ASSESSMENT OF SMALL PELAGIC FISH BY ACOUSTIC METHODS IN SOUTH WESTERN ADRIATIC SEA Leonori Iole, Azzali Massimo and De Felice Andrea Abstract An echosurvey was performed in the summer season 2005 covering the north-western part of GSA 18 (from Vieste to Brindisi) according to FAO division of the Mediterranean Sea. Acoustic data on small pelagic fish were logged by an EK500 scientific echosounder working at three frequencies: 38, 120 and 200 kHz. Biological information on fish acoustically monitored was derived from net samplings made with a mid-water trawl. In addition temperature, salinity and other environmental parameters were measured by means of CTD samplings made in correspondence of net samplings. Pelagic biomass as a whole and per species (Anchovies and Sardines) estimates are presented; total pelagic biomass spatial distribution is illustrated. Trends for total pelagic biomass and for the biomass of the target species of north-western GSA 18 are discussed; this area was studied since 1987. INTRODUCTION In August 2005 an echosurvey was conducted in the Southern part of the Adriatic Sea by the acoustic team of ISMAR-CNR of Ancona. The covered area was between Vieste and Brindisi, from Italian coast to 200 m bathymetric. The acoustic survey is part of the research project funded by the Italian Ministry of Agriculture and Forestry Policies (MIPAF) for the monitoring of the small pelagic fish in the Italian side of Adriatic Sea (GFCM sub areas 17 and 18). National Research programme: VALUTAZIONE DEGLI STOCK DI ALICI E SARDINE NEI MARI ITALIANI AL FINE DI UNA GESTIONE RAZIONALE DELLA PESCA- U. O. 4 Since 1987, ISMAR-CNR has been conducting echosurveys in the south-western Adriatic Sea (GFCM sub area 18 from Vieste to Brindisi), from Italian coast to the 200 m bathymetric, for the stock assessment of small pelagic fish, in particular anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). The area covered by the surveys was on average 2823 nm2. These surveys were carried out annually, in the warm season, using the same mid-water trawler. An environmental monitoring was performed during surveys. The main results are the temporal changes of the pelagic biomass as a whole and per species and the variability of the spatial distribution (Azzali et al., 2002). MATERIALS AND METHODS Study area The area covered by the historical acoustic surveys in the Southern Adriatic goes from Vieste to Brindisi, from Italian coast to 200 m bathymetry (Azzali, 2000). This area is characterized by a narrow shallow water strip near the coastline except for Manfredonia Gulf and a rapidly increasing depth profile going offshore. Collection of acoustic data was performed along systematic zig-zag acoustic transects (Fig. 1), during the navigation and also during biological samplings. The surveyed area was the same of the previous surveys. Data collection The acoustic data were collected using an EK 500 system (SIMRAD), operating at 38, 120 and 200 kHz simultaneously with hull-mounted split-beam transducers on the R/V G. Dallaporta. The main frequency for the assessment of small pelagic biomass is 38 kHz. The 120 kHz e a 200 kHz frequencies are used for discriminating small pelagic fish with swimbladder from fish without swimbladder, plankton, noise, etc.: moreover, within the species with swimbladder, comparing the frequencies just the sizes between 5 cm and 50 cm are left. Before the cruise, in April 2005, the hydroacoustic system was calibrated following the SIMRAD procedure. In June 2005 an intercalibration between Italian and Croatian acoustic system included the sampling nets was performed. The results were presented to the GFCM in September 2005 (Azzali et al., 2005). The speed of the ship during the survey was between 8 and 10 knots and the integration readings were recorded every 1 nautical mile. The speed and the position of the vessel were obtained by means of GPS. The geographic position of the ship and its routes were displayed during the survey on an electronic chart equipment (Shark 12 NT). The pelagic trawl samplings were collected to determine size and species composition. The net samplings were 4 per day (about a haul every 6 hours). The mid-water sampling trawl, designed by the acoustic team of ISMAR, has been used in historical surveys in the Adriatic since 1982. It has 800 mm nominal mesh size in the front and 18 mm in the codend. The mouth area was about 90 m2 (about 7 m in height and 12 m in width). The spatial position of the net in the water was monitored by the ITI (Simrad’s Integrated Trawl Instrumentation). The receiving sensor was installed on a towed body, properly built by the ISMAR acoustic group. The ITI measures the trawl depth, the vertical opening of the trawl mouth and the temperature at the trawl depth. 