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Dispatches from the field

Studying at-risk harbor seals in western Aleutians


 

harbor seals
Doctors Pam Tuomi (L), Markus Horning (C), and Stacy DiRocco (R) in the surgery van aboard the R/V Norseman in the western Aleutian Islands.  Photo: NOAA Fisheries

 
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The best little animal hospital in the Aleutians

September 22, 2016—I swung open the door and stepped from the blustery, rainy, aft deck of the R/V Norseman into a warm, brightly lit box. Out on the deck, four of our team members dressed in rain slickers and sea boots, were kneeling around a harbor seal, taking samples and measurements; inside the box, four others looked more like they were on the set of Grey’s Anatomy. Scrubs and hairnets were the garb in here. But there was no medical emergency, no drama—there were smiles all around, indicating that the surgery just completed on the latest patient had gone well.

The patient, a young female harbor seal about 3 or 4 years old, was lying on the table, breathing rhythmically to the beat of the ventilator and otherwise completely still, under the spell of isoflurane gas anesthesia. She had just undergone a procedure to have two glistening, sealed, capsules about the size of a pill bottle implanted into her abdominal cavity.

The implanted devices are part of a novel system developed by Dr. Markus Horning, Science Director of the Alaska SeaLife Center (ASLC) and Associate Professor at Oregon State University (OSU), in collaboration with Wildlife Computers, Inc., and funded by the National Science Foundation. The objective is to determine the vital rates of survival and reproduction in marine mammals, the ultimate determinants of whether a population persists. The so-called Life History Transmitters—or LHX tags—record data from multiple sensors during the life of an animal, and transmit the data via satellite only after the animal has died and the tags are liberated from the decomposing, digested or dismembered carcass. The key is that the data can be retrieved irrespective of where these animals might move to, breed, and eventually die.

The implant surgery, necessary because externally attached tags won’t reliably stay with the animal long enough, is done under full anesthesia and standard aseptic surgical conditions. On this trip, surgeries are performed by Dr. Pam Tuomi, veterinarian at the ASLC, and anesthesia is done by Dr. Stacy DiRocco, veterinarian with SeaWorld. Markus and ASLC research associate Renae Sattler are assisting in the procedures. These are the first LHX implant surgeries in harbor seals conducted at sea, and the team is confident that the animals will recover well, based on prior studies. A team from ASLC and OSU has deployed LHX tags in 45 young Steller sea lions since 2005. The researchers have demonstrated that the surgery and tags do not negatively affect sea lions, and especially their survival. In 2014, a team from the Vancouver Aquarium in Canada implanted LHX tags in three rehabilitated harbor seal pups that were monitored for 2 months at the stranded animal facility before being released and tracked for almost a year through external tags. Even so, as part of this project we will compare diving behavior and movement between the implanted animals, and non-implanted ‘controls’, for the weeks and months following their release.

For phocid seals like harbor seals and their close relatives the ice-associated bearded, ringed, spotted and ribbon seals, the LHX system could be revolutionary for measuring vital rates. The ice-associated species in particular don’t return predictably to dense breeding colonies or “rookeries” like fur seals and sea lions do, so the standard methods of marking and resighting individuals to monitor survival and reproduction aren’t practical. But with the LHX system, it’s not necessary to resight a study animal; at the end of the animal’s life, the tags phone home with the data on how long it lived, a bit of information on how it died and—for a female—when it reproduced. But, the LHX system is not for the impatient. Seals are long-lived species. Because natural mortality rates in the wild are relatively high for young seals, many do die in their first several years; but some may live for decades. For researchers patient enough to wait for the data, the LHX system, with batteries that can last for 10 years or more, may be the only practical means of measuring the seals’ survival rates in those crucial early years. For harbor seals in the western Aleutians, the technology could tell us why their numbers remain so far below historical levels.

Now, about two hours later and back out on the deck, our patient has shed the effects of the anesthesia. She’s alert, poised at the side gate with her head and fore-flippers already over the edge. She sniffs at the breeze a few times, glances alternately at the water and at us, then dives back into the sea to begin her service as a roving data collector.


Post by: Peter Boveng

 




 
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