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6 Sea Turtle Mortality Associated wig Human Activities ea turtles on nesting beaches are most susceptible to mortality asso- ciated with human activities at the egg, hatchling, and nesting female stages and in coastal waters at the subadult (including juve- nile) and adult stages. They are vulnerable to diverse potentially lethal interactions with human activities, situations including direct predation and habitat modification, incidental capture or entanglement in fishing gear, and physical damage caused by dredging of shipping chan- nels, collisions with ships and boats, and oil-rig removal or other under- water explosions. Each species in the pelagic environment is vulnerable to ingestion of plastics, debris, and petroleum residues. The species differ in behavior and habitat requirements, so they can be affected differently by various human activities. The recognized sources of mortality related to human activities are list- ed in order of estimated importance in Table 6-1 for all life stages, and order-of-magnitude mortality estimates are presented in Table 6-2 for juvenile plus adult loggerheads and Kemp's ridleys. The latter table includes the committee's judgment of the certainty of the information on which the estimates were based and lists the preventive and mitigative measures that are in place or being developed. The preventive and mit- igative measures are described and evaluated in detail in Chapter 7. The present chapter discusses the information on each mortality factor associ 74

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75 Sea Turtle Mortality Associated with Human Activities TABLE 6-1 A qualitative ranking of the relative importance of various mortality factors on juveniles or adults, eggs, and hatchlings with an indication of mortality caused primarily by human activities. Sources are listed in order of importance to juveniles or adults, because this group includes the life stages with greatest reproductive values. Life Stage Primarily Human Juveniles Source of Mortality Caused to Adults Eggs Hatchlings Shrimp trawling yes high none unimportant Other fisheries yes medium to low none unimportant Non-human predators no low high high Weather no low medium low Beach development yes low medium low Disease no low unimportant low Dredging yes low unimportant unimportant Entanglement yes low unimportant low Oil-platform removal yes low none unimportant Collisions with boats yes low none unimportant Directed take yes low medium unimportant Power plant entrainment yes low none unimportant Recreational fishing yes low none unimportant Beach vehicles yes low to unimportant medium unimportant Beach lighting yes low to unimportant unimportant medium Beach replenishment yes unimportant low low Toxins yes unknown unknown unknown Ingestion of plastics, yes unknown none unknown debris ated with human activities first for eggs and hatchlings and then for juve- niles through adults. The analyses in Chapter 5 on the reproductive value of various life stages called attention to the mortality factors that are most important for juveniles and adults in the ocean and inshore marine habitats. The most important identifiable source of mortality for loggerhead and Kemp's rid- leys is incidental capture in shrimp trawls (Table 6-21; other fisheries and fishery-related activities are also important, but collectively only one-tenth as important as shrimp trawling. Dredging, collisions with boats, and oil- rig removal are also important, but only one-hundredth as important as shrimp trawling. Mortality from entrainment in power plants and directed capture of juveniles and adults is believed to be generally low. Parasites,

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77 Sea Turtle Mortality Associated with Human Activities toxins, and ingestion of plastics and other debris also constitute prob- lems, but present information does not allow quantitative estimates of annual mortality related to them. MORTALITY OF SEA TURTLE EGGS AND HATCHLINGS Beach Erosion and Accrelion Erosion of nesting beaches can result in loss of suitable nesting habi- tat. Erosion rates are influenced by dynamic coastal processes, including sea-level rise. Human interference with natural processes through coastal development and associated activities has resulted in accelerated erosion rates in some localities and interruption of natural shoreline migration. Accretion (deposition of beach sediments) also kills eggs in a nest. Beach Armoring Where beach-front development occurs, a site is often fortified to pro- tect the property from erosion. Shoreline engineering is expensive and is virtually always carried out to save structures, not sandy beaches; it usu- ally accelerates beach erosion (NRC, 19871. Several types of shoreline engineering, collectively referred to as beach armoring, include sea walls, rock revetments, riprap, sandbag installations, groins, and jetties. Those structures can cause severe adverse effects on nesting turtles and their eggs. Beach armoring can result in permanent loss of a dry nesting beach through accelerated erosion and prevention of natural beach and dune accretion, and it can prevent or deter nesting females from reaching suitable nesting sites. Clutches deposited seaward of the structures can be inundated at high tide or washed out by increased wave action near the base of them. As the structures fail and break apart, they spread debris on the beach, which can further impede access to suitable nesting sites and result in a higher incidence of false crawls (non-nesting emergences of females) and trapping of hatchlings and nesting turtles. Sandbags are particularly susceptible to rapid failure, which results in extensive debris on nesting beaches. Rock revetments, riprap, and sandbags can cause nesting turtles to abandon nesting attempts or to construct egg cavities of improper size and shape. Groins are designed to trap sand during transport in longshore cur- rents, and jetties might keep sand from flowing into channels. Those structures prevent normal sand transport and accrete beaches on one side of the structure while starving opposite beaches, thereby causing severe

