The document discusses exponential decay models used in fisheries science to model fish population dynamics. It describes the Beverton-Holt yield-per-recruit model, which assumes constant recruitment and uses an exponential decay function to model how fishing and natural mortality impact the number of fish surviving over time. The model is used to examine how changing fishing mortality or age at first capture affects yield per recruit. The document also discusses the relative yield-per-recruit and biomass-per-recruit models, which provide additional ways to assess fishery management strategies.
This document provides an introduction to fish stock assessment and key concepts. It discusses the primary objective of fish stock assessment as determining the optimal exploitation level to achieve maximum sustainable yield. It defines the stock concept as a subset of a species inhabiting a particular area with consistent growth and mortality parameters. The document emphasizes that fish stock assessment should be performed separately for each identified stock.
Gear selectivity refers to a fishing gear's ability to target and capture certain species, sizes, or sexes of fish while allowing incidental bycatch to escape unharmed. Most gears like trawls selectively catch larger fish, while some gears like gill nets selectively catch fish within a certain size range. The selection curve shows the size ranges caught by a gear. A bell curve indicates the optimum size range, while a sigmoid curve shows how percentage retained increases with size. Gill nets catch fish by wedging, gilling, or tangling in meshes. Mesh size, net dimensions, hanging ratio, and environmental factors influence gill net selectivity. Proper understanding of selectivity allows sustainable fisheries that return juveniles.
1. SPF animals are free from specific pathogens but may still be susceptible to infection. SPR animals have been selectively bred for resistance to particular pathogens through challenge testing.
2. Non-SPF broodstock can introduce novel diseases and pass pathogens to offspring without strict biosecurity. They may not have been selectively bred.
3. True SPF status requires rigorous screening and production in biosecure facilities; outside these facilities animals may still be disease-free but are no longer considered SPF.
Virtual population analysis (VPA) is a cohort modeling technique commonly used in fisheries science for reconstructing historical fish numbers at age using information on death of individuals each year. This death is usually partitioned into catch by fisheries and natural mortality. VPA is virtual in the sense that the population size is not observed or …
This document discusses the natural food and feeding habits of fishes. It covers different types of plankton, benthos, and detritus that serve as food sources for fishes based on their ecological niche. Various feeding classifications are described, including feeding types, trophic niches, and quantitative analyses of gut content. Structural modifications in fishes related to their different feeding habits are also mentioned.
1. Von Bertalanffy's growth equation is commonly used to model fish growth and estimate growth parameters.
2. The key growth parameters estimated include asymptotic length (L∞), growth coefficient (K), and theoretical age at zero length (t0).
3. Various methods can be used to estimate the parameters from length-at-age data, including Gulland and Holt plot, Ford-Walford plot, and Chapman's method. Estimated parameters are then used in fish stock assessment models.
fish population dynamics, Population structureDegonto Islam
Estimation of fish population dynamics are often based on age structures. Understanding past
population structure is of interest to evolutionary biologists because it can reveal when migration
regimes changed in natural populations, thereby pointing to potential environmental factors such as
climate changes as driving evolutionary forces. Characterizing the structure of extent populations is also
key to conservation genetics as translocation or reintroduction decisions must preserve evolutionary
stable units. Finally, population structure has important biomedical consequences either when a number
of subpopulation groups is locally adapted to particular environmental conditions (and maladapted
when exposed to new environments) or represents a confounding factor in the study of the statistical
association between genetic variants and phenotyp
The exponential decay model is a corer-stone of the theory of exploited fish stocks because in exploited fish stock numbers surviving end to decrease exponentially with time and age according to total mortality.
This document provides an introduction to fish stock assessment and key concepts. It discusses the primary objective of fish stock assessment as determining the optimal exploitation level to achieve maximum sustainable yield. It defines the stock concept as a subset of a species inhabiting a particular area with consistent growth and mortality parameters. The document emphasizes that fish stock assessment should be performed separately for each identified stock.
Gear selectivity refers to a fishing gear's ability to target and capture certain species, sizes, or sexes of fish while allowing incidental bycatch to escape unharmed. Most gears like trawls selectively catch larger fish, while some gears like gill nets selectively catch fish within a certain size range. The selection curve shows the size ranges caught by a gear. A bell curve indicates the optimum size range, while a sigmoid curve shows how percentage retained increases with size. Gill nets catch fish by wedging, gilling, or tangling in meshes. Mesh size, net dimensions, hanging ratio, and environmental factors influence gill net selectivity. Proper understanding of selectivity allows sustainable fisheries that return juveniles.
1. SPF animals are free from specific pathogens but may still be susceptible to infection. SPR animals have been selectively bred for resistance to particular pathogens through challenge testing.
2. Non-SPF broodstock can introduce novel diseases and pass pathogens to offspring without strict biosecurity. They may not have been selectively bred.
3. True SPF status requires rigorous screening and production in biosecure facilities; outside these facilities animals may still be disease-free but are no longer considered SPF.
Virtual population analysis (VPA) is a cohort modeling technique commonly used in fisheries science for reconstructing historical fish numbers at age using information on death of individuals each year. This death is usually partitioned into catch by fisheries and natural mortality. VPA is virtual in the sense that the population size is not observed or …
This document discusses the natural food and feeding habits of fishes. It covers different types of plankton, benthos, and detritus that serve as food sources for fishes based on their ecological niche. Various feeding classifications are described, including feeding types, trophic niches, and quantitative analyses of gut content. Structural modifications in fishes related to their different feeding habits are also mentioned.
1. Von Bertalanffy's growth equation is commonly used to model fish growth and estimate growth parameters.
2. The key growth parameters estimated include asymptotic length (L∞), growth coefficient (K), and theoretical age at zero length (t0).
3. Various methods can be used to estimate the parameters from length-at-age data, including Gulland and Holt plot, Ford-Walford plot, and Chapman's method. Estimated parameters are then used in fish stock assessment models.
fish population dynamics, Population structureDegonto Islam
Estimation of fish population dynamics are often based on age structures. Understanding past
population structure is of interest to evolutionary biologists because it can reveal when migration
regimes changed in natural populations, thereby pointing to potential environmental factors such as
climate changes as driving evolutionary forces. Characterizing the structure of extent populations is also
key to conservation genetics as translocation or reintroduction decisions must preserve evolutionary
stable units. Finally, population structure has important biomedical consequences either when a number
of subpopulation groups is locally adapted to particular environmental conditions (and maladapted
when exposed to new environments) or represents a confounding factor in the study of the statistical
association between genetic variants and phenotyp
The exponential decay model is a corer-stone of the theory of exploited fish stocks because in exploited fish stock numbers surviving end to decrease exponentially with time and age according to total mortality.
This document discusses the use of lights in fishing, known as light fishing. It explains that lights attract fish and other marine organisms at night. Fishermen have taken advantage of this behavior by using lights attached to fishing gear or structures above or below the water to aggregate and catch fish. The document describes different types of lights used, including high-intensity and low-intensity lights, and discusses factors like brightness, color, and portability. It also explains photomovement responses like aggregation, photokinesis, phototaxis, and vertical migration that cause marine life to be drawn to light sources. Regulations around light fishing in the Philippines are also summarized.
These topic contains global scenario of aquaculture, demand consumption scenario and present status of aquaculture in India. These presentation also contain constraints, future prospects and challenges in aquaculture. Different aquaculture practices throughout the world.
