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Jessica DeJean THESIS 2-26-10

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Jessica DeJean THESIS 2-26-10

  1. 1. The University of Southern Mississippi AN ANALYSIS OF SEA TURTLE STRANDINGS IN LOUISIANA by Jessica L. DeJean A Thesis Submitted to the Honors College of The University of Southern Mississippi in Partial Fulfillment of the Requirements for the Degree of Bachelor of Science in the Department of Biological Sciences
  2. 2. March 2010
  3. 3. Approved by ________________________________ Patricia M. Biesiot Associate Professor of Biological Sciences ________________________________ Frank R. Moore, Chair Department of Biological Sciences ________________________________ David R. Davies, Dean Honors College
  4. 4. TABLE OF CONTENTS Abstract……………………………………………………….……………………….XX Introduction……………………………………………………….……………………XX Materials and Methods…………………………………………….…………………...XX Results………………………………………………………………….………………XX Discussion………………………………………………………………….…………..XX Summary……………………………………………………………………….………XX Acknowledgements……………………………………………………………….……XX Literature Cited…………………………………………………………………………XX
  5. 5. LIST OF TABLES Table Page 1. Shrimp Trawling Season Opening and Closing Dates A. Zone 1……………………………………………………………………….XX B. Zone 2…………………………………………………………….…………XX C. Zone 3………………………....…………………………………………….XX 2. Sea Turtle Strandings……………………………………………………………..…XX 3. Sea Turtle Strandings with Strike Marks……………………………………………XX 4. Chi Square Test of Association A. All Zones Combined………………………………………………………..XX B. Zone 1…………………………………………………………………….....XX C. Zone 2…………………………………………………………………….....XX D. Zone 3…………………………………………………………………….....XX
  6. 6. LIST OF FIGURES Figure Page 1. Louisiana Shrimp Management Zones………………………………...…………….XX 2. STSSN Stranding Form A. Front…………………………………………………………………….…..XX B. Back……………………………………………………………………..…..XX 3. Google Earth Maps of Strandings A. 2002…………..……………………………………………………………..XX B. 2003…………..……………………………………………………………..XX C. 2004…………..……………………………………………………………..XX D. 2005…………..……………………………………………………………..XX E. 2006…………..……………………………………………………………..XX F. 2007…………..……………………………………………………………..XX G. 2008…………..……………………………………………………………..XX H. 2009…………..……………………………………………………………..XX 5. Alive and Dead Strandings A. Alive Strandings…………………………………………………………….XX B. Dead Strandings…………………………………...…………………...........XX 6. Scatter Plots of Sea Strandings A. Zone 1…………………………………….…………………………………XX B. Zone 2……………………………………………………………...………..XX C. Zone 3…………………………………………………………………….....XX
  7. 7. ABSTRACT The Audubon Aquarium of the Americas (AAOA) in New Orleans has been collecting and archiving observations about strandings of marine mammals and sea turtles along the Louisiana coast. For the present study, we collated and mapped the data for 163 sea turtles (5 different species) archived over the past eight years. Recorded strandings are concentrated primarily in the Lake Charles area and along Grande Isle and Grand Terre. The strandings peak around the end of April through the beginning of June and again at the beginning of October through mid-November. About 23% of the sea turtles had obvious strike marks. The areas with high stranding concentrations are heavily used by sport and commercial fishermen. The stranding dates overlap with periods of warm weather recreational boating and with open fisheries seasons for menhaden and shrimp. We examined the association between strandings and open fisheries seasons using a chi-squared test. Most strandings occurred during open menhaden season except in 2002 and 2007 where most occurred when both menhaden and shrimp seasons were open. Although there was a statistically significant association between sea turtle strandings and open fisheries seasons, this does not imply that fishing caused the observed morbidity and mortality.
