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Earth Science Applications Travelogue: Day 5: Thursday May 15
May 15, 2014

[image-51][image-94][image-78][image-110]On Wednesday, five sites were sampled and no Bluefin tuna larvae found. Today we moved to sites further east and south for continued sampling. Sampling progress is posted on a white board in the lab to keep day and night crews updated. 

From the CTD (physical environmental conditions data); the Mississippi River outflow appears to influence fluorescence values to spike at about 80 meters depth. Typically Bluefin tuna are not found to spawn in areas affected by major watershed discharges. In regard to temperature, a thermocline feature would enhance habitat suitability; however, this temperature gradient at depth is not being seen at most of the sites this week. Water temperature has been above 21 degrees Celsius, which is a minimum threshold for Bluefin tuna spawning. These in situ data in conjunction with satellite data are critical to evaluating environmental conditions that will lead to sampling in areas with the highest probability for success.

Early Thursday morning after the night crew (midnight to noon) went on watch two locations were sampled and at station 39 (28 15.43 N 87 15.095 W) two Bluefin tuna larvae were found in the S10 net. The very small number of larvae and large size of one, which likely indicated significant drifting, resulted in the decision to move to other sites and not deploy MOCNESS for more rigorous sampling. Unfortunately after this station the winds changed as the storm front began to move through the eastern Gulf and sampling was suspended. When I awoke late this morning to prepare for day watch (noon to midnight), sampling was still suspended and seas were 10-12 feet. 

With all the changes in sampling plans due to both weather and physical conditions in the Gulf, I asked Dr. John Lamkin/NOAA, chief scientist, to discuss the process of using satellite data for cruise planning and on a daily basis during the cruise.   John indicated that he and Dr. Mitchell Roffer/PI with Roffers Ocean Fishing and Forecasting Service began talking and reviewing satellite data about 60 days before the sampling is scheduled to begin, which would typically be in the March timeframe. Discussions focus on major oceanographic physical features and the location of the loop current.

One advantage of reviewing these data in March is that temperature features are more easily identified earlier in the year due to the isothermal (slow temperature changes) nature of the Gulf.  From this pre-cruise analyses John and Mitch plan tracks and coordinates for the sampling stations. Another major value of the satellite data is for input into habitat suitability models for the Bluefin tuna and other billfish that predict habitat suitability spatially one week into the future. The habitat suitability model outputs are used in conjunction with satellite data on current physical conditions to determine sampling locations and with initial sampling results the amount of time to spend at a given station.

Without the satellite data and habitat models, cruises would be much less efficient and be more like a random sample than the current adaptive sampling approach. The adaptive sampling approach uses satellite data and predictive habitat models to guide sampling and make modifications in near real time.

An event that occurred during this cruise illustrates the value of the satellite and model data. During leg 1 sampling across the loop current in the west central Gulf was not productive and major weather changes required that sampling plans be changed.  Satellite data that indicated eddies and fronts off the loop current (Bluefin are known to spawn near but not in the loop current) and warmer water with a high potential for thermoclines, and low transport conditions led to sampling in northwest central Gulf areas that produced over fifty Bluefin larvae. 

One very unique aspect of spending time at sea is the chance to experience some beautiful sunsets. I look forward to sharing more tomorrow on sampling updates and other activities.

Watch a video of sea swells during the research expedition:[image-36]

 

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The science team deploys an S10 net for sampling.
The science team deploys an S10 net for sampling.
Image Credit: 
Maury Estes
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Example of a habitat model output paired with satellite image
Example of a habitat model output paired with satellite image.
Image Credit: 
Maury Estes
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Chief scientist John Lamkin studies satellite images.
Chief scientist John Lamkin studies satellite images.
Image Credit: 
Maury Estes
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Sunset over the Gulf of Mexico
Sunset over the Gulf of Mexico.
Image Credit: 
Maury Estes
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[image-110]
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Page Last Updated: June 9th, 2014
Page Editor: Brooke Boen