Conservation and Ecology of Marine Reptiles

MARE 490Dr. Turner

Summer 2011

Variation in Life History PatternsSea turtles – slow growing & long lived

Complex life history patterns

Diversity of ecosystems – terrestrial (oviposition & embryonic development), neritic, coastal, & oceanic zones (developmental & foraging habitats)

TerminologyStandard oceanographic terminology

Neritic zone – inshore marine environment from surface to sea floor; <200m

Oceanic zone – vast ocean environment from surface to sea floor; >200

Pelagic – if occupy water columns

Epipelagic – if occupy upper 200m

Benthic or demersal – ocean floor

Variation in Life History PatternsThree primary life history patterns-

Characteristics of developmental stages (oceanic & neritic) and adult foraging patterns (oceanic & neritic) are primary differences that distinguish

Sea Turtle Life History PatternsOnce hatchlings emerge from their nests, crawl down the beach, and enter the ocean

3 types of basic life history patterns:

Type 1: Complete development in neritic zone

Type 2: Early juvenile development in oceanic & later juvenile development in neritic zone

Type 3: Complete development in oceanic

Type 1: Neritic PatternDevelopment & adult stages in neritic

Flatback only extant example

Hatchlings are larger than other chelonids60 vs. 41-50mm; 39 vs. 15-25g

Clutch size smaller

Suggests ↑ food resources in neritic but tradeoff of ↑ predation; but “Bigger is better”

Type 1: Neritic Pattern

Type 2: Oceanic-Neritic PatternEarly development oceanic - later neritic

Best known loggerhead, also green (black?), hawksbill, Kemp’s ridley; possibly Olive

Move to oceanic after hatching for several years; 7-11.5 in loggerhead

Recruit back to neritic before maturity; often slow transition from oceanic

Return to oceanic for migration

Type 2: Oceanic-Neritic Pattern

Type 3: Oceanic PatternDevelopmental & Adult in oceanic zone

Leatherback & Olive Ridley

Little known about juvenile life history – thought to be oceanic

Very different species physiologically

Olive - spend large portion at surface (>20%)

Type 3: Oceanic Pattern

Habitat Utilization &Migration

Habitat Utilization &MigrationGeneralized habitat model for sea turtles based upon ontogenetic stages

1. Early juvenile nursery habitat (pelagic or oceanic)2. Later juvenile development habitat (demersal & neretic)3. Adult foraging habitat4. Adult inter-nesting and/or breeding habitat

Juvenile Nursery Habitats1st year known as “Lost year” as hatchlings migrate to the offshore environment and do not return to the neritic environment until they have grown into much larger juveniles

Assumed that time is spent exclusively in offshore/pelagic habitats

Early Juvenile LoggerheadsBest documented – typically associated with oceanic convergence zones - Sargassum habitat

Thought to be “lost decade” instead of “lost year” due to extreme duration in the pelagic environment

Later Juvenile LoggerheadsRecruit from oceanic to neritic after 7-10y; 25-30cm

Strong site fidelity once recruited

Return to same foraging sites after nesting

Often brumate in winter (semi-hibernation state in which a reptile sleeps a majority of the time, and eats very little)

Early Juvenile Kemp’s RidleyTypically spend first two years at sea

Move throughout the Gulf of Mexico and into South Atlantic (> 29%)

If such a large population utilizes the Atlantic then must be able to efficiently return to the GOM

No info on Olive RidleysFlatback lack pelagic stage

Later Juvenile Kemp’s RidleyRecruit from oceanic to demersal neritic at 20-25cm

Throughout Gulf of Mexico, Atlantic as far north as New York

Bays are important habitats; Chesapeake, Mobile, Galveston

Juvenile Olive RidleyNothing known about early juvenile nursery area – probably pelagic & oceanic

Little known about later juvenile habitats may use either coastal or oceanic

Juvenile FlatbackLack oceanic stage – juveniles spend entire life history in coastal neritic waters

