12 Invasive Species Destroying Fisheries.

Invasive aquatic species are unfortunately a big part of modern day aquatic ecosystems. If you recreate in public waters, be it fishing, boating, or other water sports, you've likely seen signs that have some kind of warning or instruction regarding the spread of an invasive species. The aim of this video is, one, to help people learn more about these species that may be causing harm to their local waters, and two, to help people gain a better understanding of what exactly it is that these species do to harm the ecosystem, as well as just to help others understand what they can do to prevent further spread. Zebra mussels are widely known as some of the most costly and problematic of all aquatic invasive species. Zebra mussels are small freshwater bivalves only growing around 50 millimeters. They have flat triangular shells, boldly banded in yellow, black, and white. They are native to the Ponto-Caspian region around the Black and Caspian Seas. It's believed that a ship's ballast water released millions of larval zebra mussels into the Great Lakes around 1988, and since then they have spread rapidly, fouling many of North America's major river basins. Zebra mussels hitchhike on boats, trailers, aquaculture equipment, and even on aquarium plants, allowing tiny larvae to colonize new lakes and rivers, meaning that the range of their spread is now very far, even being found in far remote places in the west like Lake Powell. The most troublesome problem caused by these little mussels is that they quickly clog pipes and intakes, whether that be industrial, hydropower, or drinking water. They can also cause damage to docks, boat motors, and fishing gear. Ecologically, their massive filter feeding clears the water of plankton. Lake studies show how chlorophyll levels and plankton populations plummet once mussels invade. The water does become clearer, but that's just because most nutrients get locked in mussel beds, and this can actually cause oxygen dips under blooms of decaying material. Another devastating impact is that zebra mussels smother and outcompete native mussels. In many lakes, they have already extirpated native freshwater clams and mussels by attaching densely to their shells. They also consume small zooplankton like daphnia and filter out tiny organisms that are key for young forage fish and other invertebrates. Some studies even link their arrival to declines in plankton-eating fish. In essence, zebra mussels starve native aquatic food chains while causing multi-million dollar damage to infrastructure. To prevent the spread, it's so important that anglers and boaters clean, drain, and dry all gear in addition to removing or killing any mussels on anchors, motors, nets, and trailers. Standard procedure in affected areas is to drain all water from boats, wash with hot water or disinfectant, and allow boats to dry for several days before moving to a new water body. Public water managers use decontamination stations and educate boaters, but once established, zebra mussels are impossible to eradicate, so prevention is really crucial. Quagga mussels are closely related to zebra mussels, but they have a rounder, more fan-shaped shell and no sharp keel on the underside. When dislodged, quaggas often fall off their base, whereas zebra mussels usually stay attached. Like zebra mussels, quagga is attached by threads, grow up to around 40 millimeters, and can form dense colonies on hard or soft sediments. Quagga mussels originated in the same general area as zebra mussels, and they also appeared in North America at the same time zebra mussels did, likely from the very same ballast water. Unlike zebra mussels, quaggas tolerate deeper, cooler water and soft bottoms, allowing them to colonize entire lake beds at depths up to 50 meters. The way they spread from water body to water body is essentially the same way as zebra mussels. Quagga mussels filter feed even larger volumes of water than zebra mussels, further depleting plankton. In fact, Lake Erie became noticeably clearer after their arrival. Quaggas also accumulate toxins in their tissues, magnifying contaminants up the food web. Both the negative impacts quagga mussels cause as well as the preventative measures taken to stop the spread are almost identical to zebra mussels. Both zebra and quagga mussels are technically edible, however as filter feeders they accumulate high levels of heavy metals, toxins, and pollutants, and they're not generally recommended for human consumption due to the significant safety and culinary issues. Plus they are pretty tiny with very little meat and they often have a poor gritty taste. Eurasian watermilfoil is a fast growing submerged aquatic plant. It has feathery finely divided leaves around one to two centimeters long in whorls of four around the