Wednesday, April 29, 2009

A whale (shark) of a tale my friends

One of the things I love doing (no really I do love it) is spending some time reading scientific journals. After all, how else can I know about all the cool stuff that my fellow travelers are doing in my name out on the high seas? This task has become somewhat easier over the years as more and more journals are available on line, and as my employer has made it a point to ensure access to those e-journals.

Of course, PLoS ONE also makes it really easy to keep up on a wide range of topics, and I am glad that many of my colleagues around the world are considering publishing there. With that in mind, here’s a recent whale shark genetic study that I find really fascinating.

The authors set out to examine the population structure of these mysterious lumbering giants. It was not an easy task, as aside from feeding aggregations, there are only occasional open ocean sightings of mature individuals to go on. So genetic work to relate the populations is extremely important.

I imagine that Schmidt and her colleagues were excited to find that most if not all whale shark populations appear closely genetically related. This discovery, presented in the usual dry scientific language reads:

Microsatellite analysis of whale sharks sampled primarily at feeding aggregations around the world showed little genetic differentiation in this study. The Pacific and Indian Ocean populations were very similar based on FST value (P×I = −0.0022), while FST values for the Caribbean population were somewhat larger when compared to both the Pacific and Indian animals (C×P = 0.0387; C×I = 0.0296). Only the C×I population approached statistical significance for genetic differentiation (p = 0.0495). It is likely this value would be more highly significant if additional Caribbean animals were available for analysis. FST for C×I remains low, however, indicating subtle differentiation between Caribbean and Indian whale sharks. Despite this finding, the data show that there has been significant gene flow between geographically disparate populations. The individual-based analyses (STRUCTURE and PCA) also indicate no clear genetic clusters of whale sharks based on sampling location (Figure 2). Gene flow between geographic sampling populations could be mediated directly, by individual animals traversing large distances to interbreed with distant populations, or could be more incremental, as animals breed with near neighbor populations and their offspring subsequently move to yet more distant areas. As data become available about additional whale shark aggregation sites, it appears that a band of whale sharks spanning the mid-latitudes is plausible.”

In other words, after analyzing the samples they could get, and running some time tested and accepted statistics, it turns out that whale sharks MAY be a world-wide metapopulation. That is significant news, because it points directly to a need for better, broader, conservation across political boundaries and jurisdictions:

As whale sharks cross geographic and political boundaries in their movements, international protection should be sought to ensure the continued survival of this species. In addition, it should be kept in mind that genetic methods of population study reflect only the history of the species. They cannot detect more recent changes in behavior that may be caused by overfishing, habitat disruption, tourism, or other anthropogenic activities currently impacting whale shark populations.”

Why does that matter, you ask? Well, in spite of the existence of such things and the IUCN Red List, conservation of marine species is still largely a nation by nation activity. As such, protection is often granted by nations that have no economic interest in harvest, while protections are often minimal, non-existent, or ignored by nations that have such an incentive. This inconsistency leads to rapid declines, habitat alterations, and poaching. We see this all the time on land – elephants and gorillas being but two examples.

So, once again, marine biologists have delivered to marine policy makers a challenge – how to conserve whale sharks when the evidence is clear that they cross national jurisdictions as true world residents. It will be very interesting to watch the additional science unfold, as well as the policy response.

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