• Application of EDA (v 2.0) to Ireland: prediction of silver eel Anguilla anguilla escapement

      de Eyto, E.; Briand, C.; Poole, R.; O'Leary, C.; Kelly, F. (Marine Institute, 2016)
      Eel Density Analysis (EDA) is a modelling framework that can be used to estimate eel populations in aquatic habitats. Survey data (primarily electrofishing operations) are used to build predictive models describing the presence/absence and the density of eel. These models are then applied to the entire network of aquatic habitat in the area of interest to estimate the total population size. The fluvial (riverine) population of yellow eel in Ireland was estimated using the EDA (v2.0) model (Jouanin et al., 2012). A total fluvial population of 8,032,834 yellow eels and 200,821 silver eels (using a silvering rate of 2.5%) was estimated for 2011. Eel presence and abundance decreased as the distance to the sea increased, and the percentage of calcareous geology in the catchments decreased. Stock indictors (B0, Bbest and Bcurrent) were calculated from these yellow eel estimates to enable the display of precautionary diagrams for each EMU in Ireland. Lake production was also calculated for 2011, using empirical data from a small number of catchments. A precautionary diagram for this total production (fluvial and lacustrine habitat) is presented, and compared with previous estimates of stock indicators for Ireland.
    • Appraisal of the whelk (Buccinum undatum) fishery on a part of the Codling Bank following aggregate extraction for beach restoration at Bray, Co Wicklow

      Fahy, E; O'Toole, M; Stokes, D; Gallagher, M (Marine Institute, 2002)
      The Codling Bank is an important contributor to the south west Irish Sea whelk fishery; a large proportion of the whelk population there are juveniles. Traditionally, whelks have been harvested ungraded from this area. Fishing trials were undertaken on the Codling Bank in May 2001 to ascertain the consequences for the whelk fishery of aggregate removal by suction dredging during the previous winter months. The results suggested some localised diminution in CPUE in the vicinity of dredging operations four months after the event. However, it is not feasible to conclusively attribute the reduction to dredging operations.
    • Appraisal of the whelk Buccinum undatum fishery of the Southern Irish Sea with proposals for a management strategy

      Fahy, E; Yalloway, G; Gleeson, P (Department of the Marine, 1995)
      A small occasional fishery for whelk in the southern Irish Sea expanded in the early 1990s, particularly in 1993, to provide meat for the Far East. Between 1990 and 1993 the weight of whelk delivered by a fisherman to factory per day remained stable but the fishing effort increased by 44%. The quality of landings declined, increasing proportions of smaller whelk being retained. The most heavily fished populations apparently display a Lee effect. An age at length key was prepared from 3,081 individuals and is used to transform length to age frequencies within the area of interest. The weight compositions of graded samples, abstracted from processors' financial accounts, were converted to population numbers. The age of full recruitment is reckoned to be five years over the area of interest although it may fall to four in the most intensely fished whelk patches. A Thompson-Bell yield per recruit curve has Fmax at F=0.3. Only one fishery, at the northern fringes of the fishing area, has an F value (read from the catch curve) of less than this. F values of fisheries at the centre and south of the exploited area are all situated on the negative slope of the yield per recruit curve. Male maturation occurs at a length of 70 - 80 mm in the least and 50 mm in the most exploited populations. Thus, a measure to protect broodstock would require a size limit of approximately 70 - 80 mm which would, coincidentally, approximate the size for maximum sustainable yield. It would also have a catastrophic effect on the existing fisheries. A size limit of 50 mm is already in force.
    • Aquaplan: health management for finfish aquaculture

      Ruane, N. M.; Geoghegan, F.; Rodger, H.; Murphy, K.; O' Sullivan, C. (Marine Institue, 2015)
      The AquaPlan project brought together key stakeholders from the finfish aquaculture industry and state agencies with the aim of drafting and implementing a national strategic plan for fish health in Ireland. Many countries already have well established comprehensive strategies for managing aquatic animal health which are deemed necessary for the sustainable development of the industry. A range of deliverables were produced by the project which are all essential components of the strategic plan for fish health management.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17) 2012 UWTV Survey Report and catch options for 2013

