Giant otter behaviour in a mega-hydroelectric reservoir, Central Amazon, Brazil

We tracked thirteen giant otters from three different groups in the Balbina Hydroelectric Reservoir. One of them was a transient animal, while the others were living in groups of five and seven individuals. Travelling was the most frequent behaviour, both for the transient otter (>40%) and group otters (46%). Diurnal resting was the longest-lasting behaviour. Most giant otter behaviour in the reservoir showed little difference when compared with the behaviour of giant otters living in nondammed areas, indicating a significant degree of resilience of this species. However, otters in the reservoir spent more time travelling, probably because their territory sizes were much greater than the territories of giant otters in nondammed areas. The frequency of fishing was similar to what has been recorded elsewhere, suggesting that current fish density and availability in the reservoir is similar to what is observed in nondammed areas. Nevertheless, otters in Balbina spent more time fishing than those in nondammed areas, which alternatively could suggest that fish density in the reservoir was low and could be compensated by increasing the time spent fishing. The high frequency of intraspecific kleptoparasitism observed in this study (62%) is noteworthy, although virtually undocumented for this species. This is the first study of giant otter behaviour in a hydroelectric reservoir that can be used for the conservation of this endangered species in man-made lakes.

Effects of Marine Reserve Protection on Adjacent Non-protected Populations in New Zealand

<p>Marine reserves (MRs) have been established in many parts of the globe for a variety of reasons and there is an increasing body of evidence that indicates they provide a wide range of benefits that can extend beyond their boundaries. In the present study, the biological effects of protection provided by MRs in New Zealand were evaluated, particularly focusing on the potential impacts of reserves on non-protected areas in terms of export of biomass. First, the biological response of two exploited species to MR protection in New Zealand was quantified by comparing meta-analysis results based on response ratio (RR) analysis and Hedges’ g statistics. Then, effect of MR size and age on those biological responses was determined. Most MRs supported a greater density of larger individuals than unprotected areas. Results indicated that the benefits provided by MRs scale with reserve size. Also, MR age explained a significant amount of the variation in the density and length of both species. Comparison of the performance of RRs with Hedges’ g revealed that RR analysis is an appropriate alternative to Hedges’ g statistic for meta-analyses of MR effectiveness because of its ease of use and interpretation. Then, a 14-year time series of fish density data was analyzed to determine early changes in a multi-species fish assemblage inside the Taputeranga Marine Reserve (TMR) compared to adjacent fishing grounds using a Before and After Control-Impact Paired Series (BACIPS) design. This analysis was performed in order to detect changes in fish density due to protection. Commercial, recreational and traditional fisheries are important in this region and the biomasses of several exploited species have been substantially depleted as a result of fishing. The exclusion of fishing from the area should enable at least some species to recover inside the reserve, as has happened in other reserves in New Zealand. The faster growing, more productive species, and those that have been heavily exploited are expected to recover within a few years. Early changes in density were evident in the area protected by the TMR for most of the species surveyed in terms of the effect size analysis. However, most of the changes were too small to be detected with the statistical analyses that were performed. To determine the most appropriate methodology to be used in a later survey in the study area, two Baited Underwater Video (BUV) methodologies (Horizontal versus Vertical set-up) were compared in terms of their ability to record the density and size of reef fish. Results indicated that both the horizontal and vertical BUV techniques are able to detect both conspicuous and cryptic species and both techniques were effective in the detection of carnivorous species, especially large predatory species such as blue cod, but also effective in the detection of fish species that have been overestimated in terms of abundance by other methodologies. The horizontal BUV technique seems to be a better technique for evaluating reef fish size, especially when measuring large fish that exhibit highly aggressive behaviour. The horizontal BUV technique was later used in conjunction with the Underwater Visual Census (UVC) technique to assess the effects of the protection provided by the TMR. A multispecies analysis was carried out to detect any differences in density and length of fish between reserve and fished areas and to detect gradients of fish density across reserve boundaries that could be related to the occurrence of spillover from the reserve to adjacent fished areas. Density gradients provide indirect evidence of spillover, defined as the movement of adult individuals from reserve to adjacent non-protected areas. Little evidence consistent with a positive effect of reserve protection in the TMR was found. Also, little evidence of spillover was found, with theexception of two target species (blue cod and blue moki). In contrast with the findings of previous studies, density gradients were found for both sedentary and vagile species. These results are consistent with the occurrence of density independent spillover that is expected to occur as soon as the density inside reserve areas is higher compared to fished areas. To further understand the patterns of fish movement relative to the effect of protection provided by MRs, spatial differences in density, length and survival of blue cod inside the TMR and adjacent fishing grounds and the movement patterns of the species across the boundaries of the reserve through a capture-mark-recapture (CMR) analysis were examined. CMR studies can provide direct evidence of spillover. Evidence of a positive effect of reserve protection in the TMR for blue cod in terms of increased density, length and survival in reserve areas was found. Also, evidence of high site fidelity of blue cod in both reserve and fished areas, with the majority of individual moving only short distances was found. However, the potential for this species to also travel long distances (>100 km) was confirmed, suggesting the possibility for spillover of the species from reserved to fished areas. Overall, the results of my thesis indicate that New Zealand MRs, consistent with a large body of earlier evidence, are having positive effects on the abundance and size of the species that afford protection to. These results also highlight that both MR age and area are important factors determining the response to protection both in terms of the effects within reserves and on adjacent non-protected areas. Finally, my results highlight the fact that the greater benefits in terms of increased abundance and size, and also movement across reserve boundaries, are obtained for highly exploited species that can potentially move between areas.</p>

