Lesson 15: How little turtles know where to go

Question 1

migration in the north Atlantic gyre

Answer 1

• evidence that turtles use positional (map) information (not just compass information) from the Earth’s magnetic field

Question 2

where does map information and earth’s magnetic field come from

Answer 2

the magnetic inclination angle and the magnetic intensity

Question 3

where does compass information come from

Answer 3

the directionality (polarity) of the field lines
- inclination angle gets steeper as you move toward the poles
- intensity gets stronger as you move toward the poles

Question 4

approaching the north pole

Answer 4

large inclination angle

Question 5

near the equator

Answer 5

small inclination angle

Question 6

isoline

Answer 6

is a line that we draw connecting all the points that are the same
- ex: everywhere along this (in the picture) inclination angle is the same: 60 degrees
- the line is called an isoline of inclination or an isocline

Question 7

magnetic coil system

Answer 7

• with this coil system, we were able to control the INTENSITY and INCLINATION at the same time

Question 8

the north atlantic gyre test

Answer 8

testing the idea that turtles can sense inclination angles and use them to figure out location
— 60 degree isoclinic in red at northern edge of gyre
– 30 degree isoclinic in red at the southern edge of gyre

Question 9

response to the 60 degree inclination angle

Answer 9

• most went south

Question 10

response to 30 degree inclination angle

Answer 10

• most went east to northeast

– east didn’t seem right – we only changed inclination – maybe they needed the field to be more realistic – not the full reaction

Question 11

main take away from the inclination experiments

Answer 11

hatchling loggerheads can distinguish between different magnetic inclination angles and respond to them in ways that make sense

Question 12

north Atlantic gyre testing: intensity

Answer 12

testing the idea that turtles can sense magnetic intensity to figure out their location

Question 13

isolines of equal magnetic intensity

Answer 13

• intensity also increases as you go north and forms isolines
• everywhere along the line indicated – the intensity is the same: 45000 nt>
  ^^ this line is called isodynamic or isoline of intensity

Question 14

isodynamic

Answer 14

isoline of intensity

Question 15

tilt of lines

Answer 15

intensity lines are tilted relative to inclination lines so individual places in the ocean have unique combinations of intensity and inclination - each place has its own magnetic address

Question 16

experiment

Answer 16

either varied just intensity or just inclination while keeping other parameters constant
- this produced combinations of inclination and intensity that don’t actually exist in nature
RESULTS

• high intensity more on west side, turtles swam east
• but if given high intensity on the other side of the gyre, ten turtles swam west
• can sense intensity – go in the directions that make sense
• hatchlings responded to different magnetic addresses in ways that kept them n the gyre system

Question 17

innate?

Answer 17

• the hatchlings had never been in the water so the gyre migration responses are clearly innate
  BUT
• we also know that turtles are capable of doing more than just responding to innate signals about position

Question 18

experimetn: can turtles use the magnetic field to find specific places along the US coast

Answer 18

• the north-south coastline intersects with the patterns of isolines so every place along the coast is marked by its own inclination angle and its own intensity
• SO THEORETICALLY a turtle could just swim north or south along the coast until it hit the magnetic field of the specific location

Question 19

magnetic field experiment set up

Answer 19

to test if turtles can find specific locations using magnetic fields, we used ocastal juveniles (teens) that had a feeding area in Melbourne Beach, FL. Then we made a really big magnetic coil system
- captured the teens from the reef in melbourne beach where they feed
- tehtered them up in a tank in melbourne beach (near capture site)
- tehter was connected to electronics that recorded the direction the turtle was swimming
- the elcetronics and coil were controlled from computers inside
- used computers to change magnetic field and monitor swimming direction

• and then we gave them the magntic field (inclination and intensity off Jekyll Island off the Georgia coast)
  OR
• gave them the magneticfield (inclination and intensity) of Tavernier Key in south flordia

CONCLUSION
- juvenile green turtles have a geomagnetic positioning system that assists them in navigating to specific locations
—- in other words — they have the basics of a magnetic map!!!!!!!

• up near jekyll island, went south
• down near tavernier key, went north

Question 20

what were the 2 islands

Answer 20

jekjyll island (north) and tavernier key (south)

Question 21

what about adult turtles

Answer 21

• female sea turtles show Natal Homing in which they come back to the nest on or near the same beaches where they themselves hatched

Question 22

Geomagnetic imprinting hypothesis

Answer 22

suggests that little turtles learn the magnetic address of their home beach and come back to it years later as adults

Question 23

why is testing the geomagnetic imprinting hypothesis a tough problem

Answer 23

• life cycle takes a minimum of 20 years so no good way to tag them and wait for them to come back

Question 24

over time what can happen to the magnetic field lines

Answer 24

they can wobble and move a little

Question 25

converging isolines

Answer 25

increased nest density

Question 26

diverging isolines

Answer 26

decreased nest density

Question 27

converging isoclinics

Answer 27

increased nest density relative to average

Question 28

diverging isoclinics

Answer 28

decreased net density relative to average

Question 29

20 years later

Answer 29

calculated the nesting density for each country in Flordia over the last 20 years and matched it to whether or not the field lines and converged

• there would be no affect of secular variation on nest density if turtles were not using magnetic field to find their favorite beach