SHARK PERSONALITY Test candidates: 14 female and 14 male juvenile lemon sharks, whose total lengths ranged from 60.5cm to 87.5cm (mean 68.5cm). Individual recognition: Each shark was colour-tagged so that we could recognise individuals. Housing conditions: The sharks were kept in a holding pen (10m diameter) built in their nursery area. While in captivity, they were fed every two days with a mix of fresh and frozen reef fish. In addition, the day before a test, each shark was fed to satiation (until food was left on the sea floor). No shark was kept captive for more than four weeks and all were released at their capture site. Open field: The open field consisted of a rectangular pen (6 x 12m) divided into 18 sectors by markers on the sea floor. A semi-circular start box (1.5m) provided entrance to the pen through a sliding door. An exit channel was built alongside the pen to facilitate the sharks’ return to their holding pen. Test schedule: Each shark was tested on six occasions (once every two days) according to the routine described below. Trials were conducted during the same tidal phase and three individuals were tested daily. Across a 12-day period six sharks could be tested. Environmental conditions: For each test, the wind, cloud cover, visibility, depth and temperature were recorded and controlled for in the analysis.
1
USHERING
To avoid stressing the sharks prior to the test, we transferred them from the holding pen to the start box by ushering them individually rather than catching and handling them. Up to four people entered the holding pen with ‘shark spoons’ (pieces of pen mesh mounted on PVC handles) and slowly corralled the test shark into the start box.
tubular PVC handles
pen mesh
1
Holding pen (10m)
HOLDING PEN
2
Start box
‘SHARK SPOON’
2
ACCESS TO THE PEN
The start box acted as a buffer zone between the holding pen and the open field. Each shark spent five minutes in it before the start of the test. This was important to standardise each shark’s entrance to the open field and give it a short recovery period from the ushering. After five minutes, a sliding door was gently opened and each shark was given 15 minutes to enter the open field. The time it took the shark to leave the start box was recorded. If the shark did not enter the open field, it was ushered back into the holding pen and the test noted as incomplete.
OPEN FIELD: SLIDING DOOR OPENED
A1 B1
A2 B2
OPEN FIELD: SLIDING DOOR CLOSED
A3 B3 Observation tower
A5 B5 Open field sliding door opened by person in the water pulling a rope (indicated by red arrow)
Sliding door closed by observer pulling a rope (indicated by blue arrow)
To read the full article: Finger, J. S., Dhellemmes, F., Guttridge, T. L., Kurvers, R. M., Gruber, S. H., & Krause, J. (2016). Rate of movement of juvenile lemon sharks, Negaprion brevirostris in a novel open field: Are we measuring activity or reaction to novelty? Animal Behaviour 116: 75–82. 122
A4 B4
A6 B6