  8. 8. INTRODUCTION There are seven identified species of sea turtles, including the leatherback turtle (Dermochelys coriace), Kemp’s ridley turtle (Lepidochelys kempii), olive ridley turtle (Lepidochelys olivacea), green turtle (Chelonia mydas), hawksbill turtle (Eretmochelys imbricate), loggerhead turtle (Caretta caretta), and flatback turtle (Natator depressus) (Castro and Huber, 2007). With the exception of the flatback turtle, which is found only in Australia, all other species can be found in the waters of the United States, and five of these six species are currently found in the Gulf of Mexico (Department of Commerce, 2003). The Endangered Species Act of 1973 classified the Kemp’s ridley, leatherback, loggerhead, hawksbill and green sea turtles as endangered species. The loggerhead and the green turtles were also classified as threatened at that time. Over the past 20 to 25 years sea turtle populations have struggled to exist around the world (Lewison and Crowder, 2007). Various natural factors contribute to sea turtles dying daily, but determination of the cause of death can be problematic in the marine environment (Crowder et al., 1995). When sea turtles start to decompose, their bodies fill with gases, and they float on the surface of the water (Crowder et al., 1995). Some wash onto shores (referred to as strandings), but many are broken apart, eaten, and may sink without ever being seen. The strandings washed onto shores can therefore only account for a small number of dead and injured turtles in a region. These strandings may provide evidence of the current human impact on sea turtle populations. The adverse conditions under which sea turtles live can be quite problematic for their survival. Humans have impacted sea turtle populations in the past with interference on beaches, by cleaning, artificial lighting, or sand mining. In addition, oil contamination
  9. 9. and other types of pollution in waters inhabited by sea turtles have the potential cause even more declines in sea turtle populations (Lewison and Crowder, 2007). Incidental capture by fishing gear has been the focus of sea turtle strandings in the past (Lewison and Crowder, 2007; Wallace et al., 2008). One of the reasons that incidental capture has such a negative affect on sea turtle populations is because it has a tendency to cause higher mortality rates in sea turtles of reproductive maturity, decreasing the number of possible reproductive offspring in the following generations. When an organism like a sea turtle is incidentally captured, it is commonly referred to as bycatch. Bycatch becomes a concern when it involves a threatened species such as a sea bird, marine mammal or sea turtle (Moore et al., 2009). Many countries including the United States are currently working to protect the threatened species that are more susceptible to becoming incidentally captured in fisheries practices. Even if greater efforts are put into other conservation strategies like nest protection for sea turtles, the populations will not be able to recover without reduction of their bycatch worldwide (Zydelis et al., 2009). Managed by the National Oceanic and Atmosheric Administraiton (NOAA), fisheries activities in the United States are under surveillance to reduce bycatch of species in recovery (Moore et al., 2009). Surveillance by actual observers on vessels is one way that NOAA can monitor the bycatch of threatened species. Under the direction of the Magnuson-Stevens Fishery Conservation and Management Act (MSA) NOAA Fisheries is sanctioned to place observers on vessels, however these observers are not required, and the NOAA’s sanctions cannot control fisheries on the state level. Not only is the state fishery difficult to control, generally very little funding is allocated to cover the expenses
  10. 10. for on vessel observers. According to Moore et al. (2009), this is very problematic because state fisheries are commonly a source of the bycatch of sea turtles. Various studies state that evidence of bycatch in fisheries can be seen in the form of strandings (Lewison et al., 2003; Cox et al., 2007). Strandings in this case are defined as turtles that have washed up on shores dead (Cox et al., 2007) or at times injured. Lewison et al. (2003) determined that a study of the reduction of sea turtle bycatch could be carried out by analyzing frequencies of sea turtle strandings and in turn the effectiveness of various bycatch reduction devices. Shrimp fisheries are considered the top contributor in the bycatch and stranding of sea turtles (Lutz and Musick 1997; Lewison et al, 2003; Cox et al, 2007; Casale et al, 2007). In the Gulf of Mexico, the shrimp fishery is dominated by two species, the white shrimp, Litopenaeus setiferus, and the brown shrimp, Farfantepenaeus