Innovative use of sclerochronology in marine resource management

In recent years, technical and analytical developments in sclerochronology, based on the analysis of accretionary hard tissues, have improved our ability to assess the life histories of a wide range of marine organisms. This Theme Section on the innovative use of sclerochronology was motivated by the cross-disciplinary session ‘Looking backwards to move ahead—how the wider application of new technologies to interpret scale, otolith, statolith and other biomineralised age-registering structures could improve management of natural resources’ convened at the 2016 ICES Annual Science Conference in Riga, Latvia. The contributions to this Theme Section provide examples of applications to improve the assessment and management of populations and habitats, or showcase the potential for sclerochronology to provide a deeper understanding of the interaction between marine life and its environment, including the effects of changing climate

Micro-scale geochemical and crystallographic analysis of Buccinum undatum statoliths supports an annual periodicity of growth ring deposition

The whelk Buccinum undatum is commercially important in the North Atlantic. However, monitoring the ontogenetic age and growth of populations has been problematic for fisheries scientists owing to the lack of a robust age determination method. We confirmed the annual periodicity of growth rings present in calcified statoliths located in the foot of field-collected and laboratory reared whelks using microscale measurements of trace element geochemistry. Using Secondary Ion Mass Spectrometry (SIMS), annual trace element profiles were quantified at 2 μm resolution in statoliths removed from whelks collected alive from three locations spanning the length of the UK; the Shetland Isles (North), the Menai Strait, North Wales (Mid) and Jersey (South). Clear cycles in the Mg/Ca ratio were apparent with minimum values corresponding with the visible dark statolith rings and comparatively higher ratios displayed in the first year of growth. Statoliths from one and two-year-old laboratory reared whelks of known age and life history contained one and two Mg/Ca cycles respectively and demonstrated that the statolith growth ring is formed during winter (February and March). Cycles of Na/Ca were found to be anti-correlated to Mg/Ca cycles, whilst ratios of Sr/Ca were inconsistent and showed an apparent ontogenetic increase, suggesting strong physiological control. Variability in elemental data will likely limit the usefulness of these structures as environmental recorders. The results obtained using SIMS for trace element analysis of statoliths confirms the robustness of the statolith rings in estimating whelk age. μXRD at 2 μm spatial resolution demonstrated the statoliths were wholly aragonitic and thus trace element variation was not the result of possible differences in CaCO3 polymorph within the statolith. Changing XRD patterns along with SEM imaging also reveal an ‘hourglass’ microstructure within each statolith. The validation of the annual periodicity of statolith growth rings now provides a robust and novel age determination technique that will lead to improved management of B. undatum stocks

Blinded by the light - Seabird collision events in South Georgia

Light-induced bird strikes on vessels occur frequently in association with areas of high seabird density, often resulting in bird mortalities. These incidents are poorly understood and likely under-reported by vessels. Here we present the details of four separate bird strike events (899, 206, 50 and 47 birds), which took place whilst vessels (two fishing trawlers and one tourist expedition ship) were navigating along the south coast of South Georgia, and discuss possible contributing factors. All species encountered in these events were burrowing petrel species in the family Procellariidae, with diving-petrel species (Pelecanoides spp.) being most commonly reported. All four events took place during the night in similar meteorological conditions, with poor visibility due to fog, light precipitation and low wind speeds. We identify the waters off the south coast, between King Haakon Bay and Drygalski Fjord, which have remained rat free and are of exceptional importance to breeding seabirds, as high risk for collisions and propose other high-risk areas. The different mortality rates recorded during these events are likely attributed to the varying actions taken by ship crew and persons on board. We propose actions that will help reduce the occurrence of events and mitigate the impact of bird strikes, including the avoidance of high-risk areas in certain night-time conditions. We give recommendations on what to do when birds land on board and stress the importance of reporting of events. Given the expected increase of both fishing and tourist ship activity in South Georgia waters, there is an increasing need to understand and mitigate this threat to seabirds

Population characteristics of benthopelagic Gymnoscopelus nicholsi (Pisces: Myctophidae) on the continental shelf of South Georgia (Southern Ocean) during austral summer

Southern Ocean myctophid fish (Family Myctophidae) are an important conduit of energy through foodwebs and between the surface layers and mesopelagic depths. Species that reside in both pelagic and near-bottom environments of continental shelves, such as Gymnoscopelus nicholsi and Gymnoscopelus bolini, may also be important in benthopelagic coupling, although their ecology and role in such processes remain unresolved. Here, we examined inter-annual variation in the depth of occurrence, biomass and population dynamics of benthopelagic G. nicholsi on the South Georgia shelf (100-350 m) using bottom trawl data collected between 1987 and 2019. Gymnoscopelus nicholsi was a regular component of the local benthopelagic community, particularly northwest of South Georgia, but was patchily distributed. It appeared to enter a benthopelagic phase at similar to 3 years, with annual growth and recruitment of year classes between similar to 3 and 5 years. However, transition of cohorts into the benthopelagic zone was not annual. There was clear inter-annual variation in G. nicholsi biomass and depth of occurrence. Shallower depth of occurrence was significantly (P < 0.05) correlated with years of warmer summer sea surface temperatures, suggesting that inter-annual variation in local environmental conditions has an important influence on its migration behaviour and ecology. Our data also suggest that Antarctic hill is an important dietary component of the older G. nicholsi cohorts (similar to 5 years) in the benthopelagic zone. We note that Gymnoscopelus bolini is rare in bottom trawl catches between 100 and 350 m, although Antarctic hill appears to dominate its diet from the available data. Our study provides important information on understudied myctophid species in a poorly investigated region of the water column that is relevant for Southern Ocean ecosystem studies, particularly in relation to understanding trophic connectivity between the pelagic and near-bottom realms

