Personality and pace-of-life in free-ranging lemon sharks: a field recipe

This blog post is provided by Félicie Dhellemmes and tells the #StoryBehindThePaper for the article “Personality‐driven life history trade‐offs differ in two subpopulations of free‐ranging predators”.

Ingredients:
  • Two (or more) wild populations of juvenile lemon sharks which are known to differ in their predator abundance
  • 15 to 23 people who are ready to fish for twelve exceptionally long nights (every year, since 1993 (or start A.S.A.P.)), to do construction work, and to track sharks twice a week for four years
  • 120m of orange construction mesh, of at least 2m in height
  • 90 steel rebars
  • 90, 15kg cinder blocks
  • Lots of wood
  • A (big) freezer full of barracuda, fully deboned and cut into baby-shark-bite-size pieces
  • Some acoustic telemetry equipment and tags
  • Flat bottomed boats: 5 or 6 with outboard engines…
  • 6, 180x2m gillnets
  • Scissors, waterproof paper, clipboards, pencils, cable ties (more than you can count, especially the cable ties)
Shark food is acquired with patience. Photo: John Pierce.

Step 1: To succeed with this project, you will have to start in February with fishing for barracuda. Go to your favourite barracuda spot and repeat anytime the weather allows it, until your freezer is full (this can take several months depending on your luck). If you already have a freezer full of baby-shark-bite-size pieces of barracuda, you can skip this step.

In half a day, a team of five built this 50m² shark enclosure. Photo: Félicie Dhellemmes

Step 2: At the beginning of April, you need to build the holding enclosure and novel open field to measure the sharks’ personalities. For this you will first need to shuttle all orange mesh, cinder blocks and rebars to the testing site in your small flat bottom boats. This will take multiple trips and probably multiple days. The set up (See Figure 2 in Dhellemmes et al. 2020 for details) can then be built in three or four days by a team of 4-5 people. Make sure there are no gaps under the enclosures for the sharks to escape.

Taking the towers to the testing site. You will need someone at the front of the boat to be the driver’s eyes. Photo: Félicie Dhellemmes

Step 3: You then need to build two, ~4m high wooden towers with your wood, load them into the boats (that are way too small) and shuttle them to the testing site. This will take a full day and 9 to 10 people are needed to lift each tower. You must then set the towers in the sand, 1m away from your testing enclosures (on the North side). Follow a few days of silent prayers every time a wind gust comes through: it takes some time for the towers to fully settle and on some occasions, they can fall into your enclosures, in which case you might have to redo step 2 and step 3.

Measuring a freshly caught shark. Photo: Charlotte Sams

Step 4: Once this is ready, the shark fishing can start (typically at the end of May). You need to fish in AT LEAST two populations that are known to differ in their predator abundance (the more the better, we only found two). Four teams will set out at 4.30pm every night, three of them will set gillnets at standardized location (at 6pm) and the fourth one will stand by the housing enclosures to measure and tag the sharks. Each gillnet must be checked every 15 minutes to minimize stress on the animals. The teams return at 7am, prepare their equipment for the next night and go straight to bed. Before the end of the 12 nights, the teams will most likely lose their minds, forget their own names, speak Latin fluently etc. These are normal side effects.

By the end of the 12 nights, your holding enclosures should be full of sharks. The one at the front sports a colour coded tag to be easily identified for personality tests. Photo: Charlotte Sams

Step 5: Great, you now have around 200 sharks in your enclosures (do not forget to feed them: that is what the barracuda pieces are for). You do not actually want to keep sharks in captivity for more than 4 weeks, and you can only test 6 per day in the novel open field (with all sharks needing to be tested twice). Release most of the sharks and keep only around 60-80 individuals for the tests.

During the novel open field tests, hats are no fashion statements. Photo: Charlotte Sams

Step 6: You will then need to test six sharks in the novel open-field every day if possible: grab a team of four and test your sharks within two hours of the low tide unless it rains or storms. This step is better achieved when sunscreen is generously applied, and water and peanut butter and jelly sandwiches are plentiful.

A week after receiving their acoustic tags, the sharks are good to go! Photo: Chelle Blais

Step 7: You can release the sharks at their site of capture as soon as they have been tested twice, but some need to be kept longer in captivity to receive their acoustic transmitter. After being surgically fitted with transmitters, keep sharks in captivity for a week to monitor their healing, and then release them at their site of capture.

The acoustic telemetry monitoring is done twice a week during a 7h transect. Photo: Charlotte Sams

Step 8: You will start the acoustic monitoring 1 month after release (In September, usually): take advantage of this “month-off” to take down and bring back on land the enclosures, and the towers. Then, every week, twice a week (weather dependent), conduct a seven hour transect with a team of four, to monitor your tagged sharks around the study site. Do this until May (but do not forget to start again at step 1 in February if you wish to repeat the field sampling yearly).

Do this yearly, for as many years as possible.

If you followed this recipe correctly you should find:

In the low predator population: Exploration personality (measured in step 6) predicts distance from the shore in the wild (Measured in step 8) with more explorative sharks swimming further away from shore. Exploration personality also predicts growth (measured in step 4), with explorative sharks growing faster. You should also find a growth-mortality trade-off with fast growing sharks being more likely to die (survival measured in step 4). In short: captive personality predicts wild behaviour and is linked to a life-history trade-off.

In the high predator population: Exploration personality does not predict distance from shore or growth. Sharks stay close to shore regardless of their personality scores. The growth mortality trade-off is however still detected. In short: captive personality is independent of an observed life-history trade-off and does not predict wild behaviour.

Good luck!

Read the paper:

Read the full paper: Dhellemmes, F, Finger, J‐S, Smukall, MJ, et al. Personality‐driven life history trade‐offs differ in two subpopulations of free‐ranging predators. J Anim Ecol. 2020; 00: 1-13. https://doi.org/10.1111/1365-2656.13283

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