Spawning season influences on commercial catch rates: computer simulations and Plectropomus leopardus, a case in point1

1999 ◽  
Vol 56 (6) ◽  
pp. 1096-1108 ◽  
Author(s):  
Elizabeth Fulton ◽  
David Kault ◽  
Bruce Mapstone ◽  
Marcus Sheaves
Keyword(s):  
Fishery Management ◽  
Spawning Season ◽  
Small Scale ◽  
Test Case ◽  
Model Output ◽  
Commercial Catch ◽  
Spawning Aggregations ◽  
Spawning Stock ◽  
Plectropomus Leopardus ◽  
Catch Rates

Spatial and temporal closures of sections of the marine environment are proposed frequently as fishery management devices, particularly when specific areas, such as spawning aggregations, can be identified. The ultimate effectiveness of spawning area closures is unknown, as spawning-related determinants of catch rate have not been studied. A simulation model, based on existing biological and fisher information, was constructed to examine the most important determinants of the spawning season catch rates using the protogynous aggregative spawner Plectropomus leopardus (Family Serranidae, Subfamily Epinephelinae) as a test case. Model output indicated that spawning season catches rose as long as catchability of spawners was equal to or greater than that of nonspawners. Greatest increases in catch were produced by fish moving from habitats inaccessible to fishers into regularly fished locations during migrations to spawning aggregations. Elevated catches were not simply dependent on the targeting of aggregations by fishers. Small-scale spatial closures around spawning aggregation sites would not be sufficient to protect the spawning stock of fish such as P. leopardus, but larger scale closures during the spawning season may be useful even when fishers are not targeting spawning aggregations.

scholarly journals Reproductive Biology and Fishery-Related Characteristics of the Malabar Grouper (Epinephelus malabaricus) Caught in the Coastal Waters of Mafia Island, Tanzania

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Lydia Gaspare ◽  
Ian Bryceson
Keyword(s):  
Reproductive Biology ◽  
Spawning Season ◽  
Small Scale ◽  
Northeast Monsoon ◽  
Independent Research ◽  
Spawning Aggregations ◽  
Gonadal Histology ◽  
Management And Conservation ◽  
Sexually Mature ◽  
Epinephelus Malabaricus

The reproductive biology and fishery-related characteristics of the Malabar grouper (Epinephelus malabaricus) (Bloch and Schneider, 1801) specimens were investigated. The size of females ranged from 25 to 113 cm total length (LT), with 50% sexually mature at 79 cmLT, and the males (97 cm to 114 cmLT) were larger than the females. Due to the sex ratios and size distribution of the sample, it appeared that the groupers change sex between 97 and 113 cmLT. However, the gonadal histology data lacked specimens in the transitional stage. The spawning peak occurred in November, as defined by the presence of ripe females, and the spawning season lasted from September to February. The size of the fish correlated positively with the water depth at capture, which is also related to oxygen levels in deep water being more favourable for larger fish. Larger specimens (>100 cmLT) were targeted by fishers between December and February, when the northeast monsoon coincides with calmer weather and the spawning season. Fishers were interviewed, and observations were made on fishing gear, vessels, and grounds. There was no indication that small-scale fishers targeted spawning aggregations; therefore, fisheries independent research is recommended in order to verify the time, location, and behaviour of the spawning of Malabar groupers for management and conservation purposes.

Biology and management of a multi-sector blue swimmer crab fishery in a subtropical embayment - Shark Bay, Western Australia

2012 ◽  
Vol 63 (11) ◽  
pp. 1165 ◽  
Author(s):  
David Harris ◽  
Danielle Johnston ◽  
Errol Sporer ◽  
Mervi Kangas ◽  
Nieves Felipe ◽  
...  
Keyword(s):  
Biological Indicators ◽  
Trawl Survey ◽  
Commercial Catch ◽  
Shark Bay ◽  
The Past ◽  
Conflicting Evidence ◽  
Spawning Stock ◽  
Catch Rates ◽  
Harvest Strategy ◽  
The Impact

