Chemistry, physics and math have given us quantitative frameworks to understand our physical world. However, we don’t yet have such a framework for understanding the ecological interactions between species and their environments in the natural world. Try keeping track of all the individuals from all the different species in one habitat and how they interact with each other, and then add in abiotic factors like weather, and it becomes obvious that ecosystems can seem far too complex to model accurately. We need a metric that is common to all systems which we can use to measure, describe and predict how ecosystems behave now and in the future.

All organisms contain and use energy, which is constantly being produced and transferred through ecosystems as organisms grow, live, and reproduce. These metabolic processes are measurable and may provide the quantitative metric we need. The field of metabolic ecology seeks to better understand this energy use and transfer to build models which can make predictions such as a species’ resilience to climate change or sensitivity to over-exploitation. However, we need more baseline knowledge of metabolic processes within and between species before we can use metabolic ecology to make these large-scale models.

My research takes a physiological approach to test the link between respiration and metabolism in fishes. Gills are the portals for oxygen transfer into a fish’s body and they have been shown to be closely tied to species-specific metabolic rate. Unfortunately, metabolic rate is difficult to measure in many large and aquatic species because they are too large to fit in laboratory respirometry equipment, but gills are much simpler to obtain and measure. If these traits are highly correlated, there is potential that gill surface area may be used to predict metabolic rate and help us better understand metabolic ecology. However, there has yet to be a study which measures both traits in the same individuals to provide a direct test of their relationship.

I was awarded the Graduate International Research and Travel Award (GIRTA) to travel to Scripps Institution of Oceanography in San Diego, California, for two and a half months this summer. There I worked with Nicholas Wegner at the Southwest Fisheries Science Center to study metabolism in Horn Sharks, and I am now working to study their gills here at SFU. These sharks are locally abundant in California and are a great study organism. I set out to test how closely gill surface area was related to metabolic rate at two activity levels, resting and maximum, which will allow us to better understand energy availability in this species.

We began by catching live Horn Sharks, from small juveniles 30cm long to adults 90cm long, in the coastal waters around Scripps and further south in San Diego. These sharks are so docile it’s easy to swim up to them while diving and simply grab them with two hands! We transported the live sharks to the lab in aerated coolers, and once there they were held in large tanks for two weeks to let them acclimate. One shark happened to be carrying eggs, laying two a few weeks after arrival. They are now developing in the aquarium and will hopefully hatch in about 4 months.

Metabolic rate is usually estimated in fishes using a respirometer. This device consists of a sealed chamber full of water to hold the fish and an oxygen probe to measure the rate of oxygen decline as the fish respires. The amount of oxygen consumed by the fish over time is used as a proxy for metabolic rate. I first worked to develop accurate respirometry methods for my Horn Sharks, as each species of fish will react differently to being placed in the chamber. Part of this was developing an exercise protocol where I chased a shark around a small tank to increase its metabolic rate, followed by quickly placing it into the respirometer chamber and immediately measuring its oxygen consumption. I was able to work out a simple and repeatable method to elicit the metabolic rate levels I needed, and so far my results look promising.

I am so grateful to have received the GIRTA and been able to go on this research trip. The facilities at Scripps are a marine biologist’s dream. There is a fully equipped dive program and top of the line lab aquariums, and they were generous enough to give me the tank space to hold as many sharks as I could bring in. I learned so much working with the amazing team at Southwest Fisheries Science Center, as everyone there is so kind, knowledgeable, and passionate about what they do. It would have been impossible to collect this quality of data otherwise and it will greatly improve the significance of my thesis research.