Satellite Tracking and the Great White Shark by Alexa Broadbent

Great White Sharks and migration: what do we know?

broadbas — 2017-02-25 00:40:36 UTC

-Genetically distinct global populations (Jorgensen, 2010)
-Extreme migrational routes which span across international waters (Anderson, 2011)
-Victims of inconsistent international laws of protection (Anderson, 2011)
-Short term data (<8 years, or approx. 25% of lifespan) indicates that whites intermittently aggregate along specific coastal sites following migrational periods (Cailliet, 1985)

Individual ID's

broadbas — 2017-02-25 01:23:59 UTC

- Sitings via individual identification
--> Distinctive natural markings
~Trail end of dorsal fin
~Distinctive gill flaps, caudal fin, or pelvic fin
~Pigmentation patterns (Domeier & Nasby, 2007)

PROS:
-Data is not at risk of disruption by the shedding of an external trading monitor (Anderson, 2011)

CONS:
-Quality of data is dependent on ideal marine conditions (water visibility, diving difficulty, intensity of labor output) (Anderson, 2011)
- Data collection is subject to human error through observation (Domeier & Nasby, 2007)
-Physical traits of sharks can modify as the animal ages (Figure. 1)
-The activity of the shark remains unconfirmed during the times that it is not seen (Anderson, 2011)
-Information is limited to coastal environments, usually around common feeding sites (coastal pinniped congregations) (Hammerschlag, 2011)

Figure 1: (a) A photograph of the leading end of the dorsal fin of a shark, identified in 2004, then featuring a large laceration in the fin in 2005, and again in 2008 with the same laceration healed and scarred. (b) A shark identified by dorsal fin tics in 2008 and then photographed two months later with new dorsal fin lacerations. (Anderson, 2011)

Tell me about SAT tags...

broadbas — 2017-02-25 15:18:28 UTC

-Provides an evaluation of long-term migrational patterns (Hammerschlag, 2011)
-Analyzes habitual depth and water temperature preferences (Hammerschlag, 2011)
-Requires a tag to "ping in" to a passing satellite two or more times (Hammerschlag, 2011)
- Argos Data Collection and Location Service process the pings via Doppler-shift calculations to eliminate possible error by the Doppler effect (Hammerschlag, 2011)
- Error is less than 1 km (Weng, 2005)
- Pings occur as signals from SPOT tags when the tag breaks the surface of the water (Jewell, 2011)

And SPOT Tags?

broadbas — 2017-02-25 15:42:24 UTC

- Provide the satellite signal for SAT tracking using GPS transmission (Jewell, 2011)
- Smart Position Only/Temperature transmitting Tags
- Shark must be lifted out of the water so that the tag may be surgically placed by drilling into the dorsal fin (Jewell, 2011)

The Controversy

broadbas — 2017-02-25 15:57:50 UTC

-SPOT Tags are highly invasive
-It is stressful for the shark as the animal is removed from the water for placement
- Causes severe long-term damage to the dorsal fin and permanent deformation, depending on the duration of the tag (Figure 2) (Jewell, 2011)
--> Tissue degradation
--> Possible infection
--> Fouling on the tag
- Affects the functionality of the dorsal fin

Figure 2: Images taken of the effect of the presence and removal of a SPOT tag over a period of 24 months (Jewell, 2011)

What about PAT Tags?

broadbas — 2017-02-25 16:17:22 UTC

- Another type of SAT transmission tag used to track shark movements
-Pop-up Archival Tags
-Monitors accurate depth, temperature, and ambient light (Sims, 2010)
-Less invasive than SPOT tags (Hammerschalg, 2011)
--> Affixed onto the body at the base of the dorsal fin by means of a tether (no need to remove the animal from the water or inflict direct human contact)
--> Detaches from the shark at a predetermined date and time, then floats to the surface to be collected and processed by scientists

CONS:
-Data collection is limited to the information derived from the PAT Tag upon deployment (Hammerschlag, 2011)
-Results in possible inaccuracy of data wherein ambient conditions vary as the shark travels (Hammerschlag, 2011)
-Deployment of the tag into the musculature of the shark can result in susceptibility to infection (Hammerschlag, 2011)
-Additionally, the tether of the tag remains embedded in the skin after the PAT tag detaches (Figure 3) (Hammerschlag, 2011)

Figure 3: An image of the remaining tether of a PAT Tag in the musculature of the shark after the tag itself has detached (Hammerschlag, 2011).

What have we learned here?

broadbas — 2017-02-25 17:00:08 UTC

- Satellite tracking of sharks has been pivotal for understanding their long-term migrational routes
- Non-invasive identification methods are best used for short-term data as sharks aggregate in known feeding areas
-There are two types of SAT tags that are deployed for the method of tracking sharks--> SPOT & PAT
- SPOT tags are highly invasive to the animal and cause significant disrepair to the dorsal fin, yet provide highly accurate data
-PAT tags are less invasive, although still harmful to the individual, and provide less accurate information than SPOT tags

Chum for thought

broadbas — 2017-02-25 17:04:18 UTC

Is it worth permanently disfiguring a few individuals for the sake of understanding more about the species in the interest of overall conservation?

Please feel free to comment on any of these slides and start a conversation!

Literature Cited

broadbas — 2017-02-25 17:08:20 UTC

Cailliet (1985). Preliminary studies on the age and growth of the white shark, Carcharodon carcharias, using vertebral bands. Memoirs of the Southern California Academy of Sciences. 9:49–60.
Jewell (2011). Effects of Smart Position Only (SPOT) Tag Deployment on White Sharks Carcharadon carcharias in South Africa. PLoS ONE 6(11): e27242.
Jorgensen (2010). Philopatry and migration of Pacific white sharks. Proceedings of the Royal Society B. 277: 679-688.
Weng (2005). Satellite tagging and cardiac physiology reveal niche expansion in salmon sharks. Science. 310:5745. 104-106

Domeier & Nasby (2007). Annual re-sightings of photographically identified white sharks (Carcharodon carcharias) at an eastern Pacific aggregation site (Guadalupe Island, Mexico). Marine Biology. 150:977–984.
Hammerschlag (2011). A review of shark satellite tagging studies. Journal of Experimental Marine Biology and Ecology. 398: 1-2. 1-8.
Sims (2010). Tracking and analysis techniques for understanding free-ranging shark movements and behavior. Biology of Sharks and Their Relatives. vol. II, CRC Press, Boca Raton. 341-392.

broadbas — 2017-02-25 17:38:35 UTC

Figure 4: Photograph taken in 2012 from a research vessel in Mossel Bay. The shark has followed a chum flow to the boat and then has been baited with a tuna head. Once the fin is exposed, photographers snap pictures of the dorsal fin to identify the individual. (Photo: Alexa Broadbent).