The Pros and Cons of Early Season Scuba Diving

The 2021 season is underway. Water temperatures finally broke the 60-degree mark here in northern Wisconsin, which moved fish out of deep water and into the shallows for spawning.  At this time of year, I don't see many panfish, but the muskies are in the littoral zone completing their spawning rituals. I'm focusing on them now and getting some excellent pictures of post-spawn fish. In the next few weeks, I'll be switching my attention to the bass and crappie that will be spawning next and providing some excellent photo opportunities. Bluegills and pumpkinseed will be the last to spawn, with many bluegills still on nests well into July.

At this time of year, water clarity varies widely. Some lakes have excellent clarity very early in the year that degrades very quickly and never clears up. Other lakes are murky in spring and gradually clear up by mid-summer. Quickly rising temperatures also cause the water to stratify. A barrier can be formed that's difficult to see through. As long as you're looking straight ahead in a horizontal column of water that's the same temperature, you can see well. However, if you look up or down, even a few feet, you won't be able to see far because of this thermal barrier. This can make finding fish difficult. Once the water temperature warms enough, this layer will fall dramatically and form the thermocline, which is typically 20-30 feet deep.

One of the best things about diving Wisconsin's lakes in May is that boat traffic is still very limited. Kids are still in school, summer visitors haven't arrived and many cottages have yet to open for the year. This usually means that during the week, I have the lakes all to myself. After Memorial Day, things get busier. The increased boating traffic always drives the fish away from the shallows to deeper stretches where they're not as easy to find and photograph. Right now, even walleyes are in untypically shallow water and I've seen a few of them near shoreline cover in less than 10 feet of water.  

If you've always wanted to see our native fish in their natural habitat, pick up a snorkel and some swim fins and jump into the closest lake near you. You'll be surprised what you can see this time of year. 

How Do Spawning Benches Work?

Spawning Bench or half-log. (C) Eric Engbretson

In northern states, fish managers sometimes use spawning benches to promote the spawning of smallmouth bass.  While largemouth bass, rock bass, and sometimes bluegill also use spawning benches, it is the spawning of smallmouth bass that inspired the design. 

 

In a healthy lake, smallmouth bass build spawning nests against rocks, sunken trees, or large pieces of wood in about four to ten feet of water.  Next to these structures, the male excavates a shallow, circular crater in the lake bottom.  This system provides good natural protection to eggs and fry. 

 

But in lakes without coarse woody habitat, large rocks or similar objects, smallmouth bass may be forced to construct their nests out in the open.  When spawning and is over and the female has deposited her eggs in the nest, the male diligently guards the eggs and later the fry from predatory fish and crayfish.  When the nests are out in the open without natural protection, the male must guard up to 360 degrees of the crater he has dug.  This is exhausting and dangerous, since his back is always turned away from part of the nest.  Far fewer eggs incubate, and far fewer fry survive their first few weeks when fish have to use nests that lack the natural shield of a habitat's woody elements. 

 

Fish managers have studied the hard work put in by bass and have noted the decreased recruitment of young fish.  The managers came up with an idea for a simple structure they hoped would meet the needs of nesting fish and make it easier for eggs and fry to survive.  The idea for spawning benches was born. 

 

A spawning bench consists of a four to six foot piece of log sawed lengthwise in half and attached to concrete or cinder blocks on each end.  Spawning benches are therefore sometimes called half-logs.  Once placed on the suitable substrate, the spawning bench provides overhead cover from birds of prey.  The concrete blocks on each end protect the nest from raiders on two sides. 

Smallmouth bass guarding nest built adjacent to one of the concrete blocks of a spawning bench. (c) Eric Engbretson

It was a sound design and one that smallmouth bass readily used, but not exactly as intended.  It turned out that smallmouth bass weren't concerned about overhead cover. The benches usually sat in water deep enough to preclude threats from above by ospreys and other birds of prey.  While nests are occasionally built between the two concrete blocks as the designers intended, smallmouth bass usually construct nests next to one side or the other, thus allowing the male to guard the nest from only three sides.  The key element seems to be the concrete block itself and not so much the half log.  In fact, if the spawning bench falls on its side, it still provides excellent protection. 

 

Spawning benches are poor substitutes for the naturally occurring woody cover that fish prefer.  But in lakes devoid of suitable wood, rocks, or trees, spawning benches provide a superb means of helping smallmouth bass defend their nests and allowing more of their offspring to survive.

How Do Spawning Benches Work?

Spawning Bench or half-log. (C) Eric Engbretson



In northern states, fish managers sometimes use spawning benches to promote the spawning of smallmouth bass.  While largemouth bass, rock bass, and sometimes bluegill also use spawning benches, it is the spawning of smallmouth bass that inspired the design. 

 

In a healthy lake, smallmouth bass build spawning nests against rocks, sunken trees, or large pieces of wood in about four to ten feet of water.  Next to these structures, the male excavates a shallow, circular crater in the lake bottom.  This system provides good natural protection to eggs and fry. 

 

But in lakes without coarse woody habitat, large rocks or similar objects, smallmouth bass may be forced to construct their nests out in the open.  When spawning and is over and the female has deposited her eggs in the nest, the male diligently guards the eggs and later the fry from predatory fish and crayfish.  When the nests are out in the open without natural protection, the male must guard up to 360 degrees of the crater he has dug.  This is exhausting and dangerous, since his back is always turned away from part of the nest.  Far fewer eggs incubate, and far fewer fry survive their first few weeks when fish have to use nests that lack the natural shield of a habitat's woody elements. 

 

Fish managers have studied the hard work put in by bass and have noted the decreased recruitment of young fish.  The managers came up with an idea for a simple structure they hoped would meet the needs of nesting fish and make it easier for eggs and fry to survive.  The idea for spawning benches was born. 

 

A spawning bench consists of a four to six foot piece of log sawed lengthwise in half and attached to concrete or cinder blocks on each end.  Spawning benches are therefore sometimes called half-logs.  Once placed on the suitable substrate, the spawning bench provides overhead cover from birds of prey.  The concrete blocks on each end protect the nest from raiders on two sides.

 

Smallmouth bass guarding nest built adjacent to one of the concrete blocks of a spawning bench. (c) Eric Engbretson

 

It was a sound design and one that smallmouth bass readily used, but not exactly as intended.  It turned out that smallmouth bass weren't concerned about overhead cover. The benches usually sat in water deep enough to preclude threats from above by ospreys and other birds of prey.  While nests are occasionally built between the two concrete blocks as the designers intended, smallmouth bass usually construct nests next to one side or the other, thus allowing the male to guard the nest from only three sides.  The key element seems to be the concrete block itself and not so much the half log.  In fact, if the spawning bench falls on its side, it still provides excellent protection. 

 

Spawning benches are poor substitutes for the naturally occurring woody cover that fish prefer.  But in lakes devoid of suitable wood, rocks, or trees, spawning benches provide a superb means of helping smallmouth bass defend their nests and allowing more of their offspring to survive.