LATIDITUDINAL CHANGES OF PLANKTON AND NEKTON BIOMASSES IN THE WESTERN TRANSITION ZONE

Transcription

1 LATIDITUDINAL CHANGES OF PLANKTON AND NEKTON BIOMASSES IN THE WESTERN TRANSITION ZONE Vadim F. Savinykh,, Vladimir A. Shelekhov,, Svetlana V. Davydova,, Svetlana V. Naydenko, Alexey A. Baytaluk, Gennady V. Khen, Gennady A. Shevtsov and Mikhail A. Zuev Pacific Scientific Research Fisheries Center (TINRO-Center), 4 Shevchenko Alley, Vladivostok, Russia,

2 INTRODUCTION Western Transition zone is one of the most productivity fishery regions of the World. There is feeding area for Japanese sardine, Pacific saury,, Anchovy, Mackerels, Skipjack, Japanese flying squid, Neon flying squid etc. However biomass and species composition of epipelagic community of this area have the evident differences from north to south.

3 INTRODUCTION There are differents points of view on the productivity of Western Transition zone. Most part of investigators are concordant that total productivity of this area decreases from north to south. However our studies show that there are different trends for upper and lower trophic layers. The subject of this paper is characteristic of plankton and nekton community of the Western Transition zone in the November, 2001.

4 GOALS AND OBJECTIVES There are differents points of view on the productivity of Western Transition zone. Most part of investigators are concordant that total productivity of this area decreases from north to south. However our studies show that there are different trends for upper and lower trophic layers. The subject of this paper is characteristic of plankton and nekton community of the Western Transition zone in the November, 2001.

5 Materials and methods The data were collected during R/V Professor Levanidov in the November, 2