FISHERIES AND ►4AARINE SERVICE Translation Stleries No. 3081
Spawning of the Alaska pollock Tfzera a chalcoc^ramma (Pallas) in the ncrtheastern part ô^ t^Bering Sea
By I.I. Sérobaba
Original title: Nerest mi.ntaya Theraqra dzalcoqranana (Pallas) v sevexn-- vOstocnnoi ctias.t
From: Izvestiya T•ikhookeanskogo Nauchno-Issledovatél'skogo Tnstitùta -Rybnogo.Rhozyaistva i Okeanografii (TINRO) Voprosy ikiztiôlogii_ (Proceeclings of the Pacific Scientifiç ibseàrch Institute of:Marine . Fisheries and Oceanography (Prc,blem5 relating to ichthyolcgy) ); 8(6(53)) : 992-1003, 1968 `i'ra,nalàted by the Translation Bureau ( GAD) 1.2u•1.ti13n8ua1 Services Division. Departmqnt of the Secretary of State of Ganada
ïlepmrtment of the EnerironmQnt Fisherieffi. and Marine Service Biological Station Nanaimo, B..G. 1974
27 pages typescript ,
• DEPATMENT OF THE SECRETARY OF STATE SECRÉTARIAT D'ÉTAT TRANSLATION BUREAU BUREAU DES TRADUCTIONS
MULTILINGUAL SERVICES DIVISION DES SERVICES
DIVISION MULTILINGUES
F15-4_,3 ôjjizi TRANSLATED FROM — TRADUCTION DE I NTO — EN Rus sian English AUTHOR — AUTEUR 1.1. Serobaba
TITLE IN ENGLISH — TITRE ANGLAIS Spawning of the Alaska pollock Theragra chalcogramma (Pallas) in the northeastern part of the Bering Sea
TITI- E IN FOREIGN LAIIGUAGE ( TRANSI I TERATE FOREIGN CHARACTERS) TITRE EN LANGUE ÉTRANGÉRE (TRANSCRIRE EN CARACTLRES ROMAINS) Nerest mintaya Theragra chalcogramm% (Pallas) v severo-vostochnoi chasti Beringova morya
REFF.RENCE IN FOREIGN LANGUAGE (RAME OF BOOK OR PUBLICATION) IN FULL. TRANSLITERATE FOREIGN CHARACTERS. RÉFÉRENCE EN LANGUE ÉTRANGÉRE (NOM DU LIVRE OU PUBLICATION), AU COMPLET, TRANSCRIRE EN CARACTÈRES ROMAINS. Voprosy ikhtiologii
REFERENCE IN ENGLISFI — RÉFÉRENCE EN ANGLAIS Problems relating to ichthyology
PUBLISHER ÉDITEUR PAGE NUMBERS IN ORIGINAL DATE OF PUBLICATION NUMÉROS DES PAGES DANS Not given DATE DE PUBLICATION L'ORIGINAL 992-1003 YEAR ISSUE NO. VOLUME PLACE OF PUBLICATION ANNÉE NUMÉRO NUMBER OF TYPED PAGES LIEU DE PUBLICATION NOMBRE BE PAGES DACTYLOGRAPHIÉES Not given 1968 8 6(5'3) 27
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PERSON REQUESTING Dr Sotie Westrheim, Nanaimo DEMANDÉ." PAR
YOUR NUMBER VOTRE DOSSIER 11 0
DATE OF REQUEST 1974 DATE DE LA DEMANDE January 28,
SOS.200-10-6 (FI E V. 5/68) 7 G30-21-029-5333 DEPARTMENT OF THE SECRETARY OF STATE SECRÉTARIAT D'ÉTAT
• TRANSLATION BUREAU BUREAU DES TRADUCTIONS
MULTILINGUAL SERVICES DIVISlOh! DES SERVICES DIVISION MULTILINGUES
CLIENT'S NO. DEPARTMENT DIVISION/BRANCH CITY NO DU CLIENT MINISTERE DIVISION/DIRECTION VILLE
Environment Fisheries Service Nanaimo, B.C.
BUREAU NO. LANGUAGE TRANSLATOR (INITIALS) NO DU BUREAU LANGUE TRADUCTEUR (INITIALES)
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Voprosy ikhtiologii, Vol. 8, No. 6 (53), 1968, pp 992-1003.
