Public Disclosure Authorized - World Bank...cable to the survey room of the vessel. The data was...

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Bowman Bishaw Pty Ltd (ABN 18 009 238 706) as Trustee for the Bowman Bishaw Unit Trust trading as Bowman Bishaw Gorham

CHINGUETTI BENTHIC SURVEY REPORT JULY 2003

Prepared for: Woodside Mauritania Pty Ltd 1 Adelaide Terrace PERTH WA 6000

Prepared by: Bowman Bishaw Gorham 290 Churchill Avenue SUBIACO WA 6008 Telephone: (08) 9382 4744 Facsimile: (08) 9382 1177

Report No: R03005FR April 2004

Chinguetti Benthic Environmental Surveys. 2004 Page No. i

BOWMAN BISHAW GORHAM

TABLE OF CONTENTS Page

No.

1.0 INTRODUCTION 1

2.0 METHODOLOGY 32.1 Video Surveys 52.2 Sediment Samples 5

2.2.1 Heavy Metals Analysis 5 2.2.2 Total Petroleum Hydrocarbon Analysis 5 2.2.3 Particle Size Analysis 6 2.2.4 Total Organic Carbon Content 6

2.3 Benthic Fauna Samples 6

3.0 RESULTS 73.1 Video Surveys 7

3.1.1 Teve’t 7 3.1.2 FPSO 7 3.1.3 Chinguetti Field 7 3.1.4 Carbonate Mounds 8

3.2 Grab Sample Visual Descriptions 83.2.1 Teve’t 9 3.2.2 FPSO 9 3.2.3 Chinguetti Field 9 3.2.4 Carbonate Mounds 9

3.3 Particle Size Analysis 103.4 Sediment Heavy Metal Concentrations 113.5 Sediment Total Petroleum Hydrocarbon Concentrations 113.6 Sediment Total Organic Carbon Content 113.7 Sediment Infauna 123.8 Benthic Sledge Samples 15

3.8.1 Teve’t 16 3.8.2 Carbonate Mounds 17

4.0 DISCUSSION AND CONCLUSIONS 22

Chinguetti Benthic Environmental Surveys. 2004 Page No. ii


LIST OF TABLES

Table Page No. No.

1 Distribution of particle sizes in sediments collected from the Chinguetti development area and surrounds in July 2003 10

2 Heavy metal concentrations in sediments collected around the Chinguetti oilfield, offshore Mauritania in July 2003 11

3 Total organic carbon content of sediment samples collected from the Chinguetti area in July 2003 12

4 Taxonomic composition of infauna by Phylum. Fauna from the three replicate samples collected at each site was pooled to produce the site total. Colonial cnidarians such as soft corals and hydroids could not be counted and so were scored as present or absent. 13

5 Taxonomic determination of specific fishes collected from the survey. 21

Chinguetti Benthic Environmental Surveys. 2004 Page No. iii


LIST OF FIGURES

Figure No.

1 Location Diagram 2

2 Sampling strategy and sites 4

3 Results of Multidimensional Scaling of the nine sites based on the Log (x+1) transformed abundance of eight invertebrate taxa. Mound sites 1 and 2 separated from other sites on the basis of echinoderm abundance. Significant physico-chemical gradients are also displayed indicating a higher mean particle size at the mound sites and higher heavy metal concentrations at the FPSO sites. 15

Chinguetti Benthic Environmental Surveys. 2004 Page No. iv


LIST OF PLATES

Plate Page No. No.

Plate 1 Representative photographs of some of the taxon encountered in Chinguetti sediments. 14

Plate 2 Macro-fauna collected by the second benthic trawl conducted in 500 m near the Teve’t location. 16

Plate 3. Macro-fauna collected from the first of the carbonate mounds, located in 420 - 550 m, adjacent to the Chinguetti location. 17

Plate 4. Macro-fauna collected from the seabed in the general area of the Chinguetti field and proposed FPSO location. 19

Plate 5. Loppe’s tadpole fish (Ijimaia loppei) collected from 700 – 850 m in the general area of the Chinguetti field and proposed FPSO location. 20

LIST OF APPENDICES

Appendix A Sediment Analysis FiguresAppendix B Chinguetti Infauna and Sediment Data

Chinguetti Benthic Environmental Surveys. 2004 Page No. 1


1.0 INTRODUCTION

Woodside Mauritania Pty Ltd (Woodside) is the operator of five hydrocarbon exploration blocks located in offshore Mauritania waters, in north-west Africa (Figure 1). Exploration drilling in 2001 and 2002 was successful and the Chinguetti discovery is presently being evaluated for commercial production.

