This paper not to be cited without prior reference to the author

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1 This paper not to be cited without prior reference to the author nternational Council for the Exploration of the Sea 1990 Demersal Fish Committee C.M. 1990/G:41 CELANDC NVESTGATONS ON THE OCEANC STOCK OF S. MENTELLA N THE RMNGER SEA, N 1989 AND N by Jakob Magmlsson and Jutta V. Magmlsson Marine Research nstitute Reykjavik, eeland ABSTRACf Oceanic-type mentella was mainly caught in m depth, in 5-6 C. The overall average size was lower in 1990 than in 1989 and males were in majority. S. mentella is heavier than the oceanic-type mentella. The infestation by Sph lumpi is higher in females than in males. The most important food components are euphausids, amphipods and copepods.

2 2 ntroduction.,, The oceanic type mentella is considered to be aseparate stock (1990; a and b). The fishery on this stock in the rminger Sea and adjacent waters has been carried out since The historic background has been briefly described by MagOllsson (1983) and Pavlov et al. (1989). The USSR fleet has dominated in this fishery from the very beginning. But the fleets of other nations have also participated : Poland in most years from the beginning, the DDRjoined in in 1983 and Bulgaria in The Faroe slands pariticpated one year (1988). n 1989,the celandic fleet cornmenced this fishery as wel as Japan,and the Norwegian fleet followed in The total nominal catches reported for the fishery on theoceanic-type mentella were about tons during the three first years,reached its maximum in 1986 with about tons,then declined to tons in 1987 and 1988 but dropped to tons in According to Soviet data (1990 b),the CPUE declined during this period from almost2 tons/hr to 1 ton/hr while the total effort tripled from 1982 (30400 hrs) to 1988 (91419 hrs) but dropped to about hrs in The celandic research on this stock carrled out in the seventies (Magnusson 1972,1977; Magnusson & Magnusson 1977) and in the early eighties (Magnusson 1983) was resumed at the beginning of the celandic fishery for the oceanic-type menteha in Provisions were made to cohect material on various aspects of its biology. Some of these are dealt with in this paper,both from 1989 and Material and methods. The material from 1989 was cohected on board 2 commercial trawlers participating in the fishery,n May-June~ n 1990,besides being cohected on board cornmercial trawlers,data from a short research vessel trip mainly aimed for an acoustic survey were also available and are dealt with here as weh as the data from 1 commercial trawler,in April-May. The fish was measured to the nearest cm. The sex and the stage of maturity were determined (stage : mmature,stage : Riperiing,stage : "Spawning",stage V: Newly spent). The weighing was carried out at sea and in the laboratory after thawing of frozen sampies. Detailed observations were made and categorized on the visual external abnormalities such as infestation of Sphyrion /umpi,coloration etc. Further,observations on the frequency of "dark spots" in the muscles of the fish were made. Some of these observations are reported on in the paper. A temperature recording device was attached to th~ head rope of the pelagic trawl and the temperature was recorded during the hau!. The ageing was carried out by Dr. Kosswig,Bremerhaven,FRG. The notes on the feeding are based on observations during the sampling. The results of a stornach sampling programme are not yet available.. Results. Acoustic trials. The research cruise in 1990 was mainly aimed as a trial for using acoustic devices for assessment purposes during the "spawning" period. The results were not satisfactory because of acoustic disturbances which could not sufficiently be

