The Fisheries Habitat and Ecosystem Program (FHEP) is working to understand how habitat changes impact Maryland's fisheries in the Chesapeake Bay. Our focus has been primarily on understanding how urbanization limits habitat for fish.
Maryland's population and land use has increased significantly. The amount of land being developed outpaces population growth. Between 1973 and 2010, developed land increased by 154 percent while population grew by only 39 percent. By 2035, 1,000,000 new residents and 500,000 new homes will be added to Maryland according to the Department of Planning.
Studies by the Fisheries Habitat and Ecosystem Program have found strong links between increased development and declining fish habitat quality in tidal tributaries of Chesapeake Bay. These links have led to creation of thresholds and targets for development to consider when managing fisheries and planning for development. These thresholds and targets use impervious cover (hard surfaces such as pavement and rooftops that are impenetrable to runoff of rain and snow melt) as a measure of development. Impervious surface thresholds describe tipping points where habitat becomes poor for fish and shellfish. This is the upper limit of impervious surface. Development beyond this limit will severely limit habitat for fish and shellfish. Impervious surface targets describe a development level that can be considered safe for fish and shellfish habitat. These targets and thresholds are being communicated to planners and the public through a simple message, "land conservation is fish conservation!" as a reminder that forests, wetlands, other natural areas, and working farms are keys to productive Chesapeake Bay fisheries.
It is clear that development is a major threat to Maryland's natural resources and the critical ecosystem functions provided by watersheds. The impact of development on aquatic habitats is quite well documented in the scientific literature. Impervious surface increases flow extremes (lower lows and more flooding), erosion, and sediment. As trees are lost, runoff temperature of water increases. Nutrients from developed lands can be as plentiful as nutrient inputs from agriculture and cause algae blooms that deplete oxygen. In winter, more roads require more salt that pollutes streams and kills freshwater organisms, including fish. Other pollutants such as toxic metals (lead for example) and organic pollutants (oil, grease, and pesticides) enter waterways in urban runoff and wastewater. Some compounds that enter wastewater treatment facilities may not be removed. These compounds may reduce success of fish spawning and make fish less safe to eat. Fish become less abundant and less diverse in polluted waters that result from high development and impervious surface.
"Every Maryland citizen lives within at least 15 minutes of a stream or river" - Maryland StreamHealth
Our goal is to develop ecosystem-based fishery management strategies that will sustain fish communities in the future. In order to do this, we are working to identify fishery and ecosystem interactions with land use and water quality stressors. We work with the public and other local, state, and federal government agencies to enable Maryland's Fisheries Service to develop ecosystem-based fishery management strategies that sustain services by fish (including shellfish) communities into the future. The role of others in ecosystem-based management is important since Fisheries Service (and even DNR) does not have authority to manage whole watersheds.
Fisheries managers do not have authority to manage land-use so they have to consider managing fish differently at different levels of development. The target level of development for fisheries is indicated by about 5% impervious surface or less. This target level of development in Maryland is characterized by forests, working farms, and wetlands that support productive fish habitat and fisheries. Land-use at this level does not undermine effectiveness of harvest controls for sustaining fish populations. Preserving watersheds at this level of development would be ideal. Once above this level of development, increasing consideration has to be given to habitat preservation and revitalization. Lowering harvest levels may be able to offset habitat degradation.
The threshold of development of 10% impervious surface represents a suburban landscape where serious aquatic habitat degradation becomes apparent. At this point, conservation of remaining natural lands and habitat revitalization will be the primary tools for fishery sustainability.
When a watershed reaches 15% impervious cover, the likelihood of recovery is marginal. At this level of disturbance, ecological functions supporting quality fish habitat have been highly altered. Presently, there is no scientific evidence that re-engineering can fully restore these functions to promote sustainable fisheries, leaving fisheries managers few options for managing populations. Harvest restrictions become increasingly ineffective in stemming fishery declines when fisheries are substantially less productive.
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