As part of the 2002 field program, Bowman Bishaw Gorham conducted some preliminary investigations of a series of bathymetric features situated in approximately 450–550 m water depth and extending parallel to the coastline. These were found to be carbonate banks apparently generated by cold-water corals.

Prior to the instigation of its 2003 drilling program, Woodside requested Bowman Bishaw Gorham to undertake an environmental field survey in the Chinguetti area and adjacent carbonate banks. These studies were designed to gain baseline data prior to the commencement of any development. Investigations were planned to include studies at the actual Chinguetti field, the likely area where a floating production, storage and offloading (FPSO) facility would be located, the carbonate mounds inshore and adjacent to the field, and at a possible exploration prospect, named Teve’t.

The survey was undertaken in July 2003 and comprised video camera investigations, the collection of representative sediment samples for physico/chemical and infauna analysis, and the collection of seabed macro-fauna.

This report documents the scope of investigations undertaken and presents the results of those studies.



2.0 METHODOLOGY

The environmental surveys were conducted aboard the “MV Clupea”, a 55 m anchor-handling vessel operating from the Port of Nouakchott. Mobilisation of the survey equipment aboard the vessel was conducted between 13–16 July. The actual surveys were undertaken between 17–25 July.

Positioning was determined using a Garmin 2 GPS receiver, linked to ArcPad software, to provide a real-time navigation aid displaying both depth and positional data. The ArcPad output was displayed on separate monitors located on the bridge and in the survey room.

The locations of sites where visual investigations and sample collection were undertaken are shown in Figure 2.



2.1 Video Surveys

Video imagery was collected using a Hitachi 3CCD camera housed in a one-atmosphere waterproof casing, mounted on a tow sled. Lighting was provided by four high-intensity 250 volt submersible lights. The imagery was transferred via an armoured optical fibre cable to the survey room of the vessel. The data was recorded on digital video (DV) tapes and digital video discs (DVD).

2.2 Sediment Samples

Seabed sediment samples were collected using a stainless steel Van Veen grab, positioned below a video camera with direct feed to the survey room. Visual contact with the grab allowed rapid initiation of recovery once the grab reached the seabed, or if the grab triggered accidentally on descent.

Upon recovery, the sediment samples were reduced to a standard surface area of 0.1 m2.These samples were used for the determination of infauna, while physico/chemical samples were collected from the surface 2 cm of the remaining sample. Physico/chemical analyses included heavy metals, total petroleum hydrocarbons, particle size, and total organic carbon content.

2.2.1 Heavy Metals Analysis

Sediment samples for heavy metals analysis were collected in 250 ml plastic screw-top jars and frozen upon collection. The samples were analysed by Analytical Reference Laboratories (ARL) in Perth, using flame ionised atomic absorption spectrometry.

2.2.2 Total Petroleum Hydrocarbon Analysis

Sediment samples for the analysis of total petroleum hydrocarbon (TPH) content were collected in pre-cleaned 250 ml glass jars. The samples were frozen for storage immediately following collection.

Sample analysis was conducted by ARL in Perth, using gas chromatographic techniques with detection limits of 0.5 mg/kg for individual alkanes.



2.2.3 Particle Size Analysis

Sediment samples for particle size analysis were collected in pre-cleaned 250 ml polyethylene jars. Analysis was conducted by the CSIRO Division of Minerals, using standard dry sieving techniques and laser diffraction for particles less than 600 µm in diameter.

The common terms used for description of particle size categories approximate the grain size classification systems in the draft sediment guidelines (ANZECC/ARMCANZ 2000) for fine particles, and the Wentworth Scale (after Holme and McIntyre, 1984) for sand. The categories have been modified slightly to suit the output from the CSIRO diffraction analyses.