Stock assessments to support sustainable management in data-limited fisheries present a challenge to fisheries scientists and managers. This is the case with the Shark Bay Crab Fishery, which has expanded rapidly in the past 10 years, to become Australia’s highest-producing blue swimmer crab fishery. The resource is harvested commercially by two sectors, the Shark Bay crab trap and trawl fisheries (combined catch of ~800 t), as well as supporting a small but important recreational fishery. Commercial catch and effort data have been collected for the fishery since the early 1980s, commercial trap-monitoring data since 1999, and fishery-independent trawl-survey data since 2001. There is conflicting evidence on the impact that significant increases in catch and effort over the past decade has made on this fishery, such as legal catch rates remaining relatively constant, but declines occurring in the abundance of large crabs. There has also been concern over the level of latent effort in the fishery, with the trap sector currently operating at 70–80% of its potential effort and the capacity for further increases in crab landings by the trawl fleet. Since July 2011, the relative abundance of all size classes of crabs declined significantly. The reasons for this unexpected decline are yet to be understood, but are likely to be linked to adverse environmental extremes (flooding and very warm water temperatures) during the summer of 2010–2011, associated with a very strong La Niňa event. Preliminary assessment indicated that the spawning stock that led to the low recruitment was within historic ranges. The current challenge for the research and management of this fishery is to clarify the causes for this recent decline, and establish suitable biological indicators that will determine the appropriate level of catch and harvest strategy to ensure the future sustainability of the stock.

scholarly journals Using a Groundwater Adjusted Water Balance Approach and Copulas to Evaluate Spatial Patterns and Dependence Structures in Remote Sensing Derived Evapotranspiration Products

2021 ◽  
Vol 13 (5) ◽  
pp. 853
Author(s):  
Mohsen Soltani ◽  
Julian Koch ◽  
Simon Stisen
Keyword(s):  
Remote Sensing ◽  
Water Balance ◽  
Spatial Pattern ◽  
Spatial Patterns ◽  
Principal Component ◽  
Small Scale ◽  
Dependence Structure ◽  
Test Case ◽  
Catchment Scale ◽  
Balance Approach

This study aims to improve the standard water balance evapotranspiration (WB ET) estimate, which is typically used as benchmark data for catchment-scale ET estimation, by accounting for net intercatchment groundwater flow in the ET calculation. Using the modified WB ET approach, we examine errors and shortcomings associated with the long-term annual mean (2002–2014) spatial patterns of three remote-sensing (RS) MODIS-based ET products from MODIS16, PML_V2, and TSEB algorithms at 1 km spatial resolution over Denmark, as a test case for small-scale, energy-limited regions. Our results indicate that the novel approach of adding groundwater net in water balance ET calculation results in a more trustworthy ET spatial pattern. This is especially relevant for smaller catchments where groundwater net can be a significant component of the catchment water balance. Nevertheless, large discrepancies are observed both amongst RS ET datasets and compared to modified water balance ET spatial pattern at the national scale; however, catchment-scale analysis highlights that difference in RS ET and WB ET decreases with increasing catchment size and that 90%, 87%, and 93% of all catchments have ∆ET < ±150 mm/year for MODIS16, PML_V2, and TSEB, respectively. In addition, Copula approach captures a nonlinear structure of the joint relationship with multiple densities amongst the RS/WB ET products, showing a complex dependence structure (correlation); however, among the three RS ET datasets, MODIS16 ET shows a closer spatial pattern to the modified WB ET, as identified by a principal component analysis also. This study will help improve the water balance approach by the addition of groundwater net in the ET estimation and contribute to better understand the true correlations amongst RS/WB ET products especially over energy-limited environments.

scholarly journals Female reproductive biology and spawning periodicity of two species of king prawns, Penaeus longistylus Kubo and Penaeus latisulcatus Kishinouye, form Queensland's East Coast Fishery

1988 ◽  
Vol 39 (6) ◽  
pp. 729 ◽  
Author(s):  
AJ Courtney ◽  
MCL Dredge
Keyword(s):  
Egg Production ◽  
East Coast ◽  
Sea Water ◽  
Coastal Region ◽  
Ovary Development ◽  
Commercial Catch ◽  
Ovary Weight ◽  
Species Population ◽  
Spawning Periodicity ◽  
Catch Rates

In the coastal region of central Queensland female red-spot king prawns, P. longistylus, and the western or blue-leg king prawns, P. latisulcatus, had high mean ovary weights and high proportions of advanced ovary development during the winter months of July and August of 1985 and 1986. On the basis of insemination, both species began copulating at the size of 26-27 mm CL, but P. longistylus matured and spawned at a smaller size than P. latisulcatus. Abundance of P. longistylus was generally three to four times greater than that of P. latisulcatus but the latter was subject to greater variation in abundance. Low mean ovary weight and low proportions of females with advanced ovaries were associated with the maximum mean bottom sea-water temperature (28.5�C) for both species. Population fecundity indices indicated that peaks in yolk or egg production (a) displayed a similar pattern for both species, (b) varied in timing from year to year for both species and (c) were strongly influenced by abundance. Generally, sample estimates of abundance and commercial catch rates (CPUE) showed similar trends. Differences between the two may have been due to changes in targeted commercial effort in this multi-species fishery.

