Fish Species of Lake Merced

Ian Singer, Graduate Student, Geography
San Francisco State University

Lake Merced is a fed by a freshwater aquifer, and at the time when Europeans first arrived probably contained cool fresh water from 10-20?C. Sacramento Blackfish (Orthodon microlepidotus) and Sacramento Perch (Archoplites interruptus) are two local native species which bred in the still, cool waters of the lake, that are still found in the lake today (EIP Associates 2000).

Historically, creeks flowed into the lake from the surrounding low mountains, particularly during periods of high rainfall. These conditions may have supported other freshwater species such as the still present Hitch (Lavinia exilicauda) and no longer found Thick-Tail Chub (Gila crassicauda), both of which need temporary streams to breed (EIP Associates 2000).

Until the 1880s the lake was separated from the ocean by a sand-bar which was breached periodically . In 1852, an earthquake opened the spit, and the lake is estimated to have lost 30 feet of water. (Campo 2000). This would have offered an opportunity for marine fish tolerant of fresh or slightly brackish water to colonize the lake. Species likely to occur under these conditions include Threespine Stickleback (Gasterosteus aculeatus), Prickly Sculpin (Cottus asper), Tule Perch (Hysterocarpus traski), Tidewater Goby (Eucyclogobius newberryi), Staghorn Sculpin (Leptocottus armatus) Starry Flounder (Platichthys stellatus), Topsmelt (Atherinops affinis) and Shiner Perch (Cymatogaster aggregata).

Since the late 1800s, the fish populations of Lake Merced have undergone dramatic changes which reflect the profound transformations of the physical conditions of the lake.

Under intense management as a recreational fishery, North and South lakes have intentionally been poisoned at least 4 times. Since 1939, the lake has been stocked with large numbers of rainbow trout (and occasionally other species) introduced for sport-fishing. The non-game fish which have managed to survive in the lake are remarkably strong and well adapted to survive under extremely stressful circumstances.

Unfortunately, studies of fish populations have used a wide variety of techniques and vary in their accuracy. Because managers have been most concerned with the rainbow trout population, data regarding changes in other species in the lake are lacking. If more complete scientific surveys are completed over the course of the next few years, biologists may be able to make recommendations regarding the restoration of fish species to Lake Merced. As a reference, a description of fish species recorded from Lake Merced is provided.

Physical Conditions of Lake Merced

Aquatic Habitats
In order to successfully live and reproduce, fish species need appropriate places to spawn and feed. A fish may need several habitats throughout its lifetime. The same species may spawn in a gravel riffle, hide in aquatic vegetation as a juvenile, and filter feed in open water as an adult.

The depth and shoreline of the various bodies of water which constitute Lake Merced have changed over the years, offering a wide variety of aquatic habitats. Today the lake contains stretches of shallow and moderately deep open water, generally less than 24 feet deep. There are several shoreline habitats, including tule reeds (see Lake Merced Flora), gently sloped mud shores, steep rocky banks and drop-offs. Historically, small local creeks which joined the lake may have provided riffles in which fish could spawn but currently, the lake is entirely still water. Also in the past the lake was periodically connected to the ocean, possibly opening sandy shallows which could host a variety of fresh-water tolerant marine species.

Water Quality 

The temperature of the Lake is largely influenced by its location. It remains relatively moderate in temperature (10-20C), a range which is below the optimum for most warm-water fishes, but not cold enough for many cold water fishes.

Dissolved oxygen concentrations at the surface are generally high (8-10mg/L) and the lake water is well mixed by wind action. However, algal blooms and other biotic factors may occasionally cause dramatic fluctuations in dissolved oxygen concentrations and precipitate fish die-offs.

The pH of Lake Merced is generally alkaline (8.7-9.0) and may be extremely turbid. Fish that persist there are well adapted to these conditions. Certain fish species, such as carp, may increase the turbidity by their feeding habits (Moyle 1976). The clarity of the water has both direct and indirect effects on fish populations. Fish not adapted to turbid conditions may suffer from clogged gills and reduced visibility. However, clear water favors piscivorous birds (see Birds of Lake Merced), such as cormorants, which hunt by sight (GEO Resource Consultants 1993).

For an in-depth look at the issues surrounding water quality refer to the Lake Merced Hydrology and Water Quality report.

Management as a Recreational Fishery

In the early 1870s, Lake Merced was one of the main sources of water for the growing city of San Francisco. Because of this, turbidity in the shallow lake became a public concern (see History of Human Use). 

The earthquake and fire of 1906 sparked the development of alternative water sources for San Francisco in San Mateo and the Sierras. With the completion of Hetch Hetchy in 1930, there was increased interest in the development of Lake Merced as a recreational fishery. In 1939, Mayor Angelo Rossi announced that the lake would be opened for public angling.

