[Automated voice] This conference will now be recorded.

[Daniel Cooper] All right.

Thank you very much. My coauthors in this project are Katrin Iken, from University of Alaska Fairbanks. Libby Logerwell, also from EcoFOCI. Emily Ryznar was a member of the Shellfish Assessment Program, in Kodiak. And Louise Copeman, who is a member of Fisheries Ecology - Behavioral Fisheries, Behavioral Ecology Program.

[Indistinct conversation]

[Daniel Cooper] So, snow crab, Chionoecetes opilio, in Alaskan waters range from the southern Chukchi Sea up through the northern Bering Sea and Chukchi Sea, all the way to the Beaufort Sea.

Southern Bering Sea, the males grow quite large in support, while historically have supported, an important fishery. North of there in the northern Bering Sea and Chukchi Sea, the crab do not get as large and it's generally 
assumed that the year-round temperatures are too cold. North of the southeast Bering to support, you know large crab. 
But they do have, you know populations that are smaller.

So I said there's an important fishery, for these in the southeast Bering Sea. This figure, can you see this moving on there? This figure shows the size frequency, in annual bottomfish or the annual trawl survey, it's the annual groundfish survey. But it's also obviously for crab, it's multispecies. And of the Bering Sea you'll be pleased to see, and there's one of these every year from 1980 down the bottom all the way through you know 2021. Top. What I want to point out is that recruitment to the survey has always been very important, to the fishery...to the population dynamics of the species and eventually to the fishery.

As you can see a small crab recruit to this fishery every once in a while. And then through time they grow. There's one pulse of recruitment there, one pulse of recruitment there, and one there. And they grow to a size where they can support the fishery. And then there's been periods of very poor recruitment. We go, so recruitment has always been very important to this fish. In 2021, the eastern Bering Sea snow crab population crashed. Leading up to that had been a period of poor recruitment. And poor recruitment isn't the only problem.

There was this pulse of recruitment, that recruited to the annual survey, in 2015. And you know there was hopes that that would continue to grow, but that pulse that year class, seemed to, seemed to die; it disappeared. The best guess is that
they had high mortality during the marine heat wave, but recruitment has always been important and now that the stock is crashed, there's no way to stock and rebuild, until there's another pulse of recruitment.

Recruitment is really important in this survey. And I keep mentioning recruitment to the survey gear. You can see it's kind of small.

This figure doesn't start until 25 millimeters. The crab really don't recruit to this, to the annual trawl survey until they're between 25 and 40 millimeters. And so we know a little about the 25 millimeter crab. This is the annual trawl survey. The mesh. You can see the holes are just too big to retain the small crab. So there's this time period when the crab are less than 25 millimeters that we know very very little about.

You know, you might think 25 millimeters that sounds very small, if that was a cod or a pollock, that would be like a late stage juvenile fish, in its first year of life.

But, these crab are actually very slow growing. These two slides are from a study that was done in the Gulf of St. Lawrence. You know in in Canada, in the Atlantic. And it's the best study I know of, that shows these very earliest benthic stages, 
shows their growth and it shows some information about their habitat. So this figure on the left, shows all of the size classes that were found in this survey area, in the Gulf of St. Lawrence.

These researchers included Dionne et al. 2003. Talk more about that paper talk, but these researchers concluded that these fish (excuse me) that these crab, molt, multiple times in their first two, you know in their age-0s and age-1s. They go through multiple molts and after that they go into a cycle of one molt per year. But I guess what I'm getting at is according to their conclusions, by the time a crab is 25 millimeters, in order to recoup to our groundfish survey, it s probably already about four years old. And so there's this gap in its life history, that our groundfish trawl survey can't tell us much about, and consequently our center knows very little about.

This figure, on the right, shows the temperature that these crab in the survey occupy. Each one of these dash (excuse me) dashed or dotted lines is one of these different size categories, that are shown here on these lines. And the x-axis is temperature. That temperatures are less than 2 degrees C, just for emphasis. And you know the lines all represent the cumulative fraction of each of the population of these life stages, that occupied different temperatures of habitat. And then this, this solid line shows the cumulative fraction of all the survey station temperatures.