ION UDC 597.0/5-11. I V Spawning of the Alaska pollock Theragra chal.cogramma' ";"tDUC , (Pallas) in the northeastern part of the Bering Sea By I.I. Serobaba (Pacific Ocean Scientific Research Institute of Fisheries and Oceanography - TINRO - Vladivostok). 992* The spa^,ming area of the Alaska pollock, which inhabits the northeastern shelf of the Bering Sea, is bounded by the ice- edge on one side and the continental slope on the other. The spawning grounds extend along the 50-300 meter isabaths from Unimak Island to 179° W.L. The total area of the spawning grounds is 175,000 lr.m2. Spawning takes place from the end of February until June. The eggs of the Alaska pollock are distributed r,iainly at depths of 50 to 300 meters. The greatest amount of eggs is observed in the southeastern area of the spawning grounds. *Nnmbers in the right-hand margin indicate the corresponding page numbers in the original. SOS-200-10-31 7530-21-029-5332 2. Soviet and foreign researchers (Rass 1949, 1965; Gorbunova, 1952; Pertseva-Ostroumova, 1961; Thompson and Van Cleve, 1936) have proven that the method of estimating the quantitative distribution of eggs is sufficiently accurate for the determination of the places, time and conditions of spawning. In addition, it is possible in practice to estimate the size of schools of spawning fish according to the abundance of floating eggs /Rass, 1949; Vedenskii, 1949; Kashkina, 1965/. Due to the fact that the number of eggs shed exceeds by tens and hundreds of thousands of times the number of spawning females, it is much more easy to find the floating eggs in the sea than the less numerous spawners, which are in addition much more difficult to catch /Rass, 1965/. Material collected in connection with analyses of mature in- dividuals only is insufficient to determine the conditions and nature of spawning. The fish car be in a prespawnirg condition for a long time before shedding eggs. In addition, females sometimes eject eggs as a resuli of the mechanical action of the fishing gear. Therefore, in study- ing the biology of the Bering Sea pollock on the expeditionary ship "Seskar" of the Far Eastern Scientific - Commercial Exploratory Fishing Service of the Pacific Ocean Scientific Research Institute of Fisheries and Oceanography (DDNPPR TINRO), in the spring-summer period of 1965, we carried out an ichthyoplankton survey to determine more precisely the time and areas of spawning of the pollock. The work site was the shelf of the northern and eastern parts of the Bering Sea from Unimak Island to Cape Navarin. 1 Ichthyoplankton was collected with a standard conical net (IKS- 80) at depths of 50 to 1000 meters. Samples were taken by the methods of vertical total and surface catches at'all stations, except for those stations where for any'reason it was not possible to use one of the methods. 3. In all, 333 catches were made» 190 samples were taken by the method of total catch; in these the eggs of the Alaska pollock were discovered at 116 stations, while larvae were also found at some stations (figure 1 and 2). The material collected was processed in the laboratories of Moscow University and the Institute of Oceanology of the Academy of Sciences of 1 the USSR (MGV and IOAN) . Maps of quantitative distribution were compiled by interpolation 993 according to the results of the egg count (Zaitsev, 1935). To determine spawning sites, catches of eggs which were at initial stages of develop- ment were plotted on the map, and to obtain a picture of the drift of developing eggs, maps were compiled of the quantitative distribution of eggs at later stages of development/Rass, 1949/. The results of. the vertical catches only were used in preparing maps. Eggs were measured by means of an eyepiece micrometer. The stages of egg development were determined according to the 4-point scale of Rass, /1933, 1946/which is used in processing mass collections, and on this basis the percentage ratio of stages of development in the sample were calculated in order to judge the time and progress of spawning of Alaska pollock. Two ichthyoplankton surveys (figures 1 and 2) were performed in the water area of the shelf from Unimak Island to Cape Navarin in the spring-summer period. The region of the first survey was bounded by ice- edge, and the outer stations were sometimes located among ice fields. The ichthyoplankton survey was begun in the middle of February. Work was carried out in the water area from Unimak Island to the Pribilof Islands 1 The author would like to express hi S sincere thanks to Professor T.S. Rass and A.A. Kashkina for their valuable advice and critical comments. 4. 170 ieo CO 65 170 160 • Pile. 1. Pam:owl:el-me ux.mormanIzTonumx CT8.11Mlii n ceBepo-Boczolmort na- Bepuuropa. mops' ( .fapT — Mail 1965 r.). 1— BeFrimaahnue li ropu3ormah- Flb10 310B11; 2 — BepTiniaamme :rionbl; 3 — 11013epX110CT111,10 1130TOPMLI Figure 1. Location of ichthyoplankton stations in the northeastern part of the Bering Sea (March - May 1965). 