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78 Decline of the Sea Turtles erosion (NRC, 1987) and corresponding degradation of nesting habitat. Even widely spaced groins can deter nesting. Drift fences, also commonly called sand fences, are erected to build and stabilize dunes by trapping sand that moves along the beach and pre- venting excessive sand loss. They also protect dune systems by deterring public access. Because of their construction, improperly placed drift fences can impede nesting and trap emergent hatchlings. Beach Nourishment Beach nourishment consists of pumping, trucking, or otherwise depositing sand on the beach to replace what has been lost to erosion. Beach nourishment can disturb nesting turtles and even bury turtle nests during the nesting season. The sand brought in might differ from native beach sediments and can affect nest-site selection, digging behavior, incu- bation temperature (and hence sex ratios), gas-exchange characteristics in incubating nests, moisture content of a nest, hatching success, and hatch- ling emergence success (Mann, 1977; Ackerman, 1980; Mortimer, 1982b; Raymond, 1984; Nelson, 19861. Beach nourishment can result in severe compaction or concretion of the beach. The trucking of sand to protect beaches can itself increase compaction. Significant reductions in nesting success on severely compacted beach- es have been documented (Raymond, 19841. Nelson and Dickerson (1989a) evaluated compaction on 10 nourished east coast Florida beaches and concluded that five were so compacted that nest digging was inhibit- ed and another three might have been too compacted for optimal dig- ging. They further concluded that, in general, beaches nourished from off- shore borrow sites are harder than natural beaches and that, although some might soften over time through erosion and accretion of sand, oth- ers can remain hard for 10 years or more. Nourished beaches develop steep escarpments in the midbeach zone that can hamper or prevent access to nesting sites. Nourishment projects involve use of heavy machinery, pipelines, increased human activity, and artificial lighting. They are normally conducted 24 hours a day and can adversely affect nesting and hatching activities. Pipelines and heavy machinery can create barriers to nesting females emerging from the surf and crawling up the beach, and so increase the incidence of false crawls. Increased human activity on a project beach at night might cause further disturbance to nesting females. Artificial lights along a project beach and in the nearshore area of the borrow site might deter nesting females and disori- ent emergent hatchlings on adjacent nonproject beaches.

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79 Sea Turtle Mortality Associated with Human Activities Artificial Lighting Extensive research has demonstrated that emergent hatchlings' princi- pal cues for finding the sea are visual responses to light (Daniel and Smith, 1947; Hendrickson, 1958; Carr and Ogren, 1960; Ehrenfeld and Carr, 1967; Dickerson and Nelson, 19891. Artificial beachfront light from buildings, streetlights, dune crossovers, vehicles, and other sources has been documented in the disorientation of hatchling turtles (McFarlane, 1963; Philibosian, 1976; Mann, 1977; Fletemeyer, 1980; Ehrhart, 19839. The results of disorientation are often fatal. As hatchlings head toward lights or meander along the beach, their exposure to predators and likeli- hood of desiccation are greatly increased. Disoriented hatchlings can become entrapped in vegetation or debris, and many hatchlings have been found dead on nearby roadways and in parking lots after being struck by vehicles. Hatchlings that find the water might be disoriented after entering the surf zone or while in nearshore water. Intense artificial light can even draw hatchlings back out of the surf (Carr and Ogren, 1960; pers. comm., L. Ehrhart, University of Central Florida, 1989~. In 1988, 10,155 disoriented hatchlings were reported to the Florida Depart- ment of Natural Resources. The problem of artificial beachfront lighting is not restricted to hatch- lings. Carrel al. (1978), Ehrhart(1979), Mortimer(1982b), andWithering- ton (1986) found that adult green turtles avoided bright areas on nesting beaches. Raymond (1984) indicated that adult loggerhead emergence pat- terns were correlated with variations in beachfront light in southern Bre- vard County, Florida, and that nesting females avoided areas where beachfront light was most intense. Witherington (1986) noted that logger- heads aborted nesting attempts at a greater frequency in lighted areas. Problem lights might not be restricted to those placed directly on or near nesting beaches. The background glow associated with intensive inland light, such as that emanating from nearby large metropolitan areas, can deter nesting females and disorient hatchlings that are navigating the nearshore waters. Cumulatively, along the heavily developed beaches of the southeastern United States, the negative effects of artificial light are profound. Beach Cleaning Several methods are used to remove human-caused and natural debris from beaches, including mechanical raking, hand raking, and hand pick- ing of debris. In mechanical raking, heavy machinery can repeatedly tra

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80 Decline of the Sea Turtles verse nests and potentially compact the sand above them; it also results in tire ruts along the beach that might hinder or trap emergent hatchlings (Hosier et al., 19811. Mann (1978) suggested that mortality within nests can increase when beach-cleaning machinery exerts pressure on soft beaches with large-grain sand. Mechanically pulled rakes and hand rakes can penetrate the surface and disturb a sealed nest or might even uncover pre-emergent hatchlings near the surface of the nest. In some areas, col- lected debris is buried on the beach; this can lead to excavation and destruction of incubating egg clutches. Disposal of debris near the dune line or on the high beach can cover incubating egg clutches, hinder and entrap emergent hatchlings, and alter nest temperatures. Mechanical beach cleaning is sometimes the sole reason for extensive nest relocation. Increased Human Presence Resident and tourist use of developed (and developing) nesting beach- es can adversely affect nesting turtles, incubating egg clutches, and hatch- lings. The most serious threat caused by increased human presence on the beach is the disturbance of nesting females. Nighttime human activity can cause nesting females to abort nesting attempts at all stages of the process. Murphy (1985) reported that beach disturbance can cause turtles to shift their nesting beaches, delay egg-laying, and select poor nesting sites. Davis and Whiting (1977) reported significantly higher rates of false crawls on nights when tagging patrols were active on an otherwise remote, undeveloped nesting beach. Nesting beaches heavily used by pedestrians might have low rates of hatchling emergence, because of compaction of the sand above nests (Mann, 1977), and pedestrian tracks can interfere with the ability of hatchling loggerheads to reach the ocean (Hosier et al., 19811. Campfires and the use of flashlights on nesting beaches disorient hatchlings and can deter nesting females (Mortimer, 19893. Recreational Beach Equipment Recreational material on nesting beaches (e.g., lounge chairs, cabanas, umbrellas, boats, and beach cycles) can deter nesting attempts and inter- fere with incubating egg clutches and the seaward journey of hatchlings. The documentation of false crawls near such obstacles is increasingly common as more recreational equipment is left in place all night on nest- ing beaches. There are also reports of nesting females that become entrapped under heavy wooden lounge chairs and cabanas on southern