aztecus (LDWF, 2006). The coastline of Louisiana is divided geographically into three separate shrimping zones (Fig. 1). Each zone has its own opening and closing dates for shrimp seasons that can be tracked by LDWF. The targeted species of shrimp are caught during the open season using funnel shaped trawl nets that are pulled through the water by a fishing vessel in a process called trawling. Observing increases in sea turtle strandings during shrimp trawling seasons can provide evidence that this human interaction is contributing to more sea turtle mortality (Lewison et al., 2003; Cox et al., 2007). During the early 1970s, the first instances of shrimp trawler interactions with sea turtles were indentified (Crowder et al,. 1995). In 1997 Lutz and Musick stated that the incidental capture of sea turtles in shrimp trawls has caused more sea turtle deaths than any other human interaction combined, and it has been estimated by NOAA that 62,000
  11. 11. loggerhead turtles and 2,300 leatherback turtles have been killed due to interactions with shrimp trawls (Department of Commerce, 2003). Over the past 20 years, over 150 bycatch reduction devices have been tested to establish one that is consistently reliable (Manjarrés et al., 2008). Turtle excluder devices (TEDs) are the most common bycatch reduction device in shrimp trawling. In order for a TED to be approved by the National Marine and Fisheries Service (NMFS), it must be proven to be at least 97% effective during testing (Department of Commerce, 2003). Approved TEDs have been implemented in the southeastern United States surrounding the Gulf of Mexico in an attempt to reduce bycatch (Spotila, 2004), and some have been quite successful, reducing bycatch numbers by up to 50% (Lewison and Crowder, 2005). Originally met with high opposition, TEDs requirements were challenged in at least ten different court cases until passing in 1991 (Lewison, et al., 2003). Even though TEDs have been highly effective in decreasing in incidental sea turtle mortality (Spotila, 2004); there is evidence that suggests that after the initial two to three years of decreases in strandings after 1991, turtle strandings in the Gulf of Mexico began to increase once again (Lewison et al., 2003). Under the regulations of the National Oceanic and Atmospheric Administration, shrimp and flounder trawlers operating in the southeastern United States are now required to use National Marine Fisheries Service (NMFS) approved TEDs. But even with federal law requiring the use of TEDs and trawls, Louisiana continues to refuse to enforce the laws and regulations (LDWF, 2006). The use of these bycatch reduction devices has been most effective in smaller sea turtles, including the Kemp’s ridley, but the effectiveness of these devices on the larger sea turtles remains a concern. In recent studies, there is evidence that 33-47 % of
  12. 12. stranded loggerheads and 1-7 % of stranded green turtles are too large to fit through TEDs. In addition, 75 % of the Loggerhead turtles in the Gulf of Mexico are too large to escape through the openings in the devices (Department of Commerce, 2003). In other parts of the world, TEDs have proven to be highly effective. Since their implementation in Australia, turtle bycatch has decreased by at least an estimated 90% (Department of Commerce, 2003). In a field study by Cox et al. (2007), vessels trawled next to each other, one with a TED and one without; the use of the TED proved to decrease the bycatch rate by 97%. This proves that it is possible for TEDs to be highly effective in the reduction of bycatch. However, shrimp trawl TEDs have little effectiveness if very low compliance exists in using the devices, especially when on vessel observers are not present (Moore et al., 2009). When states are unwilling to enforce federal regulations like Louisiana has in the past, there is very little hope for the device to work to the best of its ability. After decades of federally required TED use, the success of the device is still greatly determined by how well and accurately it is used not how long the requirements have been in place (Lewison et al., 2003). The lack of compliance with TED use in the Gulf of Mexico is a direct contributor to the high numbers of strandings (Cox et al, 2007). Another important fishery in the Gulf of Mexico is the purse-seine fishery of Gulf menhaden, Brevoortia patronus (Smith et al., 2002; Anderson, 2007; Vaughan et al., 2007). With a history as far back as the 1800s, menhaden fishing is today of the most valuable fisheries in the United States with the largest tonnage (Vaughan et al., 2007). Since 1995 when most commercial fishing equipment was banned in Florida (Vaughan et al., 2007), Louisiana has been the leader in the menhaden industry (Smith et al., 2002).
