Subsurface behavior of bottlenose dolphins (Tursiops truncatus) interacting with fish trawl nets in northwestern Australia: Implications for bycatch mitigation

Most studies of delphinid‐trawler interactions have documented the surface behavior of dolphins feeding on discarded bycatch, but not their subsurface behavior around demersal trawl gear. Using video cameras mounted inside trawl nets, we recorded the subsurface behavior of common bottlenose dolphins (Tursiops truncatus) in a demersal fish trawl fishery in northwestern Australia. Footage from 36 trawls across the fishery was analyzed to determine the extent of dolphin‐gear interactions and the behavior of dolphins inside the nets. Interaction rates were high, with dolphins present inside and outside the nets during 29 and 34 trawls, respectively, and for up to 99% of the trawl duration. The proportion of foraging behaviors exhibited inside the nets was higher than the proportions of traveling and socializing behaviors. Twenty‐nine individuals were identified inside the net, seven of which returned repeatedly within and between trawls and fishing trips, but were observed primarily in the same localized areas in which they were first recorded. Our results suggest that entering trawl nets may be a frequently occurring, yet specialized behavior exhibited by a small subset of trawler‐associated dolphins. We propose that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch.     

Potassium Fluxes during Potassium Absorption by Intact Barley Plants of Increasing Potassium Content

The presence of previously absorbed K in plants caused a marked reduction in the short term influx of ⁸⁶Rb-labeled K into roots of barley seedlings. The influx values agreed with net K absorption rates into intact plants, thus suggesting that K efflux was negligible in comparison with influx.     

Regional differences in the feeding of the ambush predator Neosebastes pandus and comparisons of diets in the Scorpaenidae,Triglidae and Platycephalidae

This study provides a comprehensive assessment of the dietary composition of the ambush predator Neosebastes pandus and compares the diets of 49 species from 39 studies of three benthic predatory families in the Scorpaeniformes: Scorpaenidae (20 species), Triglidae (19 species) and Platycephalidae (10 species). A total of 275 N. pandus were collected from the west (Rottnest Island) and south (Esperance) coasts of south‐western Australia and the percentage frequency and volumetric contribution of the stomach contents identified. Fish from the west coast consumed a greater mean number of broad taxonomic groups and were more diverse in their diet than fish from the south coast. Cephalopods, brachyurans and teleosts were the largest overall contributors to diet, with teleosts being more important to diets of west‐coast fish and polychaetes for south‐coast fish. This reflects differences in habitat between the two locations. Dietary composition also changed with increasing body size, reflecting morphological changes that allow bigger fish to capture and ingest larger, more mobile prey. Meta‐analysis of the diets of 49 species of scorpaenid, triglid and platycephalid revealed that they feed predominantly on teleosts and large crustaceans. Significant differences in diet were detected among families, with platycephalids being the most distinct and feeding more on teleosts than scorpaenids and triglids.     

Development of three copper metalloenzymes in clover leaves

Subterranean clover (Trifolium subterraneum L. cv Seaton Park) was grown in solution cultures containing adequate nitrogen both with and without Cu. After Cu deficiency had developed, Cu²⁺ was added to some deficient plants and Cu content, protein content, and activities of three Cu metalloenzymes (diamine oxidase [EC1.4.3.6], ascorbate oxidase [EC1.10.3.3] and o-diphenol oxidase [EC1.10.3.1]) were assayed in young and recently matured leaf blades over 11 days during the development of the next three leaves.

Copper deficiency had little effect on protein concentrations, but markedly depressed enzyme activities and Cu concentration in all leaf blades assayed. Within 4 d of adding Cu²⁺ to Cu-deficient plants, Cu concentrations of all the leaf blades increased to adequate values. Enzyme activities only increased to control levels in leaves which had not yet emerged at the time that Cu²⁺ was added.

The results suggest that active holoenzymes of diamine oxidase, ascorbate oxidase, and o-diphenol oxidase can only be synthesized in leaf blades during very early stages of their development.

     

Effect of fire on the topsoil seed banks of rehabilitated bauxite mine sites in the jarrah forest of Western Australia

Summary Germinable seed stores of 5- and 8-year-old rehabilitated bauxite mine pits in south-west Western Australia were assessed before and after burning. These seed stores were compared to those of adjacent unmined Jarrah ( Eucalyptus marginata ) forest, to identify at what age fire can be reintroduced, in order to measure restoration success and reduce fire hazard. Soils were sampled in early summer (before fire) and late autumn (after fire). Before fire, the mean topsoil seed bank of 5-year-old sites was 2121 seeds per m² while 8-year-old sites had a mean of 1520 seeds per m². Only the 5-year-old sites were significantly different from the forest mean of 1478 seeds per m² for the same season. After summer burns (and possibly due to seasonal effects) topsoil seed banks of rehabilitated areas (sampled in autumn) decreased by an average of 53 per cent. Topsoil seed banks of 5–8-year-old sites were resistant to lower intensity burns, with 362 seeds per m² of native species surviving mild burns and 108 seeds per m² of native species surviving after an intense summer fire. The topsoil seed reserve of 5–8-year-old rehabilitated areas had a high proportion of annual weed species while the forest sites had high levels of subshrubs and native annuals. Low-intensity burns did not alter the composition of life-forms in the soil seed bank, while intense burns favoured annual weed and shrub species. The results indicate that it is not appropriate to introduce fire to rehabilitated areas before 8 years, due to limited fuel reduction benefits and possible adverse effects on obligate seeding species. The large proportion of weed species in the soil seed bank of young rehabilitated areas is a concern, and remains a major consideration for future disturbance of these areas.     

