Comparison of three methods for estimating species and si eComparison of three methods for estimating species and size iti f kfi h i ti f t l blcomposition of rockfishes in acoustic surveys of untrawlable areas
M difi dRemote Operated Vehicle (ROV)
C. Rooper1, M. Martin1, J. Butler2, D. Jones1, T. Weber3, C. Wilson1, A. De Robertis1, M. Wilkins1,
Modified Bottom Trawl
Remote Operated Vehicle (ROV)
C. Wilson , A. De Robertis , M. Wilkins ,& M. Zimmermann11RACE Division, Alaska Fisheries Science Center, NMFS - Seattle, WA2FRD, Southwest Fisheries Science Center, NMFS – La Jolla CA3C t f C t l d O M i U i N H hi D h NH
Stereo Drop Camera (SDC)3Center for Coastal and Ocean Mapping, Univ New Hampshire – Durham NH
V Species CompositionI Background and Need Species composition by height off seafloorV. Species CompositionThe number of rockfish species observed by each method were
ROV = 10l 9
I. Background and NeedRockfish constitute an important component of both marine ecosystems and commercial fisheries in Alaska. The biomass of some species including northern rockfish (Sebastes polyspinis) and 90%
100%Walleye pollock
Unidentified rockfish
redstripe
Bottom Trawl = 9SDC = 7
Th t f fi h t id tifi d t i b h th d
in Alaska. The biomass of some species including northern rockfish (Sebastes polyspinis) and dusky rockfish (S. variabilis) is difficult to assess using bottom trawl surveys due to their propensity to aggregate in rocky high-relief (untrawlable) areas. They are also difficult to assess acoustically due to their near-bottom distribution. Thus, new methods to estimate the biomass of 70%
80%prowfish
other rockfish
The percentage of fish not identified to species by each method wereROV = 2.67%Bottom Trawl = 0.00%SDC 16 76%
y ,these rockfishes are needed.
II Overall Project Goals60%
northern rockfish
lingcod
unidentified juvenile rockfish
SDC = 16.76%
The three methods agreed that fish observed in the water column were typically dusky rockfish, northernrockfish and at location adult Pacific ocean perch
II. Overall Project Goals1) Improve rockfish distribution and abundance estimates in untrawlable areas using quantitative
echo sounder data collected at different acoustic frequencies2) Characterize rockfish school morphology to improve classification of acoustic data by species
40%
50%juvenile POP
harlequin rockfish
rockfish, and at location adult Pacific ocean perch
Fishes observed in highest abundance near the seafloor were harlequin rockfish, juvenile Pacific ocean perch,redstripe rockfish and lingcod
2) Characterize rockfish school morphology to improve classification of acoustic data by species using a newly developed fisheries multibeam sonar (Simrad ME70)
3) Develop methods to determine species and size composition of rockfishes in untrawlable areas4) Compare rockfish species distribution and abundance between trawlable and untrawlable areas
20%
30%greenling
dusky rockfish
cod
redstripe rockfish and lingcod
All rockfish species were observed in untrawlable habitats, but only Pacific ocean perch, dusky rockfish and northern rockfish were also observed in trawlable habitats
4) Compare rockfish species distribution and abundance between trawlable and untrawlable areas
III. Poster Objectives0%
10%adult POP
northern rockfish were also observed in trawlable habitats
Differences in species composition among the methods was mostly the result of deployments in different habitatsand locations
Compare the ability of a remotely operated vehicle (ROV), a modified bottom trawl, and a stereo drop camera system (SDC) to address objective #3 above. These groundtruthing methods were compared in terms of:1) h i bili di i i kfi h i i i
Stereo camera (<
0.5 m)
Stereo camera (<
1.0 m)
Stereo camera (<
1.5 m)
Stereo camera (<
2.0 m)
Bottom Trawl (0 - 7
m)
ROV (on seafloor)
ROV (< 2.0 m)
ROV (> 2.0 m)
VI. Size Composition
and locations1) their ability to discriminate rockfish species composition, 2) their ability to estimate the size of rockfish targets, 3) the time necessary to collect and process the samples, and 4) t ti l bi i th i d i iti d t
pSample sizes for length measurement varied among the three methods with the highest percentage of observed fish measured with the SDC
4) potential biases in the size and species composition data
0.50
0.60Harlequin Rockfish
ROV
Trawl
Percentage measuredSpecies ROV Bottom trawl SDCDusky rockfish 3.2% 9.3% 28.2%Harlequin rockfish 7.1% 17.8% 46.7%Pacific ocean perch 8 0% 100 0% 19 7%
Length frequency distributions were similar among the ROV, bottom trawl and SDC
There were significant differences in mean length among species between the bottom trawl and video methods for species except dusky rockfish
IV. MethodsWe conducted an experimental acoustic survey for rockfishes in the “Snakehead” area of the Gulf of Alaska
0.30
0.40
Prop
orti
on p
er le
ngth
bin
Stereo cameraPacific ocean perch 8.0% 100.0% 19.7%Northern rockfish 25.0% 39.8% 17.6%
-Mean forklengths from the ROV and SDC were smaller than the bottom trawl for harlequin rockfish, juvenile POP and northern rockfish-Mean forklengths were not significantly different between the ROV and SDC
rockfishes in the Snakehead area of the Gulf of Alaska aboard the NOAA research vessel Oscar Dyson and the Commercial fishing vessel Epic Explorer. Acoustic data were collected with a multibeam sonar and scientific 0 00
0.10
0.20
P
45
50
were collected with a multibeam sonar and scientificechosounder at multiple frequencies along 14 parallel transects (1.2 nmi spacing). Smaller scale acoustic surveys were also conducted at locations where fish sign was 0.50
0.60Dusky Rockfish
0.60
0.70Northern rockfish
0.00
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45
Forklength (cm)
0.60
0.70
juvenile POP and other rockfishROV
Trawl
35
40
ROV Bottom trawl Stereo camera
were also conducted at locations where fish sign was observed. The ROV, bottom trawl and SDC were deployed at sites where fish sign was observed to groundtruth acoustic targets 0.30
0.40
rtio
n pe
r len
gth
bin
ROV
Trawl
Stereo camera
0.40
0.50
ion
per l
engt
h bi
n
ROV
Trawl
Stereo camera
0.40
0.50
on p
er le
ngth
bin
Stereo camera
20
25
30
Fork
leng
th (c
m)
groundtruth acoustic targets.