  13. 13. Louisiana is currently responsible for 92% of the menhaden catch annually (Vaughan et al, 2007). Menhaden fishing involves the use of two boast and a purse seine net to catch entire schools of menhaden at a one time (de Silva and Condrey, 1997; Rester and Condrey, 1999; VanderKooy and Smith, 2002). Once a school of menhaden is spotted, the two boats encircle it with the net. The net is pulled closed and the contents are brought on board the mother ship. A flexible hose is used to pump the catch into the refrigerated hold. This entire process usually lasts no longer than one hour. Though bycatch numbers are much lower for the menhaden industry compared to shrimp trawling, the bycatch of large fishes and sharks in these devices is still seen as a major issue. As far back as the 1950s, efforts have been made by menhaden fisheries to reduce incidental bycatch (Rester and Condrey, 1999). Two types of bycatch reduction devices have been established and are commonly used: hose cages and large fish excluders. Hose cages are used to prevent larger fishes from getting pumped into the refrigerated hold on deck and large fish excluders are made of thick bars, also preventing larger fishes from passing into the holds. In a study by Rester and Condrey (1999) it was determined that the hose cages needed substantial improvements in order to work effectively as bycatch excluder devices. The cages allowed the passage of menhaden as well as the fins, heads, and tails of larger fishes. Less than 28% of the bycatch that encountered the menhaden fishery survived in the observations. Through the observations of Rester and Condrey (1999), it was determined that the best way to decrease the mortality of the bycatch is to make alterations to the hose cages.
  14. 14. Another study of bycatch in the menhaden fishery by de Silva and Condrey (1998), determined that the best way to eliminate bycatch of different species was to pinpoint what they referred to as “hot spots” in the Gulf of Mexico. These spots included the waters east of the Mississippi River from April to August. In these areas during these few months, large numbers of incidental catches of fin fishes, shrimp and sharks were found in purse-seine nets. De Silva and Condrey (1998) also determined that one of the best ways to decrease the mortality of the bycatch was to make modifications to the purse-seine nets. Though there is no record of sea turtle capture in purse-seine nets thus far, sea turtles have recently been capture incidentally in gillnets (Carretta et al, 2003). Over seven years, 132 sea turtles were captured as bycatch in the gillnets that are very similar to the nets used in purse-seine fisheries like menhaden. Entanglement and drowning in these nets is the generally what leads to sea turtle mortality, and with no current standards for bycatch reduction set in the menhaden fishery bycatch of various large species is inevitable (Rester and Condrey, 1999). The conservation effort of sea turtles is problematic because it interferes with a market of high economic value. Fishermen profits can be compromised in the effort to save a species that they do not find essential to their business. Increases in the convenience of these devices and possibly some economic benefit could encourage more fishers to become more accepting of safer materials and practices (Gilman et al., 2006). Various other coutries have set up incentive programs for their citizens in order to protect endangered sea turtle (Ferraro and Gjertsen, 2009). These simple and inexpensive payments to the environmentally conscious have already begun to show increases in the
  15. 15. success of juvenile and adult sea turtles. Cox et al. (2007) suggested that TED use for reduction of bycatch to targeted levels simply will not occur until some sort of incentive program is established. By implementing small yet effective techniques to decrease sea turtle bycatch, improvements in survival among sea turtle populations can be made in the Gulf of Mexico. MATERIALS AND METHODS Records of sea turtle strandings in Louisiana from 2002-2009 were reported to the AAOA. The observer of each stranding filled out a document (Fig. 2) produced by the Sea Turtle Stranding and Salvage Network (STSSN). The form included the observer’s name, address, and phone number. The details of each stranding included but were not limited to date found, number found (if more than one found in one day), species and sex (if identifiable), condition (i.e. level of decomposition), and geographic location. The observer made notes on the final state of the carcass (buried, painted, etc.) to insure the stranding would not be surveyed more than once. Details of injury could also be noted on an included diagram. Many of these forms were complete and detailed, but others included only basic information. When possible, photographs were taken and sent via email. Some species were recorded as unidentified under specific conditions. Some sea turtles were not complete specimens due to decomposition. In some, only a small portion of the turtle was found and could not be properly identified. Some sea turtles were found and referred to “hybrids.” These sea turtles displayed recognition characteristics for more than one species and could not be properly placed into one species category. However, these strandings cannot be technically classified as hybrids without proper DNA analysis (James et al., 2004). Many stranding reports noted instances of obvious
