Potential contribution that the copepod Neocalanus tonsus makes to downward carbon flux in the Southern Ocean

We estimate that Neocalanus tonsus makes a contribution to downwardscarbon flux of 1.7–9.3 g C m^–2 year^–1, insubantarctic waters, the Subtropical Front and waters immediatelyto the north, based on its ontogenetic vertical migration minusthe biomass of eggs, the products of which are returned to thesurface the following season. This flux is an order of magnitudegreater than that estimated (0.27 g C m^–2 year^–1)for vertical migration of large copepods in the North Atlantic.Over the total 55.6 x 10⁶ km² where N. tonsus is distributed,0.17 Gt C year^–1 are estimated to be lost annually tothe ocean interior. In subantarctic water, this loss represents1.4% of primary production and is 14% greater than the measuredsedimented particulate organic carbon (POC) at 300 m. Similarly,in subtropical water, carbon loss to the ocean interior fromN. tonsus seasonal migration is estimated to be 13% lower thanmeasured POC flux. Nevertheless, N. tonsus was never found intime-incremental sediment trap samples. We hypothesize thatthe apparently proportionally different role of downwards seasonalmigration of large copepods relative to sedimented POC in theNorth Atlantic compared with the subarctic North Pacific andSouthern Ocean arises because of a combination of differencesin the nutrient status of these oceans, differences in the rateof development of grazer populations in spring, and differencesin life history characteristics of large copepods. The fluxdue to the behaviour of N. tonsus in different parts of itsrange, put into the context of the estimated global-mean netflux of 1.7–3.7 g C m^–2 year^–1 taken up bythe ocean, may be a regionally significant amount. The summerdownward migration of N. tonsus, however, does not entirelyexplain the observed seasonal variation in regional measurementsof pCO₂ off New Zealand.     

A concise review of geographic variation in adult body size in anadromous masu salmon, Oncorhynchus masou

Adult body size (size at maturity) is one of the key life history traits and is well known to sometimes correlate with latitude in anadromous salmonids. However, it is poorly understood whether geographic size patterns except for latitudinal trends occur or why such patterns have been shaped. The present paper briefly reviewed body size variation between anadromous returns of masu salmon Oncorhynchus masou in the Okhotsk group (10 populations along the Sea of Okhotsk coast), the Pacific group (2 populations along the Pacific Ocean coast) and the Sea of Japan group (24 populations along the Sea of Japan coast). The Okhotsk group was smaller than the Sea of Japan group. Although the statistical analysis detected no differences among the remaining combinations, the Okhotsk group was possibly smaller than the other groups because the size of the Pacific group seemed to be within range of the Sea of Japan group but tended to be larger than that of the Okhotsk group. Future research should first test whether size at maturity genetically differs between the Okhotsk group and the other two groups to explore further evolutionary factors shaping geographic size variation.     

Larval development of bigmouth manefish Caristius macropus (Perciformes: Caristiidae) from the western North Pacific

Larvae of bigmouth manefish Caristius macropus are described and illustrated on the basis of seven specimens (4.2–10.5 mm in body length) from the Kuroshio waters (0–60 m depth) and the transition waters (surface) between the Kuroshio and Oyashio fronts of the western North Pacific. The present larvae of C. macropus are distinguished from those of Paracaristius maderensis that inhabit the North Pacific by having 39–40 myomeres, 34 dorsal-fin rays, and 22 anal-fin rays. The present study, along with previous studies of the early life stages of caristiids, shows that larvae of the family may be defined by the following characters: body elongate in preflexion stage but becoming deep bodied and hatchet shaped after notochord flexion; anus located near vertical through base of pectoral fin; head large, without spination or serration; a distinct vertical band on the posterior tail throughout the larval stages, and two bands gradually appearing on the tail and trunk during the flexion and postflexion stages; and melanophores present around the notochord tip by the flexion stage. Adult C. macropus are found in the subarctic and temperate waters of the North Pacific; however, the present study and other occurrences of early life stages of the species probably indicate that C. macropus may spawn over a wide area in the North Pacific.     

