4.20 BLACKWATER ESTUARY - BTO · The Blackwater Estuary was covered by the scheme during the winter of 1994–95, with counts being carried out during all four months. Figure 4.20.1

E S T U A R I N E W A T E R B I R D S A T L O W T I D E

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4.20 BLACKWATER ESTUARY

LTC site code: CBCentre grid: TL9507JNCC estuarine review site: 112Habitat zonation: 2368 ha intertidal, 1587 ha subtidal, 766 ha nontidalStatutory status: Blackwater Estuary SPA (UK9009245), Dengie SPA (UK9009242),

Blackwater Estuary Ramsar (7UK087), Dengie Ramsar (7UK073)Winter waterbird interest: Great Crested Grebe, Cormorant, Dark-bellied Brent Goose,

Shelduck, Wigeon, Teal, Pintail, Shoveler, Goldeneye, Red-breastedMerganser, Oystercatcher, Avocet, Ringed Plover, Golden Plover,Grey Plover, Lapwing, Knot, Dunlin, Ruff, Black-tailed Godwit,Bar-tailed Godwit, Curlew, Redshank, Waterbird assemblage

SITE DESCRIPTION

The River Blackwater opens out at Maldon on theEssex coast to form one of the largest and mostimportant estuaries in East Anglia. The site isadjacent to the Colne Estuary to the north andDengie Flats to the south. Additionally, AbbertonReservoir lies only a few miles to the north. Thereis a wide diversity of habitats, with a large area ofmudflats but also saltmarsh, creeks, channelsand islands. Deposition of shingle and shell banksand exposed gravel beds are features of the tidalflats. Behind the sea-walls, important areas ofcoastal grassland occur. Much of the Blackwatersaltmarsh is suffering erosion although in anumber of locations managed realignment of thesea-defences is taking place which will create newestuarine habitat. Many of the human activitieson the estuary are leisure-related, especiallyboating, but also beach recreation, wildfowling,

Figure 4.20.1: L L L L LTC sections at the Blackwater EstuaryTC sections at the Blackwater EstuaryTC sections at the Blackwater EstuaryTC sections at the Blackwater EstuaryTC sections at the Blackwater Estuary, winter 1994–95, winter 1994–95, winter 1994–95, winter 1994–95, winter 1994–95

fisheries and jet-skiing. The site is not heavilyurbanised.

COVERAGE AND INTERPRETATION

The Blackwater Estuary was covered by thescheme during the winter of 1994–95, with countsbeing carried out during all four months. Figure4.20.1 shows the positions of the 46 sectionscounted for the survey.

The majority of the LTC site is covered by SPAdesignation, mostly by the Blackwater EstuarySPA (which also extends a little further east onthe north shore into the area covered by the ColneLTCs) but also by some of the Dengie SPA in thesouth-east (Figure 4.20.2). The Blackwater EstuarySPA also covers additional nontidal areas aroundthe estuary, notably at Old Hall Marshes (initiallydesignated as a separate SPA but later subsumed)


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and Tollesbury Wick Marshes. Any discussion ofthe birds of the sites and/or SPAs around thispart of the Essex coast should be careful to takethese boundary differences into account. In thefuture, the subdivision of the coast into separatesites should take the SPA boundaries intoconsideration. The boundaries of the Ramsar sitesare entirely coincident with those of the SPAs.

Clearly, there is great scope for daily movementsof birds between sites. For example, many of theKnot feeding in the south-east of the Blackwaterappear to be roosting at Dengie (D. Wood pers.comm.). Similar movements of birds between theBlackwater and Colne are also likely. As well asmovements between the estuary and the imme-diately adjacent nontidal habitats, such as OldHall Marshes, the important site of AbbertonReservoir is situated only a few miles north ofthe estuary and it seems certain that birds,especially wildfowl, move between the two sites.

WATERBIRD DISTRIBUTION

Low tide distribution maps from the winter of1994–95 are presented for 21 of the 23 species ofprincipal interest listed above. For clarity, smallerdots are used to display the distributions ofGolden Plover, Lapwing and Dunlin. Additionalmaps of total birds and total birds weighted by1% threshold value are also presented (Figure4.20.3). Of the remaining species, very fewShovelers and no Avocets were recorded during

the counts, these being found mostly on adjacentnontidal habitats such as at Old Hall andTollesbury Wick Marshes.

