COSEWIC Assessment and Status Report on the Loggerhead Sea Turtle Caretta caretta in Canada – 2010
Table of Contents
- COSEWIC Assessment Summary
- COSEWIC Executive Summary
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status Designations
- Technical Summary
- Authorities Consulted
- Information Sources
- Biographical Summary of Report Writer
- Collections Examined
List of Figures
- Figure 1. External morphology and scutellation of the Loggerhead Sea Turtle
- Figure 2. Anatomical points for straight (SCL) and curved (CCL) carapace length measurements
- Figure 3. Conceptual model of the size distribution for each life stage of the Loggerhead Sea Turtle
- Figure 4. Estimated number and distribution of Loggerhead Sea Turtle nests in the southeastern United States, the Bahamas, Cuba and Mexico from 2001-2008
- Figure 5. Global distribution of Loggerhead Sea Turtle nesting assemblages
- Figure 6. Locations of Loggerhead Sea Turtle captures recorded by at–sea observers on Canadian pelagic longline fishing trips, 1999–2008
- Figure 7. Occurrences of Loggerhead Sea Turtles off eastern Canada
- Figure 8. Loggerhead Sea Turtles: Developmental stages (juveniles vs. adults); ecological stages (obligatory epipelagic vs. opportunistic amphi–habitat); habitats (epipelagic vs. benthic); and oceanographic zones (oceanic vs. neritic)
- Figure 9. Location of the four identified Loggerhead Sea Turtle recovery units in the United States
List of Tables
- Table 1. Loggerhead Sea Turtle nesting totals (1989–2009) collected from index beaches in Florida as part of the Fish and Wildlife Research Institute’s Index Nesting Beach Survey (INBS) (Florida FWC 2010)
- Table 2. Detailed list of threats facing Loggerhead Sea Turtles in the northwest Atlantic as compiled by NMFS and USFWS (2008).
- Table 3. Key used to assign estimated annual mortality to each threat category
- Table 4. Annual mortality for each life stage and ecosystem for each threat
- Table 5. Annual mortality for each threat within a threat category (Table 2)
summed for all life stages and ecosystems, and adjusted for relative reproductive values for each
List of Appendices
Loggerhead Sea Turtle
ENDANGERED – 2010
COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:
COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:
COSEWIC. 2010. COSEWIC assessment and status report on the Loggerhead Sea Turtle Caretta caretta in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. viii + 75 pp.
COSEWIC would like to acknowledge Kathleen Martin for writing the status report on the Loggerhead Sea Turtle, Caretta caretta, in Canada, prepared under contract with Environment Canada. This report was overseen and edited by Dr. Ronald J. Brooks, Chair of the COSEWIC Amphibians and Reptiles Specialist Subcommittee.
For additional copies contact:
c/o Canadian Wildlife Service
Également disponible en français sous le titre Évaluation et Rapport de situation du COSEPAC sur le tortue caouanne (Caretta caretta) au Canada.
Loggerhead Sea Turtle — illustration by Amanda Bennett.
© Her Majesty the Queen in Right of Canada, 2010.
Loggerhead Sea Turtle
Reason for designation
This species is declining globally and there are well documented, ongoing declines in the Northwest Atlantic population from which juveniles routinely enter and forage in Atlantic Canadian waters. The Canadian population is threatened directly by commercial fishing, particularly bycatch in the pelagic longline fleet, and by loss and degradation of nesting beaches in the southeastern USA and the Caribbean. Other threats include bycatch from bottom and midwater trawls, dredging, gillnets, marine debris, chemical pollution and illegal harvest of eggs and nesting females.
Pacific Ocean, Atlantic Ocean
Designated Endangered in April 2010.
The Loggerhead Sea Turtle (Caretta caretta) is one of six species of hard–shelled marine turtles that comprise the family Cheloniidae in the order Testudines. Although Atlantic and Pacific populations of the turtle are genetically distinct, there are no recognized subspecies.
The Loggerhead Sea Turtle’s head and beak are large in comparison with other sea turtles. Its head and carapace are reddish–brown, and its flippers are chestnut brown, fading to yellow at the edges. The bridge between carapace and plastron, as well as the plastron, underside of the throat, flippers and tail are yellow to creamy white. Sexual dimorphism is usually apparent in animals larger than 67 cm straight–line carapace length. The sexes are most easily distinguished by tail length (longer in males) and claws (one claw is significantly longer and curved in males).
Loggerhead Sea Turtles found in Canadian waters are likely comprised of individuals from the same nesting populations as those turtles found in the northern limits of United States’ waters (Atlantic and Pacific). For the Pacific Ocean, any individuals wandering into Canadian waters would come from nesting assemblages in Japan. Nesting populations from southern Virginia, North and South Carolina, Georgia, Florida, and the Caribbean coast of Mexico contribute to the individuals found in Atlantic Canadian waters.
Loggerhead Sea Turtles are widely distributed in the Atlantic, Pacific and Indian Oceans. There are no confirmed records of Loggerhead Sea Turtles in the Canadian Pacific. However, sightings of Loggerhead Sea Turtles in U.S. waters off Washington and Alaska indicate that the turtles may occasionally also occur off British Columbia. Juvenile Loggerhead Sea Turtles are routinely found in Atlantic Canadian waters. They are usually associated with the warmer offshore waters of the Gulf Stream and are most often encountered on the Scotian Shelf, Scotian Slope, Georges Bank and the Grand Banks.
Most loggerheads nest at the western rims of the Atlantic and Indian Oceans, with the largest nesting assemblages in southern Florida, USA and Masirah, Oman. The northern extent of the Atlantic nesting range in North America is in Virginia; the largest nesting colony is in Florida. Loggerhead Sea Turtles in the North Pacific nest almost exclusively in Japan.