2 Environmental measurements included CTD profiles made by SEABIRD 911 PLUS probe. CTD (temperature, salinity) stations were regularly distributed along systematic zig-zag transects. Satellite images concerning surface temperature (since 1982) and a-chlorophyll (since 1998) of the Adriatic Sea were acquired thanks to the collaboration with ISAC-CNR of Bologna; visual census on cetaceans was performed on board during echosurvey cruises and the data integrated with sightings made by selected personnel of Tirrenia company along the routine travels of their ferryboats. Data processing Acoustic data were recorded on Hard Disk and CD using the Simrad BI500 system and Sonar Data EchoView software and printed for each frequency. Data set originated by acoustic survey (acoustic data, catch data, position of the ship) were processed using the Sw Geographical Fishery Resources Data Base System for multifrequency analysis. From 1985 until now the SW GFRDBS originally designed by ISMAR acoustic team (Burczynski et al., 1997), has been implemented, tested and adjusted. This package system processes the acoustic, catch and satellite data in a geographical context, converting Lat&Lon into X&Y coordinates. The Elementary Sampling Distance Unit (ESDU) of the X,Y map is 1 nm. The area of the Southern Adriatic Sea is contained in an electronic window 100x180 ESDU. There are three basic functional modules of GFRDBS: Data Base Module (DBM), Mapping and Presentation Module (MPM), Computing and Processing Module (CPM). The biomass assessment and its spatial distribution was performed using the standard method of echo integration (Simmonds & MacLennan, 2005), implemented by the Split-beam and Multifrequency technology. RESULTS Echosurvey in GSA 18 The area covered by acoustic survey was GSA 18 (from Vieste to Brindisi). The echosurvey began on the 6th of August at 22:34 in front of Vieste and ended on the 12th of August at 00:43 in the same point of the start. The acoustically sampled nautical miles were 639 in an area of about 3500 nm2. Sampling was made along predetermined transects; due to bad weather 3 conditions the echosurvey was interrupted on the 7th of August at 19:18 (the ship entered Barletta harbour where it remained two days). The coverage coefficient was 18.1%, very higher respect to the requested minimum of 5% for an affordable estimate. 10 net samplings on small pelagic fish with a non-selective mid-water pelagic trawl were carried out; also 10 CTD samplings to determine temperature, salinity, turbidity and fluorescence profiles were made. The survey results are reported in Table 1. In the entire area investigated (3531 nm2) the average density of the whole pelagic biomass was estimated in 12.1 t/nm2. The biomass of anchovies is around 68.3% of the total biomass (av. density 8.2 t/nm2, biomass 29072 t). The biomass of sardines was 15.7% of the total biomass (average density 1.9 t/nm2, biomass 6683 t). Sprats were 0.1% of the total biomass (average density 0.1 t/nm2, biomass 43 t). The other pelagic species (OPS) formed 15.9% of the total biomass (average density 1.9 t/nm2, biomass 6768 t). The error in the biomass estimation was 18.25% (2.8 t/nm2). The acoustic sampling intensity was very good (CV = 10.8 >> 6). The distribution pattern of the total pelagic biomass is shown in Figure 2. The high density areas (av. density 36.5 t/nm2) represent 10.2% of the area covered and contain 30.9% of the total biomass. The medium density areas (av. density 14.6 t/nm2) represent 45.6% of the area investigated and contain 55.3% of the total pelagic