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Q & A
Warmwater/Coolwater Survival Rates
Question
What are the survival rates for warmwater/coolwater fish in Pennsylvania and how do fisheries managers determine various stocking issues?
Answer
Thank you for your interest in warmwater (channel catfish, striped bass, largemouth bass, etc.) and coolwater (walleye, muskellunge, etc.) fish the Pennsylvania Fish and Boat Commission annually stocks.

Your question focused specifically on survival of fish stocked as fry, fingerlings, and adults. The survival of fry, fingerlings, or adults is dependent upon the species in question and the characteristics of waters into which they are stocked.

Before I detail survival specifics or water characteristics let me provide some background. For the most part all warmwater and coolwater fish (all fish other than trout, which are coldwater fish) are stocked as sub-adults at sub-legal size. Warmwater fish are stocked into waters where the natural production of young is impaired or adequate spawning habitats are unavailable such that stocking is necessary to maintain a particular fish population or fishing opportunity. It usually takes stocked warmwater and coolwater fish several years to grow to legal or desirable size.

After a thorough biological assessment (enumerating sport fish abundance by electrofishing, and trap netting etc.) and physical assessment (enumeration of water depth, temperature and aquatic plant density etc.) biologists develop a management plan that describes:

  1. what warmwater or coolwater species to stock,
  2. how many of each species to stock, and,
  3. what "life-stage" to stock.

By life stage I mean fry or fingerlings (fry are fish a few days old typically less than 1 inch long and fingerlings are fish that are at least several months old, typically two or more inches long, muskellunge fingerlings may be 10 inches long when stocked in fall). As you might guess, for most species, survival is directly related to size with a greater percentage of larger fish surviving to legal or catchable size. What this means is that biologists stock more fish of small size relative to fish of large size to produce a given adult density. You might also guess that large fish cost much more to raise and require more space (pond space) than small fish.

Perhaps the most important question biologists have to answer is: what life stage will survive to produce densities of fish sufficient for a particular management purpose or sufficient to produce a pre-determined amount of fishing recreation. Can small fish (fry) produce fishing opportunities equal to that of large fish (fingerlings)? The answer to the latter question is yes. One example is the walleye fishery at Pymatuning Lake. This lakes walleye population is maintained by stocking only walleye fry (about 3 days old). Many other lakes in the Commonwealth do not possess zooplankton densities (walleye food densities) sufficient to support survival of fry and consequently are stocked with fingerlings. Angler catch rates of walleye at Pymatuning Lake are among the highest in the state a (one walleye per 2 hours fishing).

As you would expect, when deciding how many warmwater or coolwater fish to stock biologists must consider predator densities (fish that eat the fish we stock) and availability of various forage organisms (fish and invertebrates that serve as food for the fish we stock). These elements combine to describe survival of stocked fish of a particular life-stage. Secondly, biologists must take into account that there is not an "unlimited supply" of warmwater and coolwater fish for stocking and when earlier life stages produce target angling catch rates then these "less expensive" life stages should be used. Finally, since most warmwater and coolwater fish are "pond reared" the vagaries of weather play a role in production which may limit availability of a particular life stage in some years.

To account for production variability biologist request warmwater fish at a "base rate" a minimum number of fish per surface acre of lake or river section to stock. Biologists also have the option of requesting "supplement rates" which describe the additional number to stock in years when available. Since we can not predict with high accuracy the exact number to be produced we don't publish the number we "intend" stock rather we report the total we actually stocked at the end of the year (after the fish have been stocked).

Earlier I mentioned that biologists stock more smaller fish (fry) than large fish (fingerlings) to produce a predetermined amount of fishing recreation. For example walleye fry are stocked at a base rate maximum of 750 per acre of water and walleye fingerings are stocked at a base rate maximum of 20 per acre to produce similar levels of fishing recreation. This does not necessarily mean we can substitute fry at 750 per acre for fingerling stocked at 20 per acre, an accounting of biological and physical conditions at a lake, river, or stream requires consideration before a particular life stage is chosen. Survival of a particular life stage is a function of the species stocked and the characteristics of the water into which the species is stocked. Generally we stock at rates that produce a pre-determined angler catch rate or predetermined assessment catch rate (net or electrofishing catch rate), we have never had the opportunity to measure the total number of fish that survive to be caught by anglers from a particular life stage stocked.

Of the few studies detailing survival of walleye fry relative to walleye fingerlings, fingerling survival was approximately 35 times greater than that of fry. Anglers must also realize that each water has unique potential to sustain various quantities of gamefish, with some waters capable of supporting more gamefish than others. The reasons for these differences are innate, that is geology and land uses within the watershed are different and for the most part cannot be changed or cannot be changed easily. Those more productive waters, as you would expect, are stocked at greater rates because they can sustain greater quantities of fish.

Of those waters to be stocked as listed on the web site you can presume most waters will be stocked with fingerling fish, particularly in the case of lakes. Of all species we stock only walleye are stocked as fry (American shad are stocked as fry as well) and most fry are released into rivers. I hope this gives you greater insight into warmwater and coolwater stocking in Pennsylvania and clears up any questions you have. Next year we will try to be more explicit about the life stage scheduled for release, however it will be impossible to detail an exact number planned for stocking, numbers actually stocked will be detailed in our annual report.

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