Although Loggerhead Sea Turtles make use of both terrestrial and marine habitats, they spend the majority of their lives at sea. After hatching from nests laid on sand beaches, Loggerhead Sea Turtle hatchlings move immediately to the marine environment. Male turtles never return to land. Female turtles return only to nest. They do not nest in Canada.
Loggerhead Sea Turtles occupy different marine habitats at different life stages. Hatchling turtles disperse to neritic waters (waters of the Continental Shelf or areas near the shelf where bottom depths are less than 200 m) and then to oceanic waters (deeper than 200 m). Juvenile Loggerhead Sea Turtles make trans–oceanic migrations. They return to neritic zones as they mature, with nesting females homing to their natal beaches. Habitat for mature Loggerhead Sea Turtles and the movements of mature male are still relatively unknown. Current research indicates that Loggerhead Sea Turtles in Canada concentrate in areas where water temperatures are above 22°C.
Mature female Loggerhead Sea Turtles return to land only to nest. They nest on a 2–3–year interval. During a nesting season, they lay three to four clutches of approximately 112 eggs each. There are approximately 14 days between nesting events. Eggs hatch after 7–13 weeks of incubation depending on the temperature of the nest. The sex of hatchlings is temperature dependent. Incubation temperatures above 29°C produce more or all females, and incubation temperatures below 29°C produce more or all males.
Hatchlings emerge at night, and use ambient light to guide them to the ocean, where they begin a period of frenzied activity, swimming for approximately 20 to 30 hours. They stay in neritic waters (waters over continental shelf) for weeks or months, and then disperse to oceanic waters using ocean currents. Pacific Loggerhead Sea Turtles are known to go to Baja, Mexico, and to use the waters of the Kuroshio Extension Bifurcation Region in the North Pacific. Western Atlantic hatchlings are known to go to the Azores and to Madeira. Recent research suggests that a proportion of the western Atlantic population go north to Canadian waters instead.
Juvenile Loggerhead Sea Turtles recruit back to neritic waters, although this return may not be permanent. Both juvenile and adult Loggerhead Sea Turtles can alternate between neritic and oceanic waters, possibly choosing habitat based on prey availability. Loggerhead Sea Turtles reach sexual maturity at approximately 16–34 years of age, with a generation time of about 46 years. Loggerhead Sea Turtles are carnivorous, feeding on a variety of crustaceans, salps, fish, squid, and jellyfish.
Population sizes and trends
Although Loggerhead Sea Turtles routinely visit waters off Atlantic Canada, little is known about population sizes or trends. In the past, this species was thought to be a vagrant or accidental in Canada’s Atlantic waters, but from 1999–2006 it was estimated that the incidental catch for the Canadian fishery as a whole was 9,592 Loggerhead Sea Turtles (average=1,199 annually). Therefore, the species has a significant presence in Canadian waters. Nesting populations that likely contribute the Loggerhead Sea Turtles found in Canada are declining.
Limiting factors and threats
The primary known threat to Loggerhead Sea Turtles in Canadian waters is bycatch in the pelagic longline fleet. Bycatch of juvenile–stage turtles is particularly significant because changes in survivorship of this life–history stage have the largest impact on population growth. In addition, mixed–stock analyses indicate turtles from a variety of nesting assemblages mix in the oceanic zone. Significant loss of these animals may deplete nesting colonies throughout the region.
Globally, Loggerhead Sea Turtles face threats from fisheries bycatch, non–fisheries resource use (e.g., poaching), construction and development on nesting beaches, other ecosystem alterations, pollution, natural predators, and perhaps from other factors such as climate change.
Special significance of the species
The Loggerhead Sea Turtle is a highly–migratory species, and, therefore, a shared resource among many nations. Canada’s responsibility toward the species is then twofold: first, to protect it as necessary within national boundaries; second, to ensure that the level of protection we afford does not jeopardize conservation activities elsewhere. In addition, this is the only hard–shelled sea turtle to frequent Canadian waters.
Loggerhead Sea Turtles receive some protection from the Fisheries Act. The federal government fulfills its constitutional responsibilities for sea coast and inland fisheries through the administration of the Fisheries Act. The Act provides Fisheries and Oceans Canada (DFO) with powers, authorities, duties and functions for the conservation and protection of fish and fish habitat (as defined in the Fisheries Act) essential to sustaining commercial, recreational and Aboriginal fisheries.
The Loggerhead Sea Turtle receives protection from the United States’ Endangered Species Act, the Inter–American Convention for the Protection and Conservation of Sea Turtles, the Protocol Concerning Specially Protected Areas and Wildlife, the Convention on International Trade in Endangered Species and the Convention on Migratory Species.
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal–Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.
COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non–government science members and the co–chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.
A wildlife species that no longer exists.
A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.
A wildlife species facing imminent extirpation or extinction.
A wildlife species likely to become endangered if limiting factors are not reversed.
Special Concern (SC)*
A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.
Not at Risk (NAR)**
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.
Data Deficient (DD)***
A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.
* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.
The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.
COSEWIC Status Report on the Loggerhead Sea Turtle Caretta caretta in Canada – 2010.
The Loggerhead Sea Turtle was described by Linnaeus in 1758 as Testudo caretta, and has had more than 35 names since then (Dodd 1988). The species’ current and generally accepted scientific name is Caretta caretta. In French, the turtle’s common name is “tortue caouanne,” sometimes spelled “tortue caouane”. The Loggerhead Sea Turtle is one of six species of hard–shelled sea turtles that comprise the Family Cheloniidae in the Order Testudines in the Class Sauropsida. Genetic studies indicate that the Atlantic and Indo–Pacific populations are distinct, but there are no recognized subspecies (Dodd 1988; Bowen 2003; Bowen and Karl 2007).