1 - vertical and horizontal catches; 2 - vertical catches; 3 - surface isotherms; a - St. Matthew Island; b - Nunivak Island; c- Pribilof Islands; d- Unimak Island. at the end of February and beginning of March, where some individuals had already begun to spawn. Alaska pollock eggs were found for the first time on February 27th. Single egg finds were also recorded on March 9th and 12th. Eggs began to be found in massive amounts (up to 100 and more 2 eggs per 1 m ) only at the end of March. In the second half of March and in April, observations were carried out only in the area of the Pribilof Islands. Unfortunately we were unable at this . time to carry out work near Unimak Island, where large prespawning accumulations of pollock were forming. Still, it is possible to estimate the time of beginning of spawning according to 5. data Obtained in the Pribilof region at the end of March (110 eggs per 2 1 m ). All the eggs taken were at the initial stages of cleavage. Up 2 to 70 prolarvae and larvae of Alaska pollockperim were observed here, apparently brought by the current from the southeastern part of the sea. Abcordin.g to the data of A.K. Leonov /1960/, the rate of movement of the 'Pacific Ocean water masses along the Aleutia.n island chain and in the 994 seutheastern part of the Bering Sea reaches 0.3 m/sec. It is of course doubtful that these larvae could have developed from eggs shed here, «since hydrological conditions in this area are much more severe than in the southeastern part of the sea.- In -April, work was carried out to the west of 1700 -where the :region 'under study was -delimited by -natural «boundaries - the ice- -edge on the -northeast and -the drop-off on the southwest,. .Alaska pollock -egg's were observed here at almost all stations, even amidst ice -with a ,below-freezing temperature of surface and bottom layers of water (1...4 ;degrees) . :EXperimental trawl :fishing -in open patches between ice produced a :inimber of -spawning individnals. . 1‘1‘.N. coOrbunci-Va 11954*/ :observes that :in spawning the _Alaska pollo.ck ,aVoids --regiOns -Where :the ;water temperature zis .b:elow a ° :and spawning zapparetitiy doe -s :not -take :Place :at all «-beneath the ice. This zdo.e-s -_not seem Ito ',-us to :apply to the -Alaska --pcillock :in the . ea-stern ;part zaf the 33ering 'Sea -espeCial Iÿ Since -N,,N. ,Gcirbunova «herself experimentally :d -emonst r at ed '-that larvae 'really -broad ,dev-elop temperature :of -- l.L3 (degrees. EDur- :sing the eXpériments, -Alaska .pollock -eggs survived za (decrease in - water temperature --even to 12,2 -d-egrees 1-Gorbunova; :1954/. That - the Alaska ,995 7pollock -in spawning avoids regions with very :-low :temperatures .apparently 'applies :mainly to the populations -inhabiting the - middle .and so.uthern :regions Of its extensive range (Sea of japan. Sea -'of -Okhotsk, _etc.) where :spawning 6. ^a o ^^.:^^•`.^`^:.•- ^ . . 86 ^ O O^^' ^ t. •.f::^^c;' ô^6^ ';'•,S:;y:: ,2 0. Co. Jlanpenr:Es yC O ^1 O O O ' O O O ^ O. Cu AiaTeeA O. {^V . :.. :. ,• E ^J k^O O O ^O OO o Hyx:^aak . o^J o o C O O O OO p O CO 0^ . O O ^? OJ i C^ JO ' 6 O O S O ^ o-oa 7: 1 O (.b O 0 n^^^^ 00 0 6unoea^ do O O ' O o 0 O 5C^ pC^ O , I3 ^ V 4 01I ^ O O L 170 PIIC. 2. Pc1CllOJIOiN@HIIF; II1TI10IIJIAIIIiTOIIIIbL1 CTcZIiI[IIIÏ B COBO- r0-BOCTOqII0H ri1CT1I F .?CPIIHI'OBa;1tOPA (II 1011b ^IIIOab 196a r.) 1 - CTiIIIijTIII; 2 - CTclHL(IIII, ï{1 ICOTOPb[Y OT\I(;rIB$b: 11IiPc1 It JIIILIIiIIKII (B TIIICJIIITOJIe JiIILIIII[KII, IIIT,; . B 31IB.lI0HdT(3JI0•- RO- JIIVICCTBO LuipbTE IIT.); 3 - AOBOPYiIOCTIIble II30TePJIbI Figure 2 Location of ichthyoplankton stations in the northeastern part of the Bering Sea (June - July 1965). 1 - stations; 2 - stations at which eggs and larvae were observed (in numerator - number of larvae; in denominator - number of eggs); 3 - surface isotherms; a Saint Lawrence Island; b - St. Matthew Island; c - Nunivak Island; d Pribilof Islands; e - Unimak Island. t 7. takes place during the period of the spring warming up of waters. In the southern regions of the area.of distribution, where coastal waters are not'covered with ice in the winter, Alaska pollock spawning begins at the time of the fall decrease in temperature of upper layers of the sea and is completed when warming up of waters begins. In northern regions, spawning•begins in the early spring after the ice melts /Gorbunùva, 1954/. Spawning of the Alaska pollock usually lasts several months. There is very little published information on the spawning of Alaska pollock in the Bering Sea. In addition, Alaska pollock eggs taken in the Bering Sea were often mistaken for cod eggs. Alaska pollock eggs were gathered in the northwestern part of the Bering Sea only in July - September, but on the basis of findings, researchers assumed that the spawning of Alaska pollock takes place in the spring, only slightly later than it does off the coast of Kamchatka, where the Alaska pollock begin8 to spawn in the first half of April /Gorbunova, 1954/. In the northwestern part of the sea, the greatest number of Alaska pollock eggs was observed at depths of 13 to 145-meters. Spawning of the Alaska pollock in the waters of the Commander Islands and the Pribilof Islands takes place earlier than in waters off the continent, and begins in the first days of March /Kashkina, 1965/. Some regions of the Bering Sea, which penetrate especially deeply into the American and Asiatic continents (Norton Bay and Anadyr Gulf), become very cold due to severe, prolonged winters and have many features in common with Arctic Seas. From the end of November until July the northern