Implications of Seedling Emergence to Site Restoration following Bauxite Mining in Western Australia

Seedling emergence of 12 selected northern jarrah (Eucalyptus marginata Donn ex Smith) forest species were investigated to assist Alcoa of Australia Ltd. in maximizing the establishment of topsoil species in rehabilitated bauxite mining sites. The species, which encompassed a range of seed weights (0.024 mg to 87 mg), plant families, seed-storage types, life forms, and germination requirements, were placed on the soil surface and at depths of 1, 2, 5, 10, and 15 cm under controlled conditions in a glasshouse. Ability to emerge from deep burial was found to depend on seed size for species that annually release their seed to the topsoil but not for species that store their seed on the plant. All selected species were capable of emerging from 2 cm depth of burial, but eight of the 12 species were either unable to emerge from 5 cm or showed a significant reduction in emergence from 5 cm depth of burial compared to optimally buried seed. This group included two small-seeded species, Stylidium calcaratum and Chamaescilla corymbosa; the major forest dominant, Eucalyptus marginata; the serotinous canopy-borne seed of Hakea amplexicaulis; and the wind-dispersed seed of Xanthorrhoea gracilis. A few seeds of the legume species Kennedia coccinea, Acacia pulchella, and Bossiaea aquifolium established seedlings from depths of 15 cm. Currently, Alcoa removes the upper 15 cm of topsoil separately from the underlying soil prior to the commencement of mining. This topsoil is respread at a similar depth following mining as part of the rehabilitation procedure. It is recommended that Alcoa continue to strip topsoil to a depth of 15 cm but investigate the option of re-spreading topsoil onto rehabilitated pits at a shallower depth to maximize establishment via the soil seed bank.     

Plant nutrition in the 20th and perspectives for the 21st century

This paper briefly presents the knowledge of plant nutrition in 1900 and its expansion since then in two areas - the discovery of the micronutrients and the absorption of nutrients from soils.Application of macro- and micronutrient fertilizers has contributed substantially to the huge increase in world food production experienced this century. In developed countries, excessive fertilizer use has led to serious problems of nutrient pollution; here, plant nutritionists will be concerned with monitoring nutrient status of crops and soils to maintain crop production with minimum loss of nutrients to the environment, and development of cultivars with high nutrient efficiency in soils with luxury supplies of nutrients.In many developing countries, soil infertility limits productivity; here, plant nutritional research can raise productivity by diagnosis of nutrient deficiencies and toxicities of crops on previously unfertilized soils, their correction with minimal fertilizer and treatment costs, and development of cultivars with high nutrient efficiency in deficient soils and high tolerance of natural toxicities.The pre-occupation of developed countries with pollution is blinding them to the urgent needs of developing countries for fertilizers and fertilizer research to increase crop production ha-1 as an alternative to clearing more land.     

Escherichia coli O157:H7 Strains That Persist in Feedlot Cattle Are Genetically Related and Demonstrate an Enhanced Ability To Adhere to Intestinal Epithelial Cells