The terminology for particle size classification used in this report is as follows: Clays = 2.34 - 56.36 µm Silts = 2.34 - 56.36 µm Fine sands = 56.36 - 224 µm Medium sands = 224 - 500 µm Coarse sands = 500 - 1000 µm Very coarse sands = 1000 - 5000 µm

2.2.4 Total Organic Carbon Content

Sediment samples were collected in 250 ml plastic jars, frozen, and transported to Perth for analysis of total organic content by ARL. The analysis used was loss on ignition in a muffle oven after extended heating to 550° C.

2.3 Benthic Fauna Samples

Samples of the larger benthic organisms were collected using a modified Ockelmann sledge fitted with collection nets. The mouth of the sledge was 1.5 m wide and 0.6 m high, with a 1.5 cm mesh size primary net, mounted inside a 2.5 cm mesh size heavy protective net.

The sledge was lowered to the seabed and dragged at minimal vessel speed for a twenty minute period before recovery. The recovered organisms were recorded, and representative samples were collected for taxonomic analysis. Samples were either stored frozen or in 10% buffered formaldehyde, as appropriate.



3.0 RESULTS

3.1 Video Surveys

Extended video transect surveys were completed at the proposed Teve’t and FPSO locations, at the Chinguetti field, and over the carbonate banks adjacent to the field.

3.1.1 Teve’t

The video transects conducted at Teve’t encountered a seabed comprised of bioturbated silts/fine sands. Red prawns were the most numerous organisms observed, with various fish, crustaceans and sea whips. Members of the family Scorpaenidae (Scorpionfish) and rat-tailed fishes were the most common fish seen, with lesser occurrences of small conger eels. In addition to the red prawns, crustaceans were represented by galathaid and portunid crabs and shrimps.

Of note was the occurrence of numerous marks and gouges on the seabed, interpreted as being caused by trawling activities.

3.1.2 FPSO

Video transects at the proposed FPSO location comprised a short investigation that was terminated due to technical difficulties, and an extended investigation of the seabed in the area. Seabed substrates comprised heavily bioturbated muds. Small polychaete worm tubes were evident throughout the area investigated.

Other than the worm tubes, only a sparse benthic fauna, comprising red prawns, occasional sea pens, and small, unidentified fishes, was observed along the transect. Disturbance to the seabed, interpreted as being the result of trawling activity, was also present along the transect.

3.1.3 Chinguetti Field

The substrate observed at the Chinguetti field comprised grey/green, bioturbated muds. The most abundant organisms observed were red swimming ophiuroids. What appeared to be pairs of ophiuroid arms were also observed emerging from some of the burrows.



A relatively diverse benthic assemblage of less dominant organisms was encountered, including anemones, blue rat-tail fishes, red prawns and red octopi. Human disturbance of the seabed was not detected along this transect.

3.1.4 Carbonate Mounds

The camera investigations over the carbonate mounds included coverage of the base, sides and top of the features. Water depths in these areas varied between approximately 550 m at the base, and 420 m on top of the shallowest mound.

The seabed substrates and benthic communities that were investigated varied in response to their position on the mounds. The seabed at the deeper areas around the base of the mounds comprised bioturbated fine sands/muds. The epibenthic community in these areas comprised sea pens with occasional hydroids. Motile species observed included large numbers of the ubiquitous red prawn, blue rat-tail and scorpaenid fishes, crabs and small sharks.

The sides and tops of the mounds comprised sand/rubble substrates with a more diverse assemblage of epibenthic organisms. These included small gorgonians, ascidians and sponges. Some polyps, thought to be lone coral polyps, were observed, together with one small coral colony. Patches of tube worms and aggregations of pencil urchins were observed, generally on the tops of the mounds. Crustaceans were common, in particular, portunid and galathaid crabs.

The rubble appeared to mainly consist of the dead remains of hard corals and, in places, was of sufficient density to indicate a past level of live coral greatly in excess of what presently occurs . The observation of only one small coral colony and what could have been some individual polyps, suggests that the present condition of the benthic community on the mounds is greatly degraded from pristine condition.

3.2 Grab Sample Visual Descriptions

Sediment grab samples were collected from Teve’t, the proposed FPSO location, the Chinguetti field, and from the carbonate mounds.



3.2.1 Teve’t

Three sediment grabs, being three replicates from the one location, were collected from approximately 500 m water depth at Teve’t. Sediments from each of the grabs comprised silty sands with very limited obvious infauna, mainly represented by polychaete worms.