SEGREGATIVE MIGRATION OF DALL'S PORPOISE (PHOCOENOIDES DALLI) IN THE SEA OF JAPAN AND SEA OF OKHOTSK

Dall's porpoises from the Sea of Japan population taken by a dolphin fishery vessel were examined. Estimated body lengths at sexual maturity were similar to those for the truei -type population off the Pacific coast of Japan but larger than those for the offshore dalli -type in the North Pacific. The Sea of Japan population is known to migrate to the Pacific coast of Japan through Tsugaru Strait and to the Sea of Okhotsk through Soya Strait in summer. From the difference of catch composition, individuals of different reproductive status in this population are considered to have different patterns of summer migration. Most of the individuals which migrate into the Pacific Ocean through Tsugaru Strait are sexually immature, while those migrating into the Sea of Okhotsk are mature. The Sea of Okhotsk is thought to be a breeding area for this population. The calving season is estimated to be May through June, which is earlier than that of the truei -type off the Pacific coast of northern Japan. This may be an adaptation to lower water temperatures in the Sea of Japan during winter.     

Foraminiferal oxygen and carbon isotopes during the last 34 kyr off northern Japan,northwestern Pacific

Oxygen and carbon isotopes of foraminifera were analyzed in core PC4, water depth 1366 m, off northern Japan, near the east side of the Tsugaru Strait (130 m depth) between the open northwestern Pacific Ocean and the Japan Sea. At present, the site is at the confluence of the Tsugaru Warm Current which flows eastwards out of the Sea of Japan through the Tsugaru Strait, the subarctic Oyashio Current and the subtropic Kuroshio Current. During the Last Glacial Maximum (LGM), the Oyashio Current penetrated further to the South and outflow from the Japan Sea was restricted by glacio-eustatic sea level lowering.The isotopic values of the planktic foraminifer Neogloboquadrina pachyderma (sinistral) and the benthic foraminifer Uvigerina akitaensis reflect rapid millennial-scale paleoceanographic changes between 34 and 6 ka. Hydrographic changes during deglaciation were related to events at high northern latitudes, but Holocene hydrographic changes were dominated by local effects, such as the development of the outflow of the Tsugaru Warm Current. High values of planktic δ¹⁸O during the LGM reflect the southward advance of the Oyashio Current. These values decreased by 0.3‰ from 19.4 to 18.9 ka, then increased by 0.5‰ at 18 ka, with highest values between 17.5 and 15 ka. The δ¹⁸O oscillations between 19.4 and 15 ka may reflect millennial-scale warm–cold oscillations during Heinrich event 1. Planktic microfossil data indicate that cold Oyashio waters flowed from the northwestern Pacific into the Japan Sea via the Tsugaru Strait between 17 and 16 ka, consistent with the occurrence of the highest planktic δ¹⁸O values in core PC4. Planktic δ¹⁸O values rapidly decreased by 0.9‰ at 15 ka, possibly reflecting the effects of both a rapid increase in fresh water flux and rising temperatures in the subarctic North Pacific. During the Younger Dryas, cold event planktic δ¹⁸O values increased by 0.5‰, followed by a gradual decrease by 1‰ from the early to middle Holocene, reflecting a gradual increase in eastward outflow via the Tsugaru Strait with sea level rise. Both planktic and benthic foraminiferal δ¹³C values oscillated between 34 and 10 ka, at relatively large amplitudes (about 0.5‰), then remained relatively stable during the last 10 kyr. Several negative planktic and benthic (∼ − 0.7‰) δ¹³C excursions were present in sediment dated between the precipitation of secondary carbonates during episodic methane release possibly associated with methane release from continental margin sediments.     

