Learning in a degraded habitat

[Editor’s note: This article was written by Dr. Adam Reddon. Adam is a widely published fish biologist who works at McGill University in Montreal. His research focuses on aggression, learning, predator-prey relationships and neuroscience in fishes. Follow him on Twitter @adamreddon or visit his website at adamreddon.ca ]

Habitat degradation can have major impacts on fish communities. Changing the environment can shift the balance of power between species, allowing some species to flourish while others suffer. Often a small number of species will exploit the new conditions and become highly abundant while the overall diversity of animals found in a degraded area decreases. Altered habitats can reduce the amount of food, shelter and breeding substrate for certain species causing their populations to decline. There may be other, less obvious routes through which habitat degradation impacts fish. For instance, changes in the environment may have impacts on the cognitive or sensory capabilities of some fish, resulting in a reduced ability to avoid predators or find the resources they need to be successful.

McCormick and Lönnstedt (2016) examined how coral reef destruction may impair the ability of certain fish species to learn the identities of new predators and respond correctly to cues of predation risk. Many reef dwelling fish species spend a larval stage floating around the ocean amongst the plankton, before setting down on the reef to spend their adult lives. This transition is a very dangerous time for these fish because they must quickly learn whom among the reef community poses a threat and which animals are benign. Failing to react to a predator can mean certain death, but reacting to non-threatening animals can waste valuable time and energy. Learning all of this information is a challenging task and many of these newly settled reef dwellers do not last long in their new homes. The easiest way to learn if an unfamiliar animal is dangerous is through direct interaction, if a fish chases you trying to eat you and you escape, you now know that species is a threat. However, this is a pretty dangerous way to go about acquiring knowledge, as one false move could spell the end.

Luckily, fish of all kinds have evolved an ingenious system for marking unknown stimuli as dangerous using their sense of smell. Fish normally react very strongly to the smell of damaged individuals of their own species. If another member of your species has been injured or killed, chances are something dangerous is nearby and you should take heed. Fish react to these damage induced odours innately, meaning they don’t have to learn this association, they know from birth that the smell of injured members of their own species means that danger is afoot. What fish do learn is the association between these smells and other odours, sights or sounds in the environment. If a fish smells the scent of a conspecific (a member of the same species) that has been injured along with the odour of some unknown species of animal mixed together, they quickly learn that this other unfamiliar smell is probably from something dangerous and should be treated with caution when it is encountered. Using this powerful ability to form associations, fish can learn about possible dangers without having to engage in risky interactions with unfamiliar potential predators.

Recent evidence has suggested that coral reef bleaching, caused by increasing ocean temperatures and altered water chemistry may impair the ability for reef dwelling fish to learn about new predators using odour cues. McCormick and Lönnstedt (2016) sought to better understand this effect, determine if it affected different species equally and see if the fish had to be living directly on degraded corals or if dead corals nearby were enough to throw the fish off. McCormick and Lönnstedt captured ambon damselfish (Pomacentrus amboinensis) as they were approaching a reef following their larval stage. The authors then trained the fish by exposing them to a combination of the smell of damaged ambon damselfish and water that had been used to hold a novel predator, the dottyback (Pseudochromis fuscus). After this exposure, the authors placed the ambon damselfish onto one of four types of experimental habitats: a healthy piece of live coral surrounded by live corals, a dead coral surrounded by live corals, live coral surrounded by dead coral and dead coral surrounded by dead coral. The scientists then conducted a test where they gave the fish a shot of water containing either the smell of damaged conspecifics, the smell of dottyback predators or no odours at all and then watched the reactions of the ambon damselfish to each stimulus. What the authors found was that ambon damselfish living in the pristine habitat (on a live coral surrounded by live coral) reacted as one would expect. The plain sea water was ignored while the smell of either the damaged ambon damselfish or the smell of the predatory dottyback was treated with fear: the fish stopped moving, stopped eating and quickly retreated to their shelters. However, if the ambon damselfish was exposed to degraded corals, either directly or in the surrounding habitat, their reaction was very different. Instead of hiding in fear in response to the dangerous stimuli, the fish exposed to dead corals did just the opposite, they moved more, went further from their shelters and increased their foraging rate. These are risky things to do if there is a predator around and suggest that the dead corals are interfering with the ability for the ambon damselfish to respond appropriately to cues of danger, something that may get them eaten and thus potentially have a negative impact on their population. Interestingly, its not that the dead coral merely made it impossible to for the ambon damselfish to smell the predators or damaged conspecifics, because the fish exposed to dead coral still reacted to these odours, but something about the dead corals alters the behaviour in response to these cues, potentially with dangerous consequences.