half of the sea is covered with almost compact pack ice which remains in the northwestern part until as late as the middle of July. In this case,-the water of the upper layer is cooled to a depth of 200-300 8. meters. Usually only the upper 30-75 layer of water has time to warm up in the summer. Underneath this there remains a layer of permanent cold water (from 1.7 to + 2.5 0), which warms up only slightly even in the favourable conditions of the summer season. The thickness of this layer varies in different areas of the sea (from 20-30 to 200 meters). In the southeastern part of the Bering Sea, which is greatly influenced by Pacific waters, the winter temperature stratification is completely destroyed in the spring and summer as solar radiation increases and the warming of the surface layer of water is speeded up, and a cold intermediate layer is not formed /Leonov, 1960; Natarov, 1963/. In the winter, the Alaska pollock, avoiding severe conditions on the shelf, moves into the deep warm zone. Since the upper layer of water cools to a different extent in different parts of the sea and the upper boundary of the abyssal water mass is also located at different levels, the Alaska pollock winters at different depths depending on geographical location. In the northwestern part of the Bering Sea, cooling sometimes extends down to 300-400 meters in severe winters. In the shallow part of the sea, winter cooling reaches the bottom, and for this reason there is no warm abyssal layer here at all /Leonov, 1960/. Çonsequently, the Alaska pollock is forced to leave these regions. Hydrological spring is delayed here, and in addition a cold intermediate layer of water persists even in the summer. Under the influence of these factors (directly or indirectly affecting the distribution of food items), the Alaska pollock after some delay migrates for spawning and foraging to a narrow shelf in the northwestern part of the Bering Sea, to a thin (30-80 meters) warmed-up layer of the surface water mass. P.A. Moiseev /1952, 1953, 1953a, 1963/ points out that species with 9. pelagic eggs and larvae spawn in shallow coastal regions having a circular 996 current,system, whiCh must keeP . the eggs and larvae from being carried off to places with unfavourable conditions. In this way, these fish, themselves actively bring the eggs into regions with favourable conditions (spawning migrations). In some areas of the sea, migrations of Alaska pollock are also observed in the spawning period into the coastal zone or into areas with circular currents. The existence of these is mentioned by S.M. Kaganovskaya /1958/ and A.A. Kashkina /1955/. A somewhat different picture is observed for halibut, the eggs and larvae of which also develop in the water mass. According to V.P. Shuntov /1966/, halibut reproduce in regions (on the continental slope) with currents having constant direction, which carry the bathypelagic eggs and pelagic larvae into shallows, where there are whirlpools preventing the drift of eggs and larvae to greater depths. The Alaska pollock in the northeastern part of the Bering Sea reproduces in the warm layer of the Pacific Ocean water mass, for the most part at depths of 100 - 300 meters, and its spawning is confined not to • shores, but to particular hydrological conditions, in this case to the specific conditions of the continental slope and adjacent waters . (Serobaba, printing). Despite the fact that spawning of Alaska pollock begins in the hydrological winter, the ice fields covering the waters of almost the entire shelf and Part of the continental slope of this area of the sea do not impede its development. Pacific ocean waters penetrating the Bering Sea enter the shallow zone.. to a considerable extent forming there a number .of stable whirlpools /Leonov, 1969, Natarov, 1963/. This creates favourable conditions for the drift of pelagic eggs and larvae of the Alaska pollock into the shallows, into regions with circular currents enriched during the inter with 10. ,70 too o. Cu. Marsc. ' ^{^ • so . - -_ _- b o aaC - - q pffGanoea _^ÿ,•is t i 7, L]: ^^ W S ^-^- u;.s 66 ^1^' ^ ^1_1. 7`l^V ^ ^YHNMLH [M2 p;i^ .. (^^^Tj} a; ^^ W1il.LLll3 • -"^=^ . 7 ffM4 170 i6o PIIC. 3. Pa01IpegoJI0731I0 IIKP6I INIIIIITIFI B H[aPTO- ria0 1965 r. (IIIT. IIO•I( 1)6, ^. X- 1--50; 2- 51-100; 3-- 101-200; 4 - 201-500; 5 - 501-1000; 6 - 1001-2000; 7 - Go,nee 2000 nu. noA 1.0 Fig. 3. Distribution of eggs of Alaska pollock in March - May 1965 (number per 1 m2) Z - 150; 2 - 51 - 100; 3 - 101 - 200; 4 - 201 - 500;5 - 501 - 1000; 6 - 1001 - 2000;7 - more than 2000 per 1 m2. a - St. Matthew Island; b - Nunivak Island; c- Pribilof Islands, d--.Unimak Island. -11. biogenic salts and oxygen /Natarov, 1963/. In 1965, spawning of Alaska pollock began in March. It took place rather intensively over the entire area of the spawning grounds; mass spawning was observed at the end of April. Alaska pollock eggs were caught over depths of 60 to 300 meters, but hardly any eggs were found below 360 meters. Thus, over a depth of 1000 meters, despite the steep- ness of the continental slope and consequently the short distance from the lower shelf edge, where spawning for the most part takes place, we caught only I egg. Table 1 Percentage ratio of eggs of Alaska pollock at different stages of develop- ment in the eastern part of the Bering Sea (results of vertical catches) ? Gramm paaenTila 4 CT:I1,1111 p113111ITIIII 301 3 E-• - . . ,.... Meenu,b/ menum q III IV I II III Iv '',:."