Red-Throated Diver and Vessel Traffic – Investigating Realistic In-combination Disturbance Effects

Red-throated Diver Gavia stellata is the smallest member of the diver or loon family found in UK waters. It has an Arctic and sub-Arctic breeding distribution (April-August), with the UK population found on Scottish freshwater lochs and locherns where mated pairs brood and raise their chicks. During the breeding season the bird develops its distinctive red throat patch which gives the species its common name. Outside of the breeding season Red-throated Diver move to coastal waters (November-March). Significant wintering populations occur off the English east coast, and smaller numbers are found in the southern Irish Sea. During this period they moult into their winter plumage, losing the red throat patch. They associate with subtidal sandbank habitat and shallow waters (generally less than 20 m below chart datum) where they feed on fish such as Atlantic Herring and Sprat.

In 2009 the Outer Thames Estuary Special Protection Area (OTE SPA) was classified for its internationally important population of over-wintering Red-throated Diver and supporting habitats. The outer Thames estuary and Anglian coastal waters are also a  commercially important area for merchant shipping, ports, fishing, offshore renewables and marine aggregate licences and Red-throated Diver is recorded as sensitive to disturbance and displacement effects from surface vessel transits and wind turbines. Disturbance effects can result in temporary habitat loss (used for foraging and loafing) whilst the Red-throated Diver is ‘scared’ away from its preferred areas of the SPA. This can result in loss of condition and mortality for individuals and possible population-scale effects.

As part of a wider process to renew existing marine aggregate extraction licences by the end of 2013, Natural England has raised queries over the level of disturbance to Red-throated Diver arising from the activity of aggregate dredging vessels in and adjacent to the OTE SPA.  In-combination with wind farm developments within the region, Natural England feels that disturbance effects arising from aggregate extraction may be significant, and is working on the basis that the birds will be disturbed within a 2 km halo around a vessel.

The British Marine Aggregate Producers Association (BMAPA) has commissioned MarineSpace Ltd to identify the constraints, review scientific and grey literature and recent appropriate assessments of the SPA. MarineSpace has proposed data analysis to increase the level of understanding of Red-throated Diver distribution in relation to general shipping traffic activity (and, where possible, specific aggregate dredger activity) in the OTE SPA. The intention is to conduct an assessment of the spatial and temporal interactions between Red-throated Diver and shipping traffic in order to better understand the level of disturbance effects arising from vessel traffic, and help in the assessment of significance of marine aggregate dredger-related disturbance across the OTE SPA; to be conducted by the Marine Management Organisation.

 

Image by Ómar Runólfsson [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons