My alarm rudely interrupted my sleep at 2 a.m. I launched from slumber and headed for my laptop on the table in the salon. Within a minute, I was reviewing the latest sea surface conditions from overnight satellite passes. The weather still looked great for a canyon run, but the water had shifted from the last clear images I saw a couple days ago. Now we would have to run to the Norfolk Canyon instead of the Washington to intercept a strong temperature and color change I knew held our best chances for tuna and billfish. Without that intel, we might have searched for hours in an area that held fish several days ago, but would have been a desert that day.
In today’s world, if you’re not using satellite mapping to study the water and gather information in the days prior to an offshore fishing trip, you’re missing out. The ocean is a bit like a desert, in which most of the fish congregate in oases of favorable water conditions amid vast swaths of unproductive water. By doing your homework on ocean conditions, it’s possible to home in on likely areas and launch with a gameplan that can greatly increase your catching-to-fishing ratio.
How to Best Use Satellite Images for Fishing
Satellite images are an incredible tool giving offshore fishermen a way to watch the ocean’s movements and predict where to find pelagic species. By learning which indicators show conditions that concentrate fishing action instead of dispersing it, anglers can often predict when, as well as where, the bite is likely to be the hottest. As a warm-water eddy spins off from the main current, you can watch for days. Putting all that intel together will help you save fuel by spending more time fishing in productive water, rather than randomly searching the ocean for a bite.
Look for boundary zones to improve your fishing. Consider how the water is going to interact with the bottom structure. Look for indicators in satellite images that help you find the signs on the water that lead to that “20 percent of water that holds 80 percent of the fish.” Don’t focus too heavily on an exact temperature or color, think edges.
Find Waters Holding Fish
While anglers cannot see fish from satellites, they can see the physical conditions that fish prefer. Fish do not have an ability to change a thermostat, so they need to move with the water temperature they’re comfortable in. While tuna and swordfish have some limited ability to self-regulate their internal temperature, they move with favorable temperatures just like highly temperature-sensitive species such as dolphin and wahoo. Additionally, fish live to eat, and pelagic fish species have a knack for finding forage fish. Today’s satellite mapping might not be able to show you fish, but it absolutely can show the ocean conditions pelagic species prefer.
How to Read Sea Temperature Data
Temperature, color and altimetry are most useful for offshore fishing. Water temperature seems obvious, but satellite sensors can only see the very surface of the ocean, or skin temperature. During early morning hours the surface appears cooler, while after a hot day it appears warmer than the temperature displayed on your on-board water temperature sensor. And this is just the surface temperature. Don’t get hung up on the absolute temperature on your gauge or in a satellite image, rather use the temperature as an indicator of the features and circulations of different water bodies like the Gulf Stream’s warmer waters versus cooler coastal currents.
Best Chlorophyll Levels for Fishing
Some satellites provide ocean color, while others provide chlorophyll concentrations—where more chlorophyll typically means greener water and less is clear blue water. This helps us to see the clarity and the plankton or suspended sediment content of the water. Satellites can measure the top layer of water down to as deep as 100 feet, depending on just how clear and clean the water is. The key is not necessarily to identify a specific color, but rather where the boundaries are, what the circulation is like and where the current comes from. For example, anglers rarely find yellowfin tuna, wahoo or marlin in turbid coastal waters. More often they are found in the cleaner, bluer offshore waters.
Does Water Height Matter in Fishing?
Satellite altimeters measure the height of the ocean’s surface. Areas where the surface is higher typically indicate a downwelling where the water is nutrient poor and less likely to hold fish. Areas with lower sea surface height tend to coincide with upwellings that have more life. Once again, use these images to focus on the boundary areas between highs and lows.
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Fish the Eddies of Ocean Currents
Ocean currents like the Gulf Stream in the Atlantic or the Loop Current in the Gulf of Mexico tend to be comfortable for pelagic fish and the bait they love to eat. When eddies spin off these currents, the eddies often carry fish with them. Following the motion of these spin-off eddies is key to finding the best fishing conditions. Off the northeast US, the offshore season’s success is largely dictated by how and when these spin-off eddies come off the Gulf Stream and how fast they move west and south, before eventually being swallowed back up into the Gulf Stream.
