Serial No. N5121 NAFO SCR Doc. 05/35 SCIENTIFIC COUNCIL .
NOT TO CITED WITHOUT PRIORREFERENCE TO THE AUTHOR(S)Northwest AtlanticFisheries OrganizationSerial No. N5121NAFO SCR Doc. 05/35SCIENTIFIC COUNCIL MEETING – JUNE 2005Results from Bottom Trawl Survey on Flemish Cap of July 2004byJosé Miguel Casas and Diana González TroncosoInstituto Español de Oceanografía, Cabo Estay – Canido 36200 Vigo, Spainmikel.casas@vi.ieo.esAbstractA stratified random bottom trawl survey on Flemish Cap was carried out from June 25th to August 2nd 2004. Thisyear, the area surveyed was extended up to depths of 800 fathoms (1400 meters) following the same procedures asin previous years and increasing the number of hauls planned (195). The survey was carried out by the R/V Vizcondede Eza and the last eleven days of the surveys were used to make 61 paired hauls with the R/V Cornide de Saavedraand to conclude the comparative fishing trial for calibration initiated in 2003 between the former vessel and the newone. A total of 124 valid hauls were made by the vessel R/V Vizconde de Eza with the usual survey gear (Lofoten)up to 730 meters depth. Survey results including abundance indices of the main commercial species and agedistributions for cod, redfish, American plaice and Greenland halibut are presented. The general indexes for thisyear are estimated taken into account the traditional swept area (strata 1-19, up to depths of 730 m.) and the totalarea surveyed (strata 1-34, up to depths of 1400 m.).From the comparative fishing trial carried out during 2003 and 2004, the correction factors for the main specieswere estimated and the indexes from 1988 to 2002 were corrected to the scale of the new vessel. In the same waythe corrected abundance at age indices was presented for cod, American plaice, redfish and Greenland halibut.IntroductionThe survey on Flemish Cap was carried out on board R/V Vizconde de Eza in 2004. A total of 177 valid bottomtrawls were made up to a depth of 1400 m (800 fathoms) (Fig. 1). The survey covered all strata of the bankadequately with the exception of the strata 26 and 27 and the area corresponding with the Beothuk knoll in thesoutheast and southwest of the bank respectively. A synoptic sheet of the survey with vessel and gear characteristicsis shown in Table 1. This was the 17th survey of the series initiated by the EU in 1988. All surveys had a stratifiedrandom design following NAFO specifications (Doubleday, 1981). Dates of the previous surveys were:Valid111Year VesseltowsDatesYear1988 Cornide de Saavedra1158/7 – 22/719971989 Cryos11612/7 – 1/819981990 Ignat Pavlyuchenkov11318/7 – 6/819991991 Cornide de Saavedra11724/6 – 11/720001992 Cornide de Saavedra11729/6 – 18/720011993 Cornide de Saavedra10123/6 – 8/720021994 Cornide de Saavedra1166/7 – 23/720031995 Cornide de Saavedra1212/7 – 19/720041996 Cornide de Saavedra11728/6 – 14/7* 124 valid tows were carried out in depths lesser than 400 fathoms.VesselCornide de SaavedraCornide de SaavedraCornide de SaavedraCornide de SaavedraCornide de SaavedraCornide de SaavedraVizconde de EzaVizconde de EzaValidtows117119117120120120114177*Dates16/7 – 1/817/7 – 2/82/7 – 20/710/7 – 28/73/7 – 20/730/6 –17/72/6 – 27/725/6 – 2/8
2Material and MethodsAs in the last year, the R/V Vizconde de Eza carried out the survey following the same procedures as in previousyears, the same bottom trawl net Lofoten, with a cod-end mesh size of 35 mm, as well as all other details of its use(Saborido-Rey and Vazquez, 2003). Also, this year concluded the comparative fishing trials initiated in 2003 withthe former R/V Cornide de Saavedra in order to establish a link between the two sets of survey data and to developconversion factors between the two vessels. With the comparative fishing trials concluded and the conversionfactors estimated, the indices from R/V Cornide de Saavedra were transformed to the R/V Vizconde de Eza scalemake them comparable.The methodological aspects and results of the calibration are presented in SCR 05/ (González and Casas,2005).ResultsFollowing the agreement of the NAFO Standing Committee on Fisheries Science (STACFIS), on preferringmean number or weight per tow over other survey indices, most tables in the report are presented in that way.Details on changes were presented in last year report (Saborido-Rey and Vazquez, 2003)Mean catch per tow (Kg) of main species in past surveys 1998199920002001200220032004*(1-19)2004 235.2149.9626.7525.0316.49*Mean catch per tow for the comparable area and depths in the historical series.These survey indices are also presented in Table 2, and even they belong to different species and pelagic vs.demersal character and the transformation to the new scale only was carried out for the main species, a global indexis presented for each year, which minimum occurred in 2001. Redfish shows the highest annual variability, probablydue to its pelagic habitat, making accessibility to bottom gears more changeable than in the case of demersal orbenthic species. Cod reached its minimum biomass in 2003. The relative high values founded in 2004 for Americanplaice and grenadiers are probably due to the occasional increasing of catchability. Greenland halibut biomassmaintained a continuous biomass increase to reach a maximum in 1998; since then the biomass decreased up tominimum historical value in 2003. In 2004 the biomass increases, reaching the level of 2002. Shrimp catches in1998 and 2002 were the highest, but interpretation of survey results needs to take into account changes occurred incod-end mesh size.