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81 Sea Turtle Mortality Associated with Human Activities Florida nesting beaches (pers. comm., S. Bass, Gumbo Limbo Nature Cen- ter, 1989; pers. comm., J. Hoover, Dade County Beach Department, 1989~. Recreational beach equipment placed directly above incubating egg clutches can hamper emergent hatchlings and can destroy eggs by pene- tration directly into a nest (pers. comm., C. LeBuff, Caretta Research, Inc., 19891. Beach Vehicles The operation of motor vehicles on turtle nesting beaches is still per- mitted in many areas of Gulf of Mexico and Atlantic states (e.g., Florida, North Carolina, and Texas). Some areas restrict night driving, and others permit it. Driving on beaches at night during the nesting season can dis- rupt the nesting process and result in aborted nesting attempts. The adverse effect on nesting females in the surf zone can be particularly severe. Headlights can disorient emergent hatchlings and vehicles can strike and kill hatchlings attempting to reach the ocean. The tracks and ruts left by vehicles traversing the beach interfere with the ability of hatchlings to reach the ocean. The time spent in traversing tire tracks and ruts can increase the susceptibility of hatchlings to stress and predation during transit to the ocean (Hosier et al., 19811. Driving directly above incubating egg clutches compacts the sand and can decrease hatching success or kill pre-emergent hatchlings (Mann, 19771. In many areas, beach-vehicle driving is the only reason nests have to be relocated. Vehicular traffic on nesting beaches also contributes to erosion, especially during high tides or on narrow beaches, where driving is concentrated on the high beach and foredune. Exotic Dune and Beach Vegetafion Non-native vegetation has been intentionally planted in or has invaded many coastal areas and often displaces native species, such as sea oats, beach morning glory, railroad vine, sea grape, dune panic grass, and pen- nywort. The invasion of such destabilizing vegetation can lead to increased erosion and degradation of suitable nesting habitat. Exotic veg- etation can also form impenetrable root mats, which can prevent proper nest-cavity excavation, and roots can penetrate eggs, cause eggs to desic- cate, or trap hatchlings. The Australian pine (Casuarina equisetifolia) is particularly detrimen- tal. Dense stands of that species have taken over many coastal strand areas throughout central and southern Florida, causing excessive shading

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82 Decline of the Sea Turtles of the beach. Studies in southwestern Florida suggest that nests laid in the shaded areas are subjected to lower incubation temperatures, which can alter the natural hatchling sex ratio (Marcus and Maley, 1987; Schmelz and Mezich, 19881. Fallen Australian pines limit access to suitable nest sites and can entrap nesting females. Davis and Whiting (1977) reported that nesting activity declined in Everglades National Park where dense stands of Australian pine took over native beach vegetation. Schmelz and Mezich (1988) indicated that dense stands of Australian pines in south- western Florida affect nest-site selection and cause increased nesting in the middle beach area and higher ratios of false crawls to nests compared with areas of native vegetation. MORTALllY OF SEA TURTLE JUVENILES AND ADULTS Shrimp Fishing Description of the Fishery The shrimp fishery has the highest product value of any fishery in the United States. It also is the most important human-associated source of deaths of adult and subadult sea turtles. Sea turtles are captured in shrimp trawls towed along the bottom behind shrimping vessels. The vessels might tow one to four otter trawls. An otter trawl consists of a heavy mesh bag with tapered wings on each side that funnel shrimp into the cod end, or bag, of the net. To keep the trawl near the bottom and achieve horizonal opening of the mouth of the trawl, a weighted otter board is positioned at the front of each wing to serve as a hydrofoil. Tur- tles swimming, resting, or feeding on or near the bottom in the path of a trawl are overtaken and enter the trawl with the shrimp. What is often perceived as the U.S. shrimp fishery is actually a number of fisheries. Seven species of shrimp are harvested in the fishery: brown shrimp (Penaeus aztecus), white shrimp (P. setiferus), pink shrimp (P. duorarum), seabobs (Xiphopenaeus kroyeri), royal red shrimp (Hymen openaeus rousts, rock shrimp (Sicyonia brevirostr~s), and trachs (Tra- chypenaeus spy. Each shrimp species is taken by a distinct fishery, and the several fisheries are differentiated according to fishing depths, season- al landings, vessel and gear, fishing localities, fishing techniques, and other characteristics. The most valuable shrimp species in the United States are brown, white, and pink. For example, in 1985, U.S. commercial shrimp catches were 122,000 metric tons in the gulf and 13,000 metric tons in the south Atlantic. The white shrimp fishery is the most important in the U.S. south Atlantic; the brown shrimp fishery is more important in the gulf.

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83 Sea Turtle Mortality Associated with Human Activities Brown shrimp range along the north Atlantic and Gulf of Mexico coasts from Martha's Vineyard, Massachusetts, to the northwestern coast of Yucatan. The range is not continuous, but is marked by an apparent absence of brown shrimp along Florida's west coast between the Sanibel and the Apalachicola shrimping grounds (Farfante, 19691. In the U.S. Gulf of Mexico, catches are highest along the coasts of Texas, Louisiana, and Mississippi. Brown shrimp can be caught at depths of 100 m or more, but most come from depths less than 50 m. The season begins in May, peaks in June and July, and declines to an April low (Gulf of Mexico Fishery Management Council, 19811. White shrimp range along the Atlantic coast from Fire Island, New York, to Saint Lucie Inlet, Florida, and along the gulf coast from the mouth of the Ochlockonee River, in the Florida panhandle, to Campeche, Mexico. In the gulf, there are two centers of abundance: one along the Louisiana coast and one in the Campeche area. White shrimp are com- paratively shallow-water shrimp; most of the catch comes from depths less than 25 m. The catch has a major peak in late summer and early fall, with an October high and a minor peak of over-winter shrimp with a peak in May. The largest catches occur west of the Mississippi River to the Freeport, Texas, area, although the catch is considerable along the entire north central and western gulf and south Atlantic. Pink shrimp range along the Atlantic from the lower Chesapeake Bay to the Florida Keys and around the gulf coast to the Yucatan peninsula. Major concen- trations exist off southwestern Florida and in the southeastern part of the Gulf of Campeche. The two major pink shrimp grounds in the United States are the Tortugas and Sanibel grounds in southwestern Florida. The pink shrimp catch comes mainly from depths less than 50 m, with a maxi- mal catch from 20-25 m. Most of the catch is taken off Florida and is greatest in the southwestern waters of the state. The catch is high from October through May. In the south Atlantic, white shrimp account for the majority of landings in Georgia and the Atlantic coast of Florida. In South Carolina, small landings of white shrimp in the spring are augmented by a much larger catch in the fall. The spring white shrimp fishery is based on adults that have over-wintered, whereas the fall catch is based almost entirely on young of the year. White shrimp are caught in North Carolina principally during the fall, but the catch is much smaller than that of brown and pink shrimp (Carder et al., 19741. Brown shrimp predominate in the North Carolina fishery. During some years, catches of brown shrimp exceed those of white shrimp in South Carolina as well. The peak of the brown shrimp harvest occurs during the summer in all four south Atlantic states. Brown shrimp enter and leave the Florida east coast fishery earlier than in the other three states. In the south Atlantic, pink shrimp are of major

