Thursday, February 24, 2011

Multiple Sources of Gene Flow into Wild Steelhead Populations

Molecular Biology 2011

Who are the missing parents? Grandparentage analysis identifies multiple sources of gene flow into a wild population

Department of Zoology, Oregon State University, Corvallis, OR 97331-2914, USA

In order to increase the size of declining salmonid populations, supplementation programmes intentionally release fish raised in hatcheries into the wild. Because hatchery-born fish often have lower fitness than wild-born fish, estimating rates of gene flow from hatcheries into wild populations is essential for predicting the fitness cost to wild populations. Steelhead trout (Oncorhynchus mykiss) have both freshwater resident and anadromous (ocean-going) life history forms, known as rainbow trout and steelhead, respectively. Juvenile hatchery steelhead that ‘residualize’ (become residents rather than go to sea as intended) provide a previously unmeasured route for gene flow from hatchery into wild populations. We apply a combination of parentage and grandparentage methods to a three-generation pedigree of steelhead from the Hood River, Oregon, to identify the missing parents of anadromous fish. For fish with only one anadromous parent, 83% were identified as having a resident father while 17% were identified as having a resident mother. Additionally, we documented that resident hatchery males produced more offspring with wild anadromous females than with hatchery anadromous females. One explanation is the high fitness cost associated with matings between two hatchery fish. After accounting for all of the possible matings involving steelhead, we find that only 1% of steelhead genes come from residualized hatchery fish, while 20% of steelhead genes come from wild residents. A further 23% of anadromous steelhead genes come from matings between two resident parents. If these matings mirror the proportion of matings between residualized hatchery fish and anadromous partners, then closer to 40% of all steelhead genes come from wild trout each generation. These results suggest that wild resident fish contribute substantially to endangered steelhead ‘populations’ and highlight the need for conservation and management efforts to fully account for interconnected Oncorhynchus mykiss life histories.

New Study: Hatchery Fish Reduce Productivity of Wild Fish

Can. J. Fish. Aquat. Sci. 68(3): 511–522 (2011)  |  doi:10.1139/F10-168  |  Published by NRC Research Press   

Reduced recruitment performance in natural populations of anadromous salmonids associated with hatchery-reared fish

M. W. Chilcote, K. W. Goodson, and M. R. Falcy

Abstract: We found a negative relationship between the reproductive performance in natural, anadromous populations of steelhead trout (Oncorhynchus mykiss), coho salmon (O. kisutch), and Chinook salmon (O. tshawytscha), and the proportion of hatchery fish in the spawning population. We used intrinsic productivity as estimated from fitting a variety of recruitment models to abundance data for each population as our indicator of reproductive performance. The magnitude of this negative relationship is such that we predict the recruitment performance for a population composed entirely of hatchery fish would be 0.128 of that for a population composed entirely of wild fish. The effect of hatchery fish on reproductive performance was the same among all three species. Further, the impact of hatchery fish from “wild type” hatchery broodstocks was no less adverse than hatchery fish from traditional, domesticated broodstocks. We also found no support for the hypothesis that a population's reproductive performance was affected by the length of exposure to hatchery fish. In most cases, measures that minimize the interactions between wild and hatchery fish will be the best long-term conservation strategy for wild populations.

The full study can be seen at the Native Fish Society: