State of the Bay Report 2010-Final - Anchor Environmental

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Anchor Environmental Table 11.1. Taxonomic composition of waterbirds in Langebaan Lagoon (excluding rare or vagrant species). Common groupings Order SA Resident Waterfowl Podicipediformes (Grebes) 1 Cormorants, darters, pelicans Anseriformes (Ducks, geese) 9 Gruiformes (Rails, crakes, gallinules, coots) 7 Pelecaniformes (Cormorants, darters, pelicans) 7 Wading birds Ciconiiformes (Herons, egrets, ibises, spoonbill, etc.) 14 Phoenicopteriformes (Flamingos) 2 Birds of prey Falconiformes (Birds of prey) 4 Migrant Waders Charadriiformes: Waders 8 18 Gulls Gulls 2 Terns Terns 3 4 Kingfishers Alcediniformes (Kingfishers) 2 Total 59 22 Waders are the most important group of birds on Langebaan Lagoon in terms of numbers. The influx of waders into the area during summer accounts for most of the seasonal change in community composition. Most of the Palaearctic migrants depart quite synchronously around early April, but the immature birds of many of these species remain behind and do not don the breeding plumage of the rest of the flock. The resident species take advantage of relief in competition for resources and use this period to breed. The migrants return more gradually in spring, with birds beginning to trickle in from August, and numbers rising rapidly during September to November. Waders feed on invertebrates that mainly live in intertidal areas, at low tide, both by day and night (Turpie and Hockey 1995). They feed on a whole range of crustaceans, polychaete worms and gastropods, and adapting their foraging techniques to suit the type of prey available. Among the waders, plovers stand apart from the rest in that they have insensitive, robust bills and rely on their large eyes for locating prey visually. Oystercatchers have similar characteristics, using their strong bills to prise open shellfish. Most other waders have soft, highly sensitive bills and can locate prey by touch as well as visually. Those feeding by sight tend to defend feeding territories, whereas tactile foragers often forage in dense flocks. Flamingos 2% Cormorants 1% Pelicans 0% Waterfowl 0% Herons, egrets, ibises 1% Summer Gulls, terns 8% Resident waders 1% Migratory waders 87% Gulls, terns 15% Herons, egrets, ibises 7% Flamingos 37% Winter Resident waders 7% Migratory waders 30% Waterfowl 1% Pelicans 1% Cormorants 2% State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 248
Anchor Environmental Figure 11.11. Numerical composition of the birds on Langebaan Lagoon during summer and winter Waders require undisturbed sandflats in order to feed at low tide and undisturbed roosting sites at high tide. In the 1970’s it was determined that the most important sandflats, in terms of the density of waders they support, were in Rietbaai, in the upper section of Langebaan Lagoon, and at the mouth, near Oesterwal. The important roosting sites were the salt marshes, particularly between Bottelary and Geelbek (Summers 1977). Gulls and terns are common throughout the area. Although their diversity is relatively low, they make up for this in overall biomass, and form an important group. Both Kelp Gulls and Hartlaub’s Gulls occur commonly in the lagoon. Cormorants, darters and pelicans are common as a group, but are dominated by the marine cormorants which breed on the Saldanha Bay islands. Great White Pelicans visit the bay and lagoon to feed, but they breed beyond the area at Dassen Island. African Darters Anhinga rufa are uncommon, and are more typical of lower salinities and habitats with emergent vegetation which is relatively uncommon in the study area. Waterfowl occur in fairly large numbers because of the sheer size of the study area, but they are not as dense as they might be in freshwater wetland habitats or nearby areas such as the Berg River floodplain. Other birds that commonly occur on the lagoon include birds of prey such as African Fish- Eagle Haliaeetus vocifer, Osprey Pandion haliaetus and African Marsh-Harrier Circus ranivorus, and species such as Pied Kingfisher Ceryle rudis and Cape Wagtail Motacilla capensis. 11.3.3 Inter-annual variability in bird numbers Irregular waterbird surveys were conducted at Langebaan Lagoon from 1934, but, due to the large size of the lagoon, these early counts were confined to small areas. It was not until 1975 that annual summer (January or February) and winter (June or July) surveys of the total population of waders at high tide, when waders congregate to roost on saltmarshes and sand spits, were conducted by members of the Western Cape Water Study Group (WCWSG) (Underhill, 1987). An analysis of the numbers of waders over the period 1975 to 1980 showed stable summer populations, but large year to year variations in the number of Palearctic migrants that over-wintered (Robertson, 1981). The Western Cape Water Study Group monitored Langebaan continuously up to 1991, and since 1992, the Lagoon has been monitored bi-annually by the Co-ordinated Waterbird Counts (CWAC), organised by the Avian Demography Unity at the University of Cape Town. The above data sets provide the opportunity to examine the long term trends in bird numbers at Langebaan Lagoon up to the present day. This reveals a dramatic downward trend in the numbers of Palearctic waders at the Lagoon (Figure 11.12). The reasons for these declines are diverse and poorly understood, but seem to be a combination of loss and degradation of their breeding sites as well as of their over-wintering grounds during their non-breeding period (Dias et al. 2006). However, while the downward trend may echo global trends in certain wader populations, what is of more concern is that the trend appears to be echoed by resident waders, although in recent years populations numbers seem to be stabilizing (Figure 11.13). This does suggests that conditions at Langebaan Lagoon are at least partially to blame. The most likely problems are that of siltation of the system reducing the area of suitable (e.g. muddy) intertidal foraging habitat, loss of seagrass beds with their associated invertebrate fauna (Pillay et al. 2011; see §7) and human disturbance, which has been shown to have a dramatic impact on bird numbers in other estuaries (Turpie and Love 2000). State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 249
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State of the Bay 2010: Saldanha Bay
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TABLE OF CONTENTS Anchor Environmen
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11 BIRDS 234 Anchor Environmental 1
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LIST OF FIGURES Anchor Environmenta
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Anchor Environmental Figure 4.27. O
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Anchor Environmental Figure 7.3. Ch
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Anchor Environmental Figure 9.10. C
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Anchor Environmental Figure 12.1. N
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Anchor Environmental samples were c
