Embeddedness
Atlantic salmon (Salmo salar) parr use the spaces within cobble substrates, called interstitial spaces, for shelter from fast-moving currents and to find thermal refuge, particularly during winter months. Staff are measuring cobble embeddedness, the average proportion of the rocks in a stream that is buried in fine sediments to evaluate the quality of salmon habitat. An interstitial space index (ISI), derived from cobble embeddedness measures, provides a way to compare the volume of interstitial space available within different habitats through out Maine’s salmon rivers. Studies have demonstrated that high embeddedness and low ISI result in low densities of Atlantic salmon, cutthroat trout, Chinook salmon, and steelhead, as well as lower biomass of aquatic insects
In 1993, 2002, 2003 and 2004, Jonesboro staff measured embeddedness levels through out several Downeast rivers; Dennys River (16 sites), Narraguagus River (22 sites), Machias (17 sites), East Machias (8 sites), and Pleasant (1 site). On the Dennys River, population densities of juvenile salmon were highest where embeddedness levels were low and ISI was high. Further, the analysis indicates that embeddedness plays an important role in controlling the densities of juvenile salmon in the Dennys River. Recent measures work in the Narraguagus strengthens embeddedness work done by the Atlantic Salmon Commission in 1993 by measuring embeddedness at sites where population estimates are made. In 1993, we found that the middle reach of the Narraguagus mainstem had lower embeddedness than the upper and lower reaches and that the most highly embedded run habitat had the lowest parr densities. We will continue to analyze these data, and extend our field sampling through out the Downeast rivers.