Spawning season and migration of the myctophid fish <Emphasis Type="Italic">Diaphus theta </Emphasis>in the western North Pacific

 The spawning season, spawning grounds, and migration of the myctophid fish Diaphus theta were studied in the western North Pacific, based on seasonal sampling and estimation of hatching dates. The peak abundance of larvae was observed in July in the transition waters between the Oyashio and Kuroshio fronts. The spawning season ranged from late March to early September, with a peak from May to July. Larvae and juveniles <40 mm in standard length were distributed in the transition waters, whereas larger individuals were collected in the Oyashio and the Western Subarctic waters. These results indicate that this species undergoes a horizontal spawning migration from the Oyashio and Western Subarctic waters into the transition waters crossing the Oyashio front. Received: July 11, 2002 / Revised: October 2, 2002 / Accepted: October 15, 2002 Acknowledgments We are grateful to the captains, officers, and crew of FRV Hokko-Maru, FRV Tankai-Maru, and RV Hakuho-Maru for their assistance at sea. We thank Dr. H. Saito and Mr. H. Kasai for their cooperation in field sampling, and Dr. C. Sassa for his assistance with larval fish taxonomy. Correspondence to:Masatoshi Moku     

Interannual variations in abundance and body size in Neocalanus copepods in the central North Pacific

As the integral components of zooplankton in the subarctic NorthPacific, the three Neocalanus species (N. cristatus, N. plumchrusand N. flemingeri) are characterized by an annual life cycleand rapid development in the surface layer during spring–summer.Patterns of interannual variation of abundance and body sizeof these Neocalanus species were analyzed using the time-seriesdata collected during the summers of 1979–1998 (20 years)at stations along the longitudinal transect line in the centralNorth Pacific, crossing five sub-areas (Alaska Current System,Subarctic Current System, Northern Transition Domain, SouthernTransition Domain and Subtropical Current System). In the southernsub-areas, quasi-decadal oscillation was observed for the 3-yearrunning mean of abundance and prosome length for copepoditestage 5 (C5) of the three Neocalanus species. Although the oscillationsignal diminished towards northern waters, it showed a positivephase during the early 1980s and 1990s and a negative phaseduring the late 1980s. In the northern waters, a biennial patternwas pronounced for anomalies of C5 prosome length for N. plumchrusand N. flemingeri, which was large in odd years and small ineven years. Significantly positive covariations among the threespecies were found for both abundance and prosome length aroundmid-latitude, where they were abundant. In the correlation analysis,these observed yearly patterns showed a statistically insignificantcorrelation with most environmental (integrated mean temperaturein surface waters, water column stability and chlorophyll aconcentration) or climatological (North Pacific Index and SouthernOscillation Index) variables. The regional difference of theoscillation signal and the synchronized covariation among thesespecies suggest that interannual variations of their abundanceand body size are mediated by common environmental force(s)with some spatial and temporal scales in the subarctic NorthPacific.     

Depth distribution during the life history of Neocalanus plumchrus in the Strait of Georgia

Neocalanus plumchrus is the most common large copepod in theNortheast Pacific, and plays an important role in the ecosystemsof that area; it is particularly common in the Strait of Georgia.In this study, seasonal changes in the vertical distributionof late-stage N. plumchrus at a single site in the Strait ofGeorgia were measured with an optical plankton counter (OPC)and depth-stratified net samples. Particles measured in situby the OPC were compared to an empirically measured size distributionfor live N. plumchrus. Below 200 m (primarily overwinteringindividuals), OPC estimated abundance usually corresponded toabundance estimates from net samples. Abundance in the top 100m was consistently overestimated by the OPC, relative to resultsfrom net samples. During overwintering, the vertical distributionshifted downward over time, coinciding with deepwater renewalevents in the Strait, and was followed by a partial upward spawningmigration by newly moulted adults. Spatial structure at severalscales was inconsistent, but significantly different from random.A simple simulation model of depth as a function of time showedthat both hydrographic changes and endogenous changes withinthe animals may influence depth distributions, and suggeststhat maintenance of position in the water column during diapauseis not a passive process.     

Jellyfish of the Far Eastern Seas of Russia. 3. Biomass and abundance

The biomass and abundance of large jellyfish (Cnidaria: Scyphozoa, Hydrozoa) was estimated and their seasonal and interannual dynamics was studied based on the data of trawl surveys conducted by the Pacific Research Fisheries Center (TINRO Center) in the Sea of Okhotsk, Bering Sea, Sea of Japan, and the Northwestern Pacific Ocean (NWPO) in 1991–2009. Most of the jellyfish biomass (over 95%) in the Sea of Okhotsk, Bering Sea, and NWPO was formed by Chrysaora spp., Cyanea capillata, Aequorea spp., Phacellophora camtschatica, and Aurelia limbata. The same species along with Calycopsis nematophora predominated in abundance in the Bering Sea and NWPO, while Ptychogena lactea, C. capillata, and Chrysaora spp. were most abundant in the Sea of Okhotsk. In the northwestern Sea of Japan, Aurelia aurita, C. capillata, and Aequorea spp. predominated both in abundance and biomass. Generally, the jellyfish abundance reached the highest values in the summer and fall and decreased abruptly in the winter. Meanwhile, the seasonal dynamics proved to be specific for each species and were manifested in some of them by reaching maximum values at various periods of the warm season, whereas the other (Tima sachalinensis and P. lactea) showed the reverse pattern of seasonal variations, with the highest abundance in cold months. Jellyfish biomass and abundance varied greatly from year to year, which was related to the short lifecycle and alternation between sexual and asexual generations, in which reproductive success was predetermined by various environmental factors. In the fall, year-to-year fluctuations of the relative biomass could increase by ten times. In 1991–2009, it varied from 200 to 2000 kg/km² in the northern Sea of Okhotsk, from 500 to 4200 kg/km² in the northwestern Bering Sea, and from 300 to 3700 kg/km² in the southwestern Bering Sea. Taking the jellyfish abundance estimates into account, along with the vertical distribution and the seasonal dynamics, the overall biomass of large species that occurred in trawl catches in Far Eastern seas and adjacent Pacific waters during the warm season could reach 13.0–15.0 million tons, of which up to about 6.0 million tons would be concentrated in the western Bering Sea and 5.5–6.0 million tons in the Sea of Okhotsk.     

Foraminiferal oxygen and carbon isotopes during the last 34 kyr off northern Japan, northwestern Pacific

Oxygen and carbon isotopes of foraminifera were analyzed in core PC4, water depth 1366 m, off northern Japan, near the east side of the Tsugaru Strait (130 m depth) between the open northwestern Pacific Ocean and the Japan Sea. At present, the site is at the confluence of the Tsugaru Warm Current which flows eastwards out of the Sea of Japan through the Tsugaru Strait, the subarctic Oyashio Current and the subtropic Kuroshio Current. During the Last Glacial Maximum (LGM), the Oyashio Current penetrated further to the South and outflow from the Japan Sea was restricted by glacio-eustatic sea level lowering.The isotopic values of the planktic foraminifer Neogloboquadrina pachyderma (sinistral) and the benthic foraminifer Uvigerina akitaensis reflect rapid millennial-scale paleoceanographic changes between 34 and 6 ka. Hydrographic changes during deglaciation were related to events at high northern latitudes, but Holocene hydrographic changes were dominated by local effects, such as the development of the outflow of the Tsugaru Warm Current. High values of planktic δ¹⁸O during the LGM reflect the southward advance of the Oyashio Current. These values decreased by 0.3‰ from 19.4 to 18.9 ka, then increased by 0.5‰ at 18 ka, with highest values between 17.5 and 15 ka. The δ¹⁸O oscillations between 19.4 and 15 ka may reflect millennial-scale warm–cold oscillations during Heinrich event 1. Planktic microfossil data indicate that cold Oyashio waters flowed from the northwestern Pacific into the Japan Sea via the Tsugaru Strait between 17 and 16 ka, consistent with the occurrence of the highest planktic δ¹⁸O values in core PC4. Planktic δ¹⁸O values rapidly decreased by 0.9‰ at 15 ka, possibly reflecting the effects of both a rapid increase in fresh water flux and rising temperatures in the subarctic North Pacific. During the Younger Dryas, cold event planktic δ¹⁸O values increased by 0.5‰, followed by a gradual decrease by 1‰ from the early to middle Holocene, reflecting a gradual increase in eastward outflow via the Tsugaru Strait with sea level rise. Both planktic and benthic foraminiferal δ¹³C values oscillated between 34 and 10 ka, at relatively large amplitudes (about 0.5‰), then remained relatively stable during the last 10 kyr. Several negative planktic and benthic ( − 0.7‰) δ¹³C excursions were present in sediment dated between the precipitation of secondary carbonates during episodic methane release possibly associated with methane release from continental margin sediments.     