Aspects of the fishery, maturation and net selectivity of the wedge sole (Dicologoglossa cuneata) off south-western Iberia: implications for fishery management

2009 ◽  
Vol 90 (7) ◽  
pp. 1465-1474 ◽  
Author(s):  
Miguel Neves Santos ◽  
Pedro Gil Lino
Keyword(s):  
Fishery Management ◽  
River Mouth ◽  
Mesh Size ◽  
Scientific Basis ◽  
Catch Per Unit Effort ◽  
Important Species ◽  
Gill Net ◽  
Catch Rates ◽  
Log Normal ◽  
First Maturity

The wedge sole (Dicologoglossa cuneata, Moreau 1881) is a commercially important species for the artisanal fleet operating off the south-western Iberian Peninsula. During 2004 and 2005 a study was undertaken aiming to provide a scientific basis for management. Data collection included information on aspects of the fishery, spawning season, size at first maturity, tangle and gill-net selectivity. Seven nominal mesh sizes were used (40, 45 and 50 mm tangle nets and 40, 50, 60 and 70 mm gill-nets). Spawning lasts from December to June, with peaks in March and May. Length at first maturity for females was estimated at 18.5 cm. Catch rates decreased sharply with increasing mesh size, with tangle nets providing the highest yields. The log-normal selectivity model provided the best fit for specimens that were wedged. The higher catch-per-unit-effort of the smaller mesh sizes and the modal length of the fitted selectivity curve being below the size-at-maturity for wedge sole, suggests that the 50 mm nominal mesh size tangle net is the most appropriate for ensuring the fishery sustainability. Nevertheless, the minimum legal size should increase to at least 18 cm and a time–area closure should be implemented off the Guadiana River mouth.

A Web-Accessible Robotics Monitoring System Powered by a Thermoelectric Generator Connected to a Battery

2014 ◽  
Author(s):  
Robert Dell ◽  
Runar Unnthorsson ◽  
C. S. Wei ◽  
William Foley
Keyword(s):  
Peak Power ◽  
Thermoelectric Generator ◽  
Small Scale ◽  
Test Case ◽  
Test Bed ◽  
Robot System ◽  
Source Power ◽  
Power Generator ◽  
The Stability ◽  
Electrical Supply

In small source power generation scenarios in industrial or remote settings a viable small electrical supply for security and monitoring systems is often problematic due to the variability of the energy sources and the stability of the power generated. These small scale systems lack the advantages of a larger power grid. Therefore peak power requirements can be beyond the power generator necessitating energy storage such as batteries. The authors have developed and documented a reliable thermoelectric generator and a test bed. The generator was combined with a battery in order to meet peak power requirements beyond the unassisted range of the generator. This paper presents a test case result with the thermoelectric generator powering a complete web accessible mobile robot system. The robot system can be used for monitoring, physical manipulation of the environment, routine maintenance and in emergencies.

Validity of using translucent zones of otoliths to age the pilchard Sardinops sagax neopilchardus from Albany, Western Australia

1996 ◽  
Vol 47 (4) ◽  
pp. 617 ◽  
Author(s):  
WJ Fletcher ◽  
SJ Blight
Keyword(s):  
Western Australia ◽  
Age Groups ◽  
Growth Curves ◽  
Relative Number ◽  
Older Individuals ◽  
Commercial Catch ◽  
Monthly Basis ◽  
Lower Accuracy ◽  
Sardinops Sagax ◽  
Catch Rates

Otoliths (sagittae) of the pilchard (Sardinops sagax neopilchardus) from the Albany region of Western Australia were examined on a monthly basis during 1989 to 1991. When read consecutively, with the month of capture known, a clear annual cycle of an increase in marginal increments to October followed by a decline was recorded. This pattern was, however, severely distorted when samples were re-examined after having been jumbled and the month of capture concealed. Younger age groups (≤3) showed evidence of multiple rings being formed annually, but not in all years or individuals, and this was not evident in older individuals (≥4). Agreement between readings was low (43-53%), especially between different readers. Resultant growth curves showed that males grow to a smaller size (L∞ =164, K = 0.805, Φ = 1.03) than females (L∞ = 174, K = 0.584, Φ= 0.95). Agreement between counts of annuli and ages estimated by using otolith weight and length was only 54% for all individuals, but increased to 76% for individuals assigned the same age by different readers. Given the poorer predictions of future catch rates from the relative number of 2-year-olds in the commercial catch using annuli (implying lower accuracy) and increased complexity in preparation, otolith weights will be the method adopted for future ageing.

