Among the many factors that influence a successful day on the river, air pressure stands out as one of the most significant, yet often overlooked, elements. Whether you’re a seasoned angler or a beginner, understanding how barometric pressure affects salmon behaviour, or at least trying to, can give you a vital edge.
What is Barometric Pressure?
Barometric pressure, aka air pressure, is influenced by weather systems, with high pressure generally associated with calm, clear skies and low pressure linked to stormy, unsettled weather. Changes in barometric pressure can directly impact fish behaviour.
How Does Barometric Pressure Affect Salmon?
Salmon, like many fish species, are highly sensitive to their environment. It is said that their swim bladders, which help them control buoyancy, are affected by changes in atmospheric pressure. When barometric pressure changes, so does the amount of pressure exerted on their bodies, causing them to adjust their behaviour.
- High Pressure: In periods of high barometric pressure, such as during clear and settled weather, salmon tend to become more lethargic and are less likely to take. They may remain in deeper pools where the water pressure stabilises, making it harder for us anglers to tempt them. Fishing during these times can be more challenging, though not impossible. Subtle presentations and a patient approach often yield the best results, or fish in faster streamy water.
- Falling Pressure: As the pressure begins to drop ahead of a weather front, salmon are likely to become more active. Falling pressure often coincides with increased cloud cover and the anticipation of rain, both of which can spur salmon into running the river, or simply lifting their heads. This period, just before a storm or during mild overcast conditions, is often one of the best times to be on the river. Salmon are more likely to respond with greater aggression.
- Low Pressure: During periods of low barometric pressure, typically associated with rain or stormy weather, salmon may again become less responsive, especially when aligned with a East wind. However, some anglers have found success during prolonged periods of low pressure, particularly if the water is rising and fresh fish are entering the system. Some rivers respond differently to this period of deluge and rising water – they can be completely ‘shtoom’, or mad with frenzied aggressive fish, before the water colours that is. In these conditions, adjusting your tactics to retrieve faster whilst using brighter, larger flies can help attract attention.
- Rising Pressure: Following a period of low pressure, when the barometer starts climbing again, salmon behaviour can become more unpredictable. Some anglers believe that this period, particularly in the hours after a storm has passed, can be productive as fish are adjusting to the stabilising conditions, but that is difficult to determine because often the rivers are too coloured. Maybe it just depends on how your river responds to rain.
Why Is Barometric Pressure So Important for Scottish Salmon Fishing?
Scottish rivers are subject to rapidly changing weather patterns that can shift air pressure significantly in a short period. A bright sunny morning can quickly turn into a low-pressure storm front by the afternoon, dramatically changing the fishing conditions.
Practical Tips for Fishing with Barometric Pressure in Mind
- Monitor the Weather: Keep an eye on local weather reports and air pressure readings. Some apps provide detailed information on pressure trends, which can help you plan your fishing trip around optimal conditions.
- Adjust Your Tactics: If you’re fishing during a high-pressure period, slow down your presentations and fish deeper pools. When the pressure is falling, switch to more active presentations and fish areas where salmon may be on the move, or at least resting.
- Be Ready for Change: Scotland’s weather is famously unpredictable, so be prepared to adapt quickly. A sudden drop in pressure could signal a prime window for salmon activity, while a rising barometer might mean it’s time to adjust your approach or focus on different water depths.
- Gear: Your choice of flies and lines should reflect the pressure conditions. For example, brighter or larger flies may work better during low-pressure periods, while more subtle, natural-looking flies are often effective during high-pressure days.
Next time you’re planning a trip, make sure to keep one eye on the barometer.