FIRST RECREATIONAL FISHERY – 1939 to 1949

Bluegill (Lepomis macrochirus), Large Mouth Bass (Micropterus salmoides) and Sacramento Perch (Archoplites interruptus) were stocked in the Lake just before it was opened to the public in 1939. Between 1939 and 1944, the fishery was described as "poor-fair" by the California Department of Fish and Game, and investigations by biologists Leo Shapovalov and Garth Murphy determined that the water temperature and depth were not suitable for warm water spawning (Johnson 1955).

From 1944 to 1947, the California Department of Fish and Game stocked fingerling and catchable size (12" – 1/2 lb.) rainbow trout (Salmo gairdneri) in the North Lake. However, the fishery was only mediocre. It was decided that the trout could not develop because of competition from "rough fish", consequently  the decision was made to poison the lake in 1949.
 

BOOM and BUST – 1949 to 1952

On October 18th, 1949, the South Lake was treated with rotenone to kill off any fish in the lake. The North Lake was treated two days later. In the North lake, a 4% solution was used. The south lake was "purposely overdosed because volume figures were not believed to be reliable" (Calhoun 1949).   Impound lake was also treated.

In January and February of 1950, 80,000 catchable size rainbow trout were introduced into North and South Lake. This was followed by 100,000 trout placed into the North Lake in the winter of 1951. The following fishing season was the most successful the lake had yet experienced (Johnson 1955).

But in 1952, the population of trout dropped dramatically just weeks after the season opened in May. In Summer and Fall of 1952, large numbers of prickly sculpins, carp and hitch were recorded, but few trout. It was decided that the chemical treatment of 1949 was ineffective (Johnson 1955).

FLOOD OF FINGERLINGS – 1953 to 1961

Dr. Joel Gustafson at San Francisco State studied fish populations in the lake from 1951-54. He noted that in the middle of 1952, there had been large populations of sticklebacks and sculpins. These populations had drastically decreased by September, following the decline of the rainbow trout. He suggests that it was an algal bloom, not ineffective poisoning, that was responsible for the fish die-off (Gustafson 1954).

Despite his findings, the North and South lakes were chemically treated with rotenone on November 8-9, 1952. Thousands of rough fish (mostly sculpins) were recovered, but less than 50 rainbow trout (Johnson 1955).

In January and February 1953, the North Lake was restocked with 110 catchable rainbow trout. However, these were smaller fish than usual and in May and July the California Department of Fish and Game decided to stock fingerlings. That year, 300,000 fingerling rainbow trout were stocked in South Lake and 200,000 brook trout (Salvelinus fontinalis) were stocked in North and South Lakes. The fingerlings grew so fast that by August, they accounted for at least 1/3 of the catch (Johnson 1955).

The fingerlings were such a success that in 1954, only fingerling and sub-catchable trout were stocked in North and South Lakes. However, 44,000 catchable trout were stocked in Impound Lake (Johnson 1955).

From 1955-58, only fingerlings were stocked in North and South Lakes. It was discovered that Spring and early Summer plants gave the highest yields, so in 1957 winter planting was abandoned (Fisher 1958). Most of the fingerlings were rainbow trout, but brook trout were also stocked in 1957 and 1958 (Allen 1965). In late July 1957, there was an almost complete fish kill in the South Lake after a large algae bloom (Fisher 1958).

From 1959 to 1961, there was a drought which left the California Department of Fish and Game with large numbers of excess fish. In ’61, 180,799 catchable trout were stocked in North and South Lakes, bringing the average catch to 2.15 trout per angler per day (Allen 1965).

KILL AND STOCK – 1962 to 1967

During this period, Pronoxfish, a rotenone-based chemical, was used to kill fish in North, South and Impound lakes. For several years, biologists recommended the regular treatment of the lakes with Rotenone and Copper Sulfate to control "predatory-sized fish" and algae (Hansen 1963). Subsequent to chemical treatment, the lakes would be stocked with large numbers of rainbow trout fingerlings.

BACK TO CATCHABLES – 1968 to Present

For the first time in the lake's history, sampling was undertaken that focused on non-game fish species. As this period progressed, the California Department of Fish and Game began stocking larger and larger fish. In 1973, rainbow trout as small as one-tenth of a pound were stocked in North and South Lake. By 1989, most of the trout stocked were over half a pound (Poe 2000).

In 1986, the concessionaire at Lake Merced entered into an agreement with the California Department of Fish and Game to match their stocking of catchable-size fish. From 1987 until the program was terminated in 1996, the concessionaire stocked approximately 40,000 fish per year (Poe 2000).

Stocking in North and South Lakes continues today, and the most recent planting schedules can be obtained by going to the California Department of Fish and Game Website (http://www.dfg.ca.gov/fishing/fishplant.html ) or by contacting them by phone at 707-944-5581. The stocking of Impound Lake was halted in 1991 because of bad water quality (Poe 2000).

INTRODUCTION OF SPECIES OTHER THAN RAINBOW TROUT

Although rainbow trout has been the only species consistently stocked in the lake, there have been occasional introductions of other game and non-game species. The following chart lists species intentionally introduced by the San Francisco Department of Parks and Recreation or the California Department of Fish and Game.