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84 Decline of the Sea Turtles commercial significance only in North Carolina, where they account for about one fourth of the total shrimp landings. Fishing for pink shrimp usually begins in the spring and ends by midsummer. Other minor shrimp species are often fished incidentally or during the offseasons of the major shrimp fisheries. A targeted rock shrimp fishery exists in the south Atlantic off northern Florida from August to January. In recent years, vessels in the western gulf have focused their effort on "tracks" during the late winter and spring months. The trach catch is pri- marily from depths of 20-50 m. The royal red shrimp fishery is relatively insignificant, occurring at depths of 250-550 m; harvesting and marketing obstructions have limited this fishery. Seabobs are caught most often in shallow waters at 13 m or less and in the open ocean; along the Louisiana coast, catch rates are highest in October-December. The various fisheries share some similarities, in socioeconomic makeup and biology, but there are important contrasts, principally in depth of operation. The similarities and differences might have an important bear- ing on turtle bycatch. Many of the fisheries for shrimp, especially of the three major species, are timed and located in relation to the life histories of the shrimp. For example, several discrete fisheries constitute the "gulf brown shrimp fishery." Juvenile and subadult brown shrimp live in bays and estuaries and are harvested by the inshore fishery. The shrimping vessels used are usually small, from 6 to 30 m long; most are about 15 m long. As the shrimp mature, they migrate offshore. Vessels fish near shore out to a depth of 25 m, especially for subadult and adult white and pink shrimp. The larger vessels of the gulf type begin almost exclusive harvest of the species (adult brown and pink shrimp) in water deeper than 25 m; these vessels are generally 20-30 m long. As the maturing brown shrimp continue to migrate into the deeper gulf waters, the smaller inshore ves- sels are limited, and only the larger vessels can gain access to the fishery. The offshore fishery provides the basis for the adult brown shrimp fish- ery. The pink shrimp fleet off Florida uses a variety of vessels of different sizes but is associated primarily with larger offshore boats. White and brown shrimp are caught in bays and estuaries in some states by the smaller inshore vessels. Unlike the adult brown shrimp fleet, which uses larger vessels, the adult white shrimp fleet uses vessels of all sizes. Distribution and Intensity of the Fishery The distribution and intensity of fishing in inside waters were calculat- ed from raw data and summaries provided to the committee by NMFS. For waters outside the coast, the information was taken from Appendix F.

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107 Sea Turtle Mortality Associated with Human Activities leys, and the others were loggerheads, hawksbills, green turtles, and leatherbacks. The turtles were entangled in fishing line and hooks, shrimp trawls, onion sack, net and rope, tar, crab trap, and trot line. The study concluded that the pronan~ty that a sea turtle in Texas coastal waters would come into contact with marine debris is high, and that com- mercial and recreational fishermen and their discarded gear were respon- sible for most of entanglements (Plotkin and Amos, 1988; Ross et al., 19891. Balazs (1985) reported five entangled turtles in Texas in 1977-1983, including one live green turtle, three live hawksbills, and one dead hawksbill. Four of the entanglements involved monofilament fishing line, the other a piece of plastic onion bag. Amos (1989) reported that, in 77 recorded strandings of hawksbills in Texas since 1972, the incidence of entanglement in plastic was high 22% of those in which such informa- tion was recorded. The most common form of entanglement occurred when turtles' necks or limbs were caught in woven plastic produce sacks. Monofilament fishing line wrapped around limbs has also been recorded. No entanglements of recent posthatchlings have been noted, only entan- glements of yearlings. An anecdote from Paul Raymond of the NMFS Law Enforcement Divi- sion provides a dramatic example of the problem. An abandoned pom- pano trammel net (three panels) of monofilament was seized on October 16, 1989, off the beach (near shore) near Wabasso, Florida (Indian River County). It had been set 6 days before and left unchecked. In it were 10 juvenile green turtles and one juvenile loggerhead, all entangled and drowned. Pompano trammel nets are tethered in very shallow water near shore by fishermen in small boats. The industry is not well organized or documented as to size, season, or distribution. Nets set inshore (behind the coastal regulation lines) must be attended, but that is not required by Florida for nets outside the line. The net in question here had been aban- doned. An unattended but not abandoned net can also kill turtles. Dredging Dredging of harbors and entrance channels can kill sea turtles (Hop- kins and Richardson, 19843. A comprehensive survey of records and pro- ject reports recognized 149 confirmed incidents of sea turtles entrained by hopper dredges working in two shipping channels from 180 to 1990 (Table 6-6) (pers. comm., J.I. Richardson, University of Georgia, April 19901. Only verifiable records of fresh kills or live turtles were included in this table, explaining the slight difference in total counts between this survey and other reports (Rudloe, 1981; Joyce, 19821. Three species of sea