Early Juvenile GreenSwim continuously for first 24 hrs

Strong counter-coloration patterns in hatchlings/juveniles

Recruit to neritic environment at a smaller size then loggerheads – less than 2 yrs

Loggerhead Green

Later Juvenile GreenRecruit to demersal habitat at 30-40cm

Typically coral reefs, rocky shore, or seagrass meadows

Tropical-subtropical estuaries

Early Juvenile HawksbillSome remain on local reefs

Those recruiting back to neritic systems are smaller than greens & loggerheads < 1-3 yrs

Recruit at small size20-25cm

Later Juvenile HawksbillRestricted to tropical systems more than any other sea turtle

Shallow coral reefs & mangroves – both abundant with sponges

Strong site fidelity

Early Juvenile LeatherbackMove to pelagic environments immediately

Disappear to oceanic environment for 4 years based upon growth rates

Need to consumer bodyweight/day in gelatinous prey

Later Juvenile LeatherbackThought to be tied to upwelling to support high biomass of gelatinous prey

Remain in pelagic waters as adults

SurvivorshipNatural selection will favor those nesting locations with the highest survivorship during the early juvenile stage

Most important determination of nesting beach location is survivorship of hatchlings and small juveniles in the nursery habitats

SurvivorshipAs with fishes – number & diversity of predators & resulting mortality rates and inversely proportional to size of the juvenile

“Bigger is Better”

Advantage of pelagic-oceanic nurseries: low density of predatory fishes & birds due to low primary production

Adult Migration & Habitat UseExhibit longest migrations of any reptile

Hundreds to thousands of miles between feeding & breeding areas

Inter & intraspecific variation in migratory behavior in extant turtles

Probably parallel in potential navigation systems employed

LeatherbackWidely distributed throughout the world’s oceans

Highly migratory, capable of transoceanic migrations

Elusive, little known about migrations

Olive RidleyCircumtropical distribution; Atlantic, Pacific, & Indian Oceans

Little known about migrations

Spends non-breeding life cycle in oceanic zone

Occupy neretic zones during breeding seasons

Kemp’s RidleyRelatively restricted range – neritic zone of Gulf of Mexico & Atlantic

Swim through shallow coastal waters along US & Mexico

Arribadas occur every 28 days

HawksbillDistributed through tropical waters of Atlantic, Pacific, & Indian Oceans

Associated with hard-substrate community such as coral reefs – spongivory

Once thought to be non-migratory; some migrate vast distances

Locally some only migratealong the Big Island

FlatbackMost restricted migratory range of all sea turtles

Endemic to tropical waters of Australian continental shelf

Once thought non-migratory; now known long-distance migrations

LoggerheadOccur in subtropical & temperate waters across continental shelves & estuarine areas in Atlantic, Pacific, & Indian Oceans

Nearshore & inshore waters

Highly migratory, hundreds to thousands of Km between feeding & breeding

Occur in tropical & subtropical waters of Atlantic, Pacific, & Indian Oceans

Nearshore & inshore waters; forage on sea grasses & algae

Oceanic habitat between foraging & breeding areas

Locally between MHI & NWHI

Green

BlackRestricted to coastal waters, lagoons, & bays along W. coast of US to S. Peru

Feed on seagrass & algae

Nest in Central America & Mexico

Adult Migration & Habitat UseDistinct migratory patterns which are different than developmental patterns

Best understood in context of location & size of foraging area

Migrating behavior & navigation systems still much unknown

Adult Migration & Habitat Use1st pattern: Migrate to oceanic waters where they forage over very broad areas

Very spatially & temporally variable; unpredictable (Leatherback & Olive Ridley)

Adult Migration & Habitat Use2nd pattern:Migrate to highly productive neritic foraging areas located on continental shelves

(Kemp’s Ridley, Loggerhead, Flatback)

Adult Migration & Habitat Use3rd pattern:Migrate to well-established, fixed foraging areas located nearshore

Relatively small foraging area & virtually no spatial or temporal variation exists (green & hawksbill)