Species Date(s) Introduced
Muskellunge (Esox masquinongy) 1893
Bluegill (Lepomis macrochirus), 1939
Sacramento Perch (Archoplites interruptus) 1939
Largemouth Bass (Micropterus salmoides) 1939. 1983
Sockeye Salmon (Oncorhynchus nerka) 1961-62
Brook Trout (Salvelinus fontinalis) 1957-58,1965,1977
Coho Salmon (Oncorhynchus kisutch) 1982
Red-Eared Sunfish (Lepomis microlophus) 1983
Black Crappie (Pomoxis nigromaculatus) 1983
Channel Catfish (Ictalurus punctatus) 1994-98

(Trihey & Associates 1999 and Johnson: 1955)

In addition, certain other species have been introduced by the public as pet releases and escaped live bait. Both goldfish and carp probably were introduced this way.

Fish Population Surveys in Lake Merced

Lake Merced has been managed primarily as a recreational fishery since it was opened to the public in 1939. Therefore, survey data have been collected largely as the result of intensive management practices intended to improve conditions for the main sport-fish stocked in the lake, rainbow trout (Salmo gairdneri). Following is a list of surveys conducted in the Lake and their results.

ROTENONE POISONING – N, S and Impound Lakes : 

October 18, 1949

As state previously, on the above date, the South Lake was treated with rotenone to kill off any fish in the lake. The North Lake was treated two days later. In the North Lake, a 4% solution was used. The South Lake was "purposely overdosed because volume figures were not believed to be reliable" (Calhoun 1949).   Impound lake was also treated.  The following results were obtained: 

SPECIES NUMBER OF INDIVIDUALS
Prickly Sculpin Cottus asper exceedingly abundant
Sacramento Blackfish (Orthodon microlepidotus) abundant
Hitch (Lavinia exilicauda) abundant
Threespine Stickleback (Gasterosteus aculeatus) abundant
Carp (Cyprinus carpio) very abundant
White Catfish (Ictalurus catus) a few in South Lake only
Largemouth Bass (Micropterus salmoides) a few in South Lake only
Sacramento Perch (Archoplites interruptus) a few in South Lake only
Bluegill (Lepomis macrochirus) one in North Lake.

POISONING – N/S Lakes : November 8-9, 1952

Only three years after the first poisoning, the North and South lakes were chemically treated with rotenone on November 8-9, 1952. Thousands of rough fish (mostly carp, sticklebacks and sculpins) were recovered, but less than 50 rainbow trout (Johnson 1955).

On top of the fish many large freshwater shrimp (genus Gammaris) and large brown clams were killed off, but populations had recovered by 1954. Amphipods killed during the treatment had not recovered by 1954 (Gustafson 1954).

GILL NET SAMPLING – North Lake : October 4-7, 1962

In 1962, prior to a planned treatment of North Lake Merced, a survey was conducted to determine populations of sport fish in the lakes by Jack Allen. He set gill nets in 4 different locations for 24 hours each, from 3pm to 3pm. The mesh size was 2.5" (not small enough to capture small fish such as sculpins and sticklebacks). Nets were 8 feet deep and 100 feet long. His results were as follows:

SPECIES NUMBER OF INDIVIDUALS
Rainbow Trout (Salmo gairdneri ) 66 - all locations
Sacramento Blackfish (Orthodon microlepidotus) 46
Sockeye Salmon (Kokanee) (Oncorhynchus nerka) 27 - all locations
Hitch (Lavinia exilicauda) 5 - South and North shore tule beds.
Largemouth Bass (Micropterus salmoides) 2 -Tule Bed East of the cove near the golf course.
Bluegill (Lepomis macrochirus) 1 - North Shore Tule bed.

Allen recommended no chemical treatment because of the large number of game fish his sample suggests exists in the lake. He was particularly surprised by the large numbers of salmon, because they were not often captured by anglers (Allen 1962) .

PRONOXFISH POISONING – South Lake : October 26, 1963

This report contains a reference to a treatment in the North Lake in October 1962, but I was not able to locate the records for that treatment. More importantly the south lake was known to be treated in October 1963 to "eliminate predatory-sized trout." The lake was treated with pronoxfish, a combination of rotenone and a sulfoxide synergist (Hansen 1963).

SPECIES NUMBER OF INDIVIDUALS
Threespine Stickleback (Gasterosteus aculeatus) Several Hundred Thousand
Rainbow Trout (Salmo gairdneri ) 537
Bluegill (Lepomis macrochirus) 99
Sacramento Blackfish (Orthodon microlepidotus) 46
Green Sunfish (Lepomis cyanellus) 26
Hitch (Lavinia exilicauda) 5
White Catfish (Ictalurus catus) 4
Largemouth Bass (Micropterus salmoides) 3
Brown Bullhead (Ictalurus nebulosus) 1

PRONOXFISH POISONING – South / Impound Lakes: October 23, 1965

This treatment was applied to both the South Lake and the Impoundment Lake to eradicate predatory trout. The lakes were simultaneously treated with copper sulfate to reduce algae (Leiby 1965).  

