Project number: 2016-018
Project Status:
Completed
Budget expenditure: $325,000.00
Principal Investigator: Karen Evans
Organisation: CSIRO Oceans and Atmosphere Hobart
Project start/end date: 30 Jun 2016 - 29 Jun 2019
Contact:
FRDC

Need

Management of the ETBF is complex because of the cross-jurisdictional nature of the stocks and governance through the Commonwealth Harvest Strategy Policy and the WCPFC. Current assessments conducted by the WCPFC assume that these species comprise either single discrete stock units throughout the WCPFC area or across the Southern Hemisphere portion of the region and genetic methods used in the past have been unable to refute such assumptions. Biological information on growth rates and reproduction, movement data derived from tagging studies and spatial and temporal variability in catches of these species however, suggest that there is likely to be some structure to stocks throughout the WCPFC region and assumptions of single spawning populations may not be accurate.

More recently, traditional and next generation genomic methods have provided evidence of population structure in yellowfin tuna across the Pacific (e.g. Aguilar et al. 2015; Grewe et al. 2015) and provide some support to the hypothesis that yellowfin tuna fished by Australia’s tuna fisheries may be a localised stock within the Coral and Tasman Sea region. If yellowfin tuna and if any of the other principal species occurring in the ETBF do comprise localised stocks, this has obvious implications for the management both within national and regional contexts. Clarification of the connectivity and population structure of species in Australia’s Tropical Tuna fisheries with the broader WCPFC region is required for appropriate governance through the Commonwealth Harvest Strategy Policy and the WCPFC, to ensure any risks to regional stock biomass are minimised and to improve stakeholder concern over stock management.

Objectives

1. Investigate the presence of stock structure in the five principal species caught in Australia’s Eastern Tuna and Billfish Fishery and the western Pacific Ocean across spatial scales of relevance using new generation genomic methods
3. Assess the need and associated costs for research required to further reduce uncertainties in relevant harvest strategies and management frameworks
3. Inform the relevant parties in the Western and Central Pacific Fisheries Commission of the key results and, if appropriate, the need and value of extending the project throughout the western and central Pacific Ocean.

Final report

ISBN: 978-1-925994-22-3
Authors: Karen Evans Peter Grewe Scott Foster Rasanthi Gunasekera Matthew Lansdell
Final Report • 2021-04-01 • 4.13 MB
2016-018-DLD.pdf

Summary

Accessing samples from broadbill swordfish from two sites within the WCPFC area was particularly problematic and was exacerbated by a poor fishing season in 2019. This resulted in samples for broadbill swordfish consisting of samples collected from the ETBF (2 years), Norfolk Island (1 year) and New Zealand (1 year). The poor fishing season in 2019 also resulted in limited samples of striped marlin from New Zealand being collected in the second year of samples. The genetic groupings identified across bigeye and yellowfin tunas and broadbill swordfish suggest a substantial level of connectivity and mixing between each of the locations investigated, with little discernible genetic differentiation between areas. Results from albacore suggest the potential for two genetic groupings, however these were not able to be resolved by the methods used. The results from striped marlin indicate that there may be two genetic groups, with the ETBF, NZ and Hawai’i sharing the first group. The second group was identified only from samples collected from Hawai’i. The presence of two genetic populations of striped marlin in the waters of Hawai’i has been proposed previously and the results presented here lend further support to this hypothesis. The consistent absence in the ETBF and New Zealand of the second genetic group found in Hawai’i indicates a proportion of fish recruiting to the Hawai’i fishery do not contribute to the ETBF fishery and potentially represent a northern hemisphere population that doesn't migrate south of the equator. 
The results of the current study are largely consistent with previous genetic investigations into the population structure of these four species. Consistency in results across years suggest that the groupings revealed here have some temporal stability across years across those sites where multiple years of samples were collected. Although results suggest the potential for two genetic groupings among albacore samples, assignment by the methods used here was statistically uncertain and resulted in some individuals not being able to be assigned to either group in the scenario with any confidence. Further sampling from the three locations included here as well as inclusion of samples from additional sites would also be required for resolving these uncertainties. 
It should be noted that these results only apply to the sites included for each of the species in this study and therefore cannot be extrapolated across the wider western and central Pacific Ocean region with any certainty. Further sampling and analysis of sites across the western and central Pacific, including temporal replication of sampling, would be needed to investigate whether the results presented here are consistent with other locations across the western and central Pacific region or whether greater genetic differentiation is discernibly present. The resources required to support the attainment of broader insights into the connectivity of species across the WCPFC Area and connectivity between the ETBF and the western and Central Pacific Ocean will be dependent on current access to samples, the extent of further sampling required in order to attain broad spatial and temporal coverage of samples, the facilities and capability available for processing and sequencing samples and the capability available for data quality control and analysis pipelines.
As next steps, a second year of sampling for broadbill swordfish from New Zealand is planned and a preliminary small dataset from the Cook Islands (consisting of 24 samples) has been collected. These samples will be analysed and incorporated with the data from this project to provide further insights into the connectivity of broadbill swordfish across the western and central Pacific Ocean and presented to the WCPFC Scientific Committee in August 2021. 
 

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