Sibling cannibalism among juvenile vundu under controlled conditions. II. Effect of body weight and environmental variables on the periodicity and intensity of type II cannibalism

Cannibalism among starved groups of juvenile (19–48 days old) vundu catfish Heterobranchus longifilis was 66·5% nocturnal, and its impact under modified day length was proportional to the duration of the dark phase. Shallow depth and high population density decreased the intensity of cannibalism, whereas low density and deeper environments had an opposite effect. The presence of refuges had no significant effect on cannibalism. The maintenance ( R _maint) and maximum ( R _max) daily food rations (% day⁻¹) of cannibals feeding on live prey were modelled as R _maint=3·899 W _C^0·327 ( r ²=0·684; d.f.=31), and R _max=49.545 W _C^0·321 ( r ²=0·999; d.f.=5), where W _C was the body weight of the cannibal (g). The latter model indicated that the impact of a cannibal on a population decreased by a 20% margin each time the cannibal doubled its body weight, and suggested that cannibalism among vundu would become insignificant for cannibals heavier than 30 g. The significance of these findings is discussed within the contexts of vundu aquaculture and of general, conceptual models of the dynamics of cannibalism among fishes.     

Effects of isokinetic training of the knee extensors on isometric strength and peak power output during cycling

Isokinetic training of right and left quadriceps femoris was undertaken three times per week for 16 weeks. One group of subjects (n = 13) trained at an angular velocity of 4.19 rad.s-1 and a second group (n = 10) at 1.05 rad.s-1. A control group (n = 10) performed no training. Maximal voluntary contraction (MVC) of the quadriceps, and peak pedal velocity nu p,peak) and peak power output (Wpeak) during all-out cycling (against loads equivalent to 9, 10, 11, 12, 13 and 14% MVC) were assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of the performance variables (P > 0.05). No significant difference in MVC was observed for any group after the 16-week period (P = 0.167). The post-training increases in average Wpeak (7%) and nu p,peak (6%) during the cycle tests were each significantly different from the control group response (P = 0.018 and P = 0.008, respectively). It is concluded that 16 weeks of isokinetic strength training of the knee extensors is able to significantly improve nu p, peak and Wpeak during spring cycling, an activity which demands considerable involvement of the trained muscle group but with its own distinct pattern of coordination.     

Multi-scale heterogeneity in a macrobenthic epifauna community

A quantitative study, based on monthly samples taken by divers with 0.1m² quadrats, was conducted on a benthic community settling coarse sediments in an area exposed to strong water currents.The richness of the community was high both in terms of biomass (270±107 g m^–2 in ash-free dry weight) and diversity (ten zoologicals groups for a total of 98 species). Three suspension feeding species were dominant: Ophiothrix fragilis, Urticina felina and Alcyonium digitatum accounted for more than 95% of the total biomass at all sampling periods.Spatial heterogeneity analysis confirmed the role of these three dominant species. Heterogeneity revealed at a scale of 0.1 m² by dendrograms (qualitative similarity index) or by Factor Correspondence Analysis (FCA) (on biomasses) was due to the strong dispersion of rare species.The influence of the observation scale was visualised by building Rank-Frequency Diagrams using progressively aggregated replicates. The distribution of relative biomasses and the rank of the dominant species always stabilized at scale of 0.4 or 0.5 m².The three dominant species were overdispersed at a scale of 0.1 m² compared with a Poisson distribution. Spatial competition among the three species was suggested by their dispersion in the plane of the FCA. Calculation of a multiple linear regression (at the scale of 0.8 m²) showed negative relationships among these dominant species.Temporal homogeneity was indicated (at a scale of 0.8 m²) by dendrograms of species similarities among samples and by FCA performed on total biomasses.     

The Effects of Skeletal Muscle Contractions and Paralysis on Physiological Responses to Head Immersion in Pekin Duck

This study investigated whether increases and decreases in pectoral muscle metabolism influence underwater endurance time and cardiovascular responses to head submersion in Pekin ducks. Muscle metabolic rate (anaerobic ATP synthesis) was estimated using ³¹P magnetic resonance spectroscopy, and was manipulated by direct electrical stimulation and by pharmacological paralysis. These manipulations had no significant effect on underwater endurance times or cardiovascular responses to head immersion (heart rate, mean arterial blood pressure). Anaerobic ATP synthesis was not detectable in paralyzed muscle during head immersion, implying that muscle metabolic rate was reduced to less than 10% of normal resting values. Despite this, underwater endurance times were not significantly extended. We conclude that muscle metabolic rate per se does not influence the maximum breath-hold time in this species.     