SPECIES NUMBER OF INDIVIDUALS
Threespine Stickleback (Gasterosteus aculeatus) ~ 57,000
Rainbow Trout (Salmo gairdneri ) 153
Brook Trout (Salvelinus fontinalis) 91
Goldfish (Carassius auratus) 10
White Catfish (Ictalurus catus) 4
Hardhead (Mylopharadon conocephalus 4
Sacramento Blackfish (Orthodon microlepidotus) 2
Sacramento Sucker (Catostomus occidentalis 1
Bluegill (Lepomis macrochirus) 1

POPULATION SAMPLING - North Lake Merced :October 22 – November 8, 1968

This survey was conducted by Wallace Strohschein, the Assistant Fishery Biologist for Region III. He used a variety of different methods, with the following results:

GILL NETTING (Oct 22, 1968)

SPECIES NUMBER OF INDIVIDUALS
Threespine Stickleback (Gasterosteus aculeatus) many
Rainbow Trout (Salmo gairdneri ) 1

200-FOOT BEACH SEINE (Oct 22, 1968)

SPECIES NUMBER OF INDIVIDUALS
Threespine Stickleback (Gasterosteus aculeatus) 16

GILL NETTING (Oct 23, 1968)

SPECIES NUMBER OF INDIVIDUALS
Threespine Stickleback (Gasterosteus aculeatus) many
Rainbow Trout (Salmo gairdneri ) 27
Brook Trout (Salvelinus fontinalis) 1

PRONOXFISH (Oct 25, 1968)

SPECIES NUMBER OF INDIVIDUALS
Threespine Stickleback (Gasterosteus aculeatus) many

GILL NETTING (Nov 4, 1968)

SPECIES NUMBER OF INDIVIDUALS
Threespine Stickleback (Gasterosteus aculeatus) 700
Rainbow Trout (Salmo gairdneri ) 20
Sacramento Sucker (Catostomus occidentalis) 3
Brook Trout (Salvelinus fontinalis) 2
Goldfish (Carassius auratus) 1

(Strohschein 1968)

ELECTOSHOCK SAMPLING – N Lake: Fall, 1974

In 1974, Wallace Strohschein used an electo-shock boat to inspect trout in the North lake for Nematodes. Six of the nineteen rainbow trout he captured had nematodes, and the one brook trout taken did not have nematodes.

ELECTOSHOCK SAMPLING – N Lake: March 9, 1976

This is the first of a few electroshock samples taken by Gary Scoppettone, a Fish and Wildlife Aide in Region three. Of the records on file, these provide the most details about the non-game fish species in Lake Merced.

In addition to listing the species, he recorded important details regarding where and when each species was collected.

SPECIES NUMBER OF INDIVIDUALS
Tule Perch (Hyserocarpus traski) 24 – common in night sampling (6:15 – 8:45pm) in coves and exposed banks.
Prickly Sculpin (Cottus asper) 22
Largemouth Bass (Micropterus salmoides) 5 – by submerged branches
Sacramento Sucker (Catostomus occidentalis) 3 – in bulrushes 
Goldfish (Carassius auratus) 2
Rainbow Trout (Salmo gairdneri ) 1
Threespine Stickleback (Gasterosteus aculeatus) 1

From this study, Scoppettone concludes that "population densities and age class structures suggest that tule perch and prickly sculpin are the only viable breeding populations of fish in North Lake Merced." (Scoppettone : 3/9/’76)

ELECTOSHOCK SAMPLING – S Lake: March 17, 1976

This is an equivalent set of electoshock samples for the South Lake.

Scoppettone provides a map that charts the littoral zone in which he conducted his sampling. He divides it into four main habitat types:

He also recorded important details regarding where and when each species was collected. During this sampling, the exposed shallow shore adjacent to the causeway yielded no fish.

SPECIES NUMBER OF INDIVIDUALS
Prickly Sculpin (Cottus asper) 18 – Stomachs were opened and they contained shrimp and isopods. These were common on open, rocky, steep banks.
Threespine Stickleback (Gasterosteus aculeatus) 17 –Many were infected with tapeworms.
Rainbow Trout (Salmo gairdneri ) 16
Tule Perch (Hyserocarpus traski) 15 – All the same age class.
Largemouth Bass (Micropterus salmoides)
Goldfish (Carassius auratus) 1
Carp (Cyprinus carpio) 1

From this study, Scoppettone concludes that "abundance and size composition suggest that prickly sculpin and threespine stickleback are the only breeding populations in the South Lake. Tule perch may also reproduce in the lake, but it is not a prolific breeding population as found in the North Lake." (Scoppetone : 3/23/’76)

In April, 1976, 202 live Tule Perch were gathered from Lake Merced to be re-introduced into the Pajaro River and El Estero Lake. Of the fish collected, approximately 25 were pregnant. (Scoppetone : 4/14/’76)

During April and May, Scoppettone looked for eggs of prickly sculpin in the rip-rap 1-2 feet deep, and found 2 in South Lake near the impoundment and one at the eastern corner of the North Lake. He theorized that, since sticklebacks were a predator of sculpin eggs and young, as the stickleback population decreased (perhaps in part because of a high tapeworm infection rate), the sculpin population would increase. (Anderson & Scoppettone : 1976)

ELECTOSHOCK SAMPLING – S Lake: October 7, 1976

In Fall 1976, South Lake Merced was sampled to compare pre-season and post-season non-game fish populations. This sampling was conducted by Keith Anderson, Associate Fishery Biologist for Region III.

