Fisheries Science and management III - Parameters that inform fisheries management

Question 1

How do we assess stock abundance?

Answer 1

Important to detect changes in abundance

• to set total allowable catch and CAY
• to predict changes in abundance from some simple climatic factor, e.g., snapper and water surface temperature
• can estimate absolute abundance or relative abundance

Question 2

How is the data for stock parameters sourced?

Answer 2

• Commercial fishers – catch data – observers and statutory reporting of catches
• Recreational fishers – boat ramp surveys, aerial surveys
• Fisheries managers/scientists do stock assessments through time – to monitor sustainability of current catches, and make predictions about the status of a stock into the future

Question 3

How is the absolute abundance estimated?

Answer 3

• Mark-recapture methods
• mark up to 20% of the population, release, recapture
• assumptions - closed population
• Hydroacoustic survey technologies (ground truthed with actual catch data)
• Removal methods
• small, closed areas (freshwaters)

Question 4

What is CPUE?

Answer 4

Catch per unit effort

Catch (C) and fishing effort (f)

• CPUE = C/f
• number of rock lobsters per trap per night (pots)
• number of fish per hook per hour (long line)
• weight of fish per hour of trawling
• absolute abundance = q (C/f), where q=“catchability quotient”

Question 5

What are some limitations when assesing stock abundance?

Answer 5

Efficiency of fishing and gear selectivity

• unlikely that the fishing method is 100% efficient
• only some come into contact with the gear
• even fewer will be retained
• likely to select certain sizes more than others
• e.g., in trawling, large fish more likely to be retained than small fish

-> difficult to get accurate picture of populatons

Question 6

How is growth assesed with fish length?

Answer 6

Fish lengt-weight relationships

Question 7

How is growth assesed via cohort analysis?

Answer 7

• each mode denotes a cohort
• fish hatched at the same time

Question 8

Hos is growth from age assessed

Answer 8

Otoliths are crystalline structures composed of calcium carbonate

Clear band deposited in winter where less protein is incorporated in the CaCO3

Question 9

What are three ways to asses growth in fish?

Answer 9

• Fish length
• cohort analysis
• age determination from otoliths (ear bones)

Question 10

What is fecundity?

Answer 10

number of eggs produced/female

Question 11

What are the three most important stock parameters?

Answer 11

• Populatoin growth
• Stock abundance
• Natural mortality

Question 12

What needs to be put into account when MSY (maximum sustainable yield) is set?

Answer 12

natural fluctuaions of the target species due to biology, life history and environmental changes