      Lordan, Colm; Doyle, Jennifer; Hehir, Imelda; Fee, Dermot; Allsop, Chris; O'Neill, Ross (Marine Institute, 2012)
      This report provides the main results and findings of the eleventh annual underwater television on the Aran, Galway Bay and Slyne head Nephrops grounds, ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, fishing, CTD and other ecosystem data. The sampling intensity was reduced this year from around 75 stations in the past to 31 on the Aran grounds. A randomised isometric grid design was employed with UWTV stations at 3.5nmi or 6.5km intervals. Previously a 2.25 nmi square grid was used. The kigged burrow abundance estimate declined by 34% relative to 2011 with a CV (or relative standard error) of 5 %. Abundance estimates have fluctuated considerably over the time series but the 2012 abundance is the lowest in the 11 year history of the survey. Four UWTV stations were carried out on the Galway Bay and 3 on the Slyne Head Nephrops grounds. Raised abundance estimates for Galway Bay and Slyne Head are provided based on improved knowledge of the boundaries of those areas. Nephrops accounted for 85% of the benthic catch by weight from 4 beam trawl tows. The observed length frequency and maturity of female Nephops caught was similar to previous years. Various further investigations needed before the next ICES benchmark are discussed.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17) 2013 UWTV Survey Report and catch options for 2014

      Lordan, C.; Doyle, J.; Hehir, I.; Allsop, C.; Butler, R.; Burke, C. (Marine Institute, 2013)
      This report provides the main results and findings of the twelfth annual underwater television on the Aran, Galway Bay and Slyne head Nephrops grounds, ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, fishing, CTD and other ecosystem data. In total 31 UWTV stations were successfully completed in a randomised isometric grid design at 3.5nmi or 6.5km intervals over the known range of the stock on the Aran Grounds. The mean burrow density observed in 2013, adjusted for edge effect, was 0.32 burrows/m². The final krigged burrow abundance estimate was 317 million burrows with a CV (or relative standard error) of 4 %. Abundance estimates have fluctuated considerably over the time series. The abundance decreased significantly in 2012 and the 2013 estimate was 2% lower and the lowest estimate in the 12 year time series. Raised abundance estimates for Galway Bay and Slyne Head were also low for those areas. Using the 2013 abundance estimate together with updated parameters for mean weight and proportions of removals retained implies 2014 total catch advice fishing at Fmsy (=F35%spr) of 699 tonnes which results in landings of no more than 591 tonnes. Nephrops accounted for approximately 70% of the benthic catch by weight from 7 beam trawl tows. The observed length frequency and maturity of female Nephops caught was similar to previous years. Virgilaria mirabilis was the most common of the two sea-pen species observed on the UWTV footage (Pennatula phosphorea was also present).
    • Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17) 2014 UWTV Survey Report and catch options for 2015.

      Hehir, I.; Doyle, J.; Lordan, C.; O'Cuaig, M.; Hannify, O.; Fitzgerald, R.; O'Connor, S.; Keith, M.; Murphy, Á.; Sheridan, M.; et al. (Marine Institute, 2014-10)
      This report provides the main results and findings of the thirteenth annual underwater television on the Aran, Galway Bay and Slyne head Nephrops grounds, ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, fishing, CTD and other ecosystem data. In total 33 UWTV stations were successfully completed in a randomised isometric grid design at 3.5nmi or 6.5km intervals over the known range of the stock on the Aran Grounds. The mean burrow density observed in 2014, adjusted for edge effect, was 0.29 burrows/m². The final krigged burrow abundance estimate was 287 million burrows with a CV (or relative standard error) of 4 %. Abundance estimates have fluctuated considerably over the time series. The 2014 abundance estimate was 9% lower than in 2013 and the lowest estimate in the 13 year time series. Raised abundance estimates for Galway Bay and Slyne Head were also low for those areas. Using the 2014 abundance estimate together with updated parameters for mean weight and proportions of removals retained implies catch advice, fishing at Fmsy (=F35%spr), of 584 tonnes and landings of 524 tonnes in 2015. Nephrops accounted for approximately 70% of the benthic catch by weight from 5 beam trawl tows. The relatively high numbers caught around 15 CL mm (carapace length) may indicate strong incoming recruitment. Virgilaria mirabilis was the most common of the two sea-pen species observed on the UWTV footage. Funiculina quadrangularis was observed at one station on the Slyne Head Nephrops ground.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17) 2015 UWTV Survey Report and catch options for 2016