3.2.2 FPSO

Nine sediment grabs, consisting of three replicates at three locations, were collected in 700 m water depth from the proposed FPSO area. Each grab sample comprised thick, green, clay/silt sized returns.

The sediments were rich in polychaete worms, but many of these were too small to be collected on the 1 mm sieves used for separation of the infauna. Secondary organisms observed in the grab samples included amphipods, bivalves and ophiuroids.

3.2.3 Chinguetti Field

Nine sediment grabs, consisting of three replicates at three locations, were collected in 800 m water depth from the Chinguetti field area. Sediments comprised very fine clay/silty muds, and each grab sampled to total depth

Organisms observed in the sieved samples were mainly polychaete worms, with occasional ophiuroids.


Six grab samples were collected from the carbonate mounds, consisting of three replicate samples from two separate mounds. Each of the grabs had only moderate returns of material, mainly comprising the dead remains of cold-water corals.

The grab samples from the mounds contained the greatest diversity of organisms observed from the sampling program. These included sponges, hydroids ascidians, gorgonians, polychaetes, ophiuroids, molluscs, and various crustaceans.



3.3 Particle Size Analysis

The results of particle size analysis of sediments collected during the survey are contained in Table 1 and graphed in Appendix A, Figures 1a – 1i. The samples collected from the Chinguetti Field, the proposed FPSO locations and from Teve’t all comprised well-sorted sediments in the clay to fine sands ranges. The mean size of the particles from sites not including the banks appeared inversely related to water depth, ranging from 60 m at Teve’t (500 m), to 34 m at the FPSO site (700 m), and down to 24.5 mat the Chinguetti field (800 m).

The FPSO and Chinguetti sediments could best be described as being silty, while those at Teve’t are silty, fine sands. The variation within the three replicate samples collected from both the FPSO and Chinguetti sites was very small, indicating homogenous sediments at both locations.

Table 1 Distribution of particle sizes in sediments collected from the Chinguetti development area and surrounds in July 2003

Sample

ID

Site Mean

ParticleSize

( m)

Range ( m) % Clays

% Silts % Fine

Sands

%Medium

Sands

%Coarse

Sands

%Over

Size

20210 Field 1 24.29 0.25 - 140 15.11 73.97 10.92 0 0 0

20211 Field 2 24.83 0.25 - 140 15.39 73.00 11.61 0 0 0

20212 Field 3 24.55 0.22 - 140 17.92 69.19 12.89 0 0 0

20213 FPSO1 30.49 0.28 - 140 13.92 67.24 18.84 0 0 0

20214 FPSO 2 37.83 0.25 - 158 11.13 62.09 26.78 0 0 0

20215 FPSO 3 33.14 0.25 - 158 14.10 63.13 22.77 0 0 0

20216 Mound 1 1093 0.32 – 10,000 4.95 34.80 16.25 4.72 6.15 43.68

20217 Mound 2 365.87 0.28 – 10,000 5.80 33.46 41.15 10.00 1.55 8.05

20218 Teve’t 3 60.09 0.25 - 178 7.86 39.08 53.06 0 0 0

The sediments collected from the mound locations were not particularly suitable for particle size analysis, but were analysed nevertheless. These mainly comprised the skeletal remains of cold-water corals, together with unsorted sediments ranging from silts to sands. The samples were not ideal because the grab returns were reduced by poor penetration of the grab into the seabed, and by leakage caused by coral fragments jamming the jaws. The samples analysed comprised the finer material in the samples after the large, dead coral pieces had been removed.



3.4 Sediment Heavy Metal Concentrations

The results of the analysis of sediments for heavy metals concentration are contained in Table 2 and presented in Appendix A, Figures 2a – 2h.