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108 Decline of the Sea Turtles TABLE 6-6 Reported sea turtle incidents by species during dredging activities from 1980 to 1990. Site Year Loggerhead Green Turtle Unidentified Total Cape Canaveral 1980 50 3 1871 Entrance Channel 1981 1 1 13 1984-85 3 0 69 1986 5 0 05 1988 8 2 1828 1989-90 0 6 17 Totals 67 12 44123 King's Bay 1987-88t 7 1 19 Entrance Channel, 1988 3 0 27f Georgia and Florida 1989 9 0 110 Totals 19 1 26 Fragments of sea turtle carcasses not identified to species. It is assumed that most are log- gerheads. tInitia1 construction dredging for Trident submarine base. fTwo Kemp's ridleys caught in 1988 at Kings's Bay, Georgia. Source: Richardson, 1990. turtles were taken, including two individuals of the endangered Kemp's ridley. Although some entrained specimens were identified, it is estimat- ed that 90% or more of the incidents involved the loggerhead. Nearly all sea turtles entrained by hopper dredges are dead or dying when found, but an occasional small green turtle has been known to survive. Entrapment and death of turtles by hopper dredges first became an issue of concern at the Port Canaveral Entrance Channel, Florida, in 1980 after unusually high concentrations of loggerheads were noted in the area (Carr et al., 19819. Seventy-seven loggerheads were reported killed in 1980 dur- ing the removal of 2.5 million cubic yards (1.9 x 106 m3) of sediment from the channel (Rudloe, 1981;.Toyce, 19821. The rate of turtle take varied among dredges, ranging from 0.038 turtle entrained per hour (dredge McFarland) to 0.121 turtle entrained per hour (dredge Long Island) Joyce, 1982~. The very high number of turtles taken was not repeated in subse- quent years for several reasons. First, the Long Island, because it seemed to pose the greatest threat, was transferred immediately to other areas. Sec- ond, a program of gear modification to the drag heads was initiated at that time. Finally, the loggerheads did not seem to use the Canaveral Channel in the same numbers in later years. By 1989, the rate of sea turtle capture in surveys in the channel were about one-tenth the rates recorded in 1978- 1983 (pers. comm., A. Bolten, University of Florida, 19891.

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109 Sea Turtle Mortality Associated with Human Activities Although the most serious loss of turtles in hopper dredges occurs within the Port Canaveral Entrance Channel, smaller numbers have been taken at King's Bay Entrance Channel. Twelve turtles (10 juvenile logger- heads, one adult loggerhead, one juvenile green turtle) were taken dur- ing some 20,000 hours of construction dredging (Slay and Richardson, 19881. The rate of capture was less than 0.001 turtle per dredge hour. The loss of turtles to hopper dredges in other entrance channels is not yet known, but other entrance channels from North Carolina to Florida will be surveyed by NMFS to assess any potential effects on sea turtles (pers. comm., J. Richardson, University of Georgia, 19901. Data are being gathered through additional observer programs to answer the question, and the numbers of sea turtles taken are expected to be considerably smaller than observed at Port Canaveral. The data are not available, but it would not be unusual for 1,000 hours of maintenance dredging to be needed per channel per year. Collisions with Bools Another source of mortality to sea turtles associated with human activi- ty is collision with vessels. The regions of greatest concern are those with high concentrations of recreational-boat traffic, such as the south- eastern Florida coast, the Florida Keys, and the many shallow coastal bays in the Gulf of Mexico. Of the turtles stranded on the gulf and Atlantic coasts of the United States, 6% of 1,847 strandings in 1986, 7% of 2,373 in 1987, and 9% of 1,991 in 1988 had boat-related injuries for an average of about 150 turtles per year (Schroeder, 1987; Schroeder and Warner, 1988; Teas and Martinez, 19899. In most cases, it was not possi- ble to determine whether the injuries resulted in death or were post . . . mortem injuries. In the Chesapeake Bay region, boat-propeller wounds accounted for approximately 7% of the deaths of sea turtles stranded in 1979-1988 whose causes were determinable (Barnard et al., 1989), or about five to seven turtles per year. If we assume that half the boat-collision injuries documented by the STSSN were the primary causes of death of the stranded sea turtles in 1986-1988, and only about 20% of the dead turtles wash ashore, about 400 turtles are killed by boat collisions each year along the gulf and Atlantic coasts of the United States outside of coastal beaches. That esti- mate might be low, because the strandings include only the ocean beach- es (boat collisions with turtles also occur in inside waters), and an animal with an open wound has an increased probability of predation and thus a further reduction in probability of stranding. The estimate might be

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110 Decline of the Sea Turtles high, because more than half of the turtles might have been hit when they were already dead from other causes and were floating. Petroleum-Platform Removal The use of explosives in removal of petroleum structures became con- troversial with respect to turtle mortality in 1986. From March 19 to April 19, 1986, 51 turtles, primarily Kemp's ridleys, were found dead on beach- es of the upper Texas coast. Ten petroleum structures in the nearshore area of the strandings had been removed with explosives during the peri- od. Shrimping was at a seasonal low, and circumstantial evidence suggest- ed that at least some of the strandings were due to underwater explosions used in removal of the structures (Klima et al., 19881. Further evidence of the serious effects of the explosions included the stranding of 41 bot- tlenose dolphins (Tursiops truncatus) and large numbers of dead fish (Klima et al., 19881. After those incidents, attention focused on the possible effects of petroleum-platform removal. In July 1986, 11 sightings of at least three turtles (two loggerheads and one green turtle) occurred during the removal of a platform 30 miles south of Sabine Pass, Texas. What appeared to be a dead or injured turtle drifting with the current 10 feet below the surface was reported 1.5 hours after detonation of explosives (Gitschlag, 19891. Six sightings of loggerheads were reported at five other removal sites, and a green turtle was observed at another location. Those sightings and strandings resulted in a consultation under Section 7 of the Endangered Species Act of 1973 between NMFS and the Minerals Manage- ment Service (MMS). Oil and gas companies wishing to use underwater explosives were thereafter required to submit permit requests to MMS. Obtaining a permit requires use of qualified observers to monitor sea tur- tles near platforms and in some cases to remove turtles to a safe location away from the potential impact of explosive charges. Data collected by NMFS since 1986 support an association between tur- tles and some offshore platforms. Divers have reported that turtles com- monly associate with offshore structures (Rosman et al., 19879. Gitschlag (1989) reported that 36 turtle sightings near platforms scheduled to be removed were made during 1987-1988 by the NMFS observer program. Another 30 turtles were observed during that period at structures not scheduled for removal (personal communication, G. Gitschlag, NMFS, 19893. A recent NMFS observer effort indicated that turtle concentrations near a petroleum platform could be large. Twelve turtles were collected and removed from one structure off Texas in September 1989 (pers. comm., G. Gitschlag, NMFS, 19891.

