Results of an Experimental Fishery on the Crayfish Orconectes virilis

1977 ◽  
Vol 34 (11) ◽  
pp. 2041-2055 ◽  
Author(s):  
Walter T. Momot ◽  
Howard Gowing
Keyword(s):  
Egg Production ◽  
Stock Assessment ◽  
Fishing Effort ◽  
Orconectes Virilis ◽  
Potential Yield ◽  
Yield Production ◽  
Ricker Model ◽  
Maximum Sustained Yield ◽  
Two Factors ◽  
The Impact

Populations of the crayfish Orconectes virilis were exploited using the Paulik–Bayliff modification of the Ricker model in two small lakes. After harvesting with traps at maximum sustained yield (MSY) for 3 yr, fishing effort was increased fourfold in one lake, West Lost, for two successive seasons, while in North Twin Lake it was not changed. In West Lost yields were stable during MSY; yields increased with overexploitation, but growth and recruitment declined. Distortions occurred in the age composition of the catch. In North Twin this pattern was repeated except that in 1975 the catch dropped drastically even though fishing effort had not been increased. Because of declining recruitment, North Twin was actually overfished by about 20% in 1974 and greatly overfished in 1975. Decreased recruitment in both lakes can be attributed to two factors: (1) a decreased survival of hatchlings in both lakes due to a decline in nursery habitat; as a consequence the stock-recruitment relationship was altered; and (2) an increase in the density of age I (subadult) females due to the selective fishery for males; as a result density-dependent mechanisms lowered the survival of females from age I to II, producing fewer spawning adults. However, the high density of these age II females at age I decreased the egg production per adult female. The changes in the productivity of the lakes for crayfish during the period of exploitation were related to loss of microhabitat for hatchlings. This change in productivity offset the benefits of MSY management and resulted in a drastic drop in stocks when deliberate overfishing took place. West Lost gave good yields prior to its certain collapse. Yields in weight were an unreliable indicator of the impact of the fishery. Key words: crayfish, Orconectes virilis, potential yield, production, recruitment, stock assessment, experimental fishery

scholarly journals An investigation into fisheries interaction effects using Atlantis

2014 ◽  
Vol 72 (1) ◽  
pp. 275-283 ◽  
Author(s):  
Michael D. Smith ◽  
Elizabeth A. Fulton ◽  
Robert W. Day
Keyword(s):  
Fisheries Management ◽  
Carrying Capacity ◽  
Stock Assessment ◽  
Single Species ◽  
Interaction Effects ◽  
Fishing Effort ◽  
Maximum Sustainable Yield ◽  
Simultaneous Increase ◽  
Total Catch ◽  
The Impact

Abstract Fisheries management is commonly based on the outputs of single-species stock assessment models. While such models are appropriate for tactical issues such as quota setting, they typically omit explicit trophic interactions between different parts of the ecosystem. To successfully manage multiple fisheries in the same ecosystem, we need to understand how fishing one species may indirectly affect other species. In this paper, we used a simulation model of the southern Benguela ecosystem, built in the Atlantis framework, to explore fisheries interaction effects. We first measured the impact of fishing different stocks individually at FMSY, the hypothetical level of fishing effort which produces maximum sustainable yield (MSY) in a single-species modelling context. We then applied FMSY to all stocks simultaneously and compared the simultaneous yield with the sum of yields from the individual applications of FMSY. Contrary to expectations, the total catch was higher under the simultaneous scenario. We explored our results by studying the influences of trophic interaction between species at different levels of the foodweb, and found that our overall result was driven by two key factors: volumetric dominance of small pelagic fish in the total catch, and asymmetric influences of competition and predation between piscivorous and planktivorous species. The simultaneous increase in fishing pressure across multiple species in the model led to increased effective carrying capacity for small pelagic species (due to reduced competition), but reduced carrying capacity for piscivorous species (due to reduced small pelagic prey). This work has important implications for the design of tactical multispecies models for use in ecosystem-based fisheries management.

