Visual Sampling of FishesVisual Sampling of Fishes

•Introduction to SamplingIntroduction to Sampling•Visual Sampling MethodsVisual Sampling Methods•Evaluation of EffectivenessEvaluation of Effectiveness

GOAL: Describe Complex Biological Communities

PROBLEM: Complete census is impossible!!

APPROACH: ‘sub-sample’ several units

Progressive levels of sampling effort.

Quantitative - estimates species present and densities

Semi-quantitative - estimates speciespresent and relative abundance

Qualitative - estimates species present,no abundance information

Time (= cost) increases with each level

Random vs Fixed Stations

Random sampling: addresses some parametric test assumptions

Fixed-station sampling: greater power when funding limited

Spatial and Temporal ConsiderationsMany projects sample at established:

time of day, lunar cycle, tidal cycle...

Sampling day and night, or among seasons

Distributional studies sample randomly through space

1. Qualitative DescriptionPresence/absence only – no abundance estimates

Example: Timed Swim

• establish specified time• haphazard swim• record species observed

REA Fish Survey

•Depth/habitat distributions• Island checklist of species•New records, range extensions

Species-site ChecklistSpecies-site Checklist

2. Semi-Quantitative Description

Rapid Visual Transect (RVT)

Relative abundances estimated

Species-time relationships

Commoner species sighted before rarer species

Rapid Visual Transect

1. Establish time survey duration (e.g., 0.5 hrs, 1.0 hrs, etc.).

2. Divide survey period into sub-intervals (e.g., 5 or 10 mins).

3. Surveyor swims freely within sampling habitat.

4. Each species is recorded once

5. In the time interval first seen.

6. Species assigned scores based on time seen:

Time Interval Score00:00-04:59 1 505:00-09:59 2 410:00-14:59 3 315:00-19:59 4 220:00-24:59 5 1

7. Scores from multiple surveys are averaged.

8. Rank mean scores

(higher score = common; lower score = rare).

3. Quantitative Description

1. Densities are estimated

2. Sampler records:

a. species observed

b. number of individuals of each speciesc. size/position of each individual (optional)

Quantitative Descriptions

Methods taught at QUEST:

Strip Transect (SST)Stationary Point Count (Circular Plot - CPLOT)

Strip Transect (SST)Deploy transect line

Record species and number (and size) in assigned segment

In QUEST: four 25 m transects (paired) sampled per team

25 m

2 m2 m25 m

4 m

50 m transect line

4 m

Transect 125 m

Transect 125 m

Transect 225 m

Transect 225 m

Diver 1Diver 1

Diver 2Diver 2

• Fish identified to “species” & counted• Swim-out: record fish >20 cm in 4m wide swath• Swim-back: record fish <20 cm in 2m wide swath

• Fish identified to “species” & counted• Swim-out: record fish >20 cm in 4m wide swath• Swim-back: record fish <20 cm in 2m wide swath

2m2m

Fish Belt-Transect - NOAA Program MethodFish Belt-Transect - NOAA Program Method

HI-RAMP HI 05-05 Site _____ Date / /05 Time ___-___ REA Area (m2):_____ Temp __°F

Obsrvr: ___ Sta #: ___ A B C GPS: ________N,________W Depth (ft): __ Partner(s): ___,___

Butterflyfishes Parrotfishes Wrasses

C. aurig Ca. carol A. cuv

C. lunulat Ch. pers B. bilun

C. mili Ch. sord C. flavo

C. multi S. dubi C. ven

C. ornate S. psitt G. vari

C. quadri S. rubro H. ornat

C. trifas Juvs L. phth

F. flav Soldier/squirrelfishes M. geof

M. amae O. bimac

M. bern O. unifas

Damselfishes M. kunt P. evan

A. abdom N. samm P. octo

C. hanui S. xanth P. tetra

C. oval S. balt

C. vand Surgeonfishes T.dup

C. verat A. leuco

C. agilis A. nigrofus Others

P. john A. nigroris A. macu

S. fasc A. olivac A. furca

A. trio A. chin

Goatfishes C. strig C. jac

M. flavo N. litur C. pott

M. van N. uni C. vitt

P. multi Z. flav Ci. vand

P. pleuro Z. velif D. barbi

P. porp L. kasmira

Triggerfishes K. cin

Hawkfishes M. niger K. spp.

C. fasc M. vidua O. punct

C. pinn S. bursa Sebast sp.

P. arc Synodus sp.

P. fors Z. corn

• Common species Common species listed listed

• Enter number andEnter number and size of eachsize of each

• Common species Common species listed listed

• Enter number andEnter number and size of eachsize of each

Popular in Caribbean

Plots usually chosen randomly or haphazardly

In QUEST: Transect line is deployed Team waits for fishes to settle Then proceeds to pre-determined ‘point’

Stationary Point CountCircular Plot – ‘C-PLOT’

Record all fishes within a cylinder set radius height above bottom

(at QUEST r = 5 m, h = 1 m)

Cylinders cannot overlap

Each cylinder treated as a replicate

r

7.5m radius

circle7.5m radius

circle

7.5m radiuscircle

7.5m radiuscircle

Diver 1Diver 1

Diver 2Diver 2

• 4, 15-m diameter “cylinders”, 12-15m deep• 1st , 5 min. – create a list of species observed; NO counts or sizes recorded.• After 5 min. – divers count & size individuals

• 4, 15-m diameter “cylinders”, 12-15m deep• 1st , 5 min. – create a list of species observed; NO counts or sizes recorded.• After 5 min. – divers count & size individuals

30m transect 30m transect

Fish Stationary Point Count (SPC)Fish Stationary Point Count (SPC)

END

Multiple methods are used in some Programs

Evaluation of Visual Surveying

Effectiveness

A. Principal Advantages

1. least disruptive and biased method forsurveying fishes

2. fairly inexpensive

(compared to ???)

B. Principal disadvantage: some species chronically under-estimated:

1. large, mobile species (jacks, sharks).

2. schooling fishes with patchy distributions (small jacks, mullet, some goatfishes).

B. Principal disadvantage: some species chronically under-estimated:

3. cryptic species (cardinalfishes, eels, gobies,

blennies).

B. Principal disadvantage: some species chronically under-estimated:

4. rare fishes

B. Principal disadvantage: some species chronically under-estimated:

2. Swimming speed affects accuracy

a. at fast speeds, uncommon speciesoverlooked.

b. at slow speeds, mobile species overestimated.

c. rare species overlooked at all speeds.

Happy Hunting!