Sea Turtle Protection by Means of Coastal Engineering: Field Study on Sea turtle Behavior, Coastal Processes of a Nesting Beach

Sea Turtle Protection by Means of Coastal Engineering: Field Study on Sea turtle Behavior, Coastal Processes of a Nesting Beach and Shore Protection in Kagoshima, Japan- By Ryuichiro Nishi Dept. of Ocean Civil Engineering, Kagoshima University 1-21-40 Korimoto, Kagoshima City, Japan. 890-0065 sediment@oce.kagoshima-u.ac.jp Kazuyoshi Ohmuta Yakushima Sea Turtle Preservation Association, Kamiyakucho Kumagegun, Kagoshima Prefecture, Japan Masanori Ohtomi Graduate School of Science and Engineering Kagoshima University, 1-21-40 Korimoto Kagoshima City, Japan. 890-0065

ABSTRACT In April 2000, a new coastal regulations was issued in Japan. The regulation can be summarized as a management synthesis of shore protection, environment preservation, and accessibility by local residents. Therefore, hydraulically and mechanically placed beach nourishment to widen eroding beaches will be frequently applied to create a quasi-natural coastal environment, instead of the hard structures such as sea walls and mildly sloping revetments heretofore popular in Japan. However, beach nourishment might alter the ecological environment because of changes in porosity and compactness as compared to the original beach. In addition, a required beach width for sea turtle nesting is nearly 30 m and is roughly comparable with an average beach width in Japan. Coastal engineers and the public know that the width of the beach and number of sea turtles are decreasing in Japan. Thus, the loggerhead turtle is chosen as a representative index animal to investigate the preservation of coastal ecosystem and shore protection by beach nourishment, because the loggerhead turtle needs wide sand beach for landing, nesting, and hatching. Studies on the nesting of loggerhead turtles, coastal processes, and beach nourishment were conducted at Inakahama and Maehama Beaches on Yakushima Island, the most significant nesting area of loggerhead turtles in the Northern Pacific Ocean region. Procedures and results are summarized in this paper. Keywords: Sea turtle, loggerhead turtle, coastal process, shoreline change, shore protection, beach nourishment, environment, Japan 2

INTRODUCTION A new federal coastal law was issued in Japan in April, 2000. This coastal law promotes shore protection, preservation of environment, and accessibility to the beach as key policy, whereas the old law only concerned shore protection. The new, integrated concept is in a stage of trial and error. Regarding shore protection and the preservation of coastal environment, sea turtles become one of the key issues. Sea turtles such as shown in Fig. 1 are an endangered species and appear on the red list reported by the Japanese Ministry of Environment. For instance, the number of sea turtle landings has been decreasing in various places in Japan (e.g. Kamezaki et al. 1994; Ohmuta 1994, 1997a, 1997b, 1999). The decrease in the number of sea turtles is probably caused by two factors. The first is the loss of wide sandy beaches for which the nesting and hatching can take place. The second factor is fishing net, which entwines turtles and can kill them. Sea turtles need a wide sandy beach for nesting. Human beings also prefer wide sandy beaches. Coastal engineers have been working to protect the beach for human activity for many years, so knowledge and experience on coastal process and shore protection is applicable to preservation of turtle beaches, too. Therefore, loggerhead turtle (caretta caretta) is chosen as an index (representative) animal to apply the coastal engineering knowledge for the preservation of natural ecosystem, because the loggerhead turtle is a major species in Japan. Fig. 1 Green turtle and loggerhead 3

American coastal engineers have carried out extensive studies on compaction effect of nourished beaches on the loggerhead turtles especially in Florida, such as by Nelson et al. (1987), Steinitz et al. (1998), and Davis et al.(1999). Ito (1985) suggested the porosity of a sandy beach affect an ecosystem under the beach. However Japanese coastal engineers have little knowledge on the impact of beach nourishment as well as hard coastal structures on sea turtles. Therefore, studies of loggerhead turtle ecology (behavior), coastal processes of nesting beaches, as well as the shore protection works were conducted at Inakahama and Maehama Beaches in Yakushima Island, where the numbers of landings and nestings of loggerhead turtles are the largest in the Northern Pacific Ocean. In addition, the island was chosen as a world heritage for the 21 st century by UNESCO. STUDY AREAS The length of coastal line in Kagoshima Prefecture (see Fig. 2) is nearly 2,600 km, which is the third longest in Japan. There are 59 cities and towns along the coast of which 39 are known for loggerhead turtle landing. In fact, there are many more remote islands and towns for which no measurement and observation have been conducted; thus these locations are not included in the statistics. Turtle season is a period from May to September (nesting; May to July and hatching; July to September). From 1994 through 1998, the total numbers of loggerhead landing in Kagoshima Prefecture are 4,127 (42); 3,299 (9); 3,412 (38); 3139 (60) and 3,023 (101), with the number of green turtles (chelonia mydas) given in brackets. It is noted that the number of turtle landing corresponds to only the number of female turtles. Half the total number of turtle landing in Kagoshima Prefecture originate from Inakahama and Maehama Beaches in 4

