The mangrove forest as a feeding ground and nursery habitat for the ichthyofauna: Mida Creek in Kenya

peer reviewedMangrove forests are among the most productive ecosystems, sustaining both terrestrial and aquatic fauna (Kathiresan, 2011). They are important to coastal fisheries by providing foraging and hiding places for commercially valuable fishes (Tomlinson, 1986; Rönnbäck 1999). This research investigated the fish assemblage of Mida Creek (Kenya, East Africa) as well as the presumed feeding and nursery functions of the area for the ichthyofauna present. This explorative study contributes to a Kenyan-Flemish project in which scientists aim to identify the impacts of human exploitation and management regimes of mangroves on biodiversity richness and abundance, including demersal fish. The species composition of the ichthyofauna of Mida and trophic interactions therein was studied for five representative sampling areas. These sites are located at various distances from local villages in order to include the effect of different degrees of human disturbance. Samples were collected during 5-6 consecutive days close to spring tide in mid July 2011. Fishes were caught using several types of passive fishing gears such as large and small fyke nets, gill nets and occasionally beach seine. Each individual was identified to species level, measured and weighed. We performed stomach content analysis to provide information about fish diet. Furthermore, stable isotope analysis was applied on most fishes in order to detect whether the source of primary production for the higher trophic levels is mangrove-related or not. A total of 29 fish species was found with a catch of 939 teleost specimens. Our analyses showed that a majority of fish belonged to the zoobenthivorous/omnivorous trophic mode, they were mainly feeding on invertebrates. Their diet was quite similar over different locations and life stages. Two species (Sphyraena barracuda and Synodus variegatus) exhibited a mixed diet with a piscivorous preference. Results concerning the population structure suggested that the fish community of Mida consisted of both transient and resident species. Juveniles were, however, numerically more abundant in the whole area than adult specimens. Based on our restricted sampling period and methodology, we were not able to accurately detect human impacts on fish stock and species composition between locations. Finally, our results confirm that Mida Creek mangrove is an important habitat for the ichthyofauna especially for juvenile fishes. Its role as feeding and nursery ground appears well established

Determining the spatial and temporal extent of the influence of pile driving sound on harbour porpoises

Piling driving sound is known to impact harbour porpoise (Phocoena phocoena) distribution, but to date detailed knowledge on the combined spatial and temporal components of this impact over longer time periods remains lacking. From May to September 2016, pile driving was taking place at the Nobelwind wind farm located on the Bligh Bank in Belgium. In this period, porpoise activity was recorded using passive acoustic monitoring (PAM) using Continuous Porpoise Detectors (C-PoDs), at various distances from the construction site (1 – > 55 km). In this study, we compared porpoise detections before, during and after pile driving. During piling, porpoise detections decreased at stations located up to 20 km from the location of the piling event. At larger distances (20-55 km), porpoise detections either remained the same or increased slightly during piling events, which may be due to displaced porpoises entering the area. Underwater sound levels were extrapolated for the different locations. Pile driving sound levels at the furthest distance where reductions in porpoise detections were observed were ~159 dB re 1μPa (Lsub>z-p), which is close to the threshold level for major disturbance for harbour porpoise proposed in literature

Estuarine behaviour of European silver eel (<i>Anguilla anguilla</i>) in the Scheldt estuary

Estuaries are among the most productive ecosystems in the world and are characterised by high habitat diversity. As transition areas between inland rivers and the open sea, they function as transport zones for diadromous species like the European eel (Anguilla anguilla), a catadromous fish species that migrates to the Sargasso Sea for spawning. However, information on the migratory behaviour of eel in estuaries is scarce. Therefore, more insight is needed to efficiently restore and conserve the species. We tracked 47 eels with acoustic telemetry between July 2012 and October 2015 and analysed their behaviour from the Braakman creek into the Scheldt Estuary, separated by a tidal barrier. Eels arrived in the Braakman between mid-summer and early winter and stayed there on average 44 days (0 - 578 days). As such, arrival in the Scheldt Estuary was much later: between early autumn and early winter. The average residence time in the Scheldt Estuary was considerably shorter than in the Braakman, and was only five days (0 - 64 days). The long residence time in the Braakman was probably due to the discontinuous operation of the tidal barrier, which is used to control the water level in the upstream wetland area. This resulted in a discontinuous flow conditions, leading to searching behaviour in eels. Eventually 37 eels did pass the sluice and reached the Scheldt Estuary; the 10 eels which did not pass the sluice were probably caught by a commercial eel fisherman in the Braakman creek. In the Scheldt Estuary, 26 eels migrated towards the sea, whereas eight took the opposite direction and three were only detected at the first receivers downstream of the sluice. The eight eels that did not migrate towards the sea showed estuarine retention behaviour. They could have been injured by the tidal barrier or missed the right moment to migrate, and could be waiting in the estuary until favourable conditions are met to proceed their journey. Our results indicate that eel migration is obstructed by a tidal barrier, which resulted in delayed eel migration. As the migratory period occurred from mid-summer to early winter, this information can be implemented in management plans such as environmental windows to open the sluice during eel migration if circumstances allow such measurements