•= I II 1 x ... 1 23,9 31,8 40,8 3,5 586 Map' 100,0 — — — 59 Ilionh 7 50,0 35,7 7,2 7,1 14 Aupe:m 53,1 30,7 16 3 2 — 278 Moab 8 Maii 33,0 31,1. 28,1 2,8 3463 Key to table 1 1. - months 2. - stages of development 3. - number of eggs 4. - March 5. - April 6. - May 7. - June 8. - July 12. In March and April we worked only in the central area of the northeastern shelf (region between'Pribilof Islands and 179° W.L.). The southeastern part of the sea remained unstudied,.but considering the favourable hydrological conditions of this region, one can assume that spawning began there Somewhat earlier than in the western region. The eggs shed were distributed very irregularly over the entire water area.studied. In the western region, the maximum number of eggs 2 1 m did per not exceed 50 (figure 3). 2 In the eastern region, the maximum number of eggs per 1 m ex- ceeded 2000. In March,all of the eggs taken were in the stage of cleavage (0 - 1 stage, according to Rass). In April catches, around 30 percent of the eggs were in the primitive streak stage (stage II of development). During this period some of the eggs were at the stage of thee - unformed 2 embryo (stage III), and the number of eggs per 1 m was markedly greater. Consequently, the intensity of spawning had also increased, and judging by the distribution of eggs at stages of development 0 and I, spawning lasted 4 months (March - June) (Table 1, figure 4). The climax of spawning took place in May, when catches were at'a maximum and eggs at the initial stages of development predominated. At the same time, about 30 percent (table 1) - of eggs were at the III stage of development. We cannot assess the age of eggs at the stages of the unformed and formed embryo (III and IV stages), but according to N.N. Gorbunova /1954/, eggs reach these stages of development in Eastern Kamchatka at the age of 2-3 weeks. Because of increase in their specific gravity /Gorbunova, 1954; Zooten, 1961/, the Alaska pollock .eggs gradually sink beneath the surface layer during the process of development. Due to quasi-stationary circular currents preventing the drift of eggs to great 13. 60 170 • * ' O. C o. M arct eP ili 60 60 • O. Flynn.. a. b C e o-ja 11 160notia . _ d - — — – — - --i-e." r -_- ,:>:.:,.. ...... IIII 12 il .7.., U MI6 ,:,,,,,,› ., • .. • 160 I i i . 170 Pire. 4. Pacnpeenerfne nimbi mamas' ria nanazumr. CTBAIISIX pasenTim B 4 — brapTe—MEIC 1965 T. (1.11.T. 110A 1 .1L2). 1 — 1-50; 2 — 51-100: 3 — 101-200; 201-500; 5 — 501 — 1000; 6 — 1001-2000; 7 — 6onee 2000 TUT. BOA .1t.2 Figure 4 Distribution of Alaska pollock egg2 at initial stages of development in - May 1965. (number per 1 m ). Z - 1 - 50, 2 - 51 - 100; 3 - 101 - 200; 4 - 201 - 500; 5 - 501 - 1000; 6 - 1001 - 2000; 7 - more than 2000 per.1 m2 : a - St. Matthew Island, b - Nunivak Island, c- Pribilof Islands, d -- Unimak Island. • 14. 170 160 V o. Cos...Mato. _•___ÇI";)_.• GO a • o. nynonait b .. c ' 0-80 np is.. e i _ . „.• 6 ..i. o. Yooriao MEll 2 :. MI] 3 . 4 170 M PUG, 5. Pacupene.nenne'nuple mairran na III n IV CTBALIRX paarnmin B mapTe — mao 1965 r. (nrr. no,g 1 ..n. 2). 1 — 1-50; 2 — 51-100; 3 — 101-200; 4 2— 201-500 MT. BOA Fig. 5 Distribution of Alaska pollock eggs at the III and IV stages of develop- ment in March May, 1965 (number per 1 m2 ). - 1 - 50; 2 - 5i - 100; 3 - 101 - 200; 4 - 201 - 500; per 1 m2 ; a - St. Matthew Island, b Nunivak Island, c - Pribilof Islands, d - Unimak Islands. 15. depths, the developing eggs remain in the spawning zone, carx'ied west- «ard only slightly (figure 5). In order to compare our findings on the period of maximum spawning activity with the results of an analysis of spawning individuals (Serobab.a, printing), we studied the change over 10-day periods in April and May of the percentage ratio of eggs at different stages of development (ta.ble 2). Table 2 Percentage ratio of eggs of Alaska pollock at different stages of develop- ment (1-965). CT1;[II1i Pa36ITTIIii E., ^- ( CTil;[i[fI pa38I1TIIH 7[euan^ I Iï I iïI i I Ÿ M o^ 3 Aelaltil `^ a' .^- r I II I_III I IVi^^rô c ôI 1 I I -- 5 11i a 4i %+ Ail peil s 0 44 '7 7 ,3 193 70,3 ' 68 3316 I 89,7 2 II I 49,tk I 30,4 39,6 0,fi 50,0 I 70,0 I `LO,0I 0,25 24 II I - 203 111 29,2 33,3I III ^i3,0 30,8 ..21,2 I Key to table 2 1 - 10-day period 2 - stage of development 3 - number of eggs 4 - April 5 - May 16. Table 3 Water temperature in the period of massspawning of the Alaska pollock 1411IWAMMe 11013CptillOCTI11,10 TCMIlepliTyphi 5 Temne )wryina . Paiimtm nepeeTa .An Top 41111111M ym marmym MIIIIIIMpt blit7ty4 1 3 3 6 BocTounan MaCTI) - 7 - 10 Depnarona ltopil --0,3 3,38 —1,4 3,3 Muni Ranirme [Oro - 13ocire*flioe moGepe;-nbe --0,4 3,44 --2,0 0,9 . 1-ZasigaT,:n 8 11 BucTonualf nacn, sanuna —0,7 0,50 0,0 1,5., roi)tiyaona, 1954 IleTpa Beamwro 11o6epewbe CeDepuoii Hopeu 0,9 3,50 5,0 8,0 Key to table 3 1 - spawning areas 2 - bottom temperatures 3 - minimum 4 - maximum 5 - surface temperatures - author 7 - our findings 8 - Gorbunova, 1954. 