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111 Sea Turtle Mortality Associated with Human Activities Additional reports confirm the association of turtles with offshore plat- forms. Lohoefener (1988) used aerial surveys and found hard-shelled sea turtles (cheloniids) to be associated with platforms offshore of the Chan- deleur Islands (Louisiana), although their study did not indicate an associ- ation of sea turtles with platforms in the western Gulf of Mexico. They determined the daytime probability of one or more cheloniids near a platform off the Chandeleur Islands to be about 0.27 within 500 m of the structure, 0.50 within 1,000 m, and 0.65 within 1,500 m. West of the Mis- sissippi River, the probability of one or more cheloniids within 500 m of a randomly selected platform would be about 0.04, within 1,000 m about 0.08, and within 1,500 m about 0.13. Only larger turtles and only turtles on or near the surface are usually seen by aerial surveys, so the figures given should be considered low. Although information on association of sea turtles with energy plat- forms is sparse, the potential for mortality must be considered genuine. It is difficult to document a cause-effect relation between turtle deaths and offshore explosions, because no dead animals have been recovered at removal sites and freshly killed turtles sink and might drift a long way by the time putrefaction causes them to float. Association of turtles with the structures is not random; platforms apparently provide a resting place or a location where food is readily available (Klima et al., 19881. From March 1987 through 1988, 69 platforms and 39 caissons or other single- pile structures were removed in gulf waters of Louisiana and Texas. MMS estimated that there were 3,434 platforms in the federal outer continental shelf as of December 1986 and predicted that 60-120 structures would be removed each year for the next 5 years (MMS, 19881. Continuing research should identify more specifically the negative effects of explo- sive removal of offshore structures. Safeguards for protection of turtles near structures scheduled for removal are essential. To estimate the numbers of sea turtles that might be killed or injured by explosions in the future, we assumed that the injury and mortality zone will extend no farther than 1,000 m from the structure being removed (Klima et al., 19884. For the Chandeleur Islands area, where the highest densities were seen, Lohoefener et al. (1988) used aerial surveys and estimated a 0.5 probability that a turtle would be visible within 1,000 m of a given structure during the day. If about 100 platforms in gulf waters of Louisiana and Texas will be removed each year over the next 10 years, a total of 8-50 turtles each year could be killed or injured with- out protective intervention. That estimate is biased downward for two reasons: first, an aerial survey samples only during the day, when turtles are known to forge away from resting sites. Second, turbidity in the Gulf of Mexico may reduce visibility from the air, especially west of the Missis- sippi. Yet, Klima et al. (1988) estimated higher densities of turtles in this

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112 Decline of the Sea Turtles region during the observer programs. If only half of the turtles are seen during aerial surveys, the estimate could reach as high as 100 turtles pos- sibly affected each year over the 10-year period. Other uses of explosives also might have an effect. Petroleum seismo- graphic exploration ana m1lllary maneuvers can urn =~plO~lV=~. Their impact on turtle mortality has not been measured, but it might exist. In contrast, turtles nesting in areas adjacent to military bombing activities (e.g., on eastern Vieques Island, Puerto Rico) might actually benefit, because the control of human access and the danger of unexploded rounds greatly reduce the presence of egg poachers (pers. comm., P. Pritchard, Florida Audubon Society, October 19891. ~ . . . . . . - . ~ 1 ~ in: .. ~ ~ Entrainment of Sea Turtles in Power-Plan' Intake Pipes Sea turtles can become entrained in intake pipes for cooling Upstater at coastal power plants. The best-documented case is that of St. Lucie unit 2 in southeastern Florida. At that facility, nets are constantly set and moni- tored in the intake canal to remove sea turtles. In 1976-1988, 122 (7.5%) of the 1,631 loggerheads and 18 (6.7%) of the 269 green turtles entrapped in the canal were found dead, for an average of about 11 turtles per year (Applied Biology Inc., 1989a). Four Kemp's ridleys were found dead dur- ing the same period. No dead leatherback or hawksbill has been found there (Applied Biology Inc., 1989a). Deaths resulted from injuries sus- tained in transit through the intake pipe, from drowning in the capture ~ cat nets, and perhaps from causes before entrainment. At four other power plants in Florida (Port Everglades, Turkey Point, Cape Canaveral, and Riviera Beach), 21 turtles (loggerheads, green turtles, and one hawksbill) were entrained in the systems from May 1980 through December 1988. ^ ~ ~ ~ Of the 21, seven were found dead (four ot which were loggerheads), for an average of about one per year. At the Port Ever- glades plant, 25-30 hatchlings were also entrained in the system, and a few of them died (Applied Biology Inc., 1989b). Other turtle deaths at coastal power plants have been reported in New Jersey (Eggers, 1989), North Carolina, and Texas (pers. comm., T. Hen- wood, NMFS, 1989; pers. comm., B. Schroeder, Florida Department of Natural Resources, 19891. They were sporadic and apparently involved few turtles. For example, the Delaware Bay Power Plant in New Jersey entrapped 38 turtles in 9 years 26 loggerheads (18 dead) and 12 Kemp's ridleys (six dead), for an average of about three per year. Two factors cause an unusually high entrainment rate at the St. Lucie unit 2 power plant in Florida. First, the continental shelf is narrow in that area, and that seems to cause the normally high density of turtles passing

