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Joseph D. Conroy

Publications and source records attributed to Joseph D. Conroy.

2 recordsLinked to original sources

An introduction to standardized sampling

In 2009, the first edition of Standard Methods for Sampling North American Freshwater Fishes was published. This was the first time in the history of fisheries science that standardization of methods and equipment had taken place on such a large geographic scale. Since its publication, the methods have been used extensively across North America by local, state, and federal agencies, organizations, and universities who have seen the advantages of large-scale data comparison. Authors have been invited to present these methods in other locations around the world to help with standard sampling programs on other continents. Now, with large-scale issues such as human-caused climate change, effects of landscape-scale regulations, and effects of habitat degradation continuing to increase in importance, the ability to compare data across wide regions and political boundaries, compare data over time, and collect data with improved accuracy and precision is more important than ever. This new edition of Standard Methods is sponsored by the American Fisheries Society (AFS), the U.S. Fish and Wildlife Service, and the Association of Fish and Wildlife Agencies (AFWA), with contributions by numerous state, provincial and federal agencies, and numerous academic institutions and nongovernmental organizations (NGOs). It is authored by over 100 experts in fisheries sampling from across Canada, Mexico, and the United States. Most techniques for water body types addressed in the first edition have been kept the same-in the interest of standardization over time; however, many important additions have been made. Like the first edition, these methods are designed for fish community assessments in North American aquatic systems (e.g., for this edition, lakes, ponds, rivers, and streams containing warmwater and coldwater species; the Great Lakes, wetlands, and cenotes). Although other methods may be available that better target a more specific size-group or species, these techniques were selected as most effective for general surveys of these systems and typically are the most effective for capturing the common fishes found in these waters.

Book chapter

Dynamic hypoxic zones in Lake Erie compress fish habitat, altering vulnerability to fishing gears

Seasonal degradation of aquatic habitats from hypoxia occurs in numerous freshwater and coastal marine systems and can result in direct mortality or displacement of fish. Yet, fishery landings from these systems are frequently unresponsive to changes in the severity and extent of hypoxia, and population-scale effects have been difficult to measure except in extreme hypoxic conditions with hypoxia-sensitive species. We investigated fine-scale temporal and spatial variability in dissolved oxygen in Lake Erie as it related to fish distribution and catch efficiencies of both active (bottom trawls) and passive (trap nets) fishing gears. Temperature and dissolved oxygen loggers placed near the edge of the hypolimnion exhibited much higher than expected variability. Hypoxic episodes of variable durations were frequently punctuated by periods of normoxia, consistent with high-frequency internal waves. High-resolution interpolations of water quality and hydroacoustic surveys suggest that fish habitat is compressed during hypoxic episodes, resulting in higher fish densities near the edges of hypoxia. At fixed locations with passive commercial fishing gear, catches with the highest values occurred when bottom waters were hypoxic for intermediate proportions of time. Proximity to hypoxia explained significant variation in bottom trawl catches, with higher catch rates near the edge of hypoxia. These results emphasize how hypoxia may elevate catch rates in various types of fishing gears, leading to a lack of association between indices of hypoxia and fishery landings. Increased catch rates of fish at the edges of hypoxia have important implications for stock assessment models that assume catchability is spatially homogeneous.

Ohio