POC Maintenance Dredging Application | January 2014 Attachment B.2 Characteristics and Composition of the Substance or Material for Disposal Reports included as part of this attachment: • Assessment of Benthic and Fisheries Impacts of Maintenance Dredging in Lough Mahon and the Lower River Lee, Aquatic Services Unit (March 2013) [included separately within Attachment B.2]. Relevant references include: Section 2.2 – Sub-tidal Benthos Survey Section 2.4 – Inter-tidal Survey Results & Overview Section 2.5 – Sub-tidal Surveys • Water Injection Dredging Tracer Study, Van Oord (July 2012) [included as part of Attachment D.3]. Relevant references include: Section 2.2 – Tracer Particle Size Section 3.2 – Sampling Survey Section 4 – Data and Results Castletownbere Feasibility Report | December 2013 • June 2011 Sediment Sampling Results [included separately within Attachment B.2]. In summary, these results describe that the sampled material generally comprises black mud with over 50%-60% fraction size less than 63 microns. • June 2013 Sediment Sampling Results [included as part of Attachment B.1 (i)]. In summary, these results describe that the sampled material generally comprises mud with over 60% fraction size less than 63 microns. Report Reference: IBM0455/R/KG Revision Number: - 2 rpsgroup.com/ireland Assessment of Benthic and Fisheries Impacts of Maintenance Dredging in Lough Mahon and the Lower River Lee (2011-2012) Commissioned by: Port of Cork Undertaken by: Aquatic Services Unit (UCC) (March 2013) 1 TABLE OF CONTENTS SUMMARY 3 IINTRODUCTION 7 Study Outline 7 Receiving Environment 7 Sampling Areas 7 Sampling Frequency and Timing 8 Data Analysis and Study Outputs 9 Feasibility of Achieving the Study Goals 9 METHODOLOGY & RESULTS – BENTHOS 11 Intertidal Soft Sediment Survey 11 Sub-tidal Soft Benthos Survey 13 Sample Processing 16 Intertidal Survey Results & Overview 17 Community Analysis of Intertidal Data 65 Discussion of Intertidal Results 66 Subtidal Surveys 68 Community Analysis of Subtidal Data 92 Discussion of Subtidal Data 92 METHODOLOGY & RESULTS – FISH 94 Overview 94 Timing 94 Methods 94 Fisheries Results 97 Implications of Fish and Invertebrate Diet for the Dredging in Lough Mahon 121 Type of Dredging and Potential Impacts 122 Overall Conclusion from Fisheries Surveys 122 REFERENCES 124 Appendix 1: Trawl Results and Maps of Trawl Tracks 126 2 SUMMARY Introduction and Brief As part of a study to assess the potential impacts of dredging within the Lower River Lee and Lough Mahon, the Port of Cork commissioned the Aquatic Services Unit to undertake a study of the intertidal and subtidal infaunal benthos and of the fisheries within the and adjacent to the dredged channel from the City Quays upstream as far as Marino Point at the lower end of Lough Mahon. Survey Outline and Methods The survey concentrated on 4 main areas and a control site in the North Channel at Rossmore. Area 1 was between the City Quays and Marina Power Station, Area 2 stretched from the Marina Power Station as Blackrock Castle; Area 3 stretched from Blackrock Castle to approximately half way down Lough Mahon, while Area 4 continued to the end of Lough Mahon to the bend opposite Marino Point Sampling included intertidal core sampling and sub-tidal grab sampling within the study areas as well as fishing in all the same areas using a range of fishing gear types. The study comprised a main baseline and a main follow-up survey covering all sampling methods in in all survey areas in May/June 2011 i.e. pre-dredging and again in May/June 2012 about 5-9 months post-dredging. A quarterly survey was undertaken in late February/early March 2-6 months post dredging involving a reduced sampling intensity. Some additional baseline fisheries surveying (confined to beam trawling) was undertaken in late August 2011 just prior to the start of dredging. Benthic Survey – Methods and Results Intertidal Macrobenthic Sampling 4 intertidal transects were studied, T1-T3 in the greater Lough Mahon area (T1 by Hop Island, T2 by Carrigrenan, T3 inside Marino and T4 the control site in the North Channel at Rossmore). At each site, replicate stove-pipe cores were taken at three tidal heights High Shore, Mid-Shore and Low Shore. Pre-dredging sampling took place in May 2011, and post-dredging took place in February 2012 and June 2012. The results indicate that there was a pronounced difference between the numbers and biomass of macroinvertebrate infauna between the four transects with T1 and T4 having higher numbers and biomass on all sampling occasions than T2 and T3. There was also a pronounced difference between the numbers and biomass of invertebrates between shore heights at all transects with the low shore almost always having considerably lower abundances and biomass than the mid or high shore stations and the high shore sites tending to have the highest numbers and biomass at all transects during all three sampling occasions. 