Big sharks. Big mystery.

9 03 2011

My PhD student, Ana Sequeira, has just written a great little guest blog post for the Environment Institute‘s blog. Given I’m en route to Tasmania for a quick consultancy meeting, I thought I’d let myself off the hook and reproduce the post here. Well done, Ana (and hint to my other students – your time on is coming…).

This week is Seaweek and guest blogger Ana Sequeira describes how whale shark distribution might be shifting according to seasonal environmental predictors.

Ana Sequeira is a PhD student at the University of Adelaide (Global Ecology Group). Her main research interests are to develop models applied to the marine environment to describe key environmental processes, species distribution patterns and ecological interactions.

The main objective of her PhD thesis is to investigate behavioural ecology of whale sharks. She is now trying to understand which environmental variables may affect whale shark distribution.

The whale shark (Rhincodon typus, Smith 1828) is the largest fish in the ocean and can reach more than 12 m in total length. Although little is known about their habitat selection or migration patterns, the whale shark appears to be a highly mobile species. They predictably form near shore aggregations in some coastal locations (e.g. off Ningaloo reef in Western Australia) what makes them the subject of highly lucrative marine ecotourism industries. Also, artisanal and small-scale fisheries for the species still exist in many parts of the tropics.

Since the whale sharks is classified a Vulnerable species (IUCN Red List), understanding their migratory behaviour became of chief importance as they can be travelling from regions where they are protected to regions where they are still harvested.

Ana Sequeira

To identify the whale shark’s distribution patterns in the Indian Ocean, we developed multivariate distribution models of seasonal whale shark sightings – opportunistically collected by the tuna purse-seine fishery.

We used a 17-year time series of whale shark observations, bathymetric data, chlorophyll-a concentration and sea surface temperature data extracted from satellite images as inputs for generalized linear and mixed effects models.

Sea surface temperature was identified as a key component for whale shark distribution, being a forewarning that large shifts in the current aggregation locations are to be expected under climate change.

Our modelling approach can be used to predict whale shark appearance timings at specific sites (e.g. at sites where they are still currently fished) and to identify the underlying hypotheses for the current population decline.

See also some of our previous work on whale sharks:

  • SLEEMAN, JC, MG MEEKAN, SG WILSON, JJ POLOVINA, JD STEVENS, GS BOGGS, CJA BRADSHAW. 2010. To go or not to go with the flow: environmental influences on whale shark movement patterns. Journal of Experimental Marine Biology and Ecology 390: 84-98. doi:10.1016/j.jembe.2010.05.009
  • SLEEMAN, JC, MG MEEKAN, BM FITZPATRICK, CC STEINBERG, R ANCEL, CJA BRADSHAW. 2010. Oceanographic and atmospheric processes influence the abundance of whale sharks at Ningaloo Reef, Western Australia. Journal of Experimental Marine Biology and Ecology 382:77-81. doi:10.1016/j.jembe.2009.10.015
  • ROWAT, D, CW SPEED, MG MEEKAN, M GORE, CJA BRADSHAW. 2009. Population abundance and apparent survival of the Vulnerable whale shark in the Seychelles aggregation. Oryx 43: 591-598. doi:10.1017/S0030605309990408
  • ROWAT, D, M GORE, MG MEEKAN, IR LAWLER, CJA BRADSHAW. 2009. Aerial survey as a tool to estimate whale shark abundance trends. Journal of Experimental Marine Biology and Ecology 368: 1-8. doi:10.1016/j.jembe.2008.09.001
  • BRADSHAW, CJA, BM FITZPATRICK, CC STEINBERG, BW BROOK, MG MEEKAN. 2008. Decline in whale shark size and abundance at Ningaloo Reef over the past decade: the world’s largest fish is getting smaller. Biological Conservation 141: 1894-1905. doi:10.1016/j.biocon.2008.05.007
  • SPEED, CW, MG MEEKAN, D ROWAT, S PIERCE, AD MARSHALL, CJA BRADSHAW. 2008. Scarring patterns and relative mortality rates of Indian Ocean whale sharks. Journal of Fish Biology 72: 1488-1503. doi:10.1111/j.1095-8649.2008.01810.x
  • SPEED, CW, MG MEEKAN, B RUSSELL, CJA BRADSHAW. 2008. Recent whale shark (Rhincodon typus) beach strandings in Australia. Marine Biodiversity Records 2: e15. doi:10.1017/S1755267208000158
  • BRADSHAW, CJA, HF MOLLET, MG MEEKAN. 2007. Inferring population trends for the world’s largest fish from mark-recapture estimates of survival. Journal of Animal Ecology 76: 480-489. doi:10.1111/j.1365-2656.2006.01201.x
  • SPEED, CW, MG MEEKAN, CJA BRADSHAW. 2007. Spot the match – wildlife photo-identification using information theory. Frontiers in Zoology 4:2. doi:10.1186/1742-9994-4-2
  • MEEKAN, MG, CJA BRADSHAW, M PRESS, C MCLEAN, A RICHARDS, S QUASNICHKA, JG TAYLOR. 2006. Population size and structure of whale sharks (Rhincodon typus) at Ningaloo Reef, Western Australia. Marine Ecology Progress Series 319: 275-285. doi:10.3354/meps319275

and stay tuned for some of Ana’s papers to appear shortly.




2 responses

7 02 2013
Whither goest the biggest fish? «

[…] mentioned our previous whale shark research before (see here and here for previous posts, and see the end of this post for a full list of our whale shark publications), […]


9 05 2011
The Whale Sharks are Coming! « What Behaviour

[…] Big sharks. Big mystery. ( […]


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