      Doyle, J.; Lordan, C.; Fitzgerald, R.; O’Connor, S.; Fee, D.; Butler, R.; Stokes, D.; Ni Chonchuir, G.; Gallagher, J.; Sheridan, M.; et al. (Marine Institute, 2015)
      This report provides the main results and findings of the fourteenth annual underwater television on the Aran, Galway Bay and Slyne head Nephrops grounds, ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, fishing, CTD and other ecosystem data. In 2015 a total of 44 UWTV stations were successfully completed, 34 on the Aran Grounds and 5 on each of the Slyne Head and Galway Bay patches. The mean burrow density observed in 2015, adjusted for edge effect, was medium at 0.38 burrows/m². The final krigged burrow abundance estimate for the Aran Grounds was 480 million burrows with a CV (or relative standard error) of 6 %. The final abundance estimate for Galway Bay and Slyne Head was 56 and 20 million burrows with CVs of 15% and 4% respectively. The total abundance estimates have fluctuated considerably over the time series. The 2015 abundance estimate was 42% higher than in 2014 and at 556 million and is just above to the new MSY Btrigger (540 million). Using the 2015 abundance estimate and updated stock data implies catch of 991 tonnes and landings of 915 tonnes in 2016 fishing at Fmsy (assuming all catch is landed). Virgilaria mirabilis was the most common of the two sea-pen species observed on the UWTV footage. Pennatula phosphorea was observed at one station on the Slyne Head Nephrops ground. Key words: Nephrops norvegicus, stock assessment, geostatistics, underwater television (UWTV), benthos, CTD. Suggested citation:
    • Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17) 2016 UWTV Survey Report and catch options for 2017

      Doyle, J.; Lordan, C.; Stokes, D.; O'Brien, S.; Kelly, C.; Bentley, K.; Vacherot, J.P. (Marine Institute, 2016)
      This report provides the main results and findings of the fifteenth annual underwater television on the Aran, Galway Bay and Slyne head Nephrops grounds, ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, fishing, CTD and other ecosystem data. In 2016 a total of 45 UWTV stations were successfully completed, 34 on the Aran Grounds, 7 on Galway Bay and 4 on Slyne Head patches. The mean burrow density observed in 2016, adjusted for edge effect, was medium at 0.29 burrows/m². The final krigged burrow abundance estimate for the Aran Grounds was 343 million burrows with a CV (or relative standard error) of 3 %. The final abundance estimate for Galway Bay and Slyne Head was 25 and 11 million burrows with CVs of 7% and 3% respectively. The total abundance estimates have fluctuated considerably over the time series. The 2016 combined abundance estimate was 32% lower than in 2015 and at 379 million and is below the MSY Btrigger (540 million). Using the 2016 abundance estimate and updated stock data implies catch of 489 tonnes and landings of 456 tonnes in 2017 when MSY approach is applied (assuming that discard rates and fishery selection patterns do not change from the average of 2013–2015). Virgilaria mirabilis was the only sea-pen species observed on the UWTV footage. Trawl marks were present at 20% of the Aran stations surveyed.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17) 2017 UWTV Survey Report and catch options for 2018

