Sounds of the Season

The burbot is a fish that may be familiar to many readers of this blog. This handsome creature is a close relative of cod and haddock, and is the only member of the Gadiformes (the ‘cod-like’ fish) found in freshwater. Many anglers  have encountered burbot when ice fishing for lake trout. While they are not a highly sought after game-fish, they are a tenacious predator and are capable of eating fish that are nearly as large as themselves.

Interestingly, burbot are one of the few species in Canada that spawn in mid-winter, underneath lake ice. Because of this, very little is known about their reproductive ecology, and it has been challenging to prevent burbot declines because of this limited knowledge. One important question about mid-winter breeding is how male and female burbot find one another. In mid-winter lakes are dark (because of ice cover) and very cold, which means that searching for mates is challenging and energetically costly.

A recent study from a group of Canadian and Scottish researchers has found that burbot actually sing to attract mates during the breeding season. The researchers took adult burbot from the wild and kept them in a artificial under-ice enclosure that was fitted with underwater microphones. They found that burbot make a suite of different sounds, and that they probably use a drumming muscle that is attached to their swim bladder in order to do so. Burbot drumming muscles increase in size during the breeding season, and males have larger muscles than females, suggesting that males do most of the singing.

Singing to attract a mate may be a clever adaptation to breeding in a low light environment, and is yet another interesting characteristic of a very cool fish. It also suggests that noise disturbance, for example from industrial activity, could disrupt burbot reproduction. As a result, burbot conservation may depend on limiting noise pollution during winter in freshwater ecosystems.

Citation PA Cott et al. 2014. Song of the burbot: Under-ice acoustic signaling by a freshwater gadoid fish. Journal of Great Lakes Research 40:435-440.

Find the study here


Do boats spook fish?

A friend was recently steelhead fishing on a Great Lakes tributary. He had just arrived at a productive looking run and had made a few casts before he noticed a group of canoes about to float over the best water. While rage was building up inside of him and he contemplated communicating his discontent with the canoers choice of route, he was surprised when a fish smashed his fly, right under the leading canoe. The take was unexpected because he had assumed the boats would spook the fish and ruin his chances, but it begs the question of how boats influence fish behaviour.

A team of researchers from Denmark recently addressed this question using an acoustic telemetry array in a private research lake. When combined with telemetry tags that were surgically implanted in individual fish, this array gave the researchers high resolution data of where fish were in the lake. The researchers studied the effects of power boating on the behaviour of three different species: Northern pike, roach and European perch. To test whether boating, or fishing primarily influenced these species, they either boated around the lake in short intervals (for 4 hours) or boated and casted artificial lures in between engine runs. The researchers then compared the movement and location of fish during these disturbances, to other days in which they did not boat on the lake.

The researchers found that boating did influence fish behaviour, although the response differed between different species. Both the European perch and the roach had increased swimming speeds during the boating periods, with the greatest increase in swimming speeds occurring at the start of the disturbance. Additionally, roach were more commonly found in the deeper, center of the lake during boating period than when boating did not occur. Neither species showed any difference in response in relation to whether the researchers just boated, or boated and fished, suggesting that it is boating itself rather than fishing that disturbs roach and perch. Also, Northern pike showed no obvious response to boating – they didn’t change the habitat they were found in and did not change their average swimming speed.

These findings not only have implications for anglers, but also for managers. If fish grow and reproduce better in certain habitats, but are chased out of those habitats by boaters, then boating could have a direct impact on fish populations. However, this study shows that boating will have different effects on different species, and so we might need to incorporate a species ecology (are they a predator or prey species? are they pelagic or do they primarily seek cover?) when thinking about how fish are influenced by boats.

Citation: L. Jacobsen et al. 2014. Effect of boat noise and angling on lake fish behaviour. Journal of Fish Biology 84: 1768-1780.

Find the article here

The Colour of Defeat

Welcome back from the Lab and Stream. We have been off chasing fish for the last few months, and we hope you have been too!

In this post we are going to discuss some very interesting research on colour changes in salmonids. Most trout and salmon have beautiful colouration, and I am sure many readers of this blog will be familiar with changes in colour during spawning (think of the flush red cheek of a steelhead, or the bright red and green of a sockeye). However, many fish (including salmonids) also use colour to signal during fights. For example, juvenile salmonids change their colour to signal when they have been defeated in a fight. When one individual has had enough and wants to give up, they darken their skin and their eyes to signal to their opponent. In response to this darkening the winner will stop attacking them, and so the signal is useful for both parties.

