Barrier to species movement

The physical obstruction of species movements (local, regional, global), in rivers or open waters. May disrupt movements within & between roosting, breeding, feeding areas, or regional/global migrations (e.g. birds, eels, salmon, whales). Could be relevant to crabs that undertake migrations to over-winter or to breed, and where populations are dependent on larval or other propagule supply from outside the site.

Benchmark: 
Barrier to species movement
Examples: 
Infrastructure such as offshore wind farm, wave or tidal device arrays, tidal barrages & devices or dams, and mariculture could obstruct movements as well as some fishing gears (set nets & drift nets). Intensive dredging and some disposal (e.g. sewage or industrial/liquid) activities can cause turbidity that may pose as a physical barrier to fish movement; electromagnetic fields from power cables may also act as a barrier to some exclusively demersal species.
Notes: 
Excludes noisy activities which may cause barriers, as covered fully in separate pressures. Excludes fishing other than by set net or drift net, and short-term/transient pressures like shipping and disposal.

Outer Hebrides

The tables in this section reflect the output of the workshop (October 2019) when the pressures from human activities were assessed for the period 2014 to 2018 for the region. The summary text below the tables elaborates on some of the points that were made at the workshop.
This pressure assessment uses the FeAST classification which includes two abrasion pressures: surface abrasion & sub-surface abrasion. Some expert groups combined these as a single pressure "surface & sub-surface abrasion" whilst others focussed on using surface abrasion alone, hence there is a slight difference in handling for some regions.
The ranking of the pressures in terms of impact is a relative exercise within each region, and is not a statement of their absolute impact. Detailed comparison between regions on the basis of these relative pressure assessments is therefore not advisable.

Main pressures identified

Outer Hebrides

Solway

The tables in this section reflect the output of the workshop (October 2019) when the pressures from human activities were assessed for the period 2014 to 2018 for the region. The summary text below the tables elaborates on some of the points that were made at the workshop.
This pressure assessment uses the FeAST classification which includes two abrasion pressures: surface abrasion & sub-surface abrasion. Some expert groups combined these as a single pressure "surface & sub-surface abrasion" whilst others focussed on using surface abrasion alone, hence there is a slight difference in handling for some regions.
The ranking of the pressures in terms of impact is a relative exercise within each region, and is not a statement of their absolute impact. Detailed comparison between regions on the basis of these relative pressure assessments is therefore not advisable.

Main pressures identified

Solway