      Lordan, C.; Doyle, J.; Butler, R.; Sugrue, S.; Allsop, C.; O'Connor, S.; Vacherot, J.P. (Marine Institute, 2017)
      This report provides the main results and findings of the fifteenth annual underwater television on the Aran, Galway Bay and Slyne head Nephrops grounds, ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, fishing, CTD and other ecosystem data. In 2017 a total of 40 UWTV stations were successfully completed, 31 on the Aran Grounds, 5 on Galway Bay and 4 on Slyne Head patches. The mean burrow density observed in 2017, adjusted for edge effect, was medium at 0.29 burrows/m². The final krigged burrow abundance estimate for the Aran Grounds was 343 million burrows with a CV (or relative standard error) of 3 %. The final abundance estimate for Galway Bay and Slyne Head was 25 and 11 million burrows with CVs of 7% and 3% respectively. The total abundance estimates have fluctuated considerably over the time series. The 2016 combined abundance estimate was 32% lower than in 2015 and at 379 million and is below the MSY Btrigger (540 million). Using the 2017 abundance estimate and updated stock data implies catch of 551 tonnes and landings of 513 tonnes in 2018 when MSY approach is applied (assuming that discard rates and fishery selection patterns do not change from the average of 2014–2016). Virgilaria mirabilis was the only sea-pen species observed on the UWTV footage. Trawl marks were present at 20% of the Aran stations surveyed.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17) 2018 UWTV Survey Report and catch scenarios for 2019

      Doyle, J.; O’ Brien, S.; Ryan, G.; Galligan, S.; Hernon, P.; Aristegui, M.; Vacherot, J.P. (Marine Institute, 2018)
      This report provides the main results and findings of the seventeenth annual underwater television on the Aran, Galway Bay and Slyne head Nephrops grounds, ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, fishing, CTD and other ecosystem data. In 2018 a total of 43 UWTV stations were successfully completed, 33 on the Aran Grounds, 5 on Galway Bay and 5 on Slyne Head patches. The mean burrow density observed in 2018, adjusted for edge effect, was medium at 0.40 burrows/m². The final krigged burrow abundance estimate for the Aran Grounds was 488 million burrows with a CV (relative standard error) of 3%. The final abundance estimate for Galway Bay and Slyne Head was 33 million in both grounds with CVs of 17% and 12% respectively. The total abundance estimates have fluctuated considerably over the time series. The 2018 combined abundance estimate was a 37% increase compared to in 2017 and at 554 million burrows and is above the MSY Btrigger reference point (540 million burrows). Using the 2018 abundance estimate and updated stock data implies catch of 1002 tonnes and landings of 916 tonnes in 2019 when the MSY approach is applied (assuming that discard rates and fishery selection patterns do not change from the average of 2015–2017). Virgularia mirabilis was the only sea-pen species observed on the UWTV footage. Trawl marks were present at 9% of the Aran stations surveyed.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17) 2019 UWTV Survey Report and catch scenarios for 2020.

      Aristegui, M.; Doyle, J.; O’ Brien, S.; Fitzgerald, R.; Vacherot, J.P.; Sugrue, S.; Quinn, M. (Marine Institute, 2019)
      This report provides the main results and findings of the seventeenth annual underwater television on the Aran, Galway Bay and Slyne head Nephrops grounds, ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, CTD and other ecosystem data. In 2019 a total of 41 UWTV stations were successfully completed, 31 on the Aran Grounds, 5 on Galway Bay and 5 on Slyne Head patches. The mean burrow density observed in 2019, adjusted for edge effect, was medium at 0.38 burrows/m². The final krigged burrow abundance estimate for the Aran Grounds was 458 million burrows with a CV (relative standard error) of 4%. The final abundance estimate for Galway Bay was 23 million and for Slyne Head was 12 million, with CVs of 11% and 8% respectively. The total abundance estimates have fluctuated considerably over the time series. The 2019 combined abundance estimate (493 million burrows) is 11% lower than in 2018, and it is below the MSY Btrigger reference point (540 million burrows). Using the 2019 estimate of abundance and updated stock data implies catches between 696 and 800 tonnes in 2020 that correspond to the F ranges in the EU multi annual plan for Western Waters, assuming that discard rates and fishery selection patterns do not change from the average of 2016–2018. Virgularia mirabilis was the only sea-pen species observed on the UWTV footage. Trawl marks were present at 7% of the Aran stations surveyed.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds 2006 UWTV Survey Report

