1. Glass eel research on the Rangitaiki Awa
Eimear Egan (Freshwater Ecology Group, NIWA)

2. PhD - The marine life of īnanga whitebait (University of Canterbury)
Fish ear bones – otoliths

3. Postdoc – Is climate change affecting tuna populations in NZ ?
Te Waihora
Historic tuna otolith collections

4. Postdoc – Is climate change affecting tuna populations in NZ ?
Shortfin tuna annual growth rates

5. New Research - Understanding the marine life of longfin and shortfin eels in Aotearoa
MBIE Smart Idea Fund
Oct 2018 – Oct 2021
“Risky science”
2018 – 2019
Project planning, engagement + 1st field season
High risk but potentially highly transformative science

6. New Research - Understanding the marine life of longfin and shortfin eels in Aotearoa
MBIE Smart Idea Fund
Oct 2018 – Oct 2021
“Risky science”
2018 – 2019
Project planning, engagement + 1st field season
High risk but potentially highly transformative science

7. Why do we need abetter understanding of the marine life of Aotearoa's tuna?
Reproduction unknown
Glass eel recruitment
Currently only 1 monitoring programme in NZ (DOC, Ashley River Canterbury)
What is driving population declines?

8. Proposed spawning areas for LF and SF eel
Anecdotal evidence indicates longfin and shorin larvae traverse more than 20° latude from their hypothesised spawning grounds in the WPO to New Zealand [7]. Research voyages have found shorin eel larvae distributed across 10° longitude within the WPO[8] including east of Fiji, south of the Solomon Islands, around New Caledonia and in the Coral Sea (Fig. 5). Larval spaal distribuons suggest shorin eel spawning ground locaons may be: north-east of Samoa, anywhere between Fiji and Tahi, in the South Fiji Basin, west of New Caledonia, and more recently between the north-west of Fiji and west of Vanuatu[5, 8] (Fig. 5). Longfin eel larvae have never been found in the WPO and have never been described. Larval dispersal modelling studies suggest longfin eel spawning grounds are in the WPO[7] and more recently, pop-up satellite tagging showed mature females headed towards New Caledonia[9] (Fig. 5).
The western Pacific Ocean is one of the most variable ocean regions, having the fastest sea level rise in the world
The western North Pacific Ocean is characterized by major oceanic features, such as the NEC, the Kuroshio, the Subtropical Countercurrent (STCC), and eddies, which will likely vary during a changing climate. For example, the Kuroshio has warmed two times faster than the global warming rate in the past century29. The NEC bifurcation latitude is shifting southward in the past 60 years30. The Kuroshio along the East China Sea has gradually moved onshore31, and the Luzon Strait intrusion into the South China Sea is weakening in the last two decades32.

9. Larval dispersal routes unknown
Black arrows are surface ocean currents and white dashed lines are deeper currents. Dynamic and variable ocean environment that glass eels traverse
Grammer et al., 2015

10. Why do we need abetter understanding of the marine life of Aotearoa's tuna?
Panel of international experts assessed how NZ manages and protects tuna populations (2013)
Monitor glass eels recruitment
Stock assessment fishery
Need to know how many glass eels are returning to NZ
How many eels are making it to sea for reproduction

11. Why do we need abetter understanding of the marine life of Aotearoa's tuna?
Climate change
Affecting eels worldwide
Marine phase most sensitive
Marine heatwaves will increase

12. Research questions A) Spawning site origins
1. Where do longfin and shortfin eels reproduce
2. Do LF and SF eels share spawning areas?
3. Do LF and SF eels repeatedly spawn in the same place?

13. Research questions B) Larval dispersal routes
1. What oceanic larval dispersal routes do LF and SF use?
2. Do these dispersal routes differ within and among species?
3. Do these dispersal routes differ within and among years?

14. How will we sample for glass eels?
Proposed sampling dates
16th July – 19th July
31st July – 4th Aug
15th Aug – 18th Aug
29th Aug – 1st Sep
13th Sep – 16th Sep
28th Sep – 1st Oct
13th Oct – 16th Oct
27th Oct – 30th Oct
12th Nov – 15th Nov
26th Nov – 29th Nov
Spring tides
Before sunset
Between 5pm – 2am
Sample for 3 – 4 hours
2019 (maybe 2020)

15. How will we sample for glass eels?
Modified whitebait net ?
Local knowledge
At dark & before whitebait season

16. 1. Extract and polish otoliths to reveal the daily ring patterns
Identify species
Length and weight measurements

17. 2. Take measurements of the daily growth rings
Spawning ground
Marine larval dispersal
Coastal FW
A catalogue of information contained in otoliths
Age (length of time taken to reach NZ)
Birth date
Daily growth rates

18. 3. Extract chemical signature in otoliths
Spawning ground
Marine larval dispersal
Coastal FW
Oxygen 18 – Temperature
Estimate temperature at spawning ground

19. Otolith Oxygen 18 20 - 23°C = purple
24 – 26 °C = green/yellow
28 °C = red

20. Marine larval dispersal
Spawning ground
Marine larval dispersal
Coastal FW v
Measure Oxygen 18 throughout marine life
Temperature history
Ba, Mn, Mg, Zn, Rb, Sr, Pb, Li, Ca
Track movements into different water masses
Reconstruct larval dispersal histories
Temperature values from 0xygen 18 measurements used to infer origins combined with satellite derived SST data

21. Larvae record chemistry of their diet in tissues
The rational behind using CSSI-AA is that as the leptocephalili traverse the marine environment form their spawning grounds to NZ coastal waters they feed at low trophic level on particulate matter, bacteria and gelatinous matter. The baseline N isotopes values are recorded in their tissues providing an integrated measurement of the isotopic environment they have traversed.
Glass eels are model species for diet-derived isotope studies because trophic fractionation is minimal as larvae feed on organisms at the base of the food chain[13]. This means the δ13C and δ15N signatures are good proxies for an individual’s origins and movements. No feeding in coastal waters so isotope value represents marine movements
δ13C & δ15N
Compound specific stable isotopes of amino acids

22. CSSI-AA values projected onto isotopic landscape
δ15N variability exists within Western Pacific Ocean and between WPO and Aotearoa
This graph is the modelled nitrogen isoscape for the Western Pacific Ocean and NZ showing baseline δ15N isotope variability.
The Nitrogen 15 values from source amino acids of glass eel tissue can be used to refine spawning locality
δ15N isoscape

23. Patai?