Assessment of sampling methods to estimate horseshoe crab (Limulus polyphemus L.) egg density in Delaware Bay
[No abstract available]
Fishery Bulletin↗
Geology topics
P.S. Pooler
Publications and source records attributed to P.S. Pooler.
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↗
A comparison of susceptibility to Myxobolus cerebralis among strains of rainbow trout and steelhead field and laboratory trials
Three strains of rainbow trout and steelhead Oncorhynchus mykiss were evaluated for the presence of whirling disease in field and laboratory trials. In the field exposures, fingerling Salmon River steelhead and Cayuga Lake and Randolph strains of rainbow trout were placed in wire cages in an earthen, stream-fed pond in New York State that was known to harbor Myxobolus cerebralis. Control fish were held at another hatchery that was free of whirling disease. In the controlled trials at the National Fish Health Research Laboratory, fingerling steelhead and Cayuga Lake and Mount Lassen rainbow trout were exposed to triactinomyxons at low (200 triactinomyxons/fish) or high (2,000 triactinomyxons/fish) levels for 2 h. Controls of each group were sham-exposed. Following an incubation period of 154 d for laboratory trials and 180 d for field trials, cranial tissue samples were taken for spore enumeration (field and laboratory trials) and histological analyses (laboratory only). Clinical signs of disease, including whirling behavior, blacktail, and skeletal deformities, were recorded for each fish in the laboratory trial at the terminal sampling. No clinical evidence of disease was noted among fish in the field trials. Clinical signs were noted among all strains in the laboratory trials at both exposure levels, and these signs were consistently greatest for the Mount Lassen strain. Whirling and skeletal deformities were more evident in the steelhead than in the Cayuga Lake rainbow trout; blacktail was more common in the Cayuga Lake fish. In both field and laboratory trials, spore counts were significantly higher for Cayuga Lake rainbow trout than in steelhead. In laboratory trials, moderate to marked cranial tissue lesions predominated in all three strains.
New York↗