How to Read Chlorophyll Charts to Locate Pelagic Fish

Which chlorophyll image should you trust when the latest pass is cloudy?

Chlorophyll charts come from satellite sensors that each pass over once a day, so one cloudy pass can leave you with nothing. Check images from other sensors taken at different hours, and compare them with the latest sea surface temperature pass, which updates far more often, to place the color change.

Thomas Hilton shows four image options: NASA's MODIS Aqua, a NOAA MODIS Aqua backup that is a little coarser, MODIS Terra and VIIRS. The backups exist because a NASA server outage once left anglers without chlorophyll for an extended stretch. He prefers the NASA MODIS Aqua shot and was finding VIIRS very good, almost better than the original. When the overnight shot didn't come in, he laid an older MODIS Terra image against the newest SST and placed the color change from the temperature break, then saved it to navigate on.

Where do wahoo, tuna and marlin hold near muddy river water?

Pelagic fish hold on the edge where green, nutrient-rich water meets clean blue water, not in the green itself. Near a river mouth that edge is the plume's boundary: the fresh water brings the nutrients, the blue water brings the clarity, and bait and predators work the line between the two.

On the chart off Orange Beach, Hilton reads the red as "your ugly, dirty, brown, fresh river water," with water hyacinths in it, and says to stay out of it. The edge where that water meets nice blue ocean water is where he'd fish for wahoo, tuna and marlin. Captain Patrick Ivie explains why the morning check matters. In the Gulf of Mexico you can go to bed offshore and wake up to completely different water because the current switched, and in a tournament with two and a half days to fish, the crew has to adapt and move on what the chart shows that morning.

Inside the video

• What chlorophyll measures, and why greener water is more turbid
• Four image sources and the one-pass-a-day limit
• Matching an older chlorophyll shot to the newest SST pass
• Reading river water and the edge against blue water
• Saving a color change to navigate on offshore
• Captain Patrick Ivie on adjusting overnight during a tournament

Chlorophyll Chart Questions

Color Is Where the Food Chain Starts

Water color narrows the search, and the next step is matching it to the fish you're after. That's covered in planning tuna, wahoo and marlin trips with satellite charts.