(Decoded) Body condition influences ontogeny of foraging behavior in juvenile elephant seals

Original Title - Body condition influences ontogeny of foraging behavior in juvenile southern elephant seals. Full article (14 pages) can be found for free here:

Title Decoded - Body condition can have an affect on the development of feeding behavior on young southern elephant seals.

TLDR: The development of juvenile southern elephant seal feeding behavior is understudied. These big boys and girls are hard to keep track of and study since the ocean is a big place. With new technologies it may be possible to observe how their behavior develops. Since their mothers don't teach them anything, they have to learn how to find food on their own. By looking at their diving and feeding behavior immediately after leaving their mothers, there's evidence that suggests that the development of their feeding behavior is a combined result of where they look for food, and how physically fit they are (in this case fit= blubber thickness.) Basically, the thicker boys and girls that looked for food out in the open ocean had a better chance of success and long term survival than the ones that were thinner and looked for food in shallower waters. This might mean that they are quite smart and are able to adapt/learn quickly or they have strong instincts or some combination of both! This study, would have been very difficult (if not impossible) if it weren't for new technologies. The study only looked at a few individuals though, so it is important to continue researching this if we want to help understand and save this species.

(Personal thoughts on the paper can be found at the bottom)

Words/phrases to know:

• Forage/Foraging - the action of searching/looking for food

• Ontogeny - development in an organism. Ontogeny of behavior = development of behavior.

• Pinnipeds - Name for the family of animals that contain seals, sea lions, fur seals, and walruses

• Buoyancy/Buoyant- how well something floats in liquid (in this case sea water)

• Spatial Dispersion - how a species will distribute themselves within an area.

• Pelagic and Benthic - Pelagic is all open ocean waters. Benthic is ocean floor regardless of depth. See infographic here ( Note: I do not include these terms in the decoded version and instead refer to both as open water and sea floor respectively.)

Intro (Decoded): Animal behavior is often linked to evolutionary history but there have not been many studies on the development of these behaviors, especially in southern elephant seals. Southern elephant seals spend most of their time out at sea, coming to land to mate/breed and to molt. Otherwise, they are out in the open ocean foraging and migrating. Once on land they are fasting that entire time. These animals are hard to study in general because it is very challenging to keep track of them for data collection and juveniles, unfortunately, often die early. There could be many different things that affect the development of foraging behavior in juvenile seals like: body size, growth rate, lung capacity as well as learning ability. Juveniles could also behave differently based on the environment they are foraging in. Adults can out compete juveniles both mentally, and physically as they have more experience in finding food and can travel further and dive deeper. If juveniles are unable to catch prey in a particular area, then they must learn to adapt and how to adjust their foraging skills. Thanks to new technology, it is easier to track and study these animals. Pinnipeds can be studied because we are able to attach tags and data collecting devices safely and for a long time.

Southern elephant seals forage independently once they leave their mothers so there will be little to no effect on the development of foraging skills and behavior due to parent influence. Elephant seals, to reach the deep depths, perform drift dives, passively sinking deep into the ocean with minimal swimming effort. This can be affected by the animals natural buoyancy (or blubber thickness). Fat seals sink slower than skinnier seals due to the higher buoyancy of blubber. There are studies on southern elephant seals for two sub-antarctic islands and at the Macquarie Islands but not at the Kerguelen islands. (Thesis Decoded:) If there are juvenile seals of different body conditions, then we should expect to see changes in the development of their foraging behavior, specifically in the Kerguelen islands, after they are newly weaned from their mothers. By using new technologies, it's also possible to get an idea of where they go to forage, how they change their behavior based on their body condition(buoyancy), how they compare to adults who forage, and what their physical limits are.

Methods (Decoded): Procedures were approved by the Ethics Committee of the French Polar Institute. 20 juvenile southern elephant seals and 9 adult female southern elephant seals were tagged with various data gathering devices. Adult males were not used for this study due to difficulties of tagging. They would also not be a good comparison to juveniles because they tend to dive to more extreme levels. By using an accelerometer, a device used to measure how an individual is accelerating, it is possible to measure swimming effort and time spent trying to capture prey.

Body condition was measured by extrapolating how an individual would drift dive and how buoyant they were. Slow drift dives meant fatter seals. Faster drift rates would mean leaner seals. (Body condition = blubber = buoyancy)

Spatial distribution, physical limits, were measured by using various statistical analyses.

Results(Decoded): All 20 juveniles left their colonies in December 2014. Many went south-west whereas only two went south-east. After 100 days 8 tags stopped transmitting, which meant that these individual seals had passed away. Initially juveniles seemed to spent twice as long trying to capture prey than adult females.

After 100 days out at sea, the time spent started to match adult females. Most juveniles would forage out in open ocean and two were observed foraging near the Kerguelen plateau in the benthic zone. Juveniles would increase their diving depth over time reaching an average of 227 meters after 8 months. Adult females on average were diving to 474 meters. Over a period of 150 days, some juveniles were observed undergoing changes in body condition over 3 temporal phases. They start positively buoyant transitioning to negatively buoyant in the 1st phase (departure after weaning), negatively buoyant transitioning to positively buoyant in the 2nd phase (central open ocean phase), and neutral to positively buoyant in the 3rd phase (return to land.)

The individuals who were foraging by the Kerguelen plateau were mostly negatively buoyant while the ones foraging out in open ocean waters were able to reach positive buoyancy at some point. Overall 11 survived while 9 died.