  16. 16. boat strikes and propeller marks that were later noted. Few observers included measurements, and tagging information was usually not available. The documents were either faxed or emailed to AAOA. The eight years of sea turtle strandings were collated and entered into Excel spreadsheets, noting the details of each stranding. The geographic coordinates were also plotted on maps using Google Earth in order to pin point their location along the Louisiana coastline. The strandings were categorized by the week of the year that they occurred. The Louisiana Department of Wildlife and Fisheries (LDWF) was consulted regarding the dates for the opening and closing of shrimp seasons each year. The zoning for shrimp trawling was geographically defined, and the individual strandings were located within one of the three shrimp trawling zones (Fig. 1). The opening and closing dates were recorded for each of the three zones set by LDWF (Table 1). The opening and closing dates were also defined by the week of the year that they occurred. The opening and closing dates for menhaden fishing season were also obtained from LDWF. The menhaden dates were also defined by the weeks of the year that they occurred. My null hypothesis for this study was that open shrimp and menhaden fishing seasons have no effect on the frequency of sea turtle strandings in Louisiana. A chi square test of association was performed for the stranding data. RESULTS The sea turtle strandings in Louisiana from 2002-2009 included 163 turtles as follows: 102 Kemp’s ridleys, 27 loggerheads, 20 unidentified, 8 green sea turtles, 4 leatherback sea turtles, and 2 hawksbill sea turtles (Table 2). Strandings were
  17. 17. concentrated in Lake Charles (Zone 3) and Grand Isle/Grand Terre (Zone 2) (Fig. 3). On average, 87.8% of stranding in all zones between 2002 and 2009 involved dead rather than live sea turtles (Fig. 4). After the strandings were divided by zone, each was plotted on a scatter plot by week they occurred during the year (Fig. 5). The weeks of open shrimp season only, open menhaden season only, and both open shrimp and menhaden fishing seasons were indicated by shading present in figure 5. Most strandings occurred during open menhaden season except in 2002 and 2007 where most occurred when both menhaden and shrimp seasons were open. The strandings peak around the end of April through the beginning of June and again at the beginning of October through mid-November. About 23% of the sea turtles had obvious strike marks (Table 3) from what was assumed to be boats and boat propellers. The chi square test of association demonstrated a positive association between open fishing seasons and the frequency of sea turtle strandings in Louisiana (Table 4). The null hypothesis was rejected, and it was determined that open shrimp and menhaden fishing season have an effect on the frequency of sea turtle strandings in Louisiana. DISCUSSION In the present study, it was determined that sea turtle strandings in Louisiana were influenced by the shrimp and menhaden seasons. The strandings seemed to be concentrated in two main areas: the Lake Charles area and Grand Isle/Grand Terre. These areas are heavily used by sport and commercial fishermen. If the strandings were fairly evenly dispersed then it could be assumed that the chance of incidental bycatch is evenly spread over Louisiana waters. However, this clustering suggests that sea turtle
  18. 18. bycatch is more likely to be encountered in these particular fishing areas (Lewison et al., 2009). The stranding dates frequently seen in the data overlap with periods of warm weather recreational boating and with open fisheries seasons for menhaden and shrimp. However, the impact of recreation boating on sea turtle strandings was not reviewed in this study. It is possible that many of the propeller marks on stranded turtles occurred from these types of activities. Although there was a statistically significant association between sea turtle strandings and open fisheries seasons, this does not imply that all sea turtle strandings were caused by shrimp trawling and menhaden fishing. There are many other factors that could have influenced the sea turtle strandings throughout the eight years in this study. Many other human interactions have caused sea turtle mortality in the past, and it is possible that any of these could have been the cause of some of the strandings. It is also possible that some of the strandings could have died of natural causes and then washed up on the Louisiana shores. All factors must be considered when determining the cause of sea turtle strandings. While taking all of these factors into consideration, the results of this study still agree with various prior studies, stating that there are obvious patterns between sea turtle strandings and trawling fisheries (Crowder et al., 1995; TEWG, 2000; Lewison et al., 2003). However, necropsies of the strandings were never taken, eliminating almost all possibility of determining the cause of death.