Vertical distribution, life cycle and body allometry of two oceanic calanoid copepods (Pleuromamma scutullata and Heterorhabdus tanneri) in the Oyashio region, western North Pacific Ocean

 Diel and seasonal vertical distribution, life cycle andbody allometry of Pleuromamma scutullata and Heterorhabdus tanneriwere investigated in the Oyashio region during September 1996through October 1997. Monthly samples were collected with 0.1mm mesh closing nets towed through five discrete depths betweenthe surface and     

Migration and diving activity in three non‐breeding flesh‐footed shearwaters Puffinus carneipes

The flesh‐footed shearwater Puffinus carneipes is a medium‐sized shearwater and transequatorial migrant within the Pacific Ocean. We used archival data loggers to study the non‐breeding migration and diving behaviour of three flesh‐footed shearwaters following breeding in New Zealand. In early April, the birds migrated to the western North Pacific Ocean in 23±2 days, occupying core distributions within the Kuroshio/Oyashio transition system for 91±17 days. Subsequent movements were made into the Sea of Okhotsk prior to return migrations to New Zealand in mid September (19±1 days). Diving depths during migration (2.5±2.4 m), and in the western North Pacific (2.4±2.6 m) were shallower than during the onset of breeding (4.8±8.7 m). Non‐breeding flesh‐footed shearwaters occupy a region of high fisheries activity and the impact of these fisheries on adult survival in this declining species warrant further study.     

Density and distribution of bacterioplankton and planktonic ciliates in the Bering Sea and North Pacific

The total number of planktonic bacteria in the upper mixed layerof the Bering Sea during the late spring-early summer periodranged between 1 and {small tilde}4 x 10⁶ ml^–1 (biomass10–40mg C m^–3). In the northern Pacific, along 47–52⁶N,the corresponding characteristics of the bacterioplankton densityin the upper mixed water layer were: total number 1–2x 10⁶ cells ml^–1 and biomass 15–46mg C m^–3Below the thermocline at 50–100 m, the density of bacterioplanktonrapidly decreased. At 300 m depth, it stabilized at 0.1–0.2x 106 cells ml^–1. The integrated biomass of bacterioplanktonin the open Bering Sea ranged between 1.2 and 3.6 g C m^–2(wet biomass 6–18 g m^–2) Its production per dayvaried from 2 to 23 mg C m^–3 days^–1 in the upper0–100 m. The numerical abundance of planktonic ciliatesin this layer was estimated to be from 3 to l0 x 10³ cells l^–1,and in the northern Pacific from 0.4 to 4.5 x 10³ l^–2.Their populations were dominated by naked forms of Strombidium,Strombilidium and Tontonia. In some shelf areas, up to 40% ofthe total ciliate population was represented by the symbioticciliate Mesodinium rubrum. The data on the integrated biomassof basic groups of planktonic microheterotrophs are also presented,and their importance in the trophic relationships in pelagiccommunities of subarctic seas is discussed.     

Pyrosoma atlanticum (Tunicata, Thaliacea): diel migration and vertical distribution as a function of colony size

A large population of the colonial pelagic tunicate Pyrosomaatlanticum occurred in April 1991 in offshore waters of theLigurian Sea (Northwestern Mediterranean). The high numbersof colonies caught allowed their vertical distribution and dielmigration in the 0–965 m water column to be describedas a function of their size. Daytime depths and amplitudes ofthe migration were correlated with colony size. The amplitudeof the migration ranged from 90 m for 3-mm-length colonies to760 m for 51-mm-length colonies, with a mean amplitude of 410m for the whole population, all sizes pooled. The results ofhorizontal hauls at a given depth around sunrise and sunsetshowed a marked diurnal symmetry of the migratory cycle relativeto noon, and that migration of the population was not cohesive.For example, the larger the colonies, the later after sunsetthey reached the upper layers during their upward migration.     