The ROV collected video and still images to identify species, and parallel lasers to determine fish length. The drop camera system used video to identify species and stereo optic methods to determine 0.10
0.20
Prop
o
0.10
0.20
0.30
Prop
orti
0.10
0.20
0.30
Prop
orti
o
10
15
length. The drop camera system used video to identify species and stereo optic methods to determine fish size. All fish captured in the trawl were identified to species and a subsample measured to fork or total length.
0.00
30-35 35-40 40-45 45-50 50-55 55-60 60-65
Forklength (cm)
0.00
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
Forklength (cm)
0.00
5-10 10-15 15-20 20-25
Forklength (cm)0
5
dusky rockfish harlequin rockfish juvenile POP northern rockfish
VII. Spatial Distribution Dusky and northern rockfishes occurred in the t l h ll b tt d th ( 140 )
Harlequin and juvenile rockfishes occ rred in shallo ntra lable areas
Acoustic backscatter attributed to rockfishes The multibeam data indicated untrawlable areas
Acoustic transect lines and groundtruth deployments
water column over shallow bottom depths (<140 m) occurred in shallow, untrawlable areas was observed throughout the study area(green, yellow, red) and trawlable regions (blue)
Scintillation index
Adult POP occurred off the shelf break in deeper water (>140 m)
Scintillation index5 km
ROV (5 deployments)
Bottom trawl (6 deployments)
SDC (9 deployments)
VIII. Data Collection and Processing• The bottom trawl and SDC required ~ 1 hour per deployment, the ROV ~ 3.5 hours
IX. Conclusions• The ability to discriminate rockfish species decreased from bottom trawl to ROV to SDC
X. Continuing Research• Determine how close to the seafloor fish targets can be resolved from the bottom
h i ti d t• Roughly 4 - 8 hours were needed to completely process each hour of video collected • SDC = Two hours to count fish and do habitat classification on each deployment
= Two hours to measure up to 200 fish per deployment
• All three methods identified similar size distributions of fish• the bottom trawl did not appear to sample the smallest fish• the percentage of potentially measureable fish for the ROV was less than the other methods
echo in acoustic data• Need to apply species and size composition to calculate biomass of rockfish• Collect in-situ target strength using drop TS sytem (March)p p p y
• ROV = Three to eight hours to do habitat classification, count fish, and measure fishper deployment (1.5 hours of video collected)
B tt t l d t il d t h i d < 3 h f i t
p g p y• Video based methods can provide depth distribution relative to the seafloor• Fish behavior and fish-habitat associations can be resolved from the video methods
Th lt h th t l ti f th i t th d f dt thi d d th
• Complete bottom typing analysis• Complete analysis of school size structure and characteristics
XI Acknowledgements Th d f d d b h Al k Fi h i S i C d N h P ifi R h B d ( j #810) Th k D C h
• Bottom trawl data were easily processed, catch required < 3 hours of processing per tow • The results show that selection of the appropriate method for groundtruthing depends on the specific objectives, habitat types and species complexes that will be examined
XI. Acknowledgements The study was funded by the Alaska Fisheries Science Center and North Pacific Research Board (project #810). Thanks to D. Carney, the crew of the F/V Epic Explorer and NOAA research vessel Oscar Dyson for their assistance in completing this research, and D. Murfin, S. Mau and K. Steirhoff of the SWFSC.
The views expressed or implied here are those of the authors and do not necessarily reflect the policies of the National Marine Fisheries Service, NOAA, Department of Commerce.Contact info: [email protected] or (206) 526-4689