The Loggerhead Sea Turtle derives its common name from its head and beak, which are relatively large when compared with those of other sea turtles. The animal has a short neck and, like other sea turtles, cannot retract its head into its shell. The head is reddish–brown as is the carapace (top shell), and both may be tinged with olive. The scales on the head and the scutes (bony external plates) on the carapace are sometimes bordered in yellow. Its flippers are chestnut brown, fading to yellow at the edges. The bridge between the carapace and plastron (bottom shell) and the plastron itself are yellow to creamy white as are the underside of the throat, flippers and tail. There is some geographic variation in colouring of sub–adults and adults, and significant reported variation in the colouration of hatchlings (even within the same clutch), but no standardized comparison has been published (Dodd 1988; Kamezaki 2003).
The carapace of the adult Loggerhead Sea Turtle is thick and heavily keratinized (covered with a hard, protective protein) (Pritchard 1979; Dodd 1988; Ernst and Lovich 2009). It is elongated, and is often described as heart–shaped. The carapace has five vertebral scutes, usually five pairs of costal scutes, 12 or 13 pairs of marginal scutes (including the supercaudal scute) and a wide nuchal scute that contacts the first costal scute on either side (Figure 1). Kamezaki (2003) warns against using scute formation as the exclusive means of species identification, as there is sufficient variation in Loggerhead Sea Turtle scute formation to render it unreliable.
Scientists generally use a straight carapace length (SCL) to measure Loggerhead Sea Turtles. SCL is measured in one of three ways: minimum SCL, SCL notch to tip, or maximum SCL (Bolten 1999) (Figure 2).
Figure 2. Anatomical points for straight (SCL) and curved (CCL) carapace length measurements. (a) minimum SCL and minimum CCL; (b) SCL notch to tip and CCL notch to tip; (c) maximum SCL. From Bolten 1999.
Dodd (1988) separates size classes of Loggerhead Sea Turtle populations around the world by geographic region. More pertinent to the discussion of Loggerhead Sea Turtles in the Canadian context are the size classes of Atlantic Loggerhead Sea Turtles found in the northern limits of United States’ waters. The carapace lengths associated with the five Loggerhead Sea Turtle life stages as described by the Turtle Expert Working Group (TEWG) (2009) are as follows:
Stage 1—Year One (terrestrial to oceanic, egg to post–hatchling) ranges from hatchling size (average 4.5 cm SCL; Van Buskirk and Crowder 1994) to 15 cm SCL (Bjorndal et al. 2000);
Stage 2—Juvenile (1) (exclusively oceanic) ranges from 15 cm SCL to 63 cm SCL (TEWG 2009);
Stage 3—Juvenile (2) (oceanic or neritic, small benthic juveniles) ranges from 41 cm SCL to 82 cm SCL, peaking at 63 cm SCL in the Atlantic (TEWG 2009).
Stage 4—Juvenile (3) (oceanic or neritic, large benthic juveniles) ranges from 63 cm SCL to 100 cm SCL (TEWG 2009);
Stage 5—Adult (neritic or oceanic) ranges from 82 cm SCL with full recruitment to the adult stage at 100 cm SCL (TEWG 2009).
The overlap in sizes at different life stages reflects the distribution of recruitment sizes at any given stage (TEWG 2009) (Figure 3).
Measurements of Loggerhead Sea Turtles found in Atlantic Canadian waters suggest they are juvenile animals, as are those found in adjacent U.S. waters (National Marine Fisheries Service NMFS and USFWS 1998; TEWG 2000; Bowen et al. 2005; DFO 2006; Bowen and Karl 2007; Ledwell 2007; McAlpine et al. 2007; NMFS and USFWS 2007; Brazner and McMillan 2008; NMFS and USFWS 2008). The majority of the Loggerhead Sea Turtles in Atlantic Canadian waters are likely Stage 3 (Watson et al. 2005; Brazner and McMillan 2008; TEWG 2009). Loggerhead Sea Turtles captured on pelagic longline fishing gear on the Grand Banks off Newfoundland in the Northeast Distant Statistical Reporting Area (NED) (n=93) ranged in size from 32.4 cm to 68 cm SCL, averaging 56.8 cm (Watson et al. 2005). Brazner and McMillan (2008) reported measurement data from 28 Loggerhead Sea Turtles incidentally captured in Canadian waters. The sample ranged in size from 42 cm to 87 cm SCL (mean= 53.9 cm); the majority of turtles (85%) were less than 60 cm SCL and only two individuals were over 80 cm (Brazner and McMillan 2008). Three additional coastal records substantiate this size distribution. One found (live) in Connaigra Bay on the south coast of Newfoundland measured 76 cm curved carapace length (CCL) (Ledwell 2007), one captured off Devil’s Island, Nova Scotia, measured 30.5 cm carapace length (neither CCL or SCL was specified), and one captured off Chebucto Head, Nova Scotia, in 1964 measured 74.9 cm CCL (McAlpine et al. 2007).
Recorded carapace lengths for Loggerhead Sea Turtles have exceeded 210 cm and masses above 450 kg (Ernst et al. 1994). The average mean carapace length of nesting Loggerhead Sea Turtles in the Atlantic is 94 cm, and the mean body mass of female Loggerhead Sea Turtles in the Atlantic is 116 kg (derived from Dodd 1988).
There is less specific information available on the size–class distribution of Pacific Loggerhead Sea Turtles. However, growth rates of juvenile north Pacific Loggerhead Sea Turtles is equivalent to, or slower than, those of Atlantic Loggerhead Sea Turtles (Zug et al. 1995; Bjorndal et al. 2000). Pacific Loggerhead Sea Turtles do not disperse to neritic zones until they are larger than around 60 cm SCL (Conant et al. 2009). Loggerhead Sea Turtles nesting in Japan, nesting stock for North Pacific Loggerhead Sea Turtles (Hatase et al. 2002a), average 89.0 SCL and 96.8 kg (Uchida and Nishiwaki 1982).
