Age and sex specific timing, frequency, and spatial distribution of horseshoe crab spawning in Delaware Bay:Insights from a large-scale radio telemetry array

摘要

To study horseshoe crab Limulus polyphemus spawning behavior and migration over a large-spatial extent (>100 km),we arrayed fixed station radio receivers throughout Delaware Bay and deployed radio transmitters and archival tags on adulthorseshoe crabs prior to their spawning season.We tagged and released 160 females and 60 males in 2004 and 217 females in2005.The array covered approximately 140 km of shoreline.Recapture rates were >70% with multi-year recaptures.We categorizedadult age by carapace wear.Older females tended to spawn earlier in the season and more frequently than young females,but those tendencies were more apparent in 2004 when spawning overall occurred earlier than in 2005 when spawning was delayedpossibly due to decreased water temperatures.Timing of initial spawning within a year was correlated with water temperature.After adjusting for day of first spring tide,the day of first spawning was 4 days earlier for every 1 degree (℃) rise in meandaily water temperature in May.Seventy nine % of spawning occurred during nighttime high tides.Fifty five % of spawning occurredwithin 3 d of a spring tide,which was slightly higher than the 47% expected if spawning was uniformly distributed regardlessof tidal cycle.Within the same spawning season,males and females were observed spawning or intertidally resting atmore than one beach separated by >5 km.Between years,most (77%) did not return to spawn at the same beach.Probability ofstranding was strongly age dependent for males and females with older adults experiencing higher stranding rates.Horseshoecrabs staging in the shallow waters east of the channel spawned exclusively along the eastern (NJ) shoreline,but those stagingwest of the channel spawned throughout the bay.Overall,several insights emerged from the use of radio telemetry,which advancesour understanding of horseshoe crab ecology and will be useful in conserving the Delaware Bay horseshoe crab populationand