Yakushima-Island (2076, 1721, 1920, 1486, and 1333 for the years between 1994 and 1998). Therefore, both beaches were chosen as study areas. Fig. 2 Location of Yakushima Island. 5

Inakahama and Maehama Beaches Figs. 3 and 4 are overviews of Inakahama and Maehama Beaches. Inakahama Beach is extends 975 m and opens to the northwest. Maehama Beach is located at the mouth of Nagata River and extends 1,050 m. Directions of longshore sediment transport in summer and winter seasons are to the northeast and the southwest, respectively. Typical seasonal profile changes such as erosion in summer(july to September) and accretion in winter(december to Feburary) occur. Therefore, southwest side of the beach is eroded more during the summer season, and tends to create a beach scarp. Shoreline recession on the southwest side of both beaches causes the removal of turtle eggs by wave action. In addition, beach scarps interfere with landing of loggerhead turtles on the backshore if the scarp is higher than about 0.8 to 1.0 m. Figs. 5 and 6 show beach and scarp scarps for which the turtles are able and not able to climb up, respectively. Green turtles can climb up slightly higher beach scarp than loggerhead turtles. Inakahama is a natural sandy beach except the area of a stone sea wall on the northeast side of the beach. In contrast, southern half of Maehama Beach is protected by a sea wall. A jetty is also located on its northern terminus. Part of the sand spit on north side of Maehama Beach is protected by armor blocks and artificial dune-type nourishment. Fig. 3 Aerial photograph of Inakahama Beach. (Supported by Kagoshima Prefecture Government) 6

Fig. 4 Aerial photograph of Maehama beach. Fig. 5 Passage of the landing on a beach scarp which is able to climb up. Fig. 6 Passage of the landing on a beach scarp which is not able to climb up. Beach Profile Eight representative transects were surveyed along the two beaches, as shown in Fig. 7. The datum is set to be the low tide level at the day of measurement in Figs. 8 and 9, giving the crossshore profiles at Inakahama and Maehama Beaches, respectively. Field surveys were conducted in September 1999. Therefore, these profiles show the topography created by the northern 7

longshore sediment transport and offshore sediment transport during the typhoon season(august to October). A trough geometry between offshore distances of 25 and 40 m on Transect 1 shows a meander of the small river running into the beach. Fig. 7 Study area in Yakushima Island ( right); Fig. 8 Beach profiles in Inakahama beach (1999). 8

Fig. 9 Beach profiles in Maehama beach When a loggerhead turtle encounters a river, it does a U-turn often, because the temperature of fresh water coming from the mountain is usually lower than the temperature of seawater which is normally higher than 25 deg during the turtle season. The turtle then approaches the back-beach for nesting. However, some turtles cross the river. Transect 2 is located in front of the sea wall which protects a small hotel. There is a 40-m-wide beach, which seems to be sufficient for landing and nesting of turtles, but light from the hotel is interference. A large number of the sea turtles land and nest in the area of Transect 3 where a dry beach and dune are well developed. A dry (back-) beach extends from 10 to 40m. Vegetation such as sea oats and beach grass grows in an area between 40 and 60 m where the dune slope merges to the beach. Bush and coastal forests grow just behind the vegetation area. A few turtles lay eggs in the bush 9