Unfortunately, Anderson does not provide numbers for all the species.

During the Fall sampling, the shallow shore (which had no fish in Spring) yielded trout, stickleback, sculpins and tule perch.

SPECIES NUMBER OF INDIVIDUALS
Prickly Sculpin (Cottus asper) Common to Abundant – They were most common in open, shallow habitats with smooth or rocky bottoms. Population density may have increased since March. 
Threespine Stickleback (Gasterosteus aculeatus) Common – All stickleback observed were infected with the larvae of Schistocephalus solidus
Rainbow Trout (Salmo gairdneri ) 7 in excellent condition
Tule Perch (Hyserocarpus traski) ~500
Largemouth Bass (Micropterus salmoides) 14 – sampling indicates successful (but low density) reproduction. 
Green Sunfish (Lepomis cyanellus) 2

(Anderson : 10/11/’76)

ELECTOSHOCK SAMPLING – S Lake: April 5, 1977

In Spring 1977, South Lake Merced was sampled to compare non-game fish populations with those of the previous year. This sampling was conducted by Keith Anderson, Associate Fishery Biologist for Region III.

Unfortunately, like before, Anderson does not provide numbers for all the species.

SPECIES NUMBER OF INDIVIDUALS
Prickly Sculpin (Cottus asper) Common to abundant – They were most common in open, shallow habitats with smooth or rocky bottoms. Population density appears to have remained stable. 
Threespine Stickleback (Gasterosteus aculeatus) Common – All stickleback observed were infected with the larvae of Schistocephalus solidus.

No significant change since October. 

Rainbow Trout (Salmo gairdneri ) 30 – A sample of 11 were carefully examined for signs of nematode infection. Infection found in 4 of these individuals. 
Tule Perch (Hyserocarpus traski) common – not as abundant as in October 1976. Population is "well established". 
Largemouth Bass (Micropterus salmoides) 7 – 1 adult / 6 juveniles – not returned to lake. 
Goldfish (Carassius auratus) 4
Carp (Cyprinus carpio) 1

(Anderson : 4/8/’77)

GILL NET SAMPLING – N Lake: June 28-19, 1989

In Summer, 1989, three gill nets were placed in North Lake Merced by Larry Wyckoff, Fisheries Biologist, Region III.

SPECIES NUMBER OF INDIVIDUALS
Prickly Sculpin (Cottus asper)
Threespine Stickleback (Gasterosteus aculeatus) 18 
Rainbow Trout (Salmo gairdneri ) 41
Tule Perch (Hyserocarpus traski) 189
Hardhead (Mylopharadon conocephalus) 2
Largemouth Bass (Micropterus salmoides) 7 – 1 adult / 6 juveniles – not returned to lake. 
Channel Catfish (Ictalurus punctatus) 1

(Wyckoff: 8/8/’89)

Conclusion

Fish surveys of Lake Merced over the years have not been consistent. Because the timing, method and accuracy of records kept for each sample have been so different, they do not provide a good measure of the change in fish populations over time in the lake. This has been especially true for prickly sculpin and threespine stickleback, two small species which have been recorded at the lake in large numbers and probably contribute significantly to its overall ecology.

I suggest that consistent surveys begin as soon as possible. Perhaps a combination of electrofishing and gill netting should be employed, so that it can be determined to what extent galvanotaxic species are selected for using electric boats. In hindsight, Rotenone is probably not the best method of fish sampling, for one it has a number of human health risks.

"Most of the men suffered some ill effects from the powder. A scabbiness on the face for several days was the most common symptom. It was quite severe in a number of cases. At least 2 individuals developed a similar condition on the skin of the scrotum. Prolonged, continual contact with the powder is clearly undesirable." (Calhoun : 1949)

The effect of rotenone on other wildlife (particularly invertebrates) in Lake Merced appears to be largely unknown, but the die off of shrimp and clams associated with the 1953 poisoning, it appears to be negative.  In the future I would recommend against using this or any other chemical in the Lake until further studies are conducted.

Restoration of Fish Species of Lake Merced

Before fish restoration efforts can be considered, careful surveys of the lake must be conducted. These should focus on determining current breeding fish populations in the lake and assuring that habitat and water quality conditions are appropriate for the species which may be introduced.

