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 cold water fisheries deal with fisheries activity in water where temperature of water ranges from 5 to 25 degrees centigrade. The water temperature under cold water fisheries should not be more than 25°C even in summer. Such conditions in India occur in Himalayan and peninsular regions.
9 Finest Coldwater Aquarium Fish
Orangethroat Darter.
Three-Spined Stickleback.
Orange-Spotted Sunfish.
Diamond Sturgeon.
Siberian Sturgeon.
Sterlet.
Fathead Minnow.
Southern redbelly dace.
Tench.
Rosy Barb. Hailing from Afghanistan and Bangladesh, this little fish is tolerant of temperatures in …
Gold Barb. The gold bard, or Chinese barb, is an extremely popular cold-water fish. Any aquarium …
Two Spot Barb. This fish hails from Nepal, India, and Pakistan. The omnivorous two spot barb …
Bloodfin Tetra. Natives to Southern Brazil and Paraguay, both the standard bloodfin .
Coldwater fish in terms of the aquarium trade refers to any fish species that prefer cooler water temperatures. The optimal temperatures for these fish hover around the 68-degree mark, although each species’ temperature range may vary from the norm.
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
The cold water fisheries deal with fisheries activity in water where temperature of water ranges from 5 to 25 degrees centigrade. The water temperature under cold water fisheries should not be more than 25°C even in summer. Such conditions in India occur in Himalayan and peninsular regions.
9 Finest Coldwater Aquarium Fish
Orangethroat Darter.
Three-Spined Stickleback.
Orange-Spotted Sunfish.
Diamond Sturgeon.
Siberian Sturgeon.
Sterlet.
Fathead Minnow.
Southern redbelly dace.
Tench.
Rosy Barb. Hailing from Afghanistan and Bangladesh, this little fish is tolerant of temperatures in …
Gold Barb. The gold bard, or Chinese barb, is an extremely popular cold-water fish. Any aquarium …
Two Spot Barb. This fish hails from Nepal, India, and Pakistan. The omnivorous two spot barb …
Bloodfin Tetra. Natives to Southern Brazil and Paraguay, both the standard bloodfin .
Coldwater fish in terms of the aquarium trade refers to any fish species that prefer cooler water temperatures. The optimal temperatures for these fish hover around the 68-degree mark, although each species’ temperature range may vary from the norm.
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
Fish Larval Nutrition: A Review on New Developmentstheijes
Despite considerable progress in recent years, many questions regarding fishlarval nutrition remain largely unanswered, and several research avenues remain open. A holistic understanding of the supply line of nutrients is important for developing diets for use in larval culture and for the adaptation of rearing conditions that meet the larval requirements for the optimal presentation of food organisms and ⁄ or microdiets. Marine fish larvae fed microdiets have not, at this stage, matched the growth and survival performances demonstrated by larvae fed live feeds such as rotifers and Artemia. This chapter discusses the issues related to the use of microdiets as a sole or partial feed for marine fish larvae. The techniques and methods of manufacturing microdiet particles, chemical and physical properties and the relationship to the ingestion and digestion are described. The aim of the present review is to revise the state of the art and to pinpoint the gaps in knowledge regarding larval nutritional requirements, the nutritional value of live feeds and challenges and opportunities in the development of formulated larval diets.
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 …
Fishing is the art of catching fish and other aquatic animals. Many years ago man started using various type of gear used for hunting the terrestrial animals and for fishing also. It is very difficult to say which started first, but some time it is opined that fishing is younger. Reason behind it is easy to catch animals in the land than in the water. In olden days fishing was not having much importance as there was no demand for fish. Earlier fishing was restricted to a particular community but it is not so now. In order to meet the increased demand, fishing is now carried out industrially. Fishing technology not only concerns fishing gear, fishing methods and vessels but also concern Biological and Environmental factors
Modern developments in transport technology are from two levels; one is from an understanding of internal physiological mechanisms of the fish and the optimal requirements, ensuring maximum survival of fish under transport and the other is from a study of the environmental parameters of the medium in which fish are transported. Under anaesthesia fish can be transported without water even, provided the skin and gills are kept moist under low temperature. The cryopreservation of fish sperm for use at any convenient time can be referred to here, though this would concern seed production more directly than live seed transport.