But what happens in murky or turbid water, which many trout live in? Does the signal still work? Researchers from the UK performed an experiment aimed at testing how this ‘signal of defeat’ was modified by water turbidity. They allowed pairs of juvenile brown trout to fight in either clear water, water with low turbidity or water with high turbidity. What they found was that as the water turbidity increased, the ‘loser’ of the fight became even darker than those that lost fights in the clear water condition. The researchers noted that the physiology of the losers did not differ according to the water turbidity, so the only explanation was that fish in turbid conditions were actively increasing their ‘signal of defeat’ so that it was more apparent in the turbid water.

This interesting finding underlines how water turbidity can have important effects on a fish’s life. Not only does turbidity influence feeding, predation risk and respiration, but now we know that it also influences signalling.


Citation: L Eaton and KA Sloman. 2011. Subordinate brown trout exaggerate social signalling in turbid conditions. Animal Behaviour 81: 603-608.

Find the paper here

Catch-and-release and reproduction in Atlantic salmon

Atlantic salmon are incredible animals. In addition to being ferocious predators, making epic migrations and being exceptionally beautiful, they also have a very interesting method of reproducing. Most male Atlantic salmon do the typical salmon thing, they are born in freshwater, then migrate out to saltwater where they feed and grow for a few years before returning to freshwater to breed. However, some male Atlantic salmon never venture out to saltwater. These mature male ‘parr’ are much smaller than adult males (about 1/10th the size!) but they still try to reproduce with returning females. Because they are not as large and attractive as other adult males, the parr have to dart in and sneak fertilizations while a large male and female are doing their thing. For this reason, they are often called ‘sneaker males’.

Of course Atlantic salmon are also a popular game-fish, and so a recent study by researchers from Laval University wanted to investigate how catch and release angling might affect reproduction in this species, and whether it would have different effects on adult males compared to mature male parr. In the Escoumins river in eastern Quebec, the researchers were able to genetically sample every returning adult in 2009 by catching them at a fish ladder. They used this data to assign parentage to all of the offspring that were born that year, and assumed that any offspring who weren’t sired by a returning male must have been sired by a mature male parr. The researchers also collaborated with local anglers, and got the anglers to collect a small fin clip whenever they caught and released a fish. By matching the genetics from the fin clip samples with the samples from the fish ladder, the researchers could tell which fish had been caught and released.

What the researchers found was that there was huge variation in reproductive success (in terms of number of offspring produced) among the returning males. Some males were able to mate with multiple females and produce lots of offspring, while some males produced none. Also, the researchers found that 44% of the offspring were sired by mature male parr – not bad for fish that are 1/10th the size of the adult males! In comparison, females had relatively lower variation in reproductive success, with most females producing some offspring.

Fish that experienced catch-and-release angling did tend to have slightly lower reproductive success that fish that were able to avoid being caught. Interestingly, this depression in reproductive success was dependent on the size of the individual – larger fish experienced greater negative effects of catch and release angling than did smaller fish. Fish that were air exposed for a greater length of time, especially during high water temperatures, were also more affected by angling than were other fish.

Overall, the study provides some interesting data to suggest that all fish are not equally affected by catch and release angling. It also has some interesting implications in suggesting that smaller fish (i.e. parr) sire many offspring and that they might be more resilient to angling than larger fish.


Citation: A. Richard et al. 2013. Does catch and release affect the mating system and individual reproductive success of wild Atlantic salmon (Salmo salar L.). Molecular Ecology 22: 187-200.

You can find the article here


How does hydropeaking affect aquatic invertebrates?

Dams have fundamentally altered most large river systems in the world. Many of these dams are built to produce electricity, and adjust the amount of water released across the day in response to electricity needs. Since energy use typically follows a daily pattern (more use in the morning and evening, little use at night) many of these tailwaters experience daily ‘hydropeaks’, where the dam increases water release at certain times of day.

While several studies have examined how hydropeaking affects fish behaviour, there is a lack of knowledge about how hydropeaking affects fish prey. However, a recent study by researchers from Utah State University investigated how hydropeaking affects benthic invertebrates (aquatic insects), which are the primary food for most trout.

Using the natural hydropeaking cycles, as well as experimental flows from the Flaming Gorge Dam in Utah, the authors tested how hydropeaking influenced the amount of benthic invertebrates drifting in the water (and thus available as trout food).

The authors found that hydropeaking does have an effect on benthic invertebrates. The amount of benthic invertebrates drifting in the current increased when dams increased flows, but this effect did not last the entire time that the flow was elevated. The daily amount of drifting benthic invertebrates was higher when there were two hydropeaks (double peaking) rather than just one, suggesting that benthic invertebrates respond more to changes in flow rather than the absolute level of the flow. The data also suggested that hydropeaking could have a negative effect on how many different species of benthic invertebrates can live in a tailwater, although they caution that more research is needed on this topic

So how do the trout fare in all this? Well, this study found that gut fullness of both brown and rainbow trout increased immediately following hydropeaking, suggesting that they are able to take advantage of the increase in drifting invertebrates. Clearly, hydropeaking has important effects on fish and fish food.