stem. It often forms dense mats that can reach the surface and completely choke out a body of water. There have actually been documented situations where this plant completely destroys a fishery. This plant thrives in nutrient-rich lakes and tolerates a wide range of depths, often found in depths of three to six meters. This milfoil is native to Europe, Asia, and North Africa, but it was introduced to the U.S. unintentionally in the late 1800s, also likely from shipping ballast. However, it was not widely recognized as an invasive species until the mid-1900s. By the 1940s it had already spread across the entire eastern U.S. and it now occurs in almost every single U.S. state and Canadian province. Introductions occur very easily because any broken piece of milfoil can drift and colonize a new site. Boating and fishing gear easily transport these fragments. Waterfowl and flood waters can also move cut bits and as a result milfoil infestations often jump between lakes and rivers. Once established, Eurasian watermilfoil can shade out native plants entirely. This change reduces habitat and food for fish and aquatic insects. In long-infested lakes, native plant and invertebrate diversity often drop sharply and milfoil becomes the only underwater cover. Certain species of fish often can produce much more effectively on these mats of milfoil and as a result there's often an abrupt change in which species are taking over the lake. An example of this that I'm familiar with is here in Utah we have a lake called Fish Lake and there are actually two invasive species here, Eurasian watermilfoil and yellow perch. And yellow perch are really effective at laying their eggs on the milfoil and their population has just boomed in the lake. So there are many cascading effects other than just choking out native plants. Another really devastating effect that milfoil has is that it slows water flow and oxygen circulation, sometimes causing low oxygen dead zones, which can be extremely harmful to fish in the wintertime, often causing fish kills. Economically, milfoil mats jam boat propellers, foul fishing gear, hinder swimming and fishing opportunities, and clog water intake pipes. All these impacts mean worse fish habitat and more costly maintenance for anglers and utilities. Complete removal is very difficult because tiny fragments regrow into new plants. Mechanically cutting and harvesting or chemical herbicide treatments are temporary and do little to prevent the invasion long term. Once again, always clean, drain, and dry boats, trailers, and gear after leaving a lake. And especially remember to remove every single piece of mud and plant on the boat. Didymo is a freshwater diatom that grows in thick tannish brown woolly mats on stream bottoms, earning the nickname rock snot. Individual filaments look a lot like cotton balls and can cover 100% of a stream bed. Didymo is unusual because it can form massive blooms even in nutrient-poor water. Microscopic didymo cells link up and form long continuous strands. Didymo's native range is believed to be in the cold waters of northern Europe. It's believed to have been present in Canada as early as the 1800s, however serious blooms were first noted in the 1980s and 90s. It has since invaded many western, northeastern, and mid-Atlantic streams. It's assumed that fishing gear, boats, and wader boots transport cells between rivers. Felt-soled waders are especially risky as they cling to the sticky mats. Didymo mats drastically alter stream ecology. They blanket rocks and vegetation, reducing habitat for invertebrates and fish eggs. Native aquatic insects like mayflies and caddisflies decline under heavy didymo since their food and attachment sites are covered. Anglers have actually noted that once didymo is found in a river or stream, the trout numbers seem to decline, and the trout and salmon that do exist there often don't grow to be as big and healthy. Didymo itself is not toxic, but it's virtually inedible for most organisms. As far as preventing the spread, no chemical cure currently exists for didymo in open streams. So once again, it's important to clean, drain, and dry, especially washing your wader boots. As a general rule, anglers should avoid using felt waders as the spread of didymo and other invasive is much easier. The spiny water flea is a tiny predatory zooplankter around 1 cm long. It has a transparent body with a very long barbed tail spine, around 70% of its length. The body is translucent with claws that are used to grab prey. Its quill-like spines often catch on fishing line and create a gelatinous tangle. This species is native to Eurasia. It was first detected in the Great Lakes in the mid-1980s, once again, likely via ballast water. In recent decades, it has invaded hundreds of inland lakes. Most often, the transfer occurs on