      Lordan, C; Doyle, J; Sacchetti, F; O'Driscoll, D; Heir, I; Smith, T; Allsop, C (Marine Institute, 2007)
      The Nephrops fishery “at the back of the Aran Islands” is the mainstay of the Ros a Mhíl fleet and sustaining this valuable fishery would be at the heart of any management plan for fisheries in the area. In 2006 the fifth in a series of annual UWTV survey was completed, and the results of that survey together with a synthesis and analysis of the results were published. The survey is multidisciplinary in nature collecting data on burrow abundances from UWTV, Nephrops biological data from beam trawls, oceanographic data from CTD, sediment data, multi-beam and other habitat data. A geostatistical analysis indicates that burrow densities and abundances have fluctuated considerably in space and time. Highest densities occurred in 2004 with the lowest densities in the 2006 survey. There may be a negative relationship between abundance in landings in the autumn and a positive relationship between observed densities and landings the following spring.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds 2007 UWTV Survey Report

      Lordan, Colm; Doyle, Jennifer (Marine Institute, 2008)
      In 2007 the sixth in a series of annual UWTV survey was complete and the results of that survey together with a synthesis and analysis of the results. A geostatistical analysis indicates that burrow densities and abundances have fluctuated considerably in space and time. The highest densities occurred in 2004 and the lowest densities in the 2006.The 2007 survey shows an increase in burrow density. Using the survey directly for assessment and management is not yet possible. However, there appears to a negative relationship between abundance and landings in the autumn and a positive relationship between observed densities and landings the following spring. The relationship between abundance and landings is not as clear. There is no serious concern about the stock given the recent survey abundance.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds 2008 UWTV Survey Report

      Lordan, Colm; Doyle, Jennifer (Marine Institute, 2009-05)
      In 2008 the seventh in a series of annual UWTV survey was complete and the results of that survey together with a synthesis and analysis of the results is presented. A geostatistical analysis indicates that burrow densities and abundances have fluctuated considerably in space and time. The highest densities occurred in 2004 and the lowest densities in 2008.The 2008 survey shows a decrease in burrow density to the lowest observed. Using the survey directly for assessment and management has been discussed at WKNEPHTV (2007) and at SGNEP (2009).This stock was a focus at the benchmark workshop on Nephrops assessment held in Aberdeen WKNEPH, (2009). There appears to a negative relationship between abundance and landings in the autumn and a positive relationship between observed densities and landings the following spring. There is some concern about the stock given the most recent survey abundance observed to date. The time series is short and to date survey estimates have fluctuated across a large dynamic range.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds 2009 UWTV Survey Report

      Lordan, C; Doyle, J (Marine Institute, 2009-09)
      The prawn (Nephrops norvegicus) are common around the Irish coast occurring in geographically distinct sandy/muddy areas were the sediment is suitable for them to construct their burrows. The Irish Nephrops fishery is extremely valuable with landings in recent years worth around €30m at first sale supporting an important indigenous processing industry. The Nephrops fishery “at the back of the Aran Islands” can be considered the mainstay of the Ros a Mhíl fleet. Without this Nephrops fishery the majority of vessels in the fleet would cease being economically viable (Meredith, 1999). Given these socio-economic realities, good scientific information on stock status to enable sustainable management of the resources are urgently required. This is the eight data point in a time series of UWTV surveys on the ‘Aran grounds’. The survey covers three distinct mud patches; the Aran Ground, Galway Bay and Slyne Head. These have approximate areas of 940, 41 and 26sq.km respectively. In 2009 this survey was used to develop catch options for the stock using a bias corrected survey estimate as an absolute measure of stock size and recent discard rates and mean weight to forecast catch (ICES, 2009a). This report details the results of the 2009 survey and updates the catch option table using the most recent survey estimate.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds 2010 UWTV Survey Report

