A Long-Term Study of Spawning Activity in a Florida Gulf Coast Population of Horseshoe Crabs (<Emphasis Type="BoldItalic">Limulus polyphemus</Emphasis>)

Populations of the American horseshoe crab (Limulus polyphemus) differ in broad areas of their biology. We observed a non-harvested, marked Florida Gulf coast population during their spring spawning (March–May) in 11 years across a 17-year period (1992–2009). Long-term changes occurred in the number of spawning pairs: the population was stable from 1992 to 2000 but increased markedly after 2000. Short-term variation in numbers of spawning pairs, unpaired females, unpaired males, and operational sex ratios was explained by changes over the season and during each week of spring tides and by differences in actual (not predicted) maximum high tide height. Wind direction strongly affected tidal inundation and the number of spawning horseshoe crabs. Tagging individuals revealed that females returned to the nesting beach less often than males and most females were re-sighted only within 1 week of spring tides. No animals were seen across more than 6 years. Implications for management are discussed.     

Patterns of Surf Smelt, Hypomesus pretiosus, Intertidal Spawning Habitat Use in Puget Sound, Washington State

Surf smelt Hypomesus pretiosus are an important part of the Salish Sea food web and obligate beach spawners, yet little is known about the spatiotemporal distribution of spawning and beach characteristics related to spawning success. We counted smelt eggs at 51 sites around Camano Island, Puget Sound, Washington every 2?weeks for 1?year and at 13 of those 51 sites each month in the following year. At each site, we measured beach characteristics hypothesized to affect spawning habitat suitability as measured by egg abundance and mortality. Eggs were collected at 45 sites and pooled by month for analyses. Few sites (N?=?10, 19.6?%) contributed 87?% of total eggs and 89?% of all live eggs collected. Mean total egg counts at sites were higher (p?<?0.019) in Jul?CSep (1,790.7, SE?=?829.5) than in Jan?CMar (26.1, SE?=?10.2). Principal component and regression analyses suggested that aspect, fetch, solar radiation, and beach temperature predicted egg abundance but not mortality. Because a small proportion of sites appear to support most spawning activity, a conclusion consistent with year?2 egg counts, impacts to relatively few beaches could greatly affect surf smelt production.     

Spawning densities,egg densities,size structure,and movement patterns of spawning horseshoe crabs,<Emphasis Type="Italic">Limulus polyphemus</Emphasis>, within four coastal embayments on Cape Cod,Massachusetts

Spawning densities, spawning indices, egg densities, size distributions, and movement patterns of horseshoe crabs (Limulus polyphemus) were quantified for four coastal embayments (Monomoy National Wildlife Refuge, Pleasant Bay, Nauset Estuary, and Cape Cod Bay) on Cape Cod, Massachusetts from 2000 to 2002. Spawning activity was highest from mid May through mid June, but densities varied throughout the Cape Cod region. Average spawning densities (male and female crabs combined), measured using 25-m² quadrats, were lower than 1 crab 25 m^?2, although certain locations had consistently higher densities averaging 2 to 3 crabs 25 m^?2 with individual survey densities recorded as high as 17 crabs 25 m^?2. Spawning densities during night surveys were either similar or slightly higher than day surveys, except at a few sites within Pleasant Bay. Spawning indices were considerably lower ranging from 0 to 1.3 females 25 m^?2 throughout the Cape Cod region. Spawning sex ratios varied from 1∶1.6 to 1∶3.1 (females:males) throughout the region, except within Pleasant Bay where highly male skewed ratios were observed (e.g., 1∶5.8, 3-yr average). Egg densities were low overall (<1 egg cm^?2) throughout Cape Cod and egg densities tended to be higher in deeper sediments (5–20 cm deep) compared to shallow sediments (0–5 cm deep) at most locations. Over 7,800 horseshoe crabs were tagged on Cape Cod from 2000 to 2002. Average size and size frequency distributions of tagged crabs varied among regions. Larger individuals were observed at Monomoy National Wildlife Refuge while the smallest individuals were from Cape Cod Bay. We documented an overall recapture rate of 6.7% and our tag-recapture data indicated that 62% of crabs were recaptured at the original tagging location and 70% of recaptures traveled less than 2 km from the original tagging location, providing evidence for localized populations on Cape Cod. We have observed that horseshoe crabs differ among embayments within a regional area, suggesting the potential need for management plans specific to embayments or subregions depending on the characteristics of a population.     

