Thursday, May 1, 2014

Management Minute: The GRASS Carp

Photo credit:  Michigan State University Extension
Happy Thursday all and welcome to our management minute!  With the warming of spring, you are likely noticing the "greening" of just about everything around you.  Flowers blooming, birds chirping, and love in the air (along with eye swelling pollen...).  These are just a few things you might be seeing with the changing of the seasons.  All of this "new life" isn't designated solely to those things which we love..... Invasive aquatic plants are likely on the increase as well, warranting many to start thinking about management.  This week, we will discuss one of many options for managing some types of aquatic plants:  The Grass Carp.

The grass carp is native to Eastern Asia, yet over the past several decades has made its way into water bodies worldwide, specifically for vegetation control.  These fish are easily raised in a hatchery environment, making them an ideal candidate as a food source and bio-control.  The grass carp was truly built for vegetation consumption with their mouths located near the top of their heads and grinding teeth, perfectly designed to breakup vegetation.  Grass carp can live to nearly 25 years of age and reach monumental sizes of 80+ pounds.  Grass carp have amazing appetites. Fish over 15 pounds consume up to 30% of their body weight daily, whereas smaller fish (less than 10 pounds) consume as much as 150% of their body weight a day.
A large specimen from Lake Gaston, NC caught during an annual survey and released.  Photo Credit:  NCSU AWP
Hydrilla, a favorite food of the grass carp.
Photo Credit:  NCSU AWP
Grass carp are generalists feeders and will eat almost any plant material however they do prefer the more tender, soft material of submersed species over the waxy, sometimes hard material of floating and emergent plants. Grass carp have a sweet (or green rather) tooth for southern naiad, hydrilla, and duckweed. There is one exception to the grass carp's diet as they do NOT care for Eurasian water milfoil. Grass carp are also poor controllers of filamentous algae.
Carp stocked from hatcheries are triploid, which means that they are infertile and unable to reproduce. This keeps grass carp populations in a water body "in check" and allows resource managers to track and model grass carp populations over time. This is important because stocking too few grass carp annually will have little to no affect on controlling problem species like hydrilla. On the other hand, overstocking can also lead to rapid devegetation of a lake which can negatively affect water quality. Grass carp are also only stocked into water bodies in which they can be contained to prevent their escape downstream. While grass carp are extremely effective in controlling invasive submersed plant species, they will also feed on native species and if allowed to be introduced into open system, could devastate native plant populations.  This has lead some states to not allow grass carp as a means for controlling vegetation.  In many states, permits are required to obtain the fish.
Schooling juvenile grass carp.  Photo credit:  NCSU AWP.
Grass carp, where legal, can be an extremely cost effective and adequate means for controlling some types of vegetation.  Where applicable, these fish can provide decades of control.  Although large and somewhat menacing looking, these fish are merely "cattle with fins" which are an integral part of plant management in many water bodies. 

For more information about grass carp, visit out Best Management Practices Handbook, chapter 10.  

For more information on the Aquatic Ecosystem Restoration Foundation, visit our website.

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