biology of asian carps - fisheries conservation...

Biology of Asian carpsLife history of bighead, silver, black and grass carps

What we know, and what we’d like to know

Duane C. Chapman USGS Columbia Environmental Research Center

ID - Bighead vs Silver carp

Keel

Keel

ID - bighead vs silver carp

Silver carp

Bighead carp

Reproduction and Recruitment in

Asian Carps

Asian Carp Life Cycle

From Nico et al. 2005

Upstream spawning movement

• Don’t really know how far – Difficult to separate from “wanderings”– Telemetered fish travel “off-screen”– Management need

• Usually associated with rapidly increasing flows

• DeGrandchamp will speak on movement rate

Spawning locations• Based on visual observation, egg collections • Exact requirements unknown

– Thought to be in turbulent areas of rivers– Mouths of tributaries– Probably NOT in small tributaries

• 400 m3/second possible minimum?

• May occasionally spawn in lakes, but eggs not thought to survive

Spawning behavior• Unknown if species migrate/spawn together

– Bighead – silver hybrids– Black carp spawn deeper?

• Literature: Grass, silver and bighead carp active spawners in open water– Jumping from the water– Swimming upside down at surface

• Bouyant flower

– Never observed in the Missouri River

Spawning periods

• Literature: late spring, early summer for all four species– Black carp a bit later and more protracted?– Papoulias – bighead and silver carp have a

protracted spawning season, Individuals with multiple partial spawns per season

Early Life History

• Requirements for eggs and larvae probably often limiting– “Achilles heel” ?

• Literature: Temperature, current, water hardness, turbidity, river length, even vegetation

Egg Requirements• Eggs are heavier than water

– Without sufficient current will sink to bottom• This is thought to be lethal

• Temperature controls development rate– Temperature window ~ 18 – 30 C (64 – 86 F)

• In theory – can calculate minimum length of river from minimum velocity and temperature

River Length Requirements

From Nico et al. 2005

Further Uncertainty?

• Tang, 1960 – bighead, silver and grass carp reproduced in a reservoir with a small watershed

• Other Asian carps (ex. Elopichthys) may have recruited in reservoirs

• Survival of bighead carp eggs in unaerated bags of water and sediment

Nevertheless…..

• All places currently with confirmed self-sustaining populations of bighead, silver, black, or grass carp have access to a large river, with at least 80 km free-flowing.

What does this mean to a manager?

• Reservoirs with substantial river tributaries are at risk for establishment of Asian carps.

• Some uncertainty exists about other yet-to-be-invaded environments

Fecundity and Reproductive Strategy

Fecundity

• Large Asian carps of all species are capable of producing hundreds of thousands, sometimes millions, of eggs each year

• Examples:– Silver carp: 4.2 million : 12 kg fish– Bighead carp: 1.1 million : 18 kg fish– Black carp: 1 million : 4.5 kg fish

Survival

• No parental care and generally extremely low survival

• Thought to be poor at avoiding predators• Strategy:

– Overwhelm high mortality with many eggs– Grow fast and become:

• Too large to eat• Capable of producing many eggs

Implications

• Adult mortality low• Juvenile mortality varies highly between

years– Controlled by environmental conditions

• Population characterized by strong year-classes

• Removal of adult fish (harvest) works against carp reproductive strategy – as shown by Chinese experience and Mike Hoff’s models.

• Variable year-class strength may affect fishing industry

• Unknown what variables will control strong year classes– High water, access to nursery habitat?– Some of these variables might be controllable

What does this mean to a manager?

Asian Carp Feeding

Strategies

Pharyngeal gill teeth

Silver

Bighead

Grass

Black

Highly specialized;

“Novel weapon” theory

Black Carp

Black Carp• Primarily feeds on mollusks – snails,

mussels, clams • Also feeds on insects and sometimes

vegetation • Gape (mouth size) limited (probably not by

shell thickness)– Relatively small mouth:size, but grows to large

size

Corbicula, invasive Asian clam

Native Molluscivores

• Most concern about potential destruction of mollusks, rather than competition with natives

• Native molluscivores include freshwater drum, redear sunfish, and some redhorse suckers, blue catfish (also non-native common carp), none obligatory molluscivores

• See Anita Kelly’s talk

Common carp pharyngeal teeth

Grass Carp

Grass Carp• As adult, almost exclusively vegetarian

– Will take invertebrates and other high protein/calorie foods but insubstantial part of diet.