Discussion(Decoded): Spatial dispersion of juveniles is consistent with previous findings with southern elephant seals found around Macquarie Island. Juveniles dove shallower and had shorter dives than adult females. Adult females are known to be able to adjust their swimming effort in relation to their body condition and it appears that juveniles are able to do the same. This suggests that juveniles are able to very quickly adapt to foraging on their own perhaps as a result of rapid learning and/or instinct.

After leaving Kerguelen Islands post weaning, juveniles would spend twice as long as adults capturing prey but their buoyancy would drop, suggesting that they either were not getting much food, or eating less nutritionally dense foods. After 100 days out at sea, time spent would match adults and their buoyancy started to increase suggesting that they were either more successful in capturing prey or eating more nutritionally dense foods or a combination thereof. It appears that juveniles also adjusted their behavior to match their prey's daily behavior of migrating up and down in the water. Despite their increased success they are still only diving about half the depth as adults which means that adults and juveniles may not be feeding on the same resources.

Juveniles were observed to spend less time at the surface breathing , which could be due to their smaller size - being able to replace their oxygen stores faster than larger adults. Adult females however, actually decreased their time at the surface following a highly successful foraging dive which juveniles could not replicate. This suggests that despite their "faster" recovery rate, they lack the oxygen stores and endurance that adults do to go on multiple foraging dives and need to spent time at the surface.

For the 3 phases observed (initial departure post weaning, time at sea, and return to land,) there is evidence suggesting that those that are negatively buoyant (not as much blubber) may have a harder time surviving during the 1st phase. This could be due to not having a thick enough blubber layer for juveniles to survive off of while they figure out how to forage. In the 2nd phase as juveniles gained more success in foraging and their buoyancy increased (getting fatter) it may be ideal to achieve neutral buoyancy to be able to swim further and explore different foraging areas. In the 3rd phase, juveniles that returned positively buoyant remained on land longer during than juveniles that returned negatively buoyant. Indicating that buoyancy (blubber thickness/body condition) could potentially be a driving factor in when a seal returns to shore and for how long.

Conclusion(Decoded): By using new technologies like accelerometers and satellites, it's possible to get data on hard-to-study animals out in the oceans. With this technology it's possible to gather evidence in developmental processes of behavior like foraging, or habitat shifting in marine diving predators like seals. Overall juveniles could not forage in the same range as adults, but were still able to adjust their diving behavior to compensate for their body condition (buoyancy.) It is important to keep studying this to increase sample size to really understand how habitat differences and physiological changes can affect the mortality of infants. This could lead to providing better models to make predictions on populations of seals.

ConservAsianists Thoughts:

Hoo-boy this was a long one at 14 pages. It's a pretty interesting study and asks an interesting question on how animal behaviors develop, which many people don't really think about. It provides evidence that behavior can be both seemingly instinctual but also learned as we saw a difference in how some seals chose to forage off the plateau vs out in the open waters. It's amazing the level of data we can collect with new technologies but also shows that nature is not so easily studied, especially out in the ocean. Y'know how more than 80% of the ocean remains unexplored? YEAH. THAT'S BECAUSE IT'S SO HARD TO STUDY. What I thought was most interesting, is how (in this instance) the adults and juveniles would try and spend less time at the surface if their foraging dives were going well, and how they must be foraging at different zones since adults can dive deeper than juveniles can. This could be key in things like fisheries management and species conservation. If we are taking food from a zone where juveniles are foraging from then we could be preventing the juveniles from getting enough food to get into adulthood (dey ded.)

Although interesting, be sure take the results with a small grain of salt(i'm thinking fine grain) as the sample size is quite small at only 11 individuals. The authors definitely recognize this which is why they suggest doing a future study.

What I disliked about this paper is that during the introduction, the authors do not give much of a debrief on southern elephant seals (I added my own quick sentences about them in the "Decoded" portions) and assumes that the reader already knows that these animals spend most of their time out at sea only coming to land for a few months out of the year. This can make it hard for readers who are unaware about these animals to follow along as to why they chose to research the animals for the way they did and how the results came out to be the what they were. It's also just full of jargon making it just plain hard to read, and I'm not talking about the methods/materials section because, smarter more statistically savvy people then me probably understand all that better, but for example you have sentences like these:

"Day et al. (2017) showed that PrCA rates positively influenced post‐dive surface duration in adult females, likely because catching prey induces higher energy expenditure through increased swimming effort, turning movements, and digestive costs. The adult females we studied showed the contrary and tended to decrease their recovery time at the surface after a high level of PrCA rates (> 0.1, Figure 6) likely to minimize non‐foraging time. This was also the case for juveniles, even if the slope coefficient of the relationship was lower compared to adult females."

...Yikes...It basically means that in a previous study, when adult female seals spent more time foraging and had very successful dives, they had to spend more time at the surface because they had to expend more energy. But the group of individuals observed in this study all did the opposite and they actually spent less time at the surface probably because they wanted to go back down and get more food. Even the juveniles did this, but they couldn't reduce the time at the surface as well as the adults could. Phew.

This right here is why I wanted to do this website because reading those sentences are rough so I hope that those of you who read this abridged version can understand it. Language like this, is great for academic papers and for those actually in the field, but what about the rest of us? I for one refuse to continue to read sensationalist articles talking about the next cure for cancer. If the language I used is still too jargon-y and hard to understand then please let me know so I can find something that fits all of us! Thanks for reading.

P.S. Here's my sensationalist click-bait title for this article: New technology shows that skinny seals are being oppressed by fat seals. Click here to find out how. Reason 2 will blow your mind! CNN will you hire me now?