A more complicated issue is that of the existing trout fishery. Although fish may be unpalatable during times of extremely low water quality, the recreational aspects continue to provide enjoyment for residents of San Francisco and nearby communities.

Based on communication, with Dr. Peter Moyle at UC Davis, I have identified the a number of native fish species as suitable for restoration in Lake Merced.

Native species naturally occurred in Lake Merced include:

Estuarian species:
**Threespine Stickleback (Gasterosteus aculeatus)
** Prickly Sculpin (Cottus asper)
**Tule Perch (Hysterocarpus traski)

Warm / Still Water species:
**Sacramento Perch (Archoplites interruptus)
**Sacramento Blackfish (Orthodon microlepidotus)
**Hitch (Lavinia exilicauda)

Additional Native species which may be restored if a connection is re-established with the Pacific

- Tidewater Goby (Eucyclogobius newberryi)
    Staghorn Sculpin (Leptocottus armatus)

Description of Fish Species Recorded in Lake Merced: EIP Associates 2000
(Unless otherwise noted, this information is condensed from Moyle:1976)

COLD WATER SPECIES

NATIVE:
Rainbow Trout (Salmo gairdneri ) Abundant and widespread. Native to Pacific coast rivers from Northern Mexico to Alaska. Return to spawning areas, therefore, many localized populations were once found which were better adapted to different settings. River trout establish a hierarchy and are strongly territorial. Rainbows can drive other fish off feeding grounds aggressively. Lake trout eat fish as well as benthic inverts. Reproduction requires a gravel riffle (so can’t reproduce in Lake Merced). Prefer temps of 13- 21C (56 – 70F). Most trout planted are between 18 and 20cm and are caught w/in 2 weeks of planting.

Prickly Sculpin (Cottus asper) This species can occupy a wide range of bottom habitats and tolerate a diversity of salinity, temperature and flow. Sculpins feed on benthic invertebrates and serve as important forage for trout and bass. they need temperatures of 8 to 13C (46- 55F) for spawning. Males dig a nest in a protected area (under a rock, in a beer can or amidst trash) and protect and aerate eggs until they hatch.

Coho Salmon (Oncorhynchus kisutch) These anadramous fishes are found all along the North Pacific Coast from Japan to Monterey Bay. They spend a long time in fresh water, but eventually move out to sea. These salmon spawn in small, cool tributaries with a water temperature of 12-19C.

NON-NATIVE:
Brook Trout (Salvelinus fontinalis) Native to the north-east US and eastern Canada, brook trout were brought here by the California Fish Commission in 1972. Brook trout prefer clear running water and gravel bottoms to breed, and spawn at water temperatures of 4-11C.

Sockeye Salmon (Kokanee) (Oncorhynchus nerka) Popularly introduced into lakes – a non-anadramous salmonid – during the 50s and 60s as a food fish for trout. Wound up being more of a competitor and not easy to angle for (it feeds on zooplankton). Needs temps of 6-13C (44-55F) to spawn.

WARM WATER SPECIES

NATIVE:
Hitch (Lavinia exilicauda) Common name comes from the Pomo language. Found throughout the Sacramento / San Joaquin drainage. Characteristic of warm, low-elevation lakes. Fish school in open water and feed on planktonic crustaceans, phytoplankton and flying and emerging insects. Omnivorous open-water and surface feeders. Breed in fine-gravel bottoms swept clean by wave action or current and temps of 14-18C. Reproduce after heavy rains, often near lakes and can breed in streams that dry up during the summer. Considered a nuisance fish by managers.

Sacramento Sucker (Catostomus occidentalis) Tolerate a wide variety of habitats. Most abundant in clear cool streams and moderate elevation lakes and reservoirs. Usually associated with native minnows. Eat algae, detritus and bottom inverts ( Chironomid larvae). Have a hard time maintaining populations in waters dominated by introduced carp and goldfish. Spawn in riffles.(Can’t Breed in Lake Merced)

Sacramento Blackfish (Orthodon microlepidotus) Once dominated the warm, shallow, turbid lakes of the Central Valley. Filter feed on planktonic algae and zooplankton. Appear to spawn over aquatic vegetation, but few records exist because of the species’ preference for turbid water. Spawn at temps of 12-24C. Now, these fish are sold live in Asian fish markets.

Sacramento Perch (Archoplites interruptus) Originally widely distributed in Pajaro/Salinas and Sacramento/San Joaquin Rivers. Successfully tolerate alkaline water. Young eat small crustaceans, older fish eat aquatic insects (especially Chironomids). Highly opportunistic feeders. Need water temperatures of 21-29C to spawn in shallow beds of aquatic plants and algae. Good potential for development as a native game fish. NATIVE

Hardhead (Mylopharadon conocephalus) Hardheads are native to the Sacramento/San Joaquin and Russian River drainage systems. They feed on small invertebrates and aquatic plants in quiet water. They probably spawn in gravel riffles. Hardhead are generally found in less disturbed streams with few predators (such as bass) and competitors (such as carp). The common name is frequently also applied to the Sacramento Blackfish and Sacramento Squawfish.