The totals maps show that almost all of the sitewas used by large numbers of birds, although keyareas appear to be the central parts of the northshore and the channels either side of Old HallMarshes. Most of the key species were similarlywidespread, such as Brent Goose, Shelduck,Oystercatcher, Ringed Plover, Lapwing, Dunlin,Curlew and Redshank. Wigeon, Teal and Pintailwere more localised, with Old Hall Marshes clearlyimportant for the first two as well as supportingthe highest concentrations of Goldeneyes andRed-breasted Mergansers. Golden Plovers weredistributed widely but locally around the site. GreyPlovers showed a clear preference for the centralnorth shore, along with Bar-tailed Godwits. Black-tailed Godwits occurred in higher densities in theinner parts of the estuary. Knot were mostly foundbetween St Lawrence Bay and Bradwell Watersidebut with some on the inner estuary. Great CrestedGrebes were present in small numbers withCormorants more widespread. Ruff were onlynoted at Salcott Channel.

Figure 4.20.2: LLLLLTCTCTCTCTC and and and and and SP SP SP SP SPAAAAA boundaries, with boundaries, with boundaries, with boundaries, with boundaries, with overlapoverlapoverlapoverlapoverlap, at the Blackwater Estuary, at the Blackwater Estuary, at the Blackwater Estuary, at the Blackwater Estuary, at the Blackwater Estuary

B L A C K W A T E R E S T U A R Y


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TOTAL (1 DOT = 5 BIRDS) WEIGHTEDTOTAL (1 DOT = 5 BIRDS) WEIGHTED

GREAT CRESTED GREBE CORMORANT

DARK-BELLIED BRENT GOOSE SHELDUCK

WIGEON TEAL


Figure 4.20.3 (i): Low tide waterbird distributions recorded at the Blackwater Estuary, winter 1994-95


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PINTAIL GOLDENEYE

RED-BREASTED MERGANSER OYSTERCATCHER

RINGED PLOVER GOLDEN PLOVER

GREY PLOVER LAPWING


Figure 4.20.3 (ii): Low tide waterbird distributions recorded at the Blackwater Estuary, winter 1994-95


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KNOT DUNLIN

RUFF BLACK-TAILED GODWIT

BAR-TAILED GODWIT CURLEW

REDSHANK


Figure 4.20.3 (iii): Low tide waterbird distributions recorded at theBlackwater Estuary, winter 1994-95


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4.21 DENGIE FLATS

LTC site code: CDCentre grid: TM0504JNCC estuarine review site: 113Habitat zonation: 2369 ha intertidal, 713 ha subtidal, 497 ha nontidalStatutory status: Dengie SPA (UK9009242), Dengie Ramsar (7UK073)Winter waterbird interest: Red-throated Diver, Great Crested Grebe, Cormorant, Dark-bellied

Brent Goose, Oystercatcher, Grey Plover, Lapwing, Knot, Dunlin,Black-tailed Godwit, Bar-tailed Godwit, Waterbird assemblage

SITE DESCRIPTION

Dengie Flats form a continuous mudflat on theEssex coast between the mouths of the Blackwa-ter and Crouch–Roach Estuaries. There areextensive growths of Enteromorpha algae on theflats, which themselves grade into saltmarsh,relatively unusual in an open-coast situation.Most of the grazing marshes, which are nowbehind the sea-wall, have been claimed foragriculture. The site is relatively remote but somehuman activities do occur, including watersports,beach recreation, bait-digging and wildfowling.


Dengie Flats was covered by the scheme duringthe 1992–93 winter, although no February countwas made. Figure 4.21.1 shows the positions ofthe 12 sections counted for the survey.Figure 4.21.2 shows that the whole of the area

Figure 4.21.1: L L L L LTC sections at Dengie Flats, winter 1992–93TC sections at Dengie Flats, winter 1992–93TC sections at Dengie Flats, winter 1992–93TC sections at Dengie Flats, winter 1992–93TC sections at Dengie Flats, winter 1992–93

covered by the LTCs is within the Dengie SPAboundary. The SPA extends a little way north-wards and southwards, taking in parts of theBlackwater Estuary and Crouch–Roach EstuaryLTC sites respectively. Future LTCs in this areashould endeavour to match up more closely theSPA and LTC boundaries. The boundaries of theRamsar site are entirely coincident with those ofthe SPA.

