Lake Spivey Conservation

Committee Chair: David Wayne

Lake Conservation January 2007

I am pleased to present the report of our recent fisheries assessment of Lake Spivey.  We sampled the lake on 3 different occasions on Aug.1, Sept. 11, and Sept. 18, 2006.  The purpose of our assessment was to establish a baseline survey for making recommendations for improving the recreational fishing opportunities in the lake. 

 METHODS

The lake was sampled with boat-mounted electrofishing gear during early morning hours to minimize interference with recreational boaters.  Electrofishing uses a gasoline-powered generator to produce a Direct Current (DC) electrical charge in front of the boat.  Fish swimming in the field are temporarily stunned, netted, and then placed in a livewell.  Fish were identified to species, measured to nearest inch-group, and then released back into the lake or removed.   

Analysis of fish data included species composition, length frequency, and proportional stock density (PSD).  PSD is a simple ratio of the percentage of the number of quality fish captured (quality as defined by accepted standards) to the harvestable fish captured in the sample.

For largemouth bass:  Quality is defined as those fish >12”; Harvestable is all LMB >8”.

      PSDLMB =  (# bass >12”) / (# bass > 8”)  *  100

The desired PSD range is 40 to 60, a PSD less than 40 indicates too many bass and high competition for available food, while a PSD greater than 60 indicates a ‘low abundance’ situation for bass that will typically produce heavy fish at longer lengths, but in fewer numbers.

For bluegill / other sunfish:

   PSDBG = (# bluegill >6”) / (# bluegill > 3”)  *  100

The desired PSD range is 20 to 40, a PSD less than 20 indicates too many bluegills due to heavy competition for available food, while a PSD greater than 40 indicates a ‘low abundance’ situation for bluegill that typically produces larger bluegill in fewer numbers.

RESULTS

I.  Species composition

A total of 220 fish were collected during the 3 sampling efforts.  Table 1 lists all species captured and provides a description of the fishes’ role in the overall fishery of Lake Spivey.  Figure 1 is a collection of photographs of some of the catch.

Over 50% of the total catch were bluegill (n=115) although several schools of threadfin shad were seen in large numbers but not collected so as to minimize mortality and disturbance.  Bluegill are vitally important to a lake’s fishery as they are pursued by many anglers yet also provide forage for other predator sport fish, such as bass and catfish.   We also captured several different predator species: largemouth bass, hybrid striped bass, and large channel catfish.  Of these, largemouth bass were the most abundant (n=35), yet not as abundant as we typically find in other lakes.  Due to the small sample size of larger LMB (n=15), individual weights of fish were not recorded as the data would be of little use.

Table 1 presents a list of all species captured during the sampling effort along with a general category of the species’ role with regard to the lake’s recreational sport fish population.   The table presents common names, scientific names, percent composition, and relative importance to Lake Spivey’s fishery.

II.  Length Frequency

The distribution of length with a species is vitally important to understanding the fish population in the lake.  For clarity, all lengths were measured to the nearest whole inch (ex. An 11-inch bass is > 11 inches and < 12 inches).  By placing fish in inch-groups we can quickly compare size distribution and see visible patterns of vitally important game fish.

Bluegill / sunfish:   We captured a total of 115 bluegills, most of the bluegill (n=90) were < 4 inches total length and are small enough to be considered forage for the bass population.  There were very few bluegills over 6 inches in length.  The PSD for bluegills was 7.1 which indicates that a vast majority of the fish were less than 6 inches.  This translates into a less than desired bluegill fishery.  There were similar statistics even when all sunfish were grouped together.  There is an overabundance of small sunfish in the lake.

Largemouth Bass:  A total of 35 largemouth bass were captured and released; 15 bass were larger than 12 inches with 3 fish measuring 20-21 inches.  The PSD for bass was 62.5 which is on the line for being in low abundance. 

Other Species: 

Shad.  There are 2 species of shad in the lake, Threadfin shad and Gizzard shad.  Our catch did include several schools of smaller shad which were not netted as they are sensitive to electrofishing stress (initial shock, livewell crowding, and handling with nets).  We stopped applying current when shad were first seen and allowed them to swim away before continuing our sampling.  A few were obtained for identification.

Threadfin shad are smaller than Gizzard shad and provide excellent forage for largemouth bass, hybrid striped bass, and crappie.  A sexually mature threadfin shad may reach 5-6 inches which is an ideal forage size for large bass. 

Gizzard shad, however, can reach a large enough size where no predator can consume them.  We collected 2 fish that exceeded 12 inches.  These fish are too large to be consumed by all but the largest bass, but are important to the fishery as they are the brood stock for abundant shad reproduction. 

Crappie.  We only collected 3 crappie, all between 8-10 inches.  Crappie tend to school in the spring and fall and our sampling dates were a little early for the fall schooling.  Crappie are an important gamefish as many anglers enjoy catching crappie when they school. 

Hybrid Striped Bass.  We collected 2 hybrid striped bass (HSB).  Both were 24 inches long and both were caught in the far upper creeks of the lake.  HSB grow to a large size, but have a relatively small mouth size with respect to their overall length and weight.  They are voracious predators on smaller fish and are often sought by anglers wanting to hook a “freight train”.