And so what this figure shows, is that they surveyed temperatures from almost -1 to 5 degrees. But all of the crab in the survey, or nearly 100% of them, occupied temperatures of 2 degrees C or less. And so the conclusion is that these crab stages, these very small stages, are stenothermic. That they require, you know, they've got this very narrow temperature band that they can survive in.

And they require these temperatures less than 2 degrees C. This idea that these small crab are stenothermic and require small temperatures has been very influential in studies of Alaska snow crab.

All of these studies that I've listed, you know Sanctus study and kind of assume that the small stages are stenothermic. And the, and these studies are for a variety of reasons. Most of them explain you know population shifts in abundance and spatial shifts. And trying to relate that to climate; also there's some laboratory studies that you know, select temperatures based on figures and also interpret results.

So we know that temperatures have fluctuated greatly in these crab habitats; the northern Bering Sea. You know the cold pool fluctuates between being pretty much non-existent in the, in the Bering Sea in some years; all the way almost to the Alaska Peninsula. And so these two to three habitats varies a lot. And recently there's been some really warm years, where there's been very little, less than 2 degree act. Also this figures from the Chukchi Sea, you see some temperature results, model results, from the southern Chukchi Sea bottom temperatures in August.

You can see over the last 20 years they've really increased. So these temperatures are increasing. We got this idea that these early stages are stenothermic and require less than two degree water. So you know some obvious questions are: do these juvenile snow crab early stages only inhabit at cold temperatures?

And what happens in warm years and what other habitat characteristics are correlated with each. So the data that I have to present today, are from four cruises from the Chukchi Sea. They are four different, four different survey programs, initiatives, that we've pieced together to form one data set.

One is the Arctic Ecosystem Integrated Survey from 2012, and the crab sampling was done by the Kodiak Shellfish Lab. One was the Arctic Marine Biodiversity Observation Network cruise in 2015. We'll talk about how the sampling of that was different, it was trans-exibital defined spatial resolution. And then we have two Arctic Integrated Ecosystem Research Programs, sampling cruises in 2017 and 2019. I should say that 2015 the sampling was led by Iken. In 2017 and 2019, it was led by Libby Logerwell. All of these cruises were approximately at the same time of year. They all started, maybe in mid-August and ended sometime in September.

Not exactly the same time. This area is just where the surveys are. For all of these surveys we use the same basic trawl. And that's why we have different information on these stages than the annual groundfish assessment survey.

You see, this is the trawl. It's a 3 meter beam trawl. The largest mesh size is 7 millimeters. So it's a lot smaller. Seems to retain the small crab well. There were some different versions of the trawl. Some different foot ropes and different deployment methodologies. But it was the same basic trawl design, of the trawl bot.

And so for each of these cruises, I'll show a distribution and mean CPUE of the crab by some size ranges that I'll talk to you about in a moment. And we made a habitat model from the 2000, we made models for the habitat of all these life stages to 2015, when we had high density.

And also we talk about the thermal occupancy. The size categories that you'll see in the results that we used, were based on these. This figure shows the size frequency of the crab in 2015. There are a couple of small size modes, less than 7 millimeters and 7 to 10 millimeters that if it's consistent with the Canadian study are probably age-1 crab.

And then there is larger sizes, 10 to 15 millimeters,
15 to 25 millimeters, 25 to 40 millimeters and greater than 40. The greater than 40 millimeters probably represent multiple year classes, but it seems likely that the other ones are each represented.

All right, so in 2015 trend had this sampling design that was more trans-ex across some thermal boundaries. And also in 2015 there were a lot of biotic and abiotic variables, that were collected. And so we made some general additive models for each of these, life stages. The response variable, is the CPUE of the size classic station and the potential predictors are: bottom temperature, depth, sediment type either percent sand, or percent mud, or percent gravel. It sums to be 100% for each for each station; for chlorophyll and the sediment.

