Trout Nursery and Rearing Habitat

by Jerry Burton, NMT President
From the October/November 2014 Newsletter

After trout eggs that have been buried in the stream gravel hatch, the emerging fry need areas with cover and low water velocity. They need the cover to escape being a snack for larger fish and the low velocity to be safe from being washed downstream into areas with less cover. The mortality rate during those first days and months after the eggs hatch is tremendous and can have a major impact on a trout population. When fishing in late summer or early fall and I see fingerling trout darting about along the stream edges, I know some have survived and that in a couple of years I will being catching some nice wild reared trout.

439When I worked on the Eastern Band of Cherokee Reservation in North Carolina, I helped the tribe develop a sport fishing program on the reservation. I was the second U.S. Fish and Wildlife biologist to work on developing the program. For the most part the fishing program involved stocking catch-able size trout as a put and take fishery. Because of a concern that the stocking would impact a wild non-native rainbow trout population, the first biologist had initiated a study to determine if indeed the stocking did impact the wild rainbow population. The study consisted of sampling the same reach of stream, at the same time in the fall, with an electric seine to determine the wild trout population. After ten years of sampling, I compiled the data into a final report. What the data showed was that there were good years when lots of wild rainbows were found and there were other years when there were few wild rainbows found. In searching for an explanation, I looked at U.S. Geologic Survey stream flow data for the area. What I noted was that during those years with high spring flows we found lower numbers of young-of-year rainbows in our fall sampling and during low flow years there were higher numbers of young-of-year rainbows. It proved to be an excellent example of the impact that high velocity flow in the spring can have upon a wild rainbow trout population. It also showed that our stocking program had no impact upon the non-native rainbow trout population.

In New Mexico, brown trout have become the primary stream bred fish in most of our streams. They have often completely replaced the native Rio Grande cutthroat trout. Part of the reason for this replacement is that they spawn in the fall when most of the streams have low velocity flows that continue into the winter. Therefore their eggs have a greater chance of surviving and hatching and the young have a head start on the spring spawning cutthroats and rainbows. Brook trout, which spawn in late fall and early winter, enjoy the same advantage and like the brown trout, once they become established, will replace a native trout population.