Bob Stearns’ Guide to Fish Temperature Preferences

Salt Water Sportsman first published my “Preferred Temperatures of Popular Marine Game Fish” in 2000. While most of the numbers haven’t changed since then, some have been updated via input from fishermen (including SWS readers), biologists and my own observations. In addition, I’ve included the temperature preferences of popular baitfish species, which can be equally important when it comes to locating game fish.

Keep in mind that the temperature ranges you see on the following chart are not cast in concrete. Fish will often be encountered in water that’s below or above their preferred temperature range based on a number of factors, including food abundance and angling pressure. But when it comes to the extreme upper or lower limits of any species’ tolerance range – that is, temperatures that will eventually kill them – they will flee unless incapacitated by a sudden change, such as occurs during a “cold snap.”

Excessively high temperatures can also be fatal, but the effects are generally slower and often less likely to be detected by fish in time for flight. Not only will abnormally high water temperatures cause severe physiological stress in the fish, they also reduce the amount of dissolved oxygen in the water. Cold water contains a lot more usable oxygen than hot water.

Which begs a big question: Can fish evolve to survive significantly higher and/or lower temperatures on a permanent basis? The answer has be yes, and it will vary from species to species, although there is no known timetable for this. For now, the more attention we pay to water temperature and the habits of the species we pursue, the better we will understand the relationship between temperature and behavior. And remember, just because the fish are there doesn’t mean they will bite.

Weather is a major factor. A strong cold front can dramatically lower the water temperature in just a few hours. Cold, strong northerly winds create waves, which in turn entrain frigid air into the water. The rest is a matter of physics. The bay that was 72 degrees at sundown can lose ten to 20 degrees overnight, especially if it is shallow. Deeper water resists rapid changes better. That’s why a cold spell can send many species scurrying to the deeper holes and channels.

Thanks to the Internet, it is now possible to keep track of water temperatures well enough to have a good idea of what to expect before you go fishing. This doesn’t eliminate the need for an onboard water-temperature gauge, because small-scale changes can still spell the difference between success and failure. For U.S. anglers, one of the best sources of hourly water-temperature information is NOAA’s weather website, www.srh.noaa.gov. You may have to poke around a bit to find the places you want to monitor, but usually they are there – if not the exact location, then one that’s close enough to provide useful information. One way to use this information – and one that has served me well over the last few years – is to keep track of the water temperature in the areas you fish and compare them to one or more nearby stations. Once you find one that comes close to matching your own observations, you can use it as a reference point for planning future trips.

Sudden Changes

A rapid decrease in water temperature, even if it stays within the tolerance range of a particular species, can shut down the action. A drop of a few degrees over an hour or two can cause the fish to go elsewhere or just stop feeding. This is more likely to happen in shallow water because it cools more rapidly. On the other hand, a rapid change of a few degrees can be a good thing by making the temperature more comfortable. For example, a cooling breeze that lowers the temperature of a shallow area in summer can bring game fish in to feed.

Fish are, of course, happiest when they are in water that’s within their optimum temperature range. This is especially true of many inshore species, such as striped bass, bluefish, bonefish and permit. Tarpon, for example, often gang up in deep channels when the water temperature is barely 70 degrees, and rarely invade the shallow flats when the water temperature is less than 75 degrees.

Of course, there are always exceptions. A very high abundance of some preferred food item will often keep game fish in an area when the temperature is above or below their preferred range.

Offshore Temperatures

Modern satellite technology has enabled us to determine sea-surface temperatures far offshore accurately and in excellent detail. There are even several companies that provide this information in chart form for their subscribers.

When a large enough current or pocket of warmer or cooler water moves into an area where such temperatures are not normally encountered, it often brings exotic species with it. This is why many tropical and subtropical game fish appear from California to northern Washington every time there is a strong El Ni¿o. At the same time, overly warm water off some parts of Central and South America push those same species out of areas where they are normally abundant.

But if you wait for the next El Ni¿o or La Ni¿a to cause unusual fish movement, you’ll be missing a lot of action. Every year, large pools of warm water break off from the Gulf Stream and move into much cooler waters along the East Coast, ushering in an unusual abundance of warm-water game fish. Billfish appear off New England almost every summer because of this phenomenon.

Subtle Signs

On a day-to-day level, the difference of a degree or two that delineates the edge of a current rip can pay big dividends. If you aren’t able to measure this difference, you might not know the rip was there at all. Rips tend to concentrate baitfish, and fishing on the side of the rip where the temperature is best for the species you’re seeking can make all the difference in the world. This is precisely why no savvy offshore skipper would ever leave the dock without some way to monitor the water temperature.

Both inshore and off, optimum temperatures vary more between the northern and southern extremes of a given species’ range if that species does not migrate. And species that migrate tend to follow temperature curves somewhat more closely than those that do not.

It should be noted that the temperature-preference charts are far from complete. There are more game and bait species to be added, and the numbers will no doubt be tweaked with new information. If you’d like to contribute your observations, drop us an e-mail at editor@saltwatersportsman.com.