IAP-25-011

Beyond the Target: Integrating microchemistry and morphology to uncover diversity and connectivity in four non-target species from the deep waters of the Southern Ocean

Effective ecosystem-based fisheries management requires a comprehensive understanding of the diversity, biology, and connectivity of both target and non-target species. In the Southern Ocean, one of the most remote and data-deficient marine regions, such knowledge is particularly lacking, especially for deep-sea species. Among these, macrourids (grenadiers) represent the primary non-target catch in the Patagonian and Antarctic toothfish (Dissostichus spp.) longline fisheries. Despite their ecological significance, macrourids remain poorly studied and are currently unmanaged at the species level.

Within the South Georgia and South Sandwich Islands (SGSSI), four species of Macrourus are recognised: M. holotrachys, M. carinatus, M. whitsoni, and M. caml. Two of these (M. holotrachys and M. carinatus) are also present in adjacent region of the Falkland Islands. These areas span four distinct biogeographic zones: the Falkland Islands, Shag Rocks, South Georgia, and the South Sandwich Islands, yet macrourids across these zones are currently managed as a single species complex. This taxonomic aggregation presents substantial management challenges. The four species exhibit differences in depth distribution, habitat use, and potentially life-history traits, which may result in varying vulnerabilities to fishing pressure. Early evidence suggests spatial and temporal variation in species presence, along with pronounced sex biases in catch composition, particularly the overrepresentation of females. These factors indicate the potential for differential impacts from fishing activity.

Despite this, species-specific biological data are limited and the extent of population connectivity across sub-Antarctic regions remains unknown. Understanding whether populations are demographically linked or isolated is essential for assessing the resilience of local stocks and for designing spatially explicit management strategies. At present, no formal stock assessment exists for these species. The existing 5% bycatch limit, set by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), is applied uniformly and without a biological basis. Although CCAMLR promotes ecosystem-based fisheries management, non-target species such as macrourids remain understudied and poorly understood within this framework.

This project addresses these critical gaps by investigating four key research questions: (1) the spatial distribution of Macrourus species across SGSSI and surrounding regions; (2) the degree of population connectivity between sub-Antarctic zones in the South Atlantic sector; (3) species-specific biological parameters and the extent of sex bias in catch composition; and (4) spatio-temporal patterns in abundance and how they relate to broader ecological and environmental drivers.

By generating species-resolved biological, ecological, and spatial information, this project will inform the sustainability of current bycatch levels and support the development of more biologically grounded management practices. These outcomes will be essential for informing stock assessments, enhancing conservation of deep-sea non-target species, and supporting CCAMLR’s commitment to ecosystem-based management in the Southern Ocean.

This project will use an integrated approach to investigate species distribution, biological parameters, and population connectivity of Macrourus spp. across sub-Antarctic regions, focusing on data from the Falkland Islands, Shag Rocks, South Georgia, and the South Sandwich Islands. The methodology is structured around four key research questions, each aimed at addressing critical gaps in the biological and ecological understanding of these deep-sea non-target species.

1. Species Distribution Across the Scotia Arc
To investigate the distribution of Macrourus species across the northern Scotia Arc, biological samples—including otoliths and morphometric data (length, weight, sex)—will be analysed. Otoliths will be imaged for shape analysis to enable accurate species identification, particularly where visual identifications are uncertain. This refined species identification will be linked with biological and morphometric data and georeferenced catch locations to better understand catch composition and map species-specific distribution patterns. Age estimation will be conducted on the same otoliths using established zone-counting methods, providing insights into growth rates and population age structure. This study represents the first comparative analysis of Macrourus species across the entire Scotia Arc, advancing previous research by integrating otolith shape analysis, age determination, and spatial distribution modelling. The resulting improved species resolution and biological understanding will directly inform bycatch assessments and support the development of catch limit recommendations.

2. Population Connectivity Between Sub-Antarctic Regions
To evaluate connectivity between Macrourus populations in the Falkland Islands, Shag Rocks, South Georgia, and the South Sandwich Islands, otolith chemistry approaches will be employed. Otoliths from each location and available species will be analysed using Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry. This approach will identify trace element ‘fingerprints’ unique to each location, by sampling the natal and most recent growth we can infer population connectivity, and provide insights into movement and natal origin along the Scotia Arc. This combined approach will provide the first evidence of Macrourus population connectivity across the Scotia Arc and will inform the spatial scale at which management measures should be applied.