Effects of Marine Reserve Protection on Adjacent Non-protected Populations in New Zealand

<p>Marine reserves (MRs) have been established in many parts of the globe for a variety of reasons and there is an increasing body of evidence that indicates they provide a wide range of benefits that can extend beyond their boundaries. In the present study, the biological effects of protection provided by MRs in New Zealand were evaluated, particularly focusing on the potential impacts of reserves on non-protected areas in terms of export of biomass. First, the biological response of two exploited species to MR protection in New Zealand was quantified by comparing meta-analysis results based on response ratio (RR) analysis and Hedges’ g statistics. Then, effect of MR size and age on those biological responses was determined. Most MRs supported a greater density of larger individuals than unprotected areas. Results indicated that the benefits provided by MRs scale with reserve size. Also, MR age explained a significant amount of the variation in the density and length of both species. Comparison of the performance of RRs with Hedges’ g revealed that RR analysis is an appropriate alternative to Hedges’ g statistic for meta-analyses of MR effectiveness because of its ease of use and interpretation. Then, a 14-year time series of fish density data was analyzed to determine early changes in a multi-species fish assemblage inside the Taputeranga Marine Reserve (TMR) compared to adjacent fishing grounds using a Before and After Control-Impact Paired Series (BACIPS) design. This analysis was performed in order to detect changes in fish density due to protection. Commercial, recreational and traditional fisheries are important in this region and the biomasses of several exploited species have been substantially depleted as a result of fishing. The exclusion of fishing from the area should enable at least some species to recover inside the reserve, as has happened in other reserves in New Zealand. The faster growing, more productive species, and those that have been heavily exploited are expected to recover within a few years. Early changes in density were evident in the area protected by the TMR for most of the species surveyed in terms of the effect size analysis. However, most of the changes were too small to be detected with the statistical analyses that were performed. To determine the most appropriate methodology to be used in a later survey in the study area, two Baited Underwater Video (BUV) methodologies (Horizontal versus Vertical set-up) were compared in terms of their ability to record the density and size of reef fish. Results indicated that both the horizontal and vertical BUV techniques are able to detect both conspicuous and cryptic species and both techniques were effective in the detection of carnivorous species, especially large predatory species such as blue cod, but also effective in the detection of fish species that have been overestimated in terms of abundance by other methodologies. The horizontal BUV technique seems to be a better technique for evaluating reef fish size, especially when measuring large fish that exhibit highly aggressive behaviour. The horizontal BUV technique was later used in conjunction with the Underwater Visual Census (UVC) technique to assess the effects of the protection provided by the TMR. A multispecies analysis was carried out to detect any differences in density and length of fish between reserve and fished areas and to detect gradients of fish density across reserve boundaries that could be related to the occurrence of spillover from the reserve to adjacent fished areas. Density gradients provide indirect evidence of spillover, defined as the movement of adult individuals from reserve to adjacent non-protected areas. Little evidence consistent with a positive effect of reserve protection in the TMR was found. Also, little evidence of spillover was found, with theexception of two target species (blue cod and blue moki). In contrast with the findings of previous studies, density gradients were found for both sedentary and vagile species. These results are consistent with the occurrence of density independent spillover that is expected to occur as soon as the density inside reserve areas is higher compared to fished areas. To further understand the patterns of fish movement relative to the effect of protection provided by MRs, spatial differences in density, length and survival of blue cod inside the TMR and adjacent fishing grounds and the movement patterns of the species across the boundaries of the reserve through a capture-mark-recapture (CMR) analysis were examined. CMR studies can provide direct evidence of spillover. Evidence of a positive effect of reserve protection in the TMR for blue cod in terms of increased density, length and survival in reserve areas was found. Also, evidence of high site fidelity of blue cod in both reserve and fished areas, with the majority of individual moving only short distances was found. However, the potential for this species to also travel long distances (>100 km) was confirmed, suggesting the possibility for spillover of the species from reserved to fished areas. Overall, the results of my thesis indicate that New Zealand MRs, consistent with a large body of earlier evidence, are having positive effects on the abundance and size of the species that afford protection to. These results also highlight that both MR age and area are important factors determining the response to protection both in terms of the effects within reserves and on adjacent non-protected areas. Finally, my results highlight the fact that the greater benefits in terms of increased abundance and size, and also movement across reserve boundaries, are obtained for highly exploited species that can potentially move between areas.</p>