scholarly journals Assessment of the Challenges in Policy Implementation in the Small Scale Gold Mining Sector in Ghana – A Case Study

2017 ◽  
Vol 17 (1) ◽  
pp. 54-63 ◽  
Author(s):  
P. Arroja Eshun ◽  
E. Okyere
Keyword(s):  
Policy Implementation ◽  
Gold Mining ◽  
Small Scale ◽  
Mining District ◽  
Test Case ◽  
Mining Sector ◽  
Social Challenges ◽  
Mining Sites ◽  
Adequate Knowledge ◽  
Acquisition Processes

In recent times, stakeholders in the mining sector have expressed concerns about the environmental degradation and the social impacts of uncontrolled Small Scale Mining (SSM) activities in Ghana despite the existence of legislative instruments that define the procedures required for the acquisition of licences and operations of SSM activities in the country. This paper assesses the challenges in policy implementation in the small scale gold mining sector of Ghana by reviewing policies on regularisation and environmental management. It further identifies challenges faced by small scale mining operators in adhering to laid down policies for the smooth operation of the sector and furthermore assesses the views of some principal stakeholders on the benefits and challenges of small scale mining using the Dunkwa mining district as a test case. The methods employed include: field visits to some  small scale mining sites within the Dunkwa mining district; interviews and questionnaire administration; and statistical and content analysis of data. The study reveals the following factors, among others, to have contributed largely to the difficulty in regularisation, environmental and social challenges that have plagued the SSM sector: low level of education of majority of miners; bureaucracies and centralisation of licence acquisition processes; lack of sources of finance for SSM projects; lack of geological information on mineable areas; and lack of adequate knowledge of the laws and regulations on mining and environment. In addressing the challenges the following recommendations are made: decentralisation of the regularisation processes to simplify licence acquisition; adequate geological investigations should be undertaken on SSM blocked-out areas to reduce the try and error mining approach adopted by miners; and continuous education and training of miners on good mining and environmental practices. Keywords: Small Scale Mining, Mineral Policies, Environmental Impact, Regularisation, Challenges

scholarly journals Using pingers to reduce bycatch of small cetaceans in Peru's small-scale driftnet fishery

Oryx ◽  
2013 ◽  
Vol 47 (4) ◽  
pp. 595-606 ◽  
Author(s):  
Jeffrey C. Mangel ◽  
Joanna Alfaro-Shigueto ◽  
Matthew J. Witt ◽  
David J. Hodgson ◽  
Brendan J. Godley
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Marine Fauna ◽  
Incidental Capture ◽  
Small Scale Fisheries ◽  
Control Sets ◽  
Northern Peru ◽  
Catch Rates

AbstractThere is growing awareness that small-scale fisheries may have large impacts on threatened marine fauna. Bycatch of small cetaceans by the Peruvian small-scale driftnet fleet results in the deaths of thousands of animals annually. We sought to assess the effectiveness of acoustic alarms (pingers) for reducing the incidental capture of dolphins and porpoises by this fleet. Forty-three experimental trips (156 fishing sets) and 47 control trips (195 fishing sets) out of Salaverry Port, northern Peru, were observed from April 2009 to August 2011. Twenty-two percent of control sets captured small cetaceans (67 individuals) and 16% of experimental sets had captures of small cetaceans (33 individuals). The bycatch rate of experimental sets was 0.50 individuals km−2h−1, whereas for control sets the rate was 0.80 individuals km−2h−1. This 37% reduction in bycatch rate suggests that pingers may be effective in reducing the bycatch of small cetaceans in this fishery. Catch rates of the fishery's target shark and ray species were unchanged. Given the vast size of this fishery and its current levels of bycatch of small cetaceans (> 10,000 individuals annually), even the modest declines in bycatch we observed could result in reductions in mortality of hundreds or thousands of small cetaceans per annum. Challenges, including increased costs, to large-scale utilization of pingers have yet to be overcome. The harpooning of dolphins for use as bait will also need to be addressed for further reductions in dolphin and porpoise bycatch and mortality to be achievable.

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