zone. Transect 4 shows that there is a narrow dry back-beach from 10 to 30 m, and the beach is backed by bluffs, hence not suitable for climbing by turtles. The shoreline around the Transect 4 recedes because of the northern longshore sediment transport during summer season with incident typhoons; thus beach scarps are often created. Therefore, it has been suggested that turtle eggs in this region should be transplanted to the central and north part of the beach as much as possible to prevent their washout to sea during a storm. Transect 8 was located around the middle of the spit along the Nagata River mouth in Maehama Beach. It is seen that a dry back-beach exists from 5 to 40 m, and an artificial dune is set behind it. The artificial dune is composed of material dredged from the river mouth once a year. Nagata River runs through behind the nourished section toward northern terminal beach. The beach and artificial dune appear to have sufficient width and height for nesting and hatching; however, a few typhoons have inundated the artificial dune and created an overwash fan inside the river. Transect 7 represents a cross-shore profile between the sea wall area and the sand spit area. Vegetation grows and covers the upper part of the beach in the neighboring area of sea wall. This area seems to be relatively stable, because the beach is sheltered by the sea wall against typical SSW incident waves caused by typhoons. Transects 5 and 6 are located in the sea wall area. It is seen that the width of the dry backbeach is nearly 15 to 23 m. In addition, there is a beach scarp higher than 1 m on Transect 5. The beach scarp significantly interferes with sea turtle landing. Loggerhead turtles were capable of climbing the beach scarp if the scarp height is low, and some hit the sea wall several times while looking for nesting area. These turtles laid their eggs in front of the sea wall, which were 10

then vulnerable to swash during severe wave conditions. Additional beach nourishment as a point source was made farther north of Transect 6. CHARACTER OF SEDIMENT Character of the Sediment on a Beach Sediment is supplied mainly from the abrasion of rocks around the river basin and by sea cliff erosion. The rock around the study area is granite. Fig. 10 shows the mineral content of the beach sediment. The island is isolated and raised from the sea bottom, and the ocean waves arrive directly to the beach without significant dissipation. Therefore, fine sediment is lacking on the beach. Sediment samples were taken at six locations on Inakahama Beach and at four locations on Maehama beaches, and the grain-size distributions are shown in Fig. 11. The medium grain size is in a range of 1.2 to 1.3 mm, except for samples taken at the boundary of the beach and dune. As seen in the figure, the sediments are well sorted. 100 Cumulative distribution by weight (%) 90 80 70 60 50 40 30 20 10 No.1 No.2 No.3 No.4 No.5 No.6 No.7 No.8 No.9 No.10 0 0.1 1 Grain size (mm) Fig. 10 Mineral contents of beach Fig. 11 Grain size distribution of beach sand. 11

Grain Size Distribution of Nourished Sediment Beach nourishment has been conducted at both of the beaches, as shown in Photograph 12, by using material dredged from the Nagata River mouth. The material is replaced in the backbeach of terminal areas of both beaches. The beach nourishment material is subjected to swash wave attack only during the severe storms (typhoon), because it is placed beyond the average swash wave height of ordinal waves. Therefore, the fine portion of the nourished material is dispersed to the offshore only during storms. The beach quality sand sustains in the longshore sediment transport system and contributes to the sand budget. The grain-size distributions of the nourishment sediment is shown in Fig. 13, which shows that the distributions of nourished material are wider compared to the existing beach sand, containing both finer and coarser materials. 100 Cumulative distribution by weight (%) 90 80 70 60 50 40 30 20 10 No.1' No.2' No.3' No.4' No.5' No.6' No.7' No.8' No.9' No.10' 0 0.1 1 10 Grain size (mm) Fig. 12 Point-source terminal nourishment. Fig. 13 Grain size distribution of nourished material. ECOLOGICAL STUDY OF LOGGERHEAD TURTLE Ecological studies on landing and nesting of the loggerhead turtles have been conducted at Inakahama and Maehama Beaches since 1985 and 1990, respectively. The basic statistics on the 12

landing and nesting as well as sea turtle behavior are given here, and the reader may refer the annual reports of the Yakushima Sea Turtle Preservation Association, for instance (1994, 1997, 1999) for detail. The beach access was experimentally limited to visitors at Inakahama Beach, while a group of local communities in the Maehama area conducted commercial observation tours to Maehama Beach in 1999. The number of landing and nesting decreased because of disturbance by human activity by the visitors and local guides. Thus, some of the loggerhead turtles moved to Inakahama Beach for the nesting in 1999. A detailed analysis including the passage of the loggerhead turtle on the beaches and the effect of structures is currently being conducted. Therefore, human impact on sea turtle landing and nesting in Maehama Beach can be estimated. Landing, Nesting, and Hatching Observation and measurement of the number of the landing and nesting are conducted on Inakahama and Maehama Beaches every night during turtle season. Landing, nesting and hatching of loggerhead turtles, as well as the eggs, are shown in Figs. 14 through 17. Visitors and researchers should be aware of the influence of light and sound to the landing and nesting of loggerhead turtle. Loggerhead turtles move about 20 to 30 m prior to nesting, then excavate the sand surface by digging to a depth of 0.6 to 0.8 m. A turtle lays nearly 100 to 130 eggs per nesting. The eggs are breathing under a sandy beach, so a wide dry beach is necessary to keep them under incubation until hatching. The turtle eggs incubate 45 to 75 days. Newly hatched turtles move together toward the sand surface for 7 to 10 days and pause for a while near the sand surface by night. Because baby turtles tend to be attracted by light, in a natural 13