This document discusses fish feeding, including feed quality, storage, feeding correctly, selection, amount estimation, administering feed, feeding methods, frequency, response, assessing response, training fish, and managing wastes. Key points covered include the objectives of maximum growth, good health, and minimum waste; factors that influence feed quality like nutrients, processing, and storage; estimating feeding amounts based on fish size and weight; adjusting feeding based on monitoring and response; and techniques like hand feeding, demand feeders, and avoiding overfeeding.
This document discusses therapeutants and pesticides used in aquaculture. It outlines various compounds used as drugs, disinfectants, herbicides, insecticides, fungicides, anesthetics, and more. Specific compounds are discussed in detail, including their mechanisms of action, recommended dosages, and effects on fish and aquatic life. A wide range of chemicals are presented, along with factors to consider for safe and effective use in aquaculture operations.
This document discusses the Indian oil sardine fishery. It provides details on the distribution, peculiar characteristics, feeding habits, habitat, reproduction, fecundity, spawning season, age and growth, size of capture, mode of harvest, utilization, maximum sustainable yield, IUCN status, current stock status, management measures, and production trends of the Indian oil sardine. Key points include that it is distributed along India's western coast from Gujarat to Kerala, feeds mostly on plankton, reaches sexual maturity at 1 year old and 150mm in length, and production peaked at over 720,000 tonnes in 2012. Mesh size regulation is used for management.
The document provides details about a hands-on training program on seed production in fisheries. It describes the objectives, sites, and learning objectives of the program. Specifically, it focuses on carp breeding and seed production at two centers - Carp Seed Production and Rearing Center in Bodla and Carp Seed Rearing Center in Khairbanakala. It discusses the facilities at these centers and provides pictures to illustrate the spawning pools, incubation units, ponds, and other infrastructure. It also explains the standard procedures followed for induced breeding of carp and rearing of carp seeds.
1. There are three types of reservoirs in India - small (<1000 hectares), medium (1000-5000 hectares), and large (>5000 hectares). Small reservoirs account for the largest number (19,134) and area (1.48 million hectares).
2. Indian reservoirs tend to be nutrient-rich with narrow temperature fluctuations that prevent thermal stratification in many areas. Biotic communities include phytoplankton, zooplankton, fish, and decomposers like bacteria and fungi.
3. Fish production in Indian reservoirs is low on average at 20 kg/ha compared to potential yields, with room for improvement through management practices like stocking preferred fish species.
Nutritional requirement of larvae and broodstock of commercially important fi...Akhila S
the presentation provides the details regarding, Tthe broodstock nutrition, essential nutrients and recent data on broodstock nutrition; also larval nutrition; the hatchery utilised live feeds in detail and also microparticulate diet, the recent knowlwdge on essential elements amd minerals in larval nutrition, like taurine, phospholipids, liposomes, waxy spray beds etc
- Mugil cephalus, commonly known as the striped mullet, is an euryhaline fish that is cultured alone or with other fish species like tilapia.
- Grey mullet has been farmed for centuries in extensive and semi-intensive ponds in places like the Mediterranean, Southeast Asia, and Egypt.
- Major producing countries include Italy, Israel, Egypt, Mexico, Peru, Hong Kong, and Taiwan. Mullet is found worldwide in coastal waters except for some regions in the Americas.
1) Catchability is a key concept in relating fishing mortality to fishing effort and catch rates to fish biomass. It represents the proportion of the fish stock caught by each unit of fishing effort.
2) Catchability can change over time due to factors like changes in fishing methods/technology, fisher experience, and fish behavior/distribution. If catchability changes, the assumption that catch rates vary proportionally with biomass is violated.
3) Accounting for changes in catchability is important for accurately estimating fish biomass from catch rate data using stock assessment models. Failing to consider changing catchability could lead to biased biomass estimates.
This document provides information about mussel farming techniques in India. It discusses the following key points:
1. China is the world's largest producer of cultured mussels. In India, mussel culture is popular along the Malabar coast, where the two main species farmed are Perna viridis and Perna indica.
2. Common mussel farming techniques used in India include raft culture, rack culture, and long-line culture. Raft culture is conducted in deep coastal waters using rafts up to 8x8 meters with seeded ropes suspended below.
3. Rack culture is used in shallow waters up to 3 meters deep, using wooden frames built on poles to suspend seeded ropes or bags
Reservoirs in India hold potential for inland fisheries development but currently contribute less than expected to fish production. There are over 19,000 reservoirs in India covering 3.15 million hectares. The average fish yield from reservoirs is around 20 kg/ha but could be increased to 250 kg/ha through management. Key factors influencing reservoir productivity include morphometric characteristics, climate, soil properties, and chemical stratification. Management approaches for reservoirs focus on stock enhancement, species enhancement, and environmental enhancement through stocking of suitable fish species and regulating fishing efforts.
This document discusses biosecurity in aquaculture. It defines biosecurity as measures adopted to secure a disease-free environment in all phases of aquaculture. It identifies different levels of biosecurity including external and internal barriers to prevent the spread of disease. Components of biosecurity include quarantine, sanitation, and disinfection. Recommended protocols for sanitation and disinfection include being careful with live foods, proper storage and usage of manufactured feeds, and good overall system cleanliness. The document also discusses biosecurity strategies for shrimp production specifically.
This document defines aquaculture as the farming of aquatic organisms such as fish, mollusks, crustaceans, and aquatic plants. It involves interventions like regular stocking, feeding, and protection from predators to enhance production. India has a long coastline and extensive water resources that are well suited for aquaculture. The purpose of aquaculture includes increasing food production and income, as well as generating employment. There are various types of aquaculture defined by factors like the water system used, type of water, stocking combinations, and integration with other farming systems.
EXPONENTIAL DACAY MODEL & MORTALITY CONCEPT IN FISH STOCK ASSESSMENTKANTHARAJAN GANESAN
This document discusses exponential decay models and total mortality in fish stock assessment. It provides information on:
- The various risks fish face throughout their life cycles that can lead to mortality, including fishing, predation, disease, pollution, and old age.
- The components of total mortality (Z), which is the sum of fishing mortality (F) and natural mortality (M). Natural mortality includes physiological, selective, and chance mortality from factors other than fishing.
- How the exponential decay model describes how fish numbers decrease exponentially over time according to the total mortality rate (Z). Higher Z values mean faster decreases in numbers and lower maximum ages.
- Examples are given showing the percentages of fish surviving after 1
This is a presentation about the culture and breeding aspects of Red Sea bream,Pagrus major (Chrysophrys major).This fish have high aquaculture Importance today because of its meat quality and high growth rate
Zooplankton distribution and seasonal successionAl Nahian Avro
The seasonal distribution of the major components of the zooplankton community, protozooplankton, copepods and cladocerans, along a eutrophication gradient were examined in order to establish if eutrophication through increases in phytoplankton biomass and productivity has an impact on biomass and composition of the zooplankton community
At what age does a fish attain a maturity
What is the perfect catchable or mark able size of the fish
It helps to calculate the life span and longevity of fish
It enables to estimate and compare growth rates of fish in different waters.
Good or bad growth can point out the suitability for rearing and stocking purposes
The timing of spawning migration of given species can be worked out .
This document is a glossary of fisheries terms published by NOAA Fisheries. It contains definitions of over 60 common fisheries-related terms starting with A, such as abundance, anadromous, aquaculture, assessment and associated species. The glossary provides concise explanations of technical terms to facilitate communication about fisheries science and management. It is intended to help the general public and professionals in other fields understand the language used by NOAA Fisheries in their work.