3 During February 2012, some 2-3 months after the cessation of maintenance dredging in the shipping channel there was a pronounced drop in both faunal numbers and biomass at all transects including the control site (T4). Because this decrease was so clear across all sites including the control and at all tidal heights it was considered to be a normal seasonal trend. Such seasonal drops in biomass and numbers are widely reported in the scientific literature. During the June follow up survey, some 5-7 months after the cessation of maintenance dredging, macroinvertebrate populations from the February, saw a significant increase across all transects, again this would be expected as a normal seasonal trend on intertidal mudflats. The results varied between transects and between shore heights, so for instance at T1 the biomass at the high and low shore stations increased to the levels recorded in the May 2011 baseline survey, while the mid-shore sites remained as low as during February 2012. At T2, biomass remained the same or increased at all tidal heights compared to the May 2011 baseline and at T3 the low shore biomass did not increase above the levels recorded in February, whereas at the mid-shore and high shore stations they did. Finally at the control site T4 in Rossmore, while stations at all three shore heights increased in biomass compared to the February seasonal low, only the low shore site reached (and exceeded) the values recorded during the May 2011 baseline. This latter result is attributed to fine- scale patchiness in the distribution of benthic invertebrates. Finally, when all of the data from all three sampling runs is pooled and analysed using a multivariate analysis technique – MDS (Multi Dimensional Scaling), all the data points (transects, tidal heights and sampling occasions) pool together into a single cluster, which indicates that we are dealing with a single intertidal faunal community typical of sandy mud conditions. The inter-transect, inter shore height and between sampling run variation noted within the data is concluded to fall within normal temporal and spatial variability ranges typical of such communities with little if any influence from the maintenance dredging operations in the shipping channel. Subtidal benthic Infauna Subtidal benthic grabs were taken in four sampling areas (Area 1 to 4) during the study and at three stations across the channel within each of these four locations. Sampling for benthic infauna was carried out on three occasions, namely May 2011 before maintenance dredging of the channel and in February 2012 and June 2012 after the dredging had taken place. The results indicate that at virtually all stations within in all four locations there was a drop in infaunal macroinvertebrate biomass, when the May 2011 data is compared with the June 2012 data. On average the reduction in biomass is in the order of around 50%. This change has been attributed to the dredging and was expected. It is notable that localised colonies of the Peacock fan worm (Sabella pavonina) on the un-dredged margins of the channel, do not appear to have been adversely impacted by the dredging, suggesting that the impacts to the macroinvertebrate infauna were largely confined to the channel itself. Fisheries Surveys, Schedule, Methods and Results Baseline fisheries surveys were conducted in the four survey areas (Areas 1-4) and at the Rossmore control site in May/June 2011 with a main follow-up survey in May June 2012. In addition, some 4 limited additional baseline data was collected in August 2011 just prior to the commencement of dredging while a more extensive quarterly follow up survey was carried out in February 2012. 4 gear types were deployed, baited traps (Areas 1 and 2), fyke nets (Areas 1-4 and the control site), beam trawls Areas 1-4 and Rossmore and seine nets –Rossmore. The main target of the surveys were the fish species living on and in close proximity to the bottom as it would be expected that these would more likely to be impacted than mid-water (pelagic) species. In addition however the levels of larger mobile epibenthic / hyperbenthic crustaceans were also surveyed, principally Crangon (brown shrimp) and green crab (Carcinus maenas) both of which were widespread and abundant within the study area and both of which are considered important components of the estuarine food web. Both baited fish traps and fyke nets caught large amounts of green crab in May/June 2011 and again in May/June 2012 at all of the sites where they were deployed. Although biomass was reduced at some stations in 2012 compared to 2011, the data is quite variable between sites and so a definite statement of cause and effect cannot be made. In addition to crab, both traps and fyke nets caught small numbers of fish including dogfish, cod, pollack, eel, flounder, plaice, bull-rout, hooknose, sand-smelt and most frequently 5-bearded rockling.