Fish, farms and forests

Watersheds hold the key to good stream fishing

Mississippi anglers know that healthy, productive fisheries depend on good habitat. In turn, they rely on their finned quarry’s habitat preferences to help locate and catch fish. Fishery biologists, too, understand the importance of habitat and, whenever possible, use habitat management to improve the quality of sportfish populations.

While habitat management has been the foundation of good fishery management for decades, there is now a growing awareness that the quality of fish habitat includes land uses beyond the water’s edge. This paradigm shift has been facilitated by advances in spatial analysis technologies, like geographic information systems (GIS), that allow rapid assessment of characteristics and land uses of watersheds from aerial photographs and satellite imagery.

In last month’s Mississippi Sportsman, I described how lakeshore development affected crappie and largemouth bass spawning. In this column, I move farther away from the water’s edge to show that activities on the watershed — the land that drains into a lake or stream — can affect stream fisheries.

A growing list of published studies have found relationships between fish and watersheds, but a recent study by Brian Alford and Don Jackson at Mississippi State University is especially interesting because sportfish abundance was assessed by hook and line. Thus, Alford and Jackson actually developed relationships between watershed conditions and angler catch rates.

The study sites were wadeable streams — moderate-size streams generally less than 3 feet deep at normal flows — throughout Mississippi. Fish were sampled during summer months with ultralight spinning gear.

Angling success for black bass and sunfish was greater in stream reaches with greater forest cover and higher stream and road density in the watershed.

The positive relationship with forest cover makes sense. Compared to urban and agricultural land uses, forested lands are less disturbed and tend to contribute less sediment that destroys stream habitat and smothers invertebrates. Forested riparian zones stabilize stream banks, contribute woody materials to improve fish habitat and, via leaf fall, provide essential organic matter to fuel fish production.

The positive relationship between sportfish catch and road density is counter intuitive. One would think more roads means more development, more disturbance and more smothering sediment washing into the streams. Further, more roads also means better access and potentially greater fishing effort that could reduce catch rate.

But the roads were rural roads, and even streams with high road densities had fewer miles of road per acre of land compared to other parts of the United States, including wide-open and undeveloped western states like Montana and Wyoming. It may also be important that most of the streams were located in relatively flat watersheds where erosion associated with road development and maintenance would be minimal.

Reasons for positive relationship between catch rate and stream density are not obvious. I would expect, however, that sites with more streams nearby might have more stable flows and water depths because the runoff from the watershed would be distributed to more streams rather than all the runoff funneling into one or two streams.

There are important implications from this and other studies that also demonstrate that the landscape can significantly affect what is going on in the water.

First, the sportfish potential of streams can be quickly and economically predicted from satellite imagery, and wise managers can use these predictions to effectively channel their efforts and resources to those streams that have the greatest potential.

Managers can also identify those stream reaches where sportfishing can best be improved by managing the watershed rather than traditional management strategies such as adding in-stream cover, harvest regulations or stocking.

There are implications for anglers, too. Wadeable streams are often little-used resources, but they can provide excellent fishing opportunities. Use satellite imagery readily available on the Web to locate streams with more forest and less agricultural and urban land use on the watershed.