DIVING BEHAVIOR OF THE SAIMAA RINGED SEAL (PHOCA HISPIDA SAIMENSIS NORDQ.)

The activity and diving patterns of four adult Saimaa ringed seals ( Phoca hispida saimensis , a landlocked subspecies living in Lake Saimaa, Finland) were examined during spring, summer, and autumn by the use of VHF-transmitters. Over 17,000 dives were registered. The duration of the dives and diving patterns differed among individuals. The mean duration of dives increased from spring to autumn; e.g. , in one individual the mean dive duration increased from 6 min in June to 10.5 min in October. The haul-out periods of one individual in May to early June made up 46.2% of its total activity budget, but in another individual in July to August the haul-out periods made up only 11% of the budget and the seal was submerged for 80% of the time. Periods of successive long duration dives (>10 min) were observed in three individuals in summer and autumn. The longest dive measured was 23 min. The duration of the periods containing long dives was often over three hours (maximum six hours) and the mean duration of the dives about 15 min. These long duration dives are assumed to be aerobic resting dives. Generally, the dives of the Saimaa ringed seal appear to be of longer duration than previously assumed.     

DIVING BEHAVIOR AND PERFORMANCE OF HARBOR PORPOISES, PHOCOENA PHOCOENA, IN FUNKA BAY, HOKKAIDO, JAPAN

In order to monitor the diving behavior of free-ranging cetaceans, microdataloggers, with pre-programmed release mechanisms, were attached to the dorsal fins of two female harbor porpoises ( Phocoena phocoena ) in Funka Bay, Hokkaido, Japan, in 1994. The two loggers were successfully recovered and a total of 141 h of diving data (depth and water temperature in 4,671 dives) was obtained. Both porpoises dived almost continuously, rarely exhibiting long-term rest at the surface. Maximum dive depths were 98.6 m and 70.8 m, respectively, with more than 70% of diving time at 20 m or less. Most shallow dives were V-shaped with no bottom time. The V-shaped dives were significantly shallower in dive depth and shorter in dive duration than U-shaped dives. Descent rate was not constant during a dive. The deeper the dive depths, the faster the mean descent and initial descent rates. This suggests that porpoises have anticipated the depth to which they will dive before initiating the dive itself.     

FORAGING DEPTHS OF SEA OTTERS AND IMPLICATIONS TO COASTAL MARINE COMMUNITIES

We visually observed 1,251 dives, of 14 sea otters instrumented with TDRs in southeast Alaska, and used attribute values from observed dives to classify 180,848 recorded dives as foraging (0.64), or traveling (0.36). Foraging dives were significantly deeper, with longer durations, bottom times, and postdive surface intervals, and greater descent and ascent rates, compared to traveling dives. Most foraging occurred in depths between 2 and 30 m (0.84), although 0.16 of all foraging was between 30 and 100 m. Nine animals, including all five males, demonstrated bimodal patterns in foraging depths, with peaks between 5 and 15 m and 30 and 60 m, whereas five of nine females foraged at an average depth of 10 m. Mean shallow foraging depth was 8 m, and mean deep foraging depth was 44 m. Maximum foraging depths averaged 61 m (54 and 82 for females and males, respectively) and ranged from 35 to 100 m. Female sea otters dove to depths ≤20 m on 0.85 of their foraging dives while male sea otters dove to depths ≥45 m on 0.50 of their foraging dives. Less than 0.02 of all foraging dives were >55 m, suggesting that effects of sea otter foraging on nearshore marine communities should diminish at greater depths. However, recolonization of vacant habitat by high densities of adult male sea otters may result in initial reductions of some prey species at depths >55 m.     

Scalloped hammerhead shark Sphyrna lewini, utilizes deep-water, hypoxic zone in the Gulf of California

A hammerhead shark Sphyrna lewini tracked for 74 days revealed an expansion of the range of vertical distribution for the species to include the extreme hypoxic environment of the oxygen minimum layer in the Gulf of California.