A research proposal on thresher shark tail adaptations: Does the length differ between species based on prey and location?

Oct 19

A research proposal on thresher shark tail adaptations: Does the length differ between species based on prey and location?

Background

Thresher sharks (Alopiidae) are a group of pelagic sharks known for their
distinctively elongated upper caudal fin lobes (tails), which can exceed the length of their bodies6.
Thresher sharks have been observed to use their tails as a method of hunting, more specifically,
‘tail-slapping’ fish to stun them, alongside herding schools for easier predation1-5. However, it has
yet to be examined whether the length of a thresher shark's tail is relevant to diet and hunting
success. This research proposal aims to investigate the adaptive significance of tail length in
thresher sharks. It is possible that the length of the tail may be directly related to the size of
available prey in their habitat, with variations across different oceanic regions. Additionally, the
length of a thresher's tail may be linked to the individual shark's success in predation

Study System

These sharks are divided into three
species: the common thresher shark (A. vulpinus),
the bigeye thresher shark (A. superciliosus), and the
pelagic thresher shark (A. pelagicus). The common
and bigeye threshers are found in the Atlantic,
Pacific and Indian Ocean, while the pelagic thresher
is confined to the Indian and Pacific Ocean2. Pelagic
threshers measure 142-319 cm in body length, while
bigeye threshers measure 135-361 cm6. The
common thresher’s body length measures 56-264
cm3. It is estimated that thresher’s tails measure
50% - 60% of their total body length.

Hypothesis

We will investigate the adaptability concerning the dimensions of thresher shark tails
(length in cm) through both single-species and comparative methods:

(A) Within a single species, we will assess whether thresher sharks with longer tails exhibit greater
success in corralling prey.

(B) When considering multiple species, we will examine whether thresher sharks inhabiting regions with larger prey exhibit longer tail dimensions.

Methods and Materials

1. Acoustic Tagging and Tracking

We will employ acoustic tags to identify and track sharks and their feeding habits.

2. Photogrammetry for Body and Tail Length

We will utilise photogrammetry techniques to capture precise measurements of the body and tail length of the sharks. This approach will also allow us to document the species they prey on and their respective size.

3. Data Comparison and Analysis

a. Tail Length vs. Corralling Success: We will analyse the data to investigate whether sharks with longer tails are more successful in corralling prey. This comparison will provide insights into the relationship between tail length and hunting success.

b. Tail Length vs. Prey Size: We will evaluate whether sharks with longer taills tend to prey on larger fish across each species. This analysis will show the relationship between tail length and prey size. We will compare the tail size of threshers from each region/species and analyse their prey size to dictate a potential relationship.

4. Interpretation of Results

Based on the findings from our analysis, we will interpret the data to determine if there is a discernible relationship between thresher shark tail length and both prey corralling success and prey size.

References

Camhi, M., Pikitch, E. K., & Babcock, E. A. (2008). Sharks of the Open Ocean. In Wiley eBooks.
https://doi.org/10.1002/9781444302516

Dharmadi, Fahmi, F., & Wiadnyana, N. N. (2013). Biological Aspects and Catch Fluctuation of the Pelagic Thresher Shark, Alopias pelagicus from the Indian Ocean. Kyoto University Research Information Repository, 77–85. https://doi.org/10.14989/176185

Gervelis, B. J., & Natanson, L. J. (2013). Age and Growth of the Common Thresher Shark in the Western North Atlantic Ocean. Transactions of the American Fisheries Society, 142(6), 1535–1545. https://doi.org/10.1080/00028487.2013.815658

Li, Z., Pethybridge, H., Wu, F., & Li, Y. (2023). Mercury bioaccumulation in thresher sharks from the eastern tropical Pacific: Influences of body size, maturation stage, and feeding habitat. Science of the Total Environment, 872, 162248. https://doi.org/10.1016/ j.scitotenv.2023.162248

Oliver, S. P., Turner, J. R. G., Gann, K., Silvosa, M., & Jackson, T. O. (2013). Thresher sharks use Tail-Slaps as a hunting strategy. PLOS ONE, 8(7), e67380. https://doi.org/10.1371/ journal.pone.0067380

Varghese, S. P., Unnikrishnan, N., Gulati, D., & Ayoob, A. E. (2016). Size, sex and reproductive biology of seven pelagic sharks in the eastern Arabian Sea. Journal of the Marine Biological Association of the United Kingdom, 97(1), 181–196. https://doi.org/10.1017/ s0025315416000217