From sealing to the MPA-A history of exploitation, conservation and management of marine living resources at the South Sandwich Islands

The exploitation of marine resources of the South Sandwich Islands (SSI) began with the hunting of fur seals for their pelts in the early decades of the 19th Century. Pelagic whaling in the region started a century later with catches recorded until the mid-1970s. Blue and fin whales dominated the catches accounting for 80% of the total. Trawl fisheries for demersal finfish and krill (Euphausia superba) were established around many sub-Antarctic islands in the late 1960s and through the 1970s, but they did not become established at the South Sandwich Islands despite fisheries research expeditions from several nations visiting the region during this period. The first licensed demersal longline fishery for toothfish (Dissostichus spp.) was initiated by a UK flagged vessel in 2005 following earlier expeditions by Chilean and Bulgarian fishing vessels. The fishery for toothfish is now conducted by a maximum of two vessels and represents the only fishing carried out in the SSI region with total annual catches of around 40 t per annum, with a fishing footprint restricted to less than 4% of the SSI Maritime Zone (MZ). This MZ extends 200 nm from the island chain and forms the eastern half of the 1.24 million km2 MZ of the UK Overseas Territory of South Georgia & the South Sandwich Islands (SGSSI) which was established in 1993. The MZ around the SSI lies within the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) management Subarea 48.4. Fishing within the MZ is licensed by the Government of South Georgia & the South Sandwich Islands (GSGSSI) who, under domestic legislation, are required to adopt all fisheries management regulations that have been agreed for the region each year by CCAMLR. In addition, a suite of additional management measures are enforced. In 2012, GSGSSI established a sustainable use Marine Protected Area (MPA) within the SGSSI MZ to conserve the marine biodiversity of the region. Enhancements were introduced in 2013 and 2019 extending No-Take Zones (NTZs), where all fishing is prohibited, across 261,000 km2 of the MZ around the SSI including the deepest regions of the Southern Ocean, the South Sandwich Trench. The SSI marine ecosystem has been relatively poorly studied but has recently been a focus of two dedicated UK research cruises providing a considerable new amount of information to assist with the management of this remote marine region

Calibration of shell δ18O from the common whelk Buccinum undatum highlights potential for environmental reconstruction

The common whelk, Buccinum undatum, is a commercially important gastropod found throughout the North Atlantic. One method of age and life history analysis for gastropod species is the use of oxygen isotope ratio (δ18O) measurements from their shells, which is a well-established technique for the reconstruction of historical seawater temperatures at the time of shell biomineralization. Palaeotemperature calibrations have been developed for different types of calcium carbonate as well as species-specific equations to produce the most accurate seawater temperature reconstructions. Here we investigate the four-layer internal structure of B. undatum shells and confirm an aragonite composition using Micro-Raman Spectroscopy (MRS). We then calibrate a species-specific palaeotemperature equation for this gastropod species. This was achieved through the isotopic analysis of shells from laboratory reared specimens of known provenance reared at specific seawater temperatures to produce the following: t(°C) = 14.96 (± 0.15) – 4.94 (± 0.22) x (δ18Oshell – δ18Owater) The calibrated equation differs significantly from previously published data derived from both aragonite and calcite. An offset of 1.04‰ (± 0.41‰) was discovered between observed δ18OShell values and those expected under equilibrium, suggesting a species-specific vital effect. The calibrated equation was used to reconstruct accurate, high resolution historical seawater temperatures from three sites across the U.K. (Shetland, the Menai Strait and Jersey). With this new accurate calibration, both modern and fossil B. undatum shells now have the potential to be employed as high-resolution archives of recent and historical seawater temperature

Trends in population structure of Patagonian toothfish over 25 years of fishery exploitation at South Georgia