Citation: SW Miller and S Judson. 2014. Response of macroinvertebrate drift, benthic assemblages, and trout foraging to hydropeaking. Canadian Journal of Fisheries and Aquatic Science 71: 675-687.

Find the paper here

Catch-and-release angling for endangered species

Many fish populations are in serious decline as a result of human activities. Usually, commercial harvest of threatened fish is curtailed to protect the dwindling population. However, recreational angling (especially catch-and-release angling) of the same species is often allowed to continue. In a recent article in the journal Fish and Fisheries, Dr. Steven Cooke (Carleton University) and an international team of authors ask whether catch-and-release angling for endangered fish is a conservation problem, or if anglers act as protectors and stewards of threatened fish populations.

In their article, the authors review case studies of 6 fisheries where catch-and-release angling of endangered fish is common. In these fisheries (Atlantic bluefin tuna, hammerhead shark, mahseer, taimen, white sturgeon, Murray cod) the angling community is involved in a variety of conservation based actions to protect the target fish. For example, mahseer anglers in India have been involved in stocking programs and habitat protection, as well as creating antipoaching camps.  Similarly, white sturgeon anglers in British Columbia must apply for a special license to fish for the species, with proceeds from the license going to research and conservation. Additionally, most white sturgeon guides in BC participate in monitoring programs, which provide crucial data to fisheries scientists to correctly manage sturgeon populations.

The crucial question then, is whether these types of conservation programs offset the potential negative consequences of catch-and-release angling. In all species, catch-and-release angling is associated with some mortality, and can also have sub-lethal effects that can decrease fish reproduction or growth. However, for many species there is no scientific data on how catch-and-release angling affects fish. Dr. Cooke and colleagues recommend that collecting this type of data should be one of the first steps in deciding whether recreational angling should be allowed.

The authors suggest that in some cases, but not all, catch-and-release angling can have a conservation benefit for endangered species. This will primarily be the case when angling leads to low mortality rates, and anglers raise money and awareness for threatened populations. The authors also propose that strict guidelines for catch-and-release angling of endangered species need to be in place, such as having a mandatory guide and adopting closed-seasons to protect reproductive individuals. However, in some cases catch-and-release angling could hinder conservation efforts even with strict angling guidelines. As a result, managers should decide on a case-by-case basis as to whether recreational angling for endangered species should be allowed.


Citation: SJ Cooke et al. In Press. Angling for endangered fish: conservation problem or conservation action? Fish and Fisheries 00:000-000

Link to the paper

Read more about Dr. Cooke’s research here

How do hatchery conditions influence trout behaviour?

The environment that animals grow up in can have profound influences on their later life. In hatcheries, fish are often raised in unnatural conditions, and it is unclear how the hatchery environment itself influences fish behaviour. Most hatchery pens contain a very high density of fish (thousands of individuals) but are otherwise barren. These conditions obviously differ from the environment a trout fry would experience in the wild, where individuals are more spread out and the physical environment is very complex due to the presence of rock, logs, waterfalls, etc. An important question then, is how does density and the physical environment in hatcheries affect the behaviour of released fish, especially considering that a fish’s behaviour influences its ability to survive and reproduce in the wild.

To address this question, researchers from the University of Gothenburg performed an experiment on brown trout from the Dal River in Sweden. They raised brown trout fry in pens with the same density as traditional hatcheries (2500 individuals per square meter) and in two lower density treatments (600 and 150 individuals per square meter). In half of the pens, they also added artificial plants and rocks to simulate structure that would be found in the wild. The researchers then quantified their behaviour in an experimental maze and also in an enclosed natural stream.

The researchers found that rearing density had very important effects on behaviour. Individuals raised in the lower density treatments were better at finding food in the maze and were faster to eat a new type of pretty they had never seen. Additionally, the low density fish were almost twice as likely to survive in the stream as the high density fish. Conversely, the researchers did not find any difference in behaviour as a result of having structure in the rearing pen, and so it seems that the physical complexity of the environment might not be that important for young trout.

The study concluded that more natural rearing densities probably improves the learning of life skills in young trout, and so we should consider changing hatchery practices in order to produce fish that will better survive and reproduce in the wild.

Citation: S Brockmark et al. 2010. Less is more: density influences the development of behavioural life skills in trout. Proceedings of the Royal Society B: Biological Science 277:3035-3043

Angling induced evolution causes changes in foraging behavior

Every angler knows that some fish are easier to catch than others. For some reason, certain fish find lures, bait and flies irresistible, while other fish timidly lurk in deep pools and frustrate even the most persistent angler. In catch and keep fisheries, fish that are more likely to be caught are removed from the gene pool and this process can lead to what is called ‘angling induced evolution’. Over time, the characteristics that cause fish to be easily caught are eliminated from the population, and the characteristics that cause fish to avoid being caught become more common.

