Stock specific documentation of standard assessment procedures used by IC- ES. North-East Arctic Greenland Halibut. Date:

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1 ICES AFWG REPORT Anne 8 - Stock Anne ANNEX:_afwg-ghl-arct Stock specific documentation of standard assessment procedures used by IC- ES. Stock: Working Group: Date: North-East Arctic Greenland Halibut Arctic Fisheries Working Group A. General A.1 Stock definition Greenland halibut (Reinhardtius hippoglossoides, Walbaum) is distributed in the Arctic and boreal waters in the North Atlantic and in the North Pacific (Fedorov 1971; Godø and Haug 1989; Bowering and Brodie 1995; Bowering and Nedreaas 2000). In the northeastern Atlantic the distribution is more or less continuous along the continental slope from the Faeroe Islands and Shetland to north of Spitsbergen (Whitehead et al. 1986; Godø and Haug 1989), with the highest concentrations from 500 to 800 m depth between Norway and Bear Island, which is also regarded as the main spawning area (Godø and Haug 1987; Albert et al. 2001b). Peak spawning occurs in December in the main spawning area, but also in nearby localities during summer (Albert et al. 2001b). Atlantic currents transport eggs and larvae northwards and the juveniles are distributed around Svalbard and in the northeastern Barents Sea, to the waters around Franz Josef Land and Novaja Zemlya area (Godø and Haug 1987; Godø and Haug 1989; Albert et al. 2001a). As they grow older they gradually move southwards and eventually alternate between the spawning area and feeding areas in the centralwestern Barents Sea (Nizovtsev, 1989). The Northeast arctic Greenland halibut stock is a pragmatically defined management unit. The degree of echange with other stocks is not resolved, but is believed to be low. Potential routes of echange may be drift of larvae towards Greenland and migration of adults between the Barents Sea and the Iceland-Faeroe Islands area. A.2 Fishery Before the mid 1960s the fishery for Greenland halibut was mainly a coastal long line fishery off the coasts of eastern Finnmark and Vesterålen in Norway. The annual catch of the coastal fishery was about 3,000 t. In recent s this fishery has landed 3,000 6,000 t although now gillnets are also used in the fishery. In 1964 dense Greenland halibut concentrations were found by Soviet trawlers in the slope area to the west of the Bear Island (Nizovtsev, 1989). Following the introduction of international trawlers in the fishery in the mid 1960s, the total landings increased to about 80,000 t in the early 1970s.The total Greenland halibut landings decreased steadily to about 20,000 t during the early 1980s. This level was maintained until 1991, when the catch increased sharply to 33,000 t. From 1992 total landings varied between t with a peak in From 1992 the fishery has been regulated by allowing only the long line and gillnet fisheries by vessels smaller than 28 m to be directed for Greenland halibut. This fish-