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113 Sea Turtle Mortality Associated with Human Activities along the coast to be concentrated near the shore, where the coolant- water intake tube is. Second, that part of the coast appears to be on the main coastal migratory route for turtles in the region. Therefore, mortality rates for this power plant should be considered separately. A total mor- tality estimate of about 11 turtles per year might be expected in the future at current population densities: about 9.4 loggerheads, one green turtle, and 0.3 Kemp's ridley. For other power plants, far less is known. According to the Edison Electric Institute (1987), 98 power-generating facilities use ocean or estu- arine water for their cooling systems along the gulf and Atlantic coasts of the United States. If we assume that rates of turtle capture from the five power plants discussed above (excluding the St. Lucie facility) are typical for the remaining coastal facilities between New York and Texas, we can estimate an annual mortality of 48 loggerheads and 13 Kemp's ridleys (loggerheads, 98 power plants x 0.48 per year; Kemp's ridleys, 98 power plants x 0.13 per year). Adding in the estimates from the St. Lucie plant raises the loggerhead to 57 per year and Kemp's ridley to 13 per year. An important consideration for the future is that, as turtle populations increase, we would expect an increase in the number of animals entrained in the facilities, and as human populations increase, more power plants might be built. Directed Take Directed take of sea turtles and their eggs is illegal in the United States and along the Caribbean and gulf coasts of Mexico. Some illegal take does occur in the United States and Mexico, but the numbers are proba- bly negligible. Loss of eggs and adult Kemp's ridleys at Rancho Nuevo is minimal, because protection has been provided. Although directed take of sea turtles is widely considered to affect populations, at least locally (Pritchard, 1980), the committee was unable to quantify the extent of the problem. Toxicology Tissues and eggs from several species of sea turtles in the southeastern United States, Ascension Island in the South Atlantic, the coast of France, and other geographic regions have been analyzed for organochlorine compounds, heavy metals, hydrocarbons, and radionuclides (Hillestad et al., 1974; Thompson et al., 1974; Stoneburner et al., 1980; Clark and Krynitsky, 1980, 1985; Witkowski and Frazier, 1982; Bellmund et al.,

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114 Decline of the Sea Turtles 19851. Turtles were found to be contaminated to various degrees in all the studies cited. However, because of the lack of data on physiological effects of the pollutants in sea turtles, their effect on survival cannot be estimated. Additional studies are needed to determine extents of contami- nation and the physiological effects of the contaminants. Ingestion of Plastics and Other Debris About 24,000 metric tons of plastic packaging is dumped into the ocean each year (Welch, 19881. Nationwide 10-20% of beach debris is expanded polystyrene foam and 40-60% is other plastic (McGavern, 19891. An estimated 1-2 million birds and more than 100,000 marine mammals and sea turtles die from eating or becoming entangled in plastic debris each year, including netting, plastic fishing line, packing bands, and Styrofoam (Welch, 1988; McGavern, 1989; Sanders, 19899. Sea turtles ingest a wide variety of synthetic drift items, including plas- tic bags, plastic sheeting, plastic particles, balloons, Styrofoam beads, and monofilament fishing line. Specific reports have been related to green turtles in Hawaii, Florida, and Texas; loggerheads in Georgia, Florida, Texas, and Virginia; hawksbills in Florida and Hawaii; and leatherbacks in New York, New Jersey, Massachusetts, and Texas (Wallace, 1985; O'Hara et. al., 19869. Turtles can mistake plastic bags and sheets for jellyfish or other prey. Ingestion of those items can cause intestinal blockage; release toxic chemicals; reduce nutrient absorption; reduce hunger sensation; inhibit feeding and mating activity; diminish reproductive performance by leaving the turtle unable to maintain its energy requirements and cause suffocation, ulceration, intestinal injury, physical deterioration, malnutri- tion, and starvation (Wehle and Coleman, 1983; Wallace, 1985; O'Hara et al., 1986; Bryant, 1987; Farrell, 1988; Gramentz, 1988; Welch, 1988; McGavern, 19891. Absorption of toxic plasticizers (such as polychlorinated biphenyls) is also possible as a result of ingestion. Some plasticizers can concentrate in tissues, and the toxic ingredients can cause eggshell thinning, tissue dam- age, and aberrant behavior (Wehle and Coleman, 1983; O'Hara et al., 19861. Plastic bags blocked the stomach openings of 11 of 15 leatherbacks that washed ashore on Long Island during a 2-week period. Ten had four to eight quart-sized bags, and one had 15 quart-sized bags (San Francisco Chronicle, 1983; Balazs, 1985; O'Hara et al., 19861. In South Africa, Hughes extracted a ball of plastic from the intestine of an emaciated leatherback; when unraveled, it measured 9 x 12 ft. or 2.7 x 3.7 m (Bal

