Juvenile Salmon Dispersal: A Drifter-based View

~ Summer 2008 Deployments ~

32 satellite tracked drifters will be deployed in each of the 2008 and 2009 summers. Deployments are in groups of 4 drifters deployed at 10 – 30 day intervals. These drifters are carried along by the motion of the near-surface waters, motion that is driven by tides, the wind and other forces.

The drifters are being released by residents of Quinhagak, a village located on the eastern shore of Kuskokwim Bay. Our deployment photo galleries gives you a glimpse of the deployment sequence, the team out on the water and the drifters in the process of freeing themselves from within their cardboard cocoons. We have photographs from Deployment #2 and Deployment #6. MAP agent Terry Reeve gave an in-class demonstration of the drifters in September 2008.

The first drifter set began broadcasting on June 8, 2008. Each unit attempts to acquire a location fix every half hour. Drifter data is delivered to our processing center in Fairbanks once per day and the data figures shown below are updated daily at 6:30 AM Alaska time. If you have questions about the drifters, please feel free to send us an email with this link or write to Tom Weingartner at email address: weingart@ims.uaf.edu.

Note that 1 nautical mile = 1.15 statute miles = 1.85 kilometers.

As of January 8, 2009 it appears that the last transmission from the 2008 drifter deployment has occurred. The final few drifters were right at or in the ice edge when their communication ceased in the first week of January. A nice thermal image taken by satellite on January 7th shows the ice extending most of the way to St. Paul Island. We are processing the drifter data and will present some results at the 2009 Alaska Marine Science Symposium in Anchorage on January 21.

View the Powerpoint Presentation shown at the 2009 Alaska Marine Science Symposium

Skip the Rest of the Slide Show, Just See the Animation (with music!)

Thanks to Barbara Lamb for the use of her recording "Sally Goodin" from her Fiddle Fatale CD. The tune jazzes up our drifter animation, showing how tides form the "backbeat" of the ocean motion. Visit Barbara's Website at www.barbaralamb.com!

Drifter Data by deployment:

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Animation of Daily Mean Position for All Drifters: With 6-day tails!

Animated Movie of Deployment #1 moving for 2 weeks

Listen to Marine Advisory Agent Terry Reeve explain to Fish Radio's Laine Welch how we hope to encourage students to discover more about their local ocean environment by participating in a University based science research project.

Plots of Data: Individual Drifters
Drifter 1
Drifter 2
Drifter 3
Drifter 4
Deployment 1: 8 June 2008
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Deployment 2: 21 June 2008
Deployment 3: 13 July 2008
Deployment 4: 23 July 2008
Deployment 5: 3 August 2008
Deployment 6: 17 August 2008
Deployment 7: 29 August 2008
Deployment 8 : 29 September 2008

Notes about the drifters and responses to questions received:

