Sea Lions: Human Presence As a Variable in Social Behaviors*

(*): Student research from Scientific Gorlok, a publication from the Biological Sciences Department at the College of Arts & Sciences, Webster University. Download full May 2018 issue (PDF) here.


Our research goal is to observe the human impacts on the behaviors of sea lions within the Galápagos, specifically San Cristóbal, and Española. Conservation efforts need to be evaluated on their effectiveness. This research can be used alongside other behavior studies to better evaluate conservation efforts on the Galápagos islands. Various behaviors have been associated with social mammals such as stress and aggression and how ecotourism plays a role in it.

According to Wolf and others (2008), certain behaviors may be associated with evolutionary backgrounds. Some example behaviors are docileness which can be tied to sex-specific migration behavior. This behavior suggests that males are more likely to cross over habitat boundaries, while females tend to stay short range. Males also show long-term social dominance hierarchies for territory.

Specifically, our research will expand upon the knowledge gained by Cassini and others (2004) in South America with their research on fur seal colonies. The take-home messages are applicable to other marine mammals. There are numerous data on Australian sea lions and effects of ecotourism. Our research will be complementary to studies already done, but at the same time expand it out to consider regional differences.

Our research coincides with research on stress in social animals. This is significant because scientists do not fully understand the extent of the effects from human activity. Scientists conducted research on sea lions in the Dollard estuary of the Wadden Sea located in the northeast of the Netherlands where they noticed alertness to humans was one behavior associated with stress (Osinga et al. 2012).

With that in mind, we focused our research questions to data that can be obtained without permits and special attention from park personnel. Individuals are not allowed to touch or interfere with activities of the animals.

We believe these islands are a good foundation for testing the effects of humans on social organisms (San Cristóbal) while having a control group (Española) to compare to. We tested two hypotheses. The first hypothesis is that sea lions from Española will be more curious than the ones from San Cristóbal because they are exposed to humans less frequently. The second hypothesis is that male sea lions and female sea lions will vary in their behavioral characteristics; males will be more aggressive, vocal, and group up more while females will be more docile and attentive of pups.


We researched two different colonies of the Galápagos Sea Lions (Zalophus wollebaeki) on the islands of San Cristóbal and Española within the Galápagos Islands. San Cristóbal is a human-inhabited island having roughly 5,000 permanent residents where they pass by the boardwalk beside our observed group of sea lions. San Cristóbal contains an airport, cars, motorcycles, boats, and many buildings all over the island, where the sea lions are exposed daily to human activity. Española is an uninhabited island, where the sea lions do not see many humans. This island is protected and it does not have buildings or consistent human activity.

Figure 1. illustrates examples of the main behaviors observe: barking (top left), docile behavior (top right), and two examples of affection: nursing and kissing (bottom left and right).

Each researcher conducted five observations, one per day, of sea lions on San Cristóbal and one observation on Española. For San Cristóbal, we collected our data in the evenings between the times of 8pm and 9:30pm and observed for thirty minutes for each observation. For Española, our data was collected around noon. Each researcher observed the following expressed behaviors: aggressiveness, affection, barking, docile, playfulness, and acknowledgment of humans (Figure 1). For aggressiveness, examples of some actions included pushing another sea lion, growling, and head-butting. Actions such as kissing, mothers feeding, and cuddling were examples for affection. For docile, examples included the sea lions laying around, not acknowledging anything. Playfulness included actions such as swimming or moving fast. For acknowledging humans, we collected data for anytime the sea lions came up to us or expressed a behavior listed above except docile when we were near them. While sea lions can be quite inquisitive, we maintained a safe observation distance.

Two researched focused on behavior within smaller subsets of sea lions, while another observer focused on the behaviors of the overall group. We conducted our research in comparison to males and females, and one researcher added an extra set for sea lion pups.


Noting the variation in observation methods, we needed to verify that our methods were comparable and able to be pooled together. To do this, we performed a correlation analysis using cor.test in the R base statistical package (R Core Team, 2017) between data collected using Method A and Method B. This test evaluated how well the data aligned with each other. We conducted a correlation test with the data pooled across both islands. We also performed paired t-tests using t.test in the R base statistical package (R Core Team, 2017) comparing method type on each island. This test evaluates whether the data is significantly different from each other. We chose to use the paired test because the same colonies were observed.

Next, we compared the sea lion behaviors and acknowledgment of humans over a period of 5 days on San Cristóbal and 1 day on Española. The acknowledgment of humans on San Cristóbal for five days was averaged and compared to the average human acknowledgment on Española, to test for a possible relationship between human activity and sea lion behavior.

After that, we addressed various behaviors and their implications. We compared the means of barking, docile behavior, and affectionate behaviors by the sea lions on San Cristóbal among the days of observation, to test for temporal variation in behavior. In addition, we compared the behaviors affection, aggression, and docileness between the sexes. To do this, we created boxplots to represent the data for males and females over the entire duration of San Cristóbal observations. We also compared a mean number of individuals for observed behaviors of pups in a bar chart.


