Recreational fish-finders - an inexpensive alternative to scientific echo-sounders for unravelling the links between marine top predators and their prey

Studies investigating how mobile marine predators respond to their prey are limited due to the challenging nature of the environment. While marine top predators are increasingly easy to study thanks to developments in bio-logging technology, typically there is scant information on the distribution and abundance of their prey, largely due to the specialised nature of acquiring this information. We explore the potential of using single-beam recreational fish-finders (RFF) to quantify relative forage fish abundance and draw inferences of the prey distribution at a fine spatial scale. We compared fish school characteristics as inferred from the RFF with that of a calibrated scientific split-beam echo-sounder (SES) by simultaneously operating both systems from the same vessel in Algoa Bay, South Africa. Customized open-source software was developed to extract fish school information from the echo returns of the RFF. For schools insonified by both systems, there was close correspondence between estimates of mean school depth (R 2 = 0.98) and school area (R 2 = 0.70). Estimates of relative school density (mean volume backscattering strength; S v ) measured by the RFF were negatively biased through saturation of this system given its smaller dynamic range. A correction factor applied to the RFF-derived density estimates improved the comparability between the two systems. Relative abundance estimates using all schools from both systems were congruent at scales from 0.5 km to 18 km with a strong positive linear trend in model fit estimates with increasing scale. Although absolute estimates of fish abundance cannot be derived from these systems, they are effective at describing prey school characteristics and have good potential for mapping forage fish distribution and relative abundance. Using such relatively inexpensive systems could greatly enhance our understanding of predator-prey interactions

The simulation of a transient leaching circuit

Thesis (PhD (Process Engineeering))--University of Stellenbosch, 1995.The hydrometallurgical leaching of sulphide concentrates was introduced in the 1950's. Generally the leaching mechanisms of these processes are not understood fundamentally. The reasons for this are the inherently complex nature of sulphide chemistry and that the sulphide concentrates usually consist of highly intergrown sulphide minerals. The leaching kinetics of sulphide concentrates where only one metal-sulphide mineral occurs have been investigated intensively, but not for sulphide concentrates with more than one metal-sulphide mineral. The behaviour of these mixed metal-sulphide minerals has mostly been investigated on plant scale to qualitatively determine the leaching trends of the process. The consequence of the relatively unKnown leaching mechanism and kinetics is that these processes are not controlled efficiently. This study was conducted on the acid-oxygen pressure leaching of Ni-Cu matte (the first stage leach process at the Ni-Cu refinery of Impala Platinum Ltd.). As a first step to improve the control efficiency of the process, the process must be stabilised. Therefore, an off line computer simulation program is proposed to control the repulping section of the plant that has previously been controlled solely by an operator. Controlling the repulping section is very important, because conditions exist in the repulping tanks for leaching to occur. This causes perturbations in the pulp entering the pressure leach autoclave. Due to the fast reaction kinetics of the matte in the pressure leach autoclave the perturbations entering the autoclave will influence the performance of the acid-oxygen pressure leach process. The simulation program was tested on the plant and indicated that considerable improvement in the stability of the operation could be achieved. In obtaining a better understanding of the behaviour of this process, it is essential that key variables and trends are identified. A methodology is proposed to analyse and model this ill-defined and poorly understood process from historical data by v artificial neural networks (ANN), inductive learning by decision trees and statistical techniques. The back propagation neural network, learning vector quantization neural network and the decision trees yielded comparable classification rates between 73% and 84%, and could serve as a basis for the adjustment of operating conditions to improve the efficiency of the process. The relative importance of the process variables is determined by a method of sensitivity analysis and together with the statistical mean, the effect of an increase or decrease in the variable on the process is quantified. These results are substantiated by experimental findings. A leaching mechanism for the acid-oxygen pressure leach of Ni-Cu matte is postulated. The leaching sequence of the nickel and copper sulphides is Ni3Sr Ni7S" NiS-Ni3S4, and CU2S-CU31SWCU1.BS-CUS, respectively. Ni7Sa and CU31 S1a are intermediate nickel and copper sulphide phases that form during the leaching process. Ni alloy has a galvanic effect on the sulphide minerals which inhibits the overall leaching rate and results in the formation of H2S and the intermediate nickel and copper sulphides (Ni7Sa and CU31 S1a). A semi-empirical kinetic model was developed based on the chemical reaction rate expressions of the leaching mechanism. This model can accurately simulate the batch leaching process for variations in the oxygen partial pressure, oxygen flowrate, temperature, particle size, initial acid concentration and pulp density. A sensitivity analysis on the model indicated that for a matte with a lower initial Ni alloy content the leaching rate of nickel is much faster

