Brook trout conservation, new research

This December 2015 video from North America says about itself:

Brook Trout in ULTRA HD 4k (Salvelinus fontinalis): Under Water Spawning and Life Cycle

– In the last three months of the year, mature brook trout, aged 2 to 5 years, make their way to suitable spawning locations.

– Brook trout seek out very specific areas to deposit their eggs.

– Brook trout will key in on gravelly or sandy areas of lake bottoms, creeks, or rivers. In lakes where current is not present, brook trout will find upwelling springs that will serve to aerate the eggs.

– Brook trout are a highly sensitive fish species. Only lakes, creeks, and river systems unaffected by pollution and acid rain, with high oxygen content and cool temperatures, offered by up-welling springs or current, will successfully harbour populations of brook trout.

– The underwater footage of fish spawning in this video was taken in early December at the base of a long white water run.

– Once the females have located suitable spawning habitat, she will use her tail fin to excavate a shallow depression called a “redd” which will serve as a nest for the eggs.

– The debris that is turned up is carried downstream by the current.

– The female will check the depth and thus suitability of the nest by lowering herself to the river substrate. She tests it by keeping her pelvic, anal, and caudal fins stiff, to see if they touch the bottom.

– The more brightly coloured male will closely guard the female and position himself so that he can fertilize the eggs once released. The male makes various advances and passes, nudges, and comes alongside the female so that their bodies touch in order to stimulate her to release her eggs.

– When the female is finally ready to deposit her eggs she will drop her anal fin deeply into the depression and then arch her back. Both the male and female will then open their mouths wide and tremble with rapid undulations of their body as the eggs and milt are simultaneously released.

– As fertilization occurs externally, more than one male might fertilize the same batch of eggs.

– A female may lay between 20 and 5000 eggs depending on her age, overall size, and health. She does not lay her eggs all at once, but instead releases 15 to 60 at a time.

– Eggs must be fertilized within the first 3 minutes, but are most successfully fertilized immediately upon release. Fertilization success rates are often between 80 and 90 percent.

– Eggs are frequently eaten by other fish species or can even be cannibalized by other males in the vicinity. Only about 1 to 2 percent of eggs will survive to adulthood.

– After spawning, the female will cover the eggs by displacing sand and gravel. She does this with a slow-motion sweeping of her tail to gently move gravel over the eggs without touching them. This “postnuptial dance” helps protect the eggs from predators as they develop over the next 3 months.

– The female will aggressively drive off any fish that may come near the redd.

– After spawning has occurred, the male will lose interest in the female and move off in search of another female building a redd. If the male is persistent, he may fertilize the eggs of multiple females.

– The female, on the other hand, will move off a short distance, only to begin cutting a new redd for another batch of eggs.

– After about 2 weeks, the eggs will develop eyes. The eggs absorb oxygen from the water and feed off their yolk sack for nourishment.

– At this stage, it is imperative that water remains between 1 to 13 degrees Celsius. Higher temperatures will destroy the eggs, as will sub-zero temperatures.

– The eggs will hatch sometime between February and March. At this point, they will still feed off their yolk sac and are called fry or alevin (aləvən).

– Once the yolk sac is used up, usually by March or April, the fry will begin eating plankton or microscopic animals found in the lake or stream.

– By the end of the summer, the trout will be 2 to 3 inches long. As they are still quite small, they will spend much of their time hiding under and around rocks, while feeding on small insects and plankton.

– Trout will reach sexual maturity when they are around 5 to 10 inches long.

– The following clips demonstrate various spawning activity. You will see the female digging out a redd, while the male carefully monitors her movements in anticipation of fertilizing her eggs. You will also see males trying to move in and out-compete other males for breeding rights.


From Penn State University in the USA:

Larger streams are critical for wild brook trout conservation

June 3, 2020

The Latin name for brook trout — Salvelinus fontinalis — means “speckled fish of the fountains,” but a new study by Penn State researchers suggests, for the first time, that the larger streams and rivers those fountains, or headwaters, flow into may be just as important to the brook trout.

