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Entries in round goby (7)


Round Gobies: The Good, The Bad, And The Ugly

A small invader has had a large impact on some northern bass fisheries since it first was discovered in 1990 in the St. Clair River, and it's not finished yet.

A bottom-dwelling fish that can grow to 10 inches, but more commonly is 3 to 5, the round goby has gained notoriety for eating the eggs of other species, including bass, in the Great Lakes and other waters. But it also has developed a taste for shellfish, it seems, particularly zebra mussels, another exotic species. At a glance, that would seem good news, but not necessarily.

 "In the past two years, we have observed a decline in the total mussel biomass in Oneida Lake, likely because of the rapid growth of the goby population," said Stephanie Roh, a Cornell University student researcher. "If these trends continue, we expect to see lakewide ecological changes such as decreased water clarity very soon."

The implications could be significant. Although zebra and now quagga mussels have caused many problems and cost the nation billions of dollars for control and mitigation, their filter feeding has improved water clarity in many fisheries, allowing more sunlight penetration, and thus encouraging the growth of beneficial vegetation.

In general, that has been good for bass and other sport fish that primarily are sight feeders. In places such as Minnesota's Mille Lacs, however, that ecological change is suspected, along with warming waters, of contributing to the decline in walleye, which prefer darker conditions.

Also, clearer water means less productivity in the form of phytoplankton and zooplankton at the bottom of the food chain for prey fish to eat. "Walleye eat mostly fish, and there's not as many fish," said Minnesota fisheries biologist Eric Jensen, adding that smallmouth continue to thrive because they also eat crayfish.

Still, this potential impact is just speculation at this point.

"We haven't seen that yet, but are still watching things unfold," said Cornell professor Randy Jackson, who has been keeping an eye on how gobies impact Oneida's bass fishery since anglers first reported catching a few of the invaders in 2013.

"It is not my impression from the Great Lakes, where gobies have been established for much longer, that people think that are having a large impact on mussel densities," he said.

What is no longer speculation, however, is that bass, especially smallmouths, seem to grow faster and larger when their diet consists mostly of gobies.

Following a study of the diets for largemouth and smallmouth bass in eastern Lake Ontario, scientists concluded the following:

"Our results provide further support that recent increases in the size of Lake Ontario bass are a result of round goby consumption, and that the effects of this dietary shift on body condition are greater for smallmouth bass."

And from a study on Lake Erie:

"Roundy goby became the dominant prey of smallmouth bass after its invasion (observed in 73.3 percent of diets), and crayfish were only observed in 5.8 percent of diets in the post-round goby time period. Length-at-age increased following invasion of round goby and the greatest increases in length (11 to 15 percent) were observed for ages 2 to 4."

Also,  state record smallmouth bass caught in Michigan and New York during 2016 were taken from waters where gobies are established. In Michigan, the bass from Indian River  checked in at  9.98 pounds, nearly double digits! It bested a mark of 9.33 set less than a year previous. Before that, the state record of 9.25 pounds had been in place since 1906. In New York, a 8.25-pound bronzeback from the St. Lawrence tied a record first established in 1995.

Jackson is not ready to say that's going to happen on Oneida, where gobies still are settling in as permanent residents and all data is preliminary.

"It is our sense that we are seeing some larger, and fatter bass the last couple of years," he said. "But this is anecdotal. Overall it is too early to see significant increases in lengths of bass, but we seem headed in that direction. Anglers also are saying fish are bigger."

One way that gobies could be benefitting bass growth rates and size, he speculated, is that they spawn several times during a season. "With  production of small gobies all season long, I would imagine bass would have no problems remaining piscivorous all summer, which should enhance growth.

"This may be a more subtle, behind the scenes impact of gobies," he continued. "But in systems, particularly in the north, where first-year growth of young bass is important to overwinter survival, enhanced growth could ultimately lead to improved recruitment and increases in adult population size, assuming that population size is not limited by something acting on adults."
And here's another reason to like gobies:

Double-breasted cormorants seem to like them. According to Jackson, they have seem to have shifted to feeding on them in some fisheries, "which, of course, is good for sport fish that they used to eat more of. Our cormorants are starting to eat gobies as well, but we haven't seen a wholesale shift yet. Everyone is hopeful."