Response of the Crayfish Orconectes virilis to Exploitation

1977 ◽  
Vol 34 (8) ◽  
pp. 1212-1219 ◽  
Author(s):  
Walter T. Momot ◽  
Howard Gowing
Keyword(s):  
Key Words ◽  
Egg Production ◽  
Life Tables ◽  
Population Stability ◽  
Invertebrate Predation ◽  
Orconectes Virilis ◽  
Major Response ◽  
Early Portion ◽  
The Impact

Life tables can aid in assessing the impact of exploitation of the crayfish Orconectes virilis by fish, invertebrates, and man. The major response of the population to exploitation comes through an adjustment of both the mx column (egg production) and lx (survivorship). Fish and invertebrate predation were directed towards modification of the early portion of the lx column. Survivorship did not change appreciably.Exploitation by man was directed toward males rather than females. An indirect result was an increase in the lx values for females. However, this was counteracted by a decrease in mx values leading to population stability as indicated by the Ro values. Both the exploitive strategies of fish and man failed to extract the maximum available biomass from the production of a given year-class. Key words: crayfish, exploitation, Orconectes virilis, life tables

scholarly journals Effects of spatial heterogeneity in growth and fishing effort on yield-per-recruit models: an application to the US Atlantic sea scallop fishery

2015 ◽  
Vol 73 (4) ◽  
pp. 1062-1073 ◽  
Author(s):  
Samuel B. Truesdell ◽  
Deborah R. Hart ◽  
Yong Chen
Keyword(s):  
Spatial Heterogeneity ◽  
Spatial Data ◽  
Egg Production ◽  
Fishing Effort ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Sea Scallop ◽  
The Us ◽  
The Impact ◽  
Yield Per Recruit

Abstract Conventional yield-per-recruit (Y/R) and spawning-stock biomass-per-recruit (SSB/R) models make no allowance for spatial heterogeneity in fishing mortality, natural mortality, or growth across the stock area, although variability in these processes can affect model results. For example, areas with higher growth and/or lower natural mortality rates should be fished at a lower rate to maximize Y/R; however, these areas may be especially attractive to fishers and are often fished harder. Here, Y/R and SSB/R models are developed that simultaneously account for spatial heterogeneity in growth and fishing effort. These models are applied to the US Atlantic sea scallop (Placopecten magellanicus) fishery. The spatial variability in growth uses depth-integrated models from the literature and variability in effort is based on, alternatively, uniform, observed, and relative-optimal spatial harvesting distributions. The observed effort patterns are derived from vessel monitoring system positions, and illustrate one application for these widely collected but underutilized spatial data. In this example, the distribution of observed fishing effort reduces Y/R compared with the relative-optimal, or the uniform effort distribution implicitly assumed by conventional Y/R analysis. SSB/R was in some cases considerably higher under the relative-optimal distribution of effort than when calculated using observed or uniform effort patterns. Such more realistic spatially integrated Y/R and SSB/R models can help to evaluate the impact of effort patterns on fishery yield and stock egg production. These models demonstrate that the spatial distribution of effort can be as important as the overall average fishing mortality when managing fisheries to optimize Y/R, SSB/R, and yield.

scholarly journals Intensive Fishing Effort and Market Controls as Management Tools for Invasive Aquatic Species: A Review

2022 ◽  
Vol 34 (4) ◽  
Author(s):  
MICHAEL A. RICE ◽  
Keyword(s):  
Invasive Species ◽  
Policy Development ◽  
Dreissena Polymorpha ◽  
Egg Production ◽  
Stock Assessment ◽  
Fishing Effort ◽  
Human Dimensions ◽  
Aquatic Species ◽  
Invasive Aquatic Species ◽  
Intensive Fishing