Threespine Stickleback (Gasterosteus aculeatus) These are among the most common fish in coastal North America. They are found in coastal streams all over California. Males construct nests in beds of aquatic plants and entice females in to lay eggs. The males fans water over the eggs and protects them from predators. Spawn at temperatures of 18 – 20C. The male will guard the young fry in his mouth.

Tule Perch (Hyserocarpus traski) Tule perch are native to the creeks of Northern and Central California, as well as the Sacramento/San Joaquin River system. They are adapted to feed on invertebrates associated with the bottom, particularly amphipods and Chironomids. These fish are viviparous (bear live young), and therefore may breed in waters with a variety of different bottom textures or currents. They enjoy tule beds and overhanging trees. Tule perch have a low tolerance for high turbidity and pollution.

NON-NATIVE:
Largemouth Bass (Micropterus salmoides) Introduced into CA in 1874 -- native to the Mississippi River system. Like warm, quiet water with low turbidity and beds of aquatic plants. 20 – 30C (~70-85F) is optimal temp. for growth. Minimum dissolved oxygen requirement is 1.5-2.0ppm. Adults feed on large inverts and other fish. Voracious predators. Males build nests in shallow areas and defend the nest from predators until the eggs hatch. Spawning can take place at temperatures from 14 to 24C (55 – 75F). Can nest from 1-5m in depth. Ironically, many plankton species introduced as forage for Bass, such as shad, have reduced bass populations b/c of competition w/ bass fry.

Green Sunfish (Loomis canellas) Originally native to the Mississippi drainage system. Introduced into CA in 1891. Spread by folks who thought they were planting bluegill. Aggressive and territorial. Can survive high temps (over 36C (97F!) less than 3ppm dissolved O2 and high alkalinity. Opportunistic predators on large inverts and small fish. Spawn in water temps above 19C (67F). They provide little in sport or food and compete aggressively with and feed on game fishes.

Bluegill (Lepomis macrochirus) Native to Eastern and Southern North America. Introduced into CA in 1908. Can survive and reproduce in a wide variety of conditions. Do best in warm, shallow lakes. Can survive in waters with high turbidity and low oxygen content (less than 1ppm). Associated with rooted aquatic plants and seldom go deeper than 5m. Eat a wide variety of foods, esp. aquatic insect larvae (Chironomids). Spawn in water temps of 18 – 21C (lower limit). Spawn on a variety of bottom substrates. Males defend the nest and guards the young for several days after they hatch. High reproductive rates, so little affected by fishing.

Black Crappie (Pomoxis nigromaculatus) Native to Mississippi. Likes warm, clear lakes and reservoirs with large beds of aquatic plants. Eat zooplankton, Diptera larvae, fish and other aquatic. insects. Males defend nest and young fry. Breed above 14-17C. Good game fish.

Carp (Cyprinus carpio) Originally native to Asia, but brought to California in 1872 by Julius A Poppe. They are now found in all the river systems of California except the Klamath. Carp are abundant in warm, turbid water. They are active in a wide range of temperatures, 4-34c. They are bottom feeding fish, and both increase turbidity and uproot aquatic plants as they forage for food. Spawning takes place at temperatures above 15C in shallow, weedy areas. NON-NATIVE

Goldfish (Carassius auratus) These familiar fish, originally from Eurasia, are now found in warm water throughout the state. They are hardy and can survive at temperatures from 0-41C. Goldfish mostly graze on plankton and detritus. They require temperatures of 15-23C to spawn, and do so in shallow, weedy areas. NON-NATIVE.

White Catfish (Ictalurus catus) Originally from streams on the Atlantic coast of the U.S. Introduced into California in 1874. Carnivorous bottom feeders that spawn when temperatures are over 21C. The female excavates a small nest, and after the eggs are laid, one or both parents guard the nest and young fry. NON-NATIVE

Channel Catfish (Ictalurus punctatus) Native to the Mississippi river system. These are one of the fastest growing species of catfish. They need warm temperatures (21-29C) to spawn. They require nooks for nest sites, but do not guard eggs or young. NON-NATIVE

Brown Bullhead (Ictalurus nebulosus) Native to most of the U.S. east of the Mississippi River, Brown Bullheads were introduced into California in 1874. They feed on bottom invertebrates such as amphipods, isopods, crayfish, insect larvae and snails. They can live in water ranging form 0-37C but prefer warm water (20-35). The female excavates a small nest, and after the eggs are laid, one or both parents guard the nest and young fry.

Muskelunge (Esox masquinongy) These large predatory fish are common in the upper reaches of the Mississippi and the lakes of Central North America. They prefer cool, weedy waters, but can tolerate temperatures as high as 21C and spawn in river tributaries. They are voracious and can reach lengths of up to 5 ft. (http://www.fishinaction.com/musky.htm)
 

THANKS
In order to complete this report, I consulted numerous records from the California Department of Fish and Game, Region III in Yountville, CA. I would especially like to thank Sid Poe, Fish Hatchery Manager II, and John Emig, Biologist for their help and advice. Many thanks to Dr. Peter Moyle for his expertise regarding fish restoration. Finally, thanks to Nelia White, MA Candidate, San Francisco State University, for her interest in and resources relating to California Fish.