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115 Sea Turtle Mortality Associated with Human Activities ads, 1985; Coleman, 19871. In September 1988, the largest leatherback ever recorded (914 kg) was found dead on a beach in Wales. The cause of death was listed as drowning due to entanglement, but a tightly com- pacted piece of plastic (15 x 25 cm) blocked the entrance to the small intestine and might have contributed to death (Eckert and Eckert, 19881. Accumulation of pollutants and plastic debris found in sargassum drift- lines might be a source of mortality of turtles through ingestion (Mayer, 19851. Floating debris is concentrated by natural processes along lines of convergence between discrete water masses, in the core of major current gyres, or on beaches and submerged rocky outcrops. Driftlines along margins of small temporary eddies or areas of downwelling can accumu- late floating debris and provide feeding areas for turtles. Young turtles are passive migrants in offshore driftlines and can contact buoyant debris. In 1979-1988 in the New York Bight area, necropsies were performed on 116 sea turtles. Various amounts of synthetic materials were found in 10 of 33 leatherbacks, three of 35 loggerheads, one of four green turtles, and none of 44 Kemp's ridleys. Most prevalent were plastic bags, small pieces of plastic sheeting, monofilament line, small pieces of variously colored plastic, and numerous small polystyrene balls. There was strong evidence in some animals that ingestion of synthetic materials caused their deaths. There is little information on the residence times and cumu- lative effects of synthetic materials in marine animals. These observations are not well suited to quantify the frequencies of ingestion (Sadove and Morreale, 19891. Studies conducted along the Texas coast in 1986-1988 documented the effects of marine debris on sea turtles (Plotkin and Amos, 1988; Stanley et al., 1988; Plotkin, 19891. They were significantly affected by ingestion of, and to a smaller extent entanglement in, marine debris. Necropsies of Kemp's ridleys, loggerheads, and green sea turtles revealed that the intestines of at least 65 of 237 turtles examined contained marine debris, such as plastic bags, Styrofoam, monofilament fishing line, polyethylene beads, aluminum foil, tar, glass, and rubber. In a 22-month study, plastic was found in nearly 80% of the turtle stomachs that contained debris and in turtles from about 97% of the beaches surveyed (Stanley et al., 19881. All five species found in the Gulf of Mexico had eaten or were ensnared by debris. Reports of debris ingestion by species indicated that green turtles had the highest incidence (32%) followed by loggerheads (26%), leatherbacks (24%), hawksbills (14%), and Kemp's ridleys (4%~. For all species except the leatherback, immature turtles were involved more frequently than adults. The distribution of debris types was as follows: plastic bags and sheets (32.1%), tar balls (20.8%), and plastic particles (18.9%~. NMFS scientists, on the basis of the results of autopsies conducted

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116 Decline of the Sea Turtles since 1978, estimated that one-third to one-half of all turtles have ingested plastic products or byproducts (Cottingham, 19881. Mortality associated with ingestion of plastics and debris cannot be accurately quantified from available data. Of the turtles examined, green turtles ingested plastic debris most frequently, followed by loggerheads and leatherbacks. Research is needed to develop accurate postmortem techniques to determine the role of plastic ingestion on turtle deaths. However, many reported stranded turtles are in an advanced state of decomposition, so it is difficult to determine exact causes of death, although indigestible stomach contents might still be identifiable. It is possible that the enactment of Annex V of the International Convention for the Prevention of Pollution from Ships (called bLARPOL for "marine pollution") might affect the amount of plastic that sea turtles are likely to encounter in the future; but, considering the life span of plastic and the amount already present in the oceans, the possible deleterious effects of plastic on sea turtles and other wildlife will be present for generations to come. SUMMARY Sea turtles are susceptible to human-caused deaths through their entire life, from nesting females, eggs, and hatchlings on beaches to juveniles and adults of both sexes in offshore and inshore waters. The committee found that the most important source of mortality on eggs and hatchlings at present on U.S. beaches is from non-human preda- tors, whose abundance is often associated with human disturbance, but other factors are beach development, directed take, beach vehicles, and beach lighting. The most important source of mortality for juveniles to adults in the coastal zone is shrimp trawling. Other factors judged to be of significance for juveniles and adults are other fisheries and entangle- ment in lost fishing gear and marine debris. Order-of-magnitude estimates of human-caused mortality on juvenile to adult loggerheads and Kemp's ridleys were made by the committee. Shrimp trawling accounts for 5,000-50,000 loggerhead and 500-5,000 Kemp's ridley mortalities per year. Other fisheries and discarded fishing gear and debris account for 500-5,000 loggerhead and 50-500 Kemp's rid- ley mortalities. Dredging, collisions with boats, and oil-rig removal each account for 50-500 loggerhead and 5-50 Kemp's ridley deaths. Entrain- ment in electric power plants and directed take each account for fewer than 50 turtle deaths per year. Based on the committee's evaluation, about 86% of the human caused mortalities on juveniles and adults result

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117 Sea Turtle Mortality Associated with Human Activities from shrimp trawling. The committee recognized the possible effects of plastic ingestion and marine debris but was unable to quantify them. The strong evidence that shrimp trawling is the primary agent for sea turtle mortality caused by humans comes from five lines of analysis and information First, the proportion of sea turtles caught in shrimp trawls that are dead or comatose increases with an increase in tow time from 0% during the first 50 minutes to about 70% after 90 minutes. Second, the numbers of turtles stranding on the coastal beaches consistently increased in a steplike fashion when the shrimp fishery opened in South Carolina and Texas and decreased when the fishery closed in Texas. Because the openings and closings were on different dates in different years, the change in strandings can be ascribed to the fishery rather than to date per se. The change in stranding rate indicates that 70 to 90% of the turtles stranded at those times and places were killed in shrimp trawls. Based on analysis of data from loggerheads, these stranded tur- tles were also in the life stages with the highest reproductive values. Third, loggerhead nesting populations are declining in Georgia and South Carolina where shrimp fishing is intense, but appear to be increasing far- ther south in central to southern Florida where shrimp fishing is low or absent. Fourth, the estimate in the literature of 11,000 loggerheads and Kemp's ridleys killed annually by shrimp trawling was judged by the committee to be an underestimate, possibly by a factor of three to four, because that estimate accounted for neither mortality in bays, rivers, and estuaries nor the likely deaths of most comatose turtles brought onto the deck of shrimp trawlers. Many of the comatose turtles will die even when released back into the water. Fifth, in North Carolina, turtle strand- ing rates increase in summer south of Cape Hatteras when the shrimp fleet is active and north of Cape Hatteras in winter when the flounder trawling is active.