Jim Berkson

The Horseshoe Crab, Limulus polyphemus: 200 Million Years of Existence, 100 Years of Study

Management of the horseshoe crab, Limulus polyphemus, is currently surrounded by controversy. The species is considered a multiple-use resource, as it plays an important role as bait in a commercial fishery, as a source of an important biomedical product, as an important food source for multiple species of migratory shorebirds, as well as in several other minor, but important, uses. Concern has arisen that horseshoe crabs may be declining in number. However, traditional management historically data have not been kept for this species. In this review we discuss the general biology, ecology, and life history of the horseshoe crab. We discuss the role the horseshoe crab plays in the commercial fishery, in the biomedical industry, as well as for the shorebirds. We examine the economic impact the horseshoe crab has in the mid-Atlantic region and review the current developments of alternatives to the horseshoe crab resource. We discuss the management of horseshoe crabs by including a description of the Atlantic States Marine Fisheries Commission (ASMFC) and its management process. An account of the history of horseshoe crab management is included, as well as recent and current regulations and restrictions.

The Horseshoe Crab: The Battle for a True Multiple-use Resource

Abstract The horseshoe crab (Limulus polyphemus) is the target of a commercial bait fishery that historically has lacked coordinated, coastwide monitoring and regulation. Because the catch has increased substantially in recent years, agencies have been increasingly pressured to manage the fishery more intensively. The diversity of interests involved (birders, environmentalists, commercial fishers, biomedical companies, coastal residents, and the Delaware Bay ecotourism industry) makes management especially challenging. In particular, the conflict between environmentalists and commercial fishers has been gaining public attention. With stronger management, the horseshoe crab population likely could meet the basic needs of all users, including fishers. Further delay or avoidance of coordinated, coastwide management increases the likelihood of a serious conservation problem that would injure the horseshoe crab population as well as various stakeholders and the species dependent on it (especially migratory sho...

Laboratory culture and maintenance of the horseshoe crab (Limulus polyphemus)

Often referred to as a living fossil, the American horseshoe crab, Limulus polyphemus, is one of the most-studied invertebrate animals in the world. It has served as a model in Nobel Prize–winning eye research, and researchers use a component of its blood to detect bacterial contamination in medical devices and drugs. The authors review the conditions necessary for housing these animals in the laboratory.

REDUCING FALSE ABSENCES IN SURVEY DATA: DETECTION PROBABILITIES OF RED-BACKED SALAMANDERS

Abstract Surveys to determine the presence of a species may be used as the basis for monitoring programs, wildlife-habitat models, or management decisions. Errors in survey data can result from nondetections, where the species is present at the site but not detected in the survey. We designed an experiment to estimate the probability of detection of red-backed salamanders (Plethodon cinereus) using different sampling methods and salamander densities. Red-backed salamanders were introduced into enclosures (n = 124) that were randomly assigned to a sampling treatment (daytime cover-object searches or nighttime visual searches) and a density treatment (low or high densities). Probability of detection was significantly higher using daytime searches and in enclosures with higher salamander densities. Weather conditions influenced the probability of detection. Increases in temperature correlated with decreases in detection during daytime sampling. Low humidity limited detection during nighttime surveys. Recent rainfall was positively related to detection during nighttime surveys. Probabilities of detection estimates are important for future design and analysis of survey data. Because of the high mean probability of detection, daytime surveys of cover objects are recommended as the survey method of choice if only a small number of samples can be obtained. However, because of their lower variability, nighttime visual surveys are the recommended sampling method when multiple samples can be obtained. Daytime surveys may be most effective at determining presence or absence at a site, but nighttime surveys may be more useful for indices of population trends. Nondetections can be reduced by ensuring large sampling areas for daytime searches and multiple samples at the same location for nighttime searches.

Evaluation of Accuracy and Precision of Downing Population Reconstruction

Abstract Downing population reconstruction uses harvest-by-age data and backward addition of cohorts to estimate minimum population size over time. Although this technique is currently being used for management of black bear (Ursus americanus) and white-tailed deer (Odocoileus virginianus) populations, it had not undergone a rigorous evaluation of accuracy. We used computer simulations to evaluate the impacts of collapsing age classes and violating the assumptions of this technique on population reconstruction estimates and trends. Changes in harvest rate or survival over time affected accuracy of reconstructed population estimates and trends. The technique was quite robust to collapsing age classes as far as 3+ for bears and deer. This method would be suitable for estimating population growth rate (λ) for populations experiencing no trend in harvest rate or natural mortality rate over time. Our evaluation showed Downing population reconstruction to be a potentially valuable tool for managing harvested species with high harvest rates and low natural mortality, with possible application to black bear and white-tailed deer populations.