In a study in 2011, researchers from the Illinois Natural History Survey and Carleton University tested how angling induced evolution changes the foraging behavior of largemouth bass.  Using a small pond in which all largemouth bass were marked, the scientists tracked how many times each fish was captured in a given year. If a fish was captured more than 4 times in a year it was allowed to breed to produce a ‘high angling vulnerability’ line of offspring, while fish that were never captured were bred to produce a ‘low vulnerability’ line. The researchers repeated this process over 4 generations to cause evolutionary changes.

After the angling induced evolution was completed, the researchers quantified the foraging behavior of juvenile fish in tanks with small bluegill sunfish. They found that fish selected for low angling vulnerability had higher prey rejection rates and would only attack prey if it was close to them, which is consistent with the behavior of fish that are hard to catch. Interestingly though, the low vulnerability fish actually caught more prey overall than did the high vulnerability fish, and they were more efficient at converting food into growth.

The authors concluded that angling induced evolution can cause important changes in foraging behavior in relatively short time periods. If they can observe changes in only 4 generations, we can imagine the changes that thousands of years of fishing has caused on natural fish populations!


Citation: M Nannini et al. 2011. The influence of selection for vulnerability to angling on foraging ecology in largemouth bass Micropterus salmoides. Journal of Fish Biology 79: 1017-1028.

Find the paper here 

Brown trout compensate for a bad start

Some animals can overcome early life challenges (such as unfavourable environmental conditions) through compensatory growth. This process occurs when animals ‘catch-up’ to other members of their species by growing faster after the challenge is over. Compensatory growth occurs in many species in the lab, but how compensatory growth operates in nature is not well understood.

In a recent study in Public Library of Science One (an open access journal, so you can download the paper!) Fredrik Sundström and colleagues from the University of Gothenberg studied compensatory growth in one year old brown trout. They brought a bunch of fish into the lab, and restricted their food intake to simulate challenging environmental conditions. After the three-week food restriction, the fish were significantly smaller than a control group, indicating that the food restriction had been stressful. All of the fish were then released back into the wild in one of two conditions, some individuals were released in high-density areas with many other fish added by the researchers, while others were released into areas with a natural density of other fish. The authors then periodically recaptured the individuals over the next year and measured their body size.

 What the authors found was that the starved fish grew faster than the control fish over the next summer, which showed that compensatory growth does occur in the wild. However, the fish in the high-density environments grew slower than those in the low-density environments, suggesting that compensatory growth is harder to do if there are many other individuals around competing for food. By the following spring, the starved fish had completely caught up (in body size) to the control fish.  As a result, the study concluded that young brown trout can compensate for short term challenges with compensatory growth, but whether or not they can compensate for longer stressors, or if older fish also show compensatory growth are questions that remain to be answered.

Citation: LF Sundström et al. 2013. Density dependent compensatory growth in brown trout in nature. PLOS ONE e63287

Find the paper here

The author’s website is here


Is inbreeding a concern for hatchery-raised steelhead?

Because many wild fish populations are in decline, a huge effort goes into supplementing wild populations with fish raised in hatcheries. However, wild fish and hatchery-raised fish are different in many respects (see last week’s post on differences in angling vulnerability), and in many populations hatchery-raised fish are much less likely to survive and reproduce than are wild fish. This reduction in ‘fitness’ of hatchery-raised fish could actually be a conservation concern. It is possible that the release of hatchery-raised fish could decrease the overall reproduction of the population because hatchery-raised fish compete with wild fish for food, and are poorer at reproducing.

In a recent study in the Journal of Heredity, author Mark Christie and colleagues investigated whether inbreeding was responsible for lower fitness in hatchery-raised steelhead in the Hood River in Oregon. Because captive breeding programs often use only a few broodstock, hatchery-raised fish are much more closely related to one another than wild fish are. To test this hypothesis, the authors sampled over 3000 fish from 11 years, and used genetic tools to determine whether the fish were the progeny of wild or hatchery raised fish. In this river, the offspring of hatchery-raised fish are 15% less likely to survive and reproduce than are the offspring of wild fish, however the authors found that only between 1 and 4% of this reduction was attributable to inbreeding. So although the reduction in reproductive success of hatchery-raised fish is still an issue, it is probably not due to inbreeding depression. The authors suggest that other factors such as unintended adaptations to captive environments, might be the reason why hatchery-raised fish are less successful than are wild fish.

Citation: MR Christie et al. 2013. How much does inbreeding contribute to the reduced fitness of hatchery-born steelehead (Oncorhynchus mykiss) in the wild? Journal of Heredity 105: 111-119.


You can find the paper here

The author’s website is here