Dawn is breaking on the horizon, and the sea is calm and full of promise. The boat’s tanks are full, the lines are carefully set, and all the gear is perfectly organized. You’re ready to start a fantastic day of offshore fishing — but one question remains: which direction should you head?
Sea Surface Temperature (SST) maps are your best ally in finding the most productive fishing spots! Or at least, the areas most likely to attract the fish you’re targeting.
Experienced anglers know it well: more than any other factor, water temperature dictates fish behavior. Being cold-blooded, fish constantly seek out the temperature zone where they feel most comfortable — even if it means traveling thousands of kilometers. And when they come across an area where the temperature changes suddenly, they gather there in large numbers… a real boon for fishermen!
Water temperature maps also reveal the zones where the food chain begins to form — areas teeming with life that, in turn, attract an abundance of fish.
As you’ve probably guessed, in this article we’ll take a closer look at water temperature, how it influences fish behavior, and how to use this data to find the best fishing spots using TZ iBoat and the SportFishing Ocean-O module!
Simply display the SST in TZ iBoat
To locate the ideal fishing zones based on water temperature, here’s how to activate the SST data display in TZ iBoat. Start by activating the SportFishing Ocean-O layer to display the data. 
Next, activate the SST Color layer to display sea surface temperature in color. 
By default, the legend is in Automatic Mode, adjusting the Min and Max values according to the temperatures visible on screen. This mode is interesting because it maximizes contrast, making all the colors of the gradient visible on screen. When you change zones, these limits are automatically recalculated, which can alter the colors displayed. As colors are constantly changing, there is no stable reference point.
What is the temperature front and why is it important?
In the ocean, temperature fronts form an invisible boundary, acting as a natural barrier between warm and cold waters. This thermal contrast influences the behavior of marine species: forage fish stay on the more favorable side, while predators such as tuna and swordfish patrol nearby to hunt.
Why do fish love temperature fronts?
Fish gather around thermal fronts because they offer ideal feeding conditions: nutrient upwellings from the depths lead to high concentrations of plankton and small marine prey. To feed, fish move back and forth between warm and cold waters, seeking to stay in waters of optimal temperature. Forage fish mainly prefer warmer waters, while predators, such as tuna, approach these areas to hunt. Although some fish avoid excessively cold water, they may occasionally venture into cold water upwellings to feed.
Find the fronts?
Have you ever hiked in the mountains? On a topographic map, contour lines show variations in terrain elevation. The closer together they are, the faster the altitude changes over a short distance. The same applies to a thermal front: the closer the temperature lines, the faster the transition between warm and cold water. It’s an area where the ocean changes dramatically in just a few kilometers, just like a sudden mountain pass on a map.
To observe it, first activate the SST Contour Lines layer. Then look for areas where these lines are particularly tight: you’ve found a thermal front!
Finding the thermal comfort zone of fish
Some species, such as tuna or marlin, travel thousands of kilometers every year to follow ideal temperature zones, while others move over shorter distances. Fish prefer to live in waters whose temperature corresponds to their thermal comfort zone, neither too warm nor too cold. When the water is too cold or too warm, their activity decreases, they eat less and seek out more comfortable areas. The ideal temperature range varies from species to species and influences their distribution, activity and behavior.
The Blue Marlin is a migratory fish capable of traveling great distances to stay in waters that offer optimal thermal comfort. They are often seen off the Canary Islands in the Atlantic, but can migrate to other areas, such as the Caribbean or even off the coast of Brazil. These fish can travel up to 7,000 kilometers in less than six months, following ocean currents and warm zones where the water temperature is ideal for their survival.
Which temperatures for which fish?
Fish, like all marine species, have specific temperature requirements for their survival and activity. Each species looks for an ideal temperature range, called the thermal comfort zone, which varies from one species to another. For example, the Bluefish prefers water between 66 and 72°F, while the Blue Marlin is more comfortable in water between 74 and 82°F. These temperature differences influence their distribution and behavior, which can be crucial for anglers looking to target certain species.
Distribution of fish types according to Comfort Temperature. (Source: saltwatersportsman.com)
How do I display the thermal comfort zone in TZ iBoat?
