Readers Cast


Gene Murray (HideHunter) - Mar 12, 2012

Now that I have your attention, we will discuss sexual exploits - of the bluegill.

It is pretty well known that I target big bluegills with some regularity. This includes fly gear, ultra-light spinning tackle and through the ice. I often refer to the fact my fishing partners and I rarely harvest mature, male (bull) bluegills. I am sometimes asked, "Why?"

There are two times of year male bluegill are truly vulnerable – on the beds and through the ice. Extreme care should be taken at these times not to over-harvest.

Readers Cast Gene Murray
1. There's not much mistaking a bull bluegill in full spawning colors.

Readers Cast Gene Murray
2. A female may grow as large, or larger than a male. The gill flap will normally be smaller and the colors more subdued.

We now know, without a doubt, returning big, male bluegill to the fishery will help improve and maintain the availability of large bluegills within a given body of water. This I can base on both scientific and nearly 20 years of anecdotal evidence.

There are several reasons why one body of water may produce big 'gills while seemingly comparable water may not.These may include:

  1. Fertility and PH of the water
  2. Cover and "weeds" (plants, both surface and subsurface)
  3. Predator/prey "balance"
  4. Exceeding biomass or "carrying capacity"
  5. Over-fishing
  6. Removal of the largest male bluegill

A quick rundown on a couple of these: Fertility is seldom a concern in the Midwest. PH should run at about 7.5 and thisis not often a great problem in our waters.

 "Weeds" can be a blessing or a problem. Water plants are food factories and while bluegill often feed on plankton, crawfish, minnows and terrestrials; underwater "bugs" are a mainstay for bluegills as they reach larger proportions. Many people like the "looks" of a "clean" pond and use chemicals and grass carp to maintain that appearance. By doing so they may be inhibiting the growth of bluegills. That said - it is possible to reach a point of diminishing returns on weeds. When over 30% of the water is inhabited by heavy weed growth, while food is extensively available, weeds may become so thick, that feeding is actually difficult. Also, predation will likely be inhibited and over-population and "stunting" becomes a problem.

Predation is a huge factor in the growth of bluegills. Bluegills are extremely prolific and must be kept in check. While any manner of fish, including channel and flathead catfish, northern pike, smallmouth bass and large crappie may prey on bluegills, largemouth bass are their most available and effective predator. This stems from a largemouth's preference to the general shape of sunfish as prey, and their "hunting" characteristics.

Exceeding the carrying capacity may result from several reasons. Over-stocking happens with some species, especially catfish. The combination of "incompatible" species may result in overpopulation. The aforementioned lack of or excessive weed growth is another.

"Over-fishing", in the case of panfish, may almost be an oxymoron. It is almost impossible to over-fish panfish in general. Harvests of 100-200 pounds (of the "right" fish) per acre are possible, and often beneficial. It is quite possible to over-harvest the "wrong" fish. And, that brings us to the point of this article.

This information is relatively new, only coming to light in the past 20 years and researched extensively in the past 10.

A number of biologists, including those of the Minnesota and the Illinois DNR have published excellent research into the breeding habits of the bluegill. Bluegill management flies in the face of generally accepted management of most game animals and even other fish. In many cases it is the female of the species that must be protected to maintain healthy populations. Not so in the case of the bluegill.

Let's hit on a few interesting factors on bluegills. A bluegill may reach sexual maturity as early as the age of one year – and most definitely can by two. There are two "kinds" of male bluegill; "parentals" (the bulls you see on the nests) and "cuckolders" (don't ask me why not just "cuckolds" - ask the scientists). A bluegill can become sexually mature or delay that maturity at will. Once a parental bull bluegill becomes sexually mature his growth will slow to almost nothing. Mostly this is stress from building and defending nests. Females in good habitat tend to continue to grow throughout their lifetimes. Depending on the latitude and water temperatures a female may spawn 3-5 times a year and lay 10 to 60 thousand eggs per spawn. A female will often spawn with several males and will seldom lay all her eggs in one nest. Longevity of bluegills, in the Midwest, is generally thought begin to generally peak at eight years though they may live to be as old as thirteen. So, it easily may take a male bluegill seven years to become a parental and to become a true "trophy" bull.

It is the breeding characteristics of the bluegill that make it desirable to return the majority of large males back into the fishery. Bluegills are a social species and most are aware of a collection of nests known as "beds". The most desirable of these nests are in the center of the beds where predation is least likely. These nests are built and defended by the largest of the males in a body of water. Females know instinctively, these are the most desirable and tend to release most of their eggs there. This, in turn, insures they are mating with the largest of the males and thus those with the best genetics. As the edges of the bed progress outward, the sites often become less desirable and are much more likely to be preyed upon. These nests are built and guarded by progressively smaller, less "capable" bluegills and those genetics are less desirable. Males will breed with many females and studies show the center beds may contain as many as 100,000 eggs while the outer nests may contain very few to virtually none.

It is at this point a potential "parental" male bluegill has a couple of choices. He may become sexually mature and inhabit one of the less choice sites. Or he may choose to postpone maturing, continuing to grow until he is big enough to take and defend the more choice spots. In a healthy ecosystem a large number will choose to do the latter. This, obviously, results in a larger population of "big" bluegills. It follows, by returning a larger proportion of the biggest male bluegills; the overall size of the male bluegills in a given body of water will increase.

There is another form of male bluegill. These fish become sexually mature early but choose not to build and defend nests. They are known as "cuckolders". The smallest of these are called "sneakers" and will dart in and deposit sperm while the larger parentals are breeding a female. Because they are not defending nests, they continue to grow and the larger are called "satellites". They do not take on the "breeding colors" of the parental bull and actually pose as females. They thus gain access to the nesting sites and slip in and breed at the same time as defending males, even "acting" like females to disguise their spawning activities. Beyond the fry stage, cuckolds tend to grow more slowly than parentals and thus are not as desirable.

A parental bull may recognize that he has been cuckolded. This seems to be based solely on observation, as they can't differentiate between eggs they have fertilized and those of the cuckolder. If a male determines he has been cuckolded he may eat the eggs.  However, once the eggs hatch, the fry do smell differently and if too large a proportion is deemed to be "not his", he may abandon the nest almost insuring the largest percentage of the fry will perish. While cuckolding is not rare (most biologists agree as many as 20% of males may be cuckolders) if there is a good population of parentals it is usually not a serious factor in maintaining a population of large 'gills.

Well, I said all that to say all this; if you want to build and maintain a healthy population of large bluegills simply keep the females and return the large, brightly colored males. It's not rocket science – but its close. Is this fascinating stuff, or too much information?

Well, at least now, you know, "Why".

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