A little summary of Age-structured models for fisheries in particular yield-per-recruit. The slides were developed from part 2 of Chapter 2 in the fantastic book "Modeling and Quantitative Methods in Fisheries" by Malcolm Haddon.
Authors: Daniele Baker and Derek Crane
Pastoors 2011 setting objectives for fisheries managementMartin Pastoors
The document discusses a public hearing before the European Parliament's Committee on Fisheries regarding the management of fishery resources and fleets. It questions whether Maximum Sustainable Yield (MSY) is an appropriate target for fisheries management. While MSY provides a general direction, its meaning is unclear, it takes a single-species approach, and science cannot precisely estimate it. The document suggests MSY be used to facilitate stakeholder discussions and move management in the right direction, rather than be taken literally.
This document discusses the use of lights in fishing, known as light fishing. It explains that lights attract fish and other marine organisms at night. Fishermen have taken advantage of this behavior by using lights attached to fishing gear or structures above or below the water to aggregate and catch fish. The document describes different types of lights used, including high-intensity and low-intensity lights, and discusses factors like brightness, color, and portability. It also explains photomovement responses like aggregation, photokinesis, phototaxis, and vertical migration that cause marine life to be drawn to light sources. Regulations around light fishing in the Philippines are also summarized.
These topic contains global scenario of aquaculture, demand consumption scenario and present status of aquaculture in India. These presentation also contain constraints, future prospects and challenges in aquaculture. Different aquaculture practices throughout the world.
This document discusses fish feeding, including feed quality, storage, feeding correctly, selection, amount estimation, administering feed, feeding methods, frequency, response, assessing response, training fish, and managing wastes. Key points covered include the objectives of maximum growth, good health, and minimum waste; factors that influence feed quality like nutrients, processing, and storage; estimating feeding amounts based on fish size and weight; adjusting feeding based on monitoring and response; and techniques like hand feeding, demand feeders, and avoiding overfeeding.
This document discusses therapeutants and pesticides used in aquaculture. It outlines various compounds used as drugs, disinfectants, herbicides, insecticides, fungicides, anesthetics, and more. Specific compounds are discussed in detail, including their mechanisms of action, recommended dosages, and effects on fish and aquatic life. A wide range of chemicals are presented, along with factors to consider for safe and effective use in aquaculture operations.
This document discusses the Indian oil sardine fishery. It provides details on the distribution, peculiar characteristics, feeding habits, habitat, reproduction, fecundity, spawning season, age and growth, size of capture, mode of harvest, utilization, maximum sustainable yield, IUCN status, current stock status, management measures, and production trends of the Indian oil sardine. Key points include that it is distributed along India's western coast from Gujarat to Kerala, feeds mostly on plankton, reaches sexual maturity at 1 year old and 150mm in length, and production peaked at over 720,000 tonnes in 2012. Mesh size regulation is used for management.
The document provides details about a hands-on training program on seed production in fisheries. It describes the objectives, sites, and learning objectives of the program. Specifically, it focuses on carp breeding and seed production at two centers - Carp Seed Production and Rearing Center in Bodla and Carp Seed Rearing Center in Khairbanakala. It discusses the facilities at these centers and provides pictures to illustrate the spawning pools, incubation units, ponds, and other infrastructure. It also explains the standard procedures followed for induced breeding of carp and rearing of carp seeds.
1. There are three types of reservoirs in India - small (<1000 hectares), medium (1000-5000 hectares), and large (>5000 hectares). Small reservoirs account for the largest number (19,134) and area (1.48 million hectares).
2. Indian reservoirs tend to be nutrient-rich with narrow temperature fluctuations that prevent thermal stratification in many areas. Biotic communities include phytoplankton, zooplankton, fish, and decomposers like bacteria and fungi.
3. Fish production in Indian reservoirs is low on average at 20 kg/ha compared to potential yields, with room for improvement through management practices like stocking preferred fish species.
Nutritional requirement of larvae and broodstock of commercially important fi...Akhila S
the presentation provides the details regarding, Tthe broodstock nutrition, essential nutrients and recent data on broodstock nutrition; also larval nutrition; the hatchery utilised live feeds in detail and also microparticulate diet, the recent knowlwdge on essential elements amd minerals in larval nutrition, like taurine, phospholipids, liposomes, waxy spray beds etc
- Mugil cephalus, commonly known as the striped mullet, is an euryhaline fish that is cultured alone or with other fish species like tilapia.
- Grey mullet has been farmed for centuries in extensive and semi-intensive ponds in places like the Mediterranean, Southeast Asia, and Egypt.
- Major producing countries include Italy, Israel, Egypt, Mexico, Peru, Hong Kong, and Taiwan. Mullet is found worldwide in coastal waters except for some regions in the Americas.
1) Catchability is a key concept in relating fishing mortality to fishing effort and catch rates to fish biomass. It represents the proportion of the fish stock caught by each unit of fishing effort.
2) Catchability can change over time due to factors like changes in fishing methods/technology, fisher experience, and fish behavior/distribution. If catchability changes, the assumption that catch rates vary proportionally with biomass is violated.
3) Accounting for changes in catchability is important for accurately estimating fish biomass from catch rate data using stock assessment models. Failing to consider changing catchability could lead to biased biomass estimates.
This document provides information about mussel farming techniques in India. It discusses the following key points:
1. China is the world's largest producer of cultured mussels. In India, mussel culture is popular along the Malabar coast, where the two main species farmed are Perna viridis and Perna indica.
2. Common mussel farming techniques used in India include raft culture, rack culture, and long-line culture. Raft culture is conducted in deep coastal waters using rafts up to 8x8 meters with seeded ropes suspended below.
3. Rack culture is used in shallow waters up to 3 meters deep, using wooden frames built on poles to suspend seeded ropes or bags
Reservoirs in India hold potential for inland fisheries development but currently contribute less than expected to fish production. There are over 19,000 reservoirs in India covering 3.15 million hectares. The average fish yield from reservoirs is around 20 kg/ha but could be increased to 250 kg/ha through management. Key factors influencing reservoir productivity include morphometric characteristics, climate, soil properties, and chemical stratification. Management approaches for reservoirs focus on stock enhancement, species enhancement, and environmental enhancement through stocking of suitable fish species and regulating fishing efforts.
This document discusses biosecurity in aquaculture. It defines biosecurity as measures adopted to secure a disease-free environment in all phases of aquaculture. It identifies different levels of biosecurity including external and internal barriers to prevent the spread of disease. Components of biosecurity include quarantine, sanitation, and disinfection. Recommended protocols for sanitation and disinfection include being careful with live foods, proper storage and usage of manufactured feeds, and good overall system cleanliness. The document also discusses biosecurity strategies for shrimp production specifically.
This document defines aquaculture as the farming of aquatic organisms such as fish, mollusks, crustaceans, and aquatic plants. It involves interventions like regular stocking, feeding, and protection from predators to enhance production. India has a long coastline and extensive water resources that are well suited for aquaculture. The purpose of aquaculture includes increasing food production and income, as well as generating employment. There are various types of aquaculture defined by factors like the water system used, type of water, stocking combinations, and integration with other farming systems.