biomass. Finally the low density areas (av. density 3.8 t/nm2) represent 44.2% of the area investigated and contain only 13.8% of the total biomass. In Table 2 are reported the results of the biological samplings. The average length of the small pelagic fish was 8.3 cm (S.D. = 3.47; Individuals number = 3783). In the bathymetric range 60 200 m the catches are more abundant. The mean length of the anchovy samples was 7.23 cm (S.D. = 2.26, Table 2) and the mean length of sardine samples was 12.4 cm (S.D. = 2.22, Table 2). In Figure 3 size distributions of anchovies and sardines derived from all the hauls together are reported. The trends of total pelagic biomass derived from echosurveys in the time interval, 1987-2005 is shown in Figure 4. These trends refer to the south-western part of the Adriatic Sea that corresponds to the Italian portion of coastal area (within 200 m bathymetric) of GSA 18. Total pelagic biomass presents fluctuations that start from a low level then rise to higher values to decline again in recent years. The highest peaks occurred in 1994 and 1996; minimum values of pelagic biomass were registered in 1988, 1993 and 2005. In recent years the biomass is decreasing below the mean as was observed in the first years of the studied period; unfortunately in these two periods there was discontinuity in yearly sampling due to financial problems and consequently the trend is flatter. 4 Mean total pelagic biomass density from 1987 to 2005 in the Southern Adriatic was estimated to be 48.45 t/nm2. Anchovy, as can be seen in the graphic (Fig. 5), became the most important species in late 90’s exceeding sardine. Recently there has been a decline also for this species that presents levels similar to 1993 and 1996. Sardine presents several higher fluctuations in the first years of the studied period until the peak in 1996 (Fig. 6), after which there was a sudden decline with much minor oscillations below the mean value of the entire period. Conclusions The results of the studies of small pelagic populations derived from the historical surveys in the western Adriatic Sea show that these populations are affected by large variability in time and space. This variability is mostly due to environmental factors and this is why an effort is currently in progress to find possible relationships between abundance estimates and oceanographic parameters. In the present period where small pelagic populations show quite low levels of abundance, we suggest not to increase fishing effort on them. References Azzali M., V. Ticina, A. De Felice, I. Leonori, E. Paschini, M. Marini, B. Grbec, O. Vidjak, L. Grubisic, A. Pallaoro, F. Matic, 2005: Inter - ship calibration to compare acoustic estimations of small pelagic fish in the Adriatic Sea. SCSA 2005 proceedings. Azzali M., 2002: Valutazione acustica della biomassa, distribuzione e struttura delle popolazioni pelagiche in Adriatico, in relazione con i dati ambientali ricavati da satellite. MIPAF final report. Azzali M., A. De Felice, G. Cosimi, M. Luna, F. Parmiggiani, 2002: The state of the Adriatic Sea centered on the small pelagic fish populations. P.S.Z.N.: Marine Ecology, 23, Supplement 1 (2002), pp. 78-91. Burczynski, J., M. Azzali, J. Rucabado, 1997: Geographical Fishery Resources Data Base System for management and geographical presentation of Data from Acoustic Surveys and Catches: AdriaBase as a case study. In: T-ECHO AIR1 CT92 0314 - Final report and scientific & technical annexes - Section Specific Software Tools. Simmonds J., MacLennan D., 2005: Fisheries Acoustics; 2nd edition, Eds. Blackwell, 437 pp. Simrad, 1996: EK500 Scientific Echo Sounder – Operator manual. Simrad AS. Norten, Norway. 