Distribution of euphausiids in the Kuroshio front and warm water tongue with special reference to the surface aggregation of Euphausia pacifica

The distribution of euphausiids and other macrozooplankton wasinvestigated in and around the Kuroshio front formed in theKa.shima-nada Sea. Japan. during the summer of 1993. Zooplanktonwere dominated by copepods, chaetognaths and euphausiids. andtheir biomass was significantly higher at the frontal stations.Eighteen species belonging to six genera of euphausiids werecollected. The species composition and community structure ofeuphausiids changed drastically with the ‘areas’corresponding to the hydrological conditions. In the area underthe influence of the Kuroshio. most euphausiids were warm-waterspecies. In contrast. euphausiids found in the frontal areawere those usually predominating in subarctic or cold Oyashiowaters. In the area of the warm water tongue. where warm Kuroshiowater lay above cold Oyashio water, the species compositionof euphausiids represented a mixture of both warm- and cold-waterspecies. Surface aggregations of Euphausia pacifica were observedin the frontal area during the night. The biomass and densityof the aggregations ranged between 90 and 136 mg C m^–3and 164 and 238 md. m^–3 respectively. These aggregationswere mostly made up of immature individuals of < 12 mm. Passivetransportation by convergent flow at the front seems to explainthe observed surface aggregations of E.pacifica.     

Spatial heterogeneity and genetic variation in the copepod Neocalanus cristatus along two transects in the North Pacific sampled by the Continuous Plankton Recorder

We present a macrogeographic study of spatial heterogeneityin an important subarctic Pacific copepod and describe the firstgenetic analysis of population structure using Continuous PlanktonRecorder (CPR) samples. Samples of Neocalanus cristatus werecollected at a constant depth of 7 m from two CPR tow-routes,(i) an east–west 6500-km transect from Vancouver Island,Canada to Hokkaido Island, Japan, and (ii) a north–southtransect of 2250 km from Anchorage, Alaska to Tacoma, Washington.Analysis of these samples revealed three features of the biologyof N. cristatus. First, N. cristatus undergoes small-scale dielvertical migration that is larger among stages CV–adult(3–6 times more abundant at 7 m at night), than stagesCI–CIV (only 2–4 times higher at night). Secondly,while there were no regions where N. cristatus did not appear,each transect sampled a few large-scale macrogeographic patches.Thirdly, an analysis of molecular variation, using a partialsequence of the N. cristatus cytochrome oxidase I gene, revealedthat 7.3% (P < 0.0001) of the total genetic variation amongN. cristatus sampled from macrogeographic patches by the CPRcould be explained by spatial heterogeneity. We suggest thatspatial heterogeneity at macrogeographic scales may be importantin plankton evolution.     

Productivity of picoplankton compared with that of larger phytoplankton in the subarctic region

We determined the productivity (µg C µg^–1Chi a h^–1) of size-fractionated phytoplankton in the northernNorth Pacific and the Bering Sea in summer and winter. Picoplankton(<2 µm) were more productive than larger sized phytoplankton(2–10 and 10–200 µm) in the subtropical region,where the in situ temperature was >10°C; whereas picoplanktonin the subarctic region were similar in productivity or lessproductive than larger sized plankton, where the in situ temperaturewas <10°C. The result from the subtropical region inthis study agrees with previous results from tropical and subtropical waters, which indicate that phytoplankton productivitytends to decrease with increasing cell size. The result fromthe subarctic region, however, differs from previous results.We observed a positive linear regression for in situ temperatureand picoplankton productivity, but this trend was not seen inthe larger sized phytoplankton. The results show that the productivityof picoplankton is markedly influenced by in situ temperaturecompared with that of larger sized plankton. Low tem peratureappears to account largely for the observation that the productivityof picoplankton is not significantly higher than that of largersized phytoplankton in the subarctic region.     