environment they move toward the sea because the sea is often brighter than the hinterland. Artificial light from the shore can cause baby turtles to move inland, where they might be entangled by roots of vegetation and bushes, and finally dying if the inland is brighter than the sea. Fig. 14 Loggerhead turtles. Fig. 15 The passage of landing and nesting. Fig. 16 Loggerhead turtle eggs Fig. 17 Baby turtles returning to the sea. (normal and abnormal) A daytime field observation is conducted as a check of the data taken in the previous night. The number of the eggs is also measured at several nesting spots. In addition, the number of hatchlings is measured in daytime as well as occasional measurement in the night. Table 1 and 2 show the numbers of landing and nesting at Inakahama and Maehama Beaches. Numbers in 14

square brackets correspond to green turtles, and numbers in parentheses correspond to abnormal eggs. The nesting percentage is based on the total data for both of loggerhead and green turtles. The total landing and the total nesting numbers for the two beaches are 1,012 and 603, respectively in 1999. The number of landing and nesting drastically decreased by 254 and 99, respectively, compared to the data for 1998. Seventeen green turtles landed and eleven of them nested at both beaches in 1999. However, the numbers decreased by 22 and 4 compared to 1998. Five and three individual green turtles were recognized in 1998 and 1999, respectively. Table 1 Number of landings and nestings on Inakahama Beach. Month No. of landings No. of nestings No. of inspected eggs No. of turtles inspected with eggs 4 2[0] 2[0] 232 2 100.0 5 158[0] 102[0] 4430(9) 38 64.6 6 273[1] 185[1] 7318(57) 64 67.9 7 158[7] 115[5] 3716(42) 35 72.7 8 2[3] 1[3] 101 1 80.0 Total 593[11] 405[9] 15797(108) 140 68.5 Percentage of nestings Table 2 Number of landings and nestings on Maehama Beach. Month No. of landings No. of nestings No. of inspected eggs No. of turtles inspected with eggs 4 10[0] 3[0] 107 1 30.0 5 139[0] 53[0] 1745(1) 15 38.1 6 150[1] 70[0] 2459(15) 21 46.4 7 118[2] 70[0] 1211(4) 13 58.3 8 2[1] 2[0] 0 0 66.7 11 0[1] 0[1] 0 0 100.0 12 0[1] 0[1] 0 0 100.0 Total 419[6] 198[2] 5522(20) 50 47.1 Percentage of nestings Five hundred ninety three loggerhead turtles and eleven green turtles landed at Inakahama Beach. Four hundred five loggerhead turtle and nine green turtle nested in 1999. The loggerhead turtle landings increased by 14, whereas the number of green turtle landings 15

decreased by 7 at Inakahama Beach in 1999. Four hundred nineteen loggerhead turtles and six green turtles landed at the Maehama Beach, and one hundred ninety eight loggerhead turtle and two green turtle nested on the beach in 1999. The numbers of landing loggerhead and green turtles decreased by 268 and 15, respectively. The number of green turtle nesting drastically decreased at Maehama Beach in 1999. The number of landing at Maehama was usually larger than that in Inakahama Beach except for year 1990 when the observation started in Maehama Beach. However, there were 179 more landings on Inakahama Beach than at Maehama Beach in 1999. CONCLUSION Join ecological and coastal processes studies of sea turtles and their environment was made at Inakahama and Maehama Beaches. Seasonal shoreline change and generation of beach scarps, which coastal engineer can probably predict and manage, significantly influence the sea turtle landing, nesting, and hatching. Therefore, the coastal engineers can work efficiently for the protection of sea turtles. Both beaches consist of the sand originating from granite. The sediment is well sorted over the width of beaches, and the medium grain size is in the range of 1.2 to 1.3mm. The amount of fine sand was very limited. Typical seasonal shoreline and profile change was observed. Northeastern sediment transport occurs by typhoons in summer and southwestern sediment transport by winter storms. The nesting and hatching in the southwestern part of both beaches tends to be more washed away to the sea compared to the middle and northeastern part of both 16

