Abundance of adult horseshoe crabs (Limulus polylphemus) in Delaware Bay estimated from a bay-wide mark-recapture study

D. R. Smith; M. J. Millard; S. Eyler

Home/Archive/USGS

USGS · 70028062

Abundance of adult horseshoe crabs (Limulus polylphemus) in Delaware Bay estimated from a bay-wide mark-recapture study

D. R. Smith·M. J. Millard·S. Eyler

View original source ↗Read source document ↗Export metadata ↓

Abstract

Estimates of the abundance of American horseshoe crabs (Limulus polyphemus) are important to determine egg production and to manage populations for the energetic needs of shorebirds that feed on horseshoe crab eggs. In 2003, over 17,500 horseshoe crabs were tagged and released throughout Delaware Bay, and recaptured crabs came from spawning surveys that were conducted during peak spawning. We used two release cohorts to test for a temporary effect of tagging on spawning behavior and we adjusted the number of releases according to relocation rates from a telemetry study. The abundance estimate was 20 million horseshoe crabs (90% confidence interval: 13-28 million), of which 6.25 million (90% CI: 4.0-8.8 million) were females. The combined harvest rate for Delaware, New Jersey, Virginia, and Maryland in 2003 was 4% (90% CI: 3-6%) of the abundance estimate. Over-wintering of adults in Delaware Bay could explain, in part, differences in estimates from ocean-trawl surveys. Based on fecundity of 88,000 eggs per female, egg production was 5.5??1011 (90% CI: 3.5??1011, 7.7??1011), but egg availability for shorebirds also depended on overlap between horseshoe crab and shorebird migrations, density-dependent bioturbation, and wave-mediated vertical transport.

Explore related subjects

Fishery Bulletin Article

Source-reported bounding extent: 38.70694605159386° to 39.53370327008705° latitude; -75.6134033203125° to -74.849853515625° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

D. R. Smith, M. J. Millard, S. Eyler. 2006. Abundance of adult horseshoe crabs (Limulus polylphemus) in Delaware Bay estimated from a bay-wide mark-recapture study. https://pubs.usgs.gov/publication/70028062

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2018

Movement and mortality of Atlantic salmonkelts (Salmo salar) released into thePenobscot River, Maine

The Penobscot River is home to the last major run of Atlantic salmon (Salmo salar) in the United States. For over one century, the river has been stocked intensively. Since the late 1970s, most kelts are released to the Penobscot River estuary following spawning in a hatchery. Over that time, the proportion of the run made up of iteroparous individuals has declined to < 1%. These fish may make a disproportionate contribution to the spawning population because they are typically large and produce more eggs than virgin spawners. We radio-tagged 55 kelts that were artificially spawned at the Craig Brook National Fish Hatchery in 2015 and released them in two different locations in the river (head of tide and ~50 km upstream) to assess 1) when hatchery-spawned kelts leave the river, 2) whether release location influences river exit timing, and 3) if kelts from the upper river could successfully outmigrate through the lower Penobscot River’s hydroelectric complex. The kelts were tracked from November 2015 to July 2016. Although some fish from both release groups were documented leaving the system within one month, the majority of fish (84%) overwintered in freshwater habitat. Many (71%) of those kelts that overwintered in the Penobscot River made directed, upstream movements in November and December. However, there was no difference in upstream movement rates, timing of outmigration, or survival between the release groups. Survival to outmigration was 23.6%, which is considerably lower than kelt survival documented in Canadian and European rivers. Low survival to outmigration may have contributed to the disappearance of iteroparous individuals from the Penobscot River run of Atlantic salmon over the last four decades.

Maine↗

USGS2018

The influence of nutrients from carcasses of sea lamprey (Petromyzon marinus) on larval growth and spawner abundance

Migrations of anadromous sea lamprey (Petromyzon marinus) from marine ecosystems serve as vectors of nutrients into freshwater food webs. Larval sea lamprey reside in streams for 6–8 years as deposit feeders before metamorphosing into juveniles and migrating to the ocean. Previous work has shown that carcass nutrients, which result from the death of adult lamprey after spawning, increase stream productivity and are consumed by larvae. This may increase larval growth rates and enhance earlier metamorphosis. We examined the sensitivity of life-history parameters and influence of nutrients from carcasses of sea lamprey on the age and growth of larval conspecifics with a deterministic stock-recruitment model. We hypothesized that variability in growth among larval populations is productivity mediated and we compared modeled populations in which larvae receive added growth benefits from carcass nutrients with populations that do not. The results of our simulation indicate that increases in larval growth and lower age at metamorphosis over time lead to an increase in spawner abundance. Increased growth rates may also improve fitness and bolster subsequent spawning stocks. Our research characterized 2 potential ecosystem states, one in which larval sea lamprey benefit from adult conspecifics and another in which the larvae do not.

Fishery Bulletin↗

USGS2015

Effects of oyster harvest activities on Louisiana reef habitat and resident nekton communities

Oysters are often cited as “ecosystem engineers” because they modify their environment. Coastal Louisiana contains extensive oyster reef areas that have been harvested for decades, and whether differences in habitat functions exist between those areas and nonharvested reefs is unclear. We compared reef physical structure and resident community metrics between these 2 subtidal reef types. Harvested reefs were more fragmented and had lower densities of live eastern oysters ( Crassostrea virginica ) and hooked mussels ( Ischadium recurvum ) than the nonharvested reefs. Stable isotope values ( 13 C and 15 N) of dominant nekton species and basal food sources were used to compare food web characteristics. Nonpelagic source contributions and trophic positions of dominant species were slightly elevated at harvested sites. Oyster harvesting appeared to have decreased the number of large oysters and to have increased the percentage of reefs that were nonliving by decreasing water column filtration and benthopelagic coupling. The differences in reef matrix composition, however, had little effect on resident nekton communities. Understanding the thresholds of reef habitat areas, the oyster density or oyster size distribution below which ecosystem services may be compromised, remains key to sustainable management.

Louisiana↗