2 646 ICES AFWG REPORT 2011 ery is also regulated by seasonal closure. Target trawl fishery has been prohibited and trawl catches are limited to bycatch only. From 1992 to autumn 1994 bycatch in each haul was not to eceed 10% by weight. In autumn 1994 this was changed to 5% bycatch of Greenland halibut onboard at any time. In autumn 1996 it was changed to 5% bycatch in each haul, and from January 1999 this percentage was increased to 10%. In August 1999 it was adjusted further to 10% in each haul but only 5% of the landed catch. From 2001 the bycatch regulations again was changed to 12% in each haul and 7% of the landed catch. The regulations enforced in 1992 reduced the total landings of Greenland halibut by trawlers from 20,000 to about 6,000 t. Since then and until 1998 annual trawler landings have varied between 5,000 and 8,000 t without any clear trend attributable to changes in allowable bycatch. However, the increase of trawler landings in 1999 to t may be attributable partly to the less restrictive bycatch regulations. Landings of Greenland halibut from the directed longline and gillnet fisheries have also increased in recent s to well above the level of 2,500 t set by the Norwegian authorities. This is attributed to the increased difficulties of regulating a fishery that only lasts for a few weeks. The 38 th JRNFC s Session in 2009 decided to cancel the ban against targeted Greenland halibut fishery and established the TAC at 15,000 t for net three s ( ). The TAC was allocated between Norway, Russia and other countries with shares of 51, 45 and 4% respectively. The 40 th JRNFC s Session in 2011 decided to increase TAC for 2012 up to 18,000 t. During fishing for other species, it is permitted to have an intermiture of Greenland halibut of up to 7% by weight on board at the end of fishing operations and in the catch landed. Nevertheless, a bycatch of up to 12% by weight of Greenland halibut is permitted in individual catches. From early 2004 the Norwegian Ministry of Fisheries and Coastal affairs decided that for Norwegian vessels in the NEEZ allowable bycatch at any time on board and by landing should not eceed 7 %. In addition, the annual catch for each trawler are not allowed to eceed 4 % of the sum of the vessels quota on cod, haddock and saithe, and limited by a maimum annual catch of 40 t pr. vessel. The Norwegian conventional fleet, vessels smaller than 28 m, are allowed to conduct a target fishery with longlines and gillnets in a limited area in approimately one month each. For these vessels the TAC is set to 10, 12 and 14 t, dependent of size of the vessel. Minimum size regulation for Greenland halibut is 45 cm, and starting in 2012 it became mandatory to use sorting grids during target Greenland halibut trawl fishery. A.3 Ecosystem aspects As investigations show, among the variety of fish, seabirds and marine mammals Greenland halibut were found in the diet of just three species - Greenland shark (Somniosus microcephalus), cod (Gadus morhua morhua) and Greenland halibut itself. Besides, killer whale (Orcinus orca), grey seal (Halichoerus grypus) and narwhal (Monodon monoceros) could be its potential predators. However, the presence of Greenland halibut in the diet of the above species was minor. Predators fed mainly on juvenile Greenland halibut up to cm long. The mean annual percentage of Greenland halibut in cod diet in constituted 0,01-0,35% by weight (0,05% in average) (DOLGOV & SMIRNOV 2001). Low levels of

3 ICES AFWG REPORT consumption are related to the distribution pattern of juvenile Greenland halibut as they spend the first s of the life mainly in the outlying areas of their distribution, in the northern Barents Sea, where both adult Greenland halibut and other abundant predator species are virtually absent. Cannibalism was the highest in 1960 s (up to 1,2% by frequency of occurrence). During the 1980 s, in the Greenland halibut stomachs the frequency of occurrence of their own juveniles did not eceed 0,1 %. During the 1990 s, the portion of their own juveniles (by weight) was at the level of 0,6-1,3%. Food composition of the Greenland halibut in the Barents Sea includes more than 40 prey species (NIZOVTSEV 1989; DOLGOV & SMIRNOV 2001). Investigations over a wide area of the continental slope up to the Novaya Zemlya show that the main food source of Greenland halibut consists of fish, mostly capelin (Mallotus villosus villosus) and polar cod (Boreogadus saida) followed by cephalopods and shrimp (Pandalus borealis). During the 1990 s an important component of the diet was waste products from fisheries for other species (heads, guts etc.). With growth, a decrease in the importance of small food items (shrimp, capelin) in Greenland halibut diet and the increase of a portion of large fish such as cod and haddock (Melanogrammus aeglefinus) were observed. With the Greenland halibut stock being nearly tonnes, the total food consumption of the population is estimated to be about tonnes. The biomass of commercial species consumed (shrimp, capelin, herring, polar cod, cod, haddock, redfish (Sebastes sp.), long rough dab (Hippoglossoides platessoides) does not eceed tonnes per species (DOLGOV & SMIRNOV 2001). The Greenland halibut as a species thus has a negligible effect on the other commercial species in the Barents Sea both as predator and prey. Greenland halibut occurs over a wide range of depths (from 20 to 2200 m) and temperatures (from -1.5 to 10º C) (BOJE & HAREIDE, 1993; SHUNTOV, 1965; NIZOVTSEV, 1989). Young Greenland halibut occur mostly in the northeastern Barents Sea (Spitsbergen archipelago and further east to Franz Josef Land) where the presence adult Greenland halibut or other predators appears minimal. Therefore, Greenland halibut mortality after settling in the area is low and stable and driven mainly by envionmental factors. B. Data B.1 Commercial catch Norwegian commercial catch in tonnes by quarter, area and gear are derived from the sales notes statistics of the Directorate of Fisheries. Data from about 20 sub areas are aggregated on 6 main areas for the gears gill net, long line, bottom trawl and shrimp trawl. For bottom trawl the quarterly area distribution of the catches is adjusted by logbook data from The Directorate of Fisheries and the total bottom trawl catch by quarter and area is adjusted so that the total annual catch for all gears is the same as the official total catch reported to ICES. No discards are reported or accounted for in the catch statistics. Russian catch based on daily reports from the vessels are combined in the statistics of the All-Russian Research Institute of Fisheries and Oceanography (VNIRO, Moscow). Data are provided separately by ICES areas and gears.