REFERENCES:
Allen, Jack T. June, 1965. The Boat Fishery at Lake Merced, San Francisco County During 1959, 1960 and 1961.  Draft Report. California Department of Fish and Game. Allen, Jack T. Oct. 1962. Gill Net Sampling at Lake         Merced, October 4-7,1962. Draft Report.California Department of Fish and Game.

Anderson, Keith. Oct. 11, 1976. Fish Population Sampling, South Lake Merced.  Interoffice Memorandum. California Department of Fish and Game.

Anderson, Keith. April 18, 1977. Fish Population Sampling, South Lake Merced. Interoffice Memorandum. California Department of Fish and Game.

Calhoun, A.J. Nov. 3, 1949. Chemical Treatment of Lake Merced.   Letter submitted to the Region III Central Office of California Fish and Game.

Campo, Jon. 2000. Lake Merced, San Francisco.   From the pamphlet created by the San Francisco Recreation and Park District, Natural Areas Program.

EIP Associates 2000. Significant Natural Resource Areas Management Plan. Prepared for Natural Areas Program, San Francisco Recreation and Parks Department. 

Fisher, CK.  Sept. 16, 1958. Proposed Changes in the Trout Management Program at Lake Merced, San Francisco County.  Inland Fisheries Report #58-14, California Department of Fish and Game Region III

GEO / Resource Consultants, Inc. May 1993. Lake Merced Water Resource Planning Study;

Gilliam, Harold. 1967. The Natural World of San Francisco. Double Day and Company, Garden City, New York.

Gustafson, Joel . 1954. Lake Merced 1951-54 Project Summary.   Draft Report California Department of Fish and Game.

Hansen, R.J & Strohschein, W.E. 1963. The 1963 Chemical Treatment of South Lake Merced, San Francisco County.  Draft Report, California Department of Fish and Game.

Johnson, William C.. March 17, 1955. A Historical Account of the Lake Merced Fishery.  Department of Fish and Game Interoffice Correspondence to William A. Evans, Fisheries Management Supervisor Region III.

Leiby, James S. 1965.  Letter to the Bureau of Sport Fisheries and Wildlife, Nov. 16, 1965.  Draft Letter, California Department of Fish and Game.

Moyle, Peter B. 1976. Inland Fishes of California.  UC Press, Los Angeles

Moyle, Peter B. May 2000. Personal Communicationprovided feedback on fish biology and potential for restoration of selected species. Professor of Fisheries and Wildlife Conservation, UC Davis Department of Wildlife, Fish, and Conservation Biology, 530-752-6355 (tel) ,530-752-4154 (fax)

Poe, Sid. May 2000. Personal Communication .– provided copies of 20 years of fish stocking records at the California Department of Fish and Game Region III office. Hatchery Manager II, CDF Region III, Yountville, CA. (707) 945-1237.

Scoppettone, Gary.  1976Fish population sampling in North Lake Merced.  Interoffice Memorandum. California Department of Fish and Game.

Scoppettone, Gary. 1976Fish population sampling in South Lake Merced.  Interoffice Memorandum. California Department of Fish and Game.

Scoppettone, Gary.  1976 . Tule Perch Relocation.   Interoffice Memorandum. California Department of Fish and Game.

Scoppettone, Gary & Anderson, Keith. 1976.  Spawning Study of Prickly Sculpin in Lake Merced. Interoffice Memorandum. California Department of Fish and Game.

SF Public Utilities Commission.  1998.  Lake Merced Comprehensive Management Plan Appendixes.  Revised Draft, SF Parks & Rec. Department

Shoup, Lawrence H., and Baker, Suzzane. 1981. Cultural Resource Overview: Lake Merced Transport. San Francisco Clean Water Program, SF, CA. SWRCB No. C-06-1102-0:13. Prepared by Archaeological Consultants, 1464 La Playa, San Francisco, California.

Strohschein, Wallace E.  1968.  Population Sampling in North Lake Merced. October 22 – November 8, 1968. Draft Report. California Department of Fish and Game.

Strohschein, Wallace E.  1974.  Trout Inspection for Nematodes.  Draft Report. California Department of Fish and Game.

Tierney, R. 1954.  A report on the feeding habits of Salmo gairdnerii and Salmo fontinalis in Lake Merced, CA. Paper Submitted to Dr. Joel F. Gustafson, Instructor Bio 299, San Francisco State University.

Trihey & Associates, Inc.  1999.  Lake Merced 1998 Baseline Natural Resources Inventory.  SF Public Utilities Commission.

Wyckoff, Larry C. 1989. Gillnetting Samples in North Lake Merced,June 28-29, 1989. Draft Report. California Department of Fish and Game.