Spawning location and distribution of early life stages of alewife and blueback herring in a Virginia stream

During the 1992 spawning season of river herring, three sites in a tributary of the Rappahannock River, Virginia, were studied to characterize spawning and nursery habitats of alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) and to identify differences in habitat use along an upstream to downtream gradient. The sites were sampled (using drift and dip nets and a plankton sampler) and habitat variables were measured on a 5-d, four-time interval rotation: at the end of 5 d, each site had been sampled once at dawn, noon, dusk, and midnight. Considerable non-overlap in spawning seasonality was apparent between species. For both species, densities of river herring adults, eggs, and yolk-sac larvae were highest at the upstream site, indicating 1) that the upstream site is more important for spawning than downstream areas, and 2) these species do not use different spawning areas in this stream. Densities of post-yolk-sac larvae did not differ significantly among sites, indicating post-spawning dispersal to downstream areas. The upstream site was smaller in area, more acidic, had faster water flow, clearer water, more vegetation, and siltier substrate than the downstream sites. At times, pH levels in the upstream site were within the lethal range reported for blueback herring larvae. Possible reasons for selection of the upstream habitat include: 1) adults may migrate as far upstream as possible to avoid predation or potential competition with other species of fish for spawning habitat; or 2) adults may historically enjoy greater spawning success in the upstream habitat due to physicochemical features of this area. More study is needed to determine the reasons for river herring use of upstream habitats in Virginia streams.     

The breeding behavior and patterns of movement of horseshoe crabs,Limulus polyphemus,in the vicinity of breeding beaches in Apalachee Bay,Florida

Breeding activity of the horseshoe crab,Limulus polyphemus, was quantitatively monitored in Apalachee Bay, Florida, throughout one breeding season. Breeding peaked at times of full and new moon at the hour of high tide. Breeding activity was heavier on night tides than on corresponding day tides of the same date. Males routinely outnumbered females and indications of sperm competition were present. Many horseshoe crabs buried in the intertidal zone throughout the subsequent low tide and returned to the beach to breed again on the following high tide. A tagging study of the horseshoe crab indicated that male animals return to breeding beaches more frequently than females. Most animals tagged at breeding beaches did not move away from the tagging site during a breeding season and were recovered at the point of release. No long-range movements were noted. The sex ratio of animals tagged near breeding beaches was predominately male while it was predominately female for animals collected and tagged 3–6 miles offshore. A nine percent recovery rate was achieved. Existing localized populations are potentially subject to depletion due to heavy collecting pressure on breeding beaches.     

A contribution to the population biology of horseshoe crabs,Limulus polyphemus (L.), in Delaware Bay

The 1977 peak population of spawning horsehoe crabs,Limulus polyphemus, in Delaware Bay, was comprised of about 222,000 males and 51,000 females. This estimate, based upon a shoreline survey of spawning intensity along Delaware and New Jersey beaches at the time of full moon tides in June, was corroborated by a quantification of egg clusters in a beach. Fecundity of gravid females was used, in conjunction with the egg cluster estimate, to approximate the number of females responsible for the observed quantity of eggs. The present spawning population of Delaware Bay is several fold larger than that which existed during the 1960’s. From a longer historical perspective, however, the population is far from approaching the numbers and spawning intensity reported a century ago.     

