Enhancing Productive Capacity in the Canadian Arctic: Assessing the Effectiveness of Instream Habitat Structures in Habitat Compensation

Abstract

We examined the effectiveness of physical habitat structures (ramps, V-weirs, vanes, and groins) at increasing the productive capacity of a newly created 3.4-km artificial stream in the Barrenlands region of the Northwest Territories, Canada. We quantified changes in fish density and growth in the immediate area of each structure and for the artificial stream as a whole using before–after–control–impact approaches. Emphasis was on young-of-the-year (hereafter, age-0) Arctic grayling Thymallus arcticus, the dominant fish in the artificial and nearby natural streams. Structures attracted significantly higher densities of fish than did nearby reference sections, yet the age-0 Arctic grayling at the structures did not experience any density-dependent reduction in growth, suggesting that structures provided energetically favorable microhabitats. Relative to reference streams and prestructure conditions, however, the addition of these physical structures did not increase the density, biomass, or growth rates of age-0 Arctic grayling in the artificial stream as a whole. At that scale, weather conditions and a lake outlet effect strongly affected the production of Arctic grayling. We suggest that stream-scale benefits of structures may not be fully realized until more allochthonous and autochthonous organic matter is available to the benthic fauna and fish.