Table 2 Heavy metal concentrations in sediments collected around the Chinguetti oilfield, offshore Mauritania in July 2003

SampleID

Site As Cd Cr Cu Hg Ni Pb Zn

20210 Field 1 8 0.2 66 18 <0.01 32 6 36 20211 Field 2 6 0.1 56 17 0.01 29 7 33 20212 Field 3 5 0.1 60 17 <0.01 31 7 36 20213 FPSO 1 14 0.1 54 14 <0.01 25 6 30 20214 FPSO 2 <5 0.2 56 15 <0.01 27 6 29 20215 FPSO 3 16 0.2 55 14 <0.01 26 6 31 20216 Mound 1 11 0.2 12 5 <0.01 10 2 16 20217 Mound 2 13 0.2 41 7 <0.01 14 4 19 20218 Teve’t 3 10 0.2 38 6 <0.01 14 3 18

3.5 Sediment Total Petroleum Hydrocarbon Concentrations

Petroleum hydrocarbons were not detected in any of the sediment samples, except for the Field 3 sample. At that site, total n-alkanes were measured to be 6.8 mg/kg. The alkanes present were in the C8 to C12 range and were similar to a refined light fuel oil. The lack of lower alkanes was consistent with partial combustion of a fuel oil, and this result is probably caused by contamination from the vessel’s exhaust.

3.6 Sediment Total Organic Carbon Content

The results of analysis of total organic carbon content (TOC) in the sediment samples are contained in Table 3 and are displayed in Appendix A, Figure 3. TOC ranged from 4.5% in the Mound 2 sample, to 12% in the Field 2 sample. TOC increased with increased water depth, and with decreased sediment particle size.



Table 3 Total organic carbon content of sediment samples collected from the Chinguetti area in July 2003

SampleID

Site Total Organic Carbon LOI @ 550 °C %wt/wt

20210 Field 1 11 20211 Field 2 12 20212 Field 3 10 20213 FPSO 1 9 20214 FPSO 2 10 20215 FPSO 3 9 20216 Mound 1 5.3 20217 Mound 2 4.5 20218 Teve’t 3 5.0

3.7 Sediment Infauna

The detailed results of analysis of infauna content in sediments collected during the survey are contained in Appendix B. A summary of the data is presented at Phylum level in Table 3. Representative photography of selected organisms is contained in Plate 1. The infauna was dominated by polychaete annelids, accounting for nearly 65% of all animals collected. Crustaceans were second in abundance but at less than a quarter of the numbers of polychaetes, followed by molluscs and then echinoderms. Poriferans, nemerteans and nematodes were all relatively rare. Colonial cnidarians such as soft corals and hydroids were present as fragments and could not be counted accurately. They were excluded from further analysis.

On the basis of the log-transformed site totals, ordination by Multi-dimensional Scaling (MDS) showed a clear separation between the two mound sites and the other five sites (Figure 3). This separation was significant by ANOSIM (p<0.05) and primarily based on the abundance of echinoderms on the mounds compared with other sites. However, the mounds showed a number of differences from the other sites (Table 3). They were the only sites where poriferans and cnidarians were present in the samples and had over twice the species diversity shown at any other site.



Table 4 Taxonomic composition of infauna by Phylum. Fauna from the three replicate samples collected at each site was pooled to produce the site total. Colonial cnidarians such as soft corals and hydroids could not be counted and so were scored as present or absent.

Site Field 1 Field 2 Field 3 FPSO 1 FPSO 2 FPSO 3 Mound 1 Mound 2 Teve’t 3 Totals

Phylum

Porifera 0 0 0 0 0 0 13 17 0 30 Cnidaria A A A A A A P P A Nemertea 2 1 2 0 2 1 9 4 3 24 Nematoda 0 0 0 0 0 0 31 8 0 39 Mollusca 19 32 9 26 26 26 21 24 18 201 Annelida 100 80 66 72 99 85 195 206 462 1365 Crustacea 13 5 5 21 85 19 76 56 24 304 Echinodermata 4 4 5 3 3 4 66 45 6 140 Total 139 122 87 123 215 136 411 360 513 2103 No. Species 44 35 27 44 44 43 86 97 45



Anthuridae Lumbrineidae

Copepod Gastropod

Octocoral Ophiuroidea

Plate 1. Representative photographs of some of the taxon encountered in Chinguetti sediments.



Mound sites were also characterised by larger particle sizes than at the other sites, where sediments tended to silts (FPSO sites) and clays (Field sites). Principal Component Analysis on the physical parameters further separated the mound sites from the other sites based on lower concentrations of Cr, Cu, Ni, Pb and Zn. This is indicated in the overlay of physical parameter gradients on the graph of site ordination based on invertebrate abundance (Figure 3).