Notice the Gulf Stream eddy labeled A in the image below (top). This eddy is circulating clockwise, while moving from east to west. Usually, these eddies hold pelagic fish like tuna, mahi and billfish. Ideally, anglers want to fish where the current pushes from deeper to shallower into a canyon wall. You can also notice that the sea surface temperature cannot be seen through clouds. The white areas in the image are cloud locations that have been removed from the image.
In the image above (bottom), from a few days later, the eddy has pushed west. I would choose to fish along the 100-fathom curve around the “triple zeros” of the Hudson Canyon. This is where the circulation is pushing good Gulf Stream water from deeper to shallow, creating an upwelling effect against the canyon wall which is likely driving bait toward the surface. I would avoid the area north of the Hudson Canyon where water is pushing from shallower to deeper water.
Marlin Fishing in an Upwelling
Upwelling is another condition to watch for. This occurs when current hits a canyon wall or seamount. The water must go somewhere, so it goes up and over the structure. This brings cooler, nutrient-rich water toward the surface, where the sun’s energy then grows the phytoplankton, which are eaten by the zooplankton, which then becomes food for the small baitfish, who then become feed for our target species.
Large-scale upwelling can be seen on the west coast of the U.S., but any upwelling is good, especially when it has been stable for a few days. Always try to track the circulation as you are looking at imagery and find areas where the water is pushing from deep to shallow. Baitfish and other forage are either attracted to these areas or are pushed closer to the surface by the upwelling, increasing your chances for finding tuna, wahoo, dolphin and marlin.
Why Convergence Zones Attract Gamefish
A convergence zone is where two bodies of water come together. A divergence zone is an area where the water bodies are being pulled apart. Most of us have been lucky enough to see the visual signs of a convergence zone when our boat approached a weed line, or the edge of a strong green-to-blue front on the water, like the color break at the edge of the Gulf Stream. Generally, look for areas of convergence versus divergence along the edges of two water bodies.
When two bodies of water come together, one cooler than the other, the cooler water will go under the warmer water and all the sargassum and flotsam will create a weed line at this convergence edge. Bait is attracted to these areas, making it much more likely to find fish concentrated in the area hunting the bait. In a divergence zone, the weeds will be scattered and breaking up. While anglers still might find some life along divergence zones, the action is likely subsiding, as the bait is being dispersed instead of being concentrated.
Where to Find the Best Satellite Images for Fishing
While you can dive into the internet and find inexpensive, even free satellite images, you most likely want to start out paying for a more complete service that helps point out optimal fishing spots. Engage these providers in discussions to understand what they are seeing and why they believe the bite will be at one location or another. This will help you to appreciate the sometimes very minor differences in satellite image data that will highlight your best chances for catching. Additionally, as these providers are typically talking with many fishermen in the same area you are fishing, they can help identify which water bodies have been holding fish or bait, again, increasing your chances for success.
- Canyon Runner (www.canyonrunner.com) provides a concierge-level coaching service, including access to satellite images, weather and fishing reports. Their app allows you to see real-time locations of their pro staff and they highly encourage live conversations to help you develop a plan for your best chances for catching on the days you are able to fish.
- ROFFS (www.roffs.com) provides satellite images and oceanographic analyses to help direct your fishing efforts.
- Sirius XM Marine (www.siriusxm.com/marine) provides images and analyses directly to your boat.
- SatFish (www.satfish.com) provides low cost, easy to use satellite data in an app designed to help you view the images easily.
- Rutgers University (https://marine.rutgers.edu/cool/data/satellites/imagery) provides near real-time access for free to sea surface temperature data.
About the Author: Louis Chemi’s lifelong passion for fishing is deeply rooted in his extensive experience in the marine industry. From his early days fishing in Long Island Sound to his time as a captain and mate on various boats, Chemi has accumulated a vast amount of on-the-water knowledge. With a strong foundation in engineering and marine physics, Chemi has also applied his technical expertise to the fishing industry. He has worked in various roles at Raymarine, Simrad, Lowrance and B&G, including developing fish-finding services and designing marine electronics. More recently, he spent time growing Freedom Boat Club’s franchise business. Today, Chemi continues to explore new fishing waters and share his expertise as a board member of the Recreational Boating & Fishing Foundation.