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 .
Eggs and larvae identification biology in fin fish Ashish sahu
Characters most useful in identification of fish eggs are the following: (1) egg shape-spherical, ellipsoidal, irregular, or oth- erwise; (2) egg size-fish eggs range in size from 0.5 to 26.0 mm; (3) oil globules-presence or-absence.
Identification of Fish Eggs - SWFSCswfsc.noaa.gov › publications
Search for: How can you tell a fish egg?
Ppt is made vailable for public for scientifc use.
Population ecology concept and its characteristics explained by using practical examples in a simple language. data is significant for competitive examinations
Fish Larval Nutrition: A Review on New Developmentstheijes
Despite considerable progress in recent years, many questions regarding fishlarval nutrition remain largely unanswered, and several research avenues remain open. A holistic understanding of the supply line of nutrients is important for developing diets for use in larval culture and for the adaptation of rearing conditions that meet the larval requirements for the optimal presentation of food organisms and ⁄ or microdiets. Marine fish larvae fed microdiets have not, at this stage, matched the growth and survival performances demonstrated by larvae fed live feeds such as rotifers and Artemia. This chapter discusses the issues related to the use of microdiets as a sole or partial feed for marine fish larvae. The techniques and methods of manufacturing microdiet particles, chemical and physical properties and the relationship to the ingestion and digestion are described. The aim of the present review is to revise the state of the art and to pinpoint the gaps in knowledge regarding larval nutritional requirements, the nutritional value of live feeds and challenges and opportunities in the development of formulated larval diets.
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 …
Fishing is the art of catching fish and other aquatic animals. Many years ago man started using various type of gear used for hunting the terrestrial animals and for fishing also. It is very difficult to say which started first, but some time it is opined that fishing is younger. Reason behind it is easy to catch animals in the land than in the water. In olden days fishing was not having much importance as there was no demand for fish. Earlier fishing was restricted to a particular community but it is not so now. In order to meet the increased demand, fishing is now carried out industrially. Fishing technology not only concerns fishing gear, fishing methods and vessels but also concern Biological and Environmental factors
Modern developments in transport technology are from two levels; one is from an understanding of internal physiological mechanisms of the fish and the optimal requirements, ensuring maximum survival of fish under transport and the other is from a study of the environmental parameters of the medium in which fish are transported. Under anaesthesia fish can be transported without water even, provided the skin and gills are kept moist under low temperature. The cryopreservation of fish sperm for use at any convenient time can be referred to here, though this would concern seed production more directly than live seed transport.
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 .
Eggs and larvae identification biology in fin fish Ashish sahu
Characters most useful in identification of fish eggs are the following: (1) egg shape-spherical, ellipsoidal, irregular, or oth- erwise; (2) egg size-fish eggs range in size from 0.5 to 26.0 mm; (3) oil globules-presence or-absence.
Identification of Fish Eggs - SWFSCswfsc.noaa.gov › publications
Search for: How can you tell a fish egg?
Ppt is made vailable for public for scientifc use.
Population ecology concept and its characteristics explained by using practical examples in a simple language. data is significant for competitive examinations
Population ecology is a field of scientific research that examines the dynamics of populations of living organisms within a given environment. It involves the study of various aspects of populations, including their growth, distribution, density, age structure, and the factors that affect these attributes. Key components of population ecology include:
Population Dynamics: Population ecologists study how the size of a population changes over time. This involves examining birth rates (natality), death rates (mortality), immigration, and emigration.
Population Distribution: Understanding how individuals in a population are spatially distributed is essential. Populations can be clumped, evenly dispersed, or randomly distributed in a habitat.
Population Density: This refers to the number of individuals of a species per unit area or volume of habitat. Population density can have significant ecological and environmental implications.
