Populations and Production

Question 1

what is a population

Answer 1

group of similar Individuals in given area using the same resources, subject to the same dynamics, and reproductively isolated from other such groups

Recognised as major unit of evolution (Ernst Mayr ; Hedrick )
* Regarded as a gene pool with a continuity throughtime but with changing genotypes

Question 2

four major factors regulating population sizes

Answer 2

birth rate, immigration, death rate, extinction

Question 3

Life tables

Answer 3

Track changes in populations and can be used to assess their stability
* Relies on accurate estimates of Birth and Death rates

Question 4

Ro

Answer 4

he reproductive output per female x female survival to estimate reproductive rate per year class

Ro > 1 growth
Ro < 1 declines

Question 5

3 main Migration (immi- emigration) ways

Answer 5

Recruitment, or the addition of individuals through reproductions and growth where young can join the adult population (recruit to fishable stock; stock = population

• Colonization, adding individuals by movement from different habitats (e.g., nursery to adult habitat)

Migration not associated with recruitment or colonization but just the transfer of individuals from one population to another

Question 6

impacts of connected fish populations

Answer 6

Connected populations exchange genetic material leading to increased Standing Genetic Variation

Overconnected populations can lead to outbreeding depression, where dominant type maladapted to environment
(one population getting influx of migrants into pool can lead to outbreeding depression; with more inputs from other populations, the standard genetic variation is flooded from other populations. leads to population that’s sustainable but not ideal genetically to its area since there’s new genetic material tha’ts maybe not ideal for the environment. causes population to be from stable to be sink/maladaptive)

Question 7

Abundance recruitment relationships

Answer 7

abundance of fish does not mean linear relationship for stock/recruitment

*Beverton-Holt predicts recruitment slows with increasing abundance, linked to population carrying capacity
* Ricker models predict compensatory factors at high abundance further reducing recruitment (e.g., cannibalism, diseases)
* More complicated models show depensation effects with low abundances also causing low recruitment (e.g., finding mates inbreeding)

Question 8

Age-class/ size cohort

Answer 8

a group of similarly aged or sized individuals experiencing similar life history stages
* Clearly not all age-classes contribute the similarly to population size or growth
* High abundance in a single age-class, or just a few age-classes, does not translate to a healthy population*

Question 9

Population size structure

Answer 9

Knowing the size/age structure gives information on which size class(es) support the population at any given time
* From this tailored management strategies can be devised to to maintain population stability and sustainability
* Can also be useful to monitor the health of a population over time

ie ie if we know size class 3 is most important, you wouldn’t focus on protecting size class 4-5 but size classes 1-3 ie don’t allow fishing for those sizes etc

Question 10

what can happen in large size structured populations with many overlapping generations

Answer 10

some larger year classes can come to dominate others.
Can cause high intraspecific competition and interactions (including cannibalism) based on size

Question 11

ontogenetic niche shifts

Answer 11

in response to year classes dominating others, where different parts of the population specialises on different diets or habitat use

ie large mouth bass

Question 12

Niche

Answer 12

Species niche is its ecological role in its environment

• Collect parameters outlining biotic and abiotic environment in both regions and make inferences as to what species tolerances are

Question 13

Realized niche

Answer 13

Species realized niche defined as it actual mapped distribution outlining where species does and doesn’t occur

Can do it with biotic factors too
* Big part of how we understand the food-webs in most ecosystems and clarify the inter- relationships among species

Question 14

Potential/theoretical niche

Answer 14

Potential niche is where the species might be found based on our understanding of its ecological tolerances, but where it currently isn’t
can be because;
-Species hasn’t dispersed there yet
- Regimes in those areas not stable enough for colonists
- Species previously there but wiped out

Theoretical niche can be modeled using current understanding of niche parameters for species

Question 15

Mortality (death) rates

Answer 15

Most (but not all) fishes exhibit a type III survivorship (very few organisms survive their younger years)
* Mostly r-selected with many eggs and larvae produced with exponential losses through time that stabilize with increasing individual size and age

fish eggs are a big food item for many species
As individuals get bigger, faster, better hunters and reach critical size thresholds (feeding stages, etc,..), natural mortality decreases
One of the largest factors regulating many fish populations is cannibalism

Question 16

Cannibalisms

Answer 16

among top reason compensatory mechanisms introduced in stock-recruitment relationships
* Happens in many fishes not just piscivores,
* In oligotrophic lakes with only few species, cannibalistic ecotypes evolves that both regulate the species, and produces additional ecological niche

Question 17

Mortality rates

Answer 17

The number of individuals that die within a specified period (e.g. % of population ! year-1)
* Influenced by both density-dependent and Independent factors

Question 18

Mortality decomposed

Answer 18

Natural Mortality is due to predation, starvation, disease, accidents or other natural or even human induced causes
Harvest Mortality refers to human takes, by fishing (commercial – recreational etc,..)
Total Mortality = Natural + Harvest
(Z=F+M)

Question 19

Slow growing vs fast growing and natural mortality

Answer 19

Natural mortality linked to growth rates and longevity * Slow-growing, long-lived species typically lower natural
mortality (e.g., Walleye)
* Fast-growing, short-lived species typically have higher natural mortality (e.g., White/Black crappie)

Question 20

Natural mortality (and growth)& growing season link

Answer 20

fish of same size is much older in north because growing season is shortwr north so it takes longer to reach a certain size. more stable in north so mortality rate is typically less

Question 21

Harvestable surplus

Answer 21

Proportion of individuals that can be removed without negative impact on population

fishery uses harvestable surplus and introduces compensatory, not additive, mortality
70 % mortality year-1
* Compensatory mortality means that as 1 type of mortality increases, the other decreases, so, total mortality remains the same

Question 22

Production and yield

Answer 22

Biomass accumulated by a population over time

Surplus Production= the portion of production removable by natural or harvest mortality without affecting future population production

Harvestable surplus =portion of individuals that can be removed without negative impacts on population

Question 23

Yield

Answer 23

proportion of population/biomass actually taken by humans which can Sometimes can be big, sometimes can be small

Question 24

Maximum sustainable yield

Answer 24

Management philosophy aiming to maximise yields irrespective of individual size
(inflection point on S-curve)

expected growth curve; growth rate is slow at start but as time goes on , more fishies are born, then will start to decrease because too many individuals (density dependant), the ideal is max rate at which population is growing, it’s the steepest part of curve.

Question 25

Optimum sustainable yield

Answer 25

• Management philosophy considers ecological and socio-economic factors in setting more realistic target yields
• Most often targets set closer to K to maintain key population abundance (buffer)

Question 26

population & production summary

Answer 26

• Population sizes change based on birth deaths and migration rates
• Being able to predict population size changes is a large part of what fisheries science tries to do
• Most fishers are interested in doing this to predict the size of populations in the future to predict future catches but also to maintain species sustainably
• mechanisms of what regulates populations sizes need to be understood in efforts to ensure population stability over time