Spatial and temporal patterns of spawning and larval hatching by the horseshoe crab,<Emphasis Type="Italic">Limulus polyphemus</Emphasis>, in a microtidal coastal lagoon

Estuarine species with wide geographic distributions often experience tidal regimes that vary significantly throughout their range. Plasticity in behaviors associated with the tide is expected to enable synchronization with local tides. The American horseshoe crabLimulus polyphemus typically inhabits estuaries and coastal areas with pronounced semi-diurnal tides that play a role in synchronizing the timing of spawning and larval hatching, but also lives in areas that lack significant tides and associated synchronization cues. We investigated the spatial and temporal pattern of adult spawning and larval hatching ofL. polyphemus in a microtidal coastal lagoon (Indian River Lagoon, Florida, USA). Spawning activity and larval abundance were monitored weekly February 1998–August 2000 at sites spanning 100 km of the lagoon. To identify possible synchronization cues for spawning and hatching success, the presence of adult and larvalL. polyphemus were related to environmental and hydrologic variables using logistic regression. The presence of spawning adults varied significantly among the sub-basins of the lagoon, with the highest densities occurring in the Banana River. Large spawning aggregations were not observed and densities never exceeded 6 m⁻². Spawning occurred year-round but varied seasonally with episodes of increased mating activity in the early spring. The occurrence of mating pairs was episodic and was not synchronized among sites. Larval densities were low (4 m⁻³) and larvae were present at only 12 of the 21 sites. Hatching success was decoupled temporally from spawning activity, with peaks in larval abundance occurring approximately 8 wk after peaks in spawning. Larval abundance was associated with periods of high water. Reproductive activity of horseshoe crabs in the lagoon differs significantly from populations inhabiting areas with semi-diurnal and diurnal tides. These differences are likely due to the lack of periodic tidally-related synchronization cues and regular beach inundation.     

Reproductive conditions of the Atlantic sturgeon (Acipenser oxyrinchus) in the Hudson River

Ninety-four prespawning adult Atlantic sturgeon (Acipenser oxyrinchus) were sampled in the Hudson River for age, sex, body size, gonad weight, fecundity, mature oocyte size, and plasma concentrations of gonadotropins, sex steroids, and vitellogenin during the spring spawning migrations in 1992 and 1993. In males, the age and total length ranged from 12 yr to 19 yr and from 133 cm to 204 cm and in females from 14 yr to 36 yr and from 197 cm to 254 cm. The majority of males were 13–16 yr old, and females were 16–20 yr old. Some females had residual atretic ovarian bodies, presumably remaining from a previous spawning and indicating iteroparity. Pre-ovulatory condition was recognized by migration of the germinal vesicle or by germinal vesicle breakdown and by significantly elevated plasma gonadotropins, progesterone, and vitellogenin. All pre-ovulatory females were captured upriver from Hudson River kilometer 136. Individual fecundity ranged from 0.4 million to 2.0 million eggs and oocyte diameter from 2.4 mm to 2.9 mm, and both characters exhibited a significant (p<0.05) positive relationship with female body size. Iteroparous females, tentatively identified by the presence of atretic bodies remaining in the ovary from a previous spawning, had significantly (p<0.05) higher fecundity and produced larger eggs, compared with females spawning presumably for the first time.     

Influence of Environmental Factors on Spawning of the American Horseshoe Crab (<Emphasis Type="Italic">Limulus polyphemus</Emphasis>) in the Great Bay Estuary,New Hampshire,USA

The Great Bay Estuary, New Hampshire, USA is near the northern distribution limit of the American horseshoe crab (Limulus polyphemus). This estuary has few ideal beaches for spawning, yet it supports a modest population of horseshoe crabs. There is no organized monitoring program in the Great Bay Estuary, so it is unclear when and where spawning occurs. In this 2-year study (May through June, 2012 and 2013), >5,000 adult horseshoe crabs were counted at four sites in the estuary. The greatest densities of horseshoe crabs were observed at Great Bay sites in the upper, warmer reaches of the estuary. Peaks of spawning activity were not strongly correlated with the times of the new or full moons, and similar numbers of horseshoe crabs were observed mating during daytime and nighttime high tides. While many environmental factors are likely to influence the temporal and spatial patterns of spawning in this estuary, temperature appears to have the most profound impact.     