Optimising the future Belgian offshore wind farm monitoring programme

Six years of monitoring triggered a reflection on how to best continue with the monitoring programme. The basic monitoring has to be rationalised at the level of the likelihood of impact detection, the meaningfulness of impact size and representativeness of the findings. Targeted monitoring should continue to disentangle processes behind the observed impact, for instance the overarching artificial reef effect created by wind farms. The major challenge however remains to achieve a reliable assessment of the cumulative impacts. Continuing consultation and collaboration within the Belgian offshore wind farm monitoring team and with foreign marine scientists and managers will ensure an optimisation of the future monitoring programme

Trees, forests and water: Cool insights for a hot world

Forest-driven water and energy cycles are poorly integrated into regional, national, continental and global decision-making on climate change adaptation, mitigation, land use and water management. This constrains humanity’s ability to protect our planet’s climate and life-sustaining functions. The substantial body of research we review reveals that forest, water and energy interactions provide the foundations for carbon storage, for cooling terrestrial surfaces and for distributing water resources. Forests and trees must be recognized as prime regulators within the water, energy and carbon cycles. If these functions are ignored, planners will be unable to assess, adapt to or mitigate the impacts of changing land cover and climate. Our call to action targets a reversal of paradigms, from a carbon-centric model to one that treats the hydrologic and climate-cooling effects of trees and forests as the first order of priority. For reasons of sustainability, carbon storage must remain a secondary, though valuable, by-product. The effects of tree cover on climate at local, regional and continental scales offer benefits that demand wider recognition. The forest- and tree-centered research insights we review and analyze provide a knowledge-base for improving plans, policies and actions. Our understanding of how trees and forests influence water, energy and carbon cycles has important implications, both for the structure of planning, management and governance institutions, as well as for how trees and forests might be used to improve sustainability, adaptation and mitigation efforts

An echosounder view on the potential effects of impulsive noise pollution on pelagic fish around windfarms in the North Sea

Anthropogenic noise in the oceans is disturbing marine life. Among other groups, pelagic fish are likely to be affected by sound from human activities, but so far have received relatively little attention. Offshore wind farms have become numerous and will become even more abundant in the next decades. Wind farms can be interesting to pelagic fish due to food abundance or fisheries restrictions. At the same time, construction of wind farms involves high levels of anthropogenic noise, likely disturbing and/or deterring pelagic fish. Here, we investigated whether bottom-moored echosounders are a suitable tool for studying the effects of impulsive - intermittent, high-intensity - anthropogenic noise on pelagic fish around wind farms and we explored the possible nature of their responses. Three different wind farms along the Dutch and Belgian coast were examined, one with exposure to the passing by of an experimental seismic survey with a full-scale airgun array, one with pile driving activity in an adjacent wind farm construction site and one control site without exposure. Two bottom-moored echosounders were placed in each wind farm and recorded fish presence and behaviour before, during and after the exposures. The echosounders were successful in detecting variation in the number of fish schools and their behaviour. During the seismic survey exposure there were significantly fewer, but more cohesive, schools than before, whereas during pile driving fish swam shallower with more cohesive schools. However, the types and magnitudes of response patterns were also observed at the control site with no impulsive sound exposure. We therefore stress the need for thorough replication beyond single case studies, before we can conclude that impulsive sounds, from either seismic surveys or pile driving, are a disturbing factor for pelagic fish in otherwise attractive habitat around wind farms.Animal science