Indicators to support an ecosystem approach to fisheries

Indicators are needed to support the implementation of an ecosystem approach to fisheries (EAF), by providing information on the state of the ecosystem, the extent and intensity of effort or mortality and the progress of management in relation to objectives. Here, I review recent work on the development, selection and application of indicators and consider how indicators might support an EAF. Indicators should guide the management of fishing activities that have led to, or are most likely to lead to, unsustainable impacts on ecosystem components or attributes. The numbers and types of indicators used to support an EAF will vary among management regions, depending on resources available for monitoring and enforcement, and actual and potential fishing impacts. State indicators provide feedback on the state of ecosystem components or attributes and the extent to which management objectives, which usually relate to state, are met. State can only be managed if the relationships with fishing (pressure) and management (response) are known. Predicting such relationships is fundamental to developing a management system that supports the achievement of objectives. In a management framework supported by pressure, state and response indicators, the relationship between the value of an indicator and a target or limit reference point, reference trajectory or direction provides guidance on the management action to take. Values of pressure, state and response indicators may be affected by measurement, process, model and estimation error and thus different indicators, and the same indicators measured at different scales and in different ways, will detect true trends on different timescales. Managers can use several methods to estimate the effects of error on the probability of detecting true trends and/or to account for error when setting reference points, trajectories and directions. Given the high noise to signal ratio in many state indicators, pressure and response indicators would often guide short‐term management decision making more effectively, with state indicators providing longer‐term policy‐focused feedback on the effects of management action.     

Modification of marine habitats by trawling activities: prognosis and solutions

Fishing affects the seabed habitat worldwide on the continental shelf. These impacts are patchily distributed according to the spatial and temporal variation in fishing effort that results from fishers' behaviour. As a consequence, the frequency and intensity of fishing disturbance varies among different habitat types. Different fishing methodologies vary in the degree to which they affect the seabed. Structurally complex habitats (e.g. seagrass meadows, biogenic reefs) and those that are relatively undisturbed by natural perturbations (e.g. deep‐water mud substrata) are more adversely affected by fishing than unconsolidated sediment habitats that occur in shallow coastal waters. These habitats also have the longest recovery trajectories in terms of the recolonization of the habitat by the associated fauna. Comparative studies of areas of the seabed that have experienced different levels of fishing activity demonstrate that chronic fishing disturbance leads to the removal of high‐biomass species that are composed mostly of emergent seabed organisms. Contrary to the belief of fishers that fishing enhances seabed production and generates food for target fish species, productivity is actually lowered as fishing intensity increases and high‐biomass species are removed from the benthic habitat. These organisms also increase the topographic complexity of the seabed which has been shown to provide shelter for juvenile fishes, reducing their vulnerability to predation. Conversely, scavengers and small‐bodied organisms, such as polychaete worms, dominate heavily fished areas. Major changes in habitat can lead to changes in the composition of the resident fish fauna. Fishing has indirect effects on habitat through the removal of predators that control bio‐engineering organisms such as algal‐grazing urchins. Fishing gear resuspend the upper layers of sedimentary seabed habitats and hence remobilize contaminants and fine particulate matter into the water column. The ecological significance of these fishing effects has not yet been determined but could have implications for eutrophication and biogeochemical cycling. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators. In contrast, high levels of trawling disturbance cause sediment systems to become unstable due to large carbon fluxes between oxic and anoxic carbon compartments. In low energy habitats, intensive trawling disturbance may destabilize benthic system chemical fluxes, which has the potential to propagate more widely through the marine ecosystem. Management regimes that aim to incorporate both fisheries and habitat conservation objectives can be achieved through the appropriate use of a number of approaches, including total and partial exclusion of towed bottom fishing gears, and seasonal and rotational closure techniques. However, the inappropriate use of closed areas may displace fishing activities into habitats that are more vulnerable to disturbance than those currently trawled by fishers. In many cases, the behaviour of fishers constrains the extent of the impact of their fishing activities. Management actions that force them to redistribute their effort may be more damaging in the longer term.     

Campylobacter jejuni is associated with, but not sufficient to cause vibrionic hepatitis in chickens

Vibrionic hepatitis is a disease of poultry which is characterised by the presence of focal lesions in the liver, usually 1-2mm in size and greyish-white in colour. The cause of the disease remains unclear, as do the reasons for its recent re-emergence. We examined the livers of commercial broiler chickens taken during processing and found Campylobacter spp. in both normal livers and those displaying signs indicative of focal hepatitis. Livers with signs of hepatitis had significantly more Campylobacter spp. present than those without and other bacterial genera were infrequently present. We were unable to replicate the disease in a healthy host following experimental infection with a Campylobacter jejuni strain isolated from a liver showing signs of focal hepatitis. However, a significant T cell response to C. jejuni was seen in the liver of Campylobacter infected birds. We conclude that the presence of Campylobacter spp. in the liver alone is not sufficient to cause vibrionic hepatitis, but that a predisposing factor, possibly within the host is required. We also provide evidence that chickens mount an adaptive T cell response to systemic C. jejuni.     