And then the CPUE of large; and when I say large I mean 15 millimeters or larger crab. So it's still small but the thought was that we know from, diet studies and from lab studies that the smallest crabs are susceptible to cannibalization by the larger crabs. So we included that as a potential predictor of the small crab density. Of all of the,

all of the potential predictors and the models, and remove terms til we found the best one.

So, I'll orient you to this slide, because this will be a lot of the results, that will show you from each of these life stages. Up in the upper right panel, you'll see the life stage I'm talking about. And this gauge is less
than 7 millimeters. It's the smallest length. We've got maps of the distribution in every year. The catch rates are shown by these black circles and the bottom temperatures are interpolated bottom temperatures. The scale of all these interpolated bottom temperatures, you can see are the same, where anything that's kind of blue is less than 2 degrees, and anything in green or a warmer palette is warmer than 2 degrees.

You can see in 2012 the highest densities of the smallest size were in the northern part of the survey area, in this water that was less than two degrees. In 2015 our high density, you know high spatial resolution sampling, you can really see that the small stage was present in this water less than two degrees C, and largely absent from the waters.

In 2017, was a very warm year for summer bottom temperatures. You see that crab were almost absent. And in 2019 they were present at a few stations, but in 2017 and 2019, you know the mean CPUE, over here on the right was two orders of magnitude less than it was in 2012 or 2015. So there were there were very few of these of this life stage. This life stage had a model that explained a lot of the variabilities, so I'll talk about it.

And the strongest predictors of crab CPUE of the smallest crab CPUE was temperature. You can see that there's a steep decline in CPUE after about two degrees C. Kind of consistent with this idea that [indistinct]
crab [indistinct].

Also it's kind of interesting and noteworthy, that the crab, the smallest crab, were negatively related to the CPUE of the larger crab. So I won't go into that much more the rest of the talk, but I think it's kind of interesting. Also the crab were associated with [indistinct]. The next size range is a 7 to 10 millimeter crab. It looks a little bit different in 2012, there were some in the north, in cold water.

But the highest densities by far were in the southern part of the survey area grid, that was still covered by these cold temperatures. And that's a pattern that you're going to see over the next few stages. In 2015 there wasn't that much of a pattern. But in 2017 and '19 when it was warmer, the stage was also, you know, two orders of magnitude lower; CPUE was then in 2012.

So they largely decreased, largely absent from the survey. At the next size range, is 10 to 15 millimeter crab. And again they were present in 2012 at the southern area, of the survey area. In the beginning of this part it's less than 2 degrees C. In 2015 there weren't very many of this size range. And in 2017 and 2019 this crab would be present and you're going to see this trend in the future size classes, where they started being present in the northern part of the survey area, where they were absent in 2012.

The next size range is 15 to 25 millimeters sized crab. And they were also present in the south and southern part of the survey area in 2012. And then present much more to the north in 2015, '17, and '19 largely. Next one is 25 and 40 millimeters, again it's kind of the same pattern. They were present, the highest densities to the south in 2012. And they had moved north in 2015 and '17.

Finally the largest crab, got 40 millimeters plus. Again these are probably multiple age classes, but unlike the other ones, these crab were present also in high densities in a warm-up water, since 2012. And that that continues in 2015, '17, and '19. And again there was this north, this northwards shift, in a distribution between 2012 and 2019.

This life stage also had a model that explained a fair amount of the variability. The important, the strongest factors were depth. Where they you know increase with depth and temperature, which was opposite of the other stages.

Largest crab were actually more associated with warmer models. So to kind of summarize a little bit about the distribution and the spatial distribution, I've got some maps. This map shows the center of distribution of the three smallest stages in 2012. See the smallest ones were in the northern part of the survey area. And all of these life stages were largely absent, by 2017 and 2019. The next size classes, 15 to 25 millimeters, and 25 to 40 millimeters in 2012, were present in that cold area in the southern part of the survey group.