recreational boats and fishing gear. The spiny water flea preys heavily on native zooplankton, especially daphnia and other tiny aquatic creatures. A single spiny water flea can eat dozens of daphnia per day. Because it reproduces quickly, it often overgrazes the zooplankton community, causing a cascading effect and eventually harming larger fish, especially planktivorous fish, which often lose much of their food supply and tend to decline. In many invaded lakes, anglers report smaller fish or fewer catches over time. Another annoyance of the spiny water flea is that they jam up fishing gear. As anglers reel in, the fleas form jelly-like masses on lines and lures, snarling equipment, and making fishing more difficult. The barbs on the fleas make them tedious to remove, so gear must be cleaned frequently when fishing infested lakes. Like other invasives, spiny water fleas are extremely hard to eradicate once established. The only feasible defense is to keep them out of uninfested waters. Boaters and anglers should drain, clean, and dry every part of their equipment. Importantly, they should wipe down fishing lines and nets with a clean towel after use. Asian clams are small, roundish freshwater clams that vary in color, sometimes with yellowish, purplish, brown, or black shells. They have several raised rings extending from one end to the other. Native to Asia, these are filter feeders that live partially buried in sediment. They first appeared in the U.S. in the late 1930s, first being noted in the state of Washington. They were likely imported accidentally along with oyster shipments, or it may have happened deliberately for aquaculture. By the 1960s, Asian clams had colonized nearly every major river basin in the U.S., and today they occur coast to coast. Asian clams spread by releasing free-swimming larvae into water, and also by adult clams hitchhiking on boat trailers or plants. A single female can produce millions of offspring per year. Once in a river or pond, they form thick beds, sometimes thousands of individuals per square meter. These dense beds can clog irrigation canals, water treatment, and power plant intakes. Ecologically, Asian clams are filter feeders and they often outcompete native mussels and snails. Clam beds can also alter nutrient cycling and sediment composition. By consuming large amounts of microscopic algae, clams may change the base of the food web. Some studies suggest in heavily infested waters, there is less food for juvenile fish and invertebrates. However, the effect on game fish is not as dramatic as the invasive mussels or spiny fleas. That being said, Asian clams can eat the larval stages of native mussels and therefore hinder their reproduction. I know that some people may eat Asian clams. I haven't tried it myself, but I think it'd be fun to try it out someday. There is no simple treatment for an established clam bed. Controlled trials include dredging, using chemicals, or relocating the water outflow to create unsuitable habitat. But these are often costly and only local. Like always, the best defense is strict prevention. Clean, drain, and dry. New Zealand mud snails are tiny freshwater snails around four to six millimeters long, a bit smaller than a grain of rice. They're pale yellow or brown and have tightly coiled conical shells with five to seven whorls. They have a trapdoor operculum that lets them survive out of water for weeks. Native to New Zealand streams, they were first found in the U.S. in 1987 in the Snake River in Idaho. They have since spread intensely throughout western North America. These snails reproduce asexually. Every snail is female and clones itself, producing up to 230 live young per year. So just a single snail can start a new population. Mud snails colonize streams and lakes in incredibly high numbers, often hundreds of thousands per square meter. They disperse via drifting on water currents or by clutching onto boats, plants, or animals. Even fish or birds can inadvertently move these snails from one lake to another. Ecologically, mud snails graze on algae and detritus, and in high densities they can starve native snails and insect larvae. Studies show that when the mud snails invade, native invertebrate biomass like mayflies, caddisflies, and other snails plummet. Fish that feed on those insects thus lose a critical food source and tend to decline. Unfortunately, mud snails themselves are a For example, when a trout eats mud snails, up to 90% of the snails pass through undigested. So even if fish stomachs are full of mud snails, their growth and condition can decline. This effectively means that fisheries can suffer reduced growth rates and lower catches in mud snail infested streams. Eradication of mud snails is essentially impossible, so once they're established, just like the others, the key is preventing