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How Water Temperature Affects Fish Activity

Do you know how water temperature affects fishing activity and feeding? In this guide by 20Echo, we cover the key concepts you need to know. 

Taking note of environmental parameters like water temperature and its effect on fish activity is the secret to success for the thinking fisherman and fisherwoman. Maximizing your catch rate is so important, especially when life’s commitments limit our time out on the water. This is where having a great tool like 20Echo in your ‘tackle box’ really comes into play. 

In this article, let’s take a closer look at the relationship between water temperature and fish activity. We are going to get just a little technical here and there, so strap yourselves in folks.

Fish Biology

To really understand how and why different water temperatures affect fish activity, we need to understand how the fish body works. Let’s take a quick look at some key concepts:

Fish Are Cold Blooded

The first thing to understand is that fish are cold-blooded (poikilothermic). This is a term many people have heard of, but what does it really mean? 

Basically, it means that a fish’s body temperature is determined by its surroundings. So while we can maintain a stable body heat despite a wide range of ambient temperatures, fish are at the mercy of their environment.  

As a general rule, fish activity increases with temperature, but only up to a point. To summarize:

  • Environmental temperature determines the body temperature of fish
  • Increased body temperature usually equates to increased activity 

Now that you understand this key concept, it’s time to consider the next most important factor that affects fish activity: 

Oxygen Levels Vary With Water Temperature

The more active you are, or the higher your metabolic rate is, and the more oxygen you’re going to need. That is why our breathing rate increases when we’re rushing to pack the rods into the truck. Fish need oxygen just like we do, and the oxygen they use is in gas form, mixed into the water.  

The problem with an increased oxygen demand in warmer water is the inverse relationship between available oxygen and water temperature. A simple elementary school experiment demonstrates this perfectly. 

Pour water into a glass and leave it on a warm sunny window sill. What happens? Air bubbles form on the glass and rise to the surface, leaving the water. Those gas bubbles contain the oxygen that fish need to breathe. 

The take-home message here is that there is a sweet spot between higher temperature and lower oxygen availability that favors higher fish activity levels. Different species of fish are adapted to live in different geographical areas with different water temperatures, so the actual numbers are relative of course.

What Is The Best Water Temperature For Fishing?

The best water temperature for fishing is right around the average temperature for your area at the current time of year.  It will be business as usual for the fish species in your area because they are perfectly adapted to live in these conditions. 

A gradual, steady change towards the temperature that creates the highest activity level of your specific target species can turn good fishing conditions into great fishing conditions. When this sort of temperature change coincides with other positive condition intersections, fish activity can be high.  

Now, this goes both ways folks. When the water cools off in winter, it is well known that the bite gets really slow for some species. Some fish species like Bluefish undergo seasonal migrations that keep them within their optimal temperature range. 

For those that stick around, a few days of warm weather and favorable winds can bring them out of their dormancy and really light a fire under their bellies. 

Fish that are suffering from decreased available oxygen levels in the height of summer can be energized by a gradual cooling of the water and start to feed more aggressively. 

Different Tactics For Different Temperatures

Now that we know why warmer, or cooler water can decrease fish activity levels, you’re probably wondering if it’s worth fishing when the water is cold. 

Sudden temperature fluctuations in either direction can dramatically depress fish activity and feeding. You’re probably better off servicing your reels or practicing some new knots if that is the case. 

If there’s been a gradual shift towards unfavorable temperatures, the fish will probably have moved towards areas with water of their preferred temperature, and your challenge is to find them to catch them. 

Sometimes after a gradual change in water temperature, even the most favorable water temperatures around are still outside of the fish’s optimal water temperature. That’s when you’re going to need to find the fish and factor in their decreased activity levels. The fish will most likely be holding somewhere and remaining pretty inactive. 

To entice them, use smaller baits and, when using lures, work them slower. The fish aren’t going to burn up precious energy chasing after a large prey item that they may not be able to digest. A well-presented, tasty morsel is a lot more likely to get the bite. 

Stay mobile and remember that different fish species have different preferred temperature ranges. That means targeting a specific species in poor conditions might be a mistake when the conditions are perfect for another type of fish. 

Find The Right Water, Find The Fish

Fortunately for us, fish are pretty mobile creatures, and changes in water temperature are not uniform across an area of water. That means fish can move around to stay within the most comfortable water temperatures they can find. 

It does happen where a sudden drastic water temperature change catches fish off guard. Sometimes, they aren’t able to escape a temperature inversion and end up going belly-up, but usually fish know what to do. 

Where Can Fish Find Warmer Water?

  • On sunny days, water will tend to warm up in shallow areas as there is less volume of water per area there and the sun is able to heat the water faster
  • Where the water is shallow enough for the sun to penetrate to the bottom, areas with darker substrates and rocky bottoms can absorb the suns energy and warm the surrounding water
  • The surface layer of any water body will heat up in sunny, calm conditions
  • Certain wind directions can push warm surface water in specific directions. This causes warmer water to collect up against the coastline and in bays

Where Can Fish Find Cooler Water?

