DistrictCover.fm Page 1 Thursday, May 20, 2004 2:19 PM In cooperation with the U.S. Fish and Wildlife Service Occurrence of the Diamondback Terrapin (Malaclemys terrapin littoralis) at South Deer Island in Galveston Bay, Texas, April 2001–May 2002 Open-File Report 03–022 TEXAS Galveston Bay GULF OF EXICO M U.S. Department of the Interior U.S. Geological Survey Cover: Drawing of Diamondback terrapin by L.S. Coplin, U.S. Geological Survey. U.S. Department of the Interior U.S. Geological Survey Occurrence of the Diamondback Terrapin (Malaclemys terrapin littoralis) at South Deer Island in Galveston Bay, Texas, April 2001–May 2002 By Jennifer L. Hogan U.S. GEOLOGICAL SURVEY Open-File Report 03–022 In cooperation with the U.S. Fish and Wildlife Service Austin, Texas 2003 U.S. DEPARTMENT OF THE INTERIOR Gale A. Norton, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. For additional information write to District Chief U.S. Geological Survey 8027 Exchange Dr. Austin, TX 78754–4733 E-mail: [email protected] Copies of this report can be purchased from U.S. Geological Survey Information Services Box 25286 Denver, CO 80225–0286 E-mail: [email protected] ii CONTENTS Abstract ................................................................................................................................................................................ 1 Introduction .......................................................................................................................................................................... 1 Purpose and Scope .................................................................................................................................................... 2 Description of Study Area ........................................................................................................................................ 2 Previous Studies ....................................................................................................................................................... 2 Acknowledgments .................................................................................................................................................... 4 Field Surveys and Data Collected ........................................................................................................................................ 5 Occurrence Surveys .................................................................................................................................................. 5 Nesting and Basking Surveys ................................................................................................................................... 6 Biometric Data .......................................................................................................................................................... 6 Habitat Data .............................................................................................................................................................. 7 Occurrence of Terrapins ....................................................................................................................................................... 7 Terrapins Captured ................................................................................................................................................... 7 Terrapin Nesting ....................................................................................................................................................... 8 Terrapin Characteristics ............................................................................................................................................ 9 Terrapin Habitat ........................................................................................................................................................ 11 Suggestions for Further Study .............................................................................................................................................. 12 Summary .............................................................................................................................................................................. 18 References Cited .................................................................................................................................................................. 19 FIGURES 1. Map showing location of South Deer Island in Galveston Bay, Texas ................................................................. 3 2. Digital orthophoto showing South Deer Island and locations of field surveys, April 2001–May 2002 .............. 4 3. Photograph showing modified crab trap with chimney ........................................................................................ 5 4–5. Graphs showing: 4. Catch per unit effort (CPUE) of Diamondback terrapins and by-catch at South Deer Island, Texas, April 2001–May 2002 ............................................................................................................................... 8 5. Correlation of monthly catch per unit effort of (a) terrapins and crabs and (b) terrapins and fish at South Deer Island, Texas, April 2001–May 2002 ..................................................................................... 9 6–7. Photographs showing: 6. Female Diamondback terrapin covering her nest site on South Deer Island, Texas .................................. 10 7. Diamondback terrapin egg from a nest on South Deer Island, Texas ........................................................ 10 8. Graph showing female and male straight-line carapace lengths of Diamondback terrapins captured at South Deer Island, Texas, April 2001–May 2002 ................................................................................................ 11 9. Boxplots showing size data from Diamondback terrapins captured at South Deer Island, Texas, April 2001–May 2002 .................................................................................................................................................... 12 10. Graph showing correlation of straight-line carapace length with mass of Diamondback terrapins captured at South Deer Island, Texas, April 2001–May 2002 ............................................................................................ 13 11. Boxplots showing condition factor of female and male Diamondback terrapins captured at South Deer Island, Texas, April 2001–May 2002 ................................................................................................................... 13 12–14. Photographs showing variation in: 12. Color and markings among Diamondback terrapins captured at South Deer Island, Texas, April 2001–May 2002 ......................................................................................................................................... 14 13. Carapace color among Diamondback terrapins captured at South Deer Island, Texas, April 2001– May 2002 ................................................................................................................................................... 14 14. Plastron color among Diamondback terrapins captured at South Deer Island, Texas, April 2001– May 2002 ................................................................................................................................................... 15 CONTENTS iii 15–17. Graphs showing: 15. Frequency of occurrence of female and male Diamondback terrapins with lesions captured at South Deer Island, Texas, April 2001–May 2002 ................................................................................................ 15 16. Frequency of occurrence of female and male Diamondback terrapins with barnacles and algae captured at South Deer Island, Texas, April 2001–May 2002 ................................................................... 16 17. Maximum water temperature recorded manually at South Deer Island and recorded by National Ocean Service data logger in Galveston Channel during terrapin collection periods, July 2001– May 2002 ................................................................................................................................................... 16 18. Historical photographs (a, b) and digital orthophoto (c) of South Deer Island, Texas, from 1930, 1958, and 1995 ................................................................................................................................................................ 17 TABLES 1. Summary of terrapin field surveys, South Deer Island, Texas, April 2001–May 2002 ........................................ 5 2. Summary of terrapin capture and biometric data, South Deer Island, Texas, April 2001–May 2002 .................. 20 3. Maximums of field parameters recorded during periods of terrapin collection, South Deer Island, Texas, April 2001–May 2002 ........................................................................................................................................... 24 4. Vegetation species or substrate with at least 20 percent relative frequency along six transects, South Deer Island, Texas, April 2001–May 2002 ........................................................................................................... 24 iv Occurrence of the Diamondback Terrapin (Malaclemys terrapin littoralis)