Invasive aquatic species may disrupt ecosystems and cause socioeconomic damage. Biosecurity protocols were developed to prevent transport and unintended introductions of invasive species, but less attention has been paid to management once they become established. The use of classical fisheries stock assessment to determine levels at which selectively targeted fisheries elicit recruitment overfishing is discussed. Case studies of several species of invasive aquatic organisms, including lionfish Pterois spp. two species of mytilids and three species of crayfish, including Faxonius rusticus (Girard, 1852), are discussed as examples. Fecundity as measured by egg production rate (EPR) is a key factor determining how the various species react to fishing pressure. Ecosystem modelling of predatorprey relations between indigenous and invasive aquatic species suggests that restricting fishing effort on indigenous predators of invasive prey may be as effective in managing invasive species in lieu of directly increasing fishing effort on the targeted species itself. Invasive mytilids Dreissena polymorpha (Pallas, 1771) and Mytella strigata (Hanley, 1843) may not be effectively controlled by intensive fishing effort due to high EPR values. However, crayfish that brood offspring and exhibit much lower EPR values may be ideal candidates for stock assessment and setting fishing effort targets to promote recruitment overfishing. Recommendations for managing invasive aquatic species include: collecting data on population dynamics of the invasive species; assessing predator populations; developing fisheries that target the invasive species; and collecting socioeconomic data to understand the human dimensions of the impacts of the invasive species and inform subsequent policy development.

scholarly journals A modelling approach to evaluate the impact of fish spatial behavioural types on fisheries stock assessment

2018 ◽  
Vol 76 (2) ◽  
pp. 489-500 ◽  
Author(s):  
Josep Alós ◽  
Andrea Campos-Candela ◽  
Robert Arlinghaus
Keyword(s):  
Stock Assessment ◽  
Fishing Effort ◽  
Fish Stock ◽  
Catch Per Unit Effort ◽  
Wide Range ◽  
Stock Assessments ◽  
Theoretical Predictions ◽  
Behavioural Types ◽  
Catch Rates ◽  
The Impact

Abstract Spatial behavioural types (SBTs) arise from between-individual differences in behavioural traits that foster spatial behavioural patterns that are consistent over time and ecological contexts. Fish stocks are regularly assessed using catch per unit effort (CPUE) as input data that may non-linearly co-vary with the underlying abundance (N) of the exploited stock when SBT affect catchability. We hypothesized that SBT promote characteristic changes in catchability within harvesting seasons that affect catch rates and in turn catch-based fish stock assessments. To test this hypothesis, we developed a spatially explicit agent-based simulation where we measured encounters between fish and fishers and estimated the shape of the CPUE–N relationship. We ran the simulation in a prototypical fish–fisher encounter-leads-to-catch-type fishery and systematically studied outcomes in the presence or absence of SBTs. It was revealed that the existence of SBTs leads to CPUE inevitably declining faster than N (a process known as hyperdepletion) when compared with a simulation lacking SBTs. This finding was consistent in a wide range of fishing effort scenarios. The emergent hyperdepletion of catch rates was caused by fast and behavioural-selective exploitation of vulnerable SBT that encompassed the mobile component of the fish stock. The theoretical predictions received support from field data from a coastal recreational fishery. Our work suggests that the consideration of SBT when interpreting trends in CPUE data may notably improve stock assessments by providing a more reliable CPUE–N relationship.

Self-Esteem and Loneliness as Predicting Factors of Arab Children Achievement İn Kuala Lumpur

2015 ◽  
Vol 5 (1) ◽  
pp. 199 ◽  
Author(s):  
Asma'a Abdel Fattah Alhoot ◽  
Ssekamanya Sıraje Abdallah
Keyword(s):  
Academic Achievement ◽  
Relevant Literature ◽  
Self Esteem ◽  
Kuala Lumpur ◽  
Arab Children ◽  
Predicting Factors ◽  
Two Factors ◽  
Arab Schools ◽  
And Gender ◽  
The Impact