By 2017 and '19 that area warmed up and the crab had moved or not the crab, they had shifted their distribution to the northern part of the survey area. These figures are similar to the ones I showed you from Dionne et al., it's the habitat these crab were inhabiting. And for each year using 2012, '15, '17, and '19 the size ranges of the crab are represented by different colors. You see it's 2012, almost all of the crab were inhabiting water less than 2 degrees C.

Similar to what the Canadians found. Except for the largest crab, 40 plus millimeters, some of those crabs about half of the population was inhabiting water warmer than 2 degrees C, out to maybe about 6 degrees C. In 2015 there was this interesting path where the smallest size ranges that we think were age-1s,
these less than 7 millimeters and 7 to 10 millimeters, were found almost entirely in this water less than 2 degrees C.

And progressively the larger size classes can have warmer water. Then by 2017 or 2019, again the smallest size classes were much reduced and largely absent but the crab were habiting much warmer temperatures. From you know 2 degrees all the way out to, you know in 2019 like 8 degrees C. So there's this big shift in the temperature that these crabs have, you know.

So what might some of this mean? Well, I mean we see that the Chukchi Sea juvenile snow crab distribution and size structure has changed concurrently or coincidentally with warming. Could mean, a lot to the Chukchi Sea ecosystem. These crab are a big part of the benthic biomass. They're predators, they are a prey item, and so like what that means to the Chukchi Sea, you know benthic community and ecosystems is an open question.

Also you know the smallest crab in the study were only found in cold water. We didn't find large abundances anywhere except for cold water in the year we had a model. You know it showed that crab were associated with these cold temperatures. It could be that temperature has a large effect in snow crab at the earliest life stages. And that it's evident by the time they're year-1. You know could even be earlier in the life cycle. By year-1, you can see that there's this big effects with temperature.

The northern Bering Sea, you know we have these huge shifts in the cold pool; that's water less than 2 degrees C. It could be that this cold temperature is affecting the population, and always has. You know that it would be evident at the age-1 life-stage. Except in the Bering Sea we know very little about that. We assess the snow crab population every year with the annual bottom trawl survey. But it only catches large crab. So if there is an effect on these age-1 crab, we just have to wait like maybe up to four years is the guess or maybe three more years after the effect might be knowable. And we don't see these like really strong effects with the crab distribution in abundance and temperatures.

Instead what we get from the groundfish survey, is that we have you know this kind of four year black box. And we don't know what was happening with the climate or what stages might be important. Like for instance, Phyllis says it might be a cool year at each year and it may be that the crab in the Bering Sea have a big recruitment pulse. That could start to rebuild the population or it may be that they couldn't.

But the groundfish trawl survey isn't going to have any information all about that, about that at all, until like 2026. All right and then these small stages were inhabiting much warmer water than they were in that previous study in Canada. Or than they were in 2012. By 2017 and '19 they are inhabiting much warmer water. What does that mean?

That's a big question, in a big temperature shift. And Louise Copeman from the Newport lab, is leading some field investigations in the Bering Sea and also some laboratory investigations to study: what does that mean?

What does this big shift in these crabs temperature mean? If she's studying both in direct thermal effects, you know what does the change in temperature mean? And then directly in these crabs vitals, their growth rate, their metabolism, the amount of lipids they can store. Also what does it mean indirect, indirectly from the food webs. We know that the cold water is associated with the sea ice. You know the cold pool is caused by spring sea ice. And there's no pool because there was no sea ice.

And we know that causes big changes in the ecosystem, starting with the amount of phytoplankton and the type of phytoplankton. And then including the amount and type of food that falls to the floor of the benthic ecosystem. So Louise is studying that with a fatty acid biomarker approach. Where she knows the fatty acid signatures, a lot of different organisms including diatoms which is associated with sea ice. And she's tracking that through the food web, to the crab. So she can see different crab in different areas where the food that they're consuming comes from and she can look at that those crabs conditions. It's a way that she will be able to link, you know the loss of sea ice to what's happening to these crab.

