Welcome to the Speak Up for Blue podcast session 129. Have you ever wondered what scientists do with mass strandings other than the fact that they're trying to get the mass strandings of marine mammals back into the ocean? What they do with the data that they collect or did you even know that they collected data? We're going to find out that yes, they do collect data and we're going to talk about what they do with that data to determine seasonality of distribution through strandings on today's episode of the Speak Up for Blue podcast. Stay tuned. Welcome to the Speak Up for Blue podcast, helping you get involved in ocean conservation. And now, here's your host, can't get the song "Bad Blood" out of his head, Andrew Lewis. Hey everybody. Welcome back to another exciting episode of the Speak Up for Blue podcast, your voice for the ocean. I'm your host, Andrew Lewin, founder of Speak Up for Blue dot com, marine ecologist and self-proclaimed ocean printer. And welcome to research Thursdays, I'm actually recording this late on Wednesday night just because this week has been so busy. However, I did not want to miss research Thursdays. It's one of my favorite days, it's becoming one of my favorite days because it allows me to stay current on what's happening with journals that are being published and articles that are being published. And normally, I cover something in marine conservation or ocean conservation. Today, I decided to look up PLOS1 under marine biology, just to see if there's a bit of a difference. There is a little bit of a difference. And today, we're going to be covering a paper that was done in an area that we've been familiar with, that we've covered before with looking at the Franciscana or La Plata dolphin in South America near Brazil. And we're going to go back to that region and we're going to look at the long-term seasonal and inter-annual patterns of marine mammal strandings in subtropical western South Atlantic. That's a mouthful. And we're going to explain all about that in just a sec. I just wanted to first thank our supporters on Patreon. That is Dr. Judith Weiss, Chris and Claire Jefford and Ron and Judy, thank you very much for your support. If you guys want to support our ocean conservation message, you can do so at SpeakUpForBlue.com/patreon. So, let's get back into it. Essentially, like I said, the title is a mouthful of this paper. It was done by Johannes Brado, Paulo Matos, Kebler Silva and Eduardo Secchi. It was published January 27th, 2016 in PLSO1. It is a free online journal and I'll put the link to the journal in the show notes, Nathan once Nathan writes it up, we'll put it in. And the show notes will be SpeakUpForBlue.com/session129. The gist of this article is the researchers wanted to know the species distribution patterns of marine mammals along the coast of the South Atlantic, the western South Atlantic, they call it the Subtropical Western South Atlantic, which is essentially encompasses Brazil, Uruguay, area. Now, we're familiar with this area, because we've covered this when we looked at La Plata dolphin or Francescana dolphin, both the same dolphins. This study went a little bit beyond that and looked at stranding data for a various timescale, a 38 year long data set spanning 1976 to 2013. There were 12,540 stranding events and within that, they counted 4,400 more than 4,500 Francescana species or individuals, 3,400 South American fur seals, 2,000 South American sea lions and 293 bought on those dolphins and 219 sub antarctic fur seals. So really five species made up most of the data that was found, which is kind of interesting. The reason they say, the reason for this, they say the authors go on to say that the continental shelf is actually fairly narrow. It's between, I believe 1,000 meters, 1,080 meters, I believe is the actual thing, because it can't be 100 meters. It's either 100 meters or 30 meters. Let me just look it up very quickly here, because I don't want to give you the wrong number, because it makes a difference, obviously a big difference in order of magnitude difference. So let's just see what it says here. Oh, sorry. It's 100 kilometers. So yeah, 1,000 meters. So 100 kilometers to 180 kilometers. Now that's a very narrow width for a continental shelf. So what they said is that there's the coastal species, like the species that I just sounded out, then they're the offshore species, which probably don't hang around the continental shelf or close to shore. And when they die, so when the coastal species that I just read out die, they have a more of a tendency to wash up to shore and become quote unquote stranded. When the offshore species die, there's a big chance that they just die and they just float to the bottom of the ocean, because they just can't reach shore and time before they float, before they sink to the bottom of the ocean. So there's a difference between that. So that's probably why 97% of the strandings involved five species. So that makes a big difference. But it really gives you an insight on why those species are found and when those strandings have occurred and what was happening at the same time in those strandings. So it's kind of interesting because they found that, you know, first, the article in the introduction really goes on about how marine mammals are normally observed, data collected on marine mammals, how it's normally done. Normally, it's aerial and shipboard surveys and they say it improves the knowledge of marine mammal distribution. However, these aerial and shipboard surveys are very expensive. The data collection can be challenging as most marine mammals, especially cetaceans, which are whales or whales and dolphins, are highly mobile and they spend a substantial amount of time underwater. So it's very difficult to see. I've been on shipboard surveys before and you see, you know, you use binoculars, you see a whale, you