Population Structure of Adult Blue Crabs, <Emphasis Type="Italic">Callinectes sapidus</Emphasis>, in Relation to Physical Characteristics in Barnegat Bay,New Jersey

Blue crabs (Callinectes sapidus) are an important species in coastal or lagoonal estuaries where adult population characteristics may differ as compared to drowned-river estuaries. Barnegat Bay, in southern New Jersey, is composed of two large embayments: one without and one with a salinity gradient. We tested the influence of physical characteristics on the abundance, sex ratio, and size of adult blue crabs and examined variation in measures of reproductive potential (e.g., sperm stores) in both sexes in Barnegat Bay from June to September, 2008–2009. Population structure was distinct between the embayments due to sex-specific responses to salinity: male abundance was negatively correlated with salinity whereas adult females were more abundant in high salinity because of proximity to Barnegat Inlet. This produced high sex ratios in low salinity areas and low sex ratios in high salinity areas. Summer was a growing season for adult males while in late summer-early fall, juvenile males recruited to the adult size class. The spawning season lasted from May to August and ovigerous females were concentrated near the inlets. Information on female sperm stores and ovarian development identified two cohorts of adult females: females that will spawn in the current summer and females that will not spawn until the following summer. Thus, not all adult females near the spawning grounds were members of the current spawning stock. This suggests that annual estimates of spawning stock size which overlook the proximity of females to spawning are overestimating the current spawning stock in Barnegat Bay and other estuaries.     

Age- and sex-dependent migrations of striped bass in the Hudson River as determined by chemical microanalysis of otoliths

Patterns of habitat utilization and migration of Hudson River striped bass,Morone saxatilis, were estimated using otolith microchemical analysis to chart age- and sex-dependent movements. Otoliths from 25 males and 25 females were analyzed for seasonal and age-specific patterns in strontium: calcium level. These levels were converted into salinity estimates based upon a relationship derived from experimental studies. Seasonal patterns in salinity habitation indicated annual up-estuary migrations in mature age-classes of males and females, and may represent spawning migrations. Early emigration of young striped bass (<3 yr old) into polyhaline and euhaline waters was observed for both sexes, but females tended to reside at higher salinities throughout their life span. Otolith microchemical analysis indicated that 68% of the sampled females and 28% of the sampled males spent significant portions of their lives in euhaline coastal waters. A positive relationship between down-estuary movements and age was observed for both sexes, supporting the hypothesis of size-related dispersion and anadromy in striped bass populations. Individuals collected during the same season or from the same segment of the river had similar lifetime salinities. This result suggests that group cohesion (schooling) could persist for substantial periods of an individual’s life span. The most cohesive group was fall-collected males, which may reside permanently in fresh water and estuarine waters. Cohesive migratory groups would have important implications for investigations on effects of contaminants and fishing pressure on Hudson River striped bass.     

Comparison of restored and natural seagrass beds near Corpus Christi,Texas

Structural equivalence between seagrass restoration sites and adjacent natural seagrass beds on the mid Texas coast was assessed six times between April 1995 and May 1997. Throw traps and corers were used for quantitative sampling. Restoration sites were 2.7 to 6.6 yr old when first sampled and 3.7 to 8.2 yr old when last sampled. There were few significant differences in water column, seagrass, or sediment characteristics, in fish and decapod (nekton) densities, or in nekton and benthos community compositions between restored and natural seagrass habitats at any time during the study period. Differences in densities of dominant benthic invertebrates were regularly observed, with greater densities of more taxa observed in natural seagrasses than in restored beds. Densities of Class Oligochaeta and the polychaetePrionospio heterobranchiata are proposed as potential indicators of structural equivalence in restored seagrasses. This study indicates that seagrass restorations in the vicinity of Corpus Christi, Texas, exhibit minimal quantitative differences in community structure (except for benthos) relative to adjacent natural seagrass beds after 3 to 5 yr.     