Origin of juvenile chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> (Salmonidae) in the Sea of Okhotsk coastal waters off South Sakhalin

Based on the data of the analysis of distribution of juvenile chum salmon Oncorhynchus keta that were marked at salmon hatcheries in the southern part of the Sakhalin Island and Japan it has been established that their stocks in the Sea of Okhotsk coastal waters off South Sakhalin and Japan are of mixed origin. One part of the stock is composed of juveniles from hatcheries located in the southern part of Sakhalin, and the other part is composed of migrants from the waters adjacent to Japan. The first part is formed by juveniles both from hatcheries on the Sea of Okhotsk and Sea of Japan coasts of South Sakhalin. The second part is formed by juveniles reared at hatcheries in all regions of Japan: the Pacific and Sea of Okhotsk coasts of Honshu and Hokkaido, and from the Sea of Okhotsk coast of Hokkaido and Izmena (Nemuro) Strait. In July, in the Sea of Okhotsk coastal waters off South Sakhalin, the length and weight of most juvenile chum salmon of Japanese origin exceed 10 cm and 10 g, and juveniles of Sakhalin origin are always smaller than 10 cm and 10 g, which makes it possible to differentiate juveniles in trawl catches.     

Summer-autumn ichthyoplankton of the Sea of Okhotsk and the Sea of Japan and special traits of feeding of fish larvae and fry in 2003–2004

In summer-autumn of 2003–2004, the ichthyoplankton of the Sea of Okhotsk comprised 35 species. In this period the most widely distributed and numerous were larvae of the lord Hemilepidotus gilberti, the Pacific stout sand lance Ammodytes hexapterus, and the Sakhalin dab Limanda sakhalinensis. The maximum catches of fish larvae were attributed to coastal waters off eastern Sakhalin and to the shelf of the northern part of the Sea of Okhotsk. In November of 2003, the ichthyoplankton of the Sea of Japan was represented by fish larvae belonging mainly to the boreal ichthyocomplex. The catches consisted predominantly of larvae of the arabesque greenling Pleurogrammus azonus, the ronquil Bathymaster derjugini, and the rockfish Sebastes owstoni. Fish larvae and fry in the northwestern part of the Sea of Japan were caught principally within 43°–45° N and 137°–139° E above the depth 1500–2000 m. The food spectrum of fish larvae in the Sea of Okhotsk and the Sea of Japan comprised over 20 plankters of various size belonging to seven taxa. Irrespective of fish species, the food items common of all fish were copepods Pseudocalanus minutus and Oithona similis. The daily rations were calculated for mass species (Hemilepidotus gilberti, Ammodytes hexapterus, Hexagrammos stelleri, Pleurogrammus azonus, Bathymaster derjugini, and Sebastes owstoni). The larvae of all considered species in the Sea of Japan and in the Sea of Okhotsk fed predominantly in the light period of the day.     

Growth and development of Metridia pacifica (Copepoda: Calanoida) in the northern Gulf of Alaska

Juvenile growth and development rates for Metridia pacifica,one of the dominant larger copepods in the subarctic Pacific,were investigated from March through October of 2001–2004in the northern Gulf of Alaska. The relationship between prosomelength (PL, µm) and dry weight (DW, µg) was determined:log₁₀ DW = 3.29 x log₁₀ PL – 8.75. The stage durationsof copepodites ranged from 3 to 52.5 days but were 8–15days under optimal condition. Seasonally, growth rates increasedfrom March to October and typically ranged between 0.004 and0.285 day^–1, averaging 0.114 ± 0.007 day^–1(mean ± SE). After standardization to 5°C (Q₁₀ of2.7), growth rates averaged 0.083 ± 0.005 day^–1and were significantly correlated to chlorophyll a, with saturatedgrowth rates of 0.149 day^–1 for C1–C3, 0.102 day^–1for C4–C5 and 0.136 day^–1 for all stages combined.Measured juvenile growth rates were comparable with specificegg production rates in this species. The comparisons of ourrates in this study with those predicted by the global modelsof copepod growth rates suggested that further refinement ofthese models is required.