Marine Vert.-- ppt 3 (Sampling methods)

Fishery dependent

samples collected from fishery catch

What are some examples of fishery dependent methods?

landing methods and creel surveys

fishery independent

sampling program conducted separately from the fishery

what are some examples of fishery independent methods?

passive & active gear, diver/video surveys, acoustic surveys, mark and recapture

what is a pro of using landing records to record data?

cheap

what are some cons to using landing records to gather data?

limited to economically valuable species, gaps in data during closures, declines in catch due not always reflect declines in population

what are some pros of using creel surveys to gather data?

cheap, built relationship with stakeholders

what are some cons of using creel surveys to gather data?

reliant on non-expert fish IDs, resistance of fishers to talk to scientists

Overall, what are the the pros and cons of fishery dependent work?

pros: cheap

cons: biases and/or non-representative, doesn’t meet model assumption

Overall, what are the the pros and cons of fishery independent work?

pros:unbiased, representative, meets model assumptions

cons: expensive

What do we measure when using fishery independent sampling?

-relative abundance/biomass - catch per unit effort (CPUE)

-absolute abundance/biomass - organisms per unit are/volume

What are some requirements and regulations when measuring CPUE?

-requires knowledge of effort (time. distance, sampling unit)

-best for large animals and/or large areas

-Gear specific — can’t be compared over gear types

-Can not provide estimates of population size

What are some requirements and regulations when measuring absolute abundance/biomass?

-requires knowledge of effective area/volume sampling and the efficiency of the gear

-best for smaller animals in smaller areas over shorter time periods

-may allow comparison across gears

-may allow estimation of population size

what information can CPUE provide?

-relative abundance assuming mo differential sampling biases

-used as measure of changes in or differences in population density if great deal of attention given to standardization

Gear selectivity

bias of sample obtained due to gearg

Gear efficiency

proportion of target organisms in sample area that are counted

What two components does gear efficiency have?

capture efficiency and recovery efficiency

capture efficiency

proportion of individuals within sampling area that are captured by the gear

Recovery efficiency

proportion of individuals captured by the hear that are subsequently recovered from the gear and counted

T/F Capture efficiency is very difficult to measure.

true

Passive gears

not actively moved over some area by humans or machines

active gears

actively moved over some area by humans or machines

what are some examples of passive gears?

gillnets

trammel nets

fyke nets

traps

hook and line

longline

what can passive gear measure?

relative abundance only

what are some examples of active gears?

trawl nets, dredges, seine nets, throw traps, drop samplers

What can active gear measure?

absolute abundance

What are the three types of passive gears?

entanglement, entrapment, and angling

What is a trammel net? What type of passive gear is it?

-two or three layers of netting

-large mesh outer, small mesh inner

-catch large range of sizes

-entanglement

What are gill nets? what type of passive gear are they?

-entanglement

-single layer of nylon monofilament

-very size selective

-most fish “gilled” or caught behind opercula

What are some bias and gear selectivity of trammel nets/gill nets?

-target must be motile

-can be size selective

-visibility of net/behavioral avoidance

-strength of net, breakage

-saturation—if nets fills up, it becomes less effective at high target abundance

What are some examples of entrapment passive gears?

-hoop net, fyke net. weirs

-pots

-fish screws/wheels

How do pots work?

-baited

-rigid traps

-portable

-best for bottom dwelling species

-one or more funnels

-target typically unharmed

How do fish screws and wheels work?