The Dark Side

Still, predation by sport fish and cormorants on gobies is but one piece of the puzzle on how this exotic fish will ultimately will impact native species and their ecosystems. There are plenty of negatives as well.

Michigan Sea Grant points out that gobies have been linked to outbreaks of botulism, which have killed fish-eating birds around the Great Lakes.  Mussels accumulate the toxin in their flesh, as they filter feed in places where it thrives in water depleted of oxygen by decaying algae.  Gobies eat the mussels, and predatory fish and birds eat the gobies.    

Additionally, the Aquatic Nuisance Species Task Force (ANS) said, "They out-compete native fish for food due partially to an ability to feed in darkness and to the presence of a suctorial disk located on their pelvic fin, which allows them to attach to rocks/substrates and remain fixed on the bottom even in faster currents. Tubenose and round gobies are the only fish to possess this unique characteristic."

It also warns that gobies "maybe interfere with habitat restoration projects. Round gobies are aggressive toward other fish and may drive native fish away from prime spawning areas."

In the St. Clair River, where gobies were first confirmed nearly 30 years ago, populations of native sculpin and logperch have suffered substantial declines.


The Bass, Baitfish Connection


Birds, mice, frogs, snakes, lizards, and ducklings, all have met untimely demise in the bellies of opportunistic largemouth bass. Given the chance, these versatile and adaptable predators also will eat insects, invertebrates, and most any fish species small enough to swallow, from rainbow trout in California to hornpout in New England.

Bluegill and shad, however, provide most of the fuel that powers America's No. 1 sport fish. But which of the two most benefits bass, and, consequently, bass anglers?

Neither. And both.

"For bluegill, the primary benefit is their abundance," said Dan Shoup, associate professor of fisheries ecology at Oklahoma State University.  "Bass are often opportunistic foragers and when bluegill are numerically abundant, that means they end up being eaten regularly."

Additionally, he added, "shad also have very high abundance in some systems, so, just like with bluegill, a largemouth bass will often times eat a lot of shad simply because they are easy to encounter."

Still, advantage goes to bluegill because its needs and preferences so closely mirror those of its larger sunfish cousin. In fact, waters with bass and no bluegill are the exception rather than the rule, from the smallest farm pond to Lake Superior. 
"Bluegill often hang out in the same habitats as bass since both are cover-oriented species," Shoup said. "Even a moderate density of bluegill ends up being an easy choice for bass because they occur in large aggregations in places the bass frequently are located, such as brushpiles."

On the other hand, shad inhabit open water and are most numerous in large lakes and impoundments. While bass will eat them year around, they are most likely to move from shoreline cover to deep-water structure and target shad during summer and winter. Sometimes, also, they will follow these schooling fish. Bluegill might have the overall abundance advantage, but hungry bass can more quickly eat their fill by slashing into these concentrations.

And as they do so, bass are getting more bang for their buck. Advantage shad.

"Think high-calorie food, which to a wild animal is a good thing as they tend not to be too concerned about their waistline," said Shoup. "Shad have a higher lipid content than most species, which makes them a more energetically valuable food."

Also, shad are easier to swallow. Literally.

"Bluegill have a rather effective anti-predator behavior where they simply stick up their spines and orient at a 90-degree angle to the bass," the Oklahoma State fisheries expert said. "The spines make them quite a bit harder to handle than other species like shad, cisco, or minnow species."

Also, bluegill have large girths compared to length, and those spines are positioned along the deepest part of the body. "Bluegill almost have to be oriented head-first (for the bass) to swallow, and the length of bluegill that can be handled is pretty short compared to other species that do not have as deep a body," Shoup said. "So bluegill can outgrow bass a little faster and easier than other species with a similar growth rate simply because they have a deep body.

"This makes bluegill useful as a food source for only a few years, as opposed to (yellow) perch, which might be edible even when they are quite long."

Size also can be a negative for one species of shad. "Gizzard shad can be great in a trophy bass situation, but they really are not forage  because they grow faster than bass," said Gene Gilliland, B.A.S.S. National Conservation Director. "Threadfin shad are better because they spawn later and don't get as big."

Shoup echoed that assessment, pointing out that gizzard shad easily can reach more than 12 inches in length. "As such, they often outgrow the gape limitation (mouth size) that bass can handle by the time they are just 1 year old. Yet they may live 6 to 10 years, so most of their life span is spent being too large to eat.

