Post on 08-Apr-2018
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
1/20
FFB-311Population
Dynamics&
Stock Management
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
2/20
Carrying Capacity
Migration
(emigration / immigration)
Density Dependent
Mortality
Density DependentNatility
Density Dependent
Population Growth
Ecological Conditions
Density Independent
Exploitation
Density Independent
Sustainability of Stock
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
3/20
The Komering River in Indonesia now dries up almostcompletely in the dry season due to irrigation works
upstream
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
4/20
Barrier traps such as corong flume traps and tuguk suspendedtrawls in Indonesia are expensive to construct, but highly effective
at catching migrating fish
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
5/20
In Bangladesh, dry season floodplain water-bodies may even be pumped dry to extract the
last remaining fish
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
6/20
Even small floodplain water-bodies may enable manybrood fish to survive the dry season, if protected as
reserves (River Ganges, India)
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
7/20
Fish StockFish stocks are subpopulations of a particular species of
fish, for which intrinsic parameters (growth, recruitment,mortality and fishing mortality) are the only significant factors
in determining population dynamics, while extrinsic factors
(immigration and emigration) are considered to be
insignificant.
The currently accepted definition of a stock in fisheries
science, is A stock describes characteristics of semi-
discrete groups of fish with some definable attributes
which are of interest to fishery managers (Begg et
al.,1999).
In fisheries management, stock refers to a harvested or
managed unit of a fish.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
8/20
Concept of Stock In general, stock is the genetically differentiated and
geographically isolated populations of a species. In fishes, there is a tendency to form a structured series
of discrete populations which have a degree ofreproductive isolation from each other in space, in time,or in both.
This isolation resulted into the genetic differences,morphological variations and variable exposure todifferent chemical regimes and parasitic species amongthe sub-populations.
Sub-populations also respond to fishing in such a waythat fishing on one population appears to have no effecton the population dynamics of a neighbouringpopulation.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
9/20
Stocks are not always composed of a single
species. Stocks can be composed of multiple
species due to their being harvested together. An example of a multispecies stock is river
herring. Alewives and blueback herring are
labeled as river herring for management
purposes due to their similar physicalappearances and being harvested together.
Individuals within a stock are subdivided into
cohorts. A cohort is a group of fish born inthe same year within a population or stock.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
10/20
A stock can be both transboundary and straddling stock
Straddling stock stocks of fish which migrate between, or
occur in both, the economic exclusion zone (EEZ) of one or
more states and the high seas"
Transboundary stock range in the EEZs of at least two
countries.
Straddling stock include highly migratory fish stock.
Straddling stocks are usually pelagic, rather than demersal
because demersal species move less than pelagic species,
since they tend to relate to bottom topography.
Pelagic species are more mobile as their movementsinfluenced by ocean temperatures and the availability of
zooplankton as food.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
11/20
Example of straddling pelagic fish are
capelin, pollock, herring, whiting, mackereland redfish etc.
There are, however, a few demersal
species that are straddling, such as the
Greenland halibut migrates in
feeding/spawning migrations to Greenlandin the west and to the Faeroes in the east.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
12/20
What is Population Dynamics(subject of moving bodies)?
The size of population at any given time may be taken to be a convenient endindex of many forces that act upon the population.
Ultimate size of the population is determined by the forces acting on growth of thepopulation which is influenced by natality, mortalityand dispersion.
Natality has the +ve influence on population growth and mortality has veinfluence where as dispersion may be positive or negative depending uponwhether it is one of emigration or immigration. All these forces are controlledby various ecological forces which are density dependent and independentfactors.
Independent factors given are optimum ecological condition of a population by theintervention of human beings, and grows its maximum size in right proportion withthe carrying capacity of its ecosystem but exploited population never attain this levelas the actual size being the function of intensity of exploitation.
The dynamics could be allowed if the short term benefits are worth for more than thelong term benefits normally fails to receive support from conservatives and
ecologist.It is always good if the reflection are made for optimizing yield so as the sustain the
benefits for long time.
Dynamics of fish population seek to provide the basis frame work for scientificadvised in respect of optimization which is the central time of the fisheries resourcesmanagement.
F P t t t t
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
13/20
F s Popu at on tructure tsUnitsPopulation (Collection of units, which is having some common
characteristics): A fish population can be defined as aggregates ofindividuals of the same species comprising possibly in a number ofschools inhabiting in a well defined geographical area and cutoff fromanother discrete population of the same species through a discontinuitybetween their distributional ranges.
