Issues In Sustainable Fisheries Test 2

Population size structure factors to consider

Recruitment, growth, mortality

Recruitment Defintion

To population, fishery an gear

Growth

incremental increase (length or weight) of fish populations over time.

Mortality

Lack of survival from one year to the next

• the opposite of survival

• high survival= low mortality

• low survival = high mortality

Condition Factors Relative Weight

• Weight at length relationship

• standard weight = 100, like % on a test

Relative Abundance

An incomplete picture of population size structure “captured fish”

PSD

Proprtional Size Distribution

What proportion of fish in a population (Stock) are of desirable size (min)

FMZ’s in Ontario

Landscape management

• Exceptions possible based on scientific merit

Minimum Length

• Protects young fish from overexploitation

• Allows for a trophy

Maximum Length

• Protects brood stock

• Can create a trophy catch and release fishery

Slot Limits

Harvestable slot: Protects young and old fish, allows for some harvest

Protected Slot: Protects spawners, allows for take-home trophies - needs small fish harvest to work

Absolute Abundance - Theoretical

A complete picture of population size structure - often an estimated (modelled)

Condition Factors Relative Weight Wr

Weight at length relationship

Largemouth Bass Graph

Length x weight = condition factors

Year 1 - short and skinny

Year 2- big and fat

Stunting

A lot of fish that are very small

• very common in managed fisheries

• growth supression, food niche they can’t get out of (yellow -perch)

Other Stream Features Still Exist Between Beaver Dams: Attenuation

• Riffles (spawning) and lotic Inverts

• runs

• undercut banks

• coarse woody debris

Break up the cycle R-P-R

Runs, pools, riffles

Stochastic Structures

passageways change regularly - dynamic habitat (fluctuations)

Beavers

=Bad in low-gradient stream basins (shallow /low limited elevation change)

=Beneficial in high-gradient stream basins (More changes, less impact)

Round weight at total length

Early growth is called somatic; later it ages more energy into gametes called gonadal

Absolute Abundance

A complete picture of population size structure = often an estimate (confirmed /caught)

Relative Abundance

An incomplete picture of population size structure “captured fish”

(theoretical)

Land based Daily Limit

Permits harvest of numerous small fish, socio - economic factors

Case 31vRehab project assessment for lentic habitat improvement

Removed Sediment to create: island, peninsulas, irregular bottom

Created Marshes Upstream: Sediment traps, easier to clean out, natural channel design (sinuosity)

Littoral zone spiked, productivity spiked

Case 9: Crappie

What happened to fish weight as they grew longer?

In this case the fish grew the same length but had an even lower weight and size than before the regulation.

Case 9: Crappie

What could have caused this to happen?

The use of the regulation on the high density population caused the problem of overpopulation and slower growth = increasing crappie density