Let’s take the example of the Blue Marlin, whose thermal comfort zone is between 66 and 72°F. Let’s see how to display this zone in TZ iBoat. Start by displaying the SST in color. Next, switch the legend to Manual mode to see only the temperature range we’re interested in, and thus to view the zones where this fish is likely to be found! To do this, press “A” to switch to manual mode and adjust the minimum value to 66 and the maximum to 72. This will highlight on your screen the zones corresponding to the Blue Marlin’s thermal comfort zone.
What you need to know
Upwelling zones: nutrient fountains!
Upwelling zones are localized regions where cold water rises from the depths to the surface, carrying large quantities of nutrients with it. These upwellings, visible at lower surface temperatures (SST), act as veritable “nutrient fountains”, stimulating the growth of phytoplankton, the basis of the entire marine food chain. This phenomenon attracts a wide variety of species, including game fish. To optimize your chances, it’s particularly interesting to target the edges of upwelling zones, where the water becomes clearer (less turbid) and warmer.
Eddies, where currents converge
Eddies are usually detected by observing ocean currents. However, here we show that it is also possible to use SST (Sea Surface Temperature) to detect these phenomena. This highlights the power of SST, which can offer information as precise as that obtained from currents.
Eddies, or whirlpools, can be identified using SST and appear as areas where the temperature is rolled up on itself. A cold eddy appears as a pocket of water colder than its surroundings, while a warm eddy has a higher temperature. Temperature fronts are often more pronounced at the edges of ocean currents and eddies.
Effect of wind on temperature
Near the coast, winds can cause the surface layer of the ocean to shift, driving sun-warmed water out to sea. This movement creates a vacuum that is filled by the upwelling of cold, nutrient-rich water from the depths. This phenomenon, known as coastal upwelling, leads to a local drop in surface temperature (SST) and strongly stimulates the production of phytoplankton, the basis of the marine food chain. These areas then become veritable biodiversity hotspots, attracting numerous species, particularly those targeted by sport fishers.
A good example of this phenomenon can be seen off the coast of Peru, in the Humboldt Current, one of the world’s most powerful coastal upwelling systems. This phenomenon results from the combined action of trade winds, which blow from southeast to northwest along the coast, and the Coriolis force, which deflects surface water masses offshore.
Bathymetry
To identify the most interesting areas for sport fishing, take a look at the bathymetric map (Layer>Chart>TZ BathyVision). It shows where the seabed drops sharply: these steep underwater slopes, known as strong bathymetric gradients, encourage the upwelling of nutrient-laden cold water. These steep gradients are found at drop-offs, where fish can sometimes take refuge, but above all benefit from an abundance of food. This phenomenon attracts a wide variety of fish, ideal for sport fishing.
The screenshot below perfectly illustrates the relationship between a strong bathymetric gradient and a thermal front: where the relief plunges sharply, the temperature also changes rapidly, creating a zone conducive to the concentration of fish.
A closer look reveals two areas where temperature fronts cross contour lines, forming perfect spots for fish. The combination of the thermal front and the steep bathymetric gradient creates areas that offer both food and refuge, making them particularly abundant in fish and highly sought-after by anglers.
| 👉 To Go Further… |
“Satellite” or “Cloud-Free” SST data: which to choose? |
TZ iBoat offers two types of temperature models, each with its own advantages and disadvantages, which are detailed below.
SST data comes from a variety of sources, including satellites, buoys and ships. The quality of this data depends on weather conditions and the equipment used. In TZ iBoat, we use two main models: Satellite Data Model and Cloud-Free Model.
The Satellite Data Model (ACSPO data) uses raw data which may contain measurement-free zones (holes), due to clouds, which satellites cannot penetrate. The resolution of this data is 2 km, enabling precise identification of temperature variations.
In parallel, we offer the Cloud-Free Model (MUR data), an improved version of SST data without holes. Missing data is reconstructed from temperatures in neighboring areas and from advanced ocean models. The resolution of this model is 4 km.
In short: become a strategist with SST!
Of all the data available in SportFishing Ocean-O – SSH, currents, chlorophyll – SST is the flagship. It provides a wealth of crucial information for the angler, notably by pinpointing thermal fronts, targeting the thermal comfort zone of species and identifying nutrient-rich areas thanks to upwellings, eddies and wind effects. While they are all important, SST remains an indispensable ally in maximizing the chances of success at sea!
In our next article, we’ll explore how to use SSH (Sea Surface Height) to further refine your fishing strategy.
Happy fishing with TZ iBoat!