Manly Lagoon Dredging Project - Manly Council - NSW Government
Manly Lagoon Dredging Project - Manly Council - NSW Government Manly Lagoon Dredging Project - Manly Council - NSW Government
Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah CouncilsScientific Name Common Name Status Type of Presence in AreaSyngnathoides Double-ended Pipehorse,Species or species habitatListedbiaculeatus Alligator Pipefishmay occur (note 2)Trachyrhamphus Bend Stick Pipefish, Short-tailedSpecies or species habitatListedbicoarctatus Pipefishmay occur (note 2)UrocampusSpecies or species habitatHairy PipefishListedcarinirostrismay occur (note 2)VanacampusSpecies or species habitatMother-of-pearl Pipefish Listedmargaritifermay occur (note 2)ReptilesSpecies or species habitatChelonia mydas Green Turtle ListedDermochelyscoriaceaLeatherback Turtle, LeatheryTurtleListedPelamis platurus Yellow-bellied Seasnake Listedmay occur (note 3)Species or species habitatmay occur (note 3)Species or species habitatmay occur (note 3)Notes on the database search results (Table 5.11), giving consideration to the results of fiveEcology Lab fish surveys between 1993 and 2002 and professional opinion are providedbelow:Note 1: Fur seals have never been observed in Manly Lagoon and are unlikely tooccur there as appropriate habitat is not present;Note 2: Syngnathiformes (pipefish, seahorses, seadragons and their allies) havehabitat requirements or associations including seagrass and or algae. Substantialalgal beds are absent in Manly Lagoon and no seahorses or their allies have beenfound in Manly Lagoon. The seagrass beds present are located downstream of theproposed dredging area and will be protected from increased turbidity levels by theuse of silt curtains. It is therefore concluded that the proposal is unlikely to impactany of the Syngnathiformes listed in the EPBC Act or Fisheries Management Act1994;Note 3: While potentially present in the ocean off Manly, turtles and sea snakes areunlikely to be present in Manly Lagoon, as it provides no habitat or insignificanthabitat required by these species. No Assessment of Significance is considerednecessary for these species.Impact AssessmentBenthic FaunaDredging works will directly impact aquatic fauna living near or in the upper layers ofsediment (benthos) due to their removal with dredged sediments. While this represents asignificant impact on the benthos, newly exposed sediments are expected to recolonise afterdredging ceases, with new recruits migrating from undredged areas and via water-bornlarvae. The newly exposed sediments will be at a deeper depth than the existing benthiccommunities, but not sufficiently to affect the community structure of the post-dredgingassemblages. It is expected that dredging will reduce the contaminant load in the lagoonbed and that water quality will be improved as a result of dredging. These factors providethe circumstances under which the new benthic assemblages may develop greaterabundance and diversity than now occurs. Due to the low abundance of benthos in the2 July 2010 Cardno (NSW/ACT) Pty Ltd 92H:\Doc\2010\Reports.2010\Rep2580v4.doc
Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah Councilslagoon and low flushing rate of the lagoon, full recovery of benthic communities is expectedto be slower than seen after dredging in open coastal habitats or well flushed lagoons.Benthos living in areas where sediments will not be removed may be indirectly affected byincreases in turbidity and settlement of suspended sediments from nearby upstreamdredging works (Cardno Ecology Lab, 2009b).FishThe silt curtains which will be employed during dredging operations will act as barriers thatwill temporarily prevent the passage of fish and other estuarine species in the lagoon.Barriers such as this are identified in Schedule 6 of the Fisheries Management Act 1994 as akey threatening process to fish species. This matter was discussed with I&I NSW and it wasagreed that owing to the nature of the site and the proposed dredging and dewateringmethods that the benefits of restricting the potential downstream movement of sedimentoutweighed any temporary loss of fish passage. The downstream silt curtain will be sitedupstream of the side bay at Keirle Park to ensure this side bay does not become isolatedfrom the lagoon system.Any fish within the silt curtains may be impacted by changes to water quality (e.g. increasedturbidity) as they will not be able to escape from the area. As a mitigation measure, fish inthe area to be isolated by silt curtains will be, as far as possible captured using nets andmoved downstream prior to commencement of