Davis et a\ Population assessment of Limulus polyphemus 



221 



F/Fmsy 



Although harvest of horseshoe crabs has 

 decreased in recent years (Fig. 3), fishing 

 mortality remains high (Figs. 7 and 8). F.,„„.,/ 

 P\isY point estimates ranged from 2.3 to 9.5 

 for models with fishery-independent data and 

 from 0.9 to 1.8 for models with fishery-depen- 

 dent data (Table 3). 



Biomass 



Biomass of horseshoe crabs in the Delaware 

 Bay region has decreased substantially since 

 1995, such that the 2003 biomass was less 

 than 56% of the 1995 biomass. This equates 

 to an annual decline of greater than 7% 

 during this period. Point estimates for 2003 

 biomass ranged from 1084 t (596,000 crabs) 

 to 6604 t (3,632,000 crabs). As is charac- 

 teristic of production models (Prager, 1994), 

 absolute biomass was estimated much less 

 precisely than relative biomass (B/By^jj). The 

 range of 80% confidence intervals for 2003 

 biomass across all seven model runs was 524 t (288,000 

 crabs) to 12,080 t (6,644,000 crabs). 



Population projections 



We used results from production model runs to project 

 the horseshoe crab population forward in time to evalu- 

 ate potential management options. Figure 9 shows the 

 trajectory of B/B^,^y over time for model FI-1 under 

 each harvest scenario. The number of years required 



to rebuild the population to B„sy varied substantially 

 among models (Table 4). At 2003 harvest levels (i.e., 

 100%), projections showed population recovery in a mini- 

 mum of four years, although four of the seven models 

 did not reach B^^.y in the 15-year projection period. In 

 the absence of harvest (i.e., 0%), recovery could occur in 

 as few as 2 years, but two models did not reach B^^^y in 

 the projection period. Estimates of B/Bj^g^y in the final 

 year of projections (2018) also differed among model 

 applications (Table 5). 



