Clean Water or Green Water
by Phillip Kuebler
The Earth’s surface is 70% covered in water, yet abundant sea life is only found in a percentage of that water. Experienced fishermen know that the color of the ocean can change from dark blue to bright green over a short distance; the fish know this as well.
Dark blue water is usually barren of nutrients and missing high oxygen concentrations; however, green water is rich in phytoplankton. Phytoplankton are floating green microscopic plants that are rich in chlorophyll.
Once you have phytoplankton, zooplankton are not far behind as the zooplankton feed on the phytoplankton, from there the zooplankton attract baitfish and in turn the baitfish attract larger fish. From a fisherman’s perspective, more phytoplankton means more life, and in the open water that usually means more bait fish. The larger the population of bait fish, the more likely the larger fish will follow.
Research shows that in ocean waters the presence of phytoplankton can increase the amount of dissolved oxygen in the water. Phytoplankton are plants, and in sunlight they use carbon dioxide and give off oxygen, attracting baitfish and also make breathing easier for larger fish. So…. during daylight hours the phytoplankton are larger fish friendly; however, at night things reverse. Without sunlight, the phytoplankton start using up the oxygen and releasing carbon dioxide.
However, oxygen levels are only part of the story as to why larger fish like the transitions or “rips” between blue and green water. Water clarity is also very important to larger fish, too much phytoplankton in the water scatters light and restricts vision making the baitfish hard to find for predatory fish that rely on their sight to locate and catch their prey. Larger predatory fish are attracted to the edge of greener water due to the increased oxygen content and larger population of baitfish in the water, yet due to visibility restrictions, the larger fish prefer to stay close to the cleaner water. This is a basic understanding of what attracts these larger migratory fish to the rip lines, the food source, and the oxygen; however, there is more to it - just because a rip line is present it does not mean fish will be there. Other factors such as sea surface height, or altimetry, play a role as well. The higher the sea height, the more downward pressure it places on the fish. This is commonly referred to as a down-welling. Fish do not like downward pressure as it forces them to work harder to maintain buoyancy, thus they avoid these areas of down-welling. Commercial fishermen consider these areas of down-welling ocean deserts, and avoid them. Instead they concentrate efforts on areas of up-welling and transitions between up-wellings and down-wellings. Up-wellings are important as they provide the nutrients for the phytoplankton. To summarize and bring us back to the beginning…..up-wellings bring nutrients which cause phytoplankton to grow, zooplankton then arrive to feed on the phytoplankton, then baitfish arrive to feed on the zooplankton then the larger fish we target will follow to feed on the baitfish.
How satellite imagery can help:
|Since these transitions between blue and green/chlorophyll rich waters are important to locating fish, the best tools for understanding where pelagic fish might be are regular observations of altimetry, sea surface temperature and chlorophyll imagery.
Up-wellings and down-wellings that the altimetry imagery shows us give us a window into likely conditions blow the surface. In addition, the patterns of the transitions between warm and cold water on the ocean surface can tell us quite a bit about where the water has come from and whether the conditions near the surface are likely to be suitable for particular fish types. The Chlorophyll charts present a slightly different picture and give us an idea what the base of the marine food chain is doing, and by understanding what the phytoplankton is doing we can make assumptions on the rest of the food chain.
Putting it all together:
|First, you need to know your fish and you need to know its preferred habitat.
The temperatures need to be right, there needs to be a good environment for baitfish, visibility needs to be good and so do oxygen levels. Too little phytoplankton in the chlorophyll image around your favorite fishing spots and there is not likely to be much action, too much green water and the water clarity will be too poor for hunting pelagics to find their prey, or to find your lures.
Also, how long has the phytoplankton bloom been sitting there? If it is a very recent bloom, the food chain has not likely had time to form yet; however, if it has been there for a few days then the food chain will be in full progress.
It is also good to look at historical data. If you have a really successful day, print a few of the satellite images afterwards, mark on them where you picked up the fish. Then use these as a reference for future trips. If, in the future, you spot similar conditions starting to develop you will then know to call your buddies and hit the water.
In the end, no amount of technology or instruction will guarantee you a successful trip. There is no substitute for experience, and everyone, including the experts, will have a bad day. Your best chance at success will come from applying all the information that is available. Most importantly, use your head. Thinking and deducting an answer from clues that are available is all part of the sport we call fishing.
For information on satellite imagery feel free to contact the author Philip Kuebler at (713) 582-1868. You can also access up to date satellite data for $89 a year at www.ripcharts.com.