"Threadfin grow much slower and typically are vulnerable for most of their lives," he added. "This makes threadfin a better forage base in systems where they can overwinter without high mortality."

Gilliland said that area typically is not much farther north than Interstate 40, which runs from North Carolina through Arkansas and on to southern California. Bull Shoals and Table Rock on the Missouri-Arkansas border are a couple of notable exceptions, as are power plant impoundments. Unlike the much hardier gizzard shad, threadfin will start to die in water of about 40 degrees.

 While bluegill and threadfin shad provide most of the fuel to produce quality bass fisheries, too much of either can be a bad thing.

"Both prey species compete with juvenile bass for food," Shoup explained. "As such, there is a bit of a balancing act that is needed for a fishery manager. You want ample for forage, but not if it causes your predator species to grow slowly as juveniles."

For example, juvenile bluegill compete with juvenile bass for zooplankton and insect larvae throughout most of the first growing season in many fisheries. If food is abundant enough, by late summer, bass can reach 3 to 4 inches, large enough to start eating other fish. But if cover is too dense . . "Lots of research shows adult bass are really poor at capturing bluegill once the density of cover gets above some threshold level," the fisheries scientist said. "This can create a stunted bluegill fishery because bluegill do not grow well when they are hiding from bass like this. This does not help the bass population, though, even though the bluegill stay small enough to eat for a greater number of years, because the bass are having a hard time capturing the bluegill."

Additionally, bluegill are notorious egg predators, he added, hampering reproduction in systems where bluegill abundance is too high.

Shad, meanwhile, also compete for zooplankton. "You can actually lose a whole year class of bass if shad densities are too high," Shoup said. "Shad can produce a zooplankton crash just before juvenile bass need to start eating zooplankton."

Additionally, over-abundant shad can increase turbidity. "Because bass are primarily visual feeders, their foraging return drops quite a big as turbidity increases," he added. "This can lead to slow growth and/or poor condition in some systems where shad are abundant."


Best size bait for bass?

"When you look at bass diets in the field, you rarely see any size of bass frequently eating prey near the maximum size they could eat," said Dan Shoup, an Oklahoma State fisheries expert. "Most eat prey that are considerably smaller."

That's most likely because larger prey move faster and require more energy to capture than smaller forage. Related to that, a higher escape rate means it more likely that the bass will expend energy with no pay-off at the end.

"Larger bass will definitely eat larger prey," he emphasized. "But it also is not uncommon to find a 5-pound bass eating 3- or 4-inch bluegill even though they could handle much larger prey if they wanted.

"Ultimately, there is a tradeoff for a predator picking prey sizes. Going after large prey requires more energy/effort and has a lower success rate, but a big pay-off when successful. But going too small means you must eat a lot more to get full, even if capturing them is relatively easy. Each item you strike at takes time and energy, so things tend to optimize with mid-size prey as the best bang for the buck."

Other options

While bluegill and shad provide the most important prey for bass overall, plenty of other fish species are notable as well, including non-native blueback herring, alewife, round goby. The former two are difficult to distinguish from one another and often are referred to collectively as "river herring."

An anadromous species that spawns in freshwater, the blueback herring has expanded its range in New York through ship locks and canals. But it has been intentionally introduced in many other states, including Virginia, Georgia, Tennessee, and the Carolinas. Preferring deep, open water, it can grow to 12 inches, with a silvery body that is deep bluish-green on the back. In some fisheries, a decrease in game fish has coincided with introduction of this species, and fisheries managers suspect that the herring preys on the eggs and larvae of native fish, as well as competes with them for zooplankton. On the other hand, many anglers believe that they have provided a nutritional boost for some bass fisheries.

The alewife's biology and history are similar, although mostly it has become established in the Great Lakes, with a few scattered introductions to the south. It was first noted in Lake Ontario more than a century ago, and likely gained entry to the other lakes through the Welland Canal during the 1930s. Reaching 6 to 7 inches at maturity, it is more noted as forage for salmon and trout than bass. Alewives also compete with native species for zooplankton and eat eggs and larvae.