EXPONENTIAL DACAY MODEL & MORTALITY CONCEPT IN FISH STOCK ASSESSMENTKANTHARAJAN GANESAN
This document discusses exponential decay models and total mortality in fish stock assessment. It provides information on:
- The various risks fish face throughout their life cycles that can lead to mortality, including fishing, predation, disease, pollution, and old age.
- The components of total mortality (Z), which is the sum of fishing mortality (F) and natural mortality (M). Natural mortality includes physiological, selective, and chance mortality from factors other than fishing.
- How the exponential decay model describes how fish numbers decrease exponentially over time according to the total mortality rate (Z). Higher Z values mean faster decreases in numbers and lower maximum ages.
- Examples are given showing the percentages of fish surviving after 1
This is a presentation about the culture and breeding aspects of Red Sea bream,Pagrus major (Chrysophrys major).This fish have high aquaculture Importance today because of its meat quality and high growth rate
Zooplankton distribution and seasonal successionAl Nahian Avro
The seasonal distribution of the major components of the zooplankton community, protozooplankton, copepods and cladocerans, along a eutrophication gradient were examined in order to establish if eutrophication through increases in phytoplankton biomass and productivity has an impact on biomass and composition of the zooplankton community
At what age does a fish attain a maturity
What is the perfect catchable or mark able size of the fish
It helps to calculate the life span and longevity of fish
It enables to estimate and compare growth rates of fish in different waters.
Good or bad growth can point out the suitability for rearing and stocking purposes
The timing of spawning migration of given species can be worked out .
This document is a glossary of fisheries terms published by NOAA Fisheries. It contains definitions of over 60 common fisheries-related terms starting with A, such as abundance, anadromous, aquaculture, assessment and associated species. The glossary provides concise explanations of technical terms to facilitate communication about fisheries science and management. It is intended to help the general public and professionals in other fields understand the language used by NOAA Fisheries in their work.
A little summary of Age-structured models for fisheries in particular yield-per-recruit. The slides were developed from part 2 of Chapter 2 in the fantastic book "Modeling and Quantitative Methods in Fisheries" by Malcolm Haddon.
Authors: Daniele Baker and Derek Crane
Pastoors 2011 setting objectives for fisheries managementMartin Pastoors
The document discusses a public hearing before the European Parliament's Committee on Fisheries regarding the management of fishery resources and fleets. It questions whether Maximum Sustainable Yield (MSY) is an appropriate target for fisheries management. While MSY provides a general direction, its meaning is unclear, it takes a single-species approach, and science cannot precisely estimate it. The document suggests MSY be used to facilitate stakeholder discussions and move management in the right direction, rather than be taken literally.
Population dynamics refers to factors that affect the abundance and distribution of organisms within an ecosystem. These include abiotic factors like temperature and biotic factors like predator-prey interactions. Harvesting of resources can drive species to extinction if not managed sustainably. The distribution and abundance of species is important for sustainability. Factors like habitat characteristics, environmental conditions, and interactions between organisms influence where and how many individuals of a species exist in an area. Population size is determined by birth rates, death rates, immigration and emigration. Rapid population growth can occur when reproduction is high and limiting factors are absent.
Populations and sustainability :- FisheriesDaniel Sandars
An hour long lecture on the role of Management and Operational Research in the governance of global fisheries. Global fisheries, like many open access natural resources, suffer for a tragedy of the commons effect. Population dynamic modelling can help provide the insights and understanding necessary to achieve sustainability.
Illegal fishing takes place when vessels fish in violation of laws within coastal state jurisdictions or regulated high seas. It hurts developing coastal communities and funnels profits to criminal operations, damaging ocean biodiversity. Several illegal and destructive fishing methods are described, including blast fishing using explosives, cyanide fishing, and muro-ami fishing, which uses bombs and large nets that endanger children. These practices destroy coral reefs and exploit children for labor. Effective solutions to illegal fishing include improving detection technologies, establishing data transmission channels between information sources and enforcement agencies, and centralized collection and dissemination of information to coordinate responses.
While species richness and diversity have remained stable in the Severn Estuary and Bristol Channel ecosystem over 35 years of monthly sampling, individual species show great variability in their dynamics. Abundant core species demonstrate density-dependent regulation and stability in their populations, whereas lower abundance species fluctuate more widely. Species also differ markedly in their responses to environmental factors like temperature, salinity, and climate indices such as the North Atlantic Oscillation. Long-term data collection has revealed how the fish and crustacean communities in this region have responded to multi-year periods of warming and cooling conditions.
Wetlands in Bangladesh encompass a wide verity of dynamic ecosystems ranging from mangrove forest (about 577, 100 ha), natural lakes, man-made reservoir (Kaptai lake), freshwater marshes (about 400 haors), oxbow lakes (about 54488 ha, locally known as baors), freshwater depressions (about 1,000 beels), fish ponds and tanks (about 147, 000 ha), estuaries and seasonal inundated extensive floodplains (Akonda, 1989; cited in Akbar Ali Khan 1993 and DoF 1985).
This document summarizes the biodiversity of the Hooghly-Matlah estuarine system in West Bengal, India. It describes the different zones of the estuary, key physicochemical parameters, aquatic species including 172 fish species and how the estuary supports significant fishery resources and production. In particular, it notes the estuary's importance for the Hilsa fishery and as a source of cultivable fish and prawn seed. However, the biodiversity faces threats from anthropogenic pressures like pollution, overexploitation, destruction of mangroves, and damage to the ecosystem. Conservation efforts are needed to protect this important estuarine environment.
Ecosystem-based fisheries management (EBFM) takes a holistic approach by considering all impacts on the ecosystem from fisheries and related human activities. It differs from conventional fisheries management by focusing on the entire ecosystem rather than individual species. The goal of EBFM is to maintain ecosystem health, integrity, and sustainability for both current and future generations. Key tools for implementing EBFM include ecosystem models (Ecopath, Ecosim), marine protected areas, and socioeconomic analysis to evaluate management tradeoffs.
This document discusses the changing dynamics of the dairy sector in India. It provides key statistics on milk production, consumption, and the livestock population. It also outlines some of the major concerns for the dairy industry like inadequate veterinary services and inputs. Additionally, the document analyzes existing dairy supply chain models, including strong organized systems like Amul, weak organized systems, and traditional dudhiya systems. Regulatory environment changes that allow more private investment in the dairy sector are also covered.
Dynamics of development in fish processing sectorupamadas
This document discusses technological developments in the fish processing sector. It begins by defining fish processing and describing some common processing techniques like drying, salting, smoking, chilling and freezing. It then discusses developments in product development, packaging modernization, quality control and processing infrastructure in India. Specific technologies like quick freezing, IQF freezing, cryogenic freezing and types of freezers are explained. The document highlights India's growth as a major fish exporter and continued opportunities for investment and improvement in the fish processing sector through adoption of new technologies.
The document discusses the natural, physical, and human resources of the Philippines that contribute to its economic development and ability to become a newly industrialized country. It outlines that the Philippines has abundant forest and fishery resources, a large population that can be both a resource and challenge, and is increasing its physical infrastructure through projects like roads, bridges, and buildings. However, it also notes issues like rapid deforestation, overfishing, and how a growing population can strain individual resources if the population is not healthy, educated, and qualified to compete globally. Overall the document performs an inventory of the country's resources but also raises questions about ensuring their sustainable management and development of human capital.
Fishery -all the activities connected with the securing of animal and vegetable products from the earth waters.