beaches. Therefore, it is recommended to transplant the eggs in southwestern part of the beaches into the central part of the beaches as much as possible. Minimum beach width for turtle nesting is nearly 30 m, and both beaches satisfy the minimum beach width for the landing and nesting in general. In addition, the middle parts of both beaches are stable and are suitable for turtle landing and nesting. Green turtles can climb up slightly higher beach scarps (0.8 to 1.0 m) as compared to loggerhead turtles. A mildly sloping dune is necessary for hatchlings to avoid overwash by high waves, because the study beaches are open to the sea. Most of the backshore on southwest side of the beaches tended to be eroded and contained scarps during typhoons. Nourished material has been placed in the area between a dune and backshore where only storm swash waves can reach; thus the finer component of the nourished material is dispersed only during times of high waves and high tide. Thus, point source backshore nourishment has less potential to impact the ecosystem compared to nourishment material placed directly on the berm and beach face. The number of turtle nestings at Inakahama Beach was higher than at Maehama Beach where the sea wall was set and where the beach was open to the public at time during the turtle season of 1999. Even though the landing and nesting were affected by the sea wall in Maehama Beach, it was concluded that the main reason for the decrease in turtle landings and nestings was the public access and human activity on Maehama Beach. The human disturbance such as light 17

and sound by visitors must be carefully controlled in the turtle season. Thus, environmental education of local residents and visitors was a strong recommendation of this study. Research on the turtle behavior around coastal structures is continuing. Results will be presented in subsequent papers. ACKNOWLEDGEMENTS Special acknowledgement goes to the members of Yakushima Sea Turtle Preservation Association for their efforts in supporting high-quality measurements. The authors would like to express thanks to Dr. Nicholas C. Kraus for proofreading this manuscript and to Mr. Terazono and Mr. Yoshimizu for providing the Fig. 2. REFERENCES Davis, R. A., Jr., FitzGerald, M. V., and Terry, J. 1999. Turtle nesting on adjacent nourished beaches with different construction styles: Pinellas County, Florida, Journal of Coastal Research, 15(1), 111-120. Kamezaki, N. 1994. Is the number od sea turtles decreasing?, In Sea Turtle Protection and It s Future, Edited by The Japanese Sea Turtle Association, 28-75. Ito, T. 1985. Ecosystem under the sandy beach -Introduction of the ecosystem in porous sand. Kaimei L.T.D, 241 pp (in Japanese). 18

Nelson, D. A., Mauck, K., and Fletemeyer, J. 1987. Physical effects of beach nourishment on sea turtle nesting, Delray Beach, Florida, Technical report EL-87-15, US Army Corps of Engineers, 56 pp. Ohmuta, K. 1994. Annual report of sea turtles in Yakushima Island. Yakushima Sea Turtle Association, 24 pp (in Japanese). Ohmuta, K. 1997a. Annual report of sea turtles in Yakushima Island, Yakushima Sea Turtle Association, 32 pp (in Japanese). Ohmuta, K. 1997b. Passage of sea turtle, Institute of Ocean Engineering L.T.D, 237 pp (in Japanese). Ohmuta, K. 1999. Annual report of sea turtles in Yakushima Island, Yakushima Sea Turtle Association, 40 pp (in Japanese). Steinitz, M. J., Salmon, M., and Wyneken, J. 1998. Beach renourishment and loggerhead turtle reproduction: A seven year study at Jupiter Island, Florida. Journal of Coastal Research, 14(3), 1,000-1,013. 19

List of tables Table 1 Number of landing and nesting in Inakahama beach. Table 2 Number of landing and nesting in Maehama beach. List of figures Fig. 1 Green turtle and loggerhead turtle. Fig. 2 Location of Yakushima Island. Fig. 3 Aerial photograph of Inakahama Beach. (Supported by Kagoshima Prefecture Government) Fig. 4 Aerial photograph of Maehama beach. Fig. 5 Passage of the landing on a beach scarp which is able to climb up. Fig. 6 Passage of the landing on a beach scarp which is not able to climb up. Fig. 7 Study area in Yakushima Island ( right; Inakahama beach, Left; Maehama beach). Fig. 8 Beach profiles in Inakahama beach (1999). Fig. 9 Beach profiles in Maehama beach (1999). Fig. 10 Mineral contents of beach sand. Fig. 11 Grain size distribution of beach sand. Fig. 12 Point-source terminal nourishment Fig. 13 Grain size distribution of nourished material. Fig. 14 Loggerhead turtles Fig. 15 The passage of landing and nesting. Fig. 16 Loggerhead turtle eggs (normal and abnormal) Fig. 17 Baby turtles returning to the sea 20