702 



Fishery Bulletin 101(3) 



15000 30000 45000 60000 15000 30000 45000 60000 

 Predicted density of egg cores 



Figure 4 



Density curves of predicted egg densities on 100-ni beach 

 segments at six New Jersey beaches. An arrow represents 

 the egg density in the observed 100-m segment. These 

 density curves were generated by dividing the area sur- 

 veyed for spawning females into 100-m segments and 

 using the observed relationship between egg densities 

 and spawning females to predict egg density for each seg- 

 ment. The beaches shown are (A) Fortescue. (B) Highs, 

 (C) Kimbles, (D) North Cape May, (E) Reeds, and (F) South 

 Cape Shore Laboraton,'. 



random sample of eight beach segments per state would 

 result in CV sO.3 for estimates of egg densities 0-20 cm 

 deep. If this level of effort were maintained, it would be 

 sufficient to detect biologically significant declines in egg 

 density over a 5- or 10-year period. However, greater effort 

 would be required to monitor change in egg densities 0-5 

 cm deep. According to results from the May samples, to 

 estimate egg densities in shallow sediment with CV sO.3, 

 a stratified random sample of 10 segments per state would 

 be required. 



Sampling eggs is a costly process; therefore sampling 

 efficiency and reducing sample size are important consider- 

 ations. Although sediment can be collected quickly, the pro- 

 cess of extracting and enumerating eggs from the sediment 

 can be time consuming. Quantifying the eggs in surface 

 sediments to assess shorebiixi forage biomass is likely to be 

 the main objective of many egg sampling studies because 

 horseshoe crab spawning activity can be assessed by other 

 methods, such as through counts of spawning horseshoe 

 crabs (Smith et al., 2002a). However, a primary finding 

 in the present study is that estimating eggs in 0-5 cm 



5 7 10 12 15 17 20 22 



Number of beaches sampled per state 



Figure 5 



Predicted coefficient of variation (CV) shown for the pos- 

 sible range of number of beaches sampled per state. This 

 figure is based on the observed levels of bay-wide density 

 during the two sampling periods in 1999. Curves are based 

 on egg densities found at different depths and time periods: 

 triangle is shallow sediment in June, circle is shallow sedi- 

 ment in May, diamond is deep sediment in June, and square 

 is deep sediment in May. Shallow sediment is to 5 cm deep, 

 and deep sediment is to 20 cm deep. 



of sediment will be more costly than estimating eggs in 

 0-20 cm of sediment. In the future, alternatives in survey 

 design, such as stratification of the beach foreshore, should 

 be considered to reduce the amount of sediment that needs 

 to be collected for precise estimates of horseshoe crab egg 

 density. 



Acknowledgments 



This work was funded through the USGS/State Partner- 

 ship Project (no. 99HQAG0050). Additional funding was 

 provided through the New Jersey Endangered & Nongame 

 Species Program. 



Literature cited 



Botton, M. L., R. E. Loveland, and T. R. Jacobsen. 



1988. Beach erosion and geochemical factors: influence on 

 spawning success of horseshoe crabs {Limulus polyphemus) 

 in Delaware Bay Mar Biol. 99:325-332. 

 1994. Site selection by migratory shorebirds in Delaware 

 Bay, and its relationship to beach characteristics and 

 abundance of horseshoe crab (Limnlus polyphcmus) eggs. 

 Auk 111:605-616. 

 Brockmann, H. J. 



1990. Mating behavior of horseshoe crabs, Limulus 

 polyphemus. Behaviour 114:206-220. 

 Burger, J.. L. Niles, and K. E. Clark. 



1997. Importance of beach, mudflats and marsh habitats to 

 migrant shorebirds on Delaware Bay. Biol. Conserv. 79: 

 283-292. 