3 3 separated from the redfish traces. Another time of the year is considered more appropriate for these purposes (Pavlov 1989). Fishing depth and temperature.. n both years,the main fishing depth was 300 to 400 m,in temperatures between 50 and 60 C. Fig. 1 shows the temperature distribution in a west-east transsection at 'N. The eastern most station (nr. 198) is located above the Reykjanes Ridge. The largest catches were obtained between the stations nr. 207 and nr. 201,in particular nr. 205 and 203 which are appr. 25 n.m. apart. These observations are in good agreement with those made in 1983 (Magnusson 1983). Length distribution. n Fig. 2,the size distribution is shown from samples taken on board commercial trawlers in 1989 and 1990 and from samples taken during a research cruise in' 1990; n 1989,the bulk of the fish were in the size range of 35 to 39 cm while in 1990,in the comrnercial catches,the corresponding bulk was in the size range from 33 to 37 cm and in the research vessel catches,it was within 34 to 38 cm. n 1989,the mode was at'38 cm while in 1990,it was at 35 cm both for commercial and research vessel catches. The overall average size was less in 1990 than in Sex composition and maturity. n 1989,females were twice as many as males in the comrnercial catches or 68.3 % but in 1990,the females also dominated in the research vessel catches (64.5 %) while the males were in majority in the comrnercial catches (58.7 %). No significant differences were observed in the maturity stages'between the two yearsexcept for the fernales. n 1989,the majority of the fernales were recorded as newly spent (stage V) while in 1990, a higher proportion of the fernales were still in spawning condition (stage ),Le. appr. 34 %. The explanation is that the 1990 observations were made a few weeks earher than in As expected,most of the males were in the ripening phase (stage ) while hardly any were recorded as immature (stage ). Weight. During 1989, both S. mentella and the oceanic type mentella were weighed. Tbe results were compared and aconsiderable difference in the.weight-length relationship was observed (Fig.3). S. mentella was much heavier (w = L3.0406) than the oceanic type mentella (w = L2.7570). Thus,e.g.,at a length of 37 cm,the average weight of S. mentella was 674 gr but for the oceanic type mentella,it was 623 gr. Differences in the length-weight relationship were also observed between males and females (Fig. 4 ). The females (w= L3.2930) were heavier than the males (w = L3.0375). A comparison of infested oceanic type mentella to specimens without visual external infestation did not show any differences in weight.. Age. n Table 1,the age composition from sampes taken in 1989 totalling 189 specimens is shown. According to this age reading,the five year'classes 1971 to 1975 (14 to 18 years od) dominated in the catches with 71 % while in 1990,about 70 % were of the year classes 1972 to 1976 (13 to 17 years od).

4 "". 4.. ' nfestation by Sphyrion lumpi and abnonnalities in the pigmentation.' Orie of the most striking peculiarities in the oceanic type mentella is the infestation by sphyrion lumpi (Fig. 5 ). This parasitic copepod can be located almost anywhere on the fish,usually as single specimen but frequently also in groups in particular in. the anal region of the females. The same is true for the u1cers from the remnants of the parasite. Further,red and black spots or a mixture of both appear on the skin of ' the fish. Finally,dark spots are observed in the muscles.. n 1989,71.4 % and in 1990,62.7 %. of the examined fish were found to be externally infested. n Table 2,the incidence of external infestation and abnonnal pigmentation in infested fish is shown for both sexes combined,in 1989 and t should be kept in mind that many fish bear more than one of the categorized abnonnalities. The highest incidences were recorded for remnants and black spots in b9th years. However,the incidences of abnonnalities are higher for females than for males.. Thus,in 1989,76.1 % of the females and 61.4 % of the males were infested,and in 1990,the corresponding figures are 71.4 % and 50.9 % resp. Dark spots in the muscles were very common. The observations of 1989 in this respect have not yet been tabulated but in 1990,55.6 % ofthe 820 examined fish were recorded with spots in the muscles ofwhich about 15 % were heavily infested. Notes on the food. The most common food components.were euphausids,amphipods and copopods in both years. Less frequent in the food were chaetognaths. Only occasionally small cephalopods,gastropods and fish were recorded. n the northern part of the area fished by the commercial vessels,usually the euphausids dominated but the amphipods were frequent,too. Dut in the southern part (towards 59 0 N and south of it),the 'amphipods dominated and there, the copepods. were the second most impo'rtant food componenl.'. Discussion. n communication with the captains of the commercial fleet, they stated that they often got good catches in temperatures below 50 C and that in 1990,the fish. appeared to be better looking than in the previous year. These observations might.. be explained as follows: Males were in majority in the commercial catches at that. time,in They might have beeri found in temperatures somewhat lower thanthe preferred temperature for "spawning" (see also Fig. 1). According to Pavlov et a1. (1989),males prevailed in the catches in Sepl.-Ocl. but females from April to August. Apparently,at least in 1990,the males fonned concentrations at the border of the "spawning" zone. Obviously,the celandic fleet had been fishing in such male concentrations (at the time of the "spawning" of the females). " According to our. observations the males are less infested than the females, in particular by Sphyrion. lumpi which might explain the better appearance rather than a decreased infestation of the stock. Bakay et a1.(1988) reported,however, that there were no differences in the infestation of males and females. The overall average size in 1990 was less than in These size differences between the two years could partly be explained by the dominance of males in Also,according to the size and age distributiori,younger year classes appeared to be. more numerous in 1990 than in 1989.