Taking into consideration the fact that self-esteem and loneliness have an even more important role to play in students' learning, this study seeks to examine the correlation of these two factors with children academic performance. The study involved 499 (grade 4 to grade 9) Arab children studying at Arab schools in Kuala Lumpur-Malaysia. Data were collected via two questionnaires (one for loneliness and the other for self-esteem). The correlational data analysis yielded a negative correlation between loneliness and academic achievement while there is a positive correlation between self-esteem and achievement. Results also suggested that there is no correlation between students' gender, age, and academic achievement. Furthermore, the results revealed that self-esteem is a good predictor of achievement while loneliness and gender are not good predictors. The findings of the present study are discussed in relation to the relevant literature, taking into consideration the impact of children mental health on their academic achievement. Finally, recommendations for further research are presented.

scholarly journals Assessing the Potential of Catch-Only Models to Inform on the State of Global Fisheries and the UN’s SDGs

2021 ◽  
Vol 13 (11) ◽  
pp. 6101
Author(s):  
Rishi Sharma ◽  
Henning Winker ◽  
Polina Levontin ◽  
Laurence Kell ◽  
Dan Ovando ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Fishing Effort ◽  
The State ◽  
Sources Of Information ◽  
Ongoing Research ◽  
Traditional Assessment ◽  
Stock Status ◽  
Stock Assessments ◽  
Recent Developments ◽  
Measure Of Performance

Catch-only models (COMs) have been the focus of ongoing research into data-poor stock assessment methods. Two of the most recent models that are especially promising are (i) CMSY+, the latest refined version of CMSY that has progressed from Catch-MSY, and (ii) SRA+ (Stock Reduction Analysis Plus) a recent developments in field. Comparing COMs and evaluating their relative performance is essential for determining the state of regional and global fisheries that may be lacking necessary data that would be required to run traditional assessment models. In this paper we interrogate how performance of COMs can be improved by incorporating additional sources of information. We evaluate the performance of COMs on a dataset of 48 data-rich ICES (International Council for the Exploration of Seas) stock assessments. As one measure of performance, we consider the ability of the model to correctly classify stock status using FAO’s 3-tier classification that is also used for reporting on sustainable development goals to the UN. Both COMs showed notable bias when run with their inbuilt default heuristics, but as the quality of prior information increased, classification rates for the terminal year improved substantially. We conclude that although further COM refinements show some potential, most promising is the ongoing research into developing biomass or fishing effort priors for COMs in order to be able to reliably track stock status for the majority of the world’s fisheries currently lacking stock assessments.

scholarly journals Measuring the contribution of specialist vocabulary knowledge to academic achievement: disentangling effects of multiple types of word knowledge

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Ahmed Masrai ◽  
James Milton ◽  
Dina Abdel Salam El-Dakhs ◽  
Heba Elmenshawy
Keyword(s):  
Academic Achievement ◽  
Academic Success ◽  
Success Factors ◽  
Vocabulary Knowledge ◽  
The Other ◽  
Word Knowledge ◽  
Academic Vocabulary ◽  
Vocabulary Size ◽  
Two Factors ◽  
The Impact

AbstractThis study investigates the idea that knowledge of specialist subject vocabulary can make a significant and measurable impact on academic performance, separate from and additional to the impact of general and academic vocabulary knowledge. It tests the suggestion of Hyland and Tse (TESOL Quarterly, 41:235–253, 2007) that specialist vocabulary should be given more attention in teaching. Three types of vocabulary knowledge, general, academic and a specialist business vocabulary factors, are tested against GPA and a business module scores among students of business at a college in Egypt. The results show that while general vocabulary size has the greatest explanation of variance in the academic success factors, the other two factors - academic and a specialist business vocabulary - make separate and additional further contributions. The contribution to the explanation of variance made by specialist vocabulary knowledge is double that of academic vocabulary knowledge.

scholarly journals Nonstationary Responses of Demersal Fishes to Environmental Variations in Temperate Waters of the Northwestern North Pacific under a Changing Climate

