynamics and trends observed over longer timescales. Methods Suspended sediment samples from the River Aire (UK) (1989–2017) were used to (i) statistically identify factors driving SS transport over multiple timescales (high-flow events, intra- and inter-annual) and (ii) conceptualize SS transport as a fractal system to help link and interpret the effect of short-term events on long-term SS transport dynamics. Results and discussion Antecedent moisture conditions were a dominant factor controlling event-based SS transport, confirming results from previous studies. Findings also showed that extreme high-flow events (in SS concentration or discharge) mask factors controlling long-term trends. This cross-timescale effect was conceptualized as high fractal power, indicating that quantifying SS transport in the River Aire requires a multi-timescale approach. Conclusion Characterizing the fractal power of a SS transport system presents a starting point in developing transferrable process-based approaches to quantify and predict SS transport, and develop management strategies. A classification system for SS transport dynamics in river systems in terms of fractal power could be developed which expresses the dominant processes underlying SS transport

Toward a conceptual framework of hyporheic exchange across spatial scales

Rivers are not isolated systems but interact continuously with groundwater from their confined headwaters to their wide lowland floodplains. In the last few decades, research on the hyporheic zone (HZ) has increased appreciation of the hydrological importance and ecological significance of connected river and groundwater systems. While recent studies have investigated hydrological, biogeochemical and ecohydrological processes in the HZ at bedform and reach scales, a comprehensive understanding of process-based interactions between factors operating at different spatial and temporal scales driving hyporheic exchange flows (HEFs) at reach scale and larger is still missing. Therefore, this review summarizes the factors and processes at catchment, valley, and reach scales that interact to control spatial and temporal variations in hyporheic exchange flows. By using a multi-scale perspective, this review connects field observations and modelling studies to identify the process driving patterns and dynamics of HEF. Finally, the influence of process interactions over multiple spatial scales is illustrated in a case study, supported by new GIS analyses, which highlights the importance of valley-scale factors to the expression of HEF at the reach scale. This conceptual framework will aid the development of approaches to interpret hyporheic exchange across scales, infer scaling relationships, and inform catchment management decisions

Human impact on river planform within the context of multi-timescale river channel dynamics in a Himalayan river system

Rivers are dynamic landscape features which are often altered by human activity, making it difficult to disentangle human impact on geomorphic change from natural river dynamics. This study evaluated the human impact on river planform change within the context of short- and long-term river channel dynamics in the Himalayan Sutlej and Beas Rivers, by (i) systematically assessing river planform change over centennial, annual, seasonal and episodic timescales; (ii) connecting observed changes to human-environment drivers; and (iii) conceptualising these geomorphic changes in terms of timescale-dependent evolutionary trajectories (press, ramp, pulse). Landsat imagery was used to extract components of the post-monsoon active river channel (1989-2018), using the modified Normalized Differences Water Index to identify the wet river area, and visible red to determine active gravel bars. Findings were compared with a historical map to represent the pre-dam period (1847-1850) and with data on potential driving factors of change (discharge, climate and land cover). River planform characteristics changed significantly over all timescales, exhibiting strong spatiotemporal variation between and within both rivers. Dam construction likely caused channel narrowing and straightening at the centennial scale (press trajectory). In the Sutlej, this process has continued over the last 30 years, likely enforced by the cumulative effect of water abstraction and climatic changes (ramp trajectory). In the Beas, the pattern of change in river planform metrics was less pronounced over the same period and more variable along the length of the river, possibly linked to different dam operations that maintain a higher degree of flow variability and peak flows (press trajectory). High local erosion rates caused by aggregate mining (episodic) in the Sutlej were also observed (pulse trajectory). Expressed as evolutionary trajectories, the observed responses to human activity confirm the importance of legacy effects of human impact on river systems, and stress the dependency on spatial and temporal scales to determine trajectories of change. The multi-timescale assessment and conceptualisation provide insights into different dimensions of human impact on river planform change, which is pivotal to developing holistic management strategie

Temporal variation in suspended sediment transport: linking sediment sources and hydro-meteorological drivers

Suspended sediment concentrations (SSC) in rivers are variable in time due to interacting soil erosion and sediment transport processes. While many hydro‐meteorological variables are correlated to suspended sediment concentrations, interpretation of these correlations in terms of driving processes requires in‐depth knowledge of the catchment. Detailed sediment source information is needed to establish the causal linkages between driving processes and variations in SSC. This study innovatively combined sediment fingerprinting with multivariate statistical analyses of hydro‐meteorological data to investigate how differential contributions of sediment sources control SSC in response to hydro‐meteorological variables during high‐flow events in rivers. Applied to the River Aire (UK), five sediment sources were classified: grassland topsoil in three lithological areas (limestone, millstone grit and coal measures), eroding riverbanks, and street dust. A total of 159 suspended sediment samples were collected during 14 high‐flow events (2015‐2017). Results show substantial variation in sediment sources during high‐flow events. Limestone grassland and street dust, the dominant contributors to the suspended sediment, show temporal variations consistent with variations in total SSC, and are correlated with precipitation and discharge shortly prior and during high‐flow events (i.e. fast mobilisation to and within river). Contrarily, contributions from millstone and coals grassland appear to be driven by antecedent hydro‐meteorological conditions (i.e. lag‐time between soil erosion and sediment delivery). Riverbank material is poorly correlated to hydro‐meteorological variables, possibly due to weak source discrimination or the infrequent nature of its delivery to the channel. Differences in source‐specific drivers and process interactions for sediment transport demonstrate the difficulty in generalising sediment transport patterns and developing targeted suspended sediment management strategies. While more research is essential to address different uncertainties emerging from the approach, the study demonstrates how empirical data on sediment monitoring, fingerprinting, and hydro‐meteorology can be combined and analysed to better understand sediment connectivity and the factors controlling SSC

Quantifying how hydrological and geomorphical dynamics in the land-river interface create opportunities and trade-offs for sustainable development

Abstract and Poste