3Excluding redfish, the whole period could be divided in two in regards to species composition: Cod, Americanplaice and skates dominating the first half, prior to 1995, and Greenland halibut, the second half. For cod, 1995 wasthe spawning year for the first extremely weak recruitment; for American plaice, it had been 1991.CodMean catch per tow by strata and its standard error are presented in Table 3. These indices are compared withresults of previous surveys in Table 5. Total biomass calculated by the swept area method and compared withRussian survey results are:YearEU (1)Russia: (2)(3)YearEU (1)Russia: 9059,3622,4966,7408,2002003- 9909,700199360,963199426,4631) Biomass estimated from bottom trawl survey. 2) Biomass estimated from bottom trawl survey (Kiseleva and Vaskov 1994;Kiseleva 1996, 1997; Vaskov and Igashov, 2003). 3) Biomass estimated of bottom trawlable plus pelagic biomass (Borovkov etal. 1993; Kiseleva and Vaskov 1994).The mean frequency at age per tow (‘000) is shown in the table below.age1234567891011121314total1988 1989 1990 19916.05 24.38 2.86 160.4599.36 13.43 15.35 32.6061.55 113.53 6.37 21.0216.72 67.91 21.082.641.81 25.40 19.698.400.261.66 5.592.150.280.18 0.420.370.090.16 0.180.080.01 0.100.040.01 0.030.000.011992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 200488.955.07 3.75 1.77 0.04 0.05 0.03 0.01 0.22 0.590.8552.13 172.05 5.14 14.80 3.88 0.19 0.10 0.10 0.02 2.48 1.65 0.07 4.186.94 38.67 34.51 1.66 8.28 4.32 0.12 0.14 0.41 0.02 0.80 0.78 0.032.971.37 6.34 4.84 1.11 5.97 1.56 0.15 0.25 0.15 0.04 0.17 0.720.481.64 0.16 1.15 2.99 0.49 1.95 0.89 0.12 0.10 0.09 0.03 0.181.740.21 0.08 0.04 0.24 1.18 0.10 0.55 0.55 0.02 0.04 0.05 0.010.300.61 0.01 0.03 0.01 0.03 0.18 0.02 0.21 0.18 0.03 0.01 0.010.020.11 0.140.010.01 0.01 0.12 0.12 0.01 0.000.030.010.02 0.01 0.04 0.05 0.010.01 0.010.010.03 0.020.010.01 0.010.010.010.01186.13 246.66 71.67 227.78 153.53 219.72 50.14 24.33 16.56 12.23 4.05 1.87 1.83 3.67 2.81 2.04 5.16The 1990 year-class was the most abundant observed at age 1, but its level was not maintained in the followingyears, after recruitment. This may indicate that its abundance was overestimated in the 1991 survey. The abundanceof the 1991 year-class, although recording a maximum at age 2, decreased quickly as a consequence of the intensefishery on ages 2 and 3 during 1993 and 1994. Later year-classes, from 1992 onwards (ages 12 or less in 2004),were weak, weaker than the ones observed in the previous period. The 1995 to 1999 year-classes (ages 9 to 5 in2004) failed almost completely and, according to the results of the last surveys, the same failure appears to haveoccurred to the 2001 and 2003 year-classes (age 3 and 1 respectively in 2004). The 2000 and 2002 year classesabundance, although low in the historical series, was estimated to above average in the last 10 years.