Development and validation of an estuarine biotic integrity index

We tested hypotheses about how estuarine fish assemblages respond to habitat degradation and then integrated these responses into an overall index, the Estuarine Biotic Integrity Index (EBI), which summarized observed changes. Fish assemblages (based on trawl catches) and habitat quality were measured monthly or biweekly at nine sites in two estuaries from March 1988 to June 1990. Submerged aquatic vegetation habitats were classified as low or medium quality based on year-round measurements of chemical and physical characteristics (phytoplankton blooms; macroalgae; dissolved oxygen; nutrients; dredged channels). We tested 15 metrics and selected 8 for inclusion in the EBI: total number of species, dominance, fish abundance (number or biomass), number of nursery species, number of estuarine spawning species, number of resident species, proportion of benthic-associated fishes, and proportion abnormal or diseased. Fish assemblages in low-quality sites had lower number of species, density, biomass, and dominance compared with medium-quality sites. Fish abundance peaked in July and August, and was lowest in January to March. The seasonal cycle in low-quality sites was damped compared with medium-quality sites. Abundances of fishes using estuaries as a spawning and nursery area and of benthic species were lower in low-quality sites compared to medium-quality sites. The individual metrics and the overall index correlated with habitat degradation. The EBI based on biomass did not do better than the EBI based on number, indicating that the extra effort to obtain biomass may not be warranted. We suggest the EBI is a useful indicator of estuarine ecosystem status because it reflects the relationship between anthropogenic alterations in estuarine ecosystems and the status of higher trophic levels.     

Distribution and migrations of the prawnPalaemon longirostris in the Mira River estuary (southwest Portugal)

Palaemon longirostris was sampled monthly at 12 sites in the Mira River estuary (southwest Portugal) from October 1990 to September 1991. Animals were counted, measured, and sexed. The estuarine distribution of prawns appeared to follow the salinity displacement, the animals being found at river stations during summer and autumn when saline encroachment up the estuary was greater. During winter and spring when freshwater input from the river was greatest, and thus moving the salinity gradient toward the mouth, the prawns migrated downstream to brackish areas. Ovigerous females were collected only from estuarine areas (January to August), suggesting that reproduction does not take place in freshwater habitats. Higher percentages of females than males were generally observed. Females, particularly ovigerous ones, were larger than males.     

Fecundity of Atlantic menhaden,Brevoortia tyrannus

Since the 1950’s the population structure of the Atlantic menhaden,Brevoortia tyrannus, has undergone dramatic changes. High rates of fishery exploitation during the 1960’s resulted in a drastic decline in the breadth of the age structure and numbers of spawning aged fish. The stock recovered under continued exploitation during the 1970’s in spite of these unfavorable conditions. Hence, the length and age at first spawning, the seasons and areas of spawning, and the potential number of ova produced as a function of length were reexamined during the 1978, 1979, and 1981 fishing seasons. No changes were detected in the reproductive biology of Atlantic menhaden. The size at first spawning, areas, and season of spawning were similar to results of previous studies. The minimum fork length of potential spawners was 180 mm. Few age-1 fish were mature but most females were mature at age-2. Analysis of the ovaries collected along the coast indicated some spawning occurred in the spring, a limited amount occurred in the summer, and most spawning occurred during the fall and winter. There was high intra-and interyear variability in the relationship between length and potential number of ova produced, and regression coefficients encompassed values from two previous studies, each based on a single fishing year. Data from this and the previous studies were combined and equally weighted to generate a representative predictive equation for the potential number of ova spawned as a function of length: eggs = 2563e^0.0150(FL).     

