SEA TURTLES Of Delaware Bay
SEA TURTLES Of Delaware Bay
James R. Spotila Pamela Plotkin John Keinath
The Magnificent Seven Green Turtle
Herbivore-eats sea grasses and algae
Hawksbill
Spongivore
Loggerhead
A carnivore
Olive Ridley
A carnivore
A carnivore
Kemp’s Ridley
Flatback A carnivore
Only in Australia
Leatherback
Jelly-vore
Loggerhead
Kemp’s Ridley
Delaware Bay and Sea Turtles • Juvenile sea turtles in Bay June- October • Rich source of crabs and other invertebrates • Genetic studies – loggerheads along northeastern states nest in Mexico, Florida, Georgia and South Carolina
• Satellite Telemetry – Wassaw Island Georgia to mouth of Delaware Bay
Methods • Aerial Surveys
June- August 1997
– Cessna 172 • 100-224 mph • 300-500 ft above sea level
• In-Water Captures June- September 1997 – Tangle nets • • • • •
100 yd x 8 ft x 10 in mesh 100 yd x 30 ft x 6 in mesh Large bullet surface floats Retrieved every 30 minutes 25 ft Parker boat
• Sea Turtle Sighting Survey – Public users
Aerial Surveys Four transect lines Two observers One data recorder (+ pilot) Strip transect 300 m wide June- August 1997 Locations of turtles Species Time Strip transect estimates of density (Epperly et al 1995)
Sea Turtle Sighting Survey • Posters • Return post cards • Locations in New Jersey and Delaware
Close up of Response Card
Aerial Surveys • June – 10 loggerheads • July – 9 loggerheads • August- 14 loggerheads • Density- 21-33 turtles/100 km2
Red dots- June Yellow dots- July Blue dots- August
Red dots- June Yellow dots- July Blue dots- August
Turtles were found near shipping channel Question- What happens in fall and winter?
In Water Captures • • • •
2 nets on 21 days 103 hours Observed 10 loggerheads (2 juveniles) Captured 2 live male loggerheads – 90 and 108.2 cm
• Found ½ of dead loggerhead floating in water
Public Sea Turtle Sightings • 60 postcard responses – Most were recreational fishermen from lower Bay – A few sightings from Cape May- Lewes Ferry
• 65 turtles • 57 loggerheads • 4 hawksbills- probably small loggerheads or Kemp’s Ridleys- spit out bait and hissed • 2 green turtles- probably loggerheads • 2 not identified to species • 12 of 65 turtles were caught by fishermen- 18.5%
Sea Turtle Density Location • • • • • •
Density (turtles/100 km2)
Delaware BayLower Chesapeake BayMid Chesapeake BayPamlico SoundCore SoundSouthern Georgia-
21-33 0-57 0-8.5 0-6.5 0-30 0-62
Conclusions 1. Density of turtles is comparable or greater than in southeastern US 2. Lower Delaware Bay provides important habitat for loggerheads 3. Significant numbers of sea turtles are incidentally hooked by recreational fishermen 4. Many turtles swim in and around the shipping channel 5.Collision with boats and propellers may be a threat to turtles 6.Benthic trawling may be a significant threat to sea turtles in the Bay 7.Decline of horseshoe crabs threatens the food supply for these turtles.
There is a serious need for more data about sea turtles in Delaware Bay if we are to reduce human impacts on these species
James R. Spotila Pamela Plotkin John Keinath
The Magnificent Seven Green Turtle
Herbivore-eats sea grasses and algae
Hawksbill
Spongivore
Loggerhead
A carnivore
Olive Ridley
A carnivore
A carnivore
Kemp’s Ridley
Flatback A carnivore
Only in Australia
Leatherback
Jelly-vore
Loggerhead
Kemp’s Ridley
Delaware Bay and Sea Turtles • Juvenile sea turtles in Bay June- October • Rich source of crabs and other invertebrates • Genetic studies – loggerheads along northeastern states nest in Mexico, Florida, Georgia and South Carolina
• Satellite Telemetry – Wassaw Island Georgia to mouth of Delaware Bay
Methods • Aerial Surveys
June- August 1997
– Cessna 172 • 100-224 mph • 300-500 ft above sea level
• In-Water Captures June- September 1997 – Tangle nets • • • • •
100 yd x 8 ft x 10 in mesh 100 yd x 30 ft x 6 in mesh Large bullet surface floats Retrieved every 30 minutes 25 ft Parker boat
• Sea Turtle Sighting Survey – Public users
Aerial Surveys Four transect lines Two observers One data recorder (+ pilot) Strip transect 300 m wide June- August 1997 Locations of turtles Species Time Strip transect estimates of density (Epperly et al 1995)
Sea Turtle Sighting Survey • Posters • Return post cards • Locations in New Jersey and Delaware
Close up of Response Card
Aerial Surveys • June – 10 loggerheads • July – 9 loggerheads • August- 14 loggerheads • Density- 21-33 turtles/100 km2
Red dots- June Yellow dots- July Blue dots- August
Red dots- June Yellow dots- July Blue dots- August
Turtles were found near shipping channel Question- What happens in fall and winter?
In Water Captures • • • •
2 nets on 21 days 103 hours Observed 10 loggerheads (2 juveniles) Captured 2 live male loggerheads – 90 and 108.2 cm
• Found ½ of dead loggerhead floating in water
Public Sea Turtle Sightings • 60 postcard responses – Most were recreational fishermen from lower Bay – A few sightings from Cape May- Lewes Ferry
• 65 turtles • 57 loggerheads • 4 hawksbills- probably small loggerheads or Kemp’s Ridleys- spit out bait and hissed • 2 green turtles- probably loggerheads • 2 not identified to species • 12 of 65 turtles were caught by fishermen- 18.5%
Sea Turtle Density Location • • • • • •
Density (turtles/100 km2)
Delaware BayLower Chesapeake BayMid Chesapeake BayPamlico SoundCore SoundSouthern Georgia-
21-33 0-57 0-8.5 0-6.5 0-30 0-62
Conclusions 1. Density of turtles is comparable or greater than in southeastern US 2. Lower Delaware Bay provides important habitat for loggerheads 3. Significant numbers of sea turtles are incidentally hooked by recreational fishermen 4. Many turtles swim in and around the shipping channel 5.Collision with boats and propellers may be a threat to turtles 6.Benthic trawling may be a significant threat to sea turtles in the Bay 7.Decline of horseshoe crabs threatens the food supply for these turtles.
There is a serious need for more data about sea turtles in Delaware Bay if we are to reduce human impacts on these species