3. Biological Parameters and Sex Bias in Bycatch
Biological traits, including size-at-age, size-at-maturity, and sex ratios, will be derived from otolith data and associated morphometric measurements. Male and female distributions will be compared across regions to identify spatially consistent sex biases in catches and to provide insights into reproductive seasonality. Sex-based differences in growth and maturity patterns will be analysed using established statistical approaches. Results will be compared with historical datasets from periods when Macrourus species were aggregated into a single taxonomic category, to determine whether patterns in biological parameters can shed light on historical catch composition. By integrating multiple biological traits with spatial ecology, historical context, and fisheries data, this study advances previous research by providing the most comprehensive assessment to date of sex-biased impacts in Macrourus species, thereby supporting the development of science-based management measures.

4. Spatio-Temporal Dynamics and Ecosystem Context
Spatio-temporal trends in Macrourus populations will be assessed by analysing modelled catch-per-unit-effort (CPUE) data alongside historical catch records within the Vector Autoregressive Spatio-Temporal (VAST) framework. A novel aspect of this study is the incorporation of ultra-fine-scale bycatch observations from selected longline hauls, ranging from 10 to 30 km in length, which will enable detailed investigation of habitat associations, distribution shifts, and environmental drivers. Environmental data (e.g., temperature, depth) will be integrated to examine ecosystem influences on population dynamics. Spatial bycatch hotspots will be evaluated using time-area CPUE analyses at a resolution of 5 × 5 nautical miles, allowing detection of persistent localised declines and assessment of the effectiveness of the current “move-on rule,” which requires vessels to relocate by 5 nm for five days following high bycatch events. The outcomes will provide essential baseline data for preliminary stock assessments, refine bycatch avoidance strategies, and strengthen understanding of how environmental factors influence Macrourus populations across the Scotia Arc.

Year 1

• Literature review; refine research questions and sampling plan
• Initial training in otolith ageing, chemistry techniques, and data analysis (R, bioinformatics)
• Acquire and catalogue historical and observer-collected samples (SGSSI, Falklands)
• Begin otolith preparation, ageing, and shape imaging
• Attend induction workshops

Year 2

• Continue otolith processing and shape analysis (ShapeR)
• Start preliminary statistical modelling (GLMs, spatial mapping)
• Integrate environmental metadata with species distribution data
• Attend an international conference (e.g. SCAR, ICES, or CCAMLR-related)
• Begin drafting first manuscript (e.g. otolith-based species discrimination)

Year 3

• Finalise laboratory work (otolith chemistry)
• Conduct connectivity analysis and VAST modelling for spatio-temporal trends
• Complete sex-ratio and life-history parameter analyses
• Submit first manuscript; draft second (e.g. connectivity or distribution modelling)
• Present findings at an international scientific or policy-focused conference

Year 3.5

• Finalise all data interpretation and statistical validation
• Submit remaining manuscripts for publication
• Complete and revise all thesis chapters
• Internal review and supervisor feedback
• Submit thesis for examination
• Prepare and deliver final conference or stakeholder presentation (e.g. CCAMLR working group)

The student will receive comprehensive training in molecular ecology, fisheries biology, and ecological data analysis, developing a strong foundation for careers in marine science and conservation policy.

Core skills will include otolith dissection and ageing, shape analysis, otolith microchemistry analysis to assess species identity and population connectivity. The student will work with large datasets, learning data cleaning, database management, and integration of microchemistry, morphological, and spatial data.

Training in statistical modelling (e.g. GLMs, PCA, VAST) using R will support analysis of species distributions, connectivity, and spatio-temporal trends. Communication skills will be developed through opportunities to present at national and international conferences, and through contributions to peer-reviewed papers and policy outputs.

The student will be supported by interdisciplinary teams at Newcastle University and the British Antarctic Survey, with additional training opportunities available through the DTP, including scientific writing, project planning, and science communication. A key focus will be completing the full research cycle, from sample analysis to producing outputs that inform fisheries governance and CCAMLR policy.