9 - eastern part of the Bering Sea 10 - southeastern coast of Kamchatka 11 - eastern part of Peter the Great Bay 12 - coast of Northern Korea Larvae in the I stage of development predominated until the second 10-day period in May, although there were many larvae in the II and III stages. Most of the more sizeable catches of eggs (sometimes up to 6,500 eggs were taken in 10 minutes with a gill-net in the surface layer) were taken in this period. The sexual products in sexually mature individuals at this time were in the IV, V, V-VI and II (sic!) stages of maturity (on the 6-point scale). The greatest number of eggs were found with a 17, temPerature of 0.9 to 3.3 degrees in both bottom and surface layers of water. N.N Gorbunova /1954/ shows that the water temperature at which the mass spawning of the Alaska pollock takes place in the different areas of its extensive range increases in surface layers from north to south, but changes little in bottom layers (table 3). Our data donot confirm this pattern. A decline in the intensity of spawning was noticeable in the third 10-day period in May, although an additional insignificant number of individuals spawned until the middle of June and catches of eggs at some stations reached 1000 and more per 1 m2 . Eggs at late stages of development predominated at this time. On a second survey at the end of June and in July, occasional catches of eggs, not exceeding 5 eggs in vertical catches, were observed. It is interesting that eggs at early stages of development predominated at this time. Apparently, the delayed spawning of solitary individuals took place in this-period. At the same time, Alaska poilock larvae and prolarvae were caught at some stations (figure 2). Eggs were found for the last time on July 23. N.N. Gorbunova /1954/ shows:that Alaska pollock eggs were found in Anadyr Gulf and Olyutorskiy Bay in August and September. So far, we have no data on ichthyoplankton of the eastern part of the Bering Sea for August, although there were no Alaska pollock eggs in September samples. Since no eggs were found at the end of July, one can assume that the spawning of the Alaska pollock in the eastern shelf takes place more rapidly than in the northwestern regions of the Bering Sea. In any case, the entire spawning period is shifted closer to the winter months. Foreign authors, sucha.s Kobajashi /1963/ also indicate earlier spawning of Alaska pollock in the eastern part of the Bering Sea. 18. In processing material, we measured the diameter of eggs caught at different times. Since the eggs were preserved in a 2% solution of formalin, it was necessary to introduce a correction coefficient for contraction (0.020-0.021 mm), as suggested by N.N. Gorbunova /1954/. The eggs of the Alaska pollock are larger in the Bering Sea (northwestern part) and the Sea of Okhotsk than in the more southern regions; their average diameter varies from 1.48 to 1.66 mm. In the Sea of Japan, Alaska pollock eggs are smaller - from 1.41 to 1.55 mm and sometimes eggs are no larger than 1.20 mm /Gorbunova, 1954/. The diameter of eggs of Alaska 1000 pollock from eastern areas of the Bering Sea is almost the same as that of eggs of Alaska pollock inhabiting the northwestern area of the sea, and the average diameter varies from 1.46 to 1.65 mm. Our findings once again confirm the pattern established by T.S. Rass /1941, 1948/, that the size of eggs is greater in individuals living in the northern part of the range of the species. T.S. Rass /1947/ remarks that within the limits of a given species, the average size of eggs of fish shed during the course of the reproductive season changes as spawning progresses. The sizes of eggs of Alaska pollock in the eastern part of the Bering Sea gathered at the beginning, middle and end of spawning, show that as spawning progresses, the size of eggs shed decreases (figure 6). Judging by published findings (Dement i eva, 1939; Rass, 1947; Berg, 1949; Gorbunova, 1954; and others), the size of eggs decreases as spawning progresses because of decrease in the sizes Of spawning females. The number of eggs caught at spawning grounds makes it possible to evaluate roughly the density and size of the spawning stock (Vedenskii, 1949; Kashkina, 1965); In the region under consideration, the maximum 2 number of eggs of Alaska pollock per m was greater than in the other areas shown in table 4, exCept for the areas on the eastern and western coast of 19. % 60 - 2 _ 1 /\ . / ■ A 40_ / \ / \..\ , _ 20. \ „.....„.f_.... / , , • . \ .., ,--./ ._... \. , . - .,0 2,0 1, 2 1,4 16, . .ftualemp ukpumne,e114' . a • B .P110. 0. TI3meueune AnameTpa unpinioe. milwrag• itpoixornmune nepecra. 1 -- Mau — ar(penb (n -,.= 759, 31« -,...- =1153 MT., M ----- 1,65 .n.n); 2 — hiaii (n= -----.1,50 ..st.it); 3 — mom, — monb (n ----, 207 MT, i'll" .----- .=----- 1,46 .mn) • Figure 6 Change in the diameter of Alaska pollock eggs during the course of spawn- ing. / - March - April (n = 1153, M = 1.65 mm); 2 - May (n = .759, M = 1.50 millimeters); 3 - June - July (n = 207, M = 1.46 mm. a - diameter of eggs, mm. Kamchatka. Consequently, it can be assumed that the spawning school of Alaska pollock in the eastern part of the Bering Sea ranks third among the in- dicated spawning areas in terms of density and size. 2 The area of the spawning grounds is equal to 174.5 thousand km and the total number of eggs in this area is 51,206.10 6 thousand (table 5). 