Keyword Summary:
Salmon, migration, sea, rivers, Norweigian Sea, temperatures, changes, patterns, coast, sub-polar
Speakers:
Daniel Tulloch
Dr Emma Tyldesley
Dr Emma Tyldesley:
I’m Dr Emma Tyldesley. I am a postdoc (researcher) at Strathclyde University, working remotely in Moray. I also work for the Atlantic Salmon Trust. I'm doing postdoctoral research focusing on salmon, focusing on that the first few months after the young salmon go into the sea, so when they leave the rivers and go into to sea, that first few months at sea, when they're on their migration away from the rivers, and up to their feeding grounds in the Norwegian Sea.
So, looking at conditions that they experience along the way, because that part of their lifecycle is thought to be quite critical for their survival. So changes in the conditions that they’re experiencing in those first few months might be contributing to the reduction in returns of adult salmon back to the rivers.
We're doing some work to pull together lots and lots of data, on lots of different scales, from the ocean scale. Things that change on timescales of years and decades, right down to small-scale things like particular temperatures that they might be experiencing as they travel on migration routes. What are the feeding conditions that they're experiencing? So we're pulling together loads of data and doing analysis to try and see if we can explain some of the patterns of changes in the return rates of the fish from different rivers.
D T
Is this around Scotland?
Dr E T
We're focusing on a few rivers that all use the same migration routes. So, there’s a few in the north of France, and then a couple down in the south of England, and then one in Wales and a couple of Northern Ireland. And we'd like to look at some of the East Coast rivers as well, so there's North Esk. And they all take this route, where they come out along the west coast of Ireland and Scotland, out past the Faroe / Shetland Islands channel, and they pop out into the Norweigian Sea. They all leave the rivers at different times; so the ones in the southern altitude fish leave, quite early, March, April time, and then the more northerly salmon, leave later on in the season. So trying to get a range of times of when the fish leave, and then they travel on this route, and head out to sea for their feed.
One of the things we're looking at is phonology. So changing timings of when things happen, because with climate change, as people are becoming aware, climate change is altering the timings of when things happen, like butterflies coming out of their hibernation too early.
And so one of the things that might be happening is, climate change, because it’s getting warmer, the sea is getting warmer too but not as quickly, so the fish in the rivers, they’re using the temperature of the river, plus the length of day, and the flow rate of the river as indicators of when they should leave the river, and they're expecting to find good conditions for themselves when they get to sea, but if the river conditions in the river are changing then that’s maybe triggering them to leave too early, and then they’re getting to the sea, but the temperatures they’re expecting aren’t there, so that’s impacting their feeding ability and their growth rates, perhaps the predators they’re encountering. So we’re looking at phonology, changes in timings.
So one of the things I've been doing is, pulling together loads of data from satellites and ocean models on plankton, the plankton cycle: when’s the spring bloom? In the spring when it gets warmer and the sea is so mixed up, and the plankton have this big bloom, is that happening at a different time than it used to? And how are all these things changing? Are some things changing faster than others?
D T
So, sort of a ripple-down effect? From climate change, if the temperatures are warmer, the blooms happening more frequently I take it as well?
Dr E T
Yeah, just differently, just different dynamics. And there's a limit to how much things can change. So the fish maybe only have a limited capacity to adapt to that climate change, which is why climate change is going to affect everything differently, because some species are quite adaptable, and some maybe are tied more to daylight cycles for example.
So that's what I'm working on. I’ve been doing that since May 2021, so I'm working with the ecological modelling, oceanography group in Strathclyde (University), and the Atlantic Salmon Trust.
D T
So about migration routes, do you study changes to those routes?
Dr E T
Yeah, well, it's a bit of a puzzle, because, salmon are born in the rivers, and when they get to the right size, and age, to leave the river, they’re called smalls; they're very small. And once they leave the river they’re actually quite rare as well. So it's actually hard to know where they go! There's loads of tagging studies going on at the moment, electrical tags on the salmon, so they’re tracked when they leave. And there's also, there's data that’s been reanalysed, where they've actually used reanalysis to see where fish that have been caught, historically, what rivers did those fish come from? So I’m focusing on this kind of superhighway for the fish, where you can imagine the fish were coming out of all the different rivers, and they're joining this superhighway at different times and locations. That's the bit I'm looking at. And if you look at it, if you plot data of where the salmon have been caught on the map, it follows the symmetry, like, when you come off the west coast of Scotland, you're in like 100 - 200 metres of water, and suddenly, you drop off the shelf into the deep water. So you get this 200 - 800 metres water depth. That's where the smalls are travelling along, they're following the edge of the shelf, and it’s because there's currents that flow there. So there’s so many things to think about, are they, are these fishes just getting pushed along? Or are they able to make decisions? Are they going faster than the current or against the current or towards a more preferable salinity or temperature.
