Pups Take a Long Time to Move Out
A recent study of Australian sea lions indicates several things about their juveniles, their population and its correlation to the frequency of dives and depth of dives. There are three levels of dives: epipelagic, mesopelagic and benthic which indicate the depth and size of prey the sea lions go for. The study shows it takes Australian juveniles longer to reach the depths of adults than other species of pinnipeds.
Pups are suckled for 17 months, one of the longest lactations periods of pinnipeds. It is observed that young pups don’t have much room to store oxygen, they use up more oxygen due to growth development and they have more drag due to their smaller stature. Pups don’t develop complete diving skills for a long time. This could be why they aren’t wean until much later than other pinnipeds. They have extended period to develop the diving skills needed to go to the benthic depths their mothers exhibit. The pups use this time to become good hunters because of their environment which doesn't have a season like the other species of pinnipeds where their prey volume fluctuates in their environment.
Dives of 6-month-old pups, 15-month-old pups, 23-month-old pups, and mothers were recorded using an electronic time/depth recorder. Data shows that 6-month-old pups spent most of their time on shore and exhibit shallow, short dives. As the pups grew older they were diving deeper, diving for longer, and taking more trips. However, these dives were no where near the depth or time of an adult female.
For these reasons, the Australian sea lion population is leveling off or declining. It takes them longer to be independent and mature enough to be reproducing. Other species of pinnipeds wean their pups earlier and acquire the diving skills sooner. But this is also due to their richer environment. Also human-induced disturbances may alter the Australian sea lions’ environment to the point where it holds the pups back. The advantage of deep dives is the larger prey. Fishery trawls that disrupt the habitat and take the bigger prey on the benthic level affect the sea lions. With the fishery trawls, the prey are scarcer and so it affects the pups and also the adults that can hunt in the benthic level. Environmental modifications impact juveniles hunting in the deeper water depths. These things should all be taken into concern when treading in the Australian sea lion’s major colony.
Posted by Karisma (8)
posted by PWH @ 10:46 AM
5 comments
5 Comments:
This is a good article. Sometimes I find myself taking a long time to move out as well. I can really relate myself to these pups.As for the dives, the shorter the better.
Commented by NCA
This was a very well written and informative article. Those poor pups. It's truly amazing how affecting the different trophic levels impacts those above them. I would like to know what recourse the research team is enacting to help the pups. Although it is an uphill battle to change the commercial fishery patterns, there must be a compramise. Very well done.
Posted by BEK (8)
It is interesting that the pups take so long to mature and dive at those depths. It would be interesting to know if the fishery trawls did not take the bigger prey at the benthic depths would the pups survival really increase or do all the combined factors cause the decline in their population. Good post.
KVC
A very interesting article. It is interesting to see how seals will mature from one feeding level to the next as they grow. I am curious to see if maybe we'll see a shift in the developmental rates of the pups over time if the envirenmental disturbances continue. A very good article, though you might want to work on the flow.
Posted by JMSieer (8)
Thanks for the interesting article. I liked your discussion on the constraints and development of the pups, especially the restrictions on oxygen. Having done some diving myself, I can relate to how critical how much oxygen you can store is.
The connection between diving behavior and static or declining population was not clear in your post. Has something changed that has made it harder for the pups to survive or is it that this species slow maturation makes it more vulnerable to pressures such as trawling?
I also wondered whether there a benefit for Australian sea lions slower maturation rates and longer weaning times? You mentioned that other pinniped species matured more quickly due to richer environment. Would that imply that a young Australian sea lion pup would be less likely to catch something with his limited dive time compared to other pinnipeds and therefore are better off living off mother's milk until they are strong enough for longer deeper dives?
Posted by: Jonathan Caplan (8)
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