Fishery products include such items as fish, clams, oysters, lobsters, eels, shrimps, turtles, seals, and whales. Pearl sponges, coral shells, and seaweeds are also included among the products derived from the sea. Fish provides the protein which is needed in the human diet. Fisheries are perhaps the most poorly managed of all the natural resources. The unscientific assumption that man can never exhaust the resources of the sea has placed upon nature the entire responsibility for renewal and replenishment.
The document discusses Philippine laws related to fisheries and natural resources. It begins by outlining the hierarchy of laws, with the Constitution at the top, followed by national laws, international treaties, executive orders, and administrative orders from agencies like the Department of Agriculture. It then summarizes several key provisions in the Constitution related to natural resources and fisheries. Finally, it lists numerous national laws, international treaties, and executive and administrative orders that provide legal framework for managing fisheries and protecting the environment in the Philippines.
The document performs a SWOT analysis of the Indian fisheries sector, identifying strengths like being the second largest producer globally and providing livelihoods for many, as well as weaknesses like post-harvest losses and low value addition. Opportunities for growth include utilizing the potential yield from India's EEZ and growing domestic demand, while threats include overexploitation reducing marine catches and competition from imported products.
Introduction to fisheries and aquacultureOsama Zahid
This document discusses fisheries science and trends in fisheries production globally and in Pakistan. Key points include:
- World fish production in 2001 was 130 million tons, with 37 million from aquaculture and 92 million captured. China leads production.
- Fisheries provide food for 950 million people and 200 million jobs globally.
- Pakistan has rich fisheries resources but the sector contributes only 0.8% to GDP. Most caught fish is exported while domestic demand is only met at 1.6 kg per person annually compared to a global average of 16 kg.
- Pakistan has marine fisheries along its 100 km coastline and abundant freshwater fisheries in rivers and lakes. However, the fisheries department is
Aquaculture is the farming of aquatic organisms such as fish, shellfish, and plants. Major types include marine/brackishwater aquaculture of ocean species and freshwater aquaculture of native river/lake species. India is one of the top producers and exporters of aquaculture globally, dominated by species like carp, shrimp, and shellfish. The country faces challenges to its exports like market access issues, food safety concerns, and environmental impacts. It is addressing these through regulation, certification, traceability programs, and promoting sustainability and value-addition. Future prospects include growing demand, recognition of aquaculture as an economic sector, and greater awareness of sustainability needs.
Powerpoint Search Engine has collection of slides related to specific topics. Write the required keyword in the search box and it fetches you the related results.
- Mathematical models can be used to predict future fish stock levels and yields in order to help sustainably manage fisheries (1).
- The Beverton-Holt yield-per-recruit model is a classic population model that can estimate yield from a given number of recruits based on factors like fishing mortality and mesh size (2).
- Using this model and testing different fishing mortality levels, the maximum sustainable yield and optimal fishing mortality can be determined to help set management measures like mesh size regulations (3).
1. Von Bertalanffy's growth equation is commonly used to model fish growth and estimate growth parameters.
2. The key growth parameters estimated include asymptotic length (L∞), growth coefficient (K), and theoretical age at zero length (t0).
3. Various methods can be used to estimate the parameters from length-at-age data, including Gulland and Holt plot, Ford-Walford plot, and Chapman's method. Estimated parameters are then used in fish stock assessment models.
This document outlines a practical lab on fish population dynamics. It includes definitions of key terms like fish population dynamics, stock, and gonosomatic index. It also describes several common methods to estimate fish population parameters and stock abundance, like mark-recapture methods, depletion methods, and sampling surveys. Specific questions ask students to calculate growth parameters, length-weight relationships, population estimates, and compare models like the von Bertalanffy and Ford-Walford plots used for growth estimation. The document provides data to help students complete calculations and analysis for the lab.
The document describes virtual population analysis (VPA), a method used to simulate and analyze the dynamics of a fish population based on sampling. VPA involves simulating a virtual population and drawing samples from cohorts to represent the population over time. Key inputs include growth parameters, natural mortality, fishing mortality, and catch data. The method is then used to estimate population parameters and model recruitment, abundance, biomass, and yield through a series of steps involving growth models, mortality rates, and survivorship between cohorts.
Population ecology studies how organism numbers change over time and space and the factors influencing these changes. Key concepts include:
- Populations are groups of the same species in a defined area, with measures including population density and dispersion patterns.
- Populations can grow exponentially if birth and death rates remain constant, but density dependence causes logistic/sigmoidal growth towards an equilibrium carrying capacity K.
- Life histories vary along an r-K continuum, with r-selected populations having high reproduction and mortality and K-selected having lower reproduction but higher survival and competition.
- Capture-recapture methods can estimate unknown population sizes using marked and recaptured individuals.
Life tables summarize the mortality rates of a population over time. They track the number of individuals surviving (lx) and dying (dx) in each age interval. This data can be used to calculate other metrics like the proportion surviving (Sx), expected remaining life (ex), and mortality rate (qx). Survivorship curves graphically depict the decline in survivors over the lifespan based on life table data. There are three main types of survivorship curves: highly convex, intermediate, and highly concave. These curves reflect different mortality patterns across age classes.
Size distribution and biometric relationships of little tunny Euthynnus allet...inventy
This study is taken from data of commercial fishing of the little tunny, Euthynnus alletteratus (Rafinesque, 1810) caught in the Algerian coast, sampled between november 2011 and april 2016. Data were collected in order to determine size distributions of the population and biometric relationships of species including the size - weight relationships. A total of 601 fish ranged from 30.9 and 103 cm fork length (FL) were observed. The size distribution of Euthynnus alletteratus shows multiple modal values witch the most important cohort corresponds to the age class 2 (42-46 cm). The value of the allometric coefficient (b) of the FL/TW relationship is lower than 3, indicating a negative allometric growth.
Recruitment, mortality and exploitation rates estimate and stock assessment o...sarmodou
SARR Serigne Modou1,
*KABRE Tinkoudgou Jean-André1 and CECCHI Philippe2
1 Laboratoire de Recherche et de Formation en Pêche et Faune (LaRFPF/ IDR), Université de Bobo-Dioulasso, BP. 1091 Bobo 01, Burkina Faso.
2 Institut de Recherche et Développement (France).
*Corresponding author.
E-mail: ankab226@yahoo.fr
Tel: +22670231734.
The overfishing is the central problem of the Mugil cephalus fisheries in the estuary of the Senegal River. This species lives in the sea during its adult stage but returns in the Senegal River to reproduce and to spend its larval and juvenile stages. This study is aimed to pinpoint the state of exploitation dynamic and to assess the M. cephalus stock. The FISAT II software was used to perform the estimate of recruitment, mortality and exploitation rates. Meanwhile, a virtual population analysis using VIT4 software estimated yield per recruit (Y/R). The analysis yielded exploitation rates E of 0.44 and 0.23 respectively for adult fish and juveniles; therefore the adult stock is overfished during the M. cephalus life stage in sea. In addition, natural mortality (M=1.20 year-1) and total mortality (Z=1.5 year-1) are remarkably high for fish mature age groups III, IV and V. However, in the river the maximum sustainable exploitation (0.50) is not exceeded for juveniles age groups 0+, I and II. In conclusion, management policies should be introduced to safeguard the M. cephalus fishery in the estuary of the Senegal River.
1. The document discusses a study analyzing the growth rates of ferox trout using scale analysis and the Von Bertalanffy growth function model.