Age Structure: The age distribution within a population can provide insights into its growth potential and reproductive capacity. It can help in predicting future population trends.
Population Growth Models: Population ecologists use mathematical models to describe and predict population growth, such as exponential and logistic growth models.
Limiting Factors: Population growth is limited by various factors, including availability of resources, predation, competition, disease, and environmental conditions. Population ecologists study how these factors influence population dynamics.
Carrying Capacity: The carrying capacity of an environment is the maximum population size that can be sustained by available resources without causing environmental degradation or resource depletion.
Interactions: Populations do not exist in isolation. Interactions with other species, such as predation, competition, and mutualism, are essential considerations in population ecology.
Conservation and Management: Population ecology plays a critical role in the conservation and management of endangered species and ecosystems. It helps in making informed decisions to protect and sustainably manage populations.
Research Methods: Population ecologists employ various field and laboratory techniques, including population censuses, mark and recapture studies, and modeling, to gather data and understand population dynamics.
Effect of development on environment and population ecologyMegha Majoe
Brief idea on the Impact of ongoing human development on our environment and Describing and understanding population ecology - Patterns of dispersion, Survivorship curve, Population growth, Exponential growth, ecological footprint etc
Behavioral signature of intraspecific competition anddensity.docxAASTHA76
Behavioral signature of intraspecific competition and
density dependence in colony-breeding marine predators
Greg A. Breed1, W. Don Bowen2 & Marty L. Leonard1
1Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, Nova Scotia, B3H 4J1, Canada
2Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth, Nova Scotia, B2Y 4A2, Canada
Keywords
Animal movement, compensatory population
regulation, correlated random walk, foraging
ecology, juvenile mortality, marine mammal,
seal, switching state-space model.
Correspondence
Greg A. Breed, Department of Biological
Sciences University of Alberta, Edmonton, AB
T6G 2E9, Canada. Tel: 780-492-7942;
E-mail: [email protected]
Funding information
This work was supported by the Future of
Marine Animal Populations program, Fisheries
and Oceans Canada, Dalhousie University,
and NSERC grants awarded to Marty Leonard
and W. Don Bowen. This research was
conducted under the authorization of the
Canadian Ministry of Fisheries protocol nos.
04-13, 02-91, 00-051, and 98-078.
Received: 24 May 2013; Revised: 26 July
2013; Accepted: 12 August 2013
Ecology and Evolution 2013; 3(11): 3838–
3854
doi: 10.1002/ece3.754
Abstract
In populations of colony-breeding marine animals, foraging around colonies
can lead to intraspecific competition. This competition affects individual forag-
ing behavior and can cause density-dependent population growth. Where
behavioral data are available, it may be possible to infer the mechanism of
intraspecific competition. If these mechanics are understood, they can be used
to predict the population-level functional response resulting from the competi-
tion. Using satellite relocation and dive data, we studied the use of space and
foraging behavior of juvenile and adult gray seals (Halichoerus grypus) from a
large (over 200,000) and growing population breeding at Sable Island, Nova
Scotia (44.0 oN 60.0 oW). These data were first analyzed using a behaviorally
switching state-space model to infer foraging areas followed by randomization
analysis of foraging region overlap of competing age classes. Patterns of habitat
use and behavioral time budgets indicate that young-of-year juveniles (YOY)
were likely displaced from foraging areas near (<10 km) the breeding colony by
adult females. This displacement was most pronounced in the summer. Addi-
tionally, our data suggest that YOY are less capable divers than adults and this
limits the habitat available to them. However, other segregating mechanisms
cannot be ruled out, and we discuss several alternate hypotheses. Mark–resight
data indicate juveniles born between 1998 and 2002 have much reduced survi-
vorship compared with cohorts born in the late 1980s, while adult survivorship
has remained steady. Combined with behavioral observations, our data suggest
YOY are losing an intraspecific competition between adults and juveniles,
resulting in the currently observed decelerating logistic ...
Bottom clean Aquaculture system and It’s Engineering PrincipleDegonto Islam
Bottom clean Aquaculture method is considered an updated version of bio-floc.