  • Overnight, shallow water areas can cool off because of the lower volume of water to surface area ratio
  • Deeper water is generally cooler than shallow water, and the temperature remains more constant there
  • Surface water can cool off after a period of overcast weather
  • Certain wind directions can push warm surface water away from the shore. Cooler water from below then takes its place

How Do You Know The Water Temperature?

Knowing how the temperature of the water affects fish activity isn’t going to be much help without knowing what the actual temperature is. In the past, fishermen would simply ‘feel the sinker’ to know what the water felt like where they were fishing. 

Today, we can refine this a whole lot by making use of technology, forecasts, and measurements from thermal imagery. We can even measure the water temperature ourselves with a thermometer. 

The 20Echo Way

When you log a catch on 20Echo, all the environmental parameters associated with your time and location are logged and stored. What could be easier? This way, you can spend more time fishing and less time measuring.

Measuring Water Temperature

A truly accurate thermometer is a pretty expensive piece of equipment. Luckily, we need precision more than we need perfect accuracy. Achieving that precision means using the same thermometer, in the same way, every time. By doing this, we get the same degree of error and are reliably able to pick up trends. 

Purpose-made fishing thermometers are the best type to use. Some people even get away with using models designed for aquariums as well. Remember folks, recording the conditions on a poor fishing day is just as important as on a great day. 

Watch The Weather

If you don’t have regular access to the water, go ahead and keep an eye on online information sources. Start to learn how the weather affects the temperature of the water in your area. This is a great way to estimate and predict changes in water temperature from forecasts without actually measuring. 

Final Thoughts

It doesn’t matter how well you can work the topwater, if the fish are holding deep, you’re not going to get that bite. Even though a bad day’s fishing is better than a good day at the office, taking notes, and keeping records of the environmental conditions is the secret to consistent catches. This is where 20Echo really shines by maximizing your time on the water and helping you catch more fish. Developing this knowledge and working out activity patterns really makes all the difference.

Ocean Altimetry FAQs

Why is altimetry important for fishing?

We first talked about ocean altimetry in 2016 in our blog post. Why should I care about altimetry? The surface of the ocean is not flat. There are high spots and low spots. Altimetry imagery indicates the ocean surface height in relation to mean sea level in centimeters. By studying the latest altimetry imagery, you can locate areas of upwelling and downwelling and the location of ocean current features and eddies.

Where does altimetry data originate?

There are various satellites equipped with instruments called altimeters. These instruments are incredibly accurate and measure the ocean’s surface’s height from space to within a few centimeters.

How often is 20Echo.com’s altimetry data updated?

The model is updated once a day.

Why doesn’t cloud cover bother Altimetry readings like it bothers SST and Chlorophyll readings?

Altimetry is measured using an altimeter. An Altimeter works by sending out a microwave pulse, bouncing it off the ocean’s surface. Since a microwave can go straight through clouds and still measure the return signal, it is not impeded by cloud-cover like the instrumentation used to measure sea surface temperature and chlorophyll.

What does “upwelling” mean?

Upwelling is a phenomenon where water from the deep ocean rises to the surface. This cold, deep ocean water is densely packed with nutrients. When it rises to the surface and exposed to sunlight, microscopic plants (phytoplankton) and animals (zooplankton) can proliferate. Squid and baitfish feed on these tiny animals, and in turn, attract larger pelagic species.

How do you find areas of upwelling?

Upwellings are areas on the SSH (sea surface height) chart that are lower than surrounding areas. It’s a bit counter-intuitive, but water in these “low spots” is rising to the surface to achieve equilibrium. Try uploading a photo on https://20echo.com/

Where, in general, are the best altimetry areas to fish?

Generally, the best areas to fish are in the intermediate zones between regions of upwelling and convergence areas. These neutral areas — between the highs and away from the center of the low — is where the food chain will have time to develop.

How can altimetry be used in conjunction with SST and Chlorophyll data?

Where there are upwellings the water is usually cleaner, with less chlorophyll, and colder since it’s coming from deep in the ocean.

How can altimetry data be used as a substitute for SST data when there is cloud-cover?

Altimetry data overlays won’t line up precisely with SST data but it will be close. We would much prefer using altimetry data to find temperature changes than nothing at all!

What else should I know about Sea Surface Height data when thinking about eddies & currents?

The real secret — if there is one — is to understand how the altimetry level you see is created and how that will affect the data’s accuracy. Once you know the data sources’ limitations, you will understand when and how to use it properly. Remember Upwellings have LOWER elevations than Downwellings and you always want to fish where the two meet and form current or in an upwelling where nutrients are coming up from the deep! If you are still wanting to know more about Ocean Altimetry click here for a great video on the subject from the European Space Agency.