dredging. During dredging operations,attempts will be made to remove and relocate downstream any fish observed within the siltcurtains.Threatened FaunaFollowing the assessments of threatened and protected species described in this section,and the completion of two Seven Part Tests, it has been concluded that no threatenedaquatic, migratory or terrestrial fauna species listed in Tables 5.9 and 5.10 are consideredlikely to be directly or significantly impacted upon by the proposed works.Protected BirdsPotential impacts on breeding birds, both protected and unprotected species, in the vicinityof the works area could be due to:Direct impacts on the nesting site;Indirect impacts on the wider habitat and the foraging grounds; and/orDisturbances of the birds resulting in abandonment of the breeding effort.Dredging works within Manly Lagoon will not have any direct impact on the specific notednesting sites of the protected species Phalacrocorax melanoleucos (Little Pied Cormorant),as shown in Figure 5.11, since all dredging activity will be undertaken within the lagoon froma floating dredge barge, and the nest areas are not located in the vicinity of any of the shorebased treatment activities.2 July 2010 Cardno (NSW/ACT) Pty Ltd 93H:\Doc\2010\Reports.2010\Rep2580v4.doc
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<strong>Manly</strong> <strong>Lagoon</strong> <strong>Dredging</strong> <strong>Project</strong> – Review of Environmental FactorsPrepared for <strong>Manly</strong> and Warringah <strong>Council</strong>sScientific Name Common Name Status Type of Presence in AreaSyngnathoides Double-ended Pipehorse,Species or species habitatListedbiaculeatus Alligator Pipefishmay occur (note 2)Trachyrhamphus Bend Stick Pipefish, Short-tailedSpecies or species habitatListedbicoarctatus Pipefishmay occur (note 2)UrocampusSpecies or species habitatHairy PipefishListedcarinirostrismay occur (note 2)VanacampusSpecies or species habitatMother-of-pearl Pipefish Listedmargaritifermay occur (note 2)ReptilesSpecies or species habitatChelonia mydas Green Turtle ListedDermochelyscoriaceaLeatherback Turtle, LeatheryTurtleListedPelamis platurus Yellow-bellied Seasnake Listedmay occur (note 3)Species or species habitatmay occur (note 3)Species or species habitatmay occur (note 3)Notes on the database search results (Table 5.11), giving consideration to the results of fiveEcology Lab fish surveys between 1993 and 2002 and professional opinion are providedbelow:Note 1: Fur seals have never been observed in <strong>Manly</strong> <strong>Lagoon</strong> and are unlikely tooccur there as appropriate habitat is not present;Note 2: Syngnathiformes (pipefish, seahorses, seadragons and their allies) havehabitat requirements or associations including seagrass and or algae. Substantialalgal beds are absent in <strong>Manly</strong> <strong>Lagoon</strong> and no seahorses or their allies have beenfound in <strong>Manly</strong> <strong>Lagoon</strong>. The seagrass beds present are located downstream of theproposed dredging area and will be protected from increased turbidity levels by theuse of silt curtains. It is therefore concluded that the proposal is unlikely to impactany of the Syngnathiformes listed in the EPBC Act or Fisheries Management Act1994;Note 3: While potentially present in the ocean off <strong>Manly</strong>, turtles and sea snakes areunlikely to be present in <strong>Manly</strong> <strong>Lagoon</strong>, as it provides no habitat or insignificanthabitat required by these species. No Assessment of Significance is considerednecessary for these species.Impact AssessmentBenthic Fauna<strong>Dredging</strong> works will directly impact aquatic fauna living near or in the upper layers ofsediment (benthos) due to their removal with dredged sediments. While this represents asignificant impact on the benthos, newly exposed sediments are expected to recolonise afterdredging ceases, with new recruits migrating from undredged areas and via water-bornlarvae. The newly exposed sediments will be at a deeper depth than the existing benthiccommunities, but not sufficiently to affect the community structure of the post-dredgingassemblages. It is expected that dredging will reduce the contaminant load in the lagoonbed and that water quality will be improved as a result of dredging. These factors providethe circumstances under which the new benthic assemblages may develop greaterabundance and diversity than now occurs. Due to the low abundance of benthos in the2 July 2010 Cardno (<strong>NSW</strong>/ACT) Pty Ltd 92H:\Doc\2010\Reports.2010\Rep2580v4.doc
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