The most important tasks here are scientifically removing the waste from the bottom of the reservoir and the rotation of oxygen and food supply to the fishes
In this type of culture system, as the amount of oxygen is higher, it is able to culture fishes 10- 20 times more.
Separation Surplus yield model (MSY, Fmsy, MEY, Fmsy)Degonto Islam
Economic variables are often included in the biological model that suggests the relationship between sustainable revenue, fishing cost and fishing effort.
For more than 50 years, it has been generally accepted that the fishing sector stood to gain from managing fisheries at the effort level producing maximum economic yield rather than maximum sustainable yield, which occurs at a higher effort level.
Surplus production models are also called as Holistic models. This model deals with total stock biomass along with fishing effort and yield. To operate this model, catch and effort data are needed as input data. These models could be computed with less input data unlike analytic models. This model does not take into account age and growth. Hence, it could be safely applied to tropical stocks, where calculation of age of tropical fish is more cumbersome.
Programme planning and evaluation in extension workDegonto Islam
Programme is the total educational job being done in particular settings that forms the basis for extension plan. Programme planning is decision making process which actually analysis the existing condition and matter and evaluation the alternative approach to solve the crux with priorities of the human feeling and needs. Generally initial objectives are peoples participations at grass roots level.
Fishing Gear any form of equipment, implement, tool or mechanical device used to catch, collect or harvest fish. Fishermen in many parts of Bangladesh catch fish with their hands. In rural areas, in seasonal waters or beels, during winter, people can be usually seen fishing with different traditional gears while some even do so without any gear
Guidelines for the control of Aquaculture medicinal products(AMPs)Degonto Islam
Aquaculture drugs and chemicals plays a pivotal role not only in fish health management but also pond construction, soil and water management, enhancement of natural aquatic productivity, feed formulation, manipulation of reproduction, growth promotion and processing. Government of Bangladesh organized an awareness program on control of AMP to create awareness among different stakeholders. Functioning of a control system for AMP is a prerequisite for quality assurance safe fishery products
Present status of Fish Hatchery in BangladeshDegonto Islam
In the past decades the rivers of Bangladesh were the mentor natural source of carp seed production. Due to the destruction of natural habitats and also increase demand the natural available of carp seed has largely declined and the aquaculture venture and gradually replaced by the hatchery produced fry since early 80’s when artificial fish breeding technique and low cost hatchery design have been successful adapted in Bangladesh.
This world have numerous kinds and diversity .This kinds and diversity remain in whole world two two third is aquatic ,fresh water and marine water .This kinds and diversites knowledge and their total knowledge file management is very importance for fisheries science.
This freshwater and marine water has a huge number of vertebrate and invertebrate animals and plants. Thair identify and use is vary importance for fisheries and aquaculture .for that their proper file management is play a useful role in fisheries and aquaculture.
If we went to know the total plant and animals this is not possible to proper file management.
Culturable species and there predator knowledge and file management is vary importance for aquaculture .culturable species habitats and their food habit is very importance for successful aquaculture and also importance in breeding season and behavior and high growth rate fish data .There proper management and for fisheries student study documents is very important. So file management is very importance in fisheries science.
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
ANAMOLOUS SECONDARY GROWTH IN DICOT ROOTS.pptxRASHMI M G
Abnormal or anomalous secondary growth in plants. It defines secondary growth as an increase in plant girth due to vascular cambium or cork cambium. Anomalous secondary growth does not follow the normal pattern of a single vascular cambium producing xylem internally and phloem externally.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Toxic effects of heavy metals : Lead and Arsenicsanjana502982
Heavy metals are naturally occuring metallic chemical elements that have relatively high density, and are toxic at even low concentrations. All toxic metals are termed as heavy metals irrespective of their atomic mass and density, eg. arsenic, lead, mercury, cadmium, thallium, chromium, etc.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
1. 1
Index
SL Name of Contents Page
1. Introduction 2
2. Population structure 2
3. Estimation of population structure 3
4. The Gordon-Schaefer model 4
5. Sex ratio 5
6. Age distribution 6
7. Age specific birth and death rates 6
8. Age-structured model 7
9. Age-dependent method 8
10. Length frequency relationship 9
11. Conclusion 10
12. Reference 10
2. 2
Introduction
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 phenotypic traits.
