Req 2 — Major Threats to Fish and Wildlife

Your counselor will want you to connect the major threats to the specific wildlife in your home state — so while this page covers the national picture, your job is to think locally. A Scout in Louisiana faces different pressures than one in Montana, even though the categories of threats are the same. Read through the major threat categories below, then research which two or three have the biggest impact on your state. Your state fish and wildlife agency’s website is the best place to start.

Habitat Loss and Fragmentation

Habitat loss is the single greatest threat to fish and wildlife worldwide, and every state in the country faces some version of it. When forests are cleared for development, wetlands are drained for agriculture, and grasslands are converted to subdivisions, the animals that depended on those habitats have nowhere to go.

Fragmentation is equally damaging, and often harder to see. A 500-acre forest divided by a four-lane highway becomes two 250-acre fragments — and for many species, those smaller patches cannot sustain viable populations. Deer can cross roads (often fatally for both the deer and the driver). Salamanders, turtles, and many small mammals cannot. Over time, isolated populations lose genetic diversity and go locally extinct.

In your state, look for habitat loss in the form of:

• Agricultural conversion of native prairie or wetlands
• Urban and suburban sprawl
• Road construction through previously intact forests or wetlands
• Channelization of rivers and streams (straightening natural meanders for flood control)

Invasive Species

A non-native species becomes “invasive” when it establishes itself in a new ecosystem and causes ecological or economic harm. Invasive species are the second leading cause of wildlife decline globally — and they’re one of the fastest-growing threats because they’re so hard to reverse.

Invasive plants like purple loosestrife, buckthorn, and kudzu crowd out native vegetation, reducing food and cover quality for wildlife. An upland bird that evolved to nest in native switchgrass is poorly equipped to use a dense stand of invasive phragmites.

Invasive animals can devastate native species directly. Sea lampreys nearly wiped out lake trout in the Great Lakes. Asian carp outcompete native fish for food and space. Zebra and quagga mussels filter so much plankton from water bodies that they starve native fish. Brown-headed cowbirds, which expanded their range following deforestation, parasitize the nests of dozens of songbird species. Feral hogs — present in at least 35 states — root up habitat, prey on ground-nesting birds, and spread disease.

Diseases introduced via non-native species (or spread by human movement) also threaten wildlife. Chronic wasting disease (CWD) has spread to deer and elk herds in many states. White-nose syndrome, caused by a fungus accidentally introduced from Europe, has killed millions of bats.

Pollution and Water Quality Degradation

Fish and aquatic wildlife are especially vulnerable to water pollution, and most of it comes from non-point sources — meaning it doesn’t come from a single pipe but from the cumulative runoff of millions of sources: fertilized lawns, farms, parking lots, construction sites, and urban streets.

Agricultural runoff carries nitrogen and phosphorus into waterways, triggering algae blooms. When the algae die and decompose, bacteria consume all the dissolved oxygen, creating “dead zones” where fish cannot survive. The Gulf of Mexico hypoxic zone, fed by runoff from the Mississippi River basin, covers an area the size of New Jersey each summer.

Sedimentation from eroding stream banks and construction sites smothers the gravel beds where trout and salmon spawn. Larvae that hatch in those gravels cannot escape and suffocate.

Pesticides and herbicides used in agriculture and forestry accumulate in the food chain. Bald eagle and peregrine falcon populations nearly collapsed in the mid-20th century due to DDT contamination — a pesticide that thinned eggshells so severely that the birds could not reproduce.

Thermal pollution from industry and from shade removal along stream banks raises water temperatures beyond the tolerance of cold-water fish species.

Overexploitation

Legal, regulated harvest is sustainable — that’s the whole point of wildlife management. But unregulated commercial take, poaching, and harvest that outstrips the population’s reproductive rate are genuine threats.

The commercial fisheries collapse of Atlantic cod in the 1990s is a textbook case. Overharvesting can drive populations below the threshold where they can recover, even after harvest stops. Today’s regulations exist specifically to prevent this — but enforcing them requires adequate staffing of conservation officers and public compliance.

Wildlife trafficking — the illegal trade in live animals, parts, and products — remains a multi-billion-dollar global industry. While most of this trade involves tropical species, domestic poaching of black bears (for gallbladders and paws), white-tailed deer (antlers), and birds of prey affects populations in every state.

Climate Change and Weather Extremes

Climate change is an emerging and accelerating threat to fish and wildlife. Shifting temperature ranges, altered precipitation patterns, and more frequent extreme weather events all affect where species can live and reproduce.

Cold-water fish like brook trout and bull trout are losing thermal habitat as stream temperatures rise. Spring-blooming plants are flowering weeks earlier than they did a generation ago, while the migratory birds that evolved to arrive in time to eat caterpillars emerging from those buds have not shifted their schedules fast enough — a mismatch called “phenological decoupling” that reduces breeding success.

Wetland-dependent species face flooding and drought extremes that destroy nests, trap fish in shrinking pools, and alter the invertebrate communities that birds and fish depend on.

Understanding what threatens fish and wildlife is the first step. The next question is: what can you do about it?