4 648 ICES AFWG REPORT 2011 The sampling strategy is to have age-length samples from all major gears in each area and quarter. There are at present no defined criteria on how to allocate samples of catch numbers, mean length and mean weight at age to unsampled catches, but the following general process has been applied: First look for samples from a neighbouring area if the fishery etends to this area in the same quarter. If there are no samples available in neighbouring areas, search for samples from other gears with the most similar selectivity in the same area or in neighbouring areas. The last option is to search in neighbouring quarters, first from the same gear in the same area, and then from neighbouring areas and similar gears. ALKs from research surveys (shrimp trawl) are also used to fill gaps in age sampling data. Norway and Russia, on average, have accounted for about 90-95% of the Greenland halibut landings during more recent s. Data on catch in tonnes from other countries are either taken from ICES official statistics (by ICES area) or from reports to Norwegian authorities. A few countries also supply some additional data. The tet table below indicates the type of data provided by country: Kind of data Country Caton (catch in weight) Canum (catch at age in numbers) Weca (weight at age in the catch) Matprop (proportion mature by age) Length composition in catch Norway Russia Germany United Kingdom France 1 Spain 1 Portugal 1 Ireland 1 Greenland 1 Faroe Islands 1 Iceland 1 Poland 1 1 As reported to Norwegian authorities The Norwegian and Russian input files are Ecel spreadsheet files before aggregation to international data. The data are archived in the national laboratories and with the Norwegian stock co-ordinator. The national data have been aggregated with international data on Ecel spreadsheet files. The Russian and Norwegian catch-at-age data based on national landings, length composition of catches, age-length-keys (ALK) and weight at age data. Catches from the other countries were assumed to have the same age composition and weight at age as the Norwegian landings. From 2006 Norway stopped to determine the age using the traditional method. Since than the common catch-at-age files constructed on the base of the Russian ALK and weight at age data. The Ecel spreadsheet files used for age distribution, adjustments and aggregations are held by the Norwegian stock co-ordinator and for the current and previous in the ICES computer system under w:\acfm\afwg\\personal\name (of stock coordinator).

5 ICES AFWG REPORT The result files (FAD data) can be found at ICES and with the stock co-ordinator, either in the IFAP system as SAS datasets or as ASCII files on the Lowestoft format, under w:\acom\afwg\\data\ghl_arct. B.2 Biological For , separate weight at age data are used for the Norwegian and the Russian catches. Both data sets are mean values for the period and are combined as a weighted average for each. A constant set of weight-at-age data is used for the total catches in For subsequent s annual estimates are used. The mean weight at age in the catch is calculated as a weighted average of the weight in the catch from Norway and Russia. The weight at age in the stock is set equal to the weight at age in the catch for all s. A fied natural mortality of 0.15 is used both in the assessment and the forecast. Both the proportion of natural mortality before spawning (Mprop) and the proportion of fishing mortality before spawning (Fprop) are set to 0. Annual ogives based on sees combined using Russian survey data are given for the s and 1992 last data. An average ogive derived from is used for For 1984 to the last data a three- running average is used. B.3 Surveys The results from the following research vessel survey series are evaluated by the Working Group: 1 ) Norwegian bottom trawl survey in August in the Barents Sea and Svalbard from 1984 in fishing depths of less than 100 m and down to 500 m. (Table F1 and F2). 2 ) Norwegian Greenland halibut surveys in August from The surveys cover the continental slope from 68 to 80ºN, in depths of m north of 70º30 N, and m south of this latitude. This series has in 2000 been revised to also include depths between m in all s (Table F3). 3 ) Norwegian bottom trawl surveys east and north of Svalbard in autumn from 1996 (Table F4). 4 ) The Norwegian Combined Survey inde Table E5, combination of the results from Tables F1-F4. 5 ) Russian bottom trawl surveys in the Barents Sea from 1984 in fishing depths of m. This series has been revised substantially since the 1998 assessment in order to make the s more comparable with respect to area coverage and gear type (Table F6). 6 ) Spanish bottom trawl survey in the slope of Svalbard area in October, ICES Division IIb: from 1997 (Table F7). 7 ) Norwegian (from 2000 Joint) Barents Sea bottom trawl survey (winter) from 1989 in fishing depths of less than 100 m and down to 500 m. In order to utilise the last values in the VPA calibration, this series was adjusted back by one and one age group to reflect sampling as if it occurred in the autumn of the previous (Table E8). 8 ) International pelagic 0-group surveys from (Table 1.1).?