Patagonian toothfish (Dissostichus eleginoides) supports valuable fisheries across the Southern Ocean under the management of the Commission for the Conservation of Antarctic Marine Living Resources. The fishery at South Georgia accounts for 26 % of the catch of this species in the Southern Ocean in the last 25 years. This study assesses the effects of exploitation and changes in management of the fishery on long-term trends in biological traits of Patagonian toothfish at South Georgia. Our results show variability in the size of fish, but no evidence of a systematic decline during the 25-year period. The mean size of fish was linked to recruitment, with pulses of recruitment associated with a reduction in mean size of the fishery. The years when recruitment was highest were in 2000–2010, with >50 % of toothfish of length classes < 90 cm. Management measures implemented over the last 25 years, including depth restrictions and benthic closed areas, have resulted in a gradual stabilization of the population structure. Catch per unit effort (CPUE) dropped from 1997 to 2010, gradually increased until 2017 and since 2018 has returned to values typical of the mid-2010s. Monthly changes in fish length, depth of capture and CPUE confirm that the spawning peak is in July. Size at maturity has remained stable over the last 25 years, suggesting the fishery has not had a major impact on population size structure. These results illustrate the role of management regulations in limiting the impacts of commercial exploitation on the population structure of a long-lived fish species. Given the bigger-deeper size pattern in Patagonian toothfish, there may be a case for increasing the minimum depth of the fishery (currently 700 m) when strong recruitment pulses are detected

Age and growth rate estimations of the commercially fished gastropod Buccinum undatum

Calculating age and growth rate for the commercially important whelk, Buccinum undatum in the aid of fishery management has historically been undertaken using growth rings on the organic operculum. This is difficult due to their poor readability and confusion between two different sets of growth lines present. Recent work presented the calcium carbonate statolith as an alternative for age determination of B. undatum. Here we compare the use of statoliths and opercula, comparing their readability and creating growth curves for three distinct populations across the United Kingdom. Using these data, we also test the most appropriate growth equation to model this species. Lastly, we use oxygen isotope analysis of the shells to assign accurate ages to several individuals from each site. These data were used to test the accuracy of statolith and operculum ages. Statoliths, whilst more time consuming to process have improved clarity and accuracy compared with the opercula. This improved readability has highlighted that a Gompertz growth function should be used for populations of this species, when in past studies, von Bertalanffy is often used. Statoliths are a viable improvement to opercula when assessing B. undatum in the context of fishery monitoring and management

Age and growth rate estimations of the commercially fished gastropod Buccinum undatum

Calculating age and growth rate for the commercially important whelk, Buccinum undatum in the aid of fishery management has historically been undertaken using growth rings on the organic operculum. This is difficult due to their poor readability and confusion between two different sets of growth lines present. Recent work presented the calcium carbonate statolith as an alternative for age determination of B. undatum. Here we compare the use of statoliths and opercula, comparing their readability and creating growth curves for three distinct populations across the United Kingdom. Using these data, we also test the most appropriate growth equation to model this species. Lastly, we use oxygen isotope analysis of the shells to assign accurate ages to several individuals from each site. These data were used to test the accuracy of statolith and operculum ages. Statoliths, whilst more time consuming to process have improved clarity and accuracy compared with the opercula. This improved readability has highlighted that a Gompertz growth function should be used for populations of this species, when in past studies, von Bertalanffy is often used. Statoliths are a viable improvement to opercula when assessing B. undatum in the context of fishery monitoring and management

Fluid Optimisation in Emergency Laparotomy (FLO-ELA) Trial: study protocol for a multi-centre randomised trial of cardiac output-guided fluid therapy compared to usual care in patients undergoing major emergency gastrointestinal surgery

INTRODUCTION: Postoperative morbidity and mortality in patients undergoing major emergency gastrointestinal surgery are a major burden on healthcare systems. Optimal management of perioperative intravenous fluids may reduce mortality rates and improve outcomes from surgery. Previous small trials of cardiac-output guided haemodynamic therapy algorithms in patients undergoing gastrointestinal surgery have suggested this intervention results in reduced complications and a modest reduction in mortality. However, this existing evidence is based mainly on elective (planned) surgery, with little evaluation in the emergency setting. There are fundamental clinical and pathophysiological differences between the planned and emergency surgical setting which may influence the effects of this intervention. A large definitive trial in emergency surgery is needed to confirm or refute the potential benefits observed in elective surgery and to inform widespread clinical practice. METHODS: The FLO-ELA trial is a multi-centre, parallel-group, open, randomised controlled trial. 3138 patients aged 50 and over undergoing major emergency gastrointestinal surgery will be randomly allocated in a 1:1 ratio using minimisation to minimally invasive cardiac output monitoring to guide protocolised administration of intra-venous fluid, or usual care without cardiac output monitoring. The trial intervention will be carried out during surgery and for up to 6 h postoperatively. The trial is funded through an efficient design call by the National Institute for Health and Care Research Health Technology Assessment (NIHR HTA) programme and uses existing routinely collected datasets for the majority of data collection. The primary outcome is the number of days alive and out of hospital within 90 days of randomisation. Participants and those delivering the intervention will not be blinded to treatment allocation. Participant recruitment started in September 2017 with a 1-year internal pilot phase and is ongoing at the time of publication. DISCUSSION: This will be the largest contemporary randomised trial examining the effectiveness of perioperative cardiac output-guided haemodynamic therapy in patients undergoing major emergency gastrointestinal surgery. The multi-centre design and broad inclusion criteria support the external validity of the trial. Although the clinical teams delivering the trial interventions will not be blinded, significant trial outcome measures are objective and not subject to detection bias. TRIAL REGISTRATION: ISRCTN 14729158. Registered on 02 May 2017