Sexual dimorphism is usually apparent in Loggerhead Sea Turtles of more than 67 cm SCL (Dodd 1988). The most easily identifiable differences are tail length and claws (Wibbles 1999). As with other sea turtles, male Loggerhead Sea Turtles have a longer, thicker and more muscular tail than do females (Dodd 1988; Ernst et al. 1994; Wibbles 1999; Kamezaki 2003). The male turtle’s tail extends well beyond the carapace, while the tail of the female turtle barely extends beyond it (Wibbles 1999). Although both male and female Loggerhead Sea Turtles have claws on their front flippers, males have a claw on each flipper that is conspicuously larger and more strongly curved than the rest (Dodd 1988; Ernst et al. 1994; Kamezaki 2003).
The Family Cheloniidae has three deep lineages that fossil evidence suggests differentiated more than 24 million years ago (Bowen 2003). Together, the Loggerhead Sea Turtle, the Olive Ridley Sea Turtle (Lepidochelys olivacea), the Kemp’s Ridley Sea Turtle (L. kempii) and the Hawksbill Sea Turtle (Eretmochelys imbricata) comprise the Chelonini tribe (Bowen 2003). The Loggerhead Sea Turtle, based on mtDNA sequences, diverged from the Ridley and Hawksbill Sea Turtles approximately 10 million years ago, and is now a monotypic genus (Dodd 1988; Bowen 2003).
Loggerhead Sea Turtles have two lineages, which diverged approximately 3 million years ago: one in the Indian and Pacific Ocean basins, and the other in the Atlantic Ocean and Mediterranean Sea (Bowen 2003). There have been two effective transfers of matrilines between the groups, likely through the waters around South Africa (Bowen 2003). One occurred approximately 250,000 years ago and one more recently, likely less than 12,000 years ago (Bowen 2003; Bowen and Karl 2007). These rare events have been sufficient to prevent the two lineages from developing into separate species (Bowen 2003; Bowen and Karl 2007).
Genetic sequencing confirms that female Loggerhead Sea Turtles demonstrate “natal homing,” which means they return to the vicinity of their natal beaches for mating and nesting (Bowen and Karl 2007). Consequently, each nesting population can be distinguished by its unique ratio of haplotypes (Bowen et al. 2005; Bowen and Karl 2007). Studies of the mtDNA in nesting assemblages have confirmed a strong population structure among nesting colonies (Bowen and Karl 2007).
No genetic studies have been specifically conducted on the Canadian Loggerhead Sea Turtle population. In the Atlantic, however, work in the NED suggests that the Grand Banks off Newfoundland are foraging grounds for Loggerhead Sea Turtles from all Atlantic nesting beaches (Bowen et al. 2005; LaCasella et al. 2006; Bowen and Karl 2007). Contributions to the pelagic juvenile group are approximately proportional to the size of the source nesting populations (LaCasella et al. 2006) (Figure 4). Approximately 80% of all nesting in the Atlantic Ocean occurs in Peninsular Florida (Figures 4 and 5), which also produces approximately 90% of all hatchlings (NMFS and USFWS 2008; TEWG 2009).
Loggerhead Sea Turtles found in the North Pacific Ocean nest almost exclusively in Japan (Bowen et al. 1995; Hatase et al. 2002a; Bowen 2003; Kamezaki et al. 2003; NMFS and USFWS 2007; LeRoux et al. 2008), with low–level nesting in the Xisha Archipelago in the South China Sea (Chan et al. 2007) (Figure 5).
Pacific and Atlantic populations of Loggerhead Sea Turtles are both geographically and genetically distinct (Bowen 2003). The United States government, through the National Marine Fisheries Service and the U.S. Fish and Wildlife Service, convened a Biological Review Team (BRT) in February 2008 to determine whether or not Distinct Population Segments (DPS) exist for the Loggerhead Sea Turtle. Similar to the COSEWIC policy on Designatable Units, the U.S. DPS policy applies if a population is both discrete and significant relative to its taxon (U.S. Dept. of the Interior and U.S. Dept. of Commerce 1996).
The BRT unanimously concluded that there were nine Loggerhead Sea Turtle DPS globally, each representing a large portion of the species’ range and a unique ecosystem influenced by local ecological and physical factors (Conant et al. 2009). Each of the population segments is genetically unique (Conant et al. 2009). In the opinion of the BRT, the loss of any of them would represent both a significant gap in the Loggerhead Sea Turtle’s range and a significant loss in Loggerhead Sea Turtle genetic diversity (Conant et al. 2009). The global Loggerhead Sea Turtle DPSs as defined by the BRT are:
- North Pacific Ocean DPS
- South Pacific Ocean DPS
- North Indian Ocean DPS
- Southeast Indo–Pacific Ocean DPS
- Southwest Indian Ocean DPS
- Northwest Atlantic Ocean DPS
- Northeast Atlantic Ocean DPS
- Mediterranean Sea DPS
- South Atlantic Ocean DPS (Conant et al. 2009)
The DPSs most relevant to a consideration of the Loggerhead Sea Turtle in Canada are the Northwest Atlantic Ocean DPS and the North Pacific Ocean DPS. These would correspond to two separate DUs, the Pacific Ocean DU and the North–West Atlantic Ocean DU. However, no Loggerhead Sea Turtle has ever been reported from Pacific Canadian waters, and it seems likely that these waters are only used by accidental vagrants if any loggerheads occur there at all. Therefore, in this report, all Loggerhead Sea Turtles in Canada are considered as a single Designatable Unit.
Loggerhead Sea Turtles inhabit the temperate and tropical regions of the Atlantic, Pacific and Indian Oceans. In its Red List assessment of the Loggerhead Sea Turtle, the IUCN (1996) recognized it as native to 54 countries (not including Canada) with uncertain presence in an additional five. The Loggerhead Sea Turtle is found in all FAO (Food and Agriculture Organization of UN) major fishing areas, except for those in the Arctic and Antarctic (IUCN 1996; FAO 2009).
