How Wild Are RI's Stream-Bred Brook Trout

In view of the fact that trout have been reared in public and private hatcheries and stocked into Rhode Island waters for more than 100 years, a question arises regarding the genetic identity of wild brook trout caught in this state. Of particular interest is whether our brookies are “pure” in the sense that their genome has not been affected by the introduction of hatchery-reared fish. Some interesting material pertaining to this question can be found in the scientific literature. In general, the contemporary approach to addressing this kind of question has involved comparing the DNA derived from samples of trout tissue. The essential problem is what to use as a genetic benchmark.  Insofar as the introduction of hatchery trout began in the mid-nineteenth century, the ideal for comparison would be DNA from a tissue sample that predates that period. Even searching for the more common and more durable mitochondrial DNA vs nuclear DNA is a needle-in-a-haystack proposition. The approach that has been taken involves comparing the mitochondrial DNA of contemporary stream-bred fish to that of contemporary hatchery fish. One of the studies considered here compared brookies in six Cape Cod streams to their counterparts at the Sandwich Hatchery (MA). Results showed a good deal of genetic diversity – the six wild populations were different from each other and all were different from the hatchery trout (Annett 2005). Another study looked at “Coaster” brookies in rivers of the Lake Superior basin. Here too there was considerable diversity. The author of this report states that “… there appears to be minimal direct impact of hatchery fish on wild, self-sustaining populations.” (Burnham-Curtis  2001). She and others (Humston et al 2012) add that there is still the question of indirect impacts to be addressed.  That is, even if interbreeding is minimal the pool of wild genes may still be altered by the impact of competition for food and space on reproductive success and mortality. See  Dewald & Wilzbach (1992) for a specific illustration of negative impacts of hatchery trout on brook trout habitat use, feeding, and growth. The principal consequences were that in the presence of brown trout, brookies lost weight and 33% contracted a fungal disease that proved fatal. Still other research indicates that brown trout can interfere with spawning brook trout. For example, Grant et al (2002) noted that “disruptive interactions” were common when they observed brook trout and brown trout on spawning redds.

So, we have two studies cited here suggesting that despite the introduction of hatchery brook trout into so many of our RI waters, sufficient genetic diversity may persist in our stream-bred brookies so that we may regard them as truly “pure”. Insofar as a definitive answer is not likely to be available, how then to proceed? The prudent approach is to err on the side of caution. That is, to protect our stream-bred populations in every way that we can. The research cited here makes it clear that this must include the cessation of stocking of farmed fish into wild trout waters by the State of Rhode Island. PRIBT believes that by taking thoughtful action, Rhode Islanders can preserve an increasingly rare species for all to marvel at.

Annett, Conservation Genetics of Remnant Anadromous Brook Trout Populations at the Southern Limit of Their Distribution.  Boston University 2005.

Burnham-Curtis, Genetic Profiles of Selected Brook Trout Populations from Lake Superior, Lake Huron, and Selected Hatcheries. USGS 2001.

Humstan et al, Consequences of Stocking Headwater Impoundments on Native Populations of Brook Trout in Tributaries, North American Journal of Fisheries Management, 2012.

Dewald & Wilzbach, Interactions between Native Brook Trout and Hatchery Brown Trout: Effects on Habitat Use, Feeding, and Growth.  Transactions of the American Fisheries Society, 1992.

Grant et al, Spawning Interactions Between Sympatric Brown and Brook Trout May Contribute to Species Replacement, Transactions of the American Fisheries Society, 2002.