Obviously, given the proximity of the Blackwaterand Crouch–Roach Estuaries, a certain amountof movement between sites occurs. Notably, Knotfeeding on the south-east part of the BlackwaterEstuary make use of roost sites in the Dengiearea. Additionally, a number of species feeding atthe southern end of Dengie also make use ofMaplin Sands to the south of the Crouch forfeeding, and some roost on Foulness (J. Alderton,D. Wood pers. comm.). Similarly, some species(such as Lapwing) may utilise the non-estuarinehinterland.


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Low tide distribution maps from the winter of1992–93 are presented for eight of the 11 speciesof principal interest listed above. For clarity,smaller dots are used to display the distributionsof Knot and Dunlin. Additional maps of total birdsand total birds weighted by 1% threshold valueare also presented (Figure 4.21.3). Of the remainingspecies, no Red-throated Divers and only smallnumbers of Great Crested Grebes andCormorants were noted, presumably due to thedifficulties of viewing offshore species at thelonger distances occurring at low tide.

Generally, the totals maps show relatively evendistributions of birds across the site, with thehigher density on the southernmost sectionpresumably a result of the smaller shore widthhere. Most species of note occurred widely, withthe maps showing slightly different preferencesby different species. Perhaps most noteworthywas the separation of the two species of godwitinto distinct areas with a relatively small degreeof overlap between the two.

Figure 4.21.2: LLLLLTCTCTCTCTC and and and and and SPSPSPSPSPAAAAA boundaries, with boundaries, with boundaries, with boundaries, with boundaries, with overlapoverlapoverlapoverlapoverlap, at Dengie Flats, at Dengie Flats, at Dengie Flats, at Dengie Flats, at Dengie Flats

D E N G I E F L A T S

Figure 4.21.3 (i): Low tide waterbird distributions recorded at Dengie Flats, winter 1992-93

TOTAL (1 DOT = 5 BIRDS) WEIGHTEDDARK-BELLIED

BRENT GOOSE


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D E N G I E F L A T S

Figure 4.21.3 (ii): Low tide waterbird distributions recorded at DengieFlats, winter 1992-93

OYSTERCATCHER GREY PLOVER LAPWING

KNOT DUNLIN BLACK-TAILED GODWIT

BAR-TAILED GODWIT


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4.22 CROUCH–ROACH ESTUARY

LTC site code: DRCentre grid: TQ9694JNCC estuarine review site: 114Habitat zonation: 749 ha intertidal, 962 ha subtidal, 534 ha nontidalStatutory status: Crouch and Roach Estuaries SPA (UK9009244), Foulness SPA

(UK9009246), Dengie SPA (UK9009242), Crouch and RoachEstuaries Ramsar (7UK085), Foulness Ramsar (7UK102), DengieRamsar (7UK073)

Winter waterbird interest: Little Grebe, Great Crested Grebe, Cormorant, Dark-bellied BrentGoose, Shelduck, Wigeon, Oystercatcher, Avocet, Golden Plover,Grey Plover, Lapwing, Knot, Dunlin, Black-tailed Godwit, Bar-tailedGodwit, Curlew, Redshank, Waterbird assemblage.

SITE DESCRIPTION

The Crouch Estuary and its southern tributary,the Roach, are both long, narrow, muddy estuarieswhich reach the Essex coast at the northern endof Foulness Island. The estuaries are largelyflanked by farmland, much of it claimed from es-tuarine habitat, although there are some areasof saltmarsh also, especially at BridgemarshIsland, Brandy Hole Creek and Stow Creek. Thenature of the site means that the area of intertidalsubstrate is relatively small in comparison to theapparent size of the estuary. The southern partsof the Roach Estuary develop into a tangle ofcreeks, some of which extend through to MaplinSands. The site has little urbanisation orindustry, but it is widely used for watersports.Wildfowling occurs over most of the estuary.