5 5 The distinct difference in weight between S. mentella and the oceanic type mentella and the high infestation rate of the latter one are further indications for a separate stock. References Anon.,1990 a: Report of the Study Oroup on Oceanic-Type Sebastes mentella. CES,C.M. 1990/G:2 Anon.,1990 b: Report of the North-Westem Working Group. lces,c.m. 1990/Assess: 20' Bakay,YJ.,1988: Application of results from parasitological investigations in redfish (Sebastes mentella Travin) populational structure studies.ces,c.m.1988/g:35 Magnusson,J.,1972: Tilraunir til karfaveioa meo miosjavarvörpu i uthafinu (English summary). iegr,21.tbl. Magnusson,J.,1977: Pelagic Redfish in the rminger Sea. Distribution and Abundance.CES,C.M. 1977/H:43 Magnusson,J.,1983: The rminger Sea -Oceanic Stock Redfish. "Spawning" and "Spawning Area". CES,C.M. 1983/0:56 Magnusson,J. &J.V.Magnusson,1977: On th6 Distinction between Larvae ofs. marinus and S. mentella. Preliminary Report. CES,C.M. 1977/F:48 Pavlov,A.., V.S.Mamylov,A.S. Noskov,A.N. Romanchenko, A.V. vanov,1989: Results <;>f USSR investigations of Sebastes mentella Travin in (CES Subareas X and XV).CES,C.M :17

6 6 Table 1. Oceanic-type mentella. Age/length relationship. Sampie from Age Year - Number ML dass Table 2. Oceanic type mentella. ndicence ofvisual external infestation and abnormal pigmentation No. of infested fish No.offish % No.offish % Sph.lumpi Remnants Red spots Black spots Mixed spots

7 7 St D.m. )--.=.:r.:...---t-=------=:..r-=---=r---=-r:...:...-~-_.., aa '2.aa 4,5 5,5 6,a 6,:', '...,.-",--" '-...,, "" : ",, ' " ~,C) '5,'5' 6,5 Fig. 1. Temperature distribution on a west-east section at 'N between 28 S0'W and 31 40'W.

8 8.% Commercial catches n= ML:: Commercial catches n= M...= Research vessel catches n=1l05 ML:: t-rr-lrr-1--rT...--r-rr-r-r...T"T""T'""1'4f-':h...-r--rT--rT...--r..,..,,..-T=M CM Fig.2. Oceanic-type mentella in 1989 and Length distribution.

9 .. 9 g cr S.menlella 0 Male n=2147 n= r 2 = r 2 = Female Occanic mcnlcla 1200 n=507 r 2 = =1391 r 2 = CM crvl Fig.3. S. mentella and oceanic-type mentella. Fig.4. Oceanic-type mentella. Length/weight relationship, in Length/weight relationship by sex, in J 2 Fig. 5. Oceanic-type mentella, External infestation. 1. Black spot 2. Red spot 3. Mixed pot 4. Ulcer 5. Sph lumpi, single. 6. Sph. lumpi, group.