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Identifying and Managing Aquatic Rodents in Texas: Beaver, Nutria and Muskrats

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Identifying and Managing Aquatic Rodents in Texas: Beaver, Nutria and Muskrats 7 Texas Agricultural Extension Service Identifying and Managing Aquatic Rodents in Texas: Beaver, Nutria and Muskrats Texas Agricultural Extension Service The Texas A&M University System Zerle L. Carpenter, Director College Station, Texas Cover Photos Top left: Beaver Top right: Beaver Bottom left: Muskrat Bottom right: Nutria Editor: Judy Winn. Estension Communicntions Speciitli.~?, Tllc~Texcc.5 AKrM Universih System. CONTENTS BEAVER GeneralHistory ......................................................... 3 TexasHistory ........................................................... 4 Determination of Sex ..................................................... 5 BiologyandBehavior ..................................................... 5 ColonyandFamily ....................................................... 5 Movements and Dispersal ................................................. 6 Reproduction ........................................................... 6 Gestation Period and Litter Size ............................................ 6 Mortality and Life Expectancy ............................................. 6 Parasites and Diseases .................................................... 7 BenefitsofBeaver .......................................................7 Legalstatus ............................................................ 7 Management and Control of Beaver ......................................... 8 BeaverDamage .......................................................... 9 Distinguishing Beaver. Nutria and Muskrat Damage ............................ 9 Damage prevention and Control Exclusion ......................................................... 10 Cultural Methods ...................................................... 10 ChemicalMethods ..................................................... 10 Shooting ............................................................. I1 Trapping .............................................................11 NUTRIA Description ............................................................. 13 Behavior ............................................................... 13 Reproduction ........................................................ 13 Gestation and Litter Size .................................................. 14 Habitat ...................................................... :......... 14 FoodHabits ............................................................. 14 Legalstatus ............................................................ 14 NutriaDamage ...........................................................14 Nutria Damage Control ...................................................35 MUSKRATS Description ............................................................. 35 Reproduction ........................................................... 35 Legalstatus ............................................................ 36 MuskratDamage ........................................................ 36 Muskrat Damage Control .................................................. 36 MAKING WILDLIFE CONTROL DECISIONS ................................. 36 ILLUSTRATED FIELD GUIDE ..............................................15 REFERENCES ............................................................37 APPENDICES ........................................................... 42 Figures Figure 1. Beaver transplants recorded by the Texas Parks & Wildlife Department. 1939-73 ..................................................... 4 Figure 2 . Beaver distribution. 1984 ........................................... 4 Figure 3 . Comparison of beaver. nutria and muskrat .............................. 9 Figure 4 . Nutria distribution. 1984 ............................................ 13 Figure 5 . Muskrat distribution. 1984 .......................................... 35 Identifying and Managing Aquatic Rodents in Texas: Beaver, Nutria and Muskrats Dale A. Wade and Charles W. Ramsey * Beaver (Castor canadensis), nutria (Mjocastor with their influence upon the amount and quality of habi- coypu) and muskrats (Ondntra zibethica) are important tat. undoubtedly caused some population fluctuations. furbearing animals in Texas. All three species are semi- Seton (1900) estimated that in primitive times there were aquatic rodents that utilize similar habitat and are some- some 60,000,000 beaver in North America. what similar in general habits and appearance. They may The Indians killed beaver for food and used their skins simultaneously inhabit the same lakes, marshes and for clothing; they captured beaver with snares, nets and streams, but they differ substantially in size and specific deadfalls. This harvesting of beaver had little effect on habits. the total population, and could be considered simply a Beaver are the largest native rodents in North Amer- part of the natural environmental pressures upon wildlife ica; some adults weigh more than 100 pounds. Nutria are in general. However, the coming of white men dramati- native to South America and were brought into the cally changed the factors which influenced beaver popu- United States about 50 years ago; adults may weigh as lations. The invasion of North America by Europeans much as 20 to 25 pounds. Muskrats also are native to not only altered natural conditions. but also caused the North America; adults commonly weigh from 2 to 4 Indians to modify their ideas and practices. Beaver pelts pounds. became important in the fashion markets of Europe and These species are valuable as furbearers and have many beaver were killed to satisfy this demand. The positive effects on the environment. However. they may early fur trade depended almost entirely upon Indians also cause substantial economic or other losses. In order who gave furs in trade for whatever products the whites to manage these species in Texas it is necessary to under- had to offer. But this system failed to supply enough stand their ecology and damage. as well as methods of beaver pelts to satisfy demand, so the era of the "white control. The following discussion considers the species trapper" or "mountain man" came into being. Between in order of their general importance in Texas. 1800 and 1850, the major explorations in western North America were made largely to discover new areas for trapping beaver. About midway through this 50-year period, steel leg- BEAVER hold traps were invented. These traps enabled trappers to operate with much greater efficiency at a time when fur demand was reaching its peak. The extirpation of beaver General History from much of their original habitat followed shortly and The history of the beaver in North America is a by 1850, when the whims of fashion decreed that silk lengthy one, with the earliest evidence of beaver occur- hats should be the successor to beaver hats, the scarcity ring in Pleistocene deposits. It is believed that beaver of beaver had become noticeable. Trappers were going occupied streams in North America for thousands of farther into headwater areas, were staying longer and years before the first European settlers arrived. and were returning with fewer pelts. By the late 1850s, probably attained a population level which filled avail- beaver populations in most of the American West had able habitat. Climatic conditions and plant succession, been severely depleted. Even the low pelt prices common after 1850 did not *Extension wildlife specialists, The Texas A&M University System. end the exploitation of beaver. Trappers who knew no other way of life continued to eke out a living by selling pelts for whatever the market would bring, and beaver populations continued to dwindle through the last half of the 19th century. The low point probably was reached sometime between 1890 and 1900. About 1900 most western states began protecting beaver. From that time to the present, because of protec- tion and transplants, beaver populations have increased. Since much of the original beaver habitat has been al- tered, it is not likely that the total beaver population will again reach the level present before European settlement of North America. Nonetheless, in some areas beaver populations may exceed pristine levels because of the favorable habitat created by land management practices. Texas History Historical references to the early fur trade generally emphasize the Rocky Mountains and other western areas, with little mention of the beaver harvest and fur trade in Texas. Yet, Texas beaver were nearly extinct by 1900, primarily because of the fur trade. Beginning in Figure 2. Beaver distribution, 1984. 1925, beaver were protected by Texas laws and regu- lations and their harvest was controlled. Beaver that caused damage were commonly live-trapped and trans- planted to other areas. There isn't much information on successful and both protection and transplanting contrib- the number of beaver transplanted within Texas or uted to a relatively rapid increase in the Texas beaver brought in from other states, but records do show numer- population. By the mid 1960s there were many com- ous transplants from 1939 to 1961 and there were many plaints of beaver damage in Texas and transplanting to that were not recorded (Texas Parks & Wildlife Depart- protect beaver was no longer considered necessary. As ment, unpublished data. Fig. 1). These were generally damage complaints increased, restrictions on "taking" beaver were gradually reduced. At present, beaver popu- lations are quite high. Damage is serious in many areas, particularly the eastern half of Texas, and removal of beaver for damage control
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