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


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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    • "When birds specialize on particular prey items at these stopover areas, they become vulnerable to changes in the food base (Skagen 2006, Niles et al. 2009). For example, Red Knots (Calidris canutus) that forage on horseshoe crab eggs (Limulus polyphemus; Tsipoura and Burger 1999, Karpanty et al. 2006) have experienced substantial population declines as a result of human overexploitation of horseshoe crabs (Niles et al. 2009). The Semipalmated Sandpiper (C. "
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    ABSTRACT: Molecular scatology and next-generation sequencing identified previously unknown linkages among ecosystems in the diet of Semipalmated Sandpipers (Calidris pusilla) in the Bay of Fundy, Canada. During their annual migratory stopover, sandpipers consumed a wider range of prey items than previously thought, suggesting that they are not selecting for the amphipod Corophium volutator, and are acting as generalist foragers. Our analysis identified several novel prey items – arachnids, crabs, bivalves, several terrestrial and freshwater insect species, ctenophores, cnidarians, and fish (likely eggs or juveniles) – indicating that sandpipers consume prey from marine, freshwater, and terrestrial ecosystems. Connections between sandpipers and freshwater as well as terrestrial ecosystems were previously unknown in the Bay of Fundy. Current conservation efforts directed towards sandpipers focus on beach and intertidal habitats; however, we may also need to consider the surrounding freshwater and terrestrial habitat.
    Full-text · Article · Apr 2016 · The Auk
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    • "The models were used to predict Red Knot population viability (Baker et al. 2004) and to compare harvest actions and predict the effects on crab and knot populations (Sweka et al. 2007, McGowan et al. 2011a, Smith et al. 2013). Harvest management decisions in Delaware Bay have been chiefly driven by the core hypothesis that horseshoe crab egg abundance governs Red Knot weight gain during migratory stopover, and that Red Knot annual survival and reproduction are dependent on weight gain during stopover in Delaware Bay (Niles et al. 2009, McGowan et al. 2009, 2011a). However, multistate mark–recapture and mark–resight analyses concluded that although horseshoe crab spawning abundance does affect knot weight gain in Delaware Bay, stopover departure weight only weakly affects annual survival (McGowan et al. 2011b). "
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    ABSTRACT: Predictive population modeling contributes to our basic scientific understanding of population dynamics, but can also inform management decisions by evaluating alternative actions in virtual environments. Quantitative models mathematically reflect scientific hypotheses about how a system functions. In Delaware Bay, mid-Atlantic Coast, USA, to more effectively manage horseshoe crab (Limulus polyphemus) harvests and protect Red Knot (Calidris canutus rufa) populations, models are used to compare harvest actions and predict the impacts on crab and knot populations. Management has been chiefly driven by the core hypothesis that horseshoe crab egg abundance governs the survival and reproduction of migrating Red Knots that stopover in the Bay during spring migration. However, recently, hypotheses proposing that knot dynamics are governed by cyclical lemming dynamics garnered some support in data analyses. In this paper, I present alternative models of Red Knot population dynamics to reflect alternative hypotheses. Using 2 models with different lemming population cycle lengths and 2 models with different horseshoe crab effects, I project the knot population into the future under environmental stochasticity and parametric uncertainty with each model. I then compare each model's predictions to 10 yr of population monitoring from Delaware Bay. Using Bayes' theorem and model weight updating, models can accrue weight or support for one or another hypothesis of population dynamics. With 4 models of Red Knot population dynamics and only 10 yr of data, no hypothesis clearly predicted population count data better than another. The collapsed lemming cycle model performed best, accruing ∼35% of the model weight, followed closely by the horseshoe crab egg abundance model, which accrued ∼30% of the weight. The models that predicted no decline or stable populations (i.e. the 4-yr lemming cycle model and the weak horseshoe crab effect model) were the most weakly supported.
    Full-text · Article · Nov 2015 · The Condor
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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). "
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    ABSTRACT: Horseshoe crabs are living fossils known to occur along the north-east coasts of Indian mainland. Although they are exploited for various reasons, there was no information about their status and distribution in the recent past. In this connection, a survey of breeding habitats of horseshoe crabs along the Odisha coast and the adjoining coastal stretch of West Bengal (WB) and Andhra Pradesh (AP) was carried out during December 2005 to June 2007 to document their status and threats. Preliminary interviews and secondary data were also used to confirm their potential breeding habitat. During May-June of 2006 and 2007, daily monitoring of five sites for a fortnight and monthly surveys of the rest of the coast provided a lower bound of ~4000 individuals/season for Odisha coast. Densities were higher at beaches near river mouths, ranging from 60 to 100 individuals/km/season in northern and central Odisha coast, and 15-20 individuals/km/season in southern Odisha, while it was as low as ~10 individuals/km along WB and AP coasts. Sightings and incidental catch in experimental fishing net indicated the presence of two species of horseshoe crabs in inshore coastal waters. Fishery-related mortality was documented to be the major threat with the stranding of nearly 1000 dead horseshoe crabs/season, but depredation of by wild and feral animals such as wild boars, jackals and feral dogs was also wide spread. Conservation efforts need to address these issues and also coastal development especially at selected breeding habitats which support relatively high densities of horseshoe crabs.
    Full-text · Chapter · Aug 2013
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