All right. Finally, there's this idea that's been, you know, that's been discussed by other authors. Aaron Fedewa et al., have a good discussion of it in their 2020 paper, but that the early juvenile stages could be limiting. They could be the limiting stages for this population, in its response to climate change. And mostly these studies are looking at the groundfish survey results and trying to guess what's happening in this first four years of life. I think this study, you know provides some direct evidence that some of these stages, at least stage-1, might require temperatures that are less than 2 degrees C.

And so whether this population in the Bering Sea could rebuild itself or whether the population could shift to the northern Bering Sea or whether the northern Bering Sea might become too warm for snow crab. I mean even the southern Chukchi Sea might have been too warm for the smallest stages in some years of the study. We just don't know. But it seems like species response to climate change is going to be really limited by what these small, how these smallest species, react to climate change.

And we know the very least about these stages. So obviously I'm a proponent for more study of these early stages. Many people helped with this project. Funding agencies, because there were so many different studies: from NOAA, UAF, BOEM, NOPP, and NPRB. And then many people also assisted with preparing crab sampling gear or helping with this presentation.

All the scientists and crew members who helped with the data gathering survey. There's a picture here from every survey. Although there's not all the scientists.

And then I would answer any questions.
[Applause]

[Emily Lemagie] Are there any questions in the chat?

[Deana Crouser] Not yet.

That was a great presentation, Dan.
Thank you so much.

[Participant] I have a question about, what, you know in your dream world, what additional sort of surveys or sources of evidence would you have to kind of be able to target those juvenile stages?

[Daniel Cooper] In a perfect world if we had enough money, there would be either part of the groundfish survey or our organization would run an annual survey.

You know throughout the Bering Sea. Where these juvenile stages are and we could you know, track down the environmental effects and we could provide, you know knowledge about what might be coming to the groundfish survey.

We saw a pulse of age-1s. We could follow that annually. And you know give some information about what's coming.

[Phyllis] So I remember a presentation, 100 years ago or whenever it was, the idea was that most of the spawning for snow crab is in the north. And that they make their way southward. Is that still a prevailing thought? Or did I misremember?

[Daniel Cooper] No, I think that's still the
prevailing thought. That there the spawning would take place somewhere south of that. Of you know either the northern part of the southern Bering Sea or the northern Bering Sea.

Spawning would and the currents would move the planktonic stages north. They would settle in the northern Bering Sea or the northern part of the southeastern Bering Sea. And then they have to walk south.

[Phyllis] Okay, okay. Thanks.

[Daniel Cooper] So the habitat has to have connectivity, you know between the habitat times. There has to be connectivity for all of the stages. And it's got to be within walking distance.

[Phyllis] And the adult males are the ones that often walk the furthest or whatever?

[Daniel Cooper] Yeah, I think so. There's one paper, I'm sorry I can't remember which one even talks about how far the males walk. They see them walking.

[Participant] Yes, thank you for the talk. This is more of an observation. So on the age-0 juvenile survey, in the Bering last year, we were doing bongo tows at night. We, it was warm water we weren't getting any crabs. And then the second we hit the cold pool it was full of Chionoecetes megalopa, which are much smaller than all these that you were mentioning here.

[Daniel Cooper] Well they're not much smaller than some of these.

[Participant] Oh yeah. But they were like, I immediately noticed. And I know how to look for them now.

I don't know what species, but I know how to genus them. And it's like these are all crabs. And it was like we get into the cold pool. There they were.

[Daniel Cooper] I mean I think that would be fascinating data. I don't think there are sources for that.

[Participant] Yeah, but the caveat is, is that the bongo does not stay the best. That's always what we have to say to that.

[Participant] But Jared Williams, is we've been giving the samples to him and he's been sorting whole samples for those.

[Participant] Oh really.

[Daniel Cooper] Yeah, I think that could be what's going on.

[Participant] Yeah.
[Deana Crouser] I got some questions in the chat.

James Overland wants to know about predation by P-cod.

[Daniel Cooper] Well I mean, we showed that there was this possible predation by the larger crab. And the smaller crab were in this area less than the 2 degrees C. I think that the 2 degrees C, defines the cold pool. And it seems to define a lot of the species distributions for a lot of fish, including cod.