Loggerhead Sea Turtle use of the marine habitat includes both oceanic and neritic zones. Bolten (2003) defines the oceanic zone as the open ocean environment where minimum depths are greater than 200 m. The neritic zone corresponds to the Continental Shelf, or to areas where maximum depths are less than 200 m (Bolten 2003).
In the oceanic zone, Loggerhead Sea Turtles spend 75% of their time in the top 5 m of the water column (Bolten 2003). Of their dives, 80% are less than 5 m deep, and the remainder of dives are distributed throughout the top 100 m of the water column, with occasional dives greater than 200 m (Bolten 2003). Research by McCarthy et al. (2004) suggests that Loggerhead Sea Turtles concentrate near oceanographic fronts, possibly because of the associated prey density.
In the neritic zone, Loggerhead Sea Turtles are most commonly found in waters 22 to 49 m deep (Shoop and Kenney 1992; Hopkins–Murphy et al. 2003; Schroeder et al. 2003). Genetic research suggests that a proportion of juvenile Loggerhead Sea Turtles recruit to the vicinity of the beaches where they hatched, and that mature females, and possibly males, have high site fidelity to their breeding and nesting habitat (Schroeder et al. 2003; Bowen et al. 2005). There is also evidence that juvenile Loggerhead Sea Turtles exhibit site fidelity to feeding grounds (Avens et al. 2003, Avens and Lohmann 2004).
However, current research suggests that Loggerhead Sea Turtles move between oceanic and neritic zones (Hatase et al. 2002a; Bolten 2003; Ehrhart et al. 2003; Schroeder et al. 2003; Bass et al. 2004; Hawkes et al. 2006; McClellan and Read 2007; Casale et al. 2008; Mansfield et al. 2009; Reich et al. 2010). The specific factors responsible for variation in habitat choice are not yet clear. Some studies suggest that the size of the Loggerhead Sea Turtle may be a factor (Hatase et al. 2002a; Hawkes et al. 2006; Reich et al. 2010). However, size was not a factor in plasticity in McClellan’s (2007) study. McClellan (2007) also suggests that variations in age, sex, condition or nesting beach origin are unlikely explanations. It is possible that temporary or permanent fidelity to specific oceanic or neritic zones may vary among individuals or populations depending on oceanographic features and the availability of food in foraging or migratory areas (Polovina et al. 2000; Witherington 2002; Casale et al. 2008; Kobayashi et al. 2008).
The majority of Loggerhead Sea Turtle nesting takes place at the western rims of the Atlantic and Indian Oceans. The largest nesting assemblages are in southern Florida, USA, and in Masirah, Oman, a country just east of Saudi Arabia that borders the Indian Ocean (Baldwin et al. 2003; Ehrhart et al. 2003, Kamezaki et al. 2003; Limpus and Limpus 2003; Margaritoulis et al. 2003). Key nesting grounds in the Pacific Ocean are Japan (Hatase et al. 2002a; Bowen 2003; Kamezaki et al. 2003; NMFS and USFWS 2007; LeRoux et al. 2008), eastern Australia and New Caledonia (Limpus and Limpus 2003) (Figure 5).
Loggerhead Sea Turtles are found routinely in Atlantic Canadian waters (Bleakney 1965; Ladzell 1980; Witzell 1999; Javitech 2002; Javitech 2003; Ledwell 2007; McAlpine et al. 2007; Brazner and McMillan 2008; James pers. comm. 2009; Lawson pers. comm. 2009). They occur on the Scotian Shelf, Scotian Slope, Georges Bank, the Grand Banks, and waters further offshore (Witzell 1999; Javitech 2002; Javitech 2003; McAlpine et al. 2007; Brazner and McMillan 2008; Canadian Sea Turtle Sightings Database 2009, Lawson, pers. comm. 2009) (Figures 6 and 7). Existing research suggests Loggerhead Sea Turtles are present in Canadian waters in greatest numbers during the spring, summer and fall (Witzell 1999; Brazner and McMillan 2008; Canadian Sea Turtle Sightings Database 2009). These data are linked to fishing effort.
Loggerhead Sea Turtles reported incidentally captured by the Canadian Atlantic pelagic longline fleet (n=701) from 1999–2006 within Canada’s Exclusive Economic Zone concentrated in offshore areas along the Western Scotian Shelf and Georges Bank off Nova Scotia, and near the Grand Banks off Newfoundland (Figure 6). No Loggerhead Sea Turtles were observed in inshore areas of southeast Nova Scotia or northeast of the Grand Banks despite considerable observer coverage in these areas. The Loggerhead Sea Turtles were encountered along 20 to 25°C contours despite fishing effort across a range of temperatures (Brazner and McMillan 2008). None of these animals was captured when water temperatures at the sets were less than 15°C (Brazner and McMillan 2008). The bycatch of turtles was concentrated in water temperatures above 22°C (Brazner and McMillan 2008). Hawkes et al. (2007) suggests that Loggerhead Sea Turtles may winter where the Gulf Stream maintains temperatures above 14°C.
Figure 6. Locations of Loggerhead Sea Turtle captures recorded by at–sea observers on Canadian pelagic longline fishing trips, 1999–2008. Each point does not represent a single turtle. Dots represent locations where one or more Loggerhead Sea Turtles may have been caught. (Department of Fisheries and Oceans 2009).
