The Horseshoe CrabAn Ecological Keystone in Delaware Bay

Outline

• Life history

• Ecological significance of the species

• Uses throughout history– From Native American to big industry

• Current uses and issues surrounding the species

• Ongoing research to alleviate pressures on the species

In the beginning…

• Lineage pre-dates the dinosaur era– Pre-dates flying insects– Pre-dates flowering plants

Eggs and trilobite stage

• 14 day development-hatching time

• Extremely vulnerable to predation

Juvenile stage

• Maturing to adulthood takes about 10 years and 14 molts!

• Ages 1-10 live in Delaware bay or on the continental shelf

Adulthood

The Horseshoe Crab Spawn

• Occurring primarily in Spring and Summer– Activity peaks in June– Around full and new moons

• Each female may lay up to 88,000 eggs annually

• Egg predation - the base of the food web

Ecology

• Native range from Maine

to the Yucatan

• Population centered

around Delaware Bay

• Spawn in estuaries– Need well oxygenated sandy beaches– Low energy waves

Biological Importance of the Horseshoe Crab

Biological Importance of the Horseshoe Crab

• Horseshoe crab eggs are important to migratory birds

• Red knot– Uses eggs to

refuel on their

journey to the

arctic

– 95,000 visited the Delaware bay in 1989– Only 16,000 in 2003

Early uses of the Horseshoe Crab

• Native Americans– Ate muscle tissue– Used telsons as spear tips– First to use horseshoe crabs as fertilizer

• Early Americans– 1800’s - collection for farm use as fertilizer or

hog or poultry feed

The first over-harvest

• Between 1920’s to the 1950’s harvest exploded as the fertilizer business went big

Current uses

• Population rebounded from the 50’s to the 80’s

• LAL and the medical industry

• With horseshoe crabs abundant again…– Use as bait in the eel and whelk industries in

the late 1980’s

Biomedical uses

• Limulus amebocyte lysate (LAL)– A suite of proteins that

aggressively gel in the presence of bacterial endotoxins

– Ensures the sterility of intravenous drugs and medical devices to be placed in the body

The biomedical industry is required to release the

horseshoe crabs back into the wild after bleeding. Studies show

only 10% mortality.

Declining crab populations

http://www.dnrec.state.de.us/fw/hcrabs/larry%20niles%20presentation.pdf

Inconsistent data collection

ASFMC - Horseshoe Crab 2004 Stock Assessment Report

Why the rapid decline?• While the biomedical industry catches and

releases, the eel and whelk fisheries are a 100% mortality harvest.– 1 female crab per eel pot– 1-2 male crab per whelk pot

Managing the horseshoe crab• 1998 ASMFC multi-state management plan

– No harvest limits recommended (lack of data)– DE and NJ voluntarily reduced limits

• Addendums I-III– Established a horseshoe

crab sanctuary at the mouth of the Delaware bay

– Created a quota transfers between states

– Created a closed season during peak spawning

Current harvest moratorium for both Delaware and New

Jersey waters

Ongoing research

• Artificial bait for both eel and whelk– Find out why horseshoe crabs are so effective

at catching both eel and whelk

• Core questions– Are the attractants the same for both species?– If not, isolation of the attractant from the

horseshoe crab becomes even more difficult.

Laboratory bioassays

• Whelk– Modified

trap design

• Eel– Flume

tank

design

Wate

r in

put

Dra

in

Eel

tra

ps

The road ahead

• Hope to have a preliminary bait in the water by April/May 2007– Field trials during this time to refine bait

• Attractant• Delivery matrix

Questions?Questions?