Pike Country Weathermen

Pressure-Sensing Fish Can fish sense changes in atmospheric pressure? A recent study showed that movement of blacktip sharks was triggered by a drop in barometric pressure associated with Hurricane Gabrielle in 2001. Researchers with the Mote Marine Laboratory in Sarasota, Florida, report that the juvenile sharks responded to the approach of the storm by moving to deeper water, returning to shallow water after the storm’s passage. That study prompted the research being carried out by marine biology Ph.D. student Lauren Smith at the University of Aberdeen in Scotland. She’s studying pressure-sensing abilities of sharks in the wild, as well as through the use of an altitude chamber, which can mimic changes caused by weather fronts. Prior research by her supervisor, Dr. Peter Fraser, shows that sharks sense pressure using hair cells in their vestibular (balance) system. To learn more about how atmospheric pressure affects fish, Smith recommends the book Trout, Salmon, and the Evening Rise: The Barometric Breakthrough by Andrew Betts (publ. Salar Pursuits). “It provides a summary of research into pressure detection in fish,” she says. “In general terms fish with swim bladders, like pike, are able to detect pressure changes at a threshold of 0.05 millibars, while fish without swim bladders, such as sharks, have a higher but still sensitive threshold of 0.5 millibars. Physiologically speaking, there’s no reason why fish cannot detect barometric pressure changes.” (The millibar is a metric unit of atmospheric pressure; standard atmospheric pressure is about 1,013 mb at sea level). Smith explains how pressure changes in the atmosphere relate to water pressure and fish. “Say for example the air pressure rises from 1,009 to 1,010 millibars. The water pressure—the hydrostatic pressure—changes accordingly and acts as a transducer, relaying this information to the fish by having a direct effect on the swim bladder. If the air pressure remains the same, fish will be neutrally buoyant in the water column and thus able to maintain a constant depth. Increases in air pressure can cause the swim bladder to compress, so the volume of air in the fish is less, the water displaced by the fish is also less, and the fish begins to sink. “This may explain why fish with open swim bladders, like salmon and trout, come to the surface to gulp more air during increasing barometric pressure—they need to increase the volume of air in the swim bladder to become neutrally buoyant in the water column. The pike has a closed swim bladder and changes its volume of air internally.” Can dropping pressure stimulate pike to feed more actively? “Lower pressure has the opposite effect of rising air pressure, in that swim bladder volume will increase and cause the fish to rise in the water column,” Smith explains. “One hypothesis is that falling pressure causes smaller fish to become active, attracting predators such as the pike. Perhaps pike respond to an interaction of barometric pressure change, both directly on its own swim bladder and indirectly through prey response.”

Sampson finds that skyrocketing barometric pressure that moves in after major storm systems often makes for the worst possible fishing conditions. He says a classic example of this took place during the tail end of a Nor’easter, a coastal storm that hits New England, named for the direction of its strong winds. Nor’easters develop when lows containing warm air are drawn up from the south and clash with a colder, high-pressure air mass from the north. They typically blow through the region during the late summer and fall and also bring major snowstorms in winter.

“As it approaches and even during the Nor’easter itself, pressure drops, winds are high, and skies are dark, creating excellent fishing conditions, providing the winds are tolerable and not dangerous,” he says. “Then, as the storm moves through, cold, high-pressure Canadian air pulls in, killing the fishing for a few days in the process.

“This happened a couple years ago, when a major Nor’easter was buffeting our area,” Sampson recalls. “I had to work or the boat would have been launched early that morning. I had caught pike of 12.5 and 18 pounds after work during two previous Nor’easters that fall, so I couldn’t wait to get out during this third major storm in as many weeks.

“My boat was in the water by 3:30 p.m. and within 30 minutes I had landed one small pike, a 17.5, and a 15.5-pounder, which for Connecticut is a pretty good half hour of targeted pike fishing. Then winds began to swing around from the northeast to the northwest and there was brightness behind the clouds that hadn’t been there when we arrived.

“A glance at the hand-held barometer indicated that the pressure had leveled off and was just beginning to rise as this storm cleared the area,” he says. “With a sharp edge of clear blue skies pushing the storm up the coast, it was like Mother Nature hit a kill switch. We didn’t have another strike for the remainder of the day, not even at sunset.”

The Right Light

“When anglers say that changes in barometric pressure are related to fishing success, they’re probably right,” says Gord Pyzer, In-Fisherman Field Editor from Kenora, Ontario, and former manager for the Ontario Ministry of Natural Resources. “Pressure shifts are often associated with fronts that can cause changes in temperature, cloud cover, and wind levels,” he explains. “Over the years, I’ve seen on Shield lakes that weather and water conditions, in many respects, can be more important than food in determining pike activity and location.

“One of the factors that pike seem to be strongly keyed to is light. Dr. John Casselman, a former Senior Research Scientist with the Ontario Ministry of Natural Resources and a world-renowned pike specialist, has been conducting groundbreaking experiments in the laboratory, looking at ways light levels affect pike. By adjusting light intensity, he says, he can make pike become active at will, and make them inactive again. When he adjusts the light to the right level, pike rise up and execute search-and-feed behavior. He does it with a simple dimmer switch, and the results are totally independent of the pike being hungry.

“Casselman finds that pike go into their search-and-feed behavior when the light is adjusted to about 10 lux,” Pyzer reports. “This intensity mimics the first light in the morning and the last in the evening. He says that from angling studies conducted during the open-water period, it’s known that pike feed more actively on cloudy, overcast days than on bright, sunny ones. On days when light intensity is high, they feed more actively during evening and, to a lesser extent, in morning twilight.