Gerald Winegrad: We can save the horseshoe crab, but it will take more work
By Gerald Winegrad
May 22, 2020 | 4:22 PM
Despite its importance to the ecosystem, the horseshoe crab has undergone a huge population crash and is just starting to recover as threats mount to its recovery.
My last column detailed the importance of this living fossil to human health and to hundreds of thousands of shorebirds relying on their green eggs in the sand, especially threatened red knots. Many other species depend on this ancient mariner including endangered loggerhead sea turtles and rockfish.
These harmless ancient mariners were taken by the millions while spawning on Delaware Bay beaches from the 1850s well into the 20th century and used for fertilizer and livestock feed. That slaughter has been replaced by bait harvest starting in the 1990s, primarily for conch and to a lesser extent, for eels and catfish. This over-harvesting reached 2.6 million crabs in 1999 and significantly reduced crab and Red Knot populations.
Through concerted efforts of the conservation community which I proudly helped lead, such killing for bait has been reduced to an average 842,790 mostly male crabs annually from 2013 to 2018. That’s still 5 million crabs whose harvest is impeding recovery efforts for the crab and Red Knot and likely other shorebirds. Sadly, Maryland has allowed 877,257 crabs to be killed during this period, mostly by trawls in the Atlantic. The majority of these crabs were from Delaware Bay stock thus impeding recovery. Maryland, Virginia, and Delaware should follow New Jersey’s lead and stop this slaughter as New Jersey did in closing its substantial crab harvest in 2007.
Biomedical companies capture these armored arthropods, targeting larger females to bleed for production of Limulus Amoebocyte Lysate (LAL), which detects endotoxins in injectable drugs, intravenous devices, and surgical implants. This saves human lives but comes at a cost to the crabs as an estimated 15% of the crabs perish.
Biomedical harvest substantially increased from 130,000 crabs in 1989 to an average of 536,829 annually from 2009-2018. This means 805,244 crabs were killed over 10 years. An annual mortality limit was set by the Atlantic States Marine Fishery Commission (ASMFC) of 57,500 which has been exceeded every year since 2007 except in 2016. The ASMFC was to take action each year to lower this mortality but has failed to do so.
Conservationists are pushing the biomedical industry to use a synthetic agent instead of LAL called rFC which has been approved by the FDA. The industry’s switch is being led by the pharmaceutical giant Eli Lilly, which began using rFC to test its new products in 2016. Lilly expects to end LAL use.
Loss of suitable sandy beach habitat from shoreline development and erosion on Delaware Bay beaches threatens crab populations. These beaches are critical for successful crab reproduction but are severely disturbed by shoreline protection structures such as bulkheads, seawalls, and rip-rap (placement of large boulders). This minimizes potential spawning sites and creates death traps for crabs. In 1986, an estimated 200,000 stranding mortalities occurred on New Jersey beaches. Increased use of jetties and residential development also affects breeding.
Beaches are moving landward associated with erosional events aggravated by global warming and sea-level rise. New Jersey and Delaware beaches along the shores of Delaware Bay have eroded at rates averaging 3 to 5 feet per year over a century compared to Chesapeake beaches averaging 1 foot per year. Hurricane Sandy’s flooding and erosion destroyed at 50% of crab egg-laying habitat along Delaware Bay beaches.
The reTURN The Favor program has rescued 500,000 horseshoe crabs since 2013 on New Jersey’s Bay shoreline during May and June spawning. The crabs are either caught in rip-rap or other impingements or flipped on their backs where many die. Volunteers rescue the crabs and place them correct-side up.
Horseshoe crabs feed on many benthic macrofauna primarily blue mussels and surf clams. Recent declines in mid-Atlantic surf clams are being attributed to climate change increases in water temperatures. This decline may affect crab populations.
Red tide events may result in significant mortality, especially to juveniles inhabiting intertidal areas and tidal flats. Oil spills also are of concern
Fishery bycatch and discard is an emerging issue threatening horseshoe crabs. This mortality occurs when trawlers, dredgers, and gillnetters catch the crabs and discard them while fishing for other species. Preliminary data suggest that such bycatch/discard mortality may be comparable to or greater than mortality from bait landings and biomedical collection. The ASMFC concluded that the magnitude of such bycatch/discard mortality is the greatest uncertainty and highest research priority for horseshoe crab management. This should force actions to curtail it and also to reduce bait harvest and biomedical mortality.
The indomitable Limulus Polyphemus has existed for 400 million years, surviving five great extinctions. Let us show respect for our elders and work to assure that it survives the sixth great extinction, the only one caused by humans.