Systematic Errors in Length Frequency Data and their Effect on Age-Structured Stock Assessment Models and Management

Abstract Length frequency data are a central component of many statistical age-structured models, which are used widely to conduct fisheries stock assessments and produce estimates of stock status for management. However, these data can be biased due to systematic errors during the sampling process. This study examined how bias in length frequency data affected stock status estimates from an age-structured assessment model and subsequent prescribed management actions. A simulation approach was used to test the effect of two different scenarios of bias on assessment results. Populations were simulated based on life history parameters for three different serranid species in the southeastern United States and followed a trajectory that increased and then decreased over time. From these simulated populations, fishery-dependent length frequency data were generated and then altered to represent different types of systematic sampling error. Data that were biased towards larger fish had a considerable effect on t...

Density-Dependent Harvest Modeling for the Eastern Wild Turkey

Abstract Many current wild turkey (Meleagris gallopavo) harvest models assume density-independent population dynamics. We developed an alternative model incorporating both nonlinear density-dependence and stochastic density-independent effects on wild turkey populations. We examined model sensitivity to parameter changes in 5% increments and determined mean spring and fall harvests and their variability in the short term (3 yr) and long term (10 yr) from proportional harvesting under these conditions. In the long term, population growth rates were most sensitive to poult:female ratios and the form of density dependence. The nonlinear density-dependent effect produced a population that maximized yield at 40% carrying capacity. The model indicated that a spring or fall proportional harvest could be maximized for fall harvest rates between 0% and 13% of the population, assuming a 15% spring male harvest and 5% spring illegal female kill. Combined spring and fall harvests could be maximized at a 9% fall harvest, under the same assumptions. Variability in population growth and harvest rates increased uncertainty in spring and fall harvests and the probability of overharvesting annual yield, with growth rate variation having the strongest effect. Model simulations suggested fall harvest rates should be conservative (≤9%) for most management strategies.

Factors Affecting Horseshoe Crab Limulus polyphemus Trawl Survey Design

Abstract There is currently a lack of abundance information for effectively managing horseshoe crabs Limulus polyphemus. A trawl survey program that specifically targets horseshoe crabs would provide that information. We conducted a study to examine the factors that would influence the trawl survey design. Depth, topography, and time of day were examined as potential survey design influences. Horseshoe crab catches were typically greater inshore (within 5.6 km of shore), in troughs (≥2.4 m deep, ≤1.8 km wide, and >1.8 km long), and at night, but specific results varied by maturity categories. In addition, some interactions existed among factors. Trawl survey protocols incorporating those factors were developed separately for all horseshoe crabs combined and for mature females only because these categories were considered most important for management purposes. Stratified random sampling designs were more efficient for surveys than simple random sampling designs, and optimum effort allocation was more effi...

A Discussion of Horseshoe Crab Management in Five Countries: Taiwan, India, China, United States, and Mexico

A panel of five international experts was convened during the International Symposium on the Science and Conservation of Horseshoe Crabs to compare and contrast horseshoe crab management in their countries. The panel members each responded to a series of questions prepared by a facilitator. All five speakers stated that habitat degradation and destruction were a major threat to the horseshoe crab population(s) in their country. Pressure for economic development often hindered efforts to preserve and protect coastal habitats. Public education was viewed as an important step toward the implementation of effective management actions. The urgent need for conservation was viewed to be a strong, motivating factor to strengthen international management efforts.

Estimation of total hemolymph volume in the horseshoe crab Limulus polyphemus

Biomedical companies extract blood from the horseshoe crab, Limulus polyphemus, for the production of Limulus Amebocyte Lysate, used worldwide for detecting endotoxins in injectable solutions and medical devices. Despite the extensive use of horseshoe crabs by the biomedical industry, total hemolymph volume for this species is not known. The hemolymph volume of 60 adult horseshoe crabs was estimated using an inulin dilution technique. Blood volume of the horseshoe crab represented as a percentage of wet body weight was 25 ± 2.2% for males and 25 ± 5.1% (mean ± SD) for females. Relationships between hemolymph volume and weight (p = 0.0026, r 2 = 0.8762), hemolymph volume and prosomal width (p < 0.0001), and hemolymph volume and inter-ocular width (p < 0.0001) were observed. No significant differences were observed between males and females. The relationship of animal size and hemolymph volume can be used to predict how much blood can be drawn from horseshoe crabs used by the biomedical industry, and can be of further use in future bleeding mortality studies.