Ambon damselfish have trouble learning about predators in degraded habitats

Ambon damselfish have trouble learning about predators in degraded habitats

Ambon damselfish are habitat generalists, meaning they will live in a variety of different sorts of places, including both live and degraded reefs. McCormick and Lönnstedt wanted to see if they would find the same sorts of effects of dead coral on the behaviour of another species, the neon damselfish (P. coelestis). Unlike the ambon damselfish, the neon damselfish specialize on living in rubble conditions similar to those found in dead and degraded reefs. When the authors did a similar test on the neon damselfish they found that this species reacted just fine even when living on a dead coral. This suggests that the effects of habitat degradation are species specific and depend on the sorts of habitats the animals normally live on.

Together, the results of McCormick and Lönnstedt’s paper suggest that habitat degradation can affect species through less obvious means than just changes in the resources available to them. Changing habitats can also alter the cognitive abilities and behavioural responses of fish, which may have important effects on how well they adapt to changing conditions. Some species may find ways around these impacts and do well even in degraded habitats, while other species do not. It is important for us to consider the effects of climate change and habitat degradation on the cognition and behaviour of different species, and seek to understand why some species may be impacted while others are not.

Mccormick, M. I., & Lönnstedt, O. M. (2016). Disrupted learning: habitat degradation impairs crucial antipredator responses in naive prey. Proceedings Biological Sciences / the Royal Society, 283(1830), 20160441–8. http://doi.org/10.1098/rspb.2016.0441

Find the article here

Barbel Bait Buffet

[Editor’s note: This article was written by Laura King. Laura is an ecologist currently on an extended conservation expedition in Mauritius, a tiny island off the coast of Eastern Africa. Follow her adventures on Twitter @LaurasWildlife]
     Bait, lures, spinners, spoons, flies, pellets….we spend a lot of time thinking about what to use. But how often do we think about our bait affecting the ecology of a lake or stream? We do try to not dump live bait and to not use certain introduced species as bait as we know this could harm our favourite spots.
     However, a recent study demonstrated interesting impacts to rivers in the UK from pellets. Pellets (in bait balls) are popular for cyprinid fishing (carp and barbel), and are very high in calories. Anglers often use more than 1 kg of pellets per day in these rivers, so pellets are essentially a superfood that would be regularly available to fish there.
     Whenever we as humans introduce something new to any ecosystem, we never know exactly how the food web might shift. A new study looked at the diet of the European Barbel (or Common Barbel, Barbus barbus) in four rivers to see how much of its diet was made up of pellets, and if there were any other impacts from having so much extra food around.
River_Wye_barbel

Common barbel. Photo credit to VagrantDarter

     To do their study, they went fishing (of course) and took 3-5 scales off each Barbel. They also kick-sampled in the rivers for invertebrates and small fish (important parts of the Barbel’s natural diet) and then used stable isotope analysis. Stable isotopes can identify these different prey items, and so the researchers could find out just what the Barbel had been eating for the last few months from just their scales.
     They showed that the Barbel from the four different rivers ate completely different amounts of pellets. For some Barbel, the pellets made up only 9% of their diet, but in three of the four rivers, the proportion of pellets eaten by an individual Barbel could be in the 70% range, as high as 79% pellets! So, amazingly, some (but not all) Barbel are pretty much avoiding their ‘natural’ diet of invertebrates and small fish to eat delicious pellets instead. This probably shows us why anglers use pellets in the fist place!
     What are the consequences of this much added ‘food’ in the system introduced by anglers? Well, the authors cite a different paper that showed that the thousands of tonnes of bait ended up changing water chemistry because it added so many nutrients to rivers in Germany. They don’t know what the effects are in these UK rivers, but that would be another even more interesting question that would be nice to see answered in the future. Interestingly, it also shows us how adaptable Barbel can be between different rivers because many end up shifting to pellets for their main food source. Given lots of easy and nutritious extra food (that can’t even get away from them!), Barbel seriously take advantage of their all-you-can-eat bait buffet.
     Citation: T Basic et al. 2015. Angling baits and invasive crayfish as important trophic subsidies for a large cyprinid fish. Aquatic Sciences 77: 153-160. Find the paper here

Of Moons and Muskies

Article written by Sean Landsman

[Editor’s note: This article is the first in a series written by guest authors for this blog. This article was written by Sean Landsman, a PhD candidate at the University of Prince Edward Island. Sean is an incredible photographer and an accomplished angler. Check out his webpage for some amazing fishy photos].

Full moon. New moon.

These are two of the most important phases of the lunar cycle for anglers. Talk to just about any accomplished angler and they’ll tell you that catch rates around these moon phases often go up dramatically.

But is it a self-fulfilling prophecy? If the fishing community pushes the Kool-Aid for years and years, eventually you’re bound to drink it, right? I’m certainly guilty of leaning heavily on moon phases. I fish my best spots around moon rise/set and plan long-distance fishing trips around the moon phases.