Population structure
The total population or size of a community, defined geographically or administratively, is the number
of persons residing there. The term “population structure usually refers to the patterns in neutral genetic
variation that result from the past or present departure from panmixia of a population. For example,
suppose mean length of fish in standardized samples from a population is used as an index of population
structure; shifts to smaller mean lengths of sampled fish may indicate increasing exploitation. The
effectiveness of length-limit regulations are often evaluated relative to changes in proportional size
distribution
from a random sample of individual fish Indices of structure rely on
estimates of length,
weight,
age.
Maturity status and sex identification allow the calculation of several useful indices. The juvenile-to-
adult ratio can indicate important aspects of the dynamics of a fish population
To obtain an accurate estimate of age structure, biologists must obtain a random sample of a population.
Aging techniques alos for many important sport fish in have been validated and it is important to use the
3. 3
standard techniques. Determining age of fish takes considerably more effort than measuring and
weighing fish but is usually warranted during population assessments.
Figure: Fluctuations of fish populations and the magnifying effects of fishing
The concept of equilibrium in population structure is being viewed more and more as a simplification of
the effect of fishing on exploited populations. It is still difficult to account for rapid changes in species
composition in multispecies fisheries.
Estimation of population structure
Population structure are directly related to the weight, size, number, length, birth, recruitment, biomass
and death of individuals. An organism as a reacting chemical system by asserting that the processes of
anabolism and catabolism control the weight of an organism. Since the biomass of a fish stock is affected
by natural mortality, fishing mortality, recruitment and growth.
A simple yield equation,
S= R+ G-M-F
Where, S = population biomass,
R = recruitment,
G = growth,
4. 4
M = losses due to natural mortality
And F = losses due to fishing mortality.
The Gordon-Schaefer model
Figure: The Gordon-Schaefer model
The Gordon-Schaefer model describe the population growth with the following equation,
dB/dt= {rB(t) (1- B(t)}/K
Where, r is the intrinsic rate of population growth,
B(t) = population biomass in time t
K= the carrying capacity of the environment
Population structure changes (Biomass) through time can be expressed as:
dB/dt= rB[1- B/K] –Y
Where, the catch rate =Y,
B(t) = population biomass in time t
5. 5
K= the carrying capacity of the environment
When the population is at equilibrium, i.e., dB/dt=0, and thus losses by natural and fishing mortalities
are compensated by the population increase due to individual growth and recruitment.
Sex ratio
The proportional distribution of the sexes in a population aggregate, expressed as the number of males
per female. The sex ratio at birth is an important demographic indicator used for determining the sex
composition of a population.
In Monosex tilapia culture there have seen a great change in growth as the male tilapia convert their
reproductive energy to form their body mass and a big difference seen between normal and monosex
male tilapia pond.
Table: Month-wise distribution of male and female sex ration of R. Corsula from rajshahi, Bangladesh
Month Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Gran
d
total
Percent
age of
male
80.2
3
73.3
3
55.8
8
84.9
0
63.1
6
22.5
0
21.3
5
10.1
1
16.5
0
12.0
0
34.8
5
15.4
9
44.50
Percent
age of
female
19.7
7
26.6
7
44.1
2
15.1
0
36.8
4
77.5
0
78.6
5
89.8
9
83.5
0
88.0
0
65.1
5
84.5
1
55.50
Sex-
ration
1:0.
25
1:0.
36
1:0.
79
1:0.
18
1:0.
58
1:3.
44
1:3.
38
1:8.
88
1:5.
06
1:7.
30
1:1.
87
1:5.