6 650 ICES AFWG REPORT 2011 Over the last several s the Working Group has been concerned about trends in catchability within individual surveys used for tuning of the XSA. The trends were seen for younger ages of classes in the late 80 s and early 90 s that were initially estimated to be very low in abundance. With increasing age these classes were estimated to be much closer to the mean abundance. In previous meetings the Working Group therefore increased the lower age used in tuning to five s in order to reduce the problem. This only partly resolved the problem though, and in all subsequent assessments estimated recruitment of the last 2-3 s has increased from one to the net. The Norwegian bottom trawl survey in the Barents Sea and Svalbard catch Greenland halibut mainly in the range of ages 1 8, although in most s age 1 is poorly represented and all age group younger than five s are not considered to be well represented in this survey due to the limited depth range covered. The relative strength of the classes varies considerably with age. In more recent s there has been low but somewhat better representation of young fish in this survey. The Norwegian juvenile Greenland halibut survey north and east of Svalbard were started in 1996 and from 2000 this survey is conducted as a joint survey between Norway and Russia. As a result it is epected that the area coverage will improve, better representing the distribution of juveniles and will provide a more comparable time series. Only the Norwegian part of these northern surveys is currently included in the Norwegian Combined Survey inde (see below). In future, when the etended coverage in the Russian zone has been repeated for at least five s the Working Group will consider revising the combined inde. The Norwegian Greenland halibut survey along the deep continental slope south and west of Spitsbergen began in Although Greenland halibut older than 15 s are caught, few fish are represented in the catch over age 12 or less than age 5 (Table F4). Most of the abundance indices are dominated by ages 5 8. Most of the surveys considered by the Working Group in 2002 cover either the adult population in the slope area or juvenile distribution in northern areas. The problem of underestimation of recruitment in the last few s included in the analyses has been attributed to shortcomings in survey coverage. The Working Group at previous meetings has noted the need for annual surveys that sample most of the population within a short period of time. Prior to the 2002 WG meeting effort was therefore made to combine some of these surveys into a new total inde. The new inde is termed the Norwegian Combined Survey Inde and is established back to 1996, the first with survey coverage northeast of Svalbard. It includes bottom trawls from the Norwegian bottom trawl survey in August in the Barents Sea and Svalbard (Tables F1 and F2), the Norwegian Greenland halibut survey in August along the continental slope (Table F3), and the Norwegian bottom trawl survey in August- September north and east of Svalbard (Table F4). Prior to the meeting in 2003 work was done to evaluate the combination of these survey series into one inde and this was reported in Working Document 5 to the Working Group. Based on these results it was decided to use this combined inde in this s assessment. The Norwegian Combined Survey Inde (Table F5) indicates a significant increase in the total stock during the last three s and a stock size in 2002, nearly 40% above last s inde. However, there is no clear class pattern in the data and some ages are consistently underestimated relative to adjacent age groups (e.g. age 9 and partly age 4). The highest indices were observed for age seven, with eception of the two last s when age 1 was most abundant. That indicates that the catchability of