Then there's also large scale oceanographic influences that mean that they might not be following that same route year-to-year, there’s certain places where they might go one way round, other years they might go down and round a different way due to the kind of conditions that they’re experiencing. It's one of the things I'm looking at, is more larger-scale things ,like people have heard of El Nino, which is a large-scale oceanographic thing that predicts what conditions are going to be like in the sea. We're looking at the sub-polar gyre, so the strength of flow of the waters around Iceland, and how sometimes that cold water is pushing up against the UK, and sometimes you've got more of a stronger influence of the water from Spain and subtropical areas. And we're looking at changes on year - decade scales that are affecting which way the salmon might be choosing or being pushed to migrate. And also what feeding conditions are associated with those changes. So the colder waters are more associated with the kind of fatty plankton that they like to eat.
D T
Okay, so they solely eat plankton?
Dr E T
Well, they eat the larger plankton and larval fish, and they eat large fish, small fish, and their diet changes as they grow, as they go along their migration route as well. But the plankton are obviously important because they might not have eaten the plankton directly, but they'll be eating the things that are eating the plankton. So it's all -
D T
It's all connected. And what about ocean acidification, does that have anything to do with your studies?
Dr E T
It's not something, obviously it’s something that comes up when we talk about climate change, but ocean acidification, it’s not something I’ve encountered directly in the work I'm looking at at the moment. But that's not to say it's not having an influence, because obviously, ocean acidification affects how well the plankton could build their calcium-based shells, or silicate shells if they’re that sort of plankton.
D T
That’s interesting.
Dr E T
I am finding it really interesting. It's baffling. And it's overwhelming. And just because everyone's got different take on it as well, that’s one of the things I’ve found interesting, because I'm working with the Atlantic Salmon Trust, I've met a lot of people recently who are part of the Missing Salmon Alliance, which is a group of charities looking at how we can improve things for the salmon, a lot of those people are based in freshwater sites, or they've got other interests, like angling societies, game and wildlife trusts, so everyone's got a different perspective on it.
And then obviously, more locally, I think I'm very lucky that I'm because of COVID I'm able to work from home, and it seems a bit crazy living in Moray when I work in Glasgow, but I live 50 metres from the River Spey, which is a major salmon river. And people, well that ice house down there, that's where they used to pack the salmon, when they’d caught it, ready to take it down to markets in London. People around here, salmon used to be and still it is, a massive part of their heritage.
D T
Is it really? I never knew that, I’m learning so much.
Dr E T
That's the thing, this is what I find interesting; I was in Elgin museum and someone came over to me and said ‘oh I hear you’re studying salmon! Come and give us a talk about salmon.’ Well, I will, and I’d like to, I also think that a lot of the people who would be in the room, especially the older people, know a lot more about salmon than me. Because they’ve been, they’re either fishermen, they’ve held them, or they grew up - I was talking to a woman the other day who's a farmer, she remembers, you know, going down and seeing the fish being loaded onto the trains to go down to London.
D T
That’s incredible. And in those days, I think the industry would have been far more manageable, sustainable, because you know, there wasn't that scale, the large-scale, in terms of fishing boat sizes that we have today.
Dr E T
Yeah, I haven’t really caught a feel for it, because a lot of the salmon was mostly caught in the rivers. So when the salmon was migrating back upstream, it would be guys with boats making a circle of nets, I haven't really got a feel for how much they would have taken, as a proportion of the population each year.
D T
Okay, because obviously it would have been in the interest to leave some, to sustain the livelihoods of the people that live here, if they leave some salmon they’ll have the chance to come back.
Dr E T
Yeah, absolutely, through history that's been realised fairly quickly… We’ve done things like block rivers to catch the salmon, then we wonder why the salmon aren’t there any more. You need to speak to, get insights from the local community, and from the Atlantic Salmon Trust people, who know people as well.
D T
Yeah, it's really fascinating, it would be amazing to speak to some of the locals, and the people that have insight. Did the fact that the river is such a hotspot for salmon here, did that influence your move to here, to the area?
Dr E T
Well I studied Maths and Stats, so it wasn’t particularly on my radar, but I worked in fisheries when I finished my PhD, I went to Aberdeen and worked in fisheries and went off to sea. And met my husband and he was working in Glasgow, and his mom lives here, he grew up here. Okay, so we visited loads and it’s just increasingly where I wanted to live, cause I’m massively into running and cycling, and wildlife and I love being by the river. We spend a lot of time splashing around in the river in summer.
D T
See that’s sort of the benefit of living in the countryside. You’ve just got that outdoors around you and it’s beautiful. So good for your mental health as well I think.
Part 2 to follow