  19. 19. SUMMARY The strandings in this study were concentrated Lake Charles (Zone 3) and Grand Isle/Grand Terre (Zone 2). Both are major areas for commercial and recreational fishing as well as for recreational boating activities. On average, 87.8% of stranding between 2002 and 2009 involved dead rather than live sea turtles. The chi square test demonstrated a positive association between open fishing seasons and the frequency of sea turtle strandings in Louisiana. However, we did not investigate the impact of recreational fishing and boating on strandings. Other factors that may have contributed to sea turtle strandings are seasonal migrations between feeding areas and spawning areas as well as migrations based on water temperature changes (Crowder et al., 1995). There is always room for improvement in the reduction of incidental bycatch in sea turtles, but as long as budgetary and organizational constraints are affecting fisheries practices, sea turtles will continue to strand (Moore et al., 2009). Without Louisiana’s enforcement of federal TED laws, sea turtle strandings will continue in Louisiana.
  20. 20. ACKNOWLEGEDMENTS First and foremost, special thanks go to Dr. Patricia Biesiot for her assistance throughout the development of this study. Thank you to the Audubon Aquarium of the Americas and stranding coordinator, Michele Kelley for access to the data used. Special thanks for their help and expertise go to Paul Cook, Mandy Courville and Keith Ibos at the Louisiana Department of Wildlife and Fisheries for their assistance with dates of the shrimp fishing season. Also, thanks to Joseph Smith at the National Oceanic and Atmostpheric Administration for his help regarding the menhaden fishing industry. Thank you to Dr. Carl Qualls at The University of Southern Mississippi for his assistance in statistical analysis of this study. I would also like to thank the USM Department of Biological Sciences and USM Honors College for their financial support of this study.
  21. 21. LITERATURE CITED Anderson, J.D. 2007. Systematics of the North American menhadens: molecular evolutionary reconstructions in the genus Brevoortia (Clupeiformes: Clupeidae). Fishery Bulletin 205: 368-378. Carretta, J.V., T. Price, D. Petersen, R. Read. 2003. Estimates of marine mammal, sea turtle, and seabird mortality in the California drift gillnet fishery for swordfishand thresher shark, 1996-2002. Marine Fisheries Review 66: 21-30. Casale P., D. Freggi and M. Rocco. 2008. Mortality induced by drifting longline hooks and branchlines in loggerhead sea turtles, estimated through observation in captivity. Aquatic Conservation: Marine and Freshwater Ecosystems 18: 945- 954. Castro, P. and M.E. Huber. 2007. Marine Biology. McGraw-Hill, Boston, 459 pp. Cox, T.M., R.L. Lewison, R. Zydelis, L.B. Crowder, C. Safina, A.J. Read. 2007. Comparing effectiveness of experimental and implemented bycatch reduction measures: the ideal and the real. Conservation Biology 21: 1155-1164. Crowder, L.B., S.R. Hopkins-Murphy, J.A. Royle. 1995. Effects of turtle excluder devices (TEDs) on loggerhead sea turtle strandings with implications for conservation. Coperia 1994: 773-779. De Silva, J.A. and R.E. Condrey. 1998. Discerning patterns in patchy data: a categorical approach using gulf menhaden, Brevoortia patronus, bycatch. Fishery Bulletin 96: 193-209.