45
1:1.1
25
The relative condition factor (kn) was calculated for both sexes individually and combined. The kn values
range from 0.9478 to 1.2709 in male, 0.6188 to 1.2007 female and 0.1061 to 1.2084 in combined sexes.
Monthly and yearly percentage of male and female showed that the females dominated the natural
6. 6
population over the year. Out of 1200 fishes, 534 were male and 666 were females. The total sex ratio
was found to be 1:1.247.
Calculation:
Sex ratio =(Number of Resident Male Live Births/ Number of Resident Female Live Births) x 100.
Age distribution
In population studies, the proportionate numbers of persons in successive age categories in a given
population or the total population in each age group or as the percent of total population in the age
groups. . In other way we can define the age distribution, the composition of a population in terms of
the proportions of individuals of different ages; represented as a bar graph with younger ages at the
bottom and males and females on either side.
Age at maturity can be determined during a population assessment. Selection pressure (e.g., harvest
aimed at larger, older individuals) at the population level could lead to maturity at a younger average
age.
Age specific birth and death rates
AGE-SPECIFIC DEATH RATE is the total number of deaths to residents of a specified age or age group in
a specified geographic area (country, state, county, etc.) divided by the population of the same age or
age group in the same geographic area (for a specified time period, usually a calendar year) and
multiplied by 100,000 natural mortality-at-age does not arise from a fish's age itself but rather from
factors such as predation. As fish get older, the suite of predators shifts both in terms of abundance and
the species involved, and the impact declines with age. One assumption that addresses this is that the
mortality rate decline is fixed over age.
Calculation:
(Total Deaths in Specified Age Group/ Total Population in the Same Specified Age Group) x 1,00,000
in mortality estimation with relation to age relation there are different type of methd,
7. 7
INDIRECT METHODS
Age-independent methods
Age-dependent methods
DIRECT METHODS
Requirements
Catch curves
Tagging
Telemetry
Cohort analysis
The first choice that a researcher needs to make is whether to use a direct or an indirect method to
estimate mortality. Early in the assessment of a population indirect methods are used as they can
provide quick and easy results, especially for inclusion in a model. When indirect methods are used for
input into a model it is prudent to construct multiple models that use as many of the indirect estimates
as possible.
Age-structured model
A Beverton–Holt stock–recruitment relationship was assumed:
R=0.8R0hS/[0.2S0(1−h)+(h−0.2)S]
Where, spawning–stock biomass S and S0 were computed from the weight-at-age and maturity
schedules. A steepness of h = 0.9 was assigned. While steepness is notoriously difficult to estimate, the
value of 0.9 is commonly used.
8. 8
Age-dependent method
Estimation of natural mortality that varies with age using dry weight as a scaling factor. Using particle-
size theory and data from the pelagic ecosystem (including fish larvae, adult fish and chaetognaths) .the
natural mortality for a given weight organism (Mw) is
Mw = 1.92w-0.25
Where w is the dry weight of an organism. To make this estimate of natural mortality age-specific,
weight-at-age data is required. This is normally obtained from a length-weight relationship and length-
at-age data from a von Bertalanffy growth function. Such an approach yields wet weight. One criticism
of this method has been that it was developed for smaller pelagic organisms. However, McGurck (1986)
showed that it accurately predicted natural mortality rates over 16 orders of magnitude.
Chen and Watanabe (1989) recognized that natural mortality in fish populations, like most animal
populations, should have a U-shaped curve when plotted against age (they referred to it as a bathtub
curve).
To model this curve, they used two functions,
1. one describing the falling mortality rate early in life and
2. a second describing the increasing mortality towards the end of life. To scale the values of
mortality by age (M(t)), used the k and t0 parameters of the von Bertalanffy growth function.
Cortes (1999) used this method to estimate the survival of sandbar sharks (Carcharhinus plumbeus) by
age-class. He demonstrated no increasing mortality in older age classes due to senescence. The survival
values that Cortes (1999) estimated using this method were similar to those for the Peterson and
Wroblewski (1984), Hoenig (1983) and Pauly (1980) methods.