Fish community ecology in an Altered River delta: Spatial patterns in species composition, life history strategies, and biomass

We sampled nearshore fishes in the Sacramento-San Joaquin Delta, California, United States, during 2001 and 2003 with beach seines and gill nets. We addressed three questions. How and why did fish assemblages vary, and what local habitat features best explained the variation? Did spatial variation in assemblages reflect greater success of particular life history strategies? Did fish biomass vary among years or, across habitats? Nonmetric multidimensional scaling showed that habitat variables had more influence on fish assemblages than temporal variables. Results from both gear types indicated fish assemblages varied between Sacramento and San Joaquin River sampling sites. Results from gill net sampling were less pronounced than those from beach seine sampling. The Sacramento and San Joaquin river sites differed most notably in terms of water clarity and abundance of submerged aquatic vegetation (SAV), suggesting a link between these habitat characteristics and fish relative abundance. Among-site differences in the relative abundance of periodic and equilibrium strategist species suggested a gradient in the importance of abiotic versus biotic community structuring mechanisms. Fish biomass varied among years, but was generally higher in SAV-dominated habitats than the turbid, open habitats in which we found highest abundances of striped bassMorone saxatilis and special-status native fishes such as delta smeltHypomesus transpacificus, Chinook salmonOncorhyncus tschawytscha, and splittailPogonichthys macrolepidotus. The low abundance of special-status fishes in the comparatively productive SAV-dominated habitats suggests these species would benefit more from large-scale restoration actions that result in abiotic variability that mirrors natural river-estuary habitat than from actions that emphasize local (site-specific) productivity.     

Spawning of the tidewater silverside,Menidia peninsulae (goode and bean), in response to tidal and lighting schedules in the laboratory

Tidewater silversides,Menidia peninsulae (Goode and Bean) were maintained in 1.3 m diameter holding tanks in identical laboratory recirculating systems. During two weeks under constant conditions (a current velocity of 8 cm per s and continuous illumination, 24L:0D) there was a low relative frequency of arrhythmic spawning. In the subsequent two-week period, fish in one pair of tanks, were maintained under the singular influence of twice daily interruptions in current velocity (8 to 0 cm per s at 0600–0700 and 1800–1900) with continuous illumination. The relative frequency of spawning remained low and there was no evidence of a daily spawning rhythm. However, the mean number of eggs per spawn increased substantially. Fish in the second holding system were subjected to a diel light cycle of 13L:11D with a constant current velocity of 8 cm per s for two weeks. The relative frequency of spawning remained low, and there was no indication of spawning rhythmicity; moreover, there was only a slight increase in the mean number of eggs per spawn. During the third two-week period, fish in the first pair of tanks were provided a 13L:11D diel light cycle, in conjunction with preexisting twice daily interruptions in current velocity; those in the second pair of tanks were provided twice daily interruptions in current velocity in conjunction with the preexisting 13L:11D light cycle. Under the combined influence of interrupted current velocity and diel light cycle cues, there was a marked increase in the relative frequency of spawning in both pairs of tanks. Fish manifested a discernible spawning periodicity, spawns typically occurred between 1800 and 2400; the mean number of eggs per spawn also increased. When fish were returned to constant conditions, current velocity 8 cm per s and 24L:0D for two weeks, the frequency of spawning decreased and there was no indication of a spawning periodicity. Results of another experiment (interrupted current at 1200 to 1300 and 2400 to 0100 with a 13L:11D light cycle) indicated gradual expression of a tidal spawning rhythm during nighttime, 2400 to 0359. Our laboratory results indicate thatM. peninsulae is predominantly a nocturnal spawner and that spawning coincides with interruptions in current velocities.     