And so it's possible that cod could be could be eating these fish. But I think, at the size we're talking about at least, the very smallest ones are probably smaller cod.

Yes I mean I talked a little bit about predation by larger crab. But it could be that these small ones require cold temperatures that has predation defense not only for crab, but for other species.

[Deana Crouser] Nice. Thank you.

[Participant] Yes, yeah I have one. This is kind of a follow up to Phyllis's question here. It's about, you know, temperature. And how mobile you think these crab are? Do we think that juveniles have been able to just move to colder areas? That you know were not within the study limits?

Or are they just not present? And I guess the follow up to that question, is you know do you have a larger scale picture. Of you know, are, were there such cold pools available? You know, beyond the study area where they could have moved.

[Daniel Cooper] Well. You know. Especially. But I mean, you can you can see, that sometimes the distributions of these crab were right up to the survey area. So your question is really good.

Like in 2017 I don't know what was going on east of that. Then you know, if these crab could you know, if they would have, the crab in the cold pool, the megalopa, could have settled closer to Russia. I mean that's possible. I don't have much to say about that.

But I will say that it's a well known yes. These crab sometimes butt right up against the survey boundary. And that is possible.

[Deana Crouser] Piggy-backing off of that question, there's another question in the chat from Alex Andrews.

Assuming most of the larvae are being transported north through the Bering Strait, what effect do currents have during warm and cold years on the settlement of the 7 millimeters
stages or less than 7 millimeters stages?

[Daniel Cooper] I mean that could be a big effect. You know recently, well most, I know most about 2017 and 2019. There were high transport years and so like some of the differences that you see here. But you know like, some of the differences, probably like this slide. [Indistinct]

[Deana Crouser] He was asking about the settlement of the less than 7 millimeters stages.

[Daniel Cooper] Yeah, I mean, I don't know. There are differences in the habitat, but in order you know for the smallest stages to have happened, they would have had to get pushed way north, out of the survey area.

I guess it's possible. I don't know. I don't know, somebody else might know more information about that, who has been studying those years with other means of transport. But off the top of my head, I don t know.

[Phyllis] Yeah, the transport has varied since 2010. And there's a fair record of it, between Rebecca Woodgate's data and our data that we've collected in a couple of places. And Calvin Mordy's done some work with it, because it influences how much nutrients make it north before the blooms occur.

When do you think spawning occurs?

[Daniel Cooper] Honestly I don't know enough about it, to tell you what's going on.

[Phyllis] Okay.

[Daniel Cooper] But I know that, I mean it's even, these crab to me are still pretty strange. I think they've got internal fertilization and I read some paper about how some years it might take the embryos like multiple years to even develop.

Don't quote me on that, anybody wants to know more about that should [indistinct]. But you know, I think, so like, I guess you would talk about spawning when these things were released. But I don't even know what type and you know they could have been alive for some time before that.

[Participant] Yeah, so I've always been fascinated by snow crab because for almost every other arthropod species, they get bigger as you go from low latitudes to high latitudes. It's called the temperature-size role. Why are they opposite?

[Daniel Cooper] I mean the only thing I can say is, the very little I've read about this is that people assume that the temperatures are so cold in the north and have been at least year round temperatures. The temperatures I'm presenting are the summer temperatures.

And you know if you look at the Chukchi Sea, even though it's been warming now in August most of the year it's you know it's like...

[Phyllis] Minus 1.7.

[Daniel Cooper] [Laughs] Minus 1.7. Yes. You know, it's so cold, maybe that limits them. I don't know. Maybe. I mean Louise might know more about that, or some other people.

I can't tell you exactly why the data would be reversed.

[Participant] Yeah, it's very interesting.

[Another participant] Maybe it's the one closest to it,
to the actual coldest limits, I-I...

[Participant] Yeah. Threshold.

[Daniel Cooper] All right. Thank you all for coming and listening to our talk.

[Phyllis] Very nice. Thank you.
[Applause]