9. 9
Unlike the Peterson and Wroblewski (1984) method the Chen and Watanabe (1989) method
onlyrequires von Bertalannfy parameters, but the mathematics are more involved
Length frequency relationship
In this section we discuss a probability model for the length of fish. For a historical review of the model,
(1975). Assume that there are k age classes in a fish population, and that p, is the proportion of the
population of age i. Let the lengths .v of fish of age i be distributed normally with mean n, and variance
o,-2. The probability density function/(.x: 0}of .x for the population can be written as
f( 𝑥: ⦵ = ∑ Pi N(x: ϴi)
𝑘
𝑖=1
Where, ⦵= < 𝜭1, 𝜭2,….𝜭k, P1, P2, ……Pk>.
𝜭i= < µi, бi2 >,
N ( x: 𝜭i) = density function of a normal distribution with mean µi and variance бi 2 ,
10. 10
Pi = proportion of the population of age I,
K= number of age classes in the population which is generally assumed to be known.
The parameter vector 0 is related to some well-known fishery statistics. For example, the catch curve*
can be represented by the plot of logefi. against age i, and the plot of u,- against age i is the growth
curve.
If the variances of the individual normal distributions are small, then the length frequency plot will have
k well-defined modes at / i j , P j , ..., M*- If there are differential growth rates for various year classes,
the modes may not be well defined. To estimate modes from the length frequency data for fast-growing
pike iEsocidae), and he was able to identify five separate age classes. For these data, the average distance
between the mean lengths for successive age classes was 100 mm. Separations this distinct would not
be expected for most smaller or slower-growing fish.
Conclusion
The incorporation of socioeconomic variables with sustainable management including the analysis of
fishing trends introduces complexities that require more and more basic data. If fish are aged correctly,
then estimates of population dynamics will be correct and should lead to wise management and resource
allocation decisions. As the population structure are directly related to the age, length, and growth, it
need to be concerned as a exigent.
Reference
Kevin L. Pope, Steve E. Lochmann, and Michael K. Young, “Methods for Assessing Fish Populations”,
Chapter-11.
11. 11
Fredric M. Serchuk, (March 30, 1978) “POPULATION ESTIMATION”, AN INTRODUCTION TO STOCK
ASSESSMENT TECHNIQUES, Laboratory Reference No. 78-28 National Marine Fisheries Service Northeast
Fisheries Center Woods Hole Laboratory Woods Hole, Massachusetts 02543
Colin A. Simpfendorfera, Ramón Bonfilb and Robert J. Latourc, ” Mortality estimation”, aCenter for Shark
Research, Mote Marine Laboratory 1600 Ken Thompson Parkway Sarasota, Florida, 34236, USA
K. Deva Kumar and S. Marshall Adams, “Estimation of Age Structure of Fish Populations from Length-
Frequency Data”, Environmental Sciences Division Oak Ridge National Laboratory Oak Ridge, Tennessee
G.W. Ssentongo, “POPULATION STRUCTURE AND DYNAMICS STRUCTURE ET DYNAMIQUE DES
POPULATIONS”, chapter-17.
Tito de Morais, L. 2002.” Fish Population Structure and its Relation to Fisheries Yield in Small Reservoirs
in Côte d’Ivoire”. In Management and Ecology of Lake and Reservoir Fisheries. Edited by I.G. Cowx.
Blackwell Publishing Ltd. pp. 112–122.
S.M. NURUL AMIN, M.A. RAHMAN, G.C. HALDAR, M.A. MAZID and D. MILTON, (2002), “Population
Dynamics and Stock Assessment of Hilsa Shad, Tenualosa ilisha in Bangladesh”, Bangladesh Fisheries
Research Institute Riverine Station, Chandpur-3602 Bangladesh
D. Pauly, (1984), “Fish Population Dynamics in Tropical Waters: A Manual for Use with Programmable
Calculators”, INTERNATIONAL CENTER FOR LIVING AQUATIC RESOURCES MANAGEMENT MANILA,
PHILIPPINES.