Observations Of Distribution, Size, And Sex Ratio Of Mature Blue Crabs, Callinectes Sapidus, From A Chesapeake Bay Tributary In Relation To Oyster Habitat And Environmental Factors

Blue crabs Callinectes sapidus (Rathbun, 1896) \u3e 100 mm carapace width were sampled from a constructed oyster reef (1996 and 1997), a sand bar (1997) and a natural oyster bar (1997) in the Piankatank River, Chesapeake Bay, USA to describe habitat use, sex ratios, and demographics across a gradient of habitat types. Patterns of blue crab catch-per-unit-effort (CPUE), and demographics were similar on the oyster reef in 1996 and 1997. Average annual CPUE on the reef was 6-8 crabs pot(-1) with maximum CPUE of 15 crabs pot(-1). Daylength and water temperature significantly affected reef CPUE with more crabs observed in late August and early September. In 1997, average annual CPUE at the natural oyster bar was higher (9 crabs pot(-1)) than on the reef or the sand bar (both 6-7 crabs pot(-1)). Observed differences in habitat use may relate to site-specific differences in depth and tidal current as well as the presence of living oyster (biogenic) substrate. A transition in the sex ratio of crabs was observed as daylength declined seasonally. In May, males were 3-5 times more abundant than females at all sites but by early September, as daylength and water temperatures declined, female crabs were 3-4 times more abundant than males at all sites. The median size of males and females increased from spring into summer and female crabs were typically larger than males from the same habitats across all habitat types. The largest female crabs were observed in habitats with oysters. Biogenic oyster habitats are important estuarine habitats for blue crabs as well as oysters

Estimates of naked Goby (Gobiosoma bosc), striped blenny (Chasmodes bosquianus) and Eastern oyster (Crassostrea virginica) larval production around a restored Chesapeake Bay oyster reef

Naked gobies (Gobiosoma bose) and striped blennies (Chasmodes bosquianus) rely on oyster reefs for nesting sites, feeding grounds, and refugia from predation by upper level piscivores. Seasonal densities of Eastern oysters (Crassostrea virginica), naked gobies, and striped blennies on Palace Bar Reef, Piankatank River, Virginia were quantified and used to develop species-specific larval production estimates. Densities of oyster adults, juveniles, and articulated shell valves (the result of recent mortality) did not significantly change from November 1995 to November 1996. Naked goby and striped blenny densities varied with substrate type and season; peak fish densities for both species were observed in August 1996. Areas where shell substrate dominated the bottom supported fish densities up to 14 times greater than those observed in habitat areas lacking shell. Larval production and recruitment estimates for Palace Bar Reef oysters are of the same order of magnitude as observed field densities. Benthic fish production estimates are within an order of magnitude of adult densities and are similar to previous recruitment estimates for Chesapeake Bay naked gobies. Species-specific production estimates for both oysters and fishes are sufficient to sustain observed adult densities on Palace Bar Reef, Piankatank River, Virginia

Veined Rapa Whelk (Rapana Venosa) Range Extensions in the Virginia Waters Of Chesapeake Bay, USA

Three recent range extensions for the Chesapeake Bay, Virginia, veined rapa whelk (Rapana venosa) population are described. These extensions into Tangier Sound, the mid James River estuary, and to Cape Henry at the Bay mouth extend respectively, the northern, western, and southeastern boundaries of the occupied rapa whelk range in Virginia waters. Salinity and tidal circulation mediate the distribution of adults and larvae of this animal. During dry years (e.g., 2001 and 2002) adult rapa whelks may move up-estuary in western tributaries like the James River, given increased salinity and available habitat and food resources. Declines in salinities (or return to normal salinities) will either kill the rapa whelks in the upriver habitats or force a return to downstream habitats

Age And Growth Of Wild Suminoe (Crassostrea Ariakensis, Fugita 1913) And Pacific (C-Gigas, Thunberg 1793) Oysters From Laizhou Bay, China

Shell height at age estimates from Suminoe (Crassostrea ariakensis) and Pacific (C. gigas) oysters from a natural oyster reef in Laizhou Bay, China were compared with shell height at age estimates from triploid C. ariakensis of known age from the Rappahannock River, Virginia. C. ariakensis and C. gigas reach shell heights in excess of 76 mm (3 inches) within 2 years after settlement regardless of the source location. This fast growth appears to continue through at least we 4 or age 5 in wild individuals, because the growth trajectories for both specie, had not reached asymptotic height in (he oldest individuals collected. Estimates of the asymptotic maximum height (SHmax) from fitted Von Bertalanffy (VB) growth models were greatest for Chinese C. ariakensis (244.0 mm, standard error of the mean [SE] 30.4) and near the maximum shell height (227.0 mm) measured at the time of collection. Maximum shell heights measured on live Chinese C. gigas (173.0 mm) and Rappahannock C. ariakensis (190.0 mm) were also within the standard error estimates for the SHmax estimates from the fitted VB models for Chinese C. gigas (158.6 mm, SE 20.3) and Rappahannock C. ariakensis (183 mm, SE 19.1). Fitted VB growth curves were not significantly different between species within the same habitat, within species in different habitats or between species in different habitats. The ratio of shell height to shell width and shell height to shell inflation for triploid C. ariakensis was significantly less than similar ratios observed in wild C. ariakensis and C. gigas oysters

Fish species richness in relation to restored oyster reefs, Piankatank River, Virginia

