Tis' the season- the spawning season that is. We first ran this post back in March of 2015 and you'll probably see it make an appearance back on this blog each spring and fall. It's that much of a 'worth the read' . We all love our trout streams- particularly when they're full of trout. Still, there's no denying they continue to receive quite a bit of unnecessary abuse twice a year when the trout attempt to create their next generation. Take a moment and read this. You'll be a more knowledgable angler because of it. Let's all make it a point to do a better job than we ever have in the past to watch where we're walking and leave actively spawning fish to their business.
Courtesy of Toby Stuart, Senior Aquatics Biologist for Freestone Aquatics
Successful trout spawning is typically dependent on three limiting factors. Available streambed substrate, water temperatures, and stream gradient. The following paragraphs describe each of these significant limiting factors.
Water temperature is the single most limiting factor surrounding fisheries productivity and sustainability. The temperature of the aquatic environment surrounding trout usually provides the catalyst that initiates spawning behavior. Spawning behavior of different trout species is dependent on seasonal influences associated with climactic change. Rainbow and cutthroat species generally spawn in the spring months, whereas, brown and brook trout spawn in the fall months. However, the controlled environment of laboratory water temperatures has created a fall spawning rainbow trout. When spring temperatures reach approximately 45ºF rainbow and cutthroat trout begin spawning. During fall months when temperatures range from 46ºF to 51ºF, brown and brook trout will begin to exhibit spawning behavior. The incubation period is directly related to water temperature also. Eggs fertilized around 45ºF will take approximately 7 weeks to hatch, whereas, eggs fertilized around 55ºF can take only three weeks to hatch.
Rainbow, brown, brook, and cutthroat require a streambed of clean, silt-free, well-aerated substrate for spawning. Although brook trout and brown trout are primarily stream spawners, they can spawn in lakes with adequate circulation and suitable spawning substrate. Substrate (streambed composition) is preferred in the 6 to 12 millimeter range (pea sized gravel). When a suitable location is found in-stream, the female will manipulate the streambed with her fins and tail utilizing the conveyance of flowing water to remove the finer streambed material. A clean, well-sorted oval of substrate usually 1-3 feet in diameter is the result of the female’s efforts. This process is the creation of a spawning redd. The redd is where the eggs will be laid and fertilized. Following the deposition of eggs from the female, a male of the requisite species will fertilize the fresh eggs. The now fertilized embryos will incubate and hatch from this same location. The removal of the finer material allows the well-oxygenated water to reach the fertilized eggs now residing in the redd. Many studies have shown that embryo mortality increases as the increased percentage of this spawning substrate consists of fines (streambed material <6mm in diameter). These fines lead to an embedded (embeddedness is the degree to which fine sediments surround coarse substrates on the surface of a streambed) streambed and essentially starve the eggs of oxygen during the incubation period. Preferred size of substrate can vary with the size of the reproducing fish. Larger fish are capable to creating redds using larger streambed material. However, fines and embeddedness still apply to the survival of the embryos.
The third limiting factor is the gradient of the streambed. Typically, trout will spawn in areas displaying a 2% to 5% fall. Gradients less than 2% do not provide flows necessary to remove the finer sediments. Additionally, areas lacking fall will often not provide the oxygenation needed by developing embryos. Areas exhibiting fall >5% challenge trout to maintain their redds and tax their physical stature during the process. Trout expend a great deal of energy during the spawning process; therefore, undesired stress can greatly affect the success of the spawning event.
In short the three factors determining spawning success for trout species are not always at the forefront of anglers minds. Spawning trout are very territorial and will maintain and protect created redds. Often anglers will fish to spawning fish unknowingly. Traditionally, the hook-up of the fish is not because of the fishes desire to eat, but of an instinctive action to either clean, maintain or protect the redd. Because the response is instinctive, spawning fish are more susceptible to being hooked while displaying these types of behavior. Mortality rates increase significantly for spawning fish that are caught and released. For this reason, please be mindful when fishing during these spawning times. Do not fish to actively spawning fish and be careful when wading to not walk through redds. Take the time to identify when fish are in the act of spawning, and if they are, leave them to complete their reproductive process. We certainly still encourage you to continue fishing during this time of year, just to do so with ethical angling practices in mind which will only benefit our future days as a whole.
It is Freestone’s hope that the information provided will help anglers and fisheries managers become more aware of spawning trout, their environment and the delicate nature of the spawning process. As the futures of our fisheries and self-sustaining fish populations rely on their spawning success.
For questions or comments, please contact Toby Stuart at firstname.lastname@example.org
About the author/Freestone Aquatics- Toby Stuart is the Senior Aquatics Biologist for Freestone Aquatics, as well as a Professional Fly Fishing Guide. To give you a little background on Freestone Aquatics, they are a Denver, Colorado based fisheries management and freshwater habitat consulting operation. Their stream improvement/habitat restoration work can be seen all across the state of Colorado, as well as in New Mexico, Wyoming and even Washington State. In fact, if you’ve ever fished one of our exclusive properties, then you’ve fished a Freestone Aquatics property! Freestone Aquatics is responsible for the stream improvements (and phenomenal fishing!) for the Rowdy Trout, YR and WCR Ranches. In business since 1999, their mission statement pretty much sums it up perfectly, “It is the sole goal and mission of Freestone Aquatics, Inc to bring our customers the highest level of uncompromised, professional environmental services. Our customers have trusted us with an aspect of their legacy that will be enjoyed by their families, friends, and clients for years, and it is our responsibility to provide them with the highest level of service, technology, and quality available. We have a sustainable and environmental obligation and responsibility to the precious resources of each property that we evaluate, design, and construct. We conduct ourselves in an ethical and moral manner at all times, while keeping the needs and goals of our customers in focus. We are loyally devoted to serving our customers and improving the environment.”
I encourage you all to visit www.freestoneaquatics.com to learn a little more about what they do, and check out some of their past projects. It’s pretty impressive stuff. Whether you’re looking to build the pond of your dreams, or clean up the stream running through your property, Freestone Aquatics has the resources, knowledge and experience to create the aquatic habitat of your dreams.