The Use of the Inland Bays Beaches as Horseshoe Crab (Limulus Polyphemus) Nesting Sites

Date
2009-05
Authors
McCole, Kathleen
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Publisher
University of Delaware
Abstract
Horseshoe crabs are important creatures. They support the whelk and eel fisheries, provide an important food source for migrating shorebirds, and are important to the biomedical industry. All three of these industries contribute approximately $35.7 to $48 million annually to the region. Therefore, it is important to monitor and conserve their population. For eight years, spawning counts have occurred on 24 Delaware Bay beaches (DE and NJ). However, the objective of this project was to determine if beaches in the Inland Bays, Delaware, are important nesting sites for the American horseshoe crab (Limulus polyphemus). Using established methods, I performed spawning counts on James Farm Beach in Indian River Bay at Full and New Moon periods in the summers of 2007 and 2008. In addition, I counted spawning adults on beaches at Camp Arrowhead, Holts Landing/Ellis Point, and Bay Colony in 2008. I compared numbers of spawning adults per meter of shoreline for these four Indian River Bay beaches to spawning adult counts performed on Delaware Bay beaches in 2008. Data from James Farm, with many samples recording 7 or more horseshoe crabs per meter, were within range, and even surpassed some from the Delaware Bay‟s beaches. In addition, I performed egg counts on Holts Landing and James Farm in the summer of 2007 and the summer and fall of 2008. I then compared these data to one another, as well as to previous egg counts from beaches in the Delaware Bay in 1999 and in 2006. Although it was difficult to compare the numbers of eggs per square meter from different years, the numbers of eggs per square meter at James Farm and Holts Landing, roughly 200,000 per square meter were comparable to values from Delaware Bay beaches. In addition, I performed egg counts on James Farm and Holts Landing/Ellis Point in November of 2008, and I found eggs and larvae thriving in the sand, and I believe that they may “over-winter”. I recommend that sampling methodologies for spawning adult and egg be modified by sampling on more Inland Bays beaches, extending the counts into July, and increasing sample sizes. These data indicate that beaches in Indian River Bay do support spawning activity and larval productivity comparable to better known and studied beaches in Delaware Bay. These results provide a stepping stone for research determining whether the Inland Bays are important breeding grounds for Mid Atlantic horseshoe crab populations, as well as to better understand the ecological and habitat value of beaches within the Inland Bays.
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