identify that whale, and you have maybe a couple of seconds to identify that whale. It goes below for about 20 minutes and then you try and predict where it's going to surface because it could take about 20 minutes before it surfaces and then you don't know where it's going to surface and it could be very difficult because if you don't see it in time, then you're like, okay, now I'm out of luck, right? So it could be very challenging to get those marine mammals. Then you got to say, you know, you got to look at pain for a ship and pain for, or pain for a plane. Very expensive. So that can be very difficult. So the strandings allow, you know, the researchers to actually look, although it's, you know, obviously strandings are not the ideal thing that you want to use for collection because it means that animals die or that animals have a high chance of dying. I guess in this situation, the strandings are the animals are not alive. They actually just wash up on shore. So it could be very difficult, you know, in terms of actually collecting the data when there's a lot of dead cetaceans, however, it could provide a really easy way to collect data when you just do beach patrols and you have people who monitor the beaches for these types of strandings and they collect the data. It happens more than you think. It happens more than you think. It's unfortunate, but it actually happens more than we think and sometimes most of the time the animals are already dead before they wash up to the beach and it could be age. It could be due to a lot of things. They mentioned some of the things here of what it could be due and it just lost my place of where that was. Shoot, I'll try and find it as I, as I talk, but it could be, it could be a multiple thing. Oh, here it goes. So inferring the causes of marine mammal strandings is difficult as the number of beach carcasses depends on many underlying processes. Example, at sea mortality. So that means they die at sea and they come in, they float in buoyancy, that mean a drift and detection probability. So it can be very difficult because you got buoyancy. Are the whales, are the mammals buoyant? Are they synced to the bottom? Where are they drifting? Are they drifting depending on the currents? And then of course the detection probability. What is the probability that you're actually going to detect this whale, you know, based on all the other factors. So it could be very difficult. However, when you have a long term data, like a 38 year data set, you can really establish trends in what shows up and what doesn't show up in the strandings. Now the results of this, of this study really looked at, it was really interesting actually. You may notice that for the bottom nose dolphin and the Francescana dolphin, or the La Plata dolphin, it really depended on whether the waters were productive, which usually coincided with a higher fishing pressure, okay. So what that means is when the waters are more productive, you're going to get the presence of more predatory fish and a lot more fish. Because what happens is there's a lot more plankton in the water. So during the winter and spring months, there's a lot more plankton in the water, there's a lot more outflow coming from the Plata River, which is a major river there. The southern current from the Antarctic comes up north and provides nutrient rich waters, collecting a lot of different fish, marine mammals, and so forth. And then what happens is it also attracts the fishermen, it also attracts the fishermen. And when it attracts the fishermen, that means there's a high fishing pressure. And in this area until about 2013, they use gill nets. And they started using gill nets and they said, okay, now that we have, you know, they started catching more French-scanner dolphins and bought on those dolphins, and then they would wash up on shore after they get thrown back into the water. So it was very discerning to see that. However, according to the article, legislation came into effect in 2013. They're hoping to see less strandings of these species, of these dolphin species because of this new law that came into pass so that we won't see these mass strandings. So you can tell by different years, so once the years for the dolphins where there was very high productive waters, you would see a decrease or an increase in strandings because there'd be an increase in fishing, and then at one point, the fish got less, the abundance was less, but they left, so the fishermen left the gill nets out longer. So even though there was less fish available for the dolphins to eat, the pressure for fishing went out because the catch per unit effort, so that means the amount of time it takes for a fisherman to catch a fish, had to increase because they weren't catching as many fish. So they had to increase the amount of times the gill nets were in the water, catching more dolphins and not catching as many fish, so a little bit counterproductive, but that's fishing, right? You know, fishermen want to meet their quotas. They want to make the maximum amount of money they can make because they're barely making the scrape and bias is, and that's what they do. Now in 2013, they actually stopped gill netting, so we're hoping to see a decrease in the frequency of strandings by these species. Now what's interesting about the seals, the three seals species, was the difference in the stranding frequencies was there was increased frequency when the water quality was, or when the environmental, environmental, I guess, quality or the environmental parameters of variables were different. So in times when La Nina was present, they had shifts and differences in food availability, lower food. So in 1999 and 2011, when moderate and strong La Nina events occurred during La Nina, productivity on the southern Brazilian continental shelf decreases and lower food availability is expected. So