2. Significant differences were found between sympatric ferox trout and brown trout populations in Loch Awe and Loch Rannoch for certain growth parameters.
3. While scale analysis provides a non-lethal method, there are limitations to its accuracy which the study acknowledges, though it maintains scales are still preferable to otoliths for analyzing rare ferox trout.
The document discusses Von Bertalanffy growth parameters which are used as input data in fish stock assessment methods. It describes how growth parameters like length infinity, growth coefficient, and initial condition parameter are estimated. These parameters differ between species, sexes, and stocks. They are determined from length frequency data, mark recapture experiments, and age and growth estimation from hard parts. The parameters are then used to estimate mortality and in yield/recruit models to assess fish stocks.
This document discusses various indices used to summarize information, including ratios, proportions, and rates. It provides examples and definitions of each. Ratios are expressed as one number divided by another (a/b). Proportions are a ratio where the numerator is a subset of the denominator (a/(a+b)). Rates express the frequency of an event per unit of time and take the form of a ratio where the numerator is the number of events and the denominator is the total person-time at risk. The document also discusses how to calculate and interpret incidence rates, prevalence rates, and standardized mortality ratios.
1. Population ecology is the study of populations in relation to their environment, including factors influencing population size, density, age structure, and distribution.
2. A population is defined as a group of the same species living in the same area. Population density and dispersion patterns are influenced by birth, death, immigration and emigration rates.
3. Population growth models include exponential and logistic growth. Exponential growth is unlimited while logistic growth incorporates a carrying capacity, leading to an S-shaped growth curve.
GEOGRAPHY Population Ecology HSC MAHARASHTRATwinsIT2
1. Population ecology is the study of populations in relation to their environment, including factors influencing population size, density, age structure, and distribution.
2. A population is defined as a group of the same species living in the same area. Population density and dispersion patterns are influenced by birth, death, immigration and emigration rates.
3. Population growth models include exponential and logistic growth. Exponential growth is unlimited while logistic growth incorporates a carrying capacity, leading to an S-shaped growth curve.
This document analyzes the weight-length relationship of the rosy barb fish (Puntius conchonius) collected from water bodies in Nagaland, India. 50 fish ranging from 5.2-7.6cm and 1.6-7.1g were measured. Log-transformed regressions found significant correlations between length and weight for mixed, male, and female populations, though growth was negatively allometric. The relationships suggest predictive equations can estimate weight from length and vice versa. The study provides information on the growth and management of the species' fisheries in Nagaland.
Accretion Profile of the Rosy Barb, Puntius Conchonius (Hamilton- Buchanan, 1...IOSR Journals
Present study was made on 50 freshwater wild Puntius conchonius (Hamilton - Buchanan) of
various sizes ranging from a total length of 5.2 cm to 7.6 cm and weighing 1.6 gm to 7.1 gm. They were
sampled from different lentic and lotic water bodies of Nagaland, to investigate the weight-length relationship.
Each fish was measured and weight was taken. Log transformed regressions were used to test the growth trend. It was observed that growth in weight is not proportional to the cube of its length. Coefficient of correlation values for both male and female as well as for mixed population were found to be highly significant.
This document analyzes the weight-length relationship of the rosy barb fish (Puntius conchonius) collected from water bodies in Nagaland, India. 50 fish ranging from 5.2-7.6cm and 1.6-7.1g were measured. Log-transformed regressions found high correlation between length and weight. Growth was found to be negatively allometric (not proportional to the cube of length) for mixed, male, and female populations. Predictive equations were derived relating length and weight. The relationships were significant and can help studies on the species' biology, fisheries, and management.
This document discusses several topics related to ecology and population biology, including:
1) It introduces the concepts of r-selected and K-selected species, which have different life history strategies related to population stability and resource availability.
2) It discusses different types of population growth patterns (exponential, logistic) and factors (density-dependent, density-independent) that influence population growth rates.
3) It provides examples of applying mathematical models to analyze population growth and examines survivorship curves and life tables used to study reproduction and mortality among species.
This document summarizes a study on the age, growth, and mortality of Tylochromis jentinki, an important fish species for fisheries in Ebrié Lagoon, Ivory Coast. Monthly samples of 1850 T. jentinki were collected between 2004-2006. Growth parameters were estimated using length frequency data analyzed with ELEFAN, including L∞=25 cm, K=0.67 yr-1, and t0=-0.28 yr-1. Total mortality (Z) was estimated at 2.38 yr-1, with fishing mortality (F) of 0.93 yr-1 and natural mortality (M) of 1.45 yr-1. The stock was considered
Similar to Dynamic pool model for Fish stock Assessment, (20)
1. Concept of exponential decay model
A quantity is subject to exponential decay, if it decreases at a rate proportional
to its current value, time or space. In fish biology the most useful way to express
decay through the time of a group of fish born at same time is instantaneous rate of
total mortality. For estimation of mortality rate, the number of survivors in a cohort as
a function of time has to be determined. The number of survivors attaining age t is
denoted as N(t). The mortality in a fish stock occurs due to the natural or fishing
mortality.
DN/DT = e-Z=S
Where,
DN =Change in number, DT = Change in time, Z=Instantaneous rate of total
mortality=Total mortality rate= Total mortality coefficient and S =Survival rate,
S= e-Z or
ln S = - Z (survival rate) or Z= - ln S (total mortality rate)
The annual rate of total mortality (A) can be calculated as,
A=1 -S, or A= 1-e-Z
As an example, consider the number of survivors at age t = 0.5 year, N(0.5),
and the number of survivors one day later, N(0.50274) (1 day = 1/365 year = 0.00274
year). The number of specimens lost during that day is: N(0.5) - N(0.50274). To
designate the change in numbers during a relatively short time period (1 day) we use
the symbol DN; DN(0.5) = N(0.50274) - N(0.5). Note that DN is negative because it
represents a loss from the cohort. The rate of change in numbers is written: DN/DT;
where DT is the length of the time period (1 day in this case). If Z remains constant
throughout the life of a cohort it can be expressed mathematically as:
N(t)=N(Tr)*exp[-Z(t-Tr)]
This above equation is called as “Exponential Decay Model” and (together
with the growth equation) it is a corner-stone of the theory of exploited fish stocks
Baranov, 1918; Thompson and Bell, 1934; Fry, 1949 and Beverton and Holt, 1957).
2. Exponential decay curves, for Z = 0.2, 0.5, 1
and 2 per year, with recruitment, N(Tr) =
1000 fish
Dynamic pool models
The concept of the dynamic pool as a model for fish populations is
complicated. The population consists of all individuals alive at any time. This
population is continuously reduced in size by deaths, due to natural mortality or to
fishing, and is augmented by recruitment of young fish referred as “dynamic pool”.
Although, these are involved a dynamic balance between production (due to
recruitment and individual growth) and depletion (due to mortality). These are usually
described as a function of the age of the individuals involved, and there is therefore a
close correspondence between the dynamic pool concept and age-structured
methods of analysis and prediction.
The primary differences from the surplus models are
1. Dynamic pool models account for variable growth, mortality and reproductive
potential by age
2. Currently used to examine reproduction and recruitment potential
Dynamic pool methods seek to estimate number of the fish population at a
particular time from available data, and predict its future evolution under various
assumptions about natural and anthropogenic effects, especially levels of fishing.
The data to be analysed are generally some estimates of catch-at-age or length at
age. Estimates of the rates of mortality due to natural causes and that due to fishing,
3. as well as their sum, the total mortality rate, are the natural variables used to
describe the fate of the fish.