7 ICES AFWG REPORT younger ages (i.e. those primarily from northern surveys) are not comparable with the older ones (i.e. those primarily from the slope). This is probably a result of pooling different surveys using different gears. These weaknesses reduce the applicability of the combined surveys, and the Working Group advises that further work be done to improve the combined inde in the future. The Russian Barents Sea bottom trawl survey, which etends back to 1984 catch fish mainly in the range of 4 10 s old. The relative abundance of the classes against age is similar to the surveys above. This survey covers the Barents Sea including the continental slope of the Norwegian Sea. Total abundance indices from this survey show trend to grow since The Spanish bottom trawl surveys along the continental slope north of N from 1997 (Table EF) differ from the other survey series indicating reduced abundance in this area since The Norwegian bottom trawl survey during winter in the Barents Sea catch Greenland halibut older than 12 s, but are not particularly effective in catching fish older than 7 s. This is likely due to the limited depth distribution of the survey area. Nevertheless, the survey appears very effective at catching Greenland halibut up to age 6. The relative abundance of the classes against age is comparable with the survey above. The strengths of the Greenland halibut classes of from the International pelagic 0-group surveys in the Barents Sea are shown in Table 1.1. The results are highly variable over the time period. However, most of the 1970 s and 1980 s classes are represented in reasonably high numbers. In recent s the and the 1996 classes have been well below the long term average. The and classes are closer to the average. Significant increase of 0-group abundance indices with compare to previous s was observed in Than the increase in 0-group abundance seems to have stopped, and the indices were very low. It should be noted that the Ecosystem survey is not optimal for surveying 0-group Greenland halibut. All in all, the surveys seem to indicate that the catchability of the classes increased considerably as the fish becomes five s and older. Based on etremely low catch rates in the surveys, these classes were considered very poor in previous assessments by the Working Group, but improved considerably at older ages. The reason for this change in catchability is not clear. However, it is known that important areas for young Greenland halibut may be found north and east of Svalbard (Table F4). (Albert et al. 2001a) showed that the south-western end of the distribution area of age 1 fish was gradually displaced northwards along west Spitsbergen in the period and southwards in the period These displacements corresponded to changes in hydrography and may be eplained by increased migration of the classes to areas outside the survey area. Since 2006, none of the age structured tables of the Norwegian surveys have been updated due to change in age reading procedure. B.4 Commercial CPUE The restrictive regulations imposed on the trawl fishery after 1991 disrupted the traditional time series of commercial CPUE data. However, an attempt to continue the series was made through a research program using two Norwegian trawlers in a limited commercial fishery (Tables 8.6 and F9). This comprises fishing during two weeks

8 652 ICES AFWG REPORT 2011 in May-June and October, representing an effort somewhat less than 20% of the 1991 level. Since 1994 the fishery has been restricted to May-June. This fishery was conducted, as much as possible, in the same way as the commercial fishery in the previous s. The Norwegian CPUE survey was stopped from This was one of the tuning fleets, but an evaluation of this survey revealed a lot of inconsistencies in the series. Since 1997 also two Russian trawlers conducted a limited research fishery for Greenland halibut. The CPUE from the eperimental fishery was found, however, to be considerably higher than in the traditional fishery and has ehibited an increasing trend from After 1996 the Norwegian CPUE series has varied between 1200 and 1650 kg/h with the highest value in 2000 (Table F9). The Russian eperimental CPUE series shows an increasing trend since 1997, and this series also shows the highest value in B.5 Other relevant data None C. Historical stock development Model used: XSA Software used: IFAP / Lowestoft VPA suite Model Options chosen: Tapered time weighting applied, power = 3 over 20 s Catchability independent of stock size for all ages Catchability independent of age for ages >= 10 Survivor estimates shrunk towards the mean F of the final 2 s or the 5 oldest ages S.E. of the mean to which the estimate are shrunk = Minimum standard error for population estimates derived from each fleet = Prior weighting not applied

9 ICES AFWG REPORT Input data types and characteristics: Type Name Year range Age range Variable from to Yes/No Caton Catch in tonnes - (total) Yes Canum Catch at age in numbers Yes Weca West Mprop Fprop Matprop Weight at age in the commercial catch Weight at age of the spawning stock at spawning time. Proportion of natural mortality before spawning Proportion of fishing mortality before spawning Proportion mature at age Natmor Natural mortality Yes/No - constant at age from Yes/No - assumed to be the same as weight at age in the catch No set to 0 for all ages in all s No set to 0 for all ages in all s Yes/No three running mean, constant at age from No set to 0.15 for all ages in all s Tuning data: Type Name Year range Age range Tuning fleet 1 Norwegian Combined 1996 last data survey inde Tuning fleet 2 Norwegian 1992 last data 5-14 eperimental CPUE Tuning fleet 3 Russian trawl survey from last data D. Short-term projection Model used: Age structured Software used: IFAP prediction with management option table and yield per recruit routines Initial stock size. Taken from the XSA for age 6 and older. The recruitment at age 5 in the last data is estimated using the mean from 1990 to two s before the last data following the argument that recruitment at age 5 shows a sharp reduction in the most recent s in the previous assessments, which is not believed to reflect the true recruitment. Natural mortality: Set to 0.15 for all ages in all s Maturity: The same ogive as in the assessment is used for all s F and M before spawning: Set to 0 for all ages in all s Weight at age in the stock: Average weight at age for the last three s used in the assessment