There are a few inshore records of Loggerhead Sea Turtles in Atlantic Canadian waters (Bleakney 1965; Ledwell 2007; McAlpine et al. 2007, Lawson pers. comm. 2009), including a hybrid Loggerhead–Green Sea Turtle (James et al. 2004). However, Loggerhead Sea Turtles in the region are generally associated with the warmer offshore waters of the Gulf Stream (Shoop 1980; Shoop and Kenny 1992; Witzell 1999; Hawkes et al. 2007; McAlpine et al. 2007; Brazner and McMillan 2008; James pers. comm. 2009) (Figure 7). The water temperature inshore in Atlantic Canada is usually too low for the thermal tolerance levels of this animal (Hopkins–Murphy et al. 2003; Hawkes et al. 2007; James pers. comm. 2009). Loggerhead Sea Turtles become lethargic in water temperatures of approximately 13°C, and adopt a stunned, floating posture in water of approximately 10°C (Mrosovsky 1980). Loggerhead Sea Turtles found inshore are rare, and are likely the result of warm core rings that have broken off from the Gulf Stream (McAlpine et al. 2007; James pers. comm. 2009). The Canadian Sea Turtle Network (CSTN) monitoring program, which distributes information on Loggerhead and Leatherback Sea Turtles in coastal communities, has recorded significant numbers of inshore sightings of Leatherback Sea Turtles (Martin and James 2005a). There are also numerous offshore reports (n=81) of Loggerhead Sea Turtles (Martin and James 2005a; James et al. 2006; McAlpine et al. 2007; Canadian Sea Turtle Sightings Database 2009). It has not had similar numbers of reports of Loggerhead Sea Turtles inshore; this indicates that Loggerhead Sea Turtles are not regularly found inshore.
Figure 7. Occurrences of Loggerhead Sea Turtles off eastern Canada. Dots represent single occurrences and are based on published literature as well as unpublished sightings (n=17) collected during U.S. National Marine Fisheries Service aerial surveys conducted between 10–26 August 1999. Shaded areas show the approximate location of concentrations of observations of turtles believed to be Loggerhead Sea Turtles (a) collected by the participants of the Nova Scotia Leatherback Turtle Working Group, or (b) records from the pelagic longline bycatch plotted by Witzell (1999). Question marks indicate areas in need of further study. From McAlpine et al. 2007.
There are no reports of Loggerhead Sea Turtles recorded in the Pacific Ocean off British Columbia (McAlpine et al. 2007, Spaven pers. comm. 2009). However, sightings of Loggerhead Sea Turtles off the coasts of Washington and Alaska suggest that they may occur in British Columbia occasionally (Hodge 1982; Bane 1992; Hodge 1992; Hodge and Wing 2000; McAlpine et al. 2007). The British Columbia Cetacean Sightings Network, which also maintains sightings of marine turtles, has records of 31 unidentified sea turtles (Spaven pers. comm. 2009; Wild Whales 2010). It is possible that some of these are Loggerhead Sea Turtles. However, current understanding of oceanic and neritic habitat for North Pacific Loggerhead Sea Turtles indicates the species only occurs south of Canadian waters. In oceanic zones, Loggerhead Sea Turtles are found south of 44° N latitude (Kobayashi et al. 2008). In neritic zones off Pacific North America, they are found along the coast of Baja California Sur, Mexico (Bowen et al. 1995; Koch et al. 2006; Peckham and Nichols 2003; Peckham et al. 2007).
Loggerhead Sea Turtles use both terrestrial (nesting) and marine habitat.
Loggerhead Sea Turtles nest on ocean beaches and, infrequently, on estuarine shorelines. Nests are usually laid between the high–tide line and the dune front (Routa 1968; Witherington 1986; Hailman and Elowson 1992). Sea turtle eggs require beaches with high–humidity substrate that allows for sufficient gas exchange as well as temperatures conducive to egg development (Miller 1997; Miller et al. 2003). Loggerhead Sea Turtles do not nest in Canada (Figure 5). It is likely that Loggerhead Sea Turtles found in Canadian waters come from similar nesting stock as those Loggerhead Sea Turtles found in adjacent U.S. waters (NMFS and USFWS 1998; TEWG 2000; Bowen et al. 2005; DFO 2006; LaCasella et al. 2006; Bowen and Karl 2007; McAlpine et al. 2007; NMFS and USFWS 2007; Brazner and McMillan 2008; NMFS and USFWS 2008).
Nesting sites for Loggerhead Sea Turtles found in the northwest Atlantic are southern areas of Virginia, as well as in North Carolina, South Carolina, Georgia and Florida. There are also nesting sites found from the Caribbean coast of Mexico through French Guiana, the Bahamas, the Lesser Antilles and the Greater Antilles (Pearce 2001; Bowen 2003; Bowen and Karl 2007; NMFS and USFWS 2008, Conant et al. 2009; TEWG 2009). Approximately 80% of all nesting in the Atlantic Ocean occurs in Peninsular Florida (Figures 4 and 5), which also produces approximately 90% of all hatchlings (NMFS and USFWS 2008; TEWG 2009).
Loggerhead Sea Turtles found in the North Pacific nest almost exclusively in Japan (Bowen et al. 1995; Hatase et al. 2002a; Bowen 2003; Kamezaki et al. 2003; NMFS and USFWS 2007; LeRoux et al. 2008), with one report of low–level nesting in the Xisha Archipelago in the South China Sea (Chan et al. 2007). In Japan, nesting beaches are widely distributed from 24° N to 37° N latitude (Hatase et al. 2002a; Kamezaki et al. 2003). The three major nesting sites are Yakushima Island, and Miyazaki and Minabe beaches on the mainland (Kamezaki 2003) (Figure 5).
Loggerhead Sea Turtles inhabit the temperate and tropical regions of the Atlantic, Pacific and Indian Oceans, and their use of the marine habitat includes both oceanic and neritic zones. Until recently, it was assumed that the species’ choice of habitat was governed by discrete developmental shifts: Loggerhead Sea Turtles move from the oceanic zone they inhabit as juveniles to the neritic zone, where they remain permanently, making seasonal, latitudinal migrations between neritic feeding and breeding grounds (Carr 1987; Bjorndal et al. 2000; Snover 2002; Bolten 2003). However, recent research indicates that the shifts between habitats are not permanent (Hatase et al. 2002a; Bolten 2003; Ehrhart et al. 2003; Schroeder et al. 2003; Bass et al. 2004; Hawkes et al. 2006; McClellan and Read 2007; Casale et al. 2008; Kobayashi et al. 2008; Mansfield et al. 2009; Reich et al. 2010). Casale et al. (2008) suggest describing Loggerhead Sea Turtle life history not as a series of ontogenetic shifts and stages associated with oceanographic zones, but by the habitat individual animals frequent for feeding: epipelagic, benthic or both (Figure 8).
