10 Questions and our Answers

1. What is osmoregulation and why should we care?

Osmoregulation is the process of maintaining a balance between solutes (aka salts) and water in the body. All organisms osmoregulate, but the process is particularly important for aquatic and marine species since their bodies are surrounded by water. For organisms living in fresh water, the amount of salts in the body is higher than the amount in the surrounding water. As water diffuses across a concentration gradient (from places of low salt to places of high salt), organisms in fresh water systems need to prevent too much water from entering their cells (which could cause the cell to burst). In marine environments, where the environment has more salt than the organisms, organisms need to keep the water from diffusing out of their cells (which could cause the cell to shrivel). Marine organisms maintain this process by producing urea, a highly concentrated solution of salts (which increases their amount of internal salts preventing water from leaving). As the concentration of salts in the water change, organisms can use this urea to maintain their internal balance of water to salt allowing them to survive in a variety of environments (some sharks, like bull sharks, can even travel between marine and freshwater environments!)

2. Why south Florida?

Why not south Florida? No, but really!

South Florida is home to a wide variety of sharks (from nurse sharks and blacktip sharks to great hammerheads and lemon sharks). It is right along the Gulf Stream meaning that South Florida is along the migration route for many shark species. South Florida also has a variety of marine ecosystems (from seagrass beds to coral reefs) meaning that we can study sharks across a variety of habitats.

Did we chose south Florida because it is convenient? Sure. Is there be somewhere better to do this study? Unlikely.

3. Why these species?

We've suggested that this study will encompass several species including, but not limited to blacknose (Carcharhinus acronotus), lemon (Negaprion brevirostris), nurse (Ginglymostoma cirratum), and blacktip sharks (Carcharhinus limbatus). Are these all the sharks we'll study? We're not sure! Shark fishing is unpredictable--we don't know what we're going to see before we see it. These species are some of the ones we have historically seen more commonly on our routine fishing trips so we are hypothesizing that they will work well for this study. Might our study encompass other species as well? Sure--it all depends on what we are able to catch! That said, we are particularly interested in a few of these species, like the blacktip shark, as we've noticed that we can actively smell the urea on them when working them up and are particularly interested in understanding how they are using urea to osmoregulate and respond to capture and release stress.

4. What is unique about your project?

This has never been done before! Sure, some studies have looked at urea excretion in the lab in the model organism the Spiny Dogfish (see Wood et al., 1995), but no study has looked at urea excretion at the gill interface in the field or across species in the Caribbean. Osmoregulation is critical to shark survival so understanding more of its physiology might help us better understand these elusive organisms, how they use coastal habitats, the effect of capture and release on their physiology, and how they might be effected by continued environmental change.

5. Why this method?

We considered several methods of measuring urea for this study (including things like using microsensors) but sometimes tried and true is the most promising. Our proposed methodology is well established (see Price & Harrison 1987) and has been refined over the last few decades (see Langenfeld et al. 2021). We're taking this well known method and applying it to a new study organism so, while there may be some hiccups along the way (when isn't there in science?), we think this method offers us the best chance for success.

6. What is your timeline?

Thanks for asking! We're hoping to start this project during our next major field season (Summer 2023). Assuming we are able to catch enough sharks to have a decent sample size, we then hope to process and analyze our samples in early Fall 2023. Once everything is processed and analyzed, we aim to share our findings in a peer reviewed publication.

7. You're taking samples from live sharks? How will you do that?

We'll be taking samples non-invasively--using a swab of the gills--from sharks caught during routine Field School field work! You know how you swabbed your nose with a cotton swab for your covid-19 tests? It's the same concept here, just, instead of your nose, we'll be swabbing shark gills for urea!

8. What are you going to do with your results?

Once we process and analyze our data, we hope to share our findings in a peer reviewed publication. Assuming we find something of interest, there might also be an opportunity to build on this study to continue to learn about shark osmoregulation!

9. Can we get involved?

We can't, unfortunately, take everyone out on the boat with us to collect samples, but you can still be involved! How often do you get to say that your $5, $10, $15 etc. donation is helping to make real science happen? We wouldn't be able to do this project without your support, so helping us fundraise is a great way to get involved (and we'll be sure to keep you updated on how our data collection is going)!

Really want to come out with us on the boat? Check out Field School's website to learn more about opportunities to get out into the field and learn about elasmobranchs, marine conservation, and south Florida: https://www.getintothefield.com 

10. What excites you the most about this project?

So much excites me about this project--it's hard to pick just one thing. I think, first and foremost, I'm excited to try something new that's never been done before (and to problem solve as new problems arise). I'm also really excited to take a well established methodology and show how it can be used in different circumstances to produce meaningful results. More than anything though, I'm excited to contribute new knowledge to the field of shark science and to undertake a new project with an organization that I love.

Have more questions for us? Feel free to ask in the comments!