“…examining marine foraging location of Irish and Canadian Atlantic salmon in the past and present”

September 3, 2019

Dobbin Atlantic Scholarship Visit Report 2018-19

Name:                               Christina O’Toole
Home University:       Galway-Mayo Institute of Technology, Galway, Ireland
University Visited:     Stable Isotopes in Nature Laboratory (SINLAB), University of New Brunswick, Fredericton, New Brunswick, Canada

Visit Dates:                    22nd June – 20th July 2019

Title of Research:
Unlocking the archives: using fish of known feeding location to ground-truth the Atlantic isoscape method, the key to examining marine foraging location of Irish and Canadian Atlantic salmon in the past and present

Visit Details:
I am a PhD student at the Galway-Mayo Institute of Technology (GMIT) in Galway, Ireland.  My PhD is part of the Unlocking the Archive Project (Grant-Aid Agreement No.PBA/FS/16/03) which is funded by the Marine Institute.  My research is examining long-term trends in growth patterns and chemical composition of Atlantic salmon scales using scales from an archive spanning 100 years.  Through the Dobbin Atlantic Scholarship Programme, I completed a four-week research visit to the Stable Isotopes in Nature Laboratory (SINLAB) at the University of New Brunswick.  Dr Brian Hayden, Science Director of SINLAB, hosted me for my trip. The aim of my visit was to ground-truth the Atlantic isoscape method. This method could provide insight into where Atlantic salmon originating in Irish and Canadian rivers go when they leave their natal rivers by locating the areas they are using as feeding grounds during their marine phase.  Fewer and fewer Atlantic salmon are surviving their marine migration, therefore locating feeding grounds, particularly those shared by multiple populations, is increasingly important for implementing managing measures to protect this culturally and economically important species. The Atlantic isoscape (MacKenzie et al. 2011) uses sea surface temperatures and the ratio of carbon stable isotopes (12C and 13C, referred to as δ13C), incorporated into salmon scales through their diet, to determine their feeding location.  The δ13C value of each fish is compared to an isotopically derived map of the Atlantic Ocean to determine where the fish were feeding at sea.  My PhD research involves using archived scales dating back as far as the 1920s which are precious and irreplaceable, requiring me to thoroughly test any methods I plan to use in my analyses before using them on archived scales.  The Dobbin Atlantic Scholarship gave me the opportunity to test the accuracy of the isoscape method on scales dating as far back as the 1960s using tissues from fish of known feeding location.

In order to maximise my time in Canada, I spent the 8 weeks prior to departing for New Brunswick working, with the help of three interns, to prepare samples to bring with me for analysis.  On arrival at SINLAB at UNB, I was given training on the use of the isotope ratio mass spectrometer (IRMS) and shown how the morning quality checks are carried out each day to ensure the machines are running as accurately as possible.  I also became familiar with the international and in-house standard procedure used at SINLAB to determine analytical precision. The samples I prepared in Ireland were scheduled to be run for stable isotope analysis later in the week.  In the meantime, I had more Atlantic salmon scales waiting for me at UNB to prepare for analysis.  These were scales from seven different years in the Greenland scale archive dating between 1968 and 2017. These scales would be used to see if isoscape method accurately determines feeding location of fish as far back as 1968.

Christina tightening the seal on the auto-sampler after loading her samples, ready to be analysed by the IRMS

To prepare these scales for stable isotope analysis, I initially soaked them in deionised water for a minimum of 2 minutes, then used a scalpel to gently scrape the scale surface to remove any mucous or adherents from the scale. The scales were then placed on glass slides with a drop of water and a coverslip was placed on top for imaging. Images were taken of three scales per fish as a record of the fish. These images could be used in future for ageing the fish.

Image of an Atlantic salmon scale taken by Christina O’Toole. The dark band towards the edge of the scale shows one winter spent at sea.

Following imaging, scales were cut using a scalpel. All Greenland archived fish analysed here had spent one winter at sea, also known as a grilse. Due to the layered structure of the scale, the earliest portions of the scale are influenced by the isotopic composition of the more recent layers. To obtain a temporally distinct sample, I cut out the last period of growth from the scale, the portion after the last sea-winter. After cutting, the scales were dried thoroughly in an oven at 60°C. Approximately 1mg of the cut portions of scale from each fish were then weighed into tin cups to be combusted for stable isotope analysis. These samples were analysed on the IRMS with the same procedure as the samples I brought from Ireland. The last data from stable isotope analysis were acquired and compiled in the final two days of my trip. Through some basic initial statistics, I was already able to see trends emerging. I will now begin to analyse the results more thoroughly and use the isoscape method to determine feeding location. If the feeding location determined by the isoscape matches the known feeding locations of these fish, the Atlantic isoscape method can then be used to examine archived scales and determine trends in feeding location of Atlantic salmon over the past 100 years. Insight into these trends could help us better understand the marine migration of Atlantic salmon, and could be a very valuable resource for informing management and conservation measures.

Christina presenting her Dobbin Atlantic Scholarship research at UNB (Photo by Dr Brian Hayden)

Towards the end of my time at UNB, I gave a seminar to other researchers, students and staff at the university. This was a fantastic opportunity to present the research I was carrying out through the Dobbin Atlantic Scholarship, to raise awareness about my PhD research as a whole, and to discuss the aims of the Unlocking the Archive project. The presentation led to a detailed discussion afterwards and some interesting questions were asked.

Future Continuing Collaboration:
During my last week in Canada, I began writing a peer-review paper as part of a previous collaboration with Dr Hayden and Emily Weigum. This trip was an excellent opportunity to discuss our results and plan the outline of the paper together. My Dobbin Atlantic Scholarship trip also provides opportunities for future collaboration. I aim to publish the research I carried out at UNB in peer-reviewed journals and will collaborate with Brian Hayden, Kurt Samways, and Emily Weigum for those publications. As part of her PhD, Emily will use some of the data we generated during my trip for her analyses of Atlantic salmon, providing further opportunities for us to work together. The connections I have built on this trip have already sparked research collaborations and I believe this will continue in the future.

My research trip to Fredericton has been a fantastic experience, both academically and personally. I connected with people who have expertise in my area of research which allowed me to gain a lot of knowledge during my stay. I have finished my four weeks with invaluable data that will be a huge step forward in my PhD research. I was thankful for the opportunity to conduct my research in a city as welcoming as Fredericton. I had time to explore the culture of the city through the weekly markets, and explore the nature that was so close to the city in Killarney Lake Park, Hyla Nature Reserve, and the Bill Thorpe Walking Bridge. I was delighted at the wildlife I was able to see that is very different to that in Ireland, including chipmunks, American goldfinches, American robins, and I was even lucky enough to spot a black bear. I also had the opportunity to explore some of New Brunswick’s beautiful coastline, from whale watching and hiking in St. Andrews, seeing the reversing falls in Saint John, and visiting the sea caves in St. Martins. This trip was a fantastic experience that resulted in very valuable data that will greatly help my research, as well as the chance to build valuable collaborations and see wonderful places that I would not have had the opportunity to discover otherwise.

Christina at the top of the Chamcook Mountain Trail, with views of St Andrews, Passamaquoddy Bay, and the coast of Maine, USA

MacKenzie, K.M., Palmer, M.R., Moore, A., Ibbotson, A.T., Beaumont, W.R.C., Poulter, D.J.S. & Trueman, C.N., 2011. ‘Locations of marine animals revealed by carbon isotopes’. Scientific Reports, 1, Jun, p. 6.