5 16°00 ' 16°30 ' 17°00 ' 17°30 ' 18°00 ' 42°00 ' 42°00 ' 41°30 ' 41°30 ' 41°00 ' 41°00 ' 40°30 ' 16°30 ' Fig. 1. Transects plan in GSA 18 17°00 ' 17°30 ' 40°30 ' 16° 42° 41° 17° 18° ### #### # ############### ## ###### ###### ##### ## ###### ################### ############################ ##### ##### # # ################################# ######## # # # # # # # # # # # ## # #### ###### ###### ###### ###### ###### ##### #### ###### ###### ###### ###### ###### ###### # ## # #### # #### # ###### ###### ###### ###### ##### ###################################################################### # # # ###### ###### ## ################################################## # ############### ########################## ##### ###### ###### ####### # # # # # ############################################ #### ########### ## # ##### # #### ######################### ################################# # ### # #### # ######### # ######################### #### ############################ ########################## ###### ##### ###### ######### ##### ###### ###### #### #################################################### # # # # # # # # # # # # # # # # #################################################### ############################### # # # # # # # # # # # # # # # # # ######################## ########################################### ## # # # # # # # ## ###### # ################################################## # ############ # # # ###### #################################################################### # ######################################################## ### ###### ###### ## ## ### ## ######## # # # # # # # # # # # # # # # # # # ############################# ################################ #### # ### ## ###### ########################## ## # # # # # # # # # ########################## # # # # # # # # # # # # # # # # # # ########################################################################## ## ### # #### # ####### ### # ###### ###### ###### ###### ###### ###### ###### #### # # # # # # # # # ### ################## ########################################################### ##### # # # # # # # # # # # # # # # # # # # # # # # # # # # ###### # # # # # # # # # # # ###### ###### ###### ###### ###### ###### ###### ###### # #################### ### ############################################################################## ########## # # # # # ##### ###### ###### ###### # #### # #### # ###### ###### ###### ###### ### ############ ##### ###### ###### ###### ###### ###### # #### # ###### ###### ###### # # ########### # # # # # # # # # # # # # # # # # ##### ###### ###### ################# ########################################### # ######### # # # ## ###### ###### # ##### ############################# ###################### ############################## # ####################### ## # ### ###### ###### ######## # # ############# # ############### ### ### ######## ##### ########### # ################## ##### ###### ###### ######################## # # ##### ##### ###### ###### ####################### # #################### # ###### ###### # # ### ###### ################################ ##### ######### # ### ###### ###### # # # # ################################### # # # ################## # ### ################## ################ # ################################# # ### ###### #### ##################### ## ############## # ################################# # ##################### ##################### # ### ## #################################### #################### # # # # ################## ########################################### ## ######################## ## ## ## ############### # # # # # # # # # # # # # # # # # # # ### ###### ###### ###### ###### ###### ################# ##### ###### # ######################################################## # ########### ##### ###### ###### # #### # #### # ###### ####### ############# ##### # #### # #### # ################################## # ##### ###### #################### ####### ################### ##### ###### ###### ######## # # # # # # # # # ######################################### ##### ###### ###### # ############## # # # ##### ###### ###### ############# ############### # # # # # # ### ###### ###### #### ############### ## #### ### ############ ############ ### 40° 19° SA 42° 0-108 108-300 > 300 41° 40° 16° 17° 18° 19° Fig. 2. Map of the spatial distribution of total pelagic biomass in GSA 18 Tab. 1. Acoustic survey results in GSA 18 Av. Length Density Biomass (cm) (t/ nm²) (t) respect to Total Biomass % ANCHOVY 7.2 8.2 29,072 68.3 SARDINE 12.4 1.9 6,683 15.7 SPRAT 10.0 0.1 43 0.1 O.P.S. 9.6 1.9 6,768 15.9 Average Density: 12.1 t/ nm²; Total Biomass: 42565.8 t; Surveyed