Assessing ecological equivalence in biodiversity offset schemes: Key issues and solutions

Habitat loss through development is one of the major causes of biodiversity loss. The increasingly common legal requirement to first avoid, then reduce and, if necessary, offset impacts of plans and projects on biodiversity has however not always been appropriately enforced. The blame lies mainly in bad governance such as patchy monitoring or poorly defined liabilities. Biodiversity offsets also suffer from the lack of formal methods for designing and sizing offset requirements. We address this gap by reviewing different tools, methods and guidelines that have been developed in different regulatory contexts. We then formulate a typology of approaches that variously combine these methods and guidelines. We discuss how these relate to the objectives of offset policies and the components of biodiversity and ecosystems to which they apply. Together, these perspectives should contribute to improving existing methods (e.g. by incorporating time-related issues) and our typology should support the development of offset policies.     

Fluids from aging ocean crust that support microbial life

Little is known about the potential for life in the vast, low-temperature (<100 degrees C) reservoir of fluids within mid-ocean ridge flank and ocean basin crust. Recently, an overpressured 300-meter-deep borehole was fitted with an experimental seal (CORK) delivering crustal fluids to the sea floor for discrete and large-volume sampling and characterization. Results demonstrate that the 65 degrees C fluids from 3.5-million-year-old ocean crust support microbial growth. Ribosomal RNA gene sequence data indicate the presence of diverse Bacteria and Archaea, including gene clones of varying degrees of relatedness to known nitrate reducers (with ammonia production), thermophilic sulfate reducers, and thermophilic fermentative heterotrophs, all consistent with fluid chemistry.     

The scale of saproxylic beetles response to landscape structure depends on their habitat stability

Context

Forest management and disturbances cause habitat fragmentation for saproxylic species living on old-growth attributes. The degree of habitat spatiotemporal continuity required by these species is a key question for designing biodiversity-friendly forestry, and it strongly depends on species’ dispersal. The “stability–dispersal” model predicts that species using stable habitats should have lower dispersal abilities than species associated with ephemeral habitat and thus respond to habitat availability at smaller scales.

Objectives

We aimed at testing the stability–dispersal model by comparing the spatial scales at which saproxylic beetle guilds using substrates with contrasted stability (from stable to ephemeral: cavicolous, fungicolous, saproxylophagous and xylophagous guilds) are affected by landscape structure (i.e. habitat amount and aggregation).

Methods

We sampled saproxylic beetles using a spatially nested design (plots within landscape windows). We quantified habitat availability (tree cavities, polypores and deadwood) in 1-ha plots, 26-ha buffers around plots and 506-ha windows, and analyzed their effect on the abundance and diversity of associated guilds.

Results

The habitat amount within plots and buffers positively affected the abundance of the cavicolous and the fungicolous guilds whereas saproxylophagous and xylophagous did not respond at these scales. The habitat aggregation within windows only positively affected the saproxylophagous species richness within plots and also on the similarity in species composition among plots.

Conclusions

Beetle guilds specialized on more stable habitat were affected by landscape structure at smaller spatial scales, which corroborated the stability–dispersal model. In managed forests, the spatial grain of conservation efforts should therefore be adapted to the target habitat lifetime.

     

Migration behaviour and escapement of European silver eels from a large lake and wetland system subject to water level management (Grand‐Lieu Lake,France): New insights from regulated acoustic telemetry data

Current knowledge about the downstream migration of sexually mature European eels (Anguilla anguilla) remains incomplete, particularly in still water habitats such as lakes and wetlands subject to water level management. However, for the management of this endangered species, it is important to understand migration dynamics, and contribution to the breeding stock. This study aimed to assess the parameters that trigger and guide the migration of silver eels in the largest floodplain lake and associated wetlands in France (the sluice regulated Grand‐Lieu Lake). A telemetry survey of 50 acoustic and PIT‐tagged female silver eels was performed during the 2015–2016 migration period. We deployed a novel telemetric approach, using receivers to delimit several restricted virtual boxes to determine the instantaneous location of individuals and to transform simple discrete telemetric data into presence/absence data. The low numbers leaving the lake centre are probably explained by the lack of orienting water flows or other environmental clues, but whilst the fate of 34% (17/50) of the tagged eels is unknown, 18% (9/50) were caught by commercial fishermen. Modelling showed that detections were not clearly associated with environmental factors typically involved in riverine migrations (e.g. current velocity, atmospheric pressure and temperature) but they were particularly associated with higher and increasing water levels and, for eels exiting the lake, a sharp increase when sluice gates were opened to an effective gap of >75 cm. It is concluded that management of water levels and sluice gate opening during the migration period might aid escapement of silver eels.     

Thoracoscopic Lung Biopsies in Heaves‐Affected Horses Using a Bipolar Tissue Sealing System

Objective: To validate the use of the LigaSure? Vessel Sealing System (LVSS) to perform thoracoscopic lung tissue biopsies in heaves‐affected horses. Study design: Prospective clinical study. Animals: Heaves‐affected horses (n=12). Methods: Lung biopsies (n=34) were collected with the LVSS (2–4 biopsies/horse) in horses with and without clinical signs of heaves. Thoracoscope (13th intercostal space [ICS]) and 2 instruments (between the 12–15th ICS) portals were used. Selected clinical and arterial blood gas variables were monitored. Postoperative pneumothorax was evaluated. Depth of thermal injury to the surrounding tissue and representativeness of the biopsies were determined. Results: Mean surgical time was 22.9±8.0 minutes. The complication rate was 5.6%, and primarily related to a focal inadequate sealing of the biopsy margin. Five horses in exacerbation required intraoperative intranasal O₂. Mean PaO₂ was significantly lower in heaves‐affected horses with clinical signs compared with those without clinical signs. Postoperative pneumothorax was detected radiographically after 20 of the 34 procedures. One horse with clinical signs of heaves developed a fatal tension pneumothorax 5 days postoperatively despite close radiographic monitoring. Conclusion: Thoracoscopic lung biopsy using LVSS is a rapid and effective technique to harvest peripheral lung tissues from heaves‐affected horses. Although the complication rate was tolerable, tension pneumothorax was a potential life‐threatening complication because of incomplete lung sealing. Clinical Relevance: LVSS can be used with relative safety to perform thoracoscopic lung biopsy, but close postoperative monitoring is necessary to avoid tension pneumothorax.     