20. Taking the average fecundity Of the female Alaska pollock as equal to 440 thousand eggs (Serobaba, printing), it.is possible to determine the number of females corresponding to the total number of eggs laid, but the specific character of spawning of the Arctic pollock must be taken into account. In one spawning period, the female sheds only 2 batches of the eggs in the ovaries /Gorbunova, 1954; Serobaba, printing/. The third group of eggs is apparently shed in the following spawning period. Consequently, the average number of eggs laid by a female during the current spawning, is two thirds of absolute fecundity - 293 thousand eggs, or 300 thousand eggs as a round figure. Spawning of Alaska pollock is very prolonged. While the last batches of eggs are maturing in the ovaries, the incubation period of eggs which have been shed is coming to an end, lasting 20.5 days at an. average temperature of 3.40 /Gorbunova, 1954/. Thus, we counted only a certain part of the eggs laid by each female taking part in spawning. If this part is assumed to be one half of the eggs (146 thousand eggs) laid by a female during the entire spawning period (or one third of absolute fecundity), then the number of spawning females is 305,726 thousand (51,205,991•106: 146,000). Assuming that the ratio of the sexes for the Alaska pollock is 1001 one to one, it is possible to estimate the total number of spawners taking part in spawning. Since the average weight of spawning Alaska po'llock individuals in catches is equal to 1000 gm /Serobaba, 1965/, the size of the spawning school in weight units is 7 million centners (table 5). With an average fecundity of 440,000 number of spawners 701,452,000 and average weight of fish 1000 grams, the size of the spawning stock is 7,014,520 centners. The figures cited are somewhat understated, since we took a rather high value of absolute fecundity /Serobaba, pr:i.nting/. 21. Table 4 Maximal number of eggs of Alaska pollock at spawning grounds in different regions. MalieMM.11,110e liOSIMICCTBO nepecTa IniplIIKM, MT. A wmp 1 ? 110,U. 3 Jr!' Tan pcfudi nponn13 750-1000 1OA:11Lie RypInut 100-150 f (oxearimieceag nopon a) 11 3 0 Cenepnbie Hypunm ir Oxonizoe 750 Forp."53-imua , 1954. mope t 7 3anajmax 1.-Zalicumm 20 000 Bocionnafr li'am‘raTua 24 400 _ . 8 14 9 EomangoPemie o -na 832 liammiHa, 1965 0-sa ItpriGNaona 598 M-yeiletwo, 1903 IOro-nocToun an gam 2000-2500 • Baum ,qannme 1 6 BeplisroBa mopg Key to table 4 1. Spawning areas 2. Maximal number of eggs, per m2 3. Author 4. Tatar Strait 5. Southern Kuriles (oceanic side) 6. Northern Kuriles and Sea of Okhotsk 7. Western Kamchatka 8. Eastern Kamchatka 9. Commander Islands 10. Pribilof Islands 11. Southeastern part of Bering Sea 13. Gorbunova, 1954 14. Kashkina, 1965 15. Musienko, 1963 16. Our findings. Of course, these findings are applicable only to spawning fish and not to the entire spawning stock. But since research was carried on in the spawning period and the greatest number of fish is found where spawning is most intense /Vedenskii, 1949/, it can be considered that these values will be close. 22. Table 5 Number of eggs and spawned-out Alaska pollock females at the spawning grounds in the eastern part of the Bering Sea nAOTfloCTB paClipCJeJIeHIfA 111 1-50 25 95871 2 396 775-10G 16 U6 10 783 51-100 75 20 992 1574 37U•10° .5129 101-200 150 5 G59 748925- 10c, 20 279 201-500 350 8488 2960835 •100 501-1000 750 30 013 22 509 37.5 • 106 154177 1001-2000 1500 11 799 17 399 F05. 10° 119176 h, roaec 2000 2100 1 721 3 60 906 • 106 IA 766 5 .l3cero 174 544 51205 991 • 103 350 726 Key to table _r 1. Density of distribution of eggs (number of eggs per m2 2. Variation 3. Average 4. More than two thousand 5. In all 6. Area, km2 7. Total number of eggs. 8. Number of spawning females, thousands. Conclusion 1002 The spawning area of the Alaska pollock living on the north- eastern shelf of the Bering Sea is bounded by the ice-edge on one side and the continental slope on the other. The spawning ground stretches along the 50-300 meters isobaths from'Unimak Island to 179° W.L. The total area of the spax^n.ing ground is 175 thousand km2. The first females with running eggs appear in the southeastern area .of the sea, which is the warmest because of,the influence of Pacific Ocean 23. waters. Afterwards, spawning takes place rather vigorously over the entire area of the spawning grounds from March until June. Solitary Alaska pollock individuals begin to spawn during the last days of February, and mass spawning continues from the end of March until the middle of June. The intensity of spawning reaches a maximum in May and a considerable number of individuals spawn until the middle of June. Decrease in the intensity of spawning is already noticeable in the third ten-day period in May. Individuals which have matured later spawn in June and almost to the end of July. Despite the prolonged nature of spawning, it can be assumed 'that spawning of Alaska pollock on the eastern shelf takes place more rapidly and finishes earlier than that of Alaska pollock in the northwestern areas of the Bering Sea. Alaska pollock eggs are mostly located at depths of 50 to 300 meters and are hardly found over the continental slope (deeper than 300 meters). Hydrological conditions vary markedly in particular microregions over the entire