methods of tracking

[James Catlin]

It was reported in the Australian media today (see below) that a whale shark was seen at Stradbroke Island (near Brisbane), which is reasonably far south and not common. Fortunately this shark was photographed in the right spot and, consequently was checked in the Ecocean library. There was, however, no match. Considering that the recent publication on whale shark genetics indicated that the global population is largely homogenous, it would appear it is only a matter of time before there are matches between the various distant locations using photo id. Since it has not been covered on this forum as yet, it would be good use this as an instigation for a discussion on peoples' experiences and perceptions of the various methods (eg photo id, sat tags etc), including advantages and disadvantages, used to track whale sharks.  So please add your opinions regarding this topic and don't let it fade.

Cheers

James

http://www.news.com.au/couriermail/story/0,23739,23134330-3102,00.html

A JUVENILE whale shark spotted off North Stradbroke Island may be the first sighting of the giant marine creature in the area for 30 years.

Dive operator Ken Holzheimer said he and his diving team spotted the friendly whale shark while they were diving in the protected Flat Rock area.
"It was Sunday morning about 7am, we had left the beach about 6am," he said.

"The whale was visible the whole dive, within touching distance."

Mr Holzheimer, who has been operating for 39 years, said the 5-6m whale shark was the first he had seen since the early '70s.

"We used to get them in the late '60s and early '70s but we haven't seen one since," he said.

Diver Paul Sorensen said he at first mistook the whale shark for a tiger shark. "One of the divers pointed out in the deep sea area, and we saw these two fins.

"At first I assumed it was a tiger shark because you don't expect to see whale sharks this side of Australia.

"She saw us and came over and circled around us but was just having a look at us."

The lead scientist for the Manta Ray and Whale Shark Research Centre, Simon Pierce, said the sighting was unusual, as whale sharks on the east coast usually fed only in the Coral Sea.

"There are a few places in the world where you can quite consistently see them, but it is only generally in the Coral Sea that you can consistently see them on the east coast. It is quite unusual to see them down this far – she is probably just wandering, not migrating."

Mr Pierce said the shark was probably aged in her mid 20s. The species can live to more than 100.

 

[Simon Pierce]

Hi James (and list),

I'll just make a quick note on this fascinating (and rather large) topic.

Photo-ID studies, particularly cross-checking large databases between geographical locations, are a cost-effective and extremely powerful way of showing real, physical interchange between sites. If there's not much exchange between the sites you may be dealing with different 'stocks' or 'evolutionarily significant units'. A 'population' (to use one of many possible definitions) can be defined as a unit “where virtually no gene flow (less than one disperser) would be expected within a generation.” A ‘stock’ is a sub-unit with a level of gene flow greater than that of a population, but low enough to be significant for management purposes. In practice this may be set as less than 1% dispersal between units per year (definitions borrowed from Swartz et al. 2006).

So, back in the real world, you can pick whether fisheries or other threats are likely to impact on other locations. Plus, if you DO get significant interchange between sites then you may be looking at a single population, and the data can be modelled to provide broad-scale population estimates. Boo yah.

The cool thing about satellite-tagging studies is that you can get a good view of individual-level movement and behavioural patterns, leading to insights like the discovery of deep-diving behaviours. Population genetic studies can show the extent of interchange between locations on evolutionary time-scales. All three of these techniques, plus others like isotopic studies and the use of parasites as biological tags, complement each other to provide a nice holistic view of movement patterns.

Cheers,
   Simon.   

[Jason Holmberg]

I completely agree with Simon's comments. I want to expand upon one point, which is that electronic\genetic tagging studies need to be directly integrated with Photo-ID. Tagging "a random, unidentified whale shark" at "a random point in time" gains very little knowledge. We don't know whether the data represents random or systematic behavior for males/females/juveniles/adults/etc. Linking the data into a long-term catalog of identified individuals provides valuable ecological context and provides long-term utility for the data.