Short-Term Effects of Low-Head Barrier Removals on Fish Communities and Habitats

Barrier removal is increasingly being seen as the optimal solution to restore lotic habitat and fish communities, however, evidence of its efficacy is often limited to single sites or catchments. This study used a before–after methodology to examine the short-term (average, 541 days) effects of low-head (0.1–2.9 m) barrier removal at 22 sites distributed across Denmark and northern England on fish density, community, and river habitat responses. Following barrier removal, changes in the aquatic habitat were observed, such that the area immediately upstream of the former barrier location became shallower, with larger substrate and faster flow conditions. The reinstatement of this habitat was especially valuable in Danish streams, where these habitat features are rare, due to the naturally low gradients. Across all 22 sites fish species richness and diversity was similar before and after removal of barriers, likely because of the short study timescale (1–2 years). Across all sites combined, there was an increase in total fish density following barrier removal. A large increase in salmonid (Salmo trutta and Salmo salar) densities following barrier removal occurred at 7 out of 12 Danish sites. No similar response in salmonid density was observed at any of the UK sites which were mostly characterized by high channel gradients and short ponded zones. Two UK barrier removal sites showed marked increases in density of non-salmonid fish species. This study suggests that the removal of low-head barriers can be an effective method of restoring lotic habitats, and can lead to positive changes in fish density in the former ponded zone. The short-term effect of small barrier removal on the fish community is more variable and its effectiveness is likely to be determined by wider riverine processes.

Ecological ramifications of adaptation to size-selective mortality

Size-selective mortality due to harvesting is a threat to numerous exploited species, but how it affects the ecosystem remains largely unexplored. Here, we used a pond mesocosm experiment to assess how evolutionary responses to opposite size-selective mortality interacted with the environment (fish density and light intensity used as a proxy of resource availability) to modulate fish populations, prey community composition and ecosystem functions. We used medaka ( Oryzias latipes ) previously selected over 10 generations for small size (harvest-like selection; small-breeder line) or large size (large-breeder line), which displayed slow somatic growth and early maturity or fast somatic growth and late maturity, respectively. Large-breeder medaka produced more juveniles, which seemed to grow faster than small-breeder ones but only under high fish density. Additionally, large-breeder medaka had an increased impact on some benthic prey, suggesting expanded diet breadth and/or enhanced foraging abilities. As a consequence, increased light stimulated benthic algae biomass only in presence of large-breeder medaka, which were presumably better at controlling benthic grazers. Aggregated effect sizes at the community and ecosystem levels revealed that the ecological effects of medaka evolution were of similar magnitude to those induced by the environment and fish introduction. These findings indicate the important environmental dependency of evolutionary response to opposite size-selective mortality on higher levels of biological organizations.

