Walter H. Pearson

Thresholds for detection and feeding behavior in the dungeness crab, Cancer magister (Dana)

Abstract After observation and description of feeding behavior, the chemosensory ability of the Dungeness crab, Cancer magister (Dana) was measured with sea-water solutions of a freeze-dried extract of the littleneck clam, Protothaca staminea (Conrad). An abrupt change in antennular orientation accompanied by a specified increase in the antennular flicking rate indicated that a crab detected the food extract. The threshold concentration at which 50% of the crabs detected the clam extract was 10 −10 g/l At 10 −2 g/l crabs probed the substratum with the chelae and/or showed other feeding behavior. The chemosensory abilities of the Dungeness crab were compared with those of other crustaceans.

Clam burrowing behaviour: inhibition by copper-enriched sediment

Burrowing behaviour is adaptive and allows clams to escape predation; yet the effects of potentially toxic metals on such behaviour have not been adequately investigated. In natural marine sediment contaminated with copper the time for littleneck clams (Protothaca staminea) to achieve complete burial was recorded. Above a threshold of 5.8 μg g−1 Cu added to dry sediment, the time for 50% of the clams to burrow (ET50) increased logarithmically with increasing sediment copper concentration according to: logET50 = 0.15 (CU) - 1.37 (n = 4, r2 = 0.98) where ET50=time in hours for 50% of clams to burrow and Cu=μg g−1 Cu in dry sediment. Previously exposed clams had both a lower threshold to Cu and a longer reburrowing time (ET50). Clams exposed to sediment mixed with Chelex-100®-sorbed copper showed no significant change in burrowing time. Bioassays based on claim burrowing behaviour can measure both bioeffectiveness of sediment-sorbed metals and a sublethal effect with ecological meaning.

Effects of oiled sediment on the burrowing behaviour of the hard clam, Mercenaria Mercenaria

Abstract The burrowing behaviour of juvenile hard clams, Mercenaria mercenaria , in oil-contaminated sediment was examined in a series of laboratory experiments. At oil concentrations within the range that might occur after an oil spill, depth and rate of burrowing were altered. The depth to which clams in oiled sediment burrowed after 96 h was significantly shallower than the depth in the controls, while the time taken to burrow beneath the surface was longer in oil-contaminated sediment. Alterations in burrowing were indicative of avoidance behaviour rather than oil-induced debilitation. The results suggest that such alterations may increase the vulnerability of this species to predation.

Hypotheses concerning the decline and poor recovery of Pacific herring in Prince William Sound, Alaska

This paper updates previous reviews of the 1993 stock decline of Pacific herring (Clupea pallasi) in Prince William Sound, Alaska, and focuses on hypotheses about subsequent poor recovery. Recent age structured assessment modeling with covariate analysis indicates that the population dynamics of the sound’s herring are influenced by oceanic factors, nutrition, and, most substantially, hatchery releases of juvenile pink salmon. For the 1993 decline, poor nutrition remains the most probable cause with disease a secondary response. Concerning poor recovery, we examined 16 potential factors and found three to be causal: oceanic factors, poor nutrition, and hatchery releases of juvenile pink salmon. Absences of strong year classes at both Sitka and Prince William Sound after 1993 indicate the action of large-scale ocean processes. Beyond regional-scale environmental factors, two factors specific to the sound influence the population dynamics of herring and are likely impeding recovery. First, pink salmon fry releases have increased to about 600 million annually and may disrupt feeding in young herring, which require adequate nutrition for growth and overwintering survival. Juvenile pink salmon and age-1 herring co-occur in nearshore areas of bays in late spring and summer, and available data on dietary overlap indicates potential competition between the age-1 juvenile herring and juvenile pink salmon. Field studies demonstrate that juvenile herring reduce food intake substantially in the presence of juvenile pink salmon. Second, overwintering humpback whales may consume potentially large amounts of adult herring, but further studies must confirm to what extent whale predation reduces herring biomass.

Threshold for Detection of Naphthalene and Other Behavioral Responses by the Blue Crab, Callinectes sapidus

Using behavioral criteria developed in previous studies, the threshold concentration at which the blue crab,Callinectes sapidus, detected the petroleum hydrocarbon naphthalene was found to be 10−7 mg/l. Oriented locomotor activity and defensive displaying began at 2 mg/l of naphthalene. No feeding behavior was observed up to and including the maximum naphthalene concentration of 5 mg/l. Below 2 mg/l the blue crab apparently had no active behavioral response to naphthalene exposure other than detection.

Clam burrowing behaviour and mortality related to sediment copper

Abstract Gravel sediment freshly enriched with over 4.4 μg Cu g−1 significantly increased the burrowing and reburrowing times of Littleneck marine clams (Protothaca staminea). Abnormal burrowing behaviour was observed with time-lapse video. Aged (1 day) copper-enriched sediment did not affect clam burrowing time. Copper in sediment porewater declined three days after sediment enrichment to background levels without change in total sediment copper. In a long-term experiment, clams with increased burrowing time into copper-enriched sediment had up to 25% mortality after 12–29 days burial in the sediment. The majority of clam mortality was found in clams burrowing within the first 48 h. Over 7 weeks there was blackening of sediment and clam shells proportional to sediment copper enrichment.