Common carp.  We collected a total of 12 common carp in the lake and missed several other fish that escaped the electrical field.  All of these fish ranged from 22-32 inches and were captured in the upper creek areas of the lake.  A variety of common carp, koi, was collected.  These fish are used exclusively in the water garden industry and are undesirable in a sport fishing lake.  All of these fish were removed from the lake, as common carp are undesirable in a sport fishing lake.

Grass Carp.  Four grass carp were collected ranging from 26-40 inches.  The largest fish (40 inch) was disposed of with the common carp as large grass carp are not effective at controlling aquatic vegetation.  The smaller fish were released back into the lake for continued weed control.

Catfish.  We collected 7 channel catfish and one bullhead catfish.  The channel catfish are excellent game fish and provide anglers with another alternative species.  The bullhead catfish was removed from the lake as they are not desirable in a sport fishing lake due to their aggressive predation on smaller fish and mediocre table fare.

DISCUSSION

Species Composition

Lake Spivey has a vast number of species for a small reservoir.  The diversity of species provides for a varied angling experience and provides good diversity of prey species for larger predators.  However, many species captured are undesirable in a recreational fishing lake and should be removed when captured. 

The following species have a negative impact on sport fishing opportunities:

1.  Common carp:  Carp are native river fishes and have a down-turned mouth suitable for feeding along the bottom.  Carp devour many of the fish food organisms that other desirable species (bluegill, catfish, sunfish) depend on.  Due to their large size carp occupy much of the biomass (weight) of a fish population.  They are a “trash” fish and should be removed when caught by anglers or captured with sampling gear.  In short, having common carp in a small recreational fishing lake removes valuable biomass and food availability from sought after gamefish.

2.  Koi:  The brightly colored koi are varieties of the common carp bred for color through the years.  Typically, recruitment from reproduction is very low due to the bright color of the offspring, but all juvenile koi are not brightly colored.  While koi are popular and quite desirable with garden pond enthusiasts, they have the same feeding habits as their common carp brethren.  These fish most likely entered the lake from a local garden pond, either directly by the owner, or inadvertently during a period of heavy rain and garden pond overflow.  This practice should be avoided in the future.

3.  Bullhead catfish:  Any catfish with a square caudal fin (tail fin) is likely a species of bullhead catfish and should be removed if captured.  Bullheads, unlike channel catfish (with a forked caudal fin), are not desirable game fish and do compete with the other catfish and bluegills for food.  While it is not feasible to remove all bullheads from a lake, they should be on the “Remove” list for anglers.

4.  Warmouth sunfish.  Warmouths are in the same genus (Lepomis) as common bluegills, yet are considered undesirable for several reasons.  Warmouths have a large mouth for their size and compete with bluegills and small bass for available food.  Warmouths (and other large-mouthed sunfish) do not grow as large as common bluegill, thus keeping them from being sought after by anglers.  The rule for sunfish (collectively called “bream”) harvest is to remove all sunfish that have a large mouth.  Bluegills, shellcracker, and redbreast are the 3 most popular species of sunfish in recreational fishing lakes.

Population Dynamics

Proportional Stock Density (PSD) is an excellent tool for assessing the structure of important game fish populations.  The largemouth bass population currently produces some quality fish due to the low abundance and large quantity of available forage.  We have heard many reports of anglers catching several bass over 5 lbs and a few 10+ lb fish.  The PSD ratio of 62 supports this report and is presumed to be indicative of the population.  The largemouth bass population is slightly low on numbers of fish as evidenced in the PSD ratio, abundance of forage species, and presence of trash fish. 

The bluegill PSD is also indicative of a bass population low in abundance.  The overabundance of small bluegills is driven by the reduced largemouth bass numbers.  In order for bluegills to grow to a quality size, there must be ample predation from largemouth bass.  Typically, overabundant bluegills (small in size) are seen in lakes with low bass abundance.  The following graph of Bluegill PSD versus Bass PSD shows Lake Spivey in relation to “ideal” populations.

The desired range for a healthy, growing, balanced fishery is when the Bluegill PSD is between 20-40% and the Bass PSD ranges between 40-60%.  While these ranges do not take into account competition from other species, they do provide a guide for making management decisions.

Management Strategies

The first step in developing a fisheries management plan for the lake is to state the desired goal for the lake and its anglers.  While Lake Spivey is mostly used for recreational boating activities, there are some constituents that enjoy fishing in their backyard.  While one may anticipate a conflict between boaters and fishermen in regard to the management of the lake, there can be harmony with lake users and their intended goals for the lake.  This report will present an outline of options for improving the recreational fishing opportunities in Lake Spivey without any negative impact on boating and skiing.

