Water Temperature and Fish

Ken Jones

Staff member
Water Temperature

Most years the letters to the Pier Fishing in California Message Board are fairly predictable, especially those concerning the fishing—good and bad—taking place at the piers. They’re cyclical, reflecting the nature of pier fishing in our state. Winter and cold weather can bring a drop-off in success along with a general depression among the pier rats. Then summertime returns with its better weather, warmer water, and ameliorated conditions for the fish. Soon the pier rats are happily catching fish and grinning from ear to ear. Unfortunately, the wintertime letters are sometimes almost manic-depressive in nature with pier rats throwing up their hands and questioning if the fish will EVER return. It's as though incubi had cast an evil spell on the fishing—and the mood of the pier rats.

Most of this agony can be avoided. One way is to live to be as old as I am; it gives you enough years of experience to make comparisons. You soon realize some seasons are good and some are bad, just as some years are good and some are bad. You can also continue to study the ways of fish and their environment. You may not be able to change the conditions but you can at least understand what is happening.

This means, in part, understanding the water world in which fish live. Water temperature is critical! In fact, scientists say water temperature is the single most important factor affecting the behavior of fish. Water temperature largely defines the nature of California saltwater fishing, and the various sea currents that flow along California's coast help determine the water’s temperature (see the highlighted California Currents—The Angler-Scientist). Certain species are common to the warmer waters south of Point Conception while other species are indigenous to the colder waters north of the point.

However, water temperatures change. There are annual changes due to global conditions, and sometimes abnormal situations such as the El Niño (“The Christ Child”) which brings warmer water to California. During moderate/strong El Niño years (1957-58, 1965-66, 1972-73, 1976-77, 1982-83, 1987-88, 1991-92, 1997-98, 2002-03, 2015-16) central and northern California areas see warm-water fish being caught that are more normal to San Diego and Los Angeles. Los Angeles and San Diego will generally see some species that are common to Baja, California.

"There are currently several hypotheses as to why El Niño events might affect coastal organisms along the Pacific Northwest. One hypothesis is that El Niño conditions, by affecting the timing and effectiveness of upwelling, result in a diminished supply of nutrients to surface waters. Fewer nutrients adversely affect phytoplankton growth, which, in turn, means that there is less food for small animals (known as zooplankton) that feed on phytoplankton. During the El Niño event of 1982 to 1983, the average spring and summer density of zooplankton off Newport, Oregon, decreased by 70 percent. This effect can reverberate up the food web, threatening the survival of juvenile salmon that eat the zooplankton.

El Niño conditions can also reduce the movement of water away from the coast. Juvenile salmon, too small to swim against the currents, rely on the offshore transport of water to whisk them away from the coast. In El Niño years, juvenile salmon may get trapped near the shore and fall prey to seabirds and other coastal predators.

In addition, changes in the direction of coastal currents and in water temperatures can directly determine the types of fish found off the Pacific Northwest. During the El Niño of 1982 to 1983, fish that normally inhabit tropical and subtropical waters migrated northwards, following warmer waters. For example, two warmer-water species, the Pacific and jack mackerel, were unusually abundant off the coasts of Oregon and Washington. These voracious predators consume the same types of food as salmon and may have diminished the supply of phytoplankton and zooplankton; in addition these fish may have snacked on juvenile salmon." —El Niño, (Oregon Sea Grant), Sandy Ridlington, Editor, 1997

Balancing off the El Niño, warm-water conditions, is its cold-water cousin La Niña (“The Girl”) aka El Viejo (‘the Old One”) that brings unusually cold surface waters and intensified winds. Conditions can often swing between the two conditions as seen in the moderate/strong La Niña years 1955-56, 1963-64, 1966, 1970-71, 1973-74, 1975-76, 1988-89, 1998-99, 1999-00, 2007-08, 2010-11, 2011-12). Following the super-hot El Niño years of 1997-98 there occurred a La Niña in late 1998 and ‘99 that saw waters along the coast drop down to a low of 46 degrees in some areas. Talk about a contrast!

The result was a much later season and a return to the cold-water conditions more common to California. No longer were the exotic species being caught to the north but the upwelling along the coast was improved as well as the survival rate of various species of fish. Even the growth of kelp increased with the return of the needed cooler waters.

Although the positive effects from El Niño conditions seem to influence pier fishing along much of the California coast, at least north to San Francisco, the negative effects from La Niña seem primarily to affect the areas north of Point Conception (in my opinion). As example, although there was a slight decrease in the catch at southern California piers in 1999, there was a dramatic decrease along much of the central coast including San Francisco Bay.

