Shrinking global range projected for the world’s largest fish

7 08 2013
© W. Osborn (AIMS)

© W. Osborn (AIMS)

My recently finished PhD student, Ana Sequeira, has not only just had a superb paper just accepted in Global Change Biology, she’s recently been offered (and accepted) a postdoctoral position based at the University of Western Australia‘s Oceans Institute (in partnership with AIMS and CSIRO). As any supervisor, I’m certainly pleased when a student completes her PhD, but my pride as an academic papa truly soars when she gets her first job. Well done, Ana. This post by Ana is about her latest paper.

Following our previous whale shark work (see herehereherehere, here, here and here), especially the recent review where we inferred global connectivity and suggest possible pathways for their migration, we have now gone a step further and modelled the habitat suitability for the species at at global scale. This paper sets a nice scene regarding current habitat suitability, which also demonstrates the potential connectivity pathways we hypothesised previously. But the paper goes much further; we extend our predictions to a future scenario for 2070 when water temperatures are expected to increase on average by 2 °C.

Sequeira et al_GCB_Figure 3

Global predictions of current seasonal habitat suitability for whale sharks. Black triangles indicate known aggregation locations. Solid line delineates areas where habitat suitability > 0.1 was predicted.

Regarding the current range of whale sharks (i.e., its currently suitable habitat), we already know that whale sharks span latitudes between about 35 º North to South. We also know that this geographical range has been exceeded on several occasions. What we did not know was whether conditions were suitable enough for whale sharks to cross from the Indian Ocean to the Atlantic Ocean – in other words, whether they could travel between ocean basins south of South Africa. Our global model results demonstrate that suitable habitat in this region does exist at least during the summer, thus supporting our hypotheses regarding global connectivity!

It’s true that the extensive dataset we used (30 years’ worth of whale shark sightings collected by tuna purse seiners in the three major oceans – data provided by the IRD, IOTC and SPC) has many caveats (as do all opportunistically collected data), but we went to great trouble to deal with them in this paper (you can request a copy here or access it directly here). And the overall result: the current global habitat suitability for whale sharks does agree well with current locations of whale shark occurrence, with the exception of the Eastern Pacific for where we did not have enough data to validate. Read the rest of this entry »





Whither goest the biggest fish?

7 02 2013
© W Osborn (AIMS)

© W Osborn (AIMS)

Well, since my own institute beat me to the punch on announcing our latest whale shark paper (really, far too keen, ladies & gents), I thought I’d better follow up with a post of my own.

We’ve 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), but this is a lovely extension of that work by my recently completed PhD student, Ana Sequeira.

Her latest contribution, Inferred global connectivity of whale shark Rhincodon typus populations just published online in Journal of Fish Biology, describes what a lot of whale shark punters & researchers alike have suspected for a long time – global connectivity of all the oceans’ whale shark populations. The problem hasn’t been a lack of ‘evidence’ for this per se; there is now sufficient evidence from genetic studies that at least on the generational scale (a single generation could be up to 37 years long), populations among the major ocean basins are connected via migration (Castro et al. 2007Schmidt et al. 2009). The problem instead is that no one has ever observed a shark voyage between ocean basins, nor has anyone really suggested how and over what time scales this (must) happen.

Until now, that is. Read the rest of this entry »





Where are they? Finding (and conserving) the biggest fish in the sea

16 11 2011

A post from my PhD student, Ana Sequeira, on her latest paper just out in Diversity and DistributionsOcean-scale prediction of whale shark distribution.

© W Osborn (AIMS)

The ocean is our major source of water, it stabilises our breathable atmosphere and provides many supplies such as medicines (e.g., anti-cancer therapy drugs1) and food. Despite its the importance for human life, many marine species are now at a high risk of extinction owing to human changes to the oceans.

The whale shark (Rhincodon typus, Smith 1828) – an icon of the oceans of a spectacularly huge size and docile character – is just one of those species.

Despite being a fish that many people (mainly in Southeast Asia) are happy to have on their plate, whale sharks are worth millions of dollars every year in the ecotourism industry worldwide. One would then expect that being such a profitable species, their ecology would be well known and thoroughly studied.

The reality is quite different.

Basic information on whale sharks such as the whereabouts of their breeding areas, the average number of offspring per female, or even how many individuals still exist, is not currently known. Moreover, despite the genetic evidence that whale sharks worldwide are connected among different oceans, it is unclear if they move from places where they are protected to places where they are still illegally fished.

Information on distribution and patterns of occurrence in space and time is essential for conservation, and can help to save entire ecosystems if used correctly, for example: to isolate important mating and breeding areas.

To identify the whale shark’s seasonal distribution patterns in the Indian Ocean, to test if records follow a decreasing trend over time, and if occurrence is related to variation in climatic signals, we used multivariate distribution models of seasonal and inter-annual whale shark sightings opportunistically collected over 17 years by the tuna purse-seine fishery. Read the rest of this entry »





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 ConservationBytes.com 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. Read the rest of this entry »








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