The abundance of fish larvae in estuaries: Within-tide variability at inlet and immigration

The larvae of winter spawning fishes immigrating through Beaufort Inlet into the Pamlico Sound estuarine system (North Carolina, United States) were passively sampled during 14 flood tides and nine of the following ebb tides. Five taxa were abundant in the catches. Pelagic species were represented by Atlantic menhaden, Brevoortia tyrannus. Nonpelagic taxa were represented by Atlantic croaker, Micropogonias undulatus, spot, Leiostomus xanthurus, pinfish, Lagodon rhomboides, and flatfishes of the genus Paralichthys. The sampling was continuous and the sample duration varied between 4 min and 32 min. The longest samples furnished the most accurate and precise estimates of the mean tidal abundance. Sampling 10 min each hour of the tide was the most efficient protocol for determining the mean tidal abundance. The abundance patterns was shown to differ according to the pelagic or nonpelagic behavior of the larvae. Analyses suggested the nonpelagic taxa rely on astronomical tides and vertical migrations synchronous with the direction of the tide flow to be transported upstream in the estuary. These larvae were not dependent upon the strength of the tide to penetrate the inlet. In contrast, menhaden larvae seemed to rely primarily on strong food tides to enter the estuarine area, probably because the vertical positioning of the species within the water column is not dependent upon the direction of the tide. However, if larvae were present outside of the inlet, strong flood tides indiscriminately brought pelagic and nonpelagic species into the estuary.     

Using Hydroacoustics to Understand Fish Presence and Vertical Distribution in a Tidally Dynamic Region Targeted for Energy Extraction

The use of tidal currents by fishes for movements to and from onshore spawning, foraging, and nursery grounds is well documented. However, fishes’ use of the water column in tidal currents frequently exceeding 1.5 m?·?s^-1 is largely unknown. With growing interest in extracting energy from the tides, understanding animal use of these dynamic environments has become essential to determining environmental effects of tidal energy devices. To assess the effects of a tidal energy device on fishes, we used down-looking single-beam hydroacoustic technology to collect pre-deployment data on the presence and vertical distribution of fishes at a pilot project site and a control site in Cobscook Bay, ME. Twenty-four-hour stationary surveys were conducted in each season of 2010 and 2011. Relative fish density and vertical distribution were analyzed for variation with respect to site, year, month, and diel and tidal cycles. A seasonal pattern in fish density was apparent in both years at both sites, with maxima in spring and late fall. Fish density was generally highest near the sea floor. Diel changes in vertical distribution were frequently observed, but changes in distribution related to tidal cycle were inconsistent. Results from the project and control sites were very similar, demonstrating that the control site provides a reference for quantifying changes in fish density and vertical distribution related to the tidal device. This approach and baseline dataset will be used to compare hydroacoustic data collected at the project and control sites after device deployment.     

Migrations of adult horseshoe crabs,Limulus polyphemus, in the Middle Atlantic Bight: A 17-year tagging study

Adult horseshoe crabs,Limulus polyphemus, were tagged in the Middle Atlantic Bight area, from New York to Virginia on the continental shelf and within bays, to determine their migratory patterns and longevity. Of 30,432 horreshoe crabs that were tagged during the years 1986–2002, 1,122 were recovered alive, and 1,027 were dead. Many of the live recoveries were observed within 30 d (54.4%) and after years (37.53%) with one tagged animal surviving up to 10 yr. In 9 locations from Great Kills Harbor, New York, to Chesapeake Bay, Maryland, the horseshoe crabs return to their release beach within days during the spawning season. Of the 762 (100%) recoveries from crabs released along the Delaware Bay shoreline, 75.07% traveled 0–20 km, 21.0% traveled 20–50 km, 2.36% traveled 50–100 km, and 1.57% traveled over 100 km. Within Delaware Bay, 327 tagged animals (43.6%) had moved away from the release points to other locations, and 59 of these had moved out of the bay onto the continental shelf along the Mid-Atlantic Bight coastline. Horseshoe crabs migrate into Delaware Bay from waters off Ocean City, Maryland, and adjacent coastal bays. In addition to defining the range of the Delaware Bay spawning populations, 2 neighboring populations were identified by the tagging program. In one, animals tagged in southern New York mingled with those in the Sandy, Hook, New Jersey area, comprising a population that ranged from Raritan Bay across New York Harbor to Jamaica Bay. The second confirmed that a discrete population existed in northern Chesapeake Bay in the general vicinity of the Annapolis Bay Bridge.