Multispecies Modeling for Adaptive Management of Horseshoe Crabs and Red Knots in the Delaware Bay

Abstract

Adaptive management requires that predictive models be explicit and transparent to improve decisions by comparing management actions, directing further research and monitoring, and facilitating learning. The rufa subspecies of red knots (Calidris canutus rufa), which has recently exhibited steep population declines, relies on horseshoe crab (Limulus polyphemus) eggs as their primary food source during stopover in Delaware Bay during spring migration. We present a model with two different parameterizations for use in the adaptive management of horseshoe crab harvests in the Delaware Bay that links red knot mass gain, annual survival, and fecundity to horseshoe crab dynamics. The models reflect prevailing hypotheses regarding ecological links between these two species. When reported crab harvest from 1998 to 2008 was applied, projections corresponded to the observed red knot population abundances depending on strengths of the demographic relationship between these species. We compared different simulated horseshoe crab harvest strategies to evaluate whether, given this model, horseshoe crab harvest management can affect red knot conservation and found that restricting harvest can benefit red knot populations. Our model is the first to explicitly and quantitatively link these two species and will be used within an adaptive management framework to manage the Delaware Bay system and learn more about the specific nature of the linkage between the two species.

Conservation status of the American horseshoe crab, (Limulus polyphemus): a regional assessment

“…Several efforts have occurred to develop horseshoe crab population models useful for assessing population viability (Gibson and Olszewski 2001;Grady and Valiela 2006;Davis et al 2006;Sweka et al 2007;McGowan et al 2011b;Smith et al 2013). Modeling studies have focused on horseshoe crab populations in Rhode Island (Gibson and Olszewski 2001), Cape Cod , and Delaware Bay (Davis et al 2006;Sweka et al 2007;McGowan et al 2011b;Smith et al 2013).…”

“…Harvest for the marine life aquaria trade or scientific and educational collection is small in comparison to other uses, but is significant in Florida where juveniles are collected in large numbers (Gerhart 2007). Substantial evidence suggests that overharvest can result in depleted populations and localized extirpations (Widener and Barlow 1999;Carmichael et al 2003;Rutecki et al 2004;Schaller et al 2005;Gerhart 2007;Smith et al 2009b;McGowan et al 2011b). …”

“…Modeling studies have focused on horseshoe crab populations in Rhode Island (Gibson and Olszewski 2001), Cape Cod , and Delaware Bay (Davis et al 2006;Sweka et al 2007;McGowan et al 2011b;Smith et al 2013). All analyses concluded that while high harvest results in population depletion, some Additional details can be found in Sweka et al (2013: Appendix B) Rev Fish Biol Fisheries (2017) 27:135-175 159 levels of reduced harvest can be compatible with maintenance of a viable population.…”

“…New Jersey instituted a complete moratorium on harvesting horseshoe crabs from state waters in 2006, and this ban remains in effect. In February 2012, the ASMFC Horseshoe Crab Management Board approved Addendum VII, which provides for managing harvest of Delaware Bay-origin animals via an Adaptive Resource Management (ARM) framework, wherein annual harvest is derived via a suite of multispecies models and an optimization process which takes into account many biological variables, including the status of the horseshoe crab population and the red knot population (ASMFC 2009;McGowan et al 2011bMcGowan et al , 2015. The ARM framework also defines monitoring programs and procedures to update the modeling structure and parameterization including uncertainty.…”

The Role of Horseshoe Crabs in the Biomedical Industry and Recent Trends Impacting Species Sustainability

“…Once in the Delaware Bay, red knots and other shorebirds feed predominantly on the eggs laid by spawning horseshoe crabs while they are available (Tsipoura and Burger, 1999;Mizrahi and Peters, 2009;McGowan et al, 2011;Smith et al, 2013). It is unlikely that other food sources found at shorebird stopover sites would be as widely available or as nutritionally dense as horseshoe crab eggs (Mizrahi and Peters, 2009).…”