Part II: Is that a healthy pup?

With a few measures we can check on the health of pup and find out about mom too

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April 24, 2018
Brian Fadely
Biologist

 

In my last post, I shared how we use pup weights and lengths to calculate a condition index to better understand the health of the pups. When we handle Steller sea lion pups that will be marked, we also collect blood, tissue, and fur samples. Collecting blood and other tissue samples allows us to evaluate health status in another way involving work in a lab. We look at blood chemistry and hematology parameters, to test for signs of disease, contaminant exposure, or other systemic concerns.

Some degree of clinical issues or disease is normal to find in any wild population; we’re interested in determining whether there is evidence of clusters of disease, contaminant exposure, or other concerns at a rookery or greater area. This can provide insight into local conditions that may help explain population declines or lack of recovery. Samples are collected while the pup is gently but firmly restrained by hand.

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Collecting a blood sample from a restrained pup. The restraint board helps prevent wriggling so the procedure is safe for the pup and handlers.

The board that we place the pup on helps prevent wriggling so the procedure is safe for the pup and handlers. We looked at blood chemistry and hematology profiles of 1,231 pups sampled during 1998-2011 throughout Alaska. We found no indications that pup condition was compromised during their first month after being born, including pups within the declining parts of the Aleutian Islands (Lander et al. 2013).

Exposure to heavy metal contaminants (like mercury) is a concern since Steller sea lions are apex predators, or predators that feed at highest trophic level. In other words, Steller sea lions eat prey that are high up in the food web. That means, if there are contaminants in an environment, the contaminants can bioaccumulate and biomagnify through the food chain. Exposure to high levels of mercury can cause neurological disruption that may impact health and consequently survival and reproduction. Pups accumulate mercury during gestation in utero (while they are a fetus in their mothers), and again once they are born and suckling milk from their mothers. In a project led by collaborators at the University of Alaska Fairbanks and Alaska Department of Fish and Game, we’re investigating the mercury burden of pups throughout their range in Alaska and Russia. We shave off a small patch of hair from the pups when we handle them and are then able to measure the mercury content. Specifically, we can figure out the mercury concentration the pup was exposed to from its mother over a period of several months during gestation.

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The patch where hair was removed for a sample to measure mercury content is evident on this pup chilling with mom at Agattu/Gillon Point. 

We found that pups in some areas of the endangered western population had a higher mercury exposure than pups from Southeast Alaska (Castellini et al. 2012). The greatest exposure is shown by pups from the Gillon Point rookery on Agattu Island, with three pups showing exposure levels known to cause neurological effects in other fish-eating wildlife (Rea et al. 2013). If you look at the figure below, you can see the difference in mercury exposure (median values are shown by colored lines and average values by black lines) between pups from Agattu Island and other rookeries can be seen in this boxplot that was published in Rea et al. (2017).

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We do not have direct evidence that this exposure to mercury during gestation leads to health consequences for the pups and their subsequent survival, nor that it impacts adult reproduction. But, these levels of mercury exposure do indicate that further research is necessary to better understand the role of contaminants in the ecology and biology of Steller sea lions.


I am a research wildlife biologist with NOAA Fisheries Alaska Fisheries Science Center in Seattle, in the Alaska Ecosystems Program where I’ve studied Steller sea lions and northern fur seals since 2000. My primary research interest is vertebrate physiological ecology, which at NOAA Fisheries translates into studying sea lion foraging behavior, health status, and body condition to help address conservation questions and wildlife management issues.

Part I: Is that a healthy pup?

Part 1: Studying the condition of sea lion pups

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April 10, 2018
Brian Fadely
Biologist

 

When we handle Steller sea lion pups that will be marked, we also check their condition and health status, similar to when you take your pets to the veterinarian for a check-up.  Collecting health data can give an indication of local environmental conditions, and allows testing of some hypotheses for the population decline.

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Pups are weighed by holding them in a small hoop net and measuring with a digital scale suspended from a tripod. Photo by Kristen Campbell.

While we are handling the pups, we weigh them and measure their length and girth as indicators of condition. We look at these measurements relative to the weighing date (since we don’t know a pups birth date), as well as, their weight relative to their length. Both are used as indices of body condition and help us explore trends among pup measured across regions or over years.

Weighing and measuring pups is straightforward, as simple as suspending them from digital scale while nestled in a hoop net. Length is measured from the tip of nose to the tip of their tail, and girth is measured around the body just behind the front flippers.

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A pup that fell asleep in the net while being weighed

Pups are born between late May and early July but half of the pups are born by June 10th. For consistency, we try to sample pups between June 20th and July 7th, which means we’re sampling them when they are 12-25 days old, but possibly 5-37 days old. At this young age, the size and health of the pup largely reflects the mother’s condition while she was carrying the pup, since about April. Pup condition can vary with many factors including age and size of the mother and the local foraging conditions she encounters, which we typically don’t have any way to directly assess.