  22. 22. Department of Commerce, National Oceanic and Atmospheric Administration. Endangered and threatened wildlife; sea turtle conservation requirements. 2003. Federal Register 68: 8456-8471. Ferraro, P.J. and H. Gjertsen. 2009. A global review of incentive payments for sea turtle conservation. Chelonian Conservation and Biology 8: 48-56. Gilman, E., E. Zollett, S. Beverly, H. Nakano, K. Davis, D. Shiode, P. Dalzell and I. Kinan. 2006. Reducing sea turtle by-catch in pelagic longline fisheries. Fish and Fisheries 7: 2-23. James, M.C., K. Martin, P.H. Dutton. 2004. Hybridization between a green turtle, Chelonia mydas, and loggerhead turtle, Caretta caretta, and the first record of a green turtle in Atlantic Canada. Canadian Field-Naturalist 118: 579-582. Lewison, R.L., C.U. Soykan, J. Franklin. 2009. Mapping the bycatch seascape: multispecies and multi-scale spatial patterns of fisheries bycatch. Ecological Applications 19: 920-930. Lewison, R.L. and L.B. Crowder. 2007. Putting longline bycatch of sea turtles into perspective. Conservation Biology 21: 79-86. Lewison, R.L., L.B. Crowder, D.J. Shaver. 2003. The impact of turtle excluder devices and fisheries closures on loggerhead and Kemp’s ridley stranding in the western Gulf of Mexico. Conservation Biology 17: 1089-1097. Louisiana Department of Wildlife and Fisheries, Marine Fisheries Division. Louisiana Trawl Gear Characterization. Prepared for the National Marine Fisheries Service for its Atlantic and Gulf of Mexico state trawl fisheries gear characterization report (Federal Register 71: 65473065474), as part of The Strategy for Sea Turtle
  23. 23. conservation and recovery in relation to Atlantic and Gulf of Mexico Fisheries, 2006. Accessed 15 February 2009 http://www.nmfs.noaa.gov/pr/pdfs/strategy/la_trawl_gear.pdf. Lutz, P.L. and J.A. Musick. 1997. The Biology of Sea Turtles. CRC Press, Boca Raton, FL, 496 pp. Manjarrés, L., L.O. Duarte, J. Altamar, F. Escobar, C. García, F. Cuello. 2008. Effects of using bycatch reducation devices on the Colombian Caribbean Sea shrimp fishery. Ciencias Marinas 34: 223-238. Moore, J.E., B.P. Wallace, R.L. Lewison, R.Z. Zydelis, T.M. Cox, L.B. Crowder. 2009. A review of marine mammal, sea turtle and seabird bycatch in USA fisheries and the role of policy in shaping management. Marine Policy 33:435-451. Rester, J.K. and R.E. Condrey. 1999. Characterization and evaluation of bycatch reducation devices in the Gulf menhaden fishery. North American Jouranal of Fisheries Management 19:42-50. Smith, J.W., E.A. Hall, N.A. McNeill, W.B. O’Bier. 2002. The distribution of purse- seinne sets and catches in the Gulf menhaden fishering in the northern Gulf of Mexico, 1994-98. Gulf of Mexico Science 1: 12-24. Spotila, J.R., editor. 2004. Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation. The Johns Hopkins University Press, Baltimore, 227 pp. TEWG (2000) Assessment update for the Kemp’s ridely and loggerhead sea turtle populations in the Western North Atlantic. Turtle Expert Working Group. NOAA Technical Memorandum NMFS-SEFSC-444.
  24. 24. VanderKooy, S.J., Smith, J.W. (eds.), 2002. The menhaden fishery of the Gulf of Mexico, United Staes: a regional management plan, 2002 revision. Gulf States Marine Fisheries Commission Rep. No. 99. Vaughan, D.S., K.W. Shertzer, J.W. Smith. 2007. Gulf menhaden (Brevoortia patronus) in the U.S. Gulf of Mexico: fishery characteristics and biological reference points for management. Fisheries Research 83: 263-275. Wallace, B.P., S.S. Heppell, R.L. Lewison, S. Kelez, L.B. Crowder. 2008. Impacts of fisheries bycatch on loggerhead turtles worldwide inferred from reproductive value analyses. Journal of Applied Ecology 45: 1076-1085. Zydelis, R., B.P. Wallace, E.L. Gilman, T.B. Werner. 2009. Conservation of marine megafauna through minimization of fisheries bycatch. Conservation Biology 23: 608-616.

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