transfer. Hydrilla is a submerged aquatic plant native to Asia. It has long branch stems covered in whorls of three to eight narrow leaves that are around two to five centimeters long. These leaves are often toothed and may have tiny spines on the underside. This plant tolerates a wide range of conditions and can form dense mats at the water's surface. It was first introduced into Florida as an aquarium plant in the 1950s, and in consequence it was released into the canals. By the 1970s, it had spread quickly and invaded many southeastern waterways. Now hydrilla infests at least 30 states and many major rivers. As with milfoil, pieces break off easily and a single stem fragment can root in new areas. Hitchhiking on boats and fishing gear is a common pathway, especially through river systems where infestations are concentrated near marinas. Similar to Eurasian water milfoil, hydrilla is notorious for forming thick impenetrable mats that choke out native plants by blocking sunlight. Such mats also deplete oxygen and can cause fish kills due to hypoxia. Fish and wildlife that depend on submerged vegetation for food and shelter are always harmed when hydrilla takes over. Duckweed and algae may grow in open patches, but they are a poor substitute for diverse plant beds. Long-term studies show that fish diversity tends to drop heavily, especially species that spawn on gravel or shallow flats. It highly limits where you can fish, and boat motors stall on the tingles of mats. Mechanical harvesting and herbicides are used, but hydrilla regrows from fragments and tubers that are left behind. The most effective approach is again preventing spread. While this plant doesn't grow underneath the water's surface, one of the most widespread and destructive wetland invaders in North America is invasive phragmites. Phragmites is a towering reed grass capable of completely transforming wetlands, shorelines, and fish habitat. It is large perennial grass that can grow 10-15 feet tall, forming dense, nearly impenetrable stands along the shorelines. It also grows in marshes and shallow water. Key identification characteristics include the tall, hollow stem with long, blade-like leaves, 1-2 inches wide and up to 20 inches long. The tops have large, feathery seed heads that can appear purplish or tan and persist through the winter. This plant grows in dense colonies that are connected by thick, underground rhizomes. There are actually phragmites native to North America, but unlike native strains, the invasive species tend to grow much taller, denser, and more aggressively, often forming monocultures with thousands of stems per acre. Being native to Eurasia, it is now found all over North America, occupying hundreds of thousands of acres of wetlands and choking out native plants. The invasive lineage likely arrived in North America in the late 1700s or early 1800s, most likely through shipping ballast, packing materials, or soil that had come from Europe. Once introduced, it spread rapidly along transportation corridors and waterways and quickly dominated large wetland areas. The ecological impacts of invasive phragmites is severe. Once established, it forms extremely dense stands that exclude nearly all other plant species. This dramatically reduces biodiversity by eliminating native wetland plants such as plants that normally provide critical habitat for fish, amphibians, birds, and aquatic insects. When phragmites take over, the plant is so dominant that it's essentially the only living plant on the shoreline. This plant also alters wetland hydrology by trapping sediment and raising the ground level. Over time, open wetlands and shallow water habitat often become just dry reed fields. The impact on fisheries is significant but often overlooked. Many fish species depend on wetland nursery habitats for spawning and juvenile development. Dense phragmites stands can block access to spawning marshes and eliminate the shallow vegetated habitat where the juvenile fish hide from predators. Additionally, the loss of native wetland plants reduces habitat for aquatic insects and invertebrates which are key food sources for these young fish. Controlling invasive phragmites is extremely difficult once large colonies form. Management typically requires a combination of herbicide treatments, mechanical cutting, controlled burning, and restoration of native vegetation. However, just like always, prevention still remains the most effective strategy. The rusty crayfish is a robust orange-brown crayfish that is easily identified by its reddish rusty color. The claws are large with an ovoid gap when closed. Males and females look similar but males are often larger. This crayfish is native to parts of the Ohio River Basin in Ohio, Indiana, Kentucky, and Tennessee, but it was spread by humans in the mid-20th