BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

spawning grounds and juvenile nursery areas. Some shorezone protectivestructures (jetties in particular) may interfere with this migration process bymodifying currents near stream mouths. However, the extent of a problem ofthis nature in Lake Tahoe is negligible and would require a case-by-caseevaluation of each site. Similar impacts have been documented withbreakwaters on migrations of juvenile and adult fishes but not in freshwaterlentic systems. This issue has been raised primarily in association withanadromous fishes in the Pacific Northwest. Conclusive evidence supportingthese concerns has not been fully established. 1018.14.3.5 PREDATION PRESSURERubble mound structures (revetments) provide substrate that can act as coverand holding habitat. As such, some jetties and breakwaters serve as a focalpoint for congregations of some types of non-native species (e.g. largemouthbass or mysis shrimp) which may feed or find shelter there. This condition hasalso generated a concern that high densities of predators in the vicinity ofjetties and breakwaters pose a threat to egg, larval, and juvenile stages ofimportant species (e.g. macrozooplankton cladocerans species such as Daphnia).This concern is largely associated with projects in the Pacific Northwest andconclusive evidence demonstrating a significant impact is currently unavailableand may be difficult to establish. In any case, evaluations must be conducted ona site-specific basis. For example, examination of existing similar structures nearthe proposed project site could provide information on the type and extent oforganism development on jetties, breakwaters, and other rubble moundrevetment structures. 102101USACE, 1989, EM 1110-2 -5025, Environmental Engineering for Coastal Shore Protection102USACE, 1989, EM 1110-2 -5025, Environmental Engineering for Coastal Shore Protectionand USACE, 2008, Coastal Engineering Manual - Parts I-6TRPA BMP HandbookCHAPTER 8: Shorezone Protective Structures and BMPs2012 Page 8-93