A strategy for knowledge management

M.Comm

Dives_Processed

African penguin diving data, processed using MTDiv

RawDiveFiles

Unprocessed data file

Data from: Local forage fish abundance influences foraging effort and offspring condition in an Endangered marine predator

1. Understanding the functional relationship between marine predators and their prey is vital to inform ecosystem-based management. However, collecting concurrent data on predator behaviour and their prey at relevant scales is challenging. Moreover, opportunities to study these relationships in the absence of industrial fishing are extremely rare. 2. We took advantage of an experimental fisheries closure to study how local prey abundance influences foraging success and chick condition of Endangered African penguins Spheniscus demersus in the Benguela Ecosystem. 3. We tracked 75 chick-provisioning penguins with GPS-time-depth devices, measured body condition of 569 chicks, quantified the diet of 83 breeding penguins and conducted 12 forage fish hydro-acoustic surveys within a 20 km radius of Robben Island, South Africa, over three years (2011–2013). Commercial fishing for the penguins’ main prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus, was prohibited within this 20 km radius during the study period. 4. Local forage fish abundance explained 60% of the variation in time spent diving for 14 penguins at sea within 2 days of a hydro-acoustic survey. Penguin foraging effort (time spent diving, number of wiggles per trip, number of foraging dives and the maximum distance travelled) increased and offspring body condition decreased as forage fish abundance declined. In addition, quantile regression revealed that variation in foraging effort increased as prey abundance around the colony declined. 5. Policy implications. Our results demonstrate that local forage fish abundance influences seabird foraging and offspring fitness. They also highlight the potential for offspring condition and the mean-variance relationship in foraging behaviour to act as leading indicators of poor prey abundance. By rapidly indicating periods where forage resources are scarce, these metrics could help limit seabird-fisheries competition and aid the implementation of dynamic ocean management

Data from: Local forage fish abundance influences foraging effort and offspring condition in an Endangered marine predator

1. Understanding the functional relationship between marine predators and their prey is vital to inform ecosystem-based management. However, collecting concurrent data on predator behaviour and their prey at relevant scales is challenging. Moreover, opportunities to study these relationships in the absence of industrial fishing are extremely rare. 2. We took advantage of an experimental fisheries closure to study how local prey abundance influences foraging success and chick condition of Endangered African penguins Spheniscus demersus in the Benguela Ecosystem. 3. We tracked 75 chick-provisioning penguins with GPS-time-depth devices, measured body condition of 569 chicks, quantified the diet of 83 breeding penguins and conducted 12 forage fish hydro-acoustic surveys within a 20 km radius of Robben Island, South Africa, over three years (2011–2013). Commercial fishing for the penguins’ main prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus, was prohibited within this 20 km radius during the study period. 4. Local forage fish abundance explained 60% of the variation in time spent diving for 14 penguins at sea within 2 days of a hydro-acoustic survey. Penguin foraging effort (time spent diving, number of wiggles per trip, number of foraging dives and the maximum distance travelled) increased and offspring body condition decreased as forage fish abundance declined. In addition, quantile regression revealed that variation in foraging effort increased as prey abundance around the colony declined. 5. Policy implications. Our results demonstrate that local forage fish abundance influences seabird foraging and offspring fitness. They also highlight the potential for offspring condition and the mean-variance relationship in foraging behaviour to act as leading indicators of poor prey abundance. By rapidly indicating periods where forage resources are scarce, these metrics could help limit seabird-fisheries competition and aid the implementation of dynamic ocean management

Flow diagram illustrating the workflow of FISH software showing the different steps in the processing phase (steps 1–3) and the review phase (step 4).

<p>Flow diagram illustrating the workflow of FISH software showing the different steps in the processing phase (steps 1–3) and the review phase (step 4).</p

School parameters and their descriptions for Fish-finder Image Segmentation Helper (FISH) outputs.

<p>*Recreational fish-finders (RFF) typically classify pixels on a sequential numeric scale with no reference to actual dB values. These need to be calibrated to a scientific echo-sounder (SES).</p><p>School parameters and their descriptions for Fish-finder Image Segmentation Helper (FISH) outputs.</p

Frequency of fish school encounter scenarios of the recreational fish-finder (RFF) and the scientific echo-sounder (SES) quantified by 500 m Elementary Distance Sampling Units (EDSU).

<p>Frequency of fish school encounter scenarios of the recreational fish-finder (RFF) and the scientific echo-sounder (SES) quantified by 500 m Elementary Distance Sampling Units (EDSU).</p