Yesterday I may have tagged the very last brook trout of my PhD. Nearly 200 fish later, it’s hard to believe I closed that chapter of my research. The tracking will continue for at least another month, and we’ll sample again at least one more time for tissue samples, but I have officially tied my last suture. One step closer.
You may recall that in the summer we did several retagging events so that we had most of our tags running at all times. Yesterday was the only retagging for Fall for two reasons. First, between higher stream flows, tagging larger fish, and an improved suturing technique, we are finding fewer dropped tags. Second, we are very close to spawning season.
We’ve seen signs of spawning for a few weeks. The fish we tagged in September were starting to show their iconic orange-bellied spawning colors, and yesterday they were in full force. We have also seen fish moving a lot, particularly out of deeper pools and into smaller riffles and runs. These areas of faster moving water carry more oxygen than slow water in pools, making them ideal habitats for females to build their nurseries, called redds. When a female is ready to spawn, she moves into a riffle ½-2 feet deep, turns on her side, and uses her tail to clear silt and sand from around the gravel. If you’re near a trout stream in the next few weeks, keep an eye out for an area of lightly colored gravel with depressions and mounds- you’re likely looking at the trout’s labor and delivery room.
As females are building redds, males are nearby fighting with one another for the right to spawn with that particular female. They ‘strut their stuff’ and chase, bite, and engage in lateral displays until the most dominant male wins the contest and others are chased away from the redd. At that point, a male and female pair have been established, and the female will lay eggs and males release milt into the substrate. The female then uses her tail to make some final adjustments and move substrate around to ensure that the eggs have just enough flow to survive, but not too much that they get washed downstream during high flows.
The video below by my friend Derek Wheaton of Enchanting Ectotherms Photography does an excellent job of capturing redd construction and male competition.
Each female releases up to 14,000 eggs, which will overwinter in redds. During this time there is high mortality due to lack of fertilization, floods, predation, or disturbance. But, come spring, the surviving eggs hatch into alevins. At this stage, the fish continue to live in the gravel and feed off of a yolk sac that is still attached to the fish. After the yolk sac is consumed, fish transition into the fry stage and are given a cruel welcome to the real world. Tiny fry consume a lot of energy, and so need to quickly find food, avoid predators, and not get washed downstream. Fry also start competing with one another for access to good habitats, so they need to quickly gain some social skills. Once fry grow a few inches in length, they become parr named for the black ‘fingerprints’ running down their side known as parr marks. It takes about a year for parr to lose those black markings and then, nearly two years after starting as an egg, the trout is now an adult. What a cycle!
During spawning season brook trout are hyper focused on building redds or defending territories. They very often stop paying attention to predators- humans included-and are easy to sneak up on without them swimming away. Many times you’ll see a breeding pair of large trout sitting in the middle of the stream, refusing to move, but ready to eat. The easy catchability and gorgeous bright spawning colors often makes fall a popular time to fish for brook trout. For many states trout season is now closed. But, for states like Pennsylvania where it is still legal to fish for brook trout,
STOP FISHING FOR BROOK TROUT.
At least for a few weeks. Hooking and handling are significant stresses on trout, and juvenile health is a direct reflection on how healthy the parents were during spawning. And, no matter how gentle you handle them, you very likely will cause trout to vacate their territories and seek sub-optimal spawning habitats. Plus, redds are hard to spot with even the most trained eyes, so there’s a good chance you will tromp through and either directly cause egg mortality or interrupt the stream flow the female worked so hard to achieve.
If you hit the streams this winter, remember that redds are active through spring, so keep an eye out and walk on the banks when possible.