Fishes ◽  
2021 ◽  
Vol 6 (3) ◽  
pp. 22
Author(s):  
Qingsong He ◽  
Shuyang Ma ◽  
Qinwang Xing ◽  
Wenchao Zhang ◽  
Haiqing Yu ◽  
...  
Keyword(s):  
North Pacific ◽  
Negative Relationship ◽  
Demersal Fish ◽  
Fishing Effort ◽  
Asian Winter Monsoon ◽  
Changing Climate ◽  
Sst Variability ◽  
Environmental Variations ◽  
The Impact ◽  
Demersal Fishes

Although nonstationarity in marine ecosystems has attracted great attention, the nonstationary responses of demersal fishes to environmental variations induced by the changing climate are still not well understood. Here, we collected 21 time series of demersal fishes from 1956 to 2015 to investigate the climate-induced nonstationary responses in temperate waters of the northwestern North Pacific (NWP). We showed that these demersal fishes experienced state shifts in approximately 1986/87, accompanied by abrupt warming over this region. Moreover, the relationships between demersal fishes and sea surface temperature (SST) were found to change between the two identified eras (i.e., a weak relationship before 1986 and a strong negative relationship after 1986), which may be primarily caused by the alternating dominance of the East Asian winter monsoon and mega-ENSO on SST in temperate waters of the NWP. The identified climate-induced nonstationary responses of demersal fishes to SST variability in this study may provide implications for understanding climate-induced biological dynamics, predicting demersal fish fluctuations, coping with potential ecological risks, and the sustainable exploitation of fishery resources in the future climate. Note that the impact of fishing on the demersal fishes in temperate waters of the NWP was not assessed in this study due to the lack of fishing effort data and therefore the conclusions of our research should be approached with caution.

scholarly journals Radical Response: Effects of Heat Stress-Induced Oxidative Stress on Lipid Metabolism in the Avian Liver

Antioxidants ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 35
Author(s):  
Nima K. Emami ◽  
Usuk Jung ◽  
Brynn Voy ◽  
Sami Dridi
Keyword(s):  
Oxidative Stress ◽  
Heat Stress ◽  
Lipid Metabolism ◽  
Egg Production ◽  
Well Being ◽  
Enzymatic Reactions ◽  
Poultry Production ◽  
Hepatic Lipid Metabolism ◽  
Hepatic Lipid ◽  
The Impact

Lipid metabolism in avian species places unique demands on the liver in comparison to most mammals. The avian liver synthesizes the vast majority of fatty acids that provide energy and support cell membrane synthesis throughout the bird. Egg production intensifies demands to the liver as hepatic lipids are needed to create the yolk. The enzymatic reactions that underlie de novo lipogenesis are energetically demanding and require a precise balance of vitamins and cofactors to proceed efficiently. External stressors such as overnutrition or nutrient deficiency can disrupt this balance and compromise the liver’s ability to support metabolic needs. Heat stress is an increasingly prevalent environmental factor that impairs lipid metabolism in the avian liver. The effects of heat stress-induced oxidative stress on hepatic lipid metabolism are of particular concern in modern commercial chickens due to the threat to global poultry production. Chickens are highly vulnerable to heat stress because of their limited capacity to dissipate heat, high metabolic activity, high internal body temperature, and narrow zone of thermal tolerance. Modern lines of both broiler (meat-type) and layer (egg-type) chickens are especially sensitive to heat stress because of the high rates of mitochondrial metabolism. While this oxidative metabolism supports growth and egg production, it also yields oxidative stress that can damage mitochondria, cellular membranes and proteins, making the birds more vulnerable to other stressors in the environment. Studies to date indicate that oxidative and heat stress interact to disrupt hepatic lipid metabolism and compromise performance and well-being in both broilers and layers. The purpose of this review is to summarize the impact of heat stress-induced oxidative stress on lipid metabolism in the avian liver. Recent advances that shed light on molecular mechanisms and potential nutritional/managerial strategies to counteract the negative effects of heat stress-induced oxidative stress to the avian liver are also integrated.

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