With few exceptions, brook trout are found now only in small mountain streams that stay cold enough year-round to meet their biological needs, below 68 degrees Fahrenheit. Because these trout in the United States are threatened by a warming climate, many have assumed those headwater habitats alone are critical for their survival.

But a genetic analysis of brook trout in streams across the 460-square-mile Loyalsock Creek drainage in north-central Pennsylvania shows that the fish are very similar genetically, suggesting close relatedness among populations. The only way that could have happened, according to researcher Shannon White, postdoctoral scholar in the College of Agricultural Sciences, is fish moving between tributaries in the 86-mile-long Loyalsock Creek.

Temperatures in Loyalsock Creek exceed brook trout thermal tolerance from approximately June through September, White pointed out, so fish are believed to inhabit only the bigger river system during the winter. Although the behavior and survival of brook trout in Loyalsock Creek are not well understood, researchers hypothesize that some brook trout move into the mainstem after spawning in a tributary in October or November and stay until late spring, when some swim up new tributaries.

“It’s pretty simple — if widespread populations are related genetically, it indicates that fish are moving around between those populations,” she said. “There’s a high degree of genetic connectivity between populations separated by the mainstem, and that indicates that brook trout are swimming into Loyalsock Creek and using it as a movement corridor to connect populations in other tributaries.”

Understanding patterns of population connectivity is critical for species conservation, White added, because populations that are more connected typically are able to survive and adapt to disturbance and stress.

To build what White called “a family tree” of brook trout in the Loyalsock drainage, researchers collected 1,627 adult brook trout from 33 sites, with an average of 49 individuals collected from each site. They clipped the caudal fins of those fish and conducted genetic analysis on those tissue samples.

To estimate statistically how unique habitat features, such as road culverts and waterfalls found in streams, influence the movement of wild brook trout, researchers developed what they call the “bidirectional geneflow in riverscapes” model as part of a practical framework that uses genetic data to understand patterns and drivers of fish movement.

The novel modeling approach is significant, explained researcher Tyler Wagner, adjunct professor of fisheries ecology, because it shows that brook trout — at least in the Loyalsock Creek watershed — are not confined just to the headwaters. They are using the mainstem as a seasonal, thermally suitable corridor for movement.

There is no reason to expect that the Loyalsock drainage is different from others in the East, Wagner contends, so these results likely have implications for the conservation and management of wild brook trout. Specifically, these results suggest that conservation of larger streams and rivers may be necessary to protect and conserve critical brook-trout movement corridors that keep brook trout populations healthy.

“Some of the most fundamental questions in ecology relate to how organisms move through their environment,” said Wagner, who is assistant leader of the U.S. Geological Survey’s Pennsylvania Cooperative Fish and Wildlife Research Unit at Penn State. “These questions historically have been hard to address in fishes because it can be difficult statistically to estimate how unique habitat features found in streams and rivers influence movement. To address this void, we developed the riverscapes geneflow model.”

The findings of the Penn State study, recently published in Ecological Applications, contrast with other research related to brook trout behavior, White conceded. The consensus has been that trout do not move very far, she said. “But Loyalsock Creek is a fairly big watershed, and we have found that fish are moving quite a bit, and populations on opposite ends of the watershed are connected to one another genetically.”

However, White, who conducted a wide range of research on the brook trout population in the Loyalsock drainage while pursuing her doctoral degree in ecology at Penn State, noted that only a small proportion of the fish travel — and it is not just the young males that branch out. This is different from most wildlife species.

“In a separate study we used telemetry to monitor the movement of 162 fish and found that there is a small proportion of the population that moves,” she said. “It’s only about 20% of fish that get into Loyalsock Creek. In terms of males, females, and the size of fish that are moving, it doesn’t really seem to make a difference. This would suggest that there may be a genetic component to movement, in the sense that some fish have genes that are programmed to make them travel.”

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