these were high stranding rates during these times because there was lower food availability. So these seals and sea lions did not have the resources available to sustain a high population. So what happens is with low food availability, you get more seals dying off, they actually come into, they actually float to shore. So after they die, so there's just more of low food expectancy expected. And so now that means there's an increase in the frequency of strandings of these species. So that was interesting. There was a bit, so for the South American fur seal and Arctic fur seals, it was really dependent on environmental factors. With the South American sea lion, the biggest thing, they actually had two differences. One was the fishing related mortality. And the other one was the, how did they term it here? I think they called it post pup phase. So in other words, what happens is when the populations rise, the birthing rates rise, and then you get a higher mortality because there's not enough food availability to feed all the, if there's not enough food availability to feed all the populations, you get the pups that once they're post ween, once they stop feeding off their mum and they need to fend for themselves, there's higher strandings of these type of these juveniles. I guess is what you would call them because they just can't survive on their own because there's either lack of food availability or they had to go to different areas. They couldn't stay in the area just because of competition and lack of food resources or just resources in general. So you saw a lot of, of beechings or of strandings at that, at that respect. So you know, they're, they had both. So the dolphins had mostly fishing related pressures that increase the strandings. The Arctic and America, South American fur seal was more about the environmental factors that would play a role and really affect how it affected the food availability. And then you had the South American sea lion, which was really affected by both fishing related factors and environmental factors. And really it came down to, you know, the amount of population beforehand. It came down to the environmental parameters that were available, climate change plays a role in switching the food source distribution. That can affect sea lions. That can affect really anybody, but it affected the sea lions. So that made a big change. And of course there's just so many animals, individuals that it affected the actual population size and they just couldn't grow to the population size that they wanted to. So that was essentially the, the study. I found it interesting, one, how they use strandings to actually detect trends in population size and trends in how marine mammals, coastal marine mammals in this area are affected by environmental factors and human related disturbance such as fishing. And of course with the absence now of gill netting, it'll be interesting to see if the dolphin species rebound and the Americans and the South American sea lion rebounds. Just to see if those kind of management tools work, those legislative tools work, of course, it all depends on the participation from the fishing community and enforcement from the government to make sure that the fishing community is actually participating and making sure that the legal tool is being put in place and is being abided by. So yeah, it's an interesting study. I really like it. We haven't done a marine mammal study in a while and this was more on the distribution, but it does play an effect and it does have implications for management. We need to know what these seasonal and international patterns are. And this study really, really does it. It's an easy way to get data is because you just have to monitor beaches. You don't have to pay for a boat. You just have to pay for people to wander around the beaches in this area and basically count and identify species and of course get rid of the bodies, I'm sure. But it's part of the process. So I think it's a nice, it's an easy way to collect data. It's a cheaper way to collect data. And if you have a data set that's a long-term data set, so this one I think was 38 years I mentioned, that is a long-term data set that you can really decipher trends over that period of time. And in the article, if you read it more carefully, I just kind of gave you a summary, but if you read it more carefully, they talk about specific years, what happened in those years or what happened in the previous years that really resulted in the population or the frequencies or inf frequencies of strandings by the five species that they really studied. And there's also a section where they look at other species within the study that may not have had as many strandings just to kind of give you a bit of a pattern or trend to see if there is one about those species. So anyway, that's it for today. Like I said before, the link and the information for this podcast or for the study will be on the podcast show notes, which is speakupforblue.com/session129. Stay tuned for tomorrow. We're going to have an Ocean Talk Friday with Nathan Johnson talk about all the lovely things that we do that have happened this week that may not have been dwelled in detail on this podcast this week. So we're going to briefly talk about them tomorrow on Blab. So you can check that out. I believe this show will be at 7 p.m. Eastern. I'm going to schedule it. All you have to do is just look for schedule post for tomorrow on blab.im. And you can come in, participate, listen in, ask questions and so forth. And maybe this time we'll open it up to a couple people and they can actually come in and talk and we'll record it all and put it on the podcast. So thank you very much. You've been listening to the speakup for Blue Podcast. I am your host, Andrew Lewin. Happy Thursday. Thank you for your research Thursday and happy conservation.
