Study

Seawall as salmon habitat: eco-engineering improves the distribution and foraging of juvenile Pacific salmon

  • Published source details Sawyer A.C., Toft J.D. & Cordell J.R. (2020) Seawall as salmon habitat: eco-engineering improves the distribution and foraging of juvenile Pacific salmon. Ecological Engineering, 151, 105856.

Actions

This study is summarised as evidence for the following.

Action Category

Create large ridges or ledges (>50 mm) on intertidal artificial structures

Action Link
Biodiversity of Marine Artificial Structures

Create grooves and small protrusions, ridges or ledges (1–50 mm) on intertidal artificial structures

Action Link
Biodiversity of Marine Artificial Structures
  1. Create large ridges or ledges (>50 mm) on intertidal artificial structures

    A before-and-after study in 2012–2018 on an intertidal seawall in Puget Sound estuary, USA (Sawyer et al. 2020) reported that creating large ledges on the seawall, along with grooves and small protrusions, did not increase juvenile salmon Oncorhynchus spp. abundance around the wall but increased their feeding activity. Data were not statistically tested. Juvenile salmon abundances were lower after large ledges were created during seawall reconstruction (5–151 individuals/m2) compared with before (47–431/100m2), but the frequency of their feeding behaviour increased by 6–27%. It is not clear whether these effects were the direct result of creating ledges, grooves and protrusions, increased light levels or reduced water depth in front of the wall. Large ledges (length: 2 m; width: 0.6 m; height: 0.2 m) were created on concrete seawall panels using a formliner. Each panel had one horizontal ledge at high, mid or lowshore and grooves and small protrusions on their surfaces. Panels were attached to a vertical concrete seawall during reconstruction in 2017 (numbers/month not reported). Light-penetrating panels were also installed to increase light around the wall, and the seabed was raised in front. Juvenile salmon within 10 m of the wall were surveyed from 20–minute snorkels at high and low tide during March–August at three sites along the wall before reconstruction in 2012 (35 surveys), and at three different sites along the wall after reconstruction in 2018 (42 surveys).

    (Summarised by: Ally Evans)

  2. Create grooves and small protrusions, ridges or ledges (1–50 mm) on intertidal artificial structures

    A before-and-after study in 2012–2018 on an intertidal seawall in Puget Sound estuary, USA (Sawyer et al. 2020) reported that creating grooves and small protrusions, along with large ledges, on the seawall did not increase juvenile salmon Oncorhynchus spp. abundance around the wall, but increased their feeding activity. Data were not statistically tested. Juvenile salmon abundances were lower after grooves and small protrusions were created during seawall reconstruction (5–151 individuals/m2) compared with before (47–431/100m2), but the frequency of their feeding behaviour increased by 6–27%. It is not clear whether these effects were the direct result of creating grooves and protrusions, ledges, increased light levels or reduced water depth in front of the wall. Groove habitats and small protrusions (dimensions not reported) were created on concrete seawall panels using a cobble-effect formliner. Panels also had one large ledge on their surfaces. Panels were attached to a vertical concrete seawall during reconstruction in 2017 (numbers/month not reported). Light-penetrating panels were also installed to increase light around the wall, and the seabed was raised in front. Juvenile salmon within 10 m of the wall were surveyed from 20–minute snorkels at high and low tide during March–August at three sites along the wall before reconstruction in 2012 (35 surveys), and at three different sites along the wall after reconstruction in 2018 (42 surveys).

    (Summarised by: Ally Evans)

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