Live slow and prosper

I shivered as my legs slipped beneath the 42⁰F water; everyone was up to their thighs in the cold water for our first day of metabolic trials with the Pacific sleeper shark. Even with waders on, I could feel the chill in my toes. Angelica handed me a large red plastic board and I carefully scooted across the slippery floor of the pool to the edge of the shallow end. It had been a particularly low tide that morning, so the waters were silty—but somewhere in those depths beyond the drop-off was a Pacific sleeper shark.

The sleeper shark swims past Sarah and Markus, staying just a bit too far away in the deep end to coax him toward the research area.

“I see him. Heading towards you, Jared!”

Our spotters circling above on the upper deck pointed at mid-pool. With a few lazy swishes of his tail, SP19-04 emerged from the depths and swam slowly towards the surface of the water. Sarah and I shuffled our boards into position. Even though the shark had not been seen moving quickly—he still had a bitey end, and we kept the boards ready for protection. Jared and Kenny gently maneuvered a stretcher under the shark and coaxed him to swim into the shallow end—right to where Markus and Taylor were waiting with the TEC on its side. With a quick flip, the TEC was turned back over and the shark and seawater were inside.

Time to do some science.

Holding dissolved oxygen and temperature sensors, graduate student Taylor takes one last look at SP19-04 before starting a respirometry trial

Live long and prosper

Our main reason for wanting a shark small enough to bring back to the ASLC was to be able to conduct controlled experiments and measure the sharks’ metabolic rates. This effort is being led by Taylor Smith, a graduate student from California State University-Long Beach.

Metabolic rate defines the amount of energy used by an animal in a specific amount of time and will differ depending on what an animal is doing (e.g. resting vs. vigorous exercise). Being such a {potentially} long lived animal that lives in deep, cold waters—Pacific sleeper sharks likely have very low metabolic rates and therefore may not need to eat very often.

Figure from Nielsen et al. 2016, Science , showing the probability of when Greenland sharks were born based on analysis of eye tissues. This model suggests the largest sharks (TL = 500cm) would have been born between 1500 AD and 1800 AD and had a lifespan of 200-500 years! Our shark, SP19-04 was 199cm, so if we assume Pacific sleeper sharks age similarly to Greenland sharks, he is probably around 60 years old!

The way we quantify an animal’s metabolic rate is by assessing the rate of oxygen use. ASLC scientists have done this before with air-breathing animals, like our sea lions and ice seals, using tents or domes. Pacific sleeper sharks of course are using oxygen from the water to produce usable energy; so, to know how much they are using in a set amount of time, we need to have the shark in a closed space where oxygen from the air and environment won’t enter the water and affect our measurements.

Problem solving

A typical day of metabolic trials consisted of moving the TEC (transport-experiment-chamber) into the pool, dropping the water levels so we could work in the shallow end, and maneuvering the shark into the experimental chamber. However, the first day we realized that even with the best laid plans and discussing design with other shark researchers; there is always a level of uncertainty when venturing off the map into the unknown.

Taking measurements of the shark before metabolic trials start.

In our case, very few other facilities have ever tried to keep a Pacific sleeper shark for even a short time, and no one has tried to measure their metabolic rate. So, we quickly found out that while the TEC was the perfect size for the transport part, SP19-04 was actually too small for the experimental part of the design. He was able to turn himself around in the enclosed space, which could impact our measurements. We also found that when the lid was on to create that closed space, our infra-red camera had a hard time seeing the shark (which was very important to be able to monitor how he was doing!).

Getting ready to close up the TEC for a respirometry trial
Taylor is watching the shark in the closed TEC via an infrared camera system while the rate of oxygen depletion is recorded by the equipment on deck.

After a quick team discussion, we decided to let the shark back out into the pool for a day or two. Markus and Taylor went to work creating some spacers that would help keep the shark oriented in the right direction in the TEC, but still provide space to move his tail. They also created some portholes in the lid of the tank to be able to watch the shark, and modified where the camera was placed for optimal viewing.

SP19-04 back in the pool waiting for the modifications to the TEC. First our sharks were all too big…but being small has its own challenges!
The TEC with modifications ready for another trial.

A few days later, we coaxed the little guy into the modified TEC again and this time—success! Over the two weeks, rain or shine, Taylor collected metabolic data during 3 sessions. This is the first data of its kind for this species!

Taylor and an ASLC staff volunteer keeping an eye on the shark and the data during the trial. Other research essentials include coffee, soup and a good supply of peanut butter M&Ms.

But really….why is knowing a shark’s energy intake that important?

“Everything you see exists together in a delicate balance. When we die, our bodies become the grass, and the antelope eat the grass. And so, we are all connected in the great Circle of Life.”

This may have been a pep-talk between a fictional lion and his rambunctious cub, but when we talk about the concepts of healthy oceans, this scene from The Lion King always comes to my mind. A circle of life starting with the tiniest of plankton and interconnected up to the largest whales. When decisions are made about how many fish we can harvest from the ocean, how to protect endangered sea lions, or how loss of sea ice due to climate change will impact coastal communities—it is important to consider all of these linkages as a whole.

Example of multiple linkages that go into understanding the health of Alaska’s Oceans and the potential impacts of Climate Change. These models take into account climate & ocean processes, socio-economic and harvest (fisheries) scenarios, and the biological components of the system.

Scientists are currently developing ecosystem models that link multiple components of the ecosystem to better inform fisheries management– for example this integrated model for the Bering Sea (above).  Small projects, like the Sleeper shark research and others, can help improve those models by filling in our knowledge gaps. In this way, knowing how many sharks there are in the ecosystem, how much energy they need to carry out normal life, and what it might mean if they are removed from the food web –through bycatch or predation—will help us work towards sustaining a healthy ocean for everyone.

*Missed the first part of this story? Check out “Operation Sleeper Keeper” or any of our other sleeper shark posts HERE

Written by: Dr. Amy Bishop

This project is led by Dr. Markus Horning (ASLC) and Dr. Chris Lowe (California State University, Long Beach); together with graduate student Taylor Smith (CSULB), and Co-Investigators, Dr. Amy Bishop, Richard Hocking, and Jared Guthridge (ASLC).

This project is funded by the North Pacific Research Board (NPRB). The project is permitted by ASLC’s institutional ethics committee (AUP # R19-05-05) and by the Alaska Department of Fish & Game (CF-19-085).

Nielsen, J., Hedeholm, R. B., Heinemeier, J., Bushnell, P. G., Christiansen, J. S., Olsen, J., … & Steffensen, J. F. (2016). Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus). Science, 353(6300), 702-704.

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