Unit Stock: A population can be considered as a unit stock if its membersexhibit sufficiently uniform characterstics in respect of the growth,spawning, natural mortality, responses of fishing, morphometric and
meristic characters and serological properties etc.Multiple Stock: In a multiple stock population signifies differences of their
in the characters. However, these multiple stock may tend toamalgamate (unite) into a unit stock through gene flow unless theconstituents stock separate junction spatially at time of spawning.
Exception:For the purpose of fishing yield models males and females of a
population are sometimes treated as separate units if they differ fromeach other in characters such as growth mortality etc.
Population of different species co-existing in a particular area andexhibiting similar characters is some times treated as a single stock (unitstock) for modeling purposes.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
14/20
Loss of Fisheries:Due to irrational exploitation of FisheryResources
1- North sea or Norwegian Herring (Clupea harengus) : Stocks was
fluctuated with a regular periodicity since the 19th century (1950) due
over exploitation.2-Hakkaido Herring (Clupea pallasi): Peak catch in1897; it subsequently
declined and disappeared in 1960.
3- Japanese Sardine (Sardinops melanosticta): Peak catch 2 million
tones in 1936 and catch was not recovered upto ofter 30 years and it
replaced by Anchovies during 1970s.
4-Californian Sardine: Fishery flourished between 1920-1951; peak catch
in 1936 and remained high until 1947 and after the year 1949-50, it
failed completely and fishery becomes extinct.
In the Country: In our Indian water the spotted sear fish(Scomberomorus guttatus), which supported commercial fishery in
Palk Bay for over three decades and it collapsed in the early 60s dueto un-control fishery .
In the case of prawn fishery: Although absolute catch is not declinedsignificantly but exact signs of stock depletion are apparent from the
general declining trend in CPUE and the decreasing size of the
prawns in catch.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
15/20
HISTORY:
The first principle of population dynamics is
widely regarded as the exponential law ofMalthus as modelled by the Malthusian growth
model.
A more general model formulation was
proposed by F.J. Richards in 1959, by which the
models of Gompertz, Verhulst and also Ludwig
von Bertalanffy are covered as special cases ofthe general formulation.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
16/20
A fishery is an area with an associated fish or aquaticpopulation which is harvested for its commercial or
recreational value.
Population dynamics describes the ways in which a givenpopulation grows and shrinks over time, as controlled bybirth, death, and emigration or immigration.
It is the basis for understanding changing fishery patternsand issues such as habitat destruction, predation andoptimal harvesting rates.
The population dynamics of fisheries is used by fisheriesscientists to determine sustainable yields.
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
17/20
The basic accounting relation for
population dynamics is the BIDE
model:
N1 = N0 + B D + I E
where N1 is the number of individuals at time 1,
N0 is the number of individuals at time 0, B is
the number of individuals born, D the number
that died, I the number that immigrated, and Ethe number that emigrated between time 0 and
time 1. While immigration and emigration can be
present in wild fisheries, they are usually not
measured.
http://en.wikipedia.org/wiki/Matrix_population_modelshttp://en.wikipedia.org/wiki/Wild_fisheries_of_the_worldhttp://en.wikipedia.org/wiki/Wild_fisheries_of_the_worldhttp://en.wikipedia.org/wiki/Matrix_population_models8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
18/20
A fishery population is affected by three dynamic ratefunctions:
Birth rate orrecruitment: Recruitment means numberof new youmg fish that enters in a population in a given
year.
Growth rate: This measures the growth of individuals insize and length. This is important in fisheries where the
population is often measured in terms of biomass.
Mortality: This includes harvest mortality and naturalmortality. Natural mortality includes non-human
predation, disease and old age
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
19/20
Terms associated with Population Dynamics
Virtual population analysis:
Virtual population analysis (VPA) is a modelling
technique commonly used in fisheries science for
reconstructing historical fish numbers using information
on death of individuals each year. This death is usually
partitioned into catch by fisheries and natural mortality.
Minimum viable population:
MVP is the smallest possible size at which a biologicalpopulation can exist without facing extinction from naturaldisasters or demographic, environmental, or genetic
stochasticity
8/7/2019 FFB-311-L1&2-(Introd)POPULATION DYNAMICS
20/20
Maximum sustainable yield:In population ecology and economics, the maximum
sustainable yield or MSY is, theoretically, the largest catchthat can be taken from a fishery stock over an indefinite
period.
Meta-population: A metapopulation is a group of spatiallyseparated populations of the same species which interact
at some level. The term was coined by Richard Levins in
1969.
A metapopulation generally consists of several distinctpopulations together with areas of suitable habitat which
are currently unoccupied.