extensive area of the spawning grounds, which leads to irregular distribution of Alaska pollock spawners; consequently, the density of distribution of Alaska pollock eggs is very irregular. Thus in 2 the western region, the maximal number of eggs per m does not exceed 50, while in the southeastern region areas are found with a maximal density of up to 2000 and more eggs per m. Due to constant currents flowing in the direction of the shallows, Alaska pollock eggs are transported to the shelf •zone, where they come under the influence of a different type of current (quasi-stationary currents), within the zone of which their further development takes place. The 24. developing .eggs remain in the spawning.zone where the water temperature is fairly constant and meets the optimal conditions for the fertilization and development of Alaska pollock eggs. Eggs are found most often at a temperature of 1-3C. The diameter of eggs of Alaska pollock in eastern areas of the Bering Sea is almost the same as the diameter of eggs of Alaska pollock inhabiting the northwestern part of the sea, but is larger than the diameter of eggs of fish of this species from Southern areas of its range, and varies from 1.46 to 1.65 mm. The average size of eggs shed during the reproductive season decreases as spawning progresses, due basically to a decrease in the . sizes of spawning females. Comparing the areas of spawning grounds and the density of dis- tribution of eggs in all regions in which the Alaska pollock lives, one can conclude that one of the largest stocks of this fish inhabits the northeastern shelf of the Bering Sea. The stocks of Alaska pollock spawners (700 million fish) suggest that the abundance of the entire stock, which our fishery can successfully exploit is considerable. Received for publication Oct. 4, 1967. M 25. .'Rèfetèrices 1003 1. Berg, L.S. 1949. Freshwater fishes of the USSR and adjacent countries. AN SSSR Publishing House. 2. Vedenskii, A.P. 1949,, Finding accumulations of Alaska pollock from floating eggs. Izvestiya Tikhookeanskogo nauchno-issledovatel' nogo instituta rybnogo khozyaistva i okeanografii, vol. 29. 3. Gorbunova, N.N<, 1952. The effect of'the fixative on the size of Alaska pollock eggs. Doklady AN SSSR, vol. 82, No. 2, 1954. Reproduction and development of the Alaska pollock (Theragra chalgo^ramma (Pallas)). Trudy Instituta okeanologii AN SSSR, vol. 11. 4. Dement'eva, T.F., 1939. Distribution and migrations of vobla in the sea. Trudy Vsesoyuznogo n.-i.. in-ta morsk. rybn. kh-va i okeanografii, vol. 10. 5. Zaitsev, G.N. 1935. The geographical method of interpolation. Notes on hydrography, Vol. 3. 6. Zotin, A.I., 1961. The physiology of water metabolism in embryos of fish and cyclostomes. AN SSSR Publishing House. 7. Kaganovskaya, S.M. 1958. Prospects for the development of the Alaska pollock fishery in Far Eastern seas. Proceedings of the conference on the biological basis of the oceanic fishery. AN SSSR Publishing House. 8. Kashkina, A.A. 1965. Winter ichthyoplankton of the Commander Islands region. Soviet fisheries research in the northwest part of the Pacific Ocean. Trudy Vses. n.^i. in--ta morsk. ryb. kh-va i okeanogr., vol'. 58; Izvestiya Tikhookeansk. n.-i. in-ta rybn. kh-va i okeanogr., vol. 53. 9. Leonov, A.K. 1960. Regional oceanography, part I. Gidrometizdat. 10. Moiseev, P.A., 1952. Some specific features of the distribution of benthic and benthopelagic fish in Far Eastern seas. Izvestiya Tikhookeansk. n.-i. in-ta rybn. kh-va i okeanogr., vol. 37, 1953. Features of the mode of life and distribution of bottom and benthopelagic fish in Far Eastern seas. Voprosy ikhtiol., No. 1, 1953a. Cod and flounder of Far Eastern seas. Izvestiya Tikhookeansk. n.-i. in-ta rybn. kh-va i okeanogr., vol. 40, 1963. Some scientific prerequisites for the organization of a Bering Sea scientific-commercial expedition. Trudy Vses. n.-i. in-ta morsk. i rybn. kh-va i okeanogr., Vol. 48. 11. Musienko, L.N. 1963. Ichthyoplankton of the Bering Sea (from the materials of the TINRO and VNIRO Bering Sea expedition (1958- 1959)). Trudy Vses. n.-i. in-ta morsk. rybn. kh-va, vol. 48, No. 1. ■.■ 26. 12. Natarov, V.V. 1963. The water masses and currents of : the Bering Sea. 'Sàviet fisheries research in the northeast part of the Pacific Ocean, vol. 1. 13. Pertseva-Ostroumova, T.A., 1961. Reproduction and development of Far Eastern flounder. AN SSSR Publishing House. 14 , Rass, T.S. 1933. Instructions on the collection and procedure for • quantitative study of eggs and fingerlings of marine fishes. Publishing House of the State Institute of Oceanography p Ichthyological Section, 1941. Geographical parallelisms in the structure and development of teleosts of northern seas. Moscow Naturalists' Society Publishing House, 1946. Stages in the ontogenesis of teleosts (Teleostei). Zoologicheskii zhurnal, vol. 25, 1947. The taxonomic significance of egg sizes of teleosts (Teleostei). Byulleten' Mosk. o-va ispyt. prirody, otdel biologii, vol. 52, 1948. 'The life cycles and patterns in the development and growth of fish lavestiya. AN SSSR Biological Series, 1949. Materials on the reproduction of cod (Gadus mcirbua morhua L.) and the distribution of its eggs, larvae and fingerlings in the Barents Sea. Trudy. 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