Area: 3531 nm² Sampled Area: 639 nm² Interpolation Error 2.8 t/ nm² (18.25%); CV: 10.8 Stratum Density (t/ nm²) Biomass % Low density 3.8 Med. density High Density Area 13.8 % 10.2 ( nm²) 1,560 14.6 55.3 45.6 1,611 36.5 39.9 10.2 360 8 Tab. 2. Demography per species and bathymetric in GSA 18 Biological samplings elaboration - GSA 18 North-Western Side 2005 Species Depth (m) Mean Size (cm) St. Dev. N° Weight (%) referred to TOT catch (%) Anchovy 0/200 0/40 40/60 60/200 7.23 5.97 9.38 8.07 2.26 1.2 1.08 2.56 2494 1161 256 1077 100 30 10 60 68.3 73.2 26.9 88.2 Sardine 0/200 0/40 40/60 60/200 12.4 9.11 12.15 14.04 2.22 1.42 0.53 1.34 354 75 111 168 100 2 66 31 15.7 1.3 41.1 10.6 Sprat 0/200 0/40 40/60 60/200 10 0 0 10 0 0 0 0 5 0 0 5 100 0 0 100 0.1 0 0 0.1 O.P.S. 0/200 0/40 40/60 60/200 9.59 8.49 15.83 12.32 4.7 4.15 1.55 5.88 930 779 126 25 100 45 51 3 15.9 25.4 32 1.1 TOT Pelagic 0/200 0/40 40/60 60/200 8.3 7.06 11.65 8.95 3.47 3.03 2.92 3.27 3783 2015 493 1275 100 28 25 46 Sardines Anchovies 20 20 % % 0 0 2 4 6 8 10 12 14 16 18 20 2 4 6 8 LT (cm) 10 12 14 16 18 20 LT (cm) Fig. 3. Size distribution for anchovies (left) and sardines (right) in GSA 18 9 TREND OF TOTAL PELAGIC BIOMASS IN SOUTHERN ADRIATIC SEA YEAR AREA S I E II A S III O IV N 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2662 1811 2597 2597 2597 2852 1919 3364 3064 1634 2383 3136 3144 3533 3596 3569 16.1 15.4 34 55 58.5 29.6 58.3 66.3 81.7 65.4 52.7 71.5 53.1 44.2 14 18.7 39.8 58.3 54.4 24.2 81 48.8 90.9 53 61.3 68.4 48.8 21.8 13 23.1 45.4 60.2 47.6 25.4 92.6 44.7 88.5 45.7 68.6 63.6 18.8 13.4 28.3 50.6 60.4 38.5 36.6 85 60.8 78.6 46.3 71.9 58.2 Av. Area (Nm²) 1987-2005 Av. Biomass per year (t) Max. Biomass per year (t) Min. Biomass per year (t) 2,823 142,821 239,757 39,861 (Vieste/Brindisi) Av .Density (t/Nm²) : 48.45 Max. Density (t/Nm²) : 84.93 Min.Density (t/Nm²) : 14.12 2003 2004 2005 52.1 57.7 46.9 25 45.3 54.7 56.5 42.2 18.6 45.8 47.1 56.7 54.2 36.9 12.1 44.3 49.5 57.8 51 31.1 3531 (- - - - - - - - -) +75% -71% TOTAL PELAGIC DENSITY (t/nm 2) 120 100 80 60 40 20 0 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Fig. 4. Trend of total pelagic biomass in South Adriatic from 1987 to 2005 10 TREND OF ANCHOVIES IN SOUTHERN ADRIATIC SEA YEAR AREA S I E II A S III O IV N 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2662 1811 2597 2597 2597 2852 1919 3364 3064 1634 2383 3136 3144 3533 3596 3569 0.6 3.4 9.7 15.3 15.2 5.9 12.6 24.1 8 18.7 42.7 58.7 50.2 40.2 0.9 4.8 11.4 16 13.7 4 19.3 20.2 7.6 24.7 47.9 59.8 44.2 0.2 1.5 6.4 12.9 16.2 11.5 4.1 24.4 15.5 9.7 31 52.4 58.9 0.4 2.3 8 14.2 16 8.6 6.8 25.8 11 13.5 37.1 56.1 55.7 Av. Area (Nm²) 1987-2005 : 2,823 Av. Biomass per year (t) : 71,960 Max. Biomass per year (t) : 164,524 Min. Biomass per year (t) 3,755 (Vieste/Brindisi) Av .Density (t/Nm²) : 24.24 Max. Density (t/Nm²) 58.28 Min.Density (t/Nm²) : 1.33 2003 2004 2005 49.8 41.8 29.3 15.4 43.3 49 38.9 26 11.8 39.8 46.6 47.1 35.8 22.5 8.2 38.7 49.1 44.6 32.6 19 3531 (- - - - - - - - -) +140% -95 % ANCHOVIES DENSITY (t/nm 2) 120 100 80 60 40 20 0 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Fig. 5. Trend of anchovy biomass in South Adriatic from 1987 to 2005 11 TREND OF SARDINES IN SOUTHERN ADRIATIC SEA YEAR AREA S I E II A S III O IV N 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2662 1811 2597 2597 2597 2852 1919 3364 3064 1634 2383 3136 3144 3533 3596 3569 12.8 11.5 27.3 44.6 45.4 15.3 32.2 33 72.9 41.7 2.5 10.5 1 2.2 10.8 14.3 32.2 47.1 40.8 9 49.6 20.4 83.3 21.2 7.4 6.9 2.4 18.2 9.7 18.1 36.9 48.2 33.8 8.1 57.5 22.9 78 6.4 11.7 3.3 15.3 9.9 22.5 41.1 47.7 24.6 15.7 49.3 46.4 62.4 0.9 12.5 1 Av. Area (Nm²) 1987-2001 : 2,823 Av. Biomass per year (t) : 62,739 Max. Biomass per year (t) : 209,325 2,258 Min. Biomass per year (t) (Vieste/Brindisi) Av .Density (t/Nm²) : 21.349 Max. Density (t/Nm²) : 74.15 Min.Density (t/Nm²) : 0.8 2003 2004 2005 1.9 13.8 14.8 7.2 0.8 4.9 15.2 13.5 4.6 3.5 0.1 8.4 15.7 11.7 1.9 3.3 0.1 11.5 15.6 9.6 3531 (- - - - - - - - -) +247% -96 % 120 SARDINES DENSITY (t/nm 2) 100 80 60 40 20 0 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Fig. 6. Trend of sardine biomass in South Adriatic from 1987 to 2005 12