century. The primary introduction was bait bucket dumping as anglers used live rusty crayfish as fishing bait. They were also stocked deliberately in some areas as a food source. By the 1960s, rusty crayfish had spread throughout the Great Lakes region and into many other waters. Today, they are found in over 20 states from Minnesota to New England and are constantly moving via interconnected streams and intentional releases. Rusty crayfish are highly aggressive and they eat both animal and plant matter. In invaded lakes, they famously clear-cut aquatic vegetation, often reducing plant biomass to near zero. This has dramatic effects on fish habitat. The lack of plants cause the fish to lose nesting substrate, rob shelter from small fish and invertebrates, and increase erosion of sediment. They outcompete and even hybridize with native crayfish, further threatening native species. Overall, the ecological impact of the rusty crayfish is the loss of plant beds and invertebrates that normally support healthy fish populations. The best prevention method to stop the spread of these crayfish is to simply not use this species of crayfish as live bait outside of their native range. The vivile or northern crayfish is another crayfish, often reddish brown or olive green with greenish claw tips and orangish toes. It's similar in size to the rusty crayfish, normally up to 12 centimeters in body length. It's actually native to much of the northern U.S. and Canada, but it's also considered highly invasive in the surrounding areas outside of its native range. These crayfish were spread primarily by human activity. For example, Montana and Utah fish agencies stocked this species decades ago to create new angling opportunities. As a result, these northern crayfish are now established in over 20 states, primarily west of their natural range. While probably the least destructive thing on this list so far, these crayfish eat plant and animal food, and studies of impact show that they can sometimes be just as damaging as the rusty crayfish as they reduce native crayfish and snail populations by both competition and direct predation. Fisheries impact is mostly indirect with fewer plants and insects, and as a result, fish lose foraging and spawning habitat. If crayfish eat fish eggs or juvenile amphibians, it can also affect local biodiversity. However, that being said, many sport fish like bass and trout will opportunistically eat crayfish, and large numbers of crayfish can often serve as a food source, but this benefit is often offset by the damage that they cause to the ecosystem balance. Both the northern crayfish and the rusty crayfish are quite tasty, and that is always a good thing to be aware of, since for the most part, harvest is basically unlimited. Measures for prevention are the same as the rusty crayfish—do not transport live crayfish as bait. In fact, it's illegal to do so in most western states. The American bullfrog is another species that is actually native to North America, but they have invaded far outside of their native range. The American bullfrog is the largest frog in North America. Adults reach over 20 centimeters or 8 inches in body length, and can weigh 1 to 2 pounds. They are green to brown with dark modeling and have a distinctive large circular eardrum on the side of the head. Bullfrogs are native to the eastern and midwestern US, but have since been introduced far beyond that. Bullfrogs are aggressive, generous predators and pose severe threats to native aquatic life. Adults have immense appetites and will eat anything that they can swallow—insects, fish, tadpoles of other frogs, salamanders, snakes, small mammals, and birds. Both adults and tadpoles outcompete native amphibians. Adults even prey on smaller frog species. For example, bullfrogs have been linked to the extirpation of red-legged frogs in California, and the decline of leopard frogs in Colorado and Utah. Bullfrogs also carry chytrid fungus, which is a very deadly fungus to many amphibians. However, bullfrogs tolerate chytrid and act as reservoirs, spreading this deadly fungus to other species. Chytrid has decimated frog populations worldwide, and bullfrogs accelerate that threat in invaded habitats. Most people in the west don't recognize bullfrogs as invasive, and raising awareness that bullfrogs threaten native species is key. I'll also say that I've cooked up a few bullfrogs, and I've been pleasantly surprised at how good they are. I think that being educated and mindful of our surroundings is the best thing that each of us can do to help protect our local ecosystems and help prevent things like invasive species. I hope you learned something new today. If so, please like, share, and subscribe, and don't forget to check out my other videos on invasive species. Thanks, and I hope to see you on the next one!