Hood 2012 beaver in tidal marsh

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Hood, W. 2012. Beaver in Tidal Marshes: Dam Effects on Low-Tide Channel Pools and Fish Use of Estuarine Habitat. WEtlands, vol. 32, issue 3, pp. 401-410.

Beaver ( Castor spp.) are considered a riverine or lacustrine animal, but surveys of tidal channels in the Skagit Delta (Washington, USA) found beaver dams and lodges in the tidal shrub zone at densities equal or greater than in non-tidal rivers. Dams were typically flooded by a meter or more during high tide, but at low tide they impounded water, allowing beaver to swim freely while quadrupling pool habitat for fish compared to channels without dams. Seven fish species were caught in low-tide pools, including threatened juvenile Chinook salmon ( Oncorhynchus tshawytscha ), whose densities (by volume) averaged 3.2 times higher in low-tide pools than shallows. Accounting for the total contribution of pools and shallows to juvenile Chinook abundance, beaver pools tripled shrub zone channel capacity for juvenile Chinook salmon at low tide relative to herbaceous zone marsh without beaver pools. Current Chinook recovery efforts focus on restoring herbaceous zone tidal marsh for rearing juveniles, but this focus overlooks presently rare and poorly understood habitat, like tidal shrub marsh, that was historically common and likely important to beaver and small estuarine or anadromous fish.

Analysis

  • This findings is made more relevant in that these oligohaline transition woody wetlands are over 98.5% lost over the last five generations of Puget Sound development (Simenstad et al 2011). -Pcereghino
  • Due to subsidence of elevations, most restoration sites are unable to support woody vegetation. Substantial sedimentparticles of clay, silt, sand, gravel, or cobble, transported by water, are called sediment. accretion and perhaps recruitment of large woody debris (see Hood 2007) may be necessary for development of beaver populations. -Pcereghino