Roads and other transportation corridors have profound effects on wildlife populations. They represent major sources of pollutant load, and they can be barriers to dispersal for many species, fragmenting habitat and leading to genetic isolation of local populations. The ecological effects of roads are described in several reviews (Trombulak and Frissell 2000), including some focused specifically on certain taxonomic groups that are heavily impacted, such as reptiles and amphibians (Andrews et al. 2008). Previous analyses estimate that between 89 and 340 million birds die annually from vehicle collisions on U.S. roads (Loss et al. 2014). Diamondback Terrapins are heavily impacted by vehicular mortality (Wood and Herlands 1997). 

While total road mileage in Delaware increased by only 1% from 2010 to 2015 and 1.5% from 2015 to 2020, the rate of increase accelerated to more than 64% between 2020 and 2023, resulting in a total net increase of 4,351 miles of roads since 2010. 

Total Miles of Public Roads in Delaware, 2010-2023 

Road Type	2010	2015	2020	2023
Urban	2,991	3,406	3,663	4,599
Rural	3,346	3,010	2,862	6,129
Total	6,377	6,416	6,525	10,728

In Delaware, the state maintains approximately 90% of roads, as compared to a national average of 20% (Delaware OSPC 2023). This largely centralized maintenance system affords significant opportunity for coordinated action at the state level with regard to the impacts of roads and road maintenance on wildlife, including SGCN. Coordination and collaboration with the Delaware Department of Transportation (DelDOT) to minimize transportation impacts on fish and wildlife is an ongoing effort and priority. 

Road Salt 

DelDOT pretreats roads before winter storms with a liquid brine solution, then spreads road salt once snow begins to fall. Road de-icing salts are washed off roadways by meltwater and rains and enter aquatic systems via groundwater (Gedlinske 2013) and surface runoff. Salts are also sequestered in soils and are taken up by roadside vegetation. 

Salts from road de-icing have serious detrimental effects on wildlife, especially amphibians (Sanzo and Hecnar 2006). The amphibians most affected are often vernal pool breeders (Karraker et al. 2008), which are already some of the rarest and most threatened SGCN in Delaware due to many other factors, such as development, wetland loss, and climate change effects. Freshwater mussels, another highly imperiled group of SGCN, are highly affected by increased chloride concentrations in streams as a result of de-icing pollution (Todd and Kaltenecker 2012).

Because road salts cumulatively build in roadside soils, they influence both the plant species composition of these areas as well as the chemical composition of the plants themselves, which can in turn have serious detrimental effects on development of herbivorous insects, including butterflies and moths (Snell-Rood et al. 2014). The severe, long-term indirect effects of road salt are only recently being fully investigated (Findlay and Kelly 2011). Recent remote-sensing studies suggest that road salt contributes to tree mortality in forested systems with both immediate and delayed responses being evident in the data (Fan et al. 2014). Designation and signage of reduced salt areas adjacent to sensitive habitats, freshwater wetlands, and groundwater recharge areas have been accomplished in other Northeast states and should be explored for Delaware. 

Shipping Activity

Shipping activity is high in the Delaware River and Bay due to the presence of deep-water ports in Wilmington, DE and Philadelphia, PA. Direct effects of shipping activity include the potential for spills of oil and other toxic products as well as the possibility of vessel strikes of fish, turtles, marine mammals, and other SGCN. Vessel strikes are reported to be a major factor in marine mammal and sea turtle mortality and injury from the Atlantic coast states. The Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) is at especially high risk for vessel strikes due to their preference for the deeper waters of the shipping channel (Brown and Murphy 2010). Dead sturgeon with injuries consistent with vessel strikes have been found in a number of locations along the Delaware River. Studies indicate that sturgeon spend much of their time near the channel bottom and do not exhibit avoidance of dredges (Reine et al. 2014), so annual maintenance dredging of the shipping channel may also be a significant cause of mortality. Indirect effects of main channel deepening associated with shipping on the Delaware River include an estimated 4 km upstream shift in the salt front, with concurrent shift in the turbidity zone, both of which will significantly impact Atlantic Sturgeon spawning habitat (Breece et al 2013). 

Biological Resource Use

Hunting & collecting terrestrial animals

This category includes threats from the consumptive use of biological resources, including deliberate and unintentional harvesting, as well as the persecution or control of specific species (Salafsky et al. 2008). This threat has been identified as an issue for many amphibian and reptile SGCN primarily due to the collection of these animals for the pet trade.  

The collecting of reptiles and amphibians for the pet trade is a potential threat in Delaware, especially for the following SGCN: Bog Turtle (Glyptemys muhlenbergii), Spotted Turtle (Clemmys guttata), Eastern Kingsnake (Lampropeltis getula), Eastern Milk Snake (Lampropeltis triangulum), and Eastern Tiger Salamander (Ambystoma tigrinum). 

Overharvesting or bycatch of aquatic resources 

Overharvest or bycatch in legal harvest can be issues that affect many aquatic SGCN. However, regulations on harvest set by the state, as well as Atlantic States Marine Fisheries Commission (ASMFC) and Mid-Atlantic Fishery Management Council (MAFMC) help to ameliorate these threats for most managed fisheries. Nevertheless, both recreational and commercial fishermen (fin and shellfish) should take precautions to minimize impacts on nontarget species to maintain healthy ecosystem function and balance in aquatic food webs. 

A particularly important example in Delaware is the Horseshoe Crab (Limulus polyphemus). Despite a male-only harvest limit for the fishery in Delaware, the coastwide harvest for biomedical use has recently approached the same magnitude as the bait fishery, although only 15% mortality is assumed for crabs harvested for this purpose. ASMFC collects data on the biomedical harvest from the states as a requirement of Addendum III to the Horseshoe Crab Fishery Management Plan (FMP). Since 2007, the estimated annual mortality from biomedical harvest has exceeded the ASMFC’s suggested action threshold for this metric. The biomedical harvest takes a large percentage of female crabs, even though male-only harvest is currently regarded as the best management alternative for the fishery. Of the total biomedical collections in 2023, males accounted for 52.9%, and females comprised 47.1%.  Delaware currently has no biomedical collection.++

Human Disturbance 

Direct human disturbance is an issue for some SGCN and habitats in Delaware. Recreational pressure is heavy in Delaware’s State Parks system, especially on beaches and coastal dunes, which are naturally susceptible to compaction and erosion. Direct disturbance of breeding, migrating, and overwintering shorebirds and waterfowl is an issue along much of the Delaware coast, especially from uncontrolled off-road vehicle (ORV) access, much of which occurs on private lands. Some groups of SGCN, including tiger beetles, shorebirds, wading birds, and colonial nesting birds, are particularly sensitive to human and vehicle traffic in coastal areas.  

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