Figure 3: Results of Multidimensional Scaling of the nine sites based on the Log (x+1) transformed abundance of eight invertebrate taxa. Mound sites 1 and 2 separated from other sites on the basis of echinoderm abundance. Significant physico-chemical gradients are also displayed indicating a higher mean particle size at the mound sites and higher heavy metal concentrations at the FPSO sites.

3.8 Benthic Sledge Samples

Benthic sledge samples were collected from Teve’t, from the carbonate mounds, and from the 700–800 m zone between the proposed FPSO location and the Chinguetti field.

log (n+1) Invertebrate abundance excluding Cnidaria

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-1.5 -1 -0.5 0 0.5 1 1.5 2Field 1Field 2Field 3FPSO 1FPSO 2FPSO 3Mound 1Mound 2Tevet3Series10

% clays

mean particle size% coarse sands% oversize

Cr, Cu% silts

Ni



3.8.1 Teve’tTwo benthic trawls were undertaken along the 500 m depth contour through the Teve’t area. Both trawls recovered a low diversity and low abundance of benthic organisms. The dominant organism was the small red prawn observed on the video transects conducted through the area. These numbered approximately 50 individuals in the first trawl and 120 in the second (Plate 2).

Plate 2. Macro-fauna collected by the second benthic trawl conducted in 500m near the Teve’t location.

The next most common organism was a gastropod snail, with most of those collected supporting an anemone on the upper side of the shell. Thirty-five gastropods were recovered from the first trawl, with approximately one hundred obtained in the second.

The less common taxa included various fishes, including small soles, cardinal fish, frog fish, and small rat-tailed fishes. A red portunid crab was encountered in both sledge samples, while a purple calapa crab was collected in the second sample.




Sledge samples were collected from three of the carbonate mounds adjacent to the Chinguetti discovery. Each of the samples recovered from the nets were relatively small, and none contained either live or dead corals (Plate 3).

Plate 3. Macro-fauna collected from the first of the carbonate mounds, located in 420 - 550 m, adjacent to the Chinguetti location.

Sea pens were common in all samples. These were commonly observed on the silt/sand sediments around the base of the mounds, but were not observed on the mounds themselves. The red prawns that were ubiquitous in the other samples were found in low numbers here, with thirty individuals from one sample being the largest number collected.



Teleost fishes were represented by a small number of species. A small red scorpion fish was found in two of the trawls. Other fish collected included four species of rat-tail fish and a small cardinal fish. Generally, species were present in very low numbers (1–3), with ten cardinal fish in one sample being the greatest number of a single species encountered.

Other organisms collected included ten of the anemone-bearing whelks and two bivalves in one sample, a heart urchin in another, and two trochoid gastropods in the other sample.

All samples contained jellyfish, which were probably collected during the descent and ascent of the sledge.

FPSO / Chinguetti

The sledge samples from the 700–850 m deep area sampled between the proposed FPSO location and the Chinguetti field were the most diverse of the samples collected. All of the samples were dominated by a single species of red ophiuroid, with in excess of 100 individuals collected in each sample.

The samples contained a diversity of fish and invertebrate species, most of which were not encountered in any of the shallower sledge collections (Plate 4). Fishes included frog fish, conger eels, small soles, sabre-toothed eels and a large eel-tailed fish (~1.2m) identified as a Loppe's tadpole fish (Ijimaia loppei) (Plate 5).

Invertebrates collected in the three sledge trawls included ophiuroids, portunid and galathaid crabs, large anemones, and a number of gastropods. A number of delicate sand dollars were also recovered, and these appeared to have a silicious skeleton, rather than calcium carbonate as occurs in shallow-water species.



Plate 4. Macro-fauna collected from the seabed in the general area of the Chinguetti field and proposed FPSO location.



Plate 5. Loppe’s tadpole fish (Ijimaia loppei) collected from 700 – 850 m in the general area of the Chinguetti field and proposed FPSO location.



Table 5. Taxonomic determination of specific fishes collected from the survey.

