When thinking about how to increase the survival rate of newly stocked fingerling or advanced fingerlings when stocking them into an existing pond with adult predators I was asked by Greg Grimes to report on any studies I found. There are quite a few and I will check with Greg on that and figure out how to use the bits and pieces from them to post what we find.

I have posted several times on an existing expir. in which I am using blocking nets (feeding behind the net) to protect and grow out BG and RES .The idea was to protect them from large predators until they reached 6-7in. and spawned. That has worked well. I recently had some advanced fingerling (8in. feed trained) F-1 tiger LMB to add to the mix as part of the expir. The idea was to put part of them ( 33%) behind the net to let them adjust to the pond for 10 days+- before they had to face predation.

I have thought for some time that putting fingerling fish in an area with thick cover or other shelter was a way to increase their % survivability when stocking them into a pond with adult predators. Several hatchery biologists thought that would not help and even the nets would only help for a short time once removed. I think fish cages will work also.

In doing the above research I found a 2005 study that I would like to share because I think it will help any of us who need to or plan to stock into an existing pond with predators . I believe we can easily increase the % survival . I can not post the study but can post a few excerpts. Then we can have a discussion on it and its application to our ponds. I am not saying this study is correct in all its findings but I think the basic concept is sound and could benifit us ponders.

First the abstract.

Transactions of the American Fisheries Society 134:141–148, 2005 [Article] q Copyright by the American Fisheries Society 2005

A Laboratory Evaluation of Poststocking Predatory Losses for Cultured Largemouth Bass

J. WARREN SCHLECHTE,* ROBERT K. BETSILL, AND DAVID L. BUCKMEIER
Texas Parks and Wildlife, Heart of the Hills Fisheries Science Center, 5103 Junction Highway, Ingram, Texas 78025, USA

Abstract.—Stocking fish into preexisting fish communities is not always successful. Although
there may be many reasons why stockings fail, predation is perhaps the most likely reason. Reducing predation by allowing fish to become accustomed to their new environment before release (i.e.,habituation) may improve stocking efficiency. We evaluated the effect of habituation on predation of stocked, hatchery-reared fingerling Florida largemouth bass Micropterus salmoides floridanus (30–64 mm total length) in simple (i.e., open-water) and structurally complex (i.e., with vegetation
and cobble) habitats in indoor tanks.We found that fingerling largemouth bass survival significantly increased (P , 0.004) from 26% to 46% when fish were habituated in a predator-free enclosure for at least 15 min. Surviving fish spent most (95%) of their time in the structurally complex habitat. However, the survival of all fish stocked in structurally complex habitat did not differ from that of all fish stocked in open water (P 5 0.61). Although predation on nonhabituated, hatchery-reared largemouth bass approached 75%, we found that short-term habituation can enhance survival of stocked largemouth bass, as manifested by improved predator avoidance. This suggests that habituating fingerling largemouth bass before stocking may result in substantial increases in survival.

Some text.

Simpler strategies, such as habituating stocked
fish and stocking fish in suitable habitat, may be more cost-effective than rearing larger fish. Because hatchery rearing may exacerbate the problem of predation by decreasing innate behavioral skills used to avoid predators (Hossain et al. 2002; Davis et al. 2004), the concept of prerelease habituation of stocked fish has been investigated as a means of improving poststocking survival of several species, but its value for largemouth bass
has not been examined.

This is intuitively appealing and has theoretical support. Crowder and Cooper (1979, 1982) posited that predation success decreased as structural complexity of habitats
increased. Laboratory work by Savino and
Stein (1982) and Gotceitas and Colgan (1987)
showed that habitat complexity above 250 stems/
m2 decreased the efficiency of largemouth bass
predation on bluegills Lepomis macrochirus.

Observers noted that both green sunfish and
adult largemouth bass preyed on the stocked fingerlings,as anticipated. Predators were typically very aggressive and often actively attacked stocked fish. Fish stocked without habituation appeared disoriented upon release and were often eaten within minutes of release. Although predation was observed throughout the first hour of the experiment, most observers noted that the majority of the predation appeared to occur shortly after the
stocked fish were released.

Sublethal stress effects can result in decreased
predator avoidance, whether through biochemical
or behavioral responses (Olla et al. 1992; Kellison et al. 2000). Use of the predation bioassay (Kruzynski and Birtwell 1994; Berejikian 1995; Szendrey and Wahl 1995) allows one to quantify even subtle changes in a fish’s ability to adapt to a new environment. Sometimes specific mechanisms can be observed that might be linked to increased predation (Kellison et al. 2000). In this study, observers noted that hatchery-reared largemouth bass often remained where they were stocked for minutes, or until attacked. When attacked, nonhabituated fish appeared less deliberate in their movements
toward habitat.

The biggest question is whether
the improved survival comes from reduced stress
because the prey are given time to recover from
the stocking or whether learning is occurring. Given the observational data, it appears that the most likely explanation is that stocked fish are initially too stressed to actively avoid predation. Alternatively, it is possible that antipredatory conditioning (Brown and Smith 1998; Kellison et al. 2000) occurred during habituation. Cues may have been visual or chemical. Understanding how habituation
improves survival could both improve the technique and suggest when and where it would be
successful.

In general, it appears that complex
habitat can provide protection from predators, but when the predator is a conspecific, the risk can also be high, because that is where predators also prefer to reside. Future research should focus on whether fish must be stocked in complex habitat in natural conditions. We documented significant improvement in survival
with only a 15-min habituation. Fish that are
stressed and not allowed a period of habituation
are likely to suffer much higher mortality when
stocked in areas with high predator densities. Obviously, mitigating these losses by holding fish within a predator-free enclosure before release has the potential to improve stocking efficiency.

Holding stocked largemouth bass in predator-free enclosures for 15–60 min seems practical. Given the promising results in the laboratory, future research in more natural settings
should begin to address whether deploying a predator- exclusion cage and habituating stocked fish for upwards of 15 min would be a practical and inexpensive way to improve survival of stocked largemouth bass. Likely, this minor change in stocking largemouth bass will substantially increase short-term survival at minimal cost.