      Lordan, Colm; Doyle, Jennifer (Marine Institute, 2011-05)
      This is the ninth data point in a time series of UWTV surveys on the ‘Aran grounds’. The survey covers three distinct mud patches; the Aran Ground, Galway Bay and Slyne Head. These have approximate areas of 940, 41 and 26 km2 respectively. For the first time in 2009 this survey was used to develop catch options for the stock using a bias corrected survey estimate as an absolute measure of stock size and recent discard rates and mean weight to forecast catch (ICES, 2009a). This report details the results of the 2010 survey and updates the catch option table using the most recent survey estimate.
    • Aran, Galway Bay and Slyne Head Nephrops Grounds 2011 UWTV Survey Report

      Lordan, Colm; Doyle, Jennifer; Bunn, Robert; Fee, Dermot; Allsop, Chris (Marine Institute, 2011-10)
      This report provides the main results and findings of the tenth annual underwater television on the ‘Aran grounds’ ICES assessment area; Functional Unit 17. The survey was multi-disciplinary in nature collecting UWTV, fishing, CTD and other ecosystem data. In total 76, 10 and 7 UWTV stations were successfully completed on the Aran, Galway Bay and Slyne Head Nephrops Grounds. The observed abundance estimate for the main Aran ground has declined by 23% relative to 2010. Abundance estimates have fluctuated over the time series. The 2011 abundance is the third lowest in the 10 year history of the survey. This is not a cause for immediate concern about the stocks sustainability. Raised abundance estimates for Galway Bay and Slyne Head are provided for the first time based on improved knowledge of the boundaries of those areas. Nephrops accounted for 26% of the catch weight from 10 beam trawl tows. The observed length frequency and maturity of female Nephops caught was similar to previous years. Various further investigations needed before the next ICES benchmark are discussed.
    • Arsenic in Irish marine macroalgae- implications for industry

      Marine Institute; AsMARA; National University of Ireland Galway; Department of Agriculture, Food and the Marine (Marine Institute, 2015)
      There is a long tradition of using seaweeds from Irish waters as food, fertiliser and animal feed. Both nationally and globally, there is a renewed interest in using this resource for a host of products in the food, feed, agricultural, cosmetics and biotechnology sectors. According to SeaChange1 the estimated worth for the Irish seaweed sector is predicted to increase significantly by 2020. One barrier to developing seaweed-based industries relates to reported high levels of arsenic for many types of seaweed including some species of interest to Irish companies.
    • Arsenic in Irish marine waters and its potential as a water mass tracer

      Anninou, Pinelopi (National University of Ireland, Galway, 2007)
      Arsenic is a metalloid, met in both reduced (+3) and oxidised (+5) states, in a variety of inorganic and organic compounds. It is naturally and anthropogenically introduced. Globally, anthropogenic loads of arsenic exceed the natural ones. It is highly toxic, especially inorganic arsenic. Its toxicity is due to structural similarities with the essential nutrient phosphate. The phenomenon is natural and known as competitive inhibition. First order speciation between hydride (mostly inorganic) and non-hydride (mostly organic) arsenic took place during this project. An in-house, batch type system of hydride generation, electrothermal atomic absorption spectrometry was used. This study has produced baseline concentrations in aquatic environments (rivers, lakes, mines, coastal, shelf edge, oceanic), mainly from the west coast of Ireland. The measured concentrations fall within normal for seawater (15-20nM) and fresh water (0-5nM). Exceptionally high concentration (~50nM) was observed in the effluent of the Avoca Mines, in Co. Wicklow; low concentrations are restored up and downstream of the mines. Results coupled to phosphate findings, showed biological uptake of arsenic being much slower process than physical mixing of water masses. Mixing of coastal seawater with fresh water of low arsenic resulted in near linear increase in the concentration of hydride arsenic with increasing salinity (rivers Corrib and Shannon plumes). This is reversed at high salinities for a small salinity range, where fronts are formed between mixed coastal and open ocean seawater (Thermal Shelf Edge). It is proposed that enhanced biological activity in the highly active frontal zones removes arsenic from the dissolved phase. In the open ocean the positive distribution is restored to some degree, but overall a wide range of arsenic concentrations characterises different water masses despite the small salinity range. Among water masses, Mediterranean Sea Outflow Water displays great potential of being traced by its distinctive arsenic concentration.