4Tables 6, 7 and 4 show mean length frequency per tow, the age-length key and mean frequency at age per towand stratum respectively. Catch per tow distribution is presented in Figure 2.American plaiceMean catch per tow by strata is presented in Table 8. These indices are compared with results of previoussurveys in Table 10. Total biomass calculated by the swept area method and compared with Russian survey results isshown in the following 1993EU Russia ar19941995199619971998199920002001200220032004EU Russia 82,0492,2863,525tons1) Rikhter et al. 1991; Borovkov et al. 1992, 1993, 1994; Vaskov and Igashov, 2003.The mean frequency at age per tow is presented in the following table. The 1986 and 1990 year-classes, ages16 and 12 in 2002, were the most abundant cohorts in the period, but no good recruitment was observed since then.Fish aged 6 or more roughly correspond with fishable biomass. The abundance of this group (f 6 ) decreased alongthe period except in 1992, when an increase was recorded as the consequence of the income of the abundant 1986year-class.age12345678910111213141516 Totalfreq. 6 1988 19890.050.50 0.702.34 10.401.63 2.335.26 5.437.94 5.426.23 5.156.79 3.022.18 1.000.57 0.430.12 0.050.20 0.020.160.060.070.0534.09 34.0124.36 571.060.370.010.071992 1993 1994 1995 1996 1997 1998 1999 2000 2001 20020.01 0.010.01 0.021.06 0.01 0.05 0.04 0.04 0.02 0.030.03 0.050.99 1.92 0.06 0.14 0.15 0.14 0.04 0.03 0.01 0.06 0.041.33 1.35 2.65 0.92 0.32 0.03 0.06 0.08 0.10 0.07 0.082.41 0.97 1.29 2.65 0.73 0.15 0.09 0.10 0.13 0.13 0.025.93 0.52 1.09 1.70 2.07 0.52 0.33 0.10 0.19 0.07 0.111.59 5.14 1.21 1.71 1.11 1.50 0.77 0.30 0.15 0.14 0.081.87 0.56 4.26 1.13 0.68 0.34 1.12 0.59 0.19 0.33 0.161.03 0.97 0.40 1.91 0.50 0.51 0.65 0.63 0.49 0.54 0.200.47 0.46 0.81 0.20 0.78 0.36 0.44 0.32 0.53 0.72 0.240.22 0.32 0.28 0.22 0.18 0.61 0.37 0.42 0.28 0.60 0.370.12 0.38 0.28 0.18 0.10 0.16 0.36 0.26 0.23 0.52 0.280.02 0.45 0.31 0.18 0.10 0.03 0.11 0.15 0.09 0.24 0.311.33 0.65 0.36 0.13 0.12 0.14 0.15 0.07 0.20 0.180.04 0.61 0.27 0.09 0.06 0.07 0.07 0.06 0.14 0.160.05 0.01 0.04 0.03 0.14 0.13 0.12 0.07 0.12 0.2326.05 21.79 17.05 14.47 13.96 11.66 7.02 4.69 4.73 3.32 2.65 3.94 2.4512.55 10.45 11.26 10.23 9.92 7.91 5.77 4.34 4.51 3.10 2.35 3.62 31
5Global indices of the table, such as total number by tow and frequency 6 , have declined over the wholeperiod, reaching their lowest level in 2002: more than 10 times lower than in 1988-1990. Data in the table aboveindicates two periods for recruitment, and a change from an upper abundance level to a lower one. The 1991 yearclass was the first weak cohort. The relative high values founded in 2003 and 2004 for American plaice, mainly inthe ages older than 9 years old, are probably due to the occasional increasing of catchability in 2003 and 2004survey.Tables 11, 12 and 9 show mean length frequency per tow, the age-length key and mean frequency at age pertow respectively. Catch per tow distribution is presented in Figure 3.RedfishAll redfish catches were classified by species. The group name juvenile contains those individuals of small sizefor which routine classification was not possible. The 15 cm maximum length is a good reference for this group, butit was never used as a criterion. The skill required to identify the species increased over time, so the group juvenile isnot a uniform defined group, but it is maintained for practical reasons.Mean catch per tow by strata are presented in Tables 13, 15, 19 and 21 for Sebastes marinus, S. mentella, S.fasciatus and the juvenile group respectively. The following table summarize the results by species in the tes les 14, 16, 20 and 22 show mean length frequency by tow for the four groups. Age-length keys and meanfrequency at age by tow for S. mentella are presented in Tables 18 and 17 respectively. Catches per tow distributionsof the three species are presented in Figures 4, 5 and 6.More details and results are presented by Avila de Melo et al. in SCR/05-Greenland halibutMean catch per tow by strata and its standard error are presented in Table 23. These indices are compared withresults of previous surveys in Table 27 and summarised as follow:
57.7315.28Kg/towMean length frequency by tow, age-length keys and mean frequency at age per tow are presented inTables 24, 26 and 25, respectively. Catch per tow distribution is presented in Figure 7. Mean frequency at age pertow (‘000) in the historical series was calculated as 80.6490.57100.45110.18120.011314150.0216 0.01total12.47freq. 10 000.0030.650.28The tables 28 and 29 also show the abundance and biomass by age, corresponding at age greater or equalthan five years in order to compare with XSA results.ShrimpCasas et al. (2004) presented detailed results.Roughhead grenadier (Macrourus berglax)Mean catch per tow along this survey series was:
d results are presented by Murua SCR/05 .ReferencesÁvila de Melo, A. , R. Alpoim and F. Saborido-Rey – 2005. A Revised Assessment of Beaked Redfish (S. mentellaand S. fasciatus) in NAFO Division 3M Using the Original EU Survey Indices Converted to the New RVVizconde de Eza Units. NAFO SCR Doc. 05/ .Borovkov, V., S. Kovalev, P. Savvatimsky, V.A. Rikhter and I.K. Sigaev – 1992. Russian research report for 1991.NAFO SCS Doc. 92/12.Borovkov, V., K. Gorchinsky, S. Kovalev, P. Savvatimsky, V.A. Rikhter and I.K. Sigaev – 1993. Russian researchreport for 1992. NAFO SCS Doc. 93/10.Borovkov, V., K. Gorchinsky, S. Kovalev and P. Savvatimsky – 1994. Russian national research report for 1993.NAFO SCS Doc. 94/3.González Troncoso, D and J.M. Casas – 2005. Calculation of the calibration factors from the comparativeexperience between the R/V Cornide de Saavedra and the R/V Vizconde de Eza in Flemish Cap in 2003 and2004. NAFO SCR Doc. 05/Casas, J.M., J.L. del Río and D. González Troncoso – 2004. Northern shrimp (Pandalus borealis) on Flemish CapSurveys. NAFO SCR Doc. 04/77.Doubleday, W.G.- 1981. Manual of Groundfish Surveys in the Northwest Atlantic. NAFO Sci. Counc. Stud. 2, 55pp.Kiseleva, V.M.– 1996. Estimation of cod stock in Div. 3M by data of 1995 trawl survey. NAFO SCR Doc. 96/7.Kiseleva, V.M.– 1997. Assessment of cod stock on the Flemish Cap from data of trawl survey in 1996. NAFO SCRDoc. 97/7.Kiseleva, V.M. and A.A. Vaskov – 1994. Assessment of cod stock in NAFO Subarea 3 from 1993 trawl-acousticsurvey data. NAFO SCR Doc. 94/12.
8Rikhter, V.A., I.K. Sigaev, V. Borovkov, S. Kovalev and P. Savvatimsky – 1991. USSR research report for 1990.NAFO SCS Doc. 91/5.Saborido-Rey, F. And A. Vázquez. 2003. Results from Bottom Trawl Survey on Flemish Cap of July 2002. NAFOSCR Doc., Nº 42. Serial No. 4860, 40p.Murua, H.– 2005. A Review on Roughhead Grenadier (Macrourus berglax) Biology and Population Structure onFlemish Cap (NAFO Division 3M), 1991-2004. Based on EU Flemish Cap Bottom Survey Data, Serial No. N NAFO SCR Doc. 05/Vaskov, A.A. and T.M. Igashov – 2003. Results from the Russian trawl survey on the Flemish Cap Bank (Division3M) in 2002. NAFO SCS Doc. 03/9.Table 1 – Technical data of the 2004 survey.ProcedureSpecificationVesselGTPowerR/V Vizconde de Eza1 400 t1 800 HPMean trawling speed3.5 knotsTrawling time30 minutes effective timeFishing gearfootrope / handropefootgearvertical openingwarpstrawl doorswire lengthmesh size in cod-endtype Lofoten31.20 / 17.70 m27 steel bobbins of 35 cm3.0 m (SCANMAR)100 meters, 45 mm, 200 Kg/100mpolyvalent, 850 Kg1.6 depth echo sounder 430 m.35 mmType of surveyStratified samplingStation selection procedureRandomCriterion to change position of a selected tow- unsuitable bottom for trawling according to ecosonderregister.- Information on gear damage from previous surveys.Criterion to reject data from tow- tears in cod-end- severe tears in the gear- less than 20 minutes tow- bad behaviour of the gearDaily period for fishing6.00 to 22.00 hoursSpecies for samplingAll fish, squid and shrimpSpecies for age determinationCod, American plaice, redfish (Sebastes mentella),Greenland halibut and Roughhead grenadier(Macrourus berglax).
9Table 2 – Mean catch per tow for several species or groups of species in 1988-2004 surveys (Kg) in depths lesser than 400 7.76Synaphobranchus 280.310.210.490.160.680.83Urophycis sp.Antimora .33
Northwest Atlantic Fisheries Organization Serial No. N5121 NAFO SCR Doc. 05/35 SCIENTIFIC COUNCIL MEETING – JUNE 2005 Results from Bottom Trawl Survey on Flemish Cap of July 2004 by José Miguel Casas and Diana González Troncoso Instituto Español de Oceanografía, Cabo Estay – Canido 36200 Vigo, Spain mikel.casas@vi.ieo.es Abstract
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