Consider, too, the effect of lunar cycles in freshwater. Or rather, is there an effect at all? Certainly large tide swings (i.e., “spring tides”) are consistently associated with the new and full moon periods. So, for saltwater species this may have a huge impact on habitat availability and access to resources (e.g., large tidal flushing moves more food in and out of habitats).

However, in freshwater environments such as lakes, ponds, and rivers, there are no tides (Great Lakes aside). So then what is the biological effect? Is it increased light levels at full moons? If so, how would that explain higher catch rates during new moons?

The Science

Let’s examine a paper published two years ago in 2014 about moon phases and muskie (i.e., muskellunge Esox masquinongy) catch rates. For those not familiar with muskies, they are close relatives of the northern pike, sharing several similar characteristics such as large, well-developed teeth, long bodies built for speed, and a predominantly sit-and-wait foraging tactic. Muskies are native to temperate North American waters, extending south from the Carolinas up to northern Ontario.

Two scientists examined the relationship between muskie catch rates and lunar phases by studying almost 240,000 catch records from Muskies, Inc. (a conservation and fishing organization). Catch records from Minnesota, Wisconsin, Canada, and Ohio were examined. Each date a fish was caught was then related to a specific lunar phase. The authors also compiled angler effort data to address whether catch rates could be biased because anglers focus their efforts during the full and new moon periods.

After a series of complex statistical analyses, their results did indeed indicate that lunar phase has a significant impact on angler catch rates. Specifically, new and full moon periods were the best predictors (of all possible lunar phase combinations) of an angler catching a muskie. And bigger fish were also caught during these full and new moon periods.

As a default explanation for these findings, the authors’ hypothesis was that angler effort is simply more concentrated during these time periods. The authors acknowledge that this is something that cannot be ignored. However, their findings showed that lunar phase only significantly affected angling effort for one specific lake in Minnesota.

What their data point to is some sort of synchronicity occurring between muskies and the lunar cycle. The authors also noted that catch rates were similar between new and full moon periods. If this were not true (for example, if catch rates were greater during full moon periods only), then one might correctly posit that full moons lead to increased light levels and increased muskie foraging. However, the authors’ results do not support this.

So what the heck is going on then? The answer is really that we still do not understand the underlying mechanism. The authors suggest that synchronizing feeding behaviour with the lunar cycle must confer some advantage to individuals.

OLYMPUS DIGITAL CAMERA

The author with a 48 inch muskie captured almost to the minute of a rising full moon (just out of frame).

Of Moons and Anglers

 So what does this mean for us anglers? This study certainly lends quite a bit of credence to focusing efforts around the new and full moon periods, at least for muskies. Many of us cannot afford to fish whenever we want to so maximizing our time on the water becomes important. If you feel guilty about “drinking the Kool-Aid,” as I sometimes do, I think this study should allay that guilt.

To end on a personal note, I still have a hard time understanding how moon phases affect muskie behaviour. Without a clear explanation, I will continue to be skeptical. What do you think? Do you plan your fishing trips around the new and full moon periods? Do you have any hypotheses that would explain increased catch rates – muskies or otherwise – during these moon phases? Feel free to add your thoughts in the comments.

 

Citation: Vinson MR, Angradi TR. 2014. Muskie Lunacy: Does the Lunar Cycle Influence Angler Catch of Muskellunge (Esox masquinongy)? PLoS ONE 9(5): e98046.

Find the paper here.

Ice baths are relaxing for brown trout

I think that one of the reasons that people are fascinated with fish is that they are hard to observe. Fish live in a world that is difficult to visit and largely mysterious to us air breathers, even though that world might be only a few feet underneath your boat or dock. While the underwater world might seem like an alternate dimension, the under ice world is even more distant from people’s understanding. Anyone that has stood on a frozen lake has wondered what is going on underneath them, but under ice behavior is notoriously hard to study because it’s cold and dark down there.

A cool new study by researchers from Sweden and Norway has shed some light on what trout are doing under the ice. They built stream channels in the lab that had a window on one side (to observe the fish) and added ice cover to the top of the channels to simulate a frozen river environment. In each channel they added 4 brown trout and observed their feeding and swimming behaviour.

The researchers found that adding ice cover (while keeping the water temperature constant) influenced a variety of trout behaviors. Trout living under ice cover had decreased stress levels and spent more time actively swimming as opposed to holding on the stream bottom. The researchers suggested that the presence of ice could cause fish to become more active because ice decreases the risk of predation (at least from birds).

Additionally, trout living under ice had more aggressive interactions with one another than those in open streams. This effect could be due to increased activity in general from fish under ice. It is interesting that fish still had lower stress levels under ice despite the increase in aggressive interactions, which suggests that for these fish the decreased predation risk was more important than increased social aggression in determining stress levels.