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EXECUTIVE SUMMARY Anchor Environmen
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Anchor Environmental matter in the
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Anchor Environmental considered mos
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Anchor Environmental again in 2004,
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Anchor Environmental Populations of
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GLOSSARY Alien species An introduce
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1 INTRODUCTION Anchor Environmental
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2 STRUCTURE OF THIS REPORT Anchor E
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Anchor Environmental complicates ma
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Anchor Environmental observed deter
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Anchor Environmental 4 ACTIVITIES A
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Fish factories Small craft harbour
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Anchor Environmental Aerial photogr
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Anchor Environmental interferes wit
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Anchor Environmental Figure 4.7. Nu
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o Decrease in oxygen concentrations
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Anchor Environmental Upgrades to th
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Anchor Environmental Figure 4.9. A)
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Anchor Environmental (possibly link
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Anchor Environmental Prestedge Reti
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Anchor Environmental the constructi
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Number and types of vessels enterin
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Anchor Environmental is contained b
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Anchor Environmental include the be
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o 33 3’S o 33 10’S Saldanha Bay
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Anchor Environmental (1956) UNDER T
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Free ACtive Chlorine (mg/l) Amonia
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Faecal coliforms (org/100 ml) Chemi
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4.3.7 Storm water Anchor Environmen
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Anchor Environmental sites (concent
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Anchor Environmental Discharges fro
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Anchor Environmental Table 4.9. Det
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5 WATER QUALITY Anchor Environmenta
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Anchor Environmental Stander (1977)
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Anchor Environmental coast, result
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Anchor Environmental likely as a re
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Anchor Environmental Construction o
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Anchor Environmental Table 5.2. Per
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Counts per 100ml of sample Counts p
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Counts per 100ml of sample 10000 10
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5.6 Trace Metal Contaminants in the
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Lead(mg/kg) Mercury (mg/kg) Cadmium
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6 SEDIMENTS 6.1 Sediment particle s
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6.1.2 Sediment Particle size result
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100% 90% 80% 70% 60% 50% 40% 30% 20
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% POC 18 16 14 12 10 8 6 4 2 0 % PO
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Percentage Percentage 1.8 1.6 1.4 1
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o 33 3’S o 33 10’S Yacht Club B
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Figure 6.12. Variation in the conce
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The concentrations of metals in sed
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concentrations are 56 and 29 times
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threshold of 1.2 mg/kg established
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Cadmium (mg/kg) 8 7 6 5 4 3 2 1 0 C
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Copper (mg/kg) 45 40 35 30 25 20 15
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16000 14000 12000 10000 8000 6000 4
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In summary, elevated trace metal co
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6.5 Summary of sediment health stat
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7.1 Long term changes in seagrass i
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7.2 Long term changes in Saltmarshe
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Figure 8.1. Benthic macrofauna samp
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Table 8.1. Depth at each of the sit
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these species usually provide the l
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(clustering of similar groups) (Meg
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The Big Bay samples BB 25 and BB29
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2007/08 dredging. Other signs of th
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Wet mass per m² Wet mass per m² 4
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Big Bay Crustaceans and polychaetes
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Average number of individuals per m
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Number Individuals per m² Number I
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8.4.2 Abundance Biomass Indices 8.4
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and percentage organic nitrogen (PO
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Table 8.5. W statistics at all stat
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Figure 8.15: Variation in the diver
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percentage of mud compared to Lange
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Cu (mg/kg) Cd (mg/kg) Ni (mg/kg) Pb
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contaminants. Furthermore dredging
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areas even 5 months after the clear
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Brittle star ( Ophiuroidea spp) Sea
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9.2 Approach and Methodology 9.2.1
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cover data for both mobile and sess
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9.2.3 Data Analysis The similaritie
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