Within the general class of dynamic pool methods, there tends to be a fairly
clear separation between the techniques for the analysis of past data, to estimate the
current state and structure of the population, and those for forecasting its future
evolution. The former are exemplified by the ubiquitous technique known as Virtual
Population Analysis (VPA). The latter include both short-term catch forecast
methods, and long-term analyses such as that of yield-per-recruit (Beverton and Holt,
1957). These models relatively complicated considering cohort abundance, weight of
fish, mortality, growth, fishing effort, recruitment and yield.
The mathematical models used in fishery science analyses the history of a
fishery which can be transformed in such a way that the knowledge of the past can
be used to predict future yields and biomass at different levels of fishing effort. Thus,
models can be used to forecast the effects of development and management
measures such as increase or reduction of fishing fleets, changes in minimum mesh
sizes, closed seasons, closed areas etc. The first prediction model was developed by
Thompson and Bell (1934). In the mean time the Beverton and Holt’s (1957) model
based on rigorous assumptions but requiring less calculations also called the “yield-per-
recruit model” is being widely used. The yield per recruit model (Beverton and
Holt, 1957) is a model describing the state of stock and the yield in a situation when
the fishing pattern has been the same for such a long time that all fish alive have
been exposed to it since they recruited hence, called as “steady state model”.
The relationship between recruitment and spawning is still not well
understood. The only point understood is (0, 0) i.e., if there are no spawners there is
no recruitment. It is reasonable to assume that at low levels of the parent stock there
is a direct positive linear relationship with the number of offspring or recruitment, but
when it occurs we have to assume that the parental stock comes down to such a
level that recruitment over fishing can occur.
Assumptions of Beverton and Holt model (1957)
1. Recruitment is constant, yet not specified. Hence, the expression “yield per
recruit”
2. All fish of a cohort are hatched on the same date
3. Recruit and selection are ‘knife-edge’
4. The fishing and natural mortalities are constant from the entry to the exploited
phase
5. There is a complete mixing within the stock
6. The length-weight relationship has the exponent 3 i.e.,W= q*L3 or isometric
4. The assumed life history of a cohort in Beverton and Holt model is depends on
exponential decay model. The parameters required are:
1. At age Tr the cohort recruits to the fishing ground, all at the same time: ‘knife-edge
recruitment’.
2. From Tr to Tc they suffer only from natural mortality this is assumed to remain
constant throughout the lifespan of cohort.
3. At age Tc, ‘the age at first capture’, the cohort is assumed to be suddenly
exposed to full fishing mortality which is assumed remain constant for the rest
of the cohort’s life. The sigmoid shaped gear selection curve called “knife-edge
selection”.
4. The catch from the cohort therefore assumed to be zero before the cohort has
attained the age Tr.
Life history of a cohort as assumed in the Beverton and Holt model
The numbers of survivors at age Tr is the recruitment to the fishery: R = N(Tr)
The number of survivors at age Tc is : N(Tc) = R exp[ -M(Tc-Tr)]
The number of survivor at age t, where t > Tc is:
N(t) = N(Tc) – exp[- (M+F) (t- Tc) = R exp[-M(Tc – Tr) – (M+F)(t – Tc)]
The fraction of total recruitment N(Tr) or R surviving until age t is obtained by
dividing both sides of the equation by R and becomes:
N(t)/R = exp[ - M(Tc – Tr) – (M+F) (t – Tc)
5. It gives the number of fish at time t per recruit, i.e. as the fraction of each fish
that recruited to the fishery.
Beverton and Holt Yield Per Recruit (Y/R) model (1957)
Beverton and Holt (1957) developed this model describing the state of the stock and
the expected yield in a situation where a given fishing pattern has been operating for
a long time, i.e. under steady state condition. The definition of the recruits may vary
among the authors; here, it has been given as…………
(1). fully metamorphosed young fish,
(2). whose growth is described adequately by the VBGF,
(3). whose instantaneous rate of the natural mortality remains same as in adults
(4). which occur at (or swim into) the fishing ground
To derive the mathematical expression for the model we take a starting point
in the catch equation in the form of equation.
C(t, t+Δt) = Δt F N(t) …………………………………………………………………………………..1
This equation gives the number of fish caught in time period from t to t + Δt
from a cohort. To get the corresponding yield in weight, this number should be
multiplied by the individual weight of a fish. If Δt is small , then body weight of a fish
will remain approximately constant during the time period from t to t + Δt, and the
yield becomes:
Y(t, t+ Δt) = Δt *F *N(t) *w(t) ……………………………………………………………………………….…...2
Where w(t) is the body weight of a t years old fish, as defined by the weight
converted Von Bertalanffy equation. To get the yield per recruit for the time period
from t to t+Δt, Eqn.2 is divided by the no. of recruits, R:
Y(t, t+ Δt)/R = F*N(t)/R *w(t) *Δt……………………………………………………………………..………...3
(Eqn.3 is the Beverton and Holt model for a short time period)
Where, N(t)/R = exp[ - M(Tc – Tr) – (M+F) (t – Tc)……………..……………………………..4
To get the total yield per recruit for the entire life span of the cohort, Y/R, all
the small contributions defined by Eqn.3 must be summed:
Y/R = Y( Tc, Tc +Δ t)/R + Y(Tc+Δt, Tc + 2Δt)/R +Y(Tc+2Δt, Tc +3Δt)/R ………..+Y(Tc +(n-1)Δt, Tc+
nΔt)/R ………………………………………………………………….5
Where ‘n’ is some large number, so large that the number of fish older than
Tc+nΔt, i.e. N(Tc+ nΔt), is so small that it can be ignored.
6. The next step is to convert the eqn.5 into a form which can easily be
calculated. So, eqn. 5 can be converted as:
Y/R = F * exp [-M*(Tc –Tr)] *W¥ *[ - – ] …..…..6
Where,
S= exp[-k(Tc- t0)]; K= VBG parameter; t0= age at length zero; Tc= age at first capture;
Tr= age at recruitment; W∞= asymptotic body weight; F= fishing mortality; M= natural
mortality; Z= F+M, Total mortality.
Equation 6, is the “Beverton and Holt yield per recruit model”(1957) which is written
in the form suggested by Gulland (1969).
The two parameters F and Tc are those which can be controlled by fisheries
managers, because F is proportional to effort, and Tc is a function of gear selectivity.
Thus, Yw/R is considered as function of F and Tc. The Yw/R has a “maximum
sustainable yield” which depends on age of the first capture Tc.
Result of a stock and yield assessment with
the yield per recruit model
Yield per recruit curves with different ages
of first capture (Tc)
If the M is high it is difficult to point out the Fmsy and the Yw/R curve runs parallel to
the X-axis (see A).
7. Yield per recruit as a function of F for the
parameter :
K = 0.37/yr, Tc = 1.0 yr, t0 = - 0.2 year
M = 1.1/yr Tr = 0.4 year , W¥= 286 gm.
A
Yield per recruit as a function of F for
the parameter:
A: M = 1.1/yr, B: M = 0.2/yr
K = 0.37/yr, Tc = 1.0 yr, t0 = - 0.2 year
Tr = 0.4 yr, W¥ = 286 grams
B
· In graph B, the curve B has a pronounced maximum and lower value of Fmsy
and higher values of MSY/R as compared to curve A.
