Effects of Horseshoe Crab Harvest in Delaware Bay on Red Knots: Are Harvest Restrictions Working?

[ "Clive D. T. Minton is with the Victoria Wader Studies Group in Melbourne, Australia. R. I. Guy Morrison is a research scientist (National Wildlife Research Centre, Carleton University), and R. Ken Ross is head of the population management unit (Ontario Region, Ottawa), with the Canadian Wildlife Service."]
BioScience (Impact Factor: 5.38). 02/2009; 59(2):153-164. DOI: 10.1525/bio.2009.59.2.8

ABSTRACT Each May, red knots (Calidris canutus rufa) congregate in Delaware Bay during their northward migration to feed on horseshoe crab eggs (Limulus polyphemus) and refuel for breeding in the Arctic. During the 1990s, the Delaware Bay harvest of horseshoe crabs for bait increased 10-fold, leading to a more than 90% decline in the availability of their eggs for knots. The proportion of knots achieving weights of more than 180 grams by 26–28 May, their main departure period, dropped from 0.6–0.8 to 0.14–0.4 over 1997–2007. During the same period, the red knot population stopping in Delaware Bay declined by more than 75%, in part because the annual survival rate of adult knots wintering in Tierra del Fuego declined. Despite restrictions, the 2007 horseshoe crab harvest was still greater than the 1990 harvest, and no recovery of knots was detectable. We propose an adaptive management strategy with recovery goals and annual monitoring that, if adopted, will both allow red knot and horseshoe crab populations to recover and permit a sustainable harvest of horseshoe crabs.

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Available from: R. I. Guy Morrison, Aug 27, 2015
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    • "Their breeding habit and habitat being peculiar, they are vulnerable to mortality often on the beach. In Delaware Bay of North America, the number of horseshoe crabs on some beaches decreased by 90 % in 5 years (Lawrence et al. 2009). In Japan, it is estimated that only 2,000 to 4,000 horseshoe crabs are left and is now considered as a national monument (Seino et al. 2003). "
    Ecology and Conservation of Tropical Marine Faunal Communities., Edited by K. Venkataraman, C. Sivaperuman, C. Raghunathan, 01/2013: chapter Assessment of the population status and threats to the Horseshoes along the northern East Coast of India: pages 137-146; Springer-Verlag Berlin-Heidelberg.
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    • "Red knots are an indicator for the overall health of the migrant shorebirds in Delaware Bay [20]. Red knots can live up to 25 years, but very few live more than 7 years [57] "
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    ABSTRACT: With a worldwide increase in attention toward developing a reliance on renewable energy, there is a need to evaluate the effects of these facilities (solar, wind, hydropower) on ecosystems. We conduct a hazard and risk evaluation for three species of birds that are listed, or candidates for listing, as federally threatened or endangered in the US, and that might occur offshore on the Atlantic Outer Continental Shelf (AOCS) where wind power facilities could be developed. Our objectives were to: 1) provide conceptual models for exposure for each species, and 2) examine potential exposure and hazards of roseate tern (Sterna dougallii) and piping plover (Charadrius melodus, both federally endangered in the US) and red knot (Calidris canutus rufa, candidate species) in the AOCS. We used a weight-of-evidence approach to evaluate information from a review of technical literature. We developed conceptual models to examine the relative vulnerability of each species as a function of life stage and cycle (breeding, staging, migratory, wintering). These methods are useful for conducting environmental assessments when empirical data are insufficient for a full risk assessment. We determined that 1) Roseate terns are likely to be exposed to risk during the migratory and breeding season when they occur in the AOCS, as well as while staging. 2) Piping plovers are not likely to be at risk during the breeding season, but may be at risk during spring or fall migrations. Risk to this species is likely to be low from turbines located far from land as this species migrates mainly along the coast. 3) Red knots are potentially exposed to some risk during migration, especially long-distance migrants whose migratory routes take them over the AOCS. More information is required on exact spatio-temporal migration routes, flight altitudes (especially during ascent and descent), and behavioral avoidance of turbines by birds to ascertain their risk.
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    • "L. polyphemus eggs are the primary food for up to 1 million shorebirds which stage in the Delaware Bay during migration from overwintering locations in South America to breeding locations in the Arctic. Large population declines for L. polyphemus may have contributed to strong shorebird declines, especially for the American Red Knot (Calidris canutus rufa), which currently is listed as threatened under the Bonn convention (Niles et al. 2009). Limulus polyphemus populations in Florida have not been harvested to the same extent as in the mid-Atlantic region, and the direct effects of fishing are probably unimportant. "
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    ABSTRACT: Populations of the American horseshoe crab, Limulus polyphemus, have declined, but neither the causes nor the magnitude are fully understood. In order to evaluate historic demography, variation at 12 microsatellite DNA loci surveyed in 1218 L. polyphemus sampled from 28 localities was analysed with Bayesian coalescent-based methods. The analysis showed strong declines in population sizes throughout the species' distribution except in the geographically isolated southern-most population in Mexico, where a strong increase in population size was inferred. Analyses suggested that demographic changes in the core of the distribution occurred in association with the recolonization after the Ice Age and also by anthropogenic effects, such as the past overharvest of the species for fertilizer or the current use of the animals as bait for American eel (Anguilla rostrata) and whelk (Busycon spp.) fisheries. This study highlights the importance of considering both climatic changes and anthropogenic effects in efforts to understand population dynamics--a topic which is highly relevant in the ongoing assessments of the effects of climate change and overharvest.
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