Site Family Species Conf* Common Name

Mound 1 450m Scorpaenidae Helicolenusdactylopterus 2 Blackbelly rosefish

Mound 1 450m Macrouridae Trachyrincusscabrus 1 Roughsnout grenadier

BG-4-500m Epigonidae Epigonusdenticulatus 2 Pencil cardinal

BG-4-500m Trachichthyidae Hoplostethusmediterraneus 2 Black slimehead

BG-4-500m Alepocephalidae Xenodermichthyscopei 2 Bluntsnout smooth-head

BG-4-500m Moridae Gadella sp. 3 Beardless codling

BG-4-500m Ophidiidae Lamprogrammusexutus ? 3 Legless cuskeel

Field 850 m Congridae cf. Bassanago sp. 3 Conger eel Field 850 m Ateleopodidae Ijimaia loppei 1 Loppe's tadpole fish

* Confidence in the taxonomic determination, with 1 being certain and 3 being likely.



4.0 DISCUSSION AND CONCLUSIONS

The waters offshore from the Mauritanian coast are distant from any significant industrial or fluvial inputs and should be considered pristine. The most significant human impact upon the marine system is the extensive fisheries operating in the area.

The existing chemical characteristics of the marine sediments sampled should therefore reflect the natural condition. Hydrocarbons were not detected in any of the sediments, other than in one collected from the Chinguetti field. During collection of that sample the vessel moved through the wind and heavy exhaust coverage was swept over the rear deck and the exposed sediments. The chemical signature of the hydrocarbon was consistent with partially burnt light oil, suggesting the analysis had detected exhaust gas contamination.

The concentrations of listed heavy metals in the sediments were below those specified by ANZECC/ARMCANZ guidelines as triggering concern, except for nickel. Nickel concentrations were greater than the trigger levels in all six deep water sediment samples collected from the Chinguetti field and the proposed FPSO development site.

The consistent nature of the nickel concentrations encountered at the most offshore sites, together with the lower levels found at the mound and Teve’t sites, indicates the concentrations are real and not caused by contamination. The lack of possible anthropogenic sources to cause elevated nickel concentrations indicates that the levels encountered by this survey are representative of the natural condition. It is possible but unlikely that elevated nickel occured due to contamination from the stainless steel grab.

The particle size and the total organic content analyses were consistent with the trends expected in sediments increasing in depth and distance offshore. Inputs to deeper offshore sediments include biogenically derived material mainly originating in the plankton. These inputs are considered to be particularly important in Mauritanian waters where up-welling events sponsor rich plankton populations.

The obvious gouges observed on the seabed at the Teve’t and proposed FPSO area are testament to the intense fishing pressure that occurs throughout the offshore Mauritanian waters. Probably not co-incidentally, the deepest sites investigated were dominated by ophiuroids rather than prawns, and no trawl marks were found on the seabed. The low diversity of animals, both observed on the video recordings and found



in the benthic sledge samples, appears to reflect the high level of fishing pressure prevalent throughout the area.

The effects of benthic trawling operations were most evident at the mound locations. Grab samples from these structures were dominated by the dead remains of cold water corals, particularly Lophelia pertusa. Visual surveys over three mounds only encountered one positively identified live coral colony, with some lone polyps also tentatively identified. Other benthic organisms observed included small gorgonians, ascidians and sponges.

The assumption from the observations is that a catastrophic event has reduced the benthic cover on the mounds in general, and of the corals in particular. Cold water corals are expected to be very vulnerable to impact damage and slower to recover than the soft bodied animals observed on the mounds. The cause of the surmised decline in benthic cover is assumed to be trawl fishing impact.

The results of the physical, chemical, infauna, visual and benthic sampling programs provide a details of environmental conditions at locations extending across the shelf break prior to any development of the Chinguetti field. These data can be used as a baseline for comparisons with subsequent data collected to assess any impacts caused by development or production activities.

FIGURES

APPENDIX A

SEDIMENT ANALYSIS FIGURES

Field 1

0

20

40

60

80

Clays Silts Fine Sands MediumSands

CoarseSands

Over Size

Particle Size

Field 2

0

20

40

60

80


CoarseSands

Over Size

Particle Size

Field 3

0

20

40

60

80


CoarseSands

Over Size

Particle Size

Figure 1 a, b and c Particle size distribution of sediments collected from the Chinguetti development

area and surrounds.