• Selectivity – Preference for long, thin vegetation– Do not prefer filamentous algae, hard or tough

vegetation, or duckweed– In a pinch can feed on wide variety of vegetation

Grass Carp• Have the capacity to feed little or not at all

for long periods.– Gorge when opportunity presents

• Terrestrial vegetation important, during water rises

– Do not feed in winter Courtesy Josh Dunkle

Feeding behavior(personal observations)

• For items that will not reach teeth (too wide to enter throat) will pull and tear with lips

• Sometimes partially exits water to access terrestrial vegetation

• Uproots littoral grasses by digging into banks, then eats them roots-first– Effect on bank stability/erosion?

Comparison to Native Fish

• No native fish can compare to Grass Carp in vegetation consumption– Herbivory unusual in fishes

• Most concern related to habitat modification rather than competition with native fish

Bighead Carp

Pharyngeal gill teeth

Gill rakers

Bighead CarpGill rakers

Epibranchial organTaste buds, mucous

Mechanical use?

Diet of Bighead Carp• Mostly considered to be a zooplankton predator

– Consumes larger and colonial phytoplankton• Sometimes including noxious bluegreen algae• Has defenses against toxic algae

– “Detritus” (source unclear or varied)• Size of smallest filtered particles ~1/4 width of

gill raker gap (probably due to trapping on mucous)

Diet of Bighead Carp• Gape large, but food items small

– Probably limited by gap between teeth and crushing plate

– Some food items up to 3 mm• Gut long and thin (3.5 – 5.5 X Total Length)

– No stomach– Not robust – no large, sharp food items!

Feeding Behavior of Bighead Carp• Usually considered pump filterer

From Kolar et al, in press

Feeding Behavior of Bighead Carp

• Often, but not always, feed at surface of water, sometimes almost vertically

Feeding Behavior of Bighead Carp• Sometimes also ram-feed (often observed

below Bagnell Dam, Missouri at dusk)

From Kolar et al, in press

Feeding Behavior of Bighead Carp

Bighead carp ram-feeding in Iowa

Feeding Behavior of Bighead Carp• May attempt to break up large items to

manageable particles• Relative importance of different behaviors

unknown• Other behaviors possible

– Sand particles in some diet studies indicate possible bottom feeding

• Adaptable, but require small particles

Feeding Behavior of Bighead Carp• Feeding thought to be relatively continuous

– Stomachless strategy• Usually have full guts in winter

– Gut evacuation rate (and thus, feeding rate) probably low in winter

Winter Surface Feeding

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Comparison to Native Fish• Native filter feeders of basin

– Paddlefish, gizzard shad, bigmouth buffalo– See Ben Gu’s and Schuyler Sampson’s presentations today

• Can consume particles much smaller than paddlefish (an obligatory ram feeder)

Comparison to Native Fish• Capabilities of bigmouth buffalo less well

understood

Comparison to Native Fish• Bigmouth buffalo gill rakers, excised, and

epibranchial organ

Silver Carp

Pharyngeal gill teeth

Gill rakers

Silver Carp

Diet of Silver Carp• Mostly considered to be a phytoplankton feeder

– Sometimes including noxious blue-green algae– Has defenses against toxic algae– Some blue-greens benefit from being eaten

• “Detritus” (source unclear or varied)– Can silver carp effectively feed on bottom?– What else eats this “detritus”?

• Zooplankton, but ineffective on evasive ones

Diet of Silver Carp

• Size of smallest filtered particles much smaller than bighead carp (sometimes less than 4μm[0.00016 inch])

• Size of items probably limited by gap between teeth and crushing plate

Diet of Silver Carp

• Gut extremely long and thin (7.5- >10 X Total Length)– No stomach, continuous feeding– Not robust – no large, sharp food items!

• Bacterial growth in gut may be important part of diet

Feeding Behavior of Silver Carp• Pump Filter feeder• Normally do not pick out individual items of

prey• In Missouri River study, often located in areas

of higher chlorophyll concentration• Feed in schools, like bighead carp• Apparently do not feed on surface like bighead

carp

Comparison to Native Fish

• Silver carp are extremely specialized filter feeders – Feed on extremely small particles– Native fishes normally not consumers of

phytoplankton

Questions• Vast majority of information on diets and

environmental effects of Asian carp feeding strategies is on LAKES and RESERVOIRS

• USA problems are mostly in RIVERS• Rivers are more difficult to study • What are the effects on native species and

riverine environments?

What does this mean to a manager?

• Asian carp feeding strategies are effective and native fishes sometimes may be out-competed, if food resources are limiting. (see Kevin Irons’ talk)

• Asian carps have highly specialized anatomy for feeding, but often show unexpected opportunistic behavior

Finally

• There is still much to understand about biology of Asian carps

• Experiences in other countries useful, but don’t always apply

• Expect the unexpected – Asian carps continually find new ways to break the mold