The burrowing behavior of sand lance, Ammodytes hexapterus: Effects of oil-contaminated sediment

Abstract Whilst foraging in the water column for zooplankton, sand lance, Ammodytes hexapterus , are under heavy predation from marine birds and fish. To avoid predation, sand lance bury in the sand when not foraging and during overwintering. We did two experiments to determine whether oil contamination of the sand would reduce the amount of time that sand lance spent buried. In the first experiment (June, 1980) sand lance significantly decreased by 20% the time spent buried in oiled sand (306 ppm). In the second experiment (June, 1981) sand lance did not decrease time spent buried in oiled sand at 28 and 256 ppm but did at 3384 ppm. The higher condition index of the 1981 fish suggested that nutritional state may have influenced how sand lance used the sediment as a refuge and how they responded to contamination of that refuge.

Juvenile Coho Salmon Leaping Ability and Behavior in an Experimental Culvert Test Bed

Abstract As part of a research program aimed at identifying the culvert configurations and associated hydraulic conditions that foster the successful upstream movement of juvenile salmon, we investigated the ability of hatchery-raised juvenile coho salmon Oncorhynchus kisutch to leap into an experimental culvert under varying hydraulic conditions. Five outfall drops ranging from 0 to 32 cm were tested to represent differing degrees of culvert outfall drop. Trials were run at a culvert discharge of 0.028 m3/s and a tailwater pool depth of 30 cm. The median success rate was highest (85%) for the 0-cm drop, followed by 34% at 12 cm, 20% at 20 cm, 2% at 26 cm, and 0% at 32 cm. When overcoming the 0-cm (streaming flow) and 12-cm drops, fish predominantly used swimming behavior. For the outfall drops of 20 and 26 cm, leaping behavior predominated. In a typical leaping event, fish initiated the leap near the floor of the tailwater tank and used burst swimming to propel their bodies from near the standing wave (p...

TOXICITY AND PERSISTENCE OF NEARSHORE SEDIMENT CONTAMINATION FOLLOWING THE 1991 GULF WAR

Abstract In January 1991, the worlds largest oil spill inundated extensive coastal areas of the Gulf with massive quantities of crude oil. In August 1993, the authors collected sediment samples from eleven beach sites at four tidal elevations in Kuwait and Saudi Arabia. Ten-day static sediment toxicity tests with the marine amphipod Rhepoxynius abronius revealed significant sediment toxicity (reduced survival) at five sites. Infrared spectrometry indicated that the highest concentrations of petroleum hydrocarbons occurred at these same five sites. Other variables such as ammonia concentration, silt and clay content, and total organic matter in the sediment had no affect on amphipod survival. Concentrations of petroleum hydrocarbons greater than about 1 mg g −1 dry sediment caused significant amphipod mortality. Such toxic sediment concentrations occurred at Al Khiran, Kuwait, and along an extensive coastal area of Saudi Arabia from Ras Tanajib to Abu Ali (a distance of over 100 km). The overall area of sediment toxicity corresponds closely to the spill trajectory and presence of sea surface petroleum as recorded on airborne radar soon after the spill (9 March 1991). These results indicate that sediment toxicity from the worlds largest oil spill persisted for at least 30 months. Additionally, petroleum hydrocarbon concentrations in the sediments of contaminated sites were sufficiently high to cause continued leaching of oil to the sea-surface.

Effects of seismic energy releases on the survival and development of zoeal larvae of dungeness crab (Cancer magister)

In blind, controlled field experiments, early Stage II zoeae of Dungeness crab (Cancer magister DANA) were exposed to sounds from single discharges of a 13·8-litre array of seven air guns. Their survival and development were followed during subsequent laboratory culture. Immediate mortality was low (0 to 2%) and showed no significant difference between control and exposed larvae (α > 0·05). Across all treatments and blocks of the experiment, survival to the molt to Stage III averaged 88·8%. The conditional Stage IV survival rate averaged 69·8%. The times to the molts to Stage III and Stage IV averaged 14·4 and 34·9 days, respectively. For immediate and long-term survival and time to molt, the field experiment revealed no statistically significant (α > 0·05) effects on zoeae for exposures as close as I m from the array, nor for mean sound pressure as high as 231 dB re 1 μPa and cumulative energy density up to 251 J/M2. Post hoc power calculations showed that any reduction in zoeal survival as a result of sound exposure was less than 7% for survival to Stage III and less than 12% for Stage IV conditional survival (1-β = 0·90, α = 0·05 one-tailed). The sound exposures in our study were at the maximum levels likely to be experienced by a zoea during an actual survey.