  • Note that we have added bathymetric contours (20m, 40m, 60m, 80m, 100m) to some of the plots to help viewers orient themselves.
  • How long do the juvenile salmon remain near the drifters? We do not know this in a precise fashion. We do know that the young salmon probably need to get to the deep water of the Bering Sea basin before the winter cooling on the shelf lowers the water temperatures to near the freezing point. We also know from previous work (e.g., that of the BASIS sampling program and others) that young salmon shows maximal distributions in the outer coastal/inner mid-shelf region in the late summer/early fall time period, which roughly agrees with our drifter trajectories (you can see this by looking at the daily drifter movie). Perhaps some day we can have a more comprehensive program that will allow us to sample salmon in the vicinity of the pool of drifters. Until then, we can use the data collected here to gain more insight about the physical environment and speculate upon what effects this environment may impose on the young fish.
  • A question arose about the speed of the salmon noted in the ADN article (max speeds of 20 miles/day = about 40 cm/s = about 0.8 miles per hour) in comparison to the salmon that our passive drifters are trying to mimic. The chinook salmon tagged in the POST program are about 14 cm (~5.5 inches) whereas our drifters were conceived to mimic the pink salmon who out migrate from the river at lengths of about 3.5-5 cm (1.5-2 inches). These smaller juveniles can not swim as quickly as the larger ones and are less able to out swim the ocean currents. As the juveniles grow through time, however, they will eventually be able to out swim the ocean currents. Also note that a fish's average speed is probably quite a bit less than their maximum speed.
  • There was an interesting article on salmon tracking published in the Anchorage Daily News on November 30th: http://www.adn.com/wildlife/story/606448.html - the article describes some of the efforts undertaken by the Pacific Ocean Shelf Tracking Project (POST) program.
  • The 2002 drifter deployment hinted at the possibility of surface waters from the near shore dispersing across the shelf to deeper waters north of Nunivak Island. The 2008 deployment (south of Nunivak Island) has shown a similar character in these fall months: after a summer with somewhat stagnant near shore flow, since September the drifters have been headed in a west-southwesterly direction. We will be looking at the atmospheric conditions that led to this flow in the coming months.
  • The drifters are somewhat fragile devices: their antennae are liable to become damaged if the drifters are caught in heavy waves, beat upon the shore or in ice. For this reason and other possible failure modes, we expect that many of the drifters will cease transmitting before the end of their planned deployment lifetimes. Indeed, as the storms have increased in frequency and intensity through the fall, we have obtained reliable communication from a dwindling number of drifters.
  • Why not fix them once they fail? Once the drifters have ceased transmitting, we no longer have a good location fix - finding them in the water would be nearly impossible and cost prohibitive. Three beached drifters were recovered: one was deemed to be in still good operating condition and redeployed; the other two were damaged. A slightly damaged drifter will have different flow characteristics from an undamaged drifter and so we chose not to redeploy the damaged units. Since the satellite fees to transfer the data are appreciable, we want to make sure that we are only paying for data that we are confident is good.
  • Deployment #3 had three drifters ground near the mouth of the Kuskokwim River during a period of winds from the south in mid-July. We had the fortune of colleagues who were able to recover all three drifters about one week after the grounding. Two of these drifters were damaged and were not redeployed; the third drifter (#81008) was in good condition and redeployed just offshore from the grounding site.
  • Drifter #81003 from Deployment #5 failed after one week of sporadic transmissions but somehow resurrected itself in early october after nearly 2 months without communication. We are happy to have 81003 back in communication.
  • Drifters that are not on the Present Location map have ceased transmitting and have likely failed.
  • Spikes in drifter locations or Sea Surface Temperature can be due to faulty communication between the drifter and the satellite or the satellite and the ground station. Our error-checking algorithms strive to remove these bad data points, but some slip through and are plotted nonetheless.

Button and Map Legend

Button / Symbol

Close-up figure of Kuskokwim Bay

Medium-range view from Kuskokwim Bay to beyond Nunivak Island


Time Series of Longitude, Latitude and Sea Surface Temperature


First good position fix

Periodic Link (nominal 30 minute fix)
Dark trace = last 24 hours, Light trace = previous data


Last known location fix

Triangle (v)
Deployment #1
Deployment #2
Deployment #3
Deployment #4
Triangle (^)
Deployment #5
Deployment #6

Local Weather:

Click for Cape Newenham LRRS, Alaska Forecast

National Weather Service Marine Forecast

Bering Sea Related Links:

The Bering Sea and Kuskokwim Bay from above: Images from Space.

Bering Sea Ecosystem Study


Data Collection and Satellite Communications:

The drifters transmit data through the ARGOS satellite communication system. There are approximately 16,000 ARGOS platforms worldwide collecting and sending data. These satellites orbit the earth's poles at about 11,000 kilometers per hour at an altitude of 850 kilometers, and there are fifty ground stations that receive the transmitted data.

Primary location fixes are determined through communication with a Global Positioning System (GPS) satellite, with an attempt every half hour to record a fix. A secondary (less accurate) location fix comes from the ARGOS system satellite. These satellites calculate each drifter's position using the Doppler effect. As illustrated below, the signal received by the satellite gets faster as the distance between the two instruments decreases, and gets slower as they move out of range. The satellite uses the rate at which this cycle occurs in comparison with its own position and speed to estimate longitude and latitude, then sends that to grounded receivers along with any other data from the platform.

Here's some examples of the drifters being used in this project:

Photo courtesy Myrl Hendershott and Douglas Alden, U. California, San Diego


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