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S.F. Michels

Publications and source records attributed to S.F. Michels.

4 recordsLinked to original sources
USGS2006

Seeing the elephant: Importance of spatial and temporal coverage in a large-scale volunteer-based program to monitor horseshoe crabs

As in John Godfrey Saxe's poem about six blind men and an elephant, conclusions drawn from a monitoring program depend critically on where and when observations are made. We examined results from the Delaware Bay horseshoe crab (Limulus polyphemus) spawning survey to evaluate the effect of spatial and temporal coverage on conclusions about spawning activity. Declines due to previously unregulated harvest triggered an increase in monitoring. Although we detected no apparent trend in bay-wide spawning activity for 1999-2005, conclusions would have differed depending on where and when observations were made. For example, spawning activity in May during the shorebird stopover was a poor predictor of spawning activity over the whole season. Observations made only during peak spawning incorrectly suggested that spawning activity increased during 2001-2005. Trends at one place in the bay were not indicative of trends for the whole bay. Many natural resource issues begin like the blind men and the elephant with dispute partially caused by an incomplete picture of the resource. As sufficient time and funds are directed to gathering necessary data using effective sampling designs, a more complete picture can emerge.

Fisheries↗
USGS2002

Spatial and temporal distribution of horseshoe crab (Limulus polyphemus) Spawning Delaware Bay: Implications for monitoring

Concern for the status of horseshoe crab ( Limulus polyphemus ) has increased as harvest for conch and eel bait has increased and spawning habitat has decreased. In early 1999 a workshop was held at the behest of the Atlantic States Marine Fisheries Commission to design a statistically valid survey of horseshoe crab spawning in Delaware Bay. The survey that resulted was a redesign of a volunteer-based spawning survey that began in 1990, and its network of volunteers was relied on to implement the three-stage sampling design in 1999. During May and June of 1999, 163 participants surveyed during the highest of the daily high tides on 16 beaches (8 on each site of Delaware Bay). During the first half of the spawning season, spawning was associated with lunar phases, but moderated by wave height. Disproportionately more spawning occurred within 3 d of the first new and full moons, and spawning activity (measured by an index of female density) was correlated inversely to the percent of beaches with waves ≥0.3 m. Spawning was heaviest on the Delaware shore around the full moon in May in spite of low waves in New Jersey during the new and full moons in May. Number of beaches sampled was the most important factor in determining the precision of the spawning index and power to detect a decline. Explicit consideration of statistical power has been absent from the current debate on horseshoe crab status and harvest. Those who argue against harvest restrictions because of a lack of statistically significant declines take on a burden to show that the surveys they cite have high statistical power. We show the Delaware Bay spawning survey will achieve high statistical power with sufficient sampling intensity and duration. We recommend that future Delaware Bay spawning surveys sample on 3 d around each new and full moon in May and June and increase the number of beaches to ensure high statistical power to detect trends in baywide spawning activity.

Delaware, New Jersey↗
USGS2002

Horseshoe crab (Limulus polyphemus) reproductive activity on Delaware Bay beaches: Interactions with beach characteristics

We used results from a survey of horseshoe crab reproductive activity that was conducted in 1999 throughout Delaware Bay to examine the relationship between estimates of spawning females and egg deposition and analyze how that relationship varies with geography, time within a spawning season, beach morphology, and wave energy. We found that beach morphology and wave energy interacted with density of spawning females to explain variation in the density and distribution of eggs and larvae. For example, the quantity of eggs in surface sediment (i.e., eggs that are potentially available to foraging shorebirds) was associated with the density of spawning females, beach morphology, and wave energy. The association between beach morphology and live eggs in surface sediment was strong especially in late May (Percent Reduction in Error = 86% from regression tree model) where egg density was an order of magnitude higher on beaches <15 m wide (3.38*105 m-2; 90% CI: 2.29*105, 4.47*105) compared to wider beaches (1.49*104 m-2; 90% CI: 4.47*103, 2.53*104). Results also indicate that, among bay-front beaches, horseshoe crabs prefer to spawn on narrow beaches, possibly because of reduced wave energy. At peak periods of spawning activity, density of spawning females was inversely related to foreshore width on mid-latitude beaches within Delaware Bay (t = -2.68, 7 df, p = 0.03). Because the distribution of eggs across the foreshore varied with beach morphology and widened as the spawning season progressed, methods used to sample eggs need to be robust to variation in beach morphology and applicable regardless of when the samples are taken. Because beach morphology and wave energy were associated with the quantity of eggs in surface sediment, certain beach types may be critical to the conservation of shorebird foraging habitat.

Journal of Coastal Research↗