Looking at pup measurements collected throughout the Aleutian Islands from 1990 to 2017, the weight of female pups (a total of 1,958 measured) has ranged between 33 and 97 Ibs (15 to 44 kg), or an average of 62 Ibs (28 kg). The weight of male pups (a total of 2,234 measured) ranged between 29 and 115 Ibs (13 to 52 kg), with an average of 75 Ibs (34 kg). Male pups tend to weigh about 11 Ibs (5 kg) more than females. Generally, pups grow just under a pound (over a third of a kg) per day.

Just as with human infants, we can compare the size of any pup against all others to determine whether they are relatively large, small, or about average. In the figure below, the sizes of pups from Hasgox Point on Ulak Island (white squares) and Gillon Point on Agattu Island (black circles) are compared to all other Aleutian Island pups (light gray circles) for females (F, left figure) and males (M, right figure). It’s evident that while some individuals are small or large compared to others, the size ranges of pups from these islands are similar to all others.

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In these plots, each dot represents the weight of a single pup. The left plot shows females and the right, males. The two sites you may be familiar with are Hasgox Point on Ulak Island (white squares) and Gillon Point on Agattu Island (black circles). The light gray circles are all other pups in the Aleutian Islands.

Since we don’t weigh the pups on the same day and they put on weight each day as they grow, to compare pup condition over years or between rookeries, we create a condition index. The condition index compares the weight we collect to the weight we would expect to see on the weighing date, or to the weight expected for their length. This condition index is a ratio of the measured weight to the expected weight which is calculated from doing a regression of all pup masses by weighing date.

In the figure below is called a box plot (also called a box and whisker plot). This is a great way to visualize data. The condition index ratio we described above is plotted in the following two figures. Median values (black lines) are shown within the 25th and 75th data percentiles (boxes), and outlier values (black dots) are plotted outside of the whiskers (1.5 times the percentile range, showing data dispersion). This box plot above shows the data collected from female pups measured from 1994 to 2017 at rookery sites within the area we have remote cameras deployed in the Aleutian Islands. Essentially, if the observed and expected weights are the same, then the condition index ratio is 1.0 (the horizontal dashed line).

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Values above that are interpreted as ‘better’ condition (they weigh more than expected for their length), and ratios less than 1 are ‘poorer’. Pups from Agattu Island rookeries tended to weigh less for a given length than did pups at Kiska or Ulak Islands, though overall there is not a great difference among these sites.

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Alternatively, we can look at differences in pup condition over the years at specific sites or region. The box plot above shows the condition indices for female pups at Hasgox Point (Ulak Island) collected from 1994 to 2017. This data suggest that the pup cohort of 1994 was in apparently relatively poorer condition compared to later years, while cohorts since 2013 have been in relatively better condition.

All of this information are valuable pieces in the puzzle towards figuring out why Steller sea lions have not recovered in the Aleutian Islands. In the next blog, I will be sharing what we can learn from the different samples that we collect from pups along with weight and length measurements. Be sure to sign up for blog notifications by filling in your email and clicking the “Follow” button!


I am a research wildlife biologist with NOAA Fisheries Alaska Fisheries Science Center in Seattle, in the Alaska Ecosystems Program where I’ve studied Steller sea lions and northern fur seals since 2000. My primary research interest is vertebrate physiological ecology, which at NOAA Fisheries translates into studying sea lion foraging behavior, health status, and body condition to help address conservation questions and wildlife management issues.

April 1st: ~91

Sea Lion of the Month

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Happy April Fool’s day! The Sea Lion of the Month for April is no joke. This male sea lion was marked at Gillon Point (Agattu Island) on June 24, 2013. That means he will be 5 years old this summer! When he was marked he weighed about 51 pounds (23.2 kg) and was just over 3 feet (98 cm) long and 2 feet (64 cm) around his torso, just below his flippers.

According to our sighting records, the only time we see ~91 is from remote camera images captured at Alaid Island in the summer of 2014!

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We have never seen him during our summer research cruises. This is a case that definitely shows how vital these remote cameras and your efforts to classify images is to finding these marked animals! If we didn’t find animals like this that we miss during our summer cruise, we would not be able to accurately estimate important population rates that will help us figure out why this part of the population continues to decline.

Luck for us, you diligent and skilled Steller Watch citizen scientists have your eyes peeled and discovered ~91 on Gillong Point in the images posted to our current workflow. Keep up the great work!

 

Curious about other pinnipeds (seals and sea lions)? Check out our neighbors in the Pacific Islands to the south, the monk seals of the Northwest Hawaiian Islands. The Pacific Island Fisheries Science Center features their own Monk Seal of the Month!


We will share the story of one marked sea lion each month. Be sure to check our Sea Lion of the Month page on the 1st of every month to learn about our featured Steller sear lion. You may nominate a sea lion by submitting their full mark on the Sea Lion of the Month nomination forum. Thank you all for your nominations!