Improving empirical ground truthingfor interpreting plankton echoes

Transcription

1 Improving empirical ground truthingfor interpreting plankton echoes M. Iglesias, J. Miquel & A. Castellón Instituto Español de Oceanografía.-Centro Oceanográfico de Baleares Instituto de Ciencias del Mar, CSIC. IDEADOS PROJECT Final Meeting Palma de Mallorca, Spain November

2 The IDEADOS project has applied a multidisciplinary approach on the dynamics of deep water exploited ecosystems in the Balearic Islands. For that reason, this project has expanded the study to the pelagic domain, on which deep ecosystems of the Balearic Islands seem to depend, implementing acoustic technology. Here we present two softwares, developed during this project, that improves 1)the accuracy of the acoustic samplers(e.g. pelagic trawl) and 2)the post-process of the acoustic data. 2

3 Fisheries acoustics Fisheries acoustics focus principally in postlarval teleost fish(i. e. sardine, anchovy, etc). Continental shelf( m depth). During the day, when pelagic species form schools. Echosounder detect echotraces(i.e. schools) Schools are identified by means of a pelagic trawl. Anetsonderisusedtodetermine the geometry ofthegear. 3

4 12 khz Multifrequencies 70 khz 18 khz ME khz 200 khz 38 khz The use of several frequencies, together with the correct location of the transducers (coincident beams), permits the processing of acoustic data and to develop algorithms to obtain masks or virtual echograms to identify species. 4

5 The application of acoustic techniques to biological oceanography involves three primary tasks: 1. Collection and standardization of the acoustic measurements (obtaining an accurate measurement of acoustic backscatter from a volume of water or an individual target) 2. Target identification (knowing what type of target(s) produced the backscatter), and 3. Based on the above knowledge, scaling of the acoustic measurements to abundance or biomass of the target population(s) present in each acoustically-sampled volume. 5

6 Ground truthing echotraces Anchovy schools near de bottom (80 m depth), day time. Plankton layer (40 m depth) Continental shelf. Threshold -70 db. Netsonder. 6

7 Netsonder: Simrad FS20/25 Helps to define the geometry of the gear (pelagic trawl). 7

8 Netsonder: Simrad FS20/25 Helps to define the geometry of the gear (pelagic trawl). Vertical presentation Horizontal presentation 8

9 IDEADOS project: Plankton acoustics The plankton: less important in economic terms, but they are central to ecological research, being at or near the bottom of the food chain. Micronekton: small actively swimming organisms ranging in size between plankton (< 2 cm) and larger nekton (> 10 cm). Micronekton: operationally defined as taxa too agile to be caught with conventional plankton nets and too small to be retained by most large-meshed trawls. Principal groups: fishes (mainly mesopelagic species), crustaceans (euphausiids, pelagic decapods and mysids), and cephalopods (small species and juvenile stages of large oceanic species). 9

10 IDEADOS surveys 2 multidisciplinary surveys: December 2009; July R/V Sarmiento de Gamboa. Silent ship (according to the ICES CRR 2009). Scientific echosounderek60 (Simrad) equipped with 5 frequencies: 18, 38, 70, 120 and 200 khz. Pelagic trawl gear:15m opening. Netsonder: FS20/25 (Simrad); trawl eye (Scanmar). Goal: to identify the pelagic layers: Deep Scattering Layer (DSL) and Benthic Boundary Layer(BBL). 10

11 Echogram: Plankton layers 18 khz 38 khz 70 khz -Deeper waters (1000 m) -Different plankton layers (surface, DSL, BBL). -Layers: m width -Small organisms -Low density. -35 pelagic hauls 11

12 Diversity of life forms considered as micronekton. Vertical distribution, diversity and assemblages of mesopelagic fishes in the western Mediterranean. M.P.Olivar,A.Bernal,B.Molí,M.Peña,R.Balbín,A.Castellón,J.Miquel,E.Massutí.Deep-SeaResearchI62(2012) Influence of external variables in the distribution of the Deep Scattering Layers off Mallorca. M. Peña, M.P. Olivar, R. Balbin, J.L. Lopez-Jurado, M. Iglesias, J.Miquel. Submitted 12

13 Target identification: where do we have to fish? In the denser areas. Two software's have been developed during the IDEADOS project. 1. TKM software permits to see on the EK60 screen the depth of the pelagic trawl. 2. GORI software allows to create a evl data filewiththedepthofthepelagictrawl,that can be imported into the Echoview file. Goal: to improve the accuracy of the ground truthing. 13

14 The EK60 scientific echosounder is able to receive and transmit messages on serial lines or ethernet, all based onthenmea0183code. NMEA 0183 is a combined electrical and data specification for communication between marine electronic devices. Trawl eye (Scanmar) EK60 echosounder 14

15 Trawl eye (Scanmar) is able to send string datagrams (pressure data) to the EK60 echosounder. It is necessary to translate them into ITI string datagrams bymeansofasoftware(tkm). The EK60 receives the datagrams and include them into the raw file. The string is written into the RAW file. Trawl eye (Scanmar) EK60 echosounder15

16 Result:weareabletoobserveontheEK60screenthe track of the pelagic trawl(during the survey). 16

17 Post processing of the acoustic data Acoustic data are stored in raw format and they are processed with the software Echoview(Myriax Ltd). The ITI string doesn't get automatically read by Echoview when youreadarawfile. A software has been developed (Gori) to localize the NMEA sentences in the raw file, obtain the pressure data(=depth), and convert them into an evl file. EVL files are structured text data files. TheevlfilecanbeimportedintotheEchoviewfile(ev)tocreate avirtualline=thehaultrack. That makes possible to work on the echogram and integrate exactly the volume of water fished by the pelagic trawl. 17

18 Example of a raw data file generated by the EK60 echosounder. NMEA sentences define the depth of trawl below surface: $IIDBS (pressure sensor). The software finds the sentence and creates an evl file. 18

19 EVBD evl file (datetimefile) Every line includes date and time records with an associated depth. 19

20 The evl file can be imported into the Echoview file (ev) and create a virtual line = the haul track. Moreover, another virtual line is created todefinetheopeningofthegear(e.g.15m,30m). 20

21 TKM software 21

22 EK60 ECHOSOUNDER GORI software Raw file EVBD Evl file 22

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29 Summary The acoustic monitoring, along with the use of depth sensors (e.g. trawl eye) used with fishing or plankton nets (e.g. pelagic trawl, MTN, Bongo ), allows better monitoring and determination of the depthsofthecatches,optimizingtheworkofthenetsused. The implementation of the track of the sampler(e.g. pelagic nets) in the Echoview file allows to integrate the water volume fished by the trawl and permits: Calculate the volume of water filtered by the net Compare the sv(mean scattering value) with the density(catches), to see the goodness of the sampler (in process, myctophids and krill). Estimate in situ target strength measurements of mesopelagic fish and krill. Such measurements are few and new results could improve the precision in acoustic estimates of the biomass of these species. 29

30 This technology has yet been successfully applied in other surveys CRAMER project: Looking for hake larvae. Systematic grid, MultiNet Positive stations (1 hake larvae). Adaptive sampling Bongo 60, 90 30

31 This technology has yet been successfully applied in other surveys MEDIAS project: acoustic Mediterranean project: identifying the plankton layer (ecosystem indicator). 31