After collecting our data, we verified that our methods were within an acceptable range to be pooled. We display the linear models (Figure 2). The correlation analysis compared Method A (on the x-axis) with Method B (on the y-axis). The graph on the left is for San Cristóbal individually, the middle graph is Española individually, and San Cristóbal and Española combined is displayed on the right. Using default cor.test settings, correlation coefficient values are 0.273 for San Cristóbal, 0.353 for Española, and 0.273 for the islands combined. The p-values are 0.0349, 0.261, and 0.0201, respectively.

Figure 2. Linear models comparing Method A vs Method B on San Cristóbal individually(left), Española individually(middle), and San Cristóbal and Española combined(right). Correlation coefficent values are 0.273 for San Cristóba, 0.353 for Española, and 0.273 for the islands when combined. The p-values are 0.0349, 0.261, and 0.020, respectively.

The t-test for San Cristóbal had a p value of 0.1729, t.statistc of 1.38, and a mean of difference of 0.52. The t-test for Española had a p value of 0.0081, t-statistc of 3.225, and a mean of difference of 1.125. The t-test for San Cristóbal and Española combined had a p-value of 0.05575, t.statistc of 1.9449, and a mean of difference of 0.618. Española data compared by method is statistically different from each other. San Cristóbal data failed to reject the null hypothesis that the data is statistically different by method type. Since the San Cristóbal and Española combined data also failed to reject the null hypothesis, we used only the data collected via Method A when comparing the islands.

We compare average sea lion acknowledgment of humans between San Cristóbal and Española. We observed that on average there was a greater acknowledgment of humans by sea lions on Española than San Cristóbal, as predicted. The average acknowledgment of humans on San Cristóbal was 0.467 while the corresponding value on Española was 1.667 (Figure 3). The human acknowledgment by sea lions was much larger on Española where they are not exposed to human activity as often.

Figure 3. Average acknowledgment of humans between two islands; San Cristóbal (SC) and Española (E). Mean acknowledgment of humans is more than twice as large on Española (1.6667) than San Cristóbal (0.4666666).

Next, we compare average acknowledgment per capita for each of the five days on San Cristóbal and the one day on Española. We observed that out of all the days, sea lions acknowledged humans on Española more than on San Cristóbal per capita (Figure 4). Although acknowledgment varied by day on San Cristóbal, 0.012 on day one, 0.020 on day two, 0.013 on day three, 0.025 on day four, and 0 on day five, the acknowledgment was much larger on Española.

Figure 4. Average acknowledgement of humans per capita over a period of five days on San Cristóbal and one day on Española.

We then compared the various Galápagos sea lion behaviors for San Cristóbal each day per capita (Figure 5). These individuals were exposed to human behavior and were observed at night around 8pm and 9:30pm. For the first observed behavior, barking, the first three days looked similar, so there is no difference in the data. However, there was a decrease on day 4 compared to the first three days. The average per capita went from 0.06 on the first three days to 0.03. On day 5, the barking had a large increase compared to all the days. Comparing it to the first three days, the fifth day was 0.09, which is a 0.03 increase. The next observed behavior, docile, did not seem to have any differences between the days (Figure 6). The last observed behavior, affection, seemed to have some important differences. Days 1, 4, and 5 are similar, indicating that there was no effect of day. They all have an average per capita of about 0.03. On day 2, there was a large increase in the number of affectionate individuals, which increased to 0.04. On day 3, there seemed to be a large decrease in affectionate individuals, which was 0.02.

Figure 5. Sea lion behaviors over a five day period on San Cristóbal. The brackets represent the standard error for the average of that particular behavior for that day.

When separated by sex, the three most observed behaviors were affection, aggression, and docileness (Figure 6). Females had a higher average than males for affection. Males had a higher average for aggression. Females had a higher average of docileness. Males displayed a great deal of docileness too; though, there were some outliers.

Figure 6. Boxplots of data for which sex displayed which observed behaviors on San Cristóbal.Blue represents females. Red represents males. The x-axis is behaviors observed. The three behaviors referenced are affection (left), aggression (middle), and docileness (right). The y-axis is number of individuals.

One outlier is for male affection. Other outliers included one outlier for female docileness and two outliers for male docileness. The pups show a trend similar to the females who care for them (Figure 7). The most influential data collected is for the behaviors affection, docileness, vocal, and human acknowledgment.

Figure 7 Boxplot of pup data for each behavior for the entire time spent on San Cristóbal. Behaviors are listed from left to right: affection, aggressive, docileness, human acknowledgment, playfulness, and vocal. The x-axis is behaviors, while the y-axis is the average number of individuals.


Our data collection is similar to other behavioral studies with marine mammals. In Osinga and colleagues’ study (2012), seals were observed during pupping and lactating season for 15 to 30 mins at a time at least twice a week for four years. They compared seal reactions to anthropogenic events such as airplanes, boats, cars, horse riders, pedestrians, and cyclists. They found that most disturbances caused seals to at least become alert and in some cases flee into the water. While we did not directly observe and record alertness, we do believe it to be similar to acknowledgment of humans. When seals flee into the water it causes a potential risk of juveniles being separated from their mothers. We did not observe fleeing behavior, but we did notice barking behavior between pups and females that were separated. Our results (Figure 7) support this relationship of vocalization between mother and pups in San Cristóbal.

