Shark Data Mossel bay 2018.xlsx

The data comprises of white shark observation trips made in Mossel Bay, South Africa in the year 2018. Variables recorded include: Number of sharks, time taken for first shark arrival, sea state, wind direction, water visibility, number of males, number of females, maximum size, minimum size, trip duration, site location and water temperature.
Two observation sites were used within Mossel Bay. Seal Island was visited for data collection from March to December, Grootbrak for January, February and December. One to three trips took place every day for 191 days throughout 2018.
The surface water temperature was taken using the vessels onboard thermometer (Furuno integrated thermometer) recorded to nearest 0.5 degrees celsius. The water visibility and sea state was recorded. Wind direction was recorded at time of anchoring. Morning trips anchored before 11am SAST and afternoon trips took place after 11am SAST. White sharks were attracted to the vessel using chum (Lacroche et al. 2007) as an olfactory stimulus; a bait line consisting of a big eye tuna head to simulate struggling prey; and a seal decoy made from synthetic foam, cut in the shape and size of a Cape fur seal pup.
Upon anchoring the white sharks were attracted using these techniques, and the time taken for the first shark to appear was recorded. The shark was then drawn close to the vessel using the bait line for clearer observation. Great care was taken to avoid the shark consuming the bait line to prevent the sharks associating boats with feeding opportunities. Sharks were sexed once close to the vessel based on the presence or absence of claspers. observations were taken both above and below the waters surface. Underwater observations were made in a shark diving cage attached to the vessel. The shark cage (3.3m) was used as a reference to estimate shark length when the shark swam past the cage. The estimation was made by experienced shark observers. Lastly the trips duration was recorded from time of anchoring to time of departure.
All procedures performed in this study involving white sharks were in accordance with the ethical standards of national department of environmental affairs marine living resources act, 1998 (Act no.18 of 1998) policy on white shark cage diving.