Fish assemblages in relation to “reef” structures in marine habitats have been and continue to be topics for research addressing ecological and management questions. Much effort has been spent describing and defining fish assemblages, or groups of species, associated with tropical coral reefs (e.g., Sale 1991 and chapters therein), temperate hard bottom or rocky reefs (e.g., Sedberry and Van Dolah, 1984; Ambrose and Swarbrick, 1989), tropical lava flows (e.g., Godwin and Kosaki, 1989), and artificial “fishing” reefs (e.g., Chandler et al., 1985; Hueckel and Buckley, 1987; Bohnsack, 1989; Feigenbaum et al., 1989; Rountree, 1989; Stephan and Lindquist, 1989). Temperate oyster reefs, another natural reef type, host diverse finfish assemblages that are just beginning to be described (e.g., Wenner et al. 1996; Mann and Harding, 1997; Luckenbach et al. 1998 and references therein). Before Eastern oyster (Crassostrea virginica) populations were significantly reduced by environmental degradation, fishing pressure, and disease, oyster reefs dominated the intertidal areas of Chesapeake Bay and supported complex ecological communities including many fish species. The living shell matrix created by these predominantly intertidal, estuarine reefs provides structural heterogeneity and vertical relief that attract and sustain fishes from many trophic levels similar to living coral reefs (Roberts and Ormond, 1987; Ebeling and Hixon, 1991; Friedlander and Parrish, 1998). Recreationally and commercially valuable piscivorous finfishes including striped bass (Morone saxatilis), bluefish (Pomatomus saltatrix), and weakfish (Cynoscion regalis) were and are integral components of trophic networks that depend on oyster reefs (Mann and Harding, 1997, 1998). These pelagic finfishes use oyster reefs as both feeding and nursery grounds (e.g., Breitburg, 1998; Mann and Harding, 1997, 1998; J. Harding and R. Mann, unpubl. data)

Influence of habitat on diet and distribution of striped bass (Morone saxatilis) in a temperate estuary

Striped bass (Morone saxatilis) are recreationally and commercially valuable finfish along the Atlantic seaboard of North America including the Chesapeake Bay estuary. Habitat use patterns for striped bass in relation to biogenic habitat types in Chesapeake Bay tributaries are poorly described although it is widely acknowledged that these piscivorous fishes use estuarine habitat for nursery and feeding grounds during development. Striped bass diet and distribution patterns were examined in relation to a gradient of biogenic habitats ranging from complex three-dimensional oyster reef through flat oyster bar to sand bottom habitat in the Piankatank River, Virginia. Striped bass were more abundant at both sites with oysters and oyster shell substrate than at the site with sand substrate. Striped bass in association with the three-dimensional oyster reef were larger and consumed more teleosts (e.g., naked gobies) than fish at either of the non-reef sites. Striped bass estuarine habitat use is positively correlated with the presence of oyster reef habitat that includes physical structure and food resources via complex trophic communities centered on the oyster reef

Rapa Whelk Rapana Venosa (Valenciennes, 1846) Predation Rates On Hard Clams Mercenaria Mercenaria (Linnaeus, 1758)

The recent discovery of adult veined rapa whelks Rapana venosa (Valenciennes, 1846) in the Lower Chesapeake Bay, U.S.A. offers cause for both ecological and economic concern. Adult rapa whelks are large predatory gastropods that consume bivalves including commercially valuable species such as hard clams, Mercenaria mercenaria (Linnaeus, 1758). Laboratory feeding experiments were used to estimate daily consumption rates of two sizes of whelks feeding on two size classes of hard clams. Large rapa whelks (shell length, SL \u3e 101 mm) are capable of consuming up to 2.7 g wet weight of clam tissue daily, equivalent to 0.8% of their body weight. Small whelks (60-100 mm SL) ingest an average of 3.6% of their body weight per day

Gaze-contingent training enhances perceptual skill acquisition.

The purpose of this study was to determine whether decision-making skill in perceptual-cognitive tasks could be enhanced using a training technique that impaired selective areas of the visual field. Recreational basketball players performed perceptual training over 3 days while viewing with a gaze-contingent manipulation that displayed either (a) a moving window (clear central and blurred peripheral vision), (b) a moving mask (blurred central and clear peripheral vision), or (c) full (unrestricted) vision. During the training, participants watched video clips of basketball play and at the conclusion of each clip made a decision about to which teammate the player in possession of the ball should pass. A further control group watched unrelated videos with full vision. The effects of training were assessed using separate tests of decision-making skill conducted in a pretest, posttest, and 2-week retention test. The accuracy of decision making was greater in the posttest than in the pretest for all three intervention groups when compared with the control group. Remarkably, training with blurred peripheral vision resulted in a further improvement in performance from posttest to retention test that was not apparent for the other groups. The type of training had no measurable impact on the visual search strategies of the participants, and so the training improvements appear to be grounded in changes in information pickup. The findings show that learning with impaired peripheral vision offers a promising form of training to support improvements in perceptual skill

The contributions of central and peripheral vision to expertise in basketball: How blur helps to provide a clearer picture

The main purpose of this study was to examine the relative roles of central and peripheral vision when performing a dynamic forced-choice task. We did so by using a gaze-contingent display with different levels of blur in an effort to (a) test the limit of visual resolution necessary for information pick-up in each of these sectors of the visual field and, as a result, to (b) develop a more natural means of gaze-contingent display using a blurred central or peripheral visual field. The expert advantage seen in usual whole field visual presentation persists despite surprisingly high levels of impairment to central or peripheral vision. Consistent with the well-established central/peripheral differences in sensitivity to spatial frequency, high levels of blur did not prevent better-than-chance performance by skilled players when peripheral information was blurred, but they did affect response accuracy when impairing central vision. Blur was found to always alter the pattern of eye movements before it decreased task performance. The evidence accumulated across the 4 experiments provides new insights into several key questions surrounding the role that different sectors of the visual field play in expertise in dynamic, time-constrained tasks