Spawning areas and migration patterns in the early life history of Squalius cephalus (Linnaeus, 1758): Use of otolith microchemistry for conservation and sustainable management

1. In the context of the River Rhône restoration programme, the objective of this study was to assess the dispersal and population connectivity of the European chub, Squalius cephalus (Linnaeus, 1758) in a section of the natural, free-flowing part of the lower River Rhône.
2. The elemental water signatures for Sr:Ca and Ba:Ca were measured at seven stations within the river section, including its tributaries and backwaters, to determine whether they could be differentiated by microchemistry. From August to October the signatures differed among three sectors of the study reach: the Rhône; the Ardèche; and the backwaters.
3. The elemental signatures of the otoliths of 178 young-of-the-year (YOY) chub from the stations were measured to assess spawning areas and identify early migratory life histories. Analyses of otolith microchemistry identified the natal origin of 95% of the fish. Sr:Ca signatures of otoliths showed early downstream migration for 30.4% of the YOY chub; however, 70% of the fish recruited relatively close to their spawning origin suggesting a potential inshore retention of fish.
4. The results showed (i) a non-negligible contribution of the tributaries and backwaters in the recruitment of fish into the main channel; and (ii) the ability of chub to migrate over several kilometres during their first few months of life.
5. This study shows that the combination of water and otolith microchemistry analyses of fish growth increases the understanding of fish life history. Moreover, the study revealed that half of the YOY fish from this river section came from the tributaries and the other half came from reproduction in the River Rhône (despite its high anthropization).
6. These methods offer promising future applications of otolith microchemistry for river management in the context of ecological rehabilitation, especially to assess the effectiveness of measures applied in the restoration of floodplain connectivity for riverine fish population conservation.

     

Effects of natural rapids and waterfalls on fish assemblage structure in the Madeira River (Amazon Basin)

Abstract – Habitat connectivity is considered a central factor shaping ecological communities, and the effects of waterway barriers such as natural waterfalls on fish movements are expected to produce differing assemblage structures in riverine ecosystems. Here, we evaluate the influence of a sequence of waterfalls on the compositional dissimilarity of fish assemblages along the Madeira River, the largest tributary of the Amazon River. We found significant differences in species composition between rivers stretches located upstream and downstream of Teotônio waterfall and, to a less extent, Jirau waterfall, independently of the hydrological period. After accounting for the relative roles of local and regional factors in explaining fish compositional dissimilarity, we still observe a significant effect of the waterfalls. We conclude that these waterfalls act as natural ecological barriers limiting fish dispersal processes and discuss aspects of these ecological filters and the potential effects of two dams currently under construction in the Madeira River.     

Mass marking of stocked European glass eels (Anguilla anguilla) with alizarin red S

This study describes a mass marking method suitable for European glass eel Anguilla anguilla, avoiding osmotic shock and reducing fish stress. During a single day, 360,000 glass eels intended for a stocking operation were bathed into an alizarin red S (ARS) solution, at a density of 346 ind.·l^?1 before being released into a freshwater marsh along with unmarked glass eels. After 15 days, examination of marked and unmarked eels kept in enclosures in the marsh showed 100% of otoliths had been successfully marked and that no excess deaths related to marking process had occurred. Seven months after stocking, results from biometric measurements and otolith analysis, carried out on a sample of 53 elvers caught by electrofishing and belonging to the size class of the 0⁺ cohort, suggest that: (i) the proportions of marked and unmarked remained unchanged, hence suggesting that the marking process had not caused excess mortality, (ii) there was no difference in length, body mass or condition factor between marked and unmarked individuals, demonstrating that marking had caused no harmful effect after 7 months, and (iii) ARS marks in otoliths remained clearly visible. The benefits of this ARS mass marking technique are discussed through a stocking operation.     

Can drifting objects drive the movements of a vulnerable pelagic shark?

1. Juvenile silky sharks (Carcharhinus falciformis) regularly associate with floating objects yet the reasons driving this behaviour remain uncertain. Understanding the proportion of time that silky sharks spend associated with floating objects is essential for assessing the impacts of the extensive use of fish aggregating devices (FADs) in the tropical tuna purse-seine fisheries, including increased probability of incidental capture and the potential of an ecological trap.
2. Previous studies provided insight into the amount of time that silky sharks spent at an individual FAD but were unable to assess neither the time spent between two associations nor the proportion of time spent associated/unassociated.
3. The percentage of time that juvenile silky sharks spend unassociated with floating objects was estimated through the analysis of horizontal movements of 26 silky sharks monitored with pop-up archival tags. Under the assumption that a high association rate with drifting FADs would align the trajectories of tracked sharks with ocean surface currents, a novel methodology is proposed, based on the comparison of shark trajectories with simulated trajectories of passively drifting particles derived using a Lagrangian model.
4. Results revealed that silky shark trajectories were divergent from surface currents, and thus unassociated with FADs, for at least 30% of their time. The potential of the methodology and the results are discussed in the context of increasing FAD densities in the Indian Ocean.