Figure 4.22.1: L L L L LTC sections at the CrTC sections at the CrTC sections at the CrTC sections at the CrTC sections at the Crouch–Roach Estuaryouch–Roach Estuaryouch–Roach Estuaryouch–Roach Estuaryouch–Roach Estuary, winter 1995–96, winter 1995–96, winter 1995–96, winter 1995–96, winter 1995–96


The Crouch–Roach Estuary was counted at lowtide during 1995–96 with counts made in all fourmonths. Figure 4.22.1 shows the positions of the42 sections counted for the survey.

Figure 4.22.2 shows that almost the whole areacovered by the counts is designated as SPA, mostlywithin the Crouch and Roach Estuaries SPA, butfive of the count sections overlap with theFoulness SPA. Additionally, there is overlap ofthe site with the Dengie SPA but to a much lesserdegree, involving half of the outermost sectionon the north shore of the Crouch. The boundariesof the Ramsar sites are entirely coincident withthose of the SPAs.


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An assessment of waterbird use of the Crouch–Roach and adjoining sites must take into accountthe likely frequent movement of birds betweensites. At the mouth of the Crouch–Roach, dailymovement is likely to and from both Dengie Sandsand Maplin Sands, whereas along the southernedge of the site, movement will be frequentbetween here and the Foulness complex of creeksand marshes.


Low tide distribution maps from the winter of1995–96 are presented for 13 of the 17 species ofprincipal interest listed above. For clarity, smallerdots are used to display the distributions of BrentGoose, Wigeon and Dunlin. Additional maps oftotal birds and total birds weighted by 1%threshold value are also presented (Figure 4.22.3).Of the remaining species, only small numbers ofGreat Crested Grebes, Avocets and Bar-tailedGodwits were noted and Knot were not recorded.These species would not be expected in largenumbers on the Crouch–Roach Estuary itself, andtheir inclusion (and that of many of the otherspecies present) on the list of interest speciesabove is due to the small degree of overlap withthe Dengie SPA and Foulness SPA.

Overall, bird density was clearly higher on theinner parts of each river. Few species were foundat high density at the mouth, althoughconcentrations of Brent Geese and Golden Ploverswere found around the confluence of the two‘arms’ of the estuary. The Roach Estuary wasgenerally less densely occupied than the Crouch,but the Roach did support higher concentrationsof Redshanks and Curlews, plus the majority ofthe Black-tailed Godwits at the site. Shelducks,Brent Geese, Lapwings and Dunlin were alsocommon along the Roach. The Crouch, especiallythe inner parts around Bridgemarsh Island andBrandy Hole Creek, was the key area at low tidefor Wigeon, Lapwings and Little Grebes and alsoheld high concentrations of Brent Geese,Shelducks, Golden Plovers and Dunlin.Cormorants, Oystercatchers and Grey Ploverswere widespread in small numbers.

Figure 4.22.2: LLLLLTCTCTCTCTC and and and and and SPSPSPSPSPAAAAA boundaries, with boundaries, with boundaries, with boundaries, with boundaries, with overlapoverlapoverlapoverlapoverlap, at the Cr, at the Cr, at the Cr, at the Cr, at the Crouch–Roach Estuaryouch–Roach Estuaryouch–Roach Estuaryouch–Roach Estuaryouch–Roach Estuary

C R O U C H - R O A C H E S T U A R Y


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Figure 4.22.3 (i) Low tide waterbird distributions recorded at the Crouch-Roach Estuary, winter 1995-96

TOTAL WEIGHTED

LITTLE GREBE CORMORANT

DARK-BELLIED BRENT GOOSE SHELDUCK

WIGEON OYSTERCATCHER


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Figure 4.22.3 (ii) Low tide waterbird distributions recorded at theCrouch-Roach Estuary, winter 1995-96

GOLDEN PLOVER GREY PLOVER

LAPWING DUNLIN

BLACK-TAILED GODWIT CURLEW

REDSHANK

Documents

4.20 BLACKWATER ESTUARY - BTO · The Blackwater Estuary was covered by the scheme during the winter of 1994–95, with counts being carried out during all four months. Figure 4.20.1