Water depth
Many beginner anglers throw their bates and lures well past many fish that are waiting in shallow waters – deep water is not necessarily required for catching good fish. Generally, what determines how much water a fish will want over its head is how safe it feels and where the available foods is located.
For example, marling hunt and feed in depths ranging from 10-20 metres to as deep as the waters off the Continental Shelf. Australian bass feed in depths ranging from 3-5 metres to as deep as 50 metres, where they school.
Fish are often where their feed is, and small fish and plankton are usually found suspended over the thermocline – not in or below it. So you could use a quality sounder to pinpoint the thermocline and the location of the fish and their food.
Flow and turbulence
Most fish feed more actively when there is some form of water movement, such as down-stream flows, tidal flow or coastal longshore currents. They can also feed actively in large swells and heavy wind chop that cause the water to round from shoreline structures such as rocky cliffs, break walls or beaches.
When flows are turbulent, such as around submerged boulders or man-made structures like piers, predatory fish can catch disoriented weak-swimming prey.
Yet other fish, like trout, don’t feed in heavy weather. They prefer to feed as they cruise through relatively calm waters, or to hold in an eddy and grab passing food in the flow.
Water quality
For fish, the most crucial factor about water quality is the oxygen levels. Temperature, chemical composition and pollution also play a part. Fish obtain dissolved oxygen through their gills. Warm water releases dissolved oxygen into the atmosphere faster than cold water. The levels of dissolved oxygen will improve in cool water, or where the water is aerated by movement and splashing over rocks.
Heavy rain can change the temperature of the water suddenly, and can also change the salinity of estuaries and wash a lot of surface material form the ground into the waterways. How acidic or alkaline the water is can also determine where fish are – fish tend to like fresh water that is neutral or slightly acidic or alkaline, depending on the species. Too much either way will not allow fish to survive.