1.  Define the goal for the fishing opportunity in Lake Spivey.  Currently, the lake’s fishery can be classified as forage-heavy, with slightly low numbers of largemouth bass, and having competing species.  This situation will do exactly what is currently witnessed by anglers: 

• There are some nice bass caught in the lake with several over 8lbs.
• There are not an abundance of smaller bass (< 16”).
• There are not many large bream in the lake.
• The crappie population (even though our catch was very low) tends to cycle between having lots of smaller fish, then a few years later many large fish appear in the catch.  This cycle typically runs 7 to 8 years.

If the current level of fishing success is adequate, then we can let the fishery continue.  However, if the goal is to improve the fishing in Lake Spivey, then we must define what would constitute an improvement.  A lake can be managed toward a specific goal: trophy largemouth bass, trophy panfish; or towards a balanced population with good all-around fishing for bass, bream, and crappie. 

2.  Stock additional Largemouth Bass.  By adding adult largemouth bass we will not only increase the size of the bass population, but also add additional predation on the abundant forage in the lake.  Largemouth bass should be >12 inch in total length when stocked and can be added year-round when available.  The result of supplemental stocking bass will be more fish of quality size available for anglers.  A side benefit of adding more bass is that the adult bluegills should grow to a larger size.

3.  Remove Trash Fish.  If nothing else is done in the lake except remove carp, then the lake will improve over time.  Large carp are benthic feeders and compete heavily with gamefish for invertebrate food.  Carp can also occupy much “space” in the lake in terms of biomass (wt. of fish/acre of water).  For example, the 12 carp removed during this sampling effort weighed over 100 lbs. combined.  Removing 100 lbs of carp frees up space for 100 lbs of other species to eat, live, and grow.

Carp can be removed by electrofishing in shallow water, bow-fishing, or setting small gill nets in the shallow water at night.  Southeastern Lake Management can assist in removal efforts.

4.  Implement harvest recommendations.

• All Largemouth Bass less than 16” should be released.
• Remove all common carp, koi, and any grass carp >24”.
• Encourage removal of crappie, bluegill, shellcracker and other large panfish.

5.  Supplemental Feeding.  The best method for producing large bluegills is to feed the fish a commercial feed pellet.  We can assist with the purchase of the feeder and feed, if a resident wanted to install an automatic feeder on their dock or shoreline.  Also, the association may want to install a few feeders on common property.

6.  Monitor Fishing Tournaments.  Much data can be collected at weigh-in from tournament angling.  I am recommending that all fish in a tournament be identified, measured, and weighed.  This information can then be used to monitor the adult bass population.  The association may also want to host species-specific tournaments (i.e. crappie, carp rodeo, etc.)

In summary, Lake Spivey is one of the gems of the metro Atlanta area.  To my knowledge, it is the largest private lake in the Atlanta area and offers lakeside living, motorboat activities, and recreational fishing.  The value of such an aquatic asset will only rise with time and warrants sound management and stewardship from its stakeholders. 

The recreational fishing opportunity is at a point where some fisheries management efforts will transform the fishery into above-average status.  These efforts should include adding additional largemouth bass, removal of trash fish, and continuing the monitoring efforts.  Southeastern Lake Management looks forward to working with the association to developing a quality multi-purpose lake that will be enjoyed by the residents for a long time.

Respectfully submitted ,

Randy Cooper

Fisheries Biologist

Enclosures:  Table 1, Figure 1

Table 1.  List of all species collected during sampling of Lake Spivey, August-September 2006.

Common Name	Species	Total No.	% of Catch	Fisheries Importance D=desirable U= undesirable	Species’ Role G = gamefish F = forage sp W =weed control
Bluegill	Lepomis macrochirus	115	52%	D	G,F
Largemouth Bass	Micropterus salmoides	35	16%	D	G
Gizzard Shad	Dorosoma cepedianum	18	8%	D* (* - undesirable at large size)	F
Common Carp	Cyprinus carpio	11	5%	U
Shellcracker (red ear sunfish)	Lepomis microlophus	9	4%	D	G,F
Threadfin shad	Dorosoma petenense	8	4%	D	F
Channel catfish	Ictalurus punctatus	7	3%	D	G
Grass carp	Ctenopharyngodon idella	4	2%	D	W
Crappie sp.	Pomoxis sp.	3	1%	D	G
Redbreast sunfish	Lepomis auritus	3	1%	D	G,F
Hybrid Striped Bass	Morone saxatilis X Morone chrysops	2	1%	D	G
Yellow bullhead catfish	Ictalurus natalis	1	<1%	U
Koi	Cyprinus carpio	1	<1%	U
Golden Shiner	Notemigonus crysoleucas	1	<1%	D	F
Warmouth sunfish	Lepomis gulosus	1	<1%	U
Yellow perch	Perca flavescens	1	<1%	D	G, F

Note:  Categorization of species is based on whether or not species is beneficial or harmful to recreational fishing opportunities.  Species with both gamefish (G) and forage (F) designation are important to each component.

Figure 1.  Photographs of collected fish during electrofishing sampling on Lake Spivey.

 Common carp (on left) and grass carp (on right).

 Mouth differences between common carp (on left) and grass carp (on right).

Large gizzard shad (13 in. total length) collected from Lake Spivey.

Hybrid Striped Bass (24 in. total length collected from Lake Spivey.