8 replies to this topic

[martys]

For the last five years I've been traveling to Hornby Island, BC to dive and play with the Stellar sea lions that migrate there during the winter months to wait to feed on the annual herring spawn. They are an incredibly friendly bunch who are accustomed to divers visiting and interacting with them. This year we ran into one special pup who appeared to be "instrumented" ... Turns out the blue headed guy I ran into on Hornby was one of twelve instrumented animals that are part of this year's study on foraging behaviors. Peter Olesiuk from the Dept of Fisheries and Oceans generously gave his time to explain the details of the study to me by email. Each of the units records different telemetry data at 10 second intervals. The head unit records GPS data, the tail unit record depth and time while the middle unit records eating behavior by monitoring the stomach for changes in temperature. Each of the twelve sea lions have different colored units, so when the unit is eventually released and recovered the biologists know which one it came from. I have found the information on the behaviors and travel patterns of these guys so interesting from Peter's study that it makes you look at sea lions in the water in a whole new way, curious how long they've been at their current site and how far they've traveled in the last few months. The full context of Peter Olesiuk's combined mail thread on the study, additional images and a satellite map of the locations recorded from the sea lions can be found here.

[Tom_Kline]

Looks like a prototype Sony Swimman!

[Kelpfish]

Or a suicide sealion bomber.

Joe

[Kelpfish]

I am curious as to what the value of this study is for the sea lions. Any ideas?

Joe

[Tom_Kline]

There is considerable controversy (esp. here in AK) about what sealions eat and how they are counted (by us). The food: in terms of availability and energy content. Movements: because census data generally depends on counting them hauled out; as well as for food (they may have to travel to feed and their food abundance varies in space and time). The number on a given haul out site can vary. Understanding their movements such as from this study is thus critical.
Tom

[scubamarli]

Pretty interesting stuff. I've been to Hornby (Norris Rocks) a couple of times, (check my avatar), and it has ranged from exhilarating to downright scary. Divers were bitten, right through their drysuits ! Apparently the later in the winter, the more aggresive they can be. Nothing like watching your buddy's head disappearing in a massive sealion's mouth! We also wondered if being in a large group of divers provoked the aggressive response. Those divers that spread out seemed to be bothered the least.

The study will at least see how far ranging these gorgeous endangered animals travel, in hopes that if they do not tend to go too far, perhaps some marine reserve (aka anti-fishing) legislation can be pressed for in the areas they tend to inhabit. We saw several dead babies at the site when we we there. Of course, we have no way of knowing why they died.

Cheers,
Marli

[Tom_Kline]

Marli,
Very interesting observations! Were any scientists in your area informed about the corpses? They can perform necropsies, which might explain their deaths. One of the data gaps in understanding sealion population declines is the lack of dead body observations, this is magnified here as well because of the limited number of divers or other observers and general inaccessibility.
Tom

[scubamarli]

[Were any scientists in your area informed about the corpses?]
Not at the time. One was literally at the bottom of the anchor line. Due to aggressive behaviour, we called off the second day of diving. This all took place in February, three years ago.

Cheers,
Marli

[Tom_Kline]

One could speculate that their aggressive behavior was a result of these mortalities. I gather you and others have dived this site at other times (seasons as well as occasions) when sealions were present but without this behavior. There may be less food available (amount and quality) in winter to making them more stressed (and starved).
Tom