Effects of Habitat Restoration on Fish Communities in Urban Streams

Geomorphological alterations, hydrological disconnectivity and water pollution are among the dominant pressures affecting ecological integrity in urban streams. River restoration approaches often involve utilising in-stream structures to encourage flow heterogeneity and promote habitat diversity. However, few studies examine the success of such projects. In this study, fish density, biomass and community structure at paired restored and unrestored reaches across five tributaries of the River Thames were examined. Fish density varied among rivers and reaches but was generally higher at restored sites. Restored sites also exhibited higher overall fish biomass, attributed mainly to the presence of brown trout (Salmo trutta L.) at the River Wandle. Despite higher density and biomass values at restored sites, the community structure analysis did not identify strong links between either river or restoration status using either species-specific density or biomass. Our results highlight that although reach-scale restoration can lead to localised increases in species density and biomass, this may chiefly be due to aggregation owing to preferential habitats created through restoration activities at these sites. Over larger spatial scales, significant improvements to species richness and diversity are likely to be limited due to the poor water quality and disconnected nature of these urban streams. Whilst reach-scale restoration clearly has the potential to provide preferential habitats for fish species, future efforts should focus on improving connectivity for fish across the wider Thames basin network by removing barriers to passage, improving water quality, restoring watershed processes and creating well-connected, diverse habitats which can facilitate the survival of a wide array of fish species throughout their life cycle.

Production Performance and Nitrogen and Phosphorus Mass Balance in Biofloc-based African Catfish Intensive Culture at Different Densities

This study aimed to evaluate the production performance and nitrogen and phosphorus mass balance of biofloc-based intensive African catfish Clarias gariepinus culture at different densities. African catfish with an average body weight of 2.64 ± 0.06 g was randomly distributed into 12 units of round tank with a working volume of 2 m3 of water and maintained for 8 weeks. A completely randomized experimental design with four treatments (in triplicates), i.e. a control treatment at a fish density of 500 fish m-3 with regular water exchange and without organic carbon source addition, and biofloc treatments (BFT) at three different densities, i.e. 500 fish m-3 (BFT500), 750 fish m-3 (BFT750), and 1000 fish m-3 (BFT1000). Biofloc systems were performed with a regular addition of tapioca flour (40% C). The production performance between biofloc system and the control was not significantly different, however water and nitrogen utilizations were significantly more efficient in biofloc system than those of the control. The highest fish specific growth rate was observed in BFT1000 and BFT500 (6.01% day-1 and 5.96% day-1, respectively) (P<0.05). Fish density significantly affected the fish growth performance and productivity in biofloc systems, but not nitrogen and phosphorus utilizations. In conclusion, higher fish density significantly increased the production and water utilization efficiency in biofloc systems, but has no effect on nitrogen and phosphorus utilization efficiency. Furthermore, increasing the fish density could significantly reduce the fish survival and require more efforts to control biofloc biomass in the culture system.

Importance of prey size on investigating prey availability of larval fishes

Prey availability plays an important role in determining larval fish survival. Numerous studies have found close relationships between the density of mesozooplankton and larval fishes; however, emerging studies suggest that small-size zooplankton are more important prey for some larval fish species. One arising question is whether the size of zooplankton determines the relationship between zooplankton and larval fish community in natural environments. To address this question, we collected small-size (50–200 μm) zooplankton, mesozooplankton (> 330 μm), and larval fish using three different mesh-size (50, 330, 1000 μm, respectively) nets in the East China Sea, and examined their relationships in density. Both meso- and small-size zooplankton densities showed positive relationships with larval fish density, while the relationship is much stronger for the small-size zooplankton. Specifically, the smallest size classes (50–75 and 75–100 μm) of small-size zooplankton showed the highest positive relationships with larval fish density. Temperature, salinity, and chlorophyll-a concentration did not significantly explain larval fish density. Based on these findings, we demonstrate the importance of considering prey size when investigating prey availability for larval fishes.