Déjà vu

Translocations Season 1 Recap

Last season, Obedient Juvie (a.k.a. O.J.) and Curious Juvie (a.k.a. C.J.) helped me out with my first pilot study to test heat flux biologgers (what are these?) on freely swimming juvenile elephant seals. Not only did we learn what worked and what didn’t work in terms of sensor attachment and configuration, we also found out that translocations can take some unexpected plot turns, like having to drive 3 hours south to another elephant seal rookery to find C.J. and recover the instruments (read all about it here).

Pictures taken of O.J. and C.J. as they were released on a beach in Monterey. They were each equipped with a heat flux biologger, VHF transmitter, and a satellite tag on top of the head. The heat flux sensors adhered to the skin to record heat flux and skin surface temperature at two locations on the body. The cables that connect the sensors to the biologgers are glued to the hair with adhesive wrap and tape. Once they returned to land after their short journeys at sea, the tags were carefully removed to retrieve the data. (Translocation performed under NMFS permit #19108 and IACUC approval.)

Unlike O.J., none of the heat flux sensors were still attached when we found C.J., but much to my surprise, there was good data recorded on the tags!

The snapshot of the data below shows what I mean by ‘good’ data. The heat flux patterns from the two sensors were similar and seemed to vary based on dive behavior, which led me to believe the sensors remained attached for the entire 8-day trip out at sea until the juvenile got back on land. If the heat flux sensor had become detached during the trip, I would have expected to see a relatively flat line (with some noise) for the heat flux data. But there was no ‘flat line of doom’ when I downloaded and looked at the data on Instrument Helper (Wildlife Computers, Redmond, WA)—success!

A snapshot of about 1 hour of raw data collected by the tags that were on C.J. viewed in Instrument Helper (Wildlife Computers, Redmond, WA). The data includes: (1) dive profile (navy blue) (2) heat flux from the ax (light blue) and flank (lime green) sensors, (3) skin temperature from the ax (black) and flank (red) sensors (3) water temperature (light gray) (4) 3-axis accelerometer (only y-axis shown in dark green in figure). The lime green numbers on the y-axis of the plot is showing units in mV for heat flux.

After doing some preliminary analyses of O.J.’s and C.J.’s data, I realized I was only looking at a small piece of their thermal physiology. The heat flux data tells me when the animal is gaining or losing heat to its environment, but I was missing data on the regulation part of thermoregulation. In other words, I want to know whether the animal is controlling how much heat they dissipate throughout the dive.

We know that marine mammals can regulate their heat balance by controlling blood flow to the blubber layer and thermal windows, especially on land when they are more prone to overheating. More blood pumped to their periphery means more heat will be dissipated. Yet, a reduction in peripheral perfusion (i.e. less blood flow to the blubber layer) is associated with the dive response. So how much do marine mammals perfuse their blubber layer while diving to maintain thermal balance? To understand how the heat flux patterns observed result from these physiological processes, I realized I needed to search for my answer in their blubber layer.

The regulation of blood flow to the periphery/blubber layer is important for both thermoregulation (left) and the dive response (right). (Left) This figure (from Environmental Physiology of Animals – 2nd Ed) shows how the constriction (or dilation) of blood vessels in the blubber layer affects how much heat is lost from the body core. (Right) The diagram presents the three main physiological changes associated with the mammalian dive response: apnea (i.e. breath-hold), bradycardia (i.e. reduced heart rate), and peripheral vasoconstriction (i.e. reduction of blood flow to the body’s extremities). Marine mammals exhibit these changes on more extreme levels, but all mammals (even humans) experience these changes to some degree when submerged in water.

This was the motivation behind the changes I made to the sensor configuration of the heat flux biologgers for my second translocation season. In addition to the heat flux and skin temperature measurements, I decided to add thermistors to measure the temperature within the blubber layer and how it changes throughout the dive. How would this temperature measurement get me closer to answering my question about blood flow in the blubber layer? Since blood coming from the body core is warm, increasing blubber temperatures will indicate increased perfusion. After lots of planning, applying to student grants for research funds, and some tag work in Alaska, two sets of newly configured tags were ready for another translocation season!

Season 2

Meet Xena, a hefty juvenile female, and Toby, a juvenile male.

Pictures taken of Xena and Toby while they were back at the lab, posing for some infrared pictures (converted to the visible spectrum) taken with the FLIR ONE Pro before being instrumented.

Just as we did the year before with O.J. and C.J., we brought Xena and Toby back to the lab, equipped them with the newly configured instruments, and released them in Monterey. How did their journeys compare? Check out the animations below.

The animations show the estimated paths of Xena (top) and Toby (bottom) after their release in Monterey. The points are Argos satellite hits, where the colors represent the accuracy of the location estimate based on the Argos location classes (red: no accuracy estimation, orange: >1500 meters, yellow: 500-1500 meters, green: 250-500 meters, blue: <250 meters). A ‘typical’ translocation is when a juvenile returns to Año Nuevo, just as Xena did. Toby, on the other hand, decided to go to another elephant seal rookery further south at Piedras Blancas.

Are you sensing a déjà vu moment? Xena and Toby coincidentally had very similar journeys to O.J. and C.J. (check out their journeys here). Both Xena and O.J. returned to Año Nuevo in less than 3 days while Toby and C.J. decided to swim around south of Monterey for over a week to finally haul out at Piedras Blancas. What made this year different and special—that is, in addition to the new data from the thermistors—was how Toby was found. But I’ll leave that story for my next blog!

Written by: Arina Favilla, Graduate Student at the University of California, Santa Cruz

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