Acoustic-Tracking and Radio-Tracking of Horseshoe Crabs to Assess Spawning Behavior and Subtidal Habitat Use in Delaware Bay

Abstract

This study used telemetry to determine spawning behavior and subtidal habitat use of horseshoe crabs Limulus polyphemus. We attached combined acoustic and radio transmitters to 12 gravid female horseshoe crabs at Ted Harvey Beach and 12 at North Bowers Beach (both on the western shore of Delaware Bay) over a 5‐d period before peak spawning on the new moon. Horseshoe crabs were acoustically tracked and radio‐tracked daily for 8 d during both high tides and during the incoming dominant (higher) high tide. All horseshoe crabs were relocated at least once, and 83% of females spawned from two to six times (x = 3.35, SE = 0.18). Of these females, 85% spawned on two to five consecutive nights (x = 3.31, SE = 0.59). Most (95%) females spawned on the beaches where they were initially tagged. Typically, the shoreline used by an individual for spawning ranged from 70 to 1,160 m (x = 351 m, SE = 38 m). Between spawning events, horseshoe crabs remained 50–715 m offshore (x = 299 m, SE = 57 m) from their established spawning beaches. Following the new moon, all but one (96%) moved out of range of our survey area, which extended approximately 1 km from the shoreline. Multistate mark–recapture models were used to estimate recapture probabilities and daily probabilities of spawning and departure from the vicinity of the spawning beaches. The probability of recapture by acoustic telemetry was high and estimated to be 0.95 (95% confidence interval, 0.73–0.99). Horseshoe crabs equipped with acoustic and radio transmitters have high rates of recapture, can be tracked continually, and can be relocated in both foreshore and inshore habitats.

Tracked mangrove horseshoe crab Carcinoscorpius rotundicauda remain resident in a tropical estuary

“…The zone of detection was ~500 m in water ~12 m deep. This is consistent with findings at other sites in the world using the same acoustic tracking systems (Brousseau et al 2004, M.-J. James-Pirri pers.…”

“…Most work on horseshoe crabs has been done on the American horseshoe crab Limulus polyphemus (Brousseau et al 2004, Moore & Perrin 2007, Watson et al 2009, Schaller et al 2010, but an increasing body of work is now emerging from Asia on the other species, particularly in Japan (Seino et al 1995. However, there have been no studies on the movements and travel range of the Asian species in tropical waters, where there are no seasonal changes in water temperature, and the present work is the first study to track mangrove horseshoe crabs.…”

“…Therefore, the objectives of the present study were, first, to determine if the mangrove horseshoe crabs remain within the local area over an extended period, and, secondly, to determine whether they show homing behaviour when removed from the site of capture. Using methods described by Brousseau et al (2004) and James-Pirri (2010), we attached acoustic tags to adult horseshoe crabs and monitored their movements using stationary passive receivers deployed in the Strait of Johor for as long as the batteries in the tags lasted.…”

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

“…Cluster size is not correlated with female size (Brockmann 1996;Leschen et al 2006), but larger females lay more clusters per spawning season than smaller females. Females typically lay multiple nests during one tidal cycle (5 days of extra-high tides around the new or full moon) (Brockmann and Penn 1992;Brousseau et al 2004;Smith et al 2010;Beekey and Mattei 2015). Brockmann (1990) reported that in Florida, females returned to nest on average 3.4 times and most spawned during only one tidal cycle, whereas males returned over two or more tidal cycles (Brockmann and Penn 1992).…”

“…Brockmann (1990) reported that in Florida, females returned to nest on average 3.4 times and most spawned during only one tidal cycle, whereas males returned over two or more tidal cycles (Brockmann and Penn 1992). In Delaware Bay females spawned over two to five consecutive nights, remaining within 50-715 m of their established spawning beach before moving away from the beaches several days after the tidal cycle (Brousseau et al 2004;Smith et al 2010). In Long Island Sound, females can typically be found returning to nest at the same beach up to six days after their initial appearance (Beekey and Mattei 2015).…”