November 11, 2009

Fish Stocking EIR/EIS - Part 4

The DFG trout stocking program currently introduces millions of fingerling, sub-catchable, and catchable trout into lakes and streams throughout California with the goal of improving existing fisheries. In addition to stocked trout, recipient habitats typically also harbor native trout populations or established non-native populations, with the latter having become established following earlier stocking efforts (both are referred to here as “resident” populations). In light of the fact that numerous studies have indicated that trout stocking has the potential to impact these resident trout populations and thereby negatively affect fishery quality it is ironic that the EIR-EIS fails to analyze stocking impacts on recreational trout fisheries.

The court order required the DFG to analyze the environmental impacts of the current stocking program and it is difficult to conceive of such an analysis not including an assessment of impacts of stocking on resident trout fisheries. In the EIR-EIS, this analysis is restricted solely to the effects of trout stocking on a few special-status native trout species (e.g., golden trout). Such a narrow interpretation of "environmental impacts" is unacceptable. As the following discussion makes clear, the potential exists for the current trout stocking program to seriously impact resident trout populations and adversely affect recreational fishing opportunities. These impacts should be analyzed and disclosed.

In an overview paragraph describing the effects of stocked trout on other salmonids the EIR-EIS (page 4-66) states,

“Most hatchery rainbow trout that are stocked for put-and-take fisheries in streams are caught within 2 weeks of planting (Butler and Borgeson 1965; Moyle 2002), and the remainder likely die of starvation or stress within a few weeks (Moyle 2002). Therefore, the potential for impacts on native trout species through competition and predation associated with catchable-sized rainbow trout plantings in streams appears to be low.... Catchable-sized hatchery rainbow trout released into lakes survive for longer periods than stream stocked fish because of lower energy costs associated with the absence of stream currents, and a relatively lower vulnerability to angling and predation (Moyle 2002). Therefore, the duration of competitive and predatory impacts on native lake populations following stocking of catchable-sized trout should be greater than the impacts following stream stocking.”
A less selective presentation of the available scientific literature would clearly indicate that the introduction of hatchery trout can negatively impact resident trout in both streams and lakes. In streams, direct effects are well-documented and usually result from competition between stocked and resident trout. This competition can produce slower growth rates (Weiss and Schmutz 1999, Bohlin et al. 2002), increased movement (Vincent 1987), and increased mortality of resident trout (Petrosky and Bjornn 1988, Baer and Brinker 2008). In addition, stocking catchable trout can increase fishing effort and in turn increase capture and removal rates of resident trout (Baer et al. 2007). These effects can subsequently result in lower overall trout densities (Vincent 1987).

The study by Vincent (1987) provides a particularly detailed description of the consequences of stocking hatchery trout into rivers and streams that contain resident trout populations. In this study, the long-term stocking of hatchery trout into the heavily-fished Varney section of the Madison River was halted and concurrently an unstocked tributary (O’Dell Creek) began receiving plants of hatchery trout. After four years of no stocking in the Varley section, the number and biomass of 2-year-old and older resident brown trout increased by 160%. Resident rainbow trout numbers increased by 800% and biomass increased by 1000%. In contrast, three consecutive years of hatchery trout stocking into O’Dell Creek resulted in a 49% reduction in the numbers and biomass of 2-year-old and older resident brown trout. The obvious conclusion from this study is that the stocking of hatchery trout can have dramatic impacts on resident trout populations and can in some cases actually decrease the quality of trout fisheries. As a result of the Vincent (1987) study, the State of Montana eliminated all stocking of flowing waters and restricted stocking only to lakes and reservoirs.

Impacts from stocking trout into lakes that contain resident trout are more poorly understood than impacts in flowing waters. However, two studies provide important insights. Elser et al. (1995) studied the consequences of halting rainbow trout stocking in Castle Lake, a historically fishless lake in northern California that at the time of the experiment contained introduced rainbow trout and brook trout. The brook trout population was capable of natural reproduction in Castle Lake but the rainbow trout population was maintained entirely by stocking. When rainbow trout stocking was halted, brook trout recruitment increased. Three years after rainbow trout stocking was halted, total trout numbers had increased by 20% (previous dominance by rainbow trout now replaced with dominance by brook trout) and total trout biomass had increased by 30%. In the Sierra Nevada,  Armstrong and Knapp (2004) compared trout densities and growth rates in 61 alpine lakes before and after a 4-8 year period of no fish stocking ("stocking-termination" lakes), and also between the stocking-termination lakes and control lakes that continued to be stocked. Contrary to the expectation that Oncorhynchus species stocked into alpine lakes rarely establish reproducing populations, results indicated that 70% of the stocking-termination lakes actually contained reproducing trout populations. For these reproducing populations, 4-8 years of no stocking resulted in no detectable change in trout density and may have resulted in increased trout growth rates in some lakes.
Therefore, as in flowing waters the stocking of hatchery trout into lakes can actually reduce total trout numbers and biomass, with negative consequences for fishery quality.

In summary, the results from these and many other studies lead one to the unavoidable conclusion that in at least some situations no stocking will actually result in better fisheries than intensive (and expensive) fish stocking. Given the potential severity of fish stocking impacts on resident trout populations and trout fisheries (and the associated costs), it is clear that the EIR-EIS must provide a thorough analysis of these impacts. 

Armstrong, T. W. and R. A. Knapp. 2004. Response by trout populations in alpine lakes to an experimental halt to stocking. Canadian Journal of Fisheries and Aquatic Sciences 61:2025–2037.

Baer, J., K. Blasel, and M. Diekmann. 2007. Benefits of repeated stocking with adult, hatchery-reared brown trout, Salmo trutta, to recreational fisheries? Fisheries Management and Ecology 14:51-60.

Baer, J. and A. Brinker. 2008. Are growth and recapture of hatchery-reared and resident brown trout (Salmo trutta L.) density dependent after stocking? Ecology of Freshwater Fish 17:455-464.

Bohlin, T., J. I. Johnsson, and J. Pettersson. 2002. Density-dependent growth in brown trout: effects of introducing wild and hatchery fish. Journal of Animal Ecology 71:683-692.

Elser, J. J., C. Luecke, M. T. Brett, and C. R. Goldman. 1995. Effects of food web compensation after manipulation of rainbow trout in an oligotrophic lake. Ecology 76:52-69.

Petrosky, C. E. and T. C. Bjornn. 1988. Response of wild rainbow (Salmo gairdneri) and cutthroat trout (S. clarki) to stocked rainbow trout in fertile and infertile streams. Canadian Journal of Fisheries and Aquatic Sciences 45:2087-2105.

Vincent, E. R. 1987. Effects of stocking catchable-size hatchery rainbow trout on two wild trout species in the Madison River and O'Dell Creek, Montana. North American Journal of Fisheries Management 7:91-105.

Weiss, S. and S. Schmutz. 1999. Response of resident brown trout, Salmo trutta L., and rainbow trout, Oncorhynchus mykiss (Walbaum), to the stocking of hatchery-reared brown trout. Fisheries Management and Ecology 6:365-375.

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