Weaning and post-weaning performance by fall-born beef calves weaned on different dates in the spring from Neotyphodium coenophialum-infected tall fescue pastures

Fall-born calves grazing Neotyphodium coenophialum-infected tall fescue [E+; Lolium arundinaceum (Schreb.) Darbysh.] pastures should benefit from early weaning because of reduced exposure to fungal toxins. However, fall-born calves that grazed E+ and were weaned in mid-April had reduced post-weaning performance compared with calves managed similarly but weaned in early June. Gelbvieh × Angus calves (n = 238) were used in a 3-year study to determine the optimal time to wean fall-born calves grazing E+. Cow/calf pairs were allocated randomly to one of four weaning date treatments: 1) March 16 (177 ± 4.7 days of age; MarW), 2) April 13 (204 ± 4.7 days of age; AprW), 3) May 11 (236 ± 4.7 days of age; MayW), and 4) June 8 (264 ± 4.8 days of age; JuneW). On their assigned weaning date, calves were weighed, vaccinated, blood samples were collected, and calves were moved to 3.2-ha pastures adjacent to their dams for 14 days. After the weaning period, calves were weighed, blood samples were collected, and then calves were moved to pastures containing non-toxic forages. Birth weight and calf weights on MarW, AprW, and MayW weaning dates did not differ (P ≥ 0.21) across weaning date treatments. However, calf weaning weights on their respective weaning dates, weight on JuneW and on June 22 (14 days following the JuneW), daily gain between birth and June 22, and weight change between MarW and JuneW increased linearly (P < 0.05) across weaning dates. Linear decreases (P < 0.05) across weaning dates were noted for antibody titers to bovine virus diarrhea (BVD) and infectious bovine rhinotracheitis (IBR), serum Cu, and platelets at the time of actual weaning. Linear increases (P < 0.05) across weaning dates were noted for: i) total antioxidant potential and eosinophils at weaning; ii) changes in antibody titers to BVD and IBR, total antioxidant potential, and serum Zn during the 14-day post-weaning period; and iii) and changes in BVD and BRSV titers and serum Cu between actual weaning date and June 22. Heifer weight at breeding increased (P < 0.05) and steer weight at shipping, hot carcass weight and backfat thickness tended (P ≤ 0.10) to increase linearly across weaning dates. Final feedlot weight and gain did not differ (P ≥ 0.18) among weaning dates. Therefore, delaying weaning of fall-born calves grazing E+ pastures until early June may be beneficial for calf weight and immune function at weaning, and heifer weight at breeding, but those benefits in steers may be mitigated through the feedlot period.     

Indirect effects of bottom fishing on the productivity of marine fish

One quarter of marine fish production is caught with bottom trawls and dredges on continental shelves around the world. Towed bottom‐fishing gears typically kill 20–50 per cent of the benthic invertebrates in their path, depending on gear type, substrate and vulnerability of particular taxa. Particularly vulnerable are epifaunal species, which stabilize the sediment and provide habitat for benthic invertebrates. To identify the habitats, fisheries or target species most likely to be affected, we review evidence of the indirect effects of bottom fishing on fish production. Recent studies have found differences in the diets of certain species in relation to bottom fishing intensity, thereby linking demersal fish to their benthic habitats at spatial scales of ~10 km. Bottom fishing affects diet composition and prey quality rather than the amount of prey consumed; scavenging of discarded by‐catch makes only a small contribution to yearly food intake. Flatfish may benefit from light trawling levels on sandy seabeds, while higher‐intensity trawling on more vulnerable habitats has a negative effect. Models suggest that reduction in the carrying capacity of habitats by bottom fishing could lead to lower equilibrium yield and a lower level of fishing mortality to obtain maximum yield. Trawling effort is patchily distributed – small fractions of fishing grounds are heavily fished, while large fractions are lightly fished or unfished. This patchiness, coupled with the foraging behaviour of demersal fish, may mitigate the indirect effects of bottom fishing on fish productivity. Current research attempts to scale up these localized effects to the population level.     

Pathogenicity and immunogenicity of a mutagen-attenuated Rift Valley fever virus immunogen in pregnant ewes

A mutagenized clone of Rift Valley fever virus (RVFV; MV P12) used in inoculation of 3 pregnant ewes was immunogenic, nonpathogenic, and nonabortogenic. In contrast, inoculation of a matched group of 3 pregnant ewes with parent RVFV induced clinical disease and abortions. Ewes given MV P12 delivered healthy lambs that had RVFV antibody titers of less than 1:10 at birth, increasing to greater than or equal to 1:80 after ingestion of colostrum. Ewes inoculated with parent RVFV developed marked viremia, followed by RVFV antibody titers greater than or equal to 1:1,280; ewes inoculated with MV P12 developed low viremia titers and RVFV antibody titers of 1:80 to 1:320. Postpartum challenge exposure of the previously MV P12-inoculated ewes with virulent Zagazig human 501 strain RVFV indicated that the ewes were protected from clinical disease. The RVFV-susceptible female Culex pipiens that fed on the MV P12-inoculated ewes failed to transmit RVFV to hamsters; mosquitoes that fed on the parent RVFV-inoculated ewes became infected and transmitted RVFV to hamsters.     

Rapid assay for repair of damage induced by ultraviolet light in bovine lymphocytes

Bovine peripheral blood lymphocytes exhibit a peak of deoxyribonucleic acid (DNA) repair, measured after exposure of cells to ultraviolet light, three to four days after phytohaemagglutinin addition to diluted blood cultures. This peak of DNA repair is induced coincidentally with that of DNA replication. DNA repair is determined in the presence of hydroxyurea which inhibits DNA replication. This assay provides a rapid screening method for deficits in DNA repair synthesis in cattle.