A longitudinal study was conducted to investigate the nature of Escherichia coli O157:H7 colonization of feedlot cattle over the final 100 to 110 days of finishing. Rectal fecal grab samples were collected from an initial sample population of 788 steers every 20 to 22 days and microbiologically analyzed to detect E. coli O157:H7. The identities of presumptive colonies were confirmed using a multiplex PCR assay that screened for gene fragments unique to E. coli O157:H7 (rfbE and fliC_h7) and other key virulence genes (eae, stx₁, and stx₂). Animals were classified as having persistent shedding (PS), transient shedding (TS), or nonshedding (NS) status if they consecutively shed the same E. coli O157:H7 genotype (based on the multiplex PCR profile), exhibited variable E. coli O157 shedding, or never shed morphologically typical E. coli O157, respectively. Overall, 1.0% and 1.4% of steers were classified as PS and NS animals, respectively. Characterization of 132 E. coli O157:H7 isolates from PS and TS animals by pulsed-field gel electrophoresis (PFGE) typing yielded 32 unique PFGE types. One predominant PFGE type accounted for 53% of all isolates characterized and persisted in cattle throughout the study. Isolates belonging to this predominant and persistent PFGE type demonstrated an enhanced (P < 0.0001) ability to adhere to Caco-2 human intestinal epithelial cells compared to isolates belonging to less common PFGE types but exhibited equal virulence expression. Interestingly, the attachment efficacy decreased as the genetic divergence from the predominant and persistent subtype increased. Our data support the hypothesis that certain E. coli O157:H7 strains persist in feedlot cattle, which may be partially explained by an enhanced ability to colonize the intestinal epithelium.Escherichia coli serotype O157:H7 was first linked to human illness in the early 1980s, when it was determined to cause severe abdominal pain with initially watery diarrhea that progressed to grossly bloody diarrhea accompanied by little or no fever (42). Initially, E. coli O157:H7 can cause nonbloody diarrhea through attachment to, and subsequent destruction of, intestinal microvilli (24). In addition to microvillus damage, serious health complications can arise due to the ability of E. coli O157:H7 to produce Shiga toxins (Stx1 and Stx2). Shiga toxins are very potent cytotoxins that are absorbed into the intestinal microvasculature and initiate apoptosis of vascular epithelium, resulting in hemorrhagic colitis (41). Persistent uptake of these toxins may lead to more severe manifestations of disease, such as hemolytic-uremic syndrome, which may ultimately result in kidney failure (24). Most recent estimates have identified E. coli O157:H7 as the cause of at least 70,000 cases of food-borne illness annually in the United States, and in 4% of cases life-threatening hemolytic-uremic syndrome develops (37). Epidemiological studies have implicated the consumption of meat, dairy products, produce, and water contaminated by animal feces, as well as person-to-person contact and direct contact with farm animals or their environment, as routes of E. coli O157:H7 transmission leading to human illness (36).It is generally accepted that cattle and other animals are the major reservoir of E. coli O157:H7, but it is still not clear if animals are colonized for prolonged periods with E. coli O157:H7 or if they transiently shed this organism following repeated exposure to it through ingestion of contaminated feedstuffs or water or through exposure to other contaminated environmental sources. Based on results of numerous epidemiological studies (4, 6, 21, 30, 32), the prevalence of E. coli O157:H7 in feedlot cattle is highly variable and can range from less than 1% to 80%. Several other studies (7, 8, 23) have found evidence of persistent E. coli O157:H7 colonization in individual cattle, supporting the hypothesis that at least some animals are susceptible to persistent E. coli O157:H7 colonization. Multiple experimental inoculation studies (15, 23, 39, 46) showed that E. coli O157:H7 persists in the bovine gastrointestinal (GI) tract for at least 14 days up to 140 days postinfection. Studies have implicated the lower GI tract and specifically the recto-anal junction (RAJ) as the major location of E. coli O157:H7 colonization and proliferation (9, 12, 23, 39); however, this organism also can be found throughout the bovine GI tract (7, 8, 31, 40, 54).It stands to reason that if the E. coli O157:H7 prevalence in cattle presented for harvest were reduced, there would be a decrease in the probability of beef product contamination, if good manufacturing procedures were used. Although there is consensus concerning the importance of preharvest pathogen mitigation and its role in minimizing entry of E. coli O157:H7 into harvest facilities, there is disagreement about the significance of “supershedders” (animals that excrete large quantities of a pathogen for various amounts of time) for E. coli O157:H7 transmission dynamics at the preharvest level (12, 34, 35, 39). Utilizing statistical modeling, researchers have estimated that, on average, the prevalence of “supershedders” in a population is 4% and that these animals excrete 50 times more E. coli O157:H7 than other animals colonized by this organism (34). Additionally, the same researchers suggested that approximately 80% of E. coli O157:H7 transmission is generated by a few “supershedders” (35).Research by our group discovered a unique association between E. coli O157:H7 prevalence in pen floor fecal pats and carcass contamination by this pathogen (57). When the prevalence in fecal pats from a pen floor exceeded 20%, carcasses of animals from the pen had E. coli O157:H7 prevalence values of 14.3, 2.9, and 0.7% before evisceration, after evisceration, and after final intervention, respectively. However, when the prevalence in pen floor fecal pats was less than 20%, the preeviscerated carcass prevalence value was 6.3%, and there was no detectable E. coli O157:H7 contamination of carcass samples after evisceration and after final intervention (57). Thus, we hypothesize that animals which persistently excrete normal levels of E. coli O157:H7 over prolonged periods (persistent shedders [PS]) rather than animals that periodically shed abnormally high levels (supershedders) are the most significant source of E. coli O157:H7 contamination in the food continuum. Although previous studies suggested that cattle may be persistently colonized by E. coli O157:H7 and shed this organism in their feces for prolonged periods, molecular subtyping data are required to further investigate whether cattle are persistently colonized by the same strain (i.e., molecular subtype) or if they are repeatedly exposed to different strains through contaminated feedstuffs, water, or other environmental sources. Thus, the objectives of this study were to determine if naturally colonized feedlot cattle persistently shed E. coli O157:H7, using combined cultural microbiological analyses, molecular subtyping approaches, and in vitro virulence phenotype assays to probe the factors (agent, host, environment, or a combination of these factors) that contribute to the complex ecology of E. coli O157:H7 persistence at the preharvest level.