Learning to recognize novel predators under weakly acidic conditions: the effects of reduced pH on acquired predator recognition by juvenile rainbow trout

Summary. Recent studies have demonstrated that under weakly acidic conditions (pH 6.0), many prey fishes, including juvenile rainbow trout (Onchorhynchus mykiss), do not exhibit overt antipredator responses to conspecific chemical alarm cues. In laboratory trials, we investigated the potential effects of reduced pH on the ability of hatchery reared, predator naïve juvenile rainbow trout to acquire the recognition of a novel predator (yellow perch, Perca flavenscens). Initially, we exposed trout to the odour of a predatory yellow perch, buffered to pH 6.0 (weakly acidic) or pH 7.0 (neutral) paired with conspecific skin extracts (also buffered to pH 6.0 or 7.0) or a distilled water control. Juvenile trout exhibited significant increase in antipredator behaviour when exposed to neutral skin extract (pH 7.0). When retested 48 hours later to perch odour alone (pH 7.0), only trout initially conditioned with neutral skin extracts (pairs with either neutral or acidic perch odour) exhibited a learned recognition of perch odour as a predator risk. Those initially exposed to weakly acidic skin extract or the distilled water control did not show a learned response to predator odour. These results demonstrate that the ability to acquire the recognition of novel predators is impaired under weakly acidic conditions, as would occur in natural waterways affected by acidic precipitation.     

PLANNING FOR DROUGHT: MOVING FROM CRISIS TO RISK MANAGEMENT1

ABSTRACT: Severe drought is a recurring problem for the United States, as illustrated by widespread economic, social, and environmental impacts. Recent drought episodes and the widespread drought conditions in 1996, 1998, and 1999 emphasized this vulnerability and the need for a more proactive, risk management approach to drought management that would place greater emphasis on preparedness planning and mitigation actions. Drought planning has become a principal tool of states and other levels of government to improve their response to droughts. For example, since 1982, the number of states with drought plans has increased from 3 to 29. Many local governments have also adopted drought or water shortage plans. Unfortunately, most state drought plans were established during the 1980s and early 1990s and emphasize emergency response or crisis management rather than risk management. This paper presents a substantive revision of a 10‐step drought planning process that has been applied widely in the United States and elsewhere. The revised planning process places more weight on risk assessment and the development and implementation of mitigation actions and programs. The goal of this paper is to encourage states to adopt this planning process in the revision of existing drought plans or, for states without plans, in the development of new plans.     

Foliar absorption of intercepted rainfall improves woody plant water status most during drought

A large proportion of rainfall in dryland ecosystems is intercepted by plant foliage and is generally assumed to evaporate to the atmosphere or drip onto the soil surface without being absorbed. We demonstrate foliar absorption of intercepted rainfall in a widely distributed, continental dryland, woody-plant genus: Juniperus. We observed substantial improvement in plant water status, exceeding 1.0 MPa water potential for drought-stressed plants, following precipitation on an experimental plot that excluded soil water infiltration. Experiments that wetted shoots with unlabeled and with isotopically labeled water confirmed that water potential responded substantially to foliar wetting, that these responses were not attributable to re-equilibration with other portions of the xylem, and that magnitude of response increased with water stress. Foliar absorption is not included in most ecological, hydrological, and atmospheric models; has implications for interpreting plant isotopic signatures; and not only supplements water acquisition associated with increases in soil moisture that follow large or repeated precipitation events, but also enables plants to bypass soil water uptake and benefit from the majority of precipitation events, which wet foliage but do not increase soil moisture substantially. Foliar absorption of intercepted water could be more important than previously appreciated, especially during drought when water stress is greatest.     

Effects of human activities (raking,scraping, off-road vehicles) and natural resource protections on the spatial distribution of beach vegetation and related shoreline features in New Jersey

This study examined the relative impacts of different human activities and natural resource protections on the spatial distribution of beach vegetation and related habitat features (wrack, dune succession) in New Jersey (USA). Field surveys of the 209-km shoreline categorized beach segments according to vegetation cover classes, human activities, protection measures (exclosures, beach management plans, access restrictions) and ownership status (federal, state, etc.). A partition model (classification tree) was used to confirm the relative dominance hierarchy of human actions on the distribution of beach vegetation observed, and quantitative comparisons of dominant activities were conducted using vegetation data collected on 218 transects. The spatial extent of beach vegetation was found to be severely restricted by human activities when unconstrained by resource protections. The greatest reductions were found to result from mechanical raking (?99 %), scraping (?91 %) and all-year recreational ORV use (?86 %), which were dominant on nearly 70 % of the state shoreline. Beaches containing larger areas of vegetation (>5 m) were concentrated in areas with resource protections of various kinds (99 %), and on federal or other public parklands (68 %). Exclosures resulted in the greatest coverage of vegetation (48 % of beach surface) compared to public access restricted areas (41 %), beach management plans (31 %), government-only ORV use (31 %), and off-season recreational ORVs (15 %). Greater protection and recovery of beach vegetation and habitat is needed for species conservation and erosion protection in New Jersey and other coastal environments where these activities occur.     

Recognize fish as food in policy discourse and development funding

The international development community is off-track from meeting targets for alleviating global malnutrition. Meanwhile, there is growing consensus across scientific disciplines that fish plays a crucial role in food and nutrition security. However, this ‘fish as food’ perspective has yet to translate into policy and development funding priorities. We argue that the traditional framing of fish as a natural resource emphasizes economic development and biodiversity conservation objectives, whereas situating fish within a food systems perspective can lead to innovative policies and investments that promote nutrition-sensitive and socially equitable capture fisheries and aquaculture. This paper highlights four pillars of research needs and policy directions toward this end. Ultimately, recognizing and working to enhance the role of fish in alleviating hunger and malnutrition can provide an additional long-term development incentive, beyond revenue generation and biodiversity conservation, for governments, international development organizations, and society more broadly to invest in the sustainability of capture fisheries and aquaculture.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01451-4) contains supplementary material, which is available to authorized users.     

Monitoring Fish Contaminant Responses to Abatement Actions: Factors that Affect Recovery

Monitoring of contaminant accumulation in fish has been conducted in East Fork Poplar Creek (EFPC) in Oak Ridge, Tennessee since 1985. Bioaccumulation trends are examined over a twenty year period coinciding with major pollution abatement actions by a Department of Energy facility at the stream’s headwaters. Although EFPC is enriched in many contaminants relative to other local streams, only polychlorinated biphenyls (PCBs) and mercury (Hg) were found to accumulate in the edible portions of fish to levels of human health concern. Mercury concentrations in redbreast sunfish were found to vary with season of collection, sex and size of individual fish. Over the course of the monitoring, waterborne Hg concentrations were reduced >80%; however, this did not translate into a comparable decrease in Hg bioaccumulation at most sites. Mercury bioaccumulation in fish did respond to decreased inputs in the industrialized headwater reach, but paradoxically increased in the lowermost reach of EFPC. As a result, the downstream pattern of Hg concentration in fish changed from one resembling dilution of a headwater point source in the 1980s to a uniform distribution in the 2000s. The reason for this remains unknown, but is hypothesized to involve changes in the chemical form and reactivity of waterborne Hg associated with the removal of residual chlorine and the addition of suspended particulates to the streamflow. PCB concentrations in fish varied greatly from year-to-year, but always exhibited a pronounced downstream decrease, and appeared to respond to management practices that limited episodic inputs from legacy sources within the facility.