· Graph A, does not have maximum level, in such cases one must not conclude
that effort should be increased or decreased. Rather, it is the biomass per
recruit which should be examined or another version of Y/R model should be
used.
Beverton and Holt’s Relative Yield per Recruit (Y’/R) Model (1966)
For fisheries management purposes, it is important to be able to determine
changes in the Y/R for different values of F, for example if F is increased by 20%
then the yield may decrease by 15%. The absolute values of Y/R expressed in grams
per recruit are not important for this purpose. Therefore, Beverton and Holt (1966)
also developed a "relative yield per recruit model" which can provide the kind of
information needed for management. This model has the great advantage of
requiring fewer parameters, while it is especially suitable for assessing the effect of
mesh size regulations. It belongs to the category of length-based models, because it
is based on lengths rather than ages.
The formula given is…
(Y’/R) = E * U M/K * [1- + – ]
The relative yield per recruit (Y’/R) is a function of U and E and the only parameter
required here is M/K.
8. M = = K/Z
U =1–Lc/L¥, the fraction of growth to be completed after entry into exploited phase.
E = F/Z, the exploitation rate. (U= F/Z*(1-e-Z) exploitation ratio)
Beverton and Holt’s relative yield per
recruit (Y/R)’ curve corresponding to the
Y/R-curve
· The relative yield per recruit (Y’/R)
can be transformed into yield per
recruit (Y/R) as
Y’/R = Y/R*exp[M*(Tr-to)/ W¥]
.
Beverton and Holt’s Biomass Per Recruit (B/R) model
Beverton and Holt's biomass per recruit model expresses the annual average
biomass of survivors as a function of fishing mortality (or effort). The average
biomass is related to the catch per unit of effort. The relationship between CPUE and
numbers caught, which multiplied by the body weight on both sides gives following
equation.
CPUE (t) = q * N (t) · CPUE is the weight of catch per
unit of effort.
CPUE (t) * W(t) = q * W (t) · multiplied by the body weight on
both sides
CPUE W(t) = q * B (t) · If N (t) * W (t) is replaced by B (t),
the symbol of biomass
The catch in number / year can be expressed as C = F * and yield per year as Y =
F * B’ ; Where, B’ is the average biomass in sea during a year. Where average
biomass ,B’ follows that, B/R = Y/R*1/F. Because of the assumption of a constant
parameter system the yield from a stock during one year is equal to the yield from a
single cohort during its life span.
9. Therefore we have the following simple relationship between Y /R, and
average biomass per recruit (B’/R) as: Y/R = F* B’/R
B’/R can be calculated as:
(B’/R) = exp[-M(Tc-Tr)] * W¥ * [ ]
Biomass curve of (CPUE in weight) as a function of effort
Advantages of Y/R models
Both F and M are explicit in the model
Increased biological realism
Avoid having to address year-to-year variation in recruitment
Can see effects of F and Age of Entry on age and size in the catch
Disadvantages/ Limitations of Y/R
· assume constant recruitment
· This assumes age-structure remains stable
· Ignore any temporal variation in F and M
· Stable environment
· No density-dependence in growth and mortality.
· Yield-per-Recruit is good for determining if ‘growth overfishing’ is occurring.
But, since the models assume constant recruitment, they can’t detect
‘recruitment overfishing’. One of the serious drawbacks of the yield per recruit
model is that it disregards ‘recruitment overfishing’. With an ever decreasing
10. biomass for increasing effort a point may be reached when the stock is no
longer big enough to sustain the constant recruitment assumed.
Length based Thompson and Bell Model (1934)
The first predictive model was developed much earlier than the Beverton and
Holt model by Thompson and Bell (1934). The Thompson and Bell model is the exact
opposite of the VPA or cohort analysis and inverse of length structured VPA. It is
used to predict the effects of changes in the fishing effort on future yields, while VPA
or cohort analysis are used to determine the numbers of fish that must have been
present in the sea, to account for a known sustained catch, and the fishing effort that
must have been expended on each age or length group to obtain the numbers
caught. Therefore, VPA or cohort analysis is called historic or retrospective models,
while the Thompson and Bell model is predictive. The Thompson and Bell method
consists of two main stages:
· An analysis based on fishing mortality per size (age) group (so called F-array),
size (age) group-specific catches, death, yield, biomass and value
· A prediction of the effect of change in F-array on the catches, death, yield,
biomass and value in future.
The first of these two parts can be achieved through VPA or slight modification
of the catch curve routine, where the fishing mortality are estimated for each age or
length group.
Input parameters: The "length-based Thompson and Bell model" takes its inputs
from a length-based cohort analysis. The inputs consist of the fishing mortalities by
length group (the so-called F-at-length array), the number of fish entering the
smallest length group, and the natural mortality factor ‘H’ by length group, which must
be the same as the ones used in the cohort analysis. Additional inputs are the
parameters of a length-weight relationship (or the average weight of a single fish by
length group) and the average price per kg by length group.
Output parameters: The outputs for each length group the number at the lower limit
of the length group, N(L1), the catch in numbers, the yield in weight, the biomass
multiplied by Δt, i.e. the time required to grow from the lower limit to the upper limit of
the length group and the value.
· Thompson and Bell formula is based on Jones length based cohort analysis
which is given as follows:
It can be rewritten as
11. Where,
Which, is the same factor as used in Jones' length-based cohort analysis
· In order to calculate the yield (catch in weight) by length group the catch C (in
numbers) has to be multiplied by the mean weight of the length group, (L1,L2),
which is obtained from
Where, q and b are the parameters of the length-weight relationship
The yield of this length group will be,
The value of the yield is given by:
Where, (L1,L2) is the average price per kg of fish between lengths L1 and L2
The corresponding mean biomass * Δt is:
The annual yield is simply the sum of the yield of all length groups for each month:
Y = ƩYi
The annual value is likewise the sum of the value of all length groups for each month:
V = ƩVi
Basic features of the length-based Thompson and Bell analysis
12. Since the length-based Thompson and Bell analysis is derived from Jones'
length-based cohort analysis which in turn is based on Pope's age-based cohort
analysis, the length-based Thompson and Bell method has the same limitations as
Pope's age-based cohort analysis. The approximation to VPA in the predictive mode
is valid for values of F*Δt up to 1.2 and of M*Δt up to 0.3 (Pope, 1972). If the F's are
high, nonsensical results will come out of the analysis, such as negative stock
numbers.
Yield, biomass and value of yield per 1000 shrimps calculated by the age-based
Thompson and Bell model (1934), data collected from Kuwait shrimp fishery (Garcia
& van Zalinge 1982)
REFERENCES
1. Sparre, P. and Venema, S.C.,1989. “Prediction models”, Introduction to Tropical Fish
Stock Assessment. FAO Fisheries Technical Paper No. 306/1. 231-234
2. Gayanilo F.C. and Pauly D., 1997. “Yeild per recruit and prediction”, FAO-Iclarm Fish
Stock Assessment Tools. 178-207
3. Beverton, R.J.H. and S.J. Holt, 1957. On the dynamics of exploited fish populations.
Fish. Invest. Minist. Agric. Fish. Food G.B.(2 Sea fish)- 553.
4. Vivekanandan, E.(2005). “Analytical models of stock assessment”, Stock Assessment
of Tropical Fishes. ICAR. 70-75
5. Chakraborty, S. K., 2010. “Prediction models” in CAFT programme on Fisheries
Resources management (course manual). CIFE Mumbai, p208-215