Since global warming is reducing the duration that rivers are ice covered, studies like this help us understand how the changing climate will influence fish behaviour. Previous studies have already shown that salmonid production is higher in ice-covered rivers than in rivers that are ice-free, and now we know that fish are more stressed when their icey ceilings melt away.

 

Citation: J Watz et al. 2015. Ice cover alters the behavior and stress level of brown trout Salmo trutta. Behavioral Ecology 26: 820-827

 

Find the paper here

Different angling methods have different influences on fish populations

There’s no doubt that fishing causes changes to fish populations, which is why anglers dream of travelling to remote locations where few people have fished before. In some fisheries, larger individuals are selectively removed, which can result in a decrease in growth rate of individuals over time (since those who grow fastest get big, and then get caught). In other fisheries, aggressive and bold individuals may be more likely to be captured, resulting in the evolution of a more passive, shy population over time. These changes are referred to as ‘angling induced evolution’, and can have a very strong influence on fish behaviour.

However, two recent papers have suggested that different methods of fishing can select against individuals with different traits, and could cause different evolutionary outcomes for fish populations. In one of those studies, Dr. Alex Wilson and colleagues from Carleton University tested whether fish caught with hard-bodied ‘crank-bait’ type lures were behaviourally different than fish caught with soft plastic worms. First, they angled wild rock bass and large mouth bass using the different lures, and then brought the fish back to the lab for behavioral testing. They found that fish caught with crank-baits were generally bolder than fish caught with plastic worms, suggesting that the evolutionary consequences of angling might be dependent on the type of lure used!

Additional evidence that different fishing methods capture individuals with different behaviour came from a study by researchers at the University of Bergen (in Norway). The Norwegian team tested whether individuals captured by trawl fishing were behaviourally different than those captured with a passive minnow trap. They performed their study in the lab on guppies, using miniaturized trawls and traps to simulate a larger fishery. What they found was that bolder individuals were more likely to be caught by the trap than shy individuals, but were less likely to be caught by the trawl. The exact same individuals that were more likely to be caught by one method, were less likely to be caught by the other!

Taken together, the results provide some pretty strong evidence that different types of fishing capture fish with different personalities. As a result, it could be beneficial to have a diverse mix of angling activity (e.g. fly fishing, bait fishing, traps) in order to maintain behavioural diversity in a population. Furthermore, the results of these studies suggest that in areas with high fishing pressure it might be a good idea to try an unconventional tactic – if you do, you might just have evolution on your side!

Citations:

ADM Wilson et al. 2015. Does angling technique selectively target fishes based on their behavioural type? Public Library of Science One. e0135848

Link to the paper here

B Diaz Pauli et al. 2015. Opposite selection on behavioural types by active and passive fishing gears in a a simulated guppy Poecilia reticulata fishery. Journal of Fish Biology 86:1030-1045.

Link to the paper here

 

 

Is climate change driving Arctic char upriver?

Arctic char are a pretty incredible animal. They are the most northern freshwater fish on earth, can live for over 20 years, have incredible coloration, can grow to over 30 pounds and are voracious cannibals. Arctic char are the trout of the north, and they thrive in frigid, dark habitats.

In most of their range, Arctic char are classified as semi-anadromous. Many adult fish migrate out into the ocean in the spring and return to freshwater in the fall, where they spawn and overwinter in lakes. However some individuals stay put in freshwater year round, and in some cases entire populations stay permanently in freshwater.

In a study in the journal Global Change Biology, researchers from Norway and Sweden investigated how Arctic char migrations might change with a warming climate in the north. Many bird populations are showing altered migratory timing in response to climate change, but would there be similar effects on fish?

First the researchers needed to determine what factors influenced migratory behaviour in Arctic char. Why did some some populations migrate out to the ocean while others stayed put in freshwater? They found out that migration was more common in areas with low primary productivity, and in areas with shorter migration distances to the sea. So if there was lots of food around, and the sea was hard to reach, char might be convinced to stay in freshwater throughout the year.

Next, the researchers used climate models to predict the change in productivity of lakes along the coast of Norway, and how this might influence the range of Arctic char. Various climate models predicted that primary production in lakes will increase with climate change, and as a result there will be more food available for char in freshwater. This led the researchers to predict that there will be less anadromous populations, and more freshwater populations of Arctic char in the future. Ultimately, this will decrease the range of Arctic char, since less fish will migrate out to the ocean. The researchers don’t speculate on whether this will influence overall population size of Arctic char, but there might be fewer spots to fish for them in the future.

Citation: AG Finstad and CL Hein. 2012. Migrate or stay: terrestrial primary productivity and climate drive anadromy in Arctic char. Global Change Research 18, 2487-2497.

Link to the paper here

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