If Loggerhead Sea Turtles’ habitat use is guided by oceanographic features and food availability (Polovina et al. 2000; Witherington 2002; Casale et al. 2008; Kobayashi et al. 2008), their use of the marine habitat may fluctuate as a result of climate change and associated increased sea surface temperatures (Chaloupka et al. 2008). The level to which Loggerhead Sea Turtles and their prey respond to thermal shifts in the marine environment is still poorly understood. However, some studies have documented a shift in nesting behaviour (earlier onset nesting and fewer clutches) occasioned by increased sea surface temperature (Chaloupka et al. 2008; Mazaris et al. 2008; Mazaris et al. 2009).
Post–hatchling Loggerhead Sea Turtles in the northwest Atlantic migrate offshore and become associated with convergence zones, such as Sargassum habitats and driftlines (Carr 1986; Witherington 2002). Loggerhead Sea Turtles use the North Atlantic gyre, and enter the northeast Atlantic and the Mediterranean Sea, including the waters around the Azores and Madeira (Carr 1987; Bolten 2003; Carreras et al. 2006; Eckert et al. 2008). Oceanic juveniles are also found in Canadian waters and in offshore waters adjacent to Canadian jurisdiction (Bleakney 1965; Ladzell 1980; Witzell 1999; Javitech 2002; Javitech 2003; Bowen et al. 2005; LaCasella et al. 2006; Ledwell 2007; McAlpine et al. 2007; Brazner and McMillan 2008; James pers. comm. 2009; Lawson pers. comm. 2009).
Juvenile Loggerhead Sea Turtles in neritic zones are found from Cape Cod Bay, Massachusetts south through the Gulf of Mexico. Estuarine waters in the United States comprise important inshore habitat (e.g., Long Island Sound, Chesapeake Bay, Pamlico and Core Sounds, Mosquito and Indian River Lagoons, Biscayne Bay, Florida Bay, and embayments fringing the Gulf of Mexico) (Conant et al. 2009).
Relatively enclosed, shallow water estuarine habitats with limited ocean access are less frequently used by non–nesting adult Loggerhead Sea Turtles in the neritic zone (Conant et al. 2009). Estuarine areas with more open ocean access (e.g., Chesapeake Bay) are used by both juveniles and adults (Conant et al. 2009). Shallow water habitat with large expanses of open ocean habitat (e.g., Florida Bay), provide important, year–round resident foraging areas for male and female adult Loggerhead Sea Turtles (Conant et al. 2009). Adult Loggerhead Sea Turtles primarily inhabit the continental shelf waters from New York south through the Gulf of Mexico in the offshore (Conant et al. 2009). There is also some evidence of seasonal use of mid–Atlantic shelf waters (Hawkes et al. 2007), and possibly also of Canadian waters (n=2) (Brazner and McMillan 2008).
Important foraging areas for juvenile Pacific Loggerhead Sea Turtles include the waters of the central North Pacific, including the Kuroshio Extension Bifurcation Region (Polovina et al. 2004, 2006) and coastal waters of Baja California Sur, Mexico (Bowen et al. 1995; Pitman 1990; Nichols et al. 2000; Peckham and Nichols 2003; Peckham et al. 2007). The East China Sea is important habitat for post–nesting adult female Loggerhead Sea Turtles, who make seasonal breeding migrations between the feeding grounds and nesting beaches (Iwamoto et al. 1985; Kamezaki et al. 1997; Conant et al. 2009).
A 10–yr satellite–telemetry study of Loggerhead Sea Turtles (n=186) conducted in the North Pacific demonstrated that the animals occurred between 150°E–130°W longitude and 27°N–44°N latitude (Kobayashi et al. 2008). Loggerheads were found in water temperatures ranging from 14.45°C to 19.95°C and where surface chlorophyll a is between 0.11 mg/m³ to 0.31 mg/m³ (Kobayashi et al. 2008). Chlorophyll a preferences suggest that the Transition Zone Chlorophyll Front (TZCF) is an important Loggerhead Sea Turtle foraging habitat (Kobayashi et al. 2008). The TZCF is thought to be a zone of surface convergence that would concentrate the buoyant surface prey of Loggerhead Sea Turtles (Polovina et al. 2001; Parker et al. 2005; Kobayashi et al. 2008).
Figure 8. Loggerhead Sea Turtles: Developmental stages (juveniles vs. adults); ecological stages (obligatory epipelagic vs. opportunistic amphi–habitat); habitats (epipelagic vs. benthic); and oceanographic zones (oceanic vs. neritic). Rectangle width represents the total of the population at a given age. From Casale et al. 2008.
The data required to determine habitat trends over the last three generations (>100 years) are not available. The following is a consideration of those factors that currently affect, or are likely to affect in the future, the loss of habitat area or quality. The factors affect both the North Atlantic and North Pacific populations of Loggerhead Sea Turtles. Although Loggerhead Sea Turtles do not nest in Canada, a discussion of the nesting habitat is relevant; Loggerhead Sea Turtles found in Canadian waters hatch and reproduce on nesting beaches.
The main factors affecting Loggerhead Sea Turtle nesting habitat are:
Coastal development and construction, such as the construction of roads, buildings, harbours and breakwaters, alter nesting habitat to some degree, usually making it less suitable for nesting females, egg incubation and/or hatchling emergence (Mrosovsky et al. 1995; NMFS and USFWS 2008; Conant et al. 2009).