10 654 ICES AFWG REPORT 2011 Weight at age in the catch: Average weight at age for the last three s used in the assessment Eploitation pattern: Average of the three last s Intermediate assumptions: Catch constraint Stock recruitment model used: Constant recruitment as described earlier Procedures used for splitting projected catches: Not relevant E. Medium-term projections Not done F. Long-term projections Not done G. Biological reference points No limit or precautionary reference points for the fishing mortality or the spawning stock biomass are proposed. Other issues None I References Albert, O.T., E.M. Nilssen, K.H. Nedreaas & A.C. Gundersen 2001a. Distribution and abundance of juvenile Northeast Arctic Greenland halibut (Reinhardtius hippoglossoides) in relation to survey coverage and physical environment. ICES Journal of Marine Science 58: Albert, O.T., E.M. Nilssen, A. Stene, A.C. Gundersen & K.H. Nedreaas 2001b. Maturity classes and spawning behaviour of Greenland halibut (Reinhardtius hippoglossoides). Fisheries Research 51: Boje, J., & N.R. Hareide Trial deepwater longline fishery in Davis Strait, May-June NAFO SCR Doc. 93/53, Serial No. N2236, 6 pp. Borkin, I.V Results from research on ichthyophauna in the Frantz-Josef Land area and north of Svalbard. In: Research into biology, morphology and physiology of marine organisms. USSR Academy of Science Publishers, Apatity, pp (in Russian). Bowering, W.R. & W.B. Brodie Greenland halibut (Reinhardtius hippoglossoides). A review of the dynamics of its distribution and fisheries off eastern Canada and Greenland. -Pp in: Hopper, A.G. (ed.). Deep-Water Fisheries of the North Atlantic Oceanic Slope. Kluwer Academic Publishers, Boston, USA. Bowering, W.R. & K.H. Nedreaas A comparison of Greenland halibut (Reinhardtius hippoglossoides, Walbaum) fisheries and distribution in the Nortwest and Northeast Atlantic. Sarsia 85: Fedorov, K.Y Zoogeographic characteristics of the Greenland halibut (Reinhardtius hippoglossoides, Walbaum). Journal of Ichthyology 11:

11 ICES AFWG REPORT Godø, O.R. & T. Haug Migration and recruitment to the commercial stock of Greenland halibut, Reinhardtius hippoglossoides (Walbaum), in the Svalbard area. FiskeridirektoratetsSkrifterSerieHavundersøkelser 18: Godø, O.R. & T. Haug A review of the natural history, fisheries and management of Greenland halibut (Reinhardtius hippoglossoides) in the eastern Norwegian and Barents Seas. Journal du Conseil. Conseil international pour l'eploration de la Mer 46: Nizovtsev, G.P Distribution and age-length characteristics of Greenland halibut (Reinhardtius hippoglossoides Walbaum) catches in the Barents sea in Trudy PINRO,23: (in Russian). Nizovtsev, G.P Distribution of young Greenland halibut in the Barents Sea and in the eastern Norwegian Sea. Rybnoye khozyaistvo, 12:26-28 (in Russian). Nizovtsev, G.P Recommendations on rational eploitation of Greenland halibut stocks in the Barents and Norwegian seas. USSR Ministry of Fisheries, PINRO, Murmansk, 93 pp. (in Russian). Shuntov, V.P Distribution of Greenland halibut and arrowtooth flounder in the northern Pacific.Trudy VNIRO, 58: (in Russian). Whitehead, P.J.P., M.-L. Bauchot, J.-C. Hureau, J. Nielsen & E. Tortonese Fishes of the North-eastern Atlantic and the Mediterranean. UNESCO, Paris, France, 1473 pp.