Hah!
Looks like the
Megalobomb is human after all - did I just detect a soft spot for the researchers at
DICT?
Where is the critical analysis?
That is, apart from whinging about the dismal number of GWS! Talk about the lady being totally jaded - where I come from, 900-odd big Sharks from one single location is actually totally awesome!
Especially considering that previous white shark population estimates suggest that white shark numbers are small relative to other apex predators which is a statement I totally support see below!
Mind you, the paper is quite nice.
I was actually impressed - especially by the meticulous data collection, and by the various programs used for the analysis that are really quite epic. Boy things sure have changed since I did my few semesters of Biology courses back then in the 70ies!
BUT - of course, there has to be a but! :)
I'm slightly underwhelmed by the conclusions and also by the infographic, and this is why.
1. Mark-recapture
And I cite
A common bias in many mark-recapture studies is capture heterogeneity.
In our study we attracted sharks by bait, thus some individuals may have become ‘trap happy’ or ‘trap shy’ over time. This may lead to bias on estimates, but the effects of baiting on individual sharks remains undetermined. To address this, future work should focus on the effects of shyness or boldness in individual white sharks and assess whether they are more or less likely to appear close to a baiting vessel over time as well as incorporating such heterogeneity in behaviour in population size estimation.
Indeed!
This is also one of the principal flaws of the controversial (=
flawed)
Chapple paper, ie that over time, individual Sharks may develop gradual repulsion or special affinity for the vessels - but much more than that: some Sharks may
never approach the bait, decoy or vessel to start with, let alone come to the surface for a picture of their fin, and this despite of very much being in the vicinity!
I don't know about those GWS - but when it comes to our Bulls, I could tell you stories about several known individuals that have been visiting for years and not once approached the feeder. And
Juerg's paper also teaches us that whilst we're feeding, there are several individuals in the vicinity that we never get to see, quite possibly because they don't like approaching humans or also, because other individuals may out-rank them and thus monopolize the feeding area.
Long story short?
The postulated bias is highly likely, is likely to result in numbers that are too low and the effect, whilst unknown in its magnitude, could potentially be highly significant = there may be significantly more GWS than postulated!
2. Population Size and Conservation Status.
And then there is the whole rare vs endangered controversy.
Yes, globally, there are likely not a lot of GWS - but isn't that what is to be expected simply from their position atop the trophic web? Think about the famous pyramid - the volume at the top is tiny!
Also keep in mind that albeit being temperate water Sharks with a potentially enormous range, they have not at all colonized all available habitats, likely because philopatry is largely preventing them from straying too far from their established hot spots and migration corridors. Thus there are no reliable reports about established populations around South America or in the Eastern Atlantic (and David, don't you start...), with the only exception, i.e. the the Med
having likely been colonized by a possibly single Aussie female that had lost its way.
And what about the number of GWS in their known ranges?
We don't dispose of reliable population estimates about most of them, namely
the Med (likely very small);
the NW Atlantic (more and more sightings but no census)
; the NE Pacific (currently
in revision when it comes to California, but with no published census for the Mexican population),
the NW Pacific (where there is little literature apart from sporadic reports of sighted and killed GWS from Japan, Taiwan and Vietnam - tho in view of the status of Asian fisheries, the situation is likely to be grim);
Australia that boasts two populations but no published census (tho after so many years of protection, they may well be on the upswing); and
New Zealand where research is still very much in its infancy.
And finally, South Africa where the present paper smells like the start of a country-wide revision of previous assumptions.
So yes, indeed, we don't know whether globally, they are 3,000, 5,000 or 10,000 - with my money being on the latter!
And if so, what does that mean?
Does rarity automatically imply that the animals are endangered?
To a certain degree, the answer is
yes, and this for the rather trivial reason that smaller populations are generally more prone to be effected by risk - which is quite possibly why
the IUCN has classified them as vulnerable despite of not really disposing of much supporting data.
Further conclusions, at least at this point in time, are however problematic.
Thus, comparisons to terrestrial species whose massive population declines and partial extinctions are amply documented, or that are trapped in a population bottleneck
like the Cheetah are highly questionable.
We simply don't know, and I've also not seen any plausible guesstimates about the global rate of depletion of GWS or about the carrying capacity of their global habitats - back then and especially now that the latter are likely equally depleted, see the
comments about bottom-up effects!
There are simply not enough data allowing us to make any such assertions, let alone proffer that this already threatened species may be closer to extinction than we previously thought!
I say, be careful with such statements!
Only because one local census results in numbers that are 50% lower than previously assumed, this cannot just simply be extrapolated for global populations! Just think of the California numbers that are likely to be trebled, or think about the dramatic increase of GWS sightings on the East Coast of the US!
I don't believe for a picosecond that
Michelle Wcisel has
stated that
it was possible that the great white could be one of the most endangered species in the world - but the ingress to the infographic is certainly highly misleading, to the point that the sharktivists are already sharing it as the latest fact, see the image at the top!
It is not!
Anyway, just my 2 cents as usual.
But
read the paper and make up your own mind!
PS: Michael Domeier's take
here.
In all fairness and at the risk of committing sacrilege by posting a dissenting opinion, the paper does not claim to be anything else than a census for Gansbaai - hence if there are principally subadults, than that's what has been counted.
The question about the numbers of YOY, juveniles and adults becomes only relevant once somebody will publish a paper about the entire GWS population of SA.. Incidentally, that's another major flaw of the Chapple paper where the only animals that were actually recorded, and this in
only two of the known aggregation sites were adult GWS.
PS2: more lousy journalism
here!
