Figure 9

Potential impact of changing net depth on Sockeye and Chinook salmon harvest levels. (A) Comparison of Chinook and Sockeye salmon cumulative depth distribution along the western boundary of the ESSN and on all offshore marine receivers (those not sited along the boundary). (B) Projected relative harvest if maximum allowable net depth was varied from the 45 mesh standard (ca. 5.5 m), but net length was held constant. (C) Projected harvest if the net area is held constant by increasing the length of the nets to exactly compensate for reducing the net depth. Large gains in Sockeye Salmon harvests are predicted under (C), while only small gains in Chinook salmon conservation can be achieved (and only for nets <4 m deep). If net length is kept invariant, (B) predicts that Chinook salmon losses would decrease to approximately 30% of baseline at a net depth of 3 m, while Sockeye Salmon harvest would be approximately 80% of current values. As discussed in the text, relative harvests are calibrated to absolute depths from tag sensors, but maximum net depths are assumed to be directly proportional to the number of meshes; if the effective maximum depth of the net is different (because mesh size varies or nets billow under strong tidal currents), this would amount to a lateral shift of the curves along the x-axis.