According to Wolf et al. (2008), sea lions are social animals. The offspring are dependent on their mothers and have long-term memory and cognitive abilities. Many of these behaviors derived from a pre-zygotic isolation such as by habitat (Wolf et al. 2008). Our data corresponds to females being observed as more docile than males (Figure 6). Wolf also describes males as very territorial. Figure 6 shows that males are observed to be more aggressive than females. Affection and docileness are fairly consistent throughout the days. Barking data has a dramatic increase on day 5, for which we do not know the cause.

Overall, we have found support for our primary hypothesis that Sea lions from Española will be more curious than the ones from San Cristóbal because they are exposed to humans less frequently (Figures 3 and 4). Curiosity encompasses more than one behavior. Curiosity may manifest in the forms of excitement, agitation, or even fear. Building upon data from Cassini and colleagues (2004), animals that are not fenced off from tourists will have stronger behavioral effects from the intrusion of humans. Behaviors such as aggression and retreatment into the ocean are expected responses. The conditions of Española support this by being uninhabited by humans and lacking man-made structures such as fences. The sea lions on Española took a strong interest in humans since we were moving through their territory as a large group. Cassini acknowledges that groups provoke stronger responses than one or two people. Groups are bigger threats. On San Cristóbal, the conditions include fencing and raised ground from the beach. These structures create a boundary line. With these blockades, sea lions have smaller behavioral effects, viewing the fencing as an obstacle that protects them from attacks (Cassini et al. 2004). Behaviors such as aggression and fear are expected to be reduced, as long as humans are respecting the compromising boundaries.

For the follow-up hypothesis, our results comparing male and female expression of traits supports the idea that females will be more docile and affectionate, while males will be more aggressive (Figure 6). In addition to this, the graph for pup behavior displays that pups demonstrate similar behaviors to their mothers. The graph also demonstrates that pups are susceptible to stress from humans.

The main weakness of this study is the amount of time. The length of stay and amount of observations on each island need to be extended. Española has too few observations for it to be a reliable dataset and has potential to skew the overall data. Another weakness is that we did not conduct enough research on the species prior to arrival to focus in on a smaller range of behaviors. This lack of research spread our data too thin with us focused on too many variables at once.


  • Cassini, M.H., Szteren, D. & Fernández-Juricic, E. J Ethol (2004) Fence effects on the behavioural responses of South American fur seals to tourist approaches. Journal of Ethology. 22: 127. DOI:10.1007/s10164-003-0112-0
  • Hadley Wickham (2011). The Split-Apply-Combine Strategy for Data Analysis. Journal of Statistical Software, 40(1), 1-29. URL
  • Osinga, Nynka, Nussbaum, Sandra B, Brakefield, Paul M, and Udo de Haes, Helias A. (2012) Response of common seals to human disturbances in the Dollard estuary of the Wadden Sea. Mammalian Biology, 77(4), 281-287.
  • R Core Team (2017) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL
  • Wolf, J.B.W., Harrod, C., Brunner, S., Salazar, S.,Trillmich, F., Tautz, D (2008). Tracing early stages of species differentiation: Ecological, morphological and genetic divergence of Galápagos sea lion populations. BMC Evolutionary Biology, 8, 1-14. doi:10.1186/1471-2148-8-150


Meredith Harrison is a biology major with an emphasis on biodiversity at Webster University. She aspires to be involved with marine biology and work.

The coolest things I saw were from the ocean. I got to snorkel for the first time in the Galápagos. It encouraged me even more to get my diving certification this summer. I saw eagle rays, hammerheads, and sea turtles for the first time. Seeing sharks in their natural habitat was the most memorable part of the trip. I saw schools of fish so big that it blocked out the sunlight below. Some schools of fish looked like they were sitting in rush hour traffic in the middle of the water. I did not know that stingrays travel in packs. I saw them sneak up on each other and then rebury themselves in the sand. Cerro Tijeretas was my favorite spot on San Cristóbal. I highly recommend snorkeling here.

Amber White is a biology major with an emphasis in research at Webster University. Her hobbies include painting and photography.

The coolest thing that happened to me on the field was when we were taking pictures on the beach La Lobería, this male sea lion swam up to us and wanted to get his picture taken with us. It was really neat to have such an amazing experience like that. It really surprised me how fearless he was.

Lauren Coleman studies as a biology major with an emphasis in health and medicine at Webster University. In her free time, she enjoys running and playing soccer.

An amazing experience that I had while in the field was when we were on Española and our tour guide was talking to us, we were all standing in a circle and this juvenile sea lion came waddling over to us. He was very energetic. After trying to get everyone to play with him, he finally laid down in the middle of our group and went to sleep. This is a perfect example of how trusting animals are on the Galápagos and an experience you won’t get anywhere else.