Beachfront “armouring” (rigid structures placed parallel to the shoreline, such as seawalls, bulkheads, soil retaining walls, and sandbags) negatively impact nesting and hatchling success for Loggerhead Sea Turtles. Fewer Loggerhead Sea Turtles make nesting attempts on armoured beaches than on non–armoured beaches (Mosier 1998). Armoured structures can block a Loggerhead Sea Turtle’s access to the upper areas of beach, causing them to nest at lower elevations than they would normally. This puts the nests at greater risk of repeated tidal inundation and erosion, which can alter thermal regimes and, thus, sex ratios (Mrosovsky and Provancha 1992; Mrosovsky 1994; Ackerman 1997; NMFS and USFWS 2008; Conant et al. 2009).
Beachfront lighting associated with coastal development disorients hatchling Loggerhead Sea Turtles and disrupts their movement from their nests to the ocean (Witherington 1997). This increases mortality from dehydration, exhaustion, predation, and anthropomorphic causes such as vehicle strikes (Ehrhart and Witherington 1987; Witherington and Martin 1996).
Coastal development can increase the number of people and vehicles on nesting beaches, causing sand compaction and nest trampling (Hosier et al. 1981; Cox et al. 1994; Hughes and Caine 1994; Kudo et al. 2003). Changes to the nesting environment from recreational beach equipment and debris affect where females can excavate nests as well as hatchlings’ progress from nest to ocean (Hosier et al. 1981; Sobel 2002; Margaritoulis et al. 2007).
Beach nourishment affects nesting success and the incubation environment. Although artificial beaches may provide more nesting habitat, their quality may be less suitable than natural beaches (Ackerman 1997; Milton et al. 1997; Ernest and Martin 1999; Conant et al. 2009). Increased sand compaction, formation of escarpments, and changes of beach profile can result from beach nourishment and have all been attributed to reduced nesting success in Loggerhead Sea Turtles (Nelson et al. 1987; Crain et al. 1995; Lutcavage et al. 1997; Steinitz et al. 1998; Ernest and Martin 1999; Rumbold et al. 2001).
Removal of native vegetation through coastal development can cause beach erosion; native dune vegetation enhances beach stability and is an integral buffer between land and sea (NMFS and USFWS 2008; Conant et al. 2009).
The planting or invasion of non–native vegetation that does not stabilize the beach environment can lead to increased erosion and the degradation of suitable nesting habitat (Schmelz and Mezich 1988). Taller plants can increase shading and alter natural sex ratios of hatchlings (Mrosovsky et al. 1995). Non–native plants may also form root mats that are so dense they prevent females from excavating nests properly and/or may trap hatchlings trying to emerge from nests (NMFS and USFWS 2008; Conant et al. 2009).
Climate change will increase the erosion rate along nesting beaches as a result of factors such as rising sea levels, and the increase of storm frequency and/or changes in prevailing currents (Antonelis et al. 2006; Baker et al. 2006). In low–lying nesting areas, erosion will cause the sea to inundate nesting sites and decrease available nesting habitat (Daniels et al. 1993; Fish et al. 2005; Baker et al. 2006). In addition, climate change may also affect Loggerhead Sea Turtle sex ratios because the species exhibits temperature–dependent sex determination. Increasing global temperatures may result in warmer incubation temperatures and, therefore, highly female–biased sex ratios (Mrosovsky and Provancha 1992; Davenport 1997; Glen and Mrosovsky 2004; Hawkes et al. 2009).
Factors that affect the quality of the Loggerhead Sea Turtle marine habitat include:
Direct alteration of bottom habitat from activities such as bottom trawl and dredge fishing, channel dredging and sand extraction (Conant et al. 2009). The effects of trawling and dredging on the marine environment have been likened to the effects of clear cutting forests on the terrestrial environment (Watling and Norse 1998). There is evidence that mobile fishing gear results in short– and long–term changes to the composition of benthic communities, including species groups on which Loggerhead Sea Turtles forage (Gordon et al. 1998).
Where foraging areas coincide with fishing zones, the incidental capture of Loggerhead Sea Turtles and/or the harvest of fish populations (affecting predator–prey interaction) change the ecosystem. Bycatch of Loggerhead Sea Turtles is the major threat to the species survival (see Limiting Factors and Threats). There is evidence that alterations in prey availability affect the Loggerhead Sea Turtle diet (Seney and Musick 2007).
Indirect alteration of habitat by marine pollution, including contamination from herbicides, pesticides, chemical spills, oil spills, and tar balls, as well as direct sewage discharge (Vargo et al. 1986; Lutz and Lutcavage 1989; Lutcavage et al. 1995; Tomás et al. 2002; Conant et al. 2009).
In all life stages, Loggerhead Sea Turtles ingest pieces of marine debris, such as plastic or Styrofoam (Lutcavage et al. 1997). Loggerhead Sea Turtles likely ingest these materials because they mistake them for prey items. The effect of ingesting marine debris can be lethal or non–lethal, and cause side effects that may increase the probability of death (Balazs 1985; Carr 1987; McCauley and Bjorndal 1999; Witherington 2002; Mrosovsky et al. 2009).
Climate change and the associated rise in sea surface temperatures may result in trophic level alterations that could affect the abundance and/or distribution of Loggerhead Sea Turtle prey (Conant et al. 2009).
The Loggerhead Sea Turtles’ habitat in Canada receives some protection from the Fisheries Act. The federal government fulfills its constitutional responsibilities for sea coast and inland fisheries through the administration of the Fisheries Act. The Act provides Fisheries and Oceans Canada (DFO) with powers, authorities, duties and functions for the conservation and protection of fish and fish habitat (as defined in the Fisheries Act) essential to sustaining commercial, recreational and Aboriginal fisheries.
Loggerhead Sea Turtle habitat also receives some protection from the Oceans Act. The Oceans Act provides for DFO to establish Marine Protected Areas (MPAs) to protect and conserve important fish and marine mammal habitats, including some Loggerhead Sea Turtle habitat. The Gully Marine Protected Area, approximately 200 km off Nova Scotia (Department of Justice Canada 2004) includes some loggerhead habitat.
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