Since 1800, there have been approximately 48 El Niño events, with a mean frequency of one event every 4.1 years. Although El Nino events occur frequently, they are difficult to predict and highly variable in intensity. Some El Nino events are relatively weak whereas others may affect the entire Pacific Basin. Particularly strong El Nino events occurred during 1957-1958, 1982-1983, and the strongest El Nino on record occurred in 1997-1998.—Satie Airame Steven Gaines and Chris Caldow, Ecological Linkages: Marine and Estuarine Ecosystems of Central and Northern California, NOAA, November 2003

There are also normal seasonal variations in water temperature, and some species enter or leave our California waters accordingly. Finally, there are daily variations depending on weather conditions. Shallow water areas tend to both warm and cool at a quicker rate. Deeper water maintains a more constant temperature. During abnormally hot weather, fish may migrate into deeper areas where the water is cooler. During a cold spell it can be just the opposite; fish may move into shallow water during the middle of the day because it is warmer. Thus, if you are fishing a pier during the middle of a hot, sunny, summer day you might want to first try the areas of the pier with deeper water. At dusk, as the water begins to cool, inshore fish will move back to their preferred habitat and you should seek them in the shallower waters.

“Off Southern California, upwelling, which brings close to shore deep water that is low in temperature and oxygen and high in salinity, causes dramatic changes in the distribution patterns of inshore the fishes. Seasonal changes less dramatic than upwelling also have a profound effect on the soft-bottomed fish fauna.—Peter B. Moyle and Joseph J. Cech, Fishes: An Introduction to Ichthyology

Remember too that in some ways fish are like humans. A quick change in weather conditions will often put fish “off their feed” for a couple of days; they will not seem to bite as well and there is little the angler can do. Why this happens is unclear but scientists now know that fish are extremely sensitive to changes in temperature. In fact, some fish can detect changes as little as 1/50 of a degree Fahrenheit in temperature, sensitivity unmatched by any warm-blooded animals. And, since fish are cold-blooded creatures, their metabolism slows down with a drop in water temperature. A change in water temperature does not always mean a decrease in the quality of fishing but often times that is the result—at least for a few days.

Unlike humans who are warm blooded and maintain a constant 98.6 degree body temperature, fish are cold blooded and their bodies adjust to match the water they are in. As a result, their metabolism can change drastically depending upon the temperature of the water. Typically when a fish experiences a decrease in water temperature (especially if less than it is used to), it will become lethargic, eat less and move around less. If the water shows a drastic drop in temperature, the fish may almost cease to eat altogether. Although every fish is different, some preferring warm water, and some cold water, the change to their preferred water temperature is one key to their behavior. It also explains why warmer weather (and water temperatures) often sees an increase in fish activity and fishing success.

Temperature is also one of the main signals for fish to spawn. A prime example is barred surfperch, which in southern California typically spawn during the winter months. In some areas, concentrations of the fish show up ready to spawn in December. In other areas, it may be a few weeks or a few months later. Water temperature is the critical factor, and a variance of only a few degrees signals the start, stop, or restart of spawning behavior. Up north, in Mendocino County, you can generally count on May 1 as being the time local estuaries become populated by swarms of striped seaperch. If water temperature warms earlier, the spawning may begin in April. If water is a little colder, the spawn may start several weeks late. Since times of spawning are one of the best times to fish, due to the concentrations of the fish, water temperature records should also be kept and used as guidelines once ideal temperatures are established.

A clue to one of the great mysteries of marine life—the migrations of fish—may be found in the behavior of one of the clam’s near relatives, the mussel. The bay mussel, a black-shelled mollusk which clamps itself firmly to rocks or pilings, is a species distinct from those outside the Gate, and its spawn forms one of the most important food sources for the bay’s fish. In the spring, influenced by unknown forces-possibly changes in the bay's salinity or temperature-it throws out vast quantities of cells called gametes, which combine to form the mussel larvae. Biologists speculate that this great seasonal larva production of the mussels may determine in some degree the migrations of the fish which depend upon on it for food. —Harold Gilliam, San Francisco Bay, 1957


Well-Known Member
A great article that despite the passage of time makes some points that certainly still apply today.
Since I came here to Idaho, I've had friends give me plenty of advice on where and when to fish.
In the three years I've been here, the temperature fluctuations from season to season and between years have taught me more than much of the observations of even the seasoned locals.
This year, my area had a more temperate winter than previously. The snowpack has been minimal and the reservoirs and rivers were forecast to be adversely affected.
You probably heard how Yellowstone to the north was wiped out by flooding.
This spring and summer we've had more than our fair share of storms so far.
Whay does it mean for fishing here or down there? I dunno for sure, but as long as there're no lighting bolts lighting up the sky, I suggest we get out and give it a shot.🙂