Introduced in the ballast water of ocean-going ships, the round goby also is mostly a Great Lakes occupant, although it has been found in nearby inland waters. It first was discovered in the St. Clair river in 1990 and has spread rapidly since. Growing to about 10 inches, they are prolific, spawning several times a year. They compete with native species for habitat, as well as feed on their eggs and young. Also, they are notorious bait stealers. On the plus side, anecdotal evidence suggests that smallmouth bass are growing faster and larger because of goby diets.

(A variation of this article appeared originally in B.A.S.S. Times.)


That's Not a Goby . . . THIS Is a Goby!

Fish in the top photo is a round goby, an exotic fish introduced to the Great Lakes in the ballast water of ocean-going ships. They grow to about 6 inches maximum, but 3 to 4 inches is the norm. Also, they have proven to be among the favorite forage for smallmouth bass, and anecdotal evidence suggests that they are growing faster and larger on a goby diet.

Fish in the bottom photo is the world record marbled goby, caught in Thailand by John Merritt. It checked in at 5 pound, 3 ounces. IGFA says that it is "likely the largest of gobies." And with a mouth like that, it likely could turn the tables on some of those smallmouth bass that are eating its smaller, globe-trotting cousin.

You can see more "weird world records" at Sport Fishing.

The International Sport Fishing Association (IGFA) is the official record keeper for both fresh and saltwater species. You can see the full list here. For line class records and additional information, you must become a member.


New Invader in Great Lakes: Thermocyclops Crassus

It's not much to look at. In fact, it's impossible to see without a microscope.

But for the first time in a decade, an exotic aquatic species has been found in the Great Lakes. That makes 185 or 186  non-native species, depending on who's counting, now established in the basin. Some, including the lamprey and alewife, migrated up the St. Lawrence Seaway, but most, including the zebra mussel as well as this latest, probably were introduced via ballast water from ocean-going ships.

Thermocyclops crassus, a type of zooplankton, was discovered in water samples taken from Lake Erie by limnology technician Joe Connolly of Cornell University.

“It’s kind of like looking for a needle in a haystack,” Connolly said. “I didn’t know what it was, but I knew it wasn’t something we’d seen before.”

He found both male and female specimens in low numbers, but enough to say that an established population exists of the invertebrate that is native to Europe, Asia, and Australia. Officials from both the U.S. and Canada have planned more sampling to determine how widespread this new invader is and what its impact may be.

 “We don’t know enough yet about what this species could or could not do in the Great Lakes,” said Elizabeth Hinchey Malloy, an environmental scientist with the U.S. Environmental Protection Agency.

Size isn't an indicator of impact, as the zebra mussel, a fingernail-sized shellfish, and the round goby, a small bottom-dwelling fish, have proven.

Confirmed in 2006, the bloody red shrimp was the last previously discovered invader. It now swarms in excess of 135 individuals per square foot.

"The impact of this species on the Great Lakes is yet unknown, but based on its history of invasion across Europe, significant impacts are possible," said Wisconsin Sea Grant Institute. "The bloody red shrimp is an omnivore. Its diet includes waterfleas and algae. They may compete with young fish, while providing food for larger fish. The invasion of this species in some European reservoirs has been documented to accelerate silica cycling, resulting in blooms of diatoms and, in some cases, plating out of silica onto pipes."


Mapping the Invasion

This screen shot shows zebra and quagga mussel invasion as of 2006.

Nature Conservancy has produced some great interactive maps showing how invasive aquatic species have spread out across the country from their point of introduction.

Featured species include bighead and silver carp, zebra and quagga mussels, Eurasian ruffe, round goby, sea lamprey, and black carp.

Also, in late 2012, the organization released a report saying that aquatic invasive species “cost businesses and consumer in the Great Lakes region hundreds of millions of dollars annually in direct costs and even more from indirect costs related to removal, maintenance, and management of those species.

“Meanwhile, state and federal governments are currently forced to spend additional millions as they attempt to control the impacts and prevent the spread of AIS (aquatic invasive species).”

According to the report, the largest industry affected by AIS in the Great Lakes is tourism and recreation, which is responsible for employing more than 90,000 people in the region, generating $30.3 billion annually in revenue. Costs range from monitoring and controlling AIS to lost revenue from beach closings affecting hotels, restaurants and other tourism-related businesses.