FPSO 1

0

20

40

60

80


CoarseSands

Over Size

Particle Size

FPSO 2

0

20

40

60

80


CoarseSands

Over Size

Particle Size

FPSO 3

0

20

40

60

80


CoarseSands

Over Size

Particle Size

Figure 1. d, e and f Particle size distribution of sediments collected from the Chinguetti development

area and surrounds.

Mound 1

0

20

40

60

80


CoarseSands

Over Size

Particle Size

Mound 2

0

20

40

60

80


CoarseSands

Over Size

Particle Size

Teve't 3

0

20

40

60

80


CoarseSands

Over Size

Particle Size

Figure 1. g, h and i Particle size distribution of sediments collected from the Chinguetti development area and surrounds.

a) Arsenic

b) Cadmium

c) Chromium

Figure 2. a, b, and c. Heavy metal concentrations in sediments collected around the Chinguetti oilfield,

offshore Mauritania. July 2003. Unfilled columns represent levels below detection limits.

Trigger Levels = concentrations above which further investigation may be required (ANZECC/ARMCANZ, 2000).

Trigger Level

0

5

10

15

20

25

Field 1 Field 2 Field 3 FPSO 1 FPSO 2 FPSO 3 Mound 1 Mound 2 Teve't 3

Trigger Level

0

10

20

30

40

50

60

70

80

90


Trigger Level

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6


d) Copper

e) Mercury

f) Nickel Figure 2. d, e and f

Heavy metal concentrations in sediments collected around the Chinguetti oilfield, offshore Mauritania. July 2003.

Unfilled columns represent levels below detection limits. Trigger Levels = concentrations above which further investigation may be required

(ANZECC/ARMCANZ, 2000).

Trigger Level

0

10

20

30

40

50

60

70


Trigger Level

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16


Trigger Level

0

5

10

15

20

25

30

35


g) Lead

h) Zinc

Figure 2. g and h

Heavy metal concentrations in sediments collected around the Chinguetti oilfield, offshore Mauritania. July 2003.

Unfilled columns represent levels below detection limits. Trigger Levels = concentrations above which further investigation may be required

(ANZECC/ARMCANZ, 2000).

Trigger Level

0

10

20

30

40

50

60


Trigger Level

0

50

100

150

200

250


0

2

4

6

8

10

12

14

Figure 3

Total organic content of sediment samples collected from the Chinguetti area in July 2003.

APPENDIX B

Chinguetti Infauna and Sediment Data

Chinguetti Infauna and Sediment Data

SiteField

1

Field

2

Field

3

FPSO

1

FPSO

2

FPSO

3

Mound

1

Mound

2

Teve’t

3

TOC 11 12 10 9 10 9 5.3 4.5 5

As 8 6 5 14 4 16 11 13 10

Cd 0.2 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.2

Cr 66 56 60 54 56 55 12 41 38

Cu 18 17 17 14 15 14 5 7 6

Ni 32 29 31 25 27 26 10 14 14

Pb 6 7 7 6 6 6 2 4 3

Zn 36 33 36 30 29 31 16 19 18

Mean Particle Size

(mm)24.29 24.83 24.55 30.49 37.83 33.14 1093 365.87 60.09

% Clays 15.11 15.39 17.92 13.92 11.13 14.1 4.95 5.8 7.86

% Silts 73.97 73 69.19 67.24 62.09 63.13 34.8 33.46 39.08

% Fine Sands 10.92 11.61 12.89 18.84 26.78 22.77 16.25 41.15 53.06

% Medium Sands 0 0 0 0 0 0 4.72 10 0

% Coarse Sands 0 0 0 0 0 0 6.15 1.55 0

% Over Size 0 0 0 0 0 0 43.68 8.05 0

PORIFERA 0 0 0 0 0 0 13 17 0

CNIDARIA 0 0 0 0 0 0 300 105 0

NEMERTEA 2 1 2 0 2 1 9 4 3

NEMATODA 0 0 0 0 0 0 31 8 0

MOLLUSCA 19 32 9 26 26 26 21 24 18

ANNELIDA 100 80 66 72 99 85 195 206 462

Crustacea 13 5 5 21 85 19 76 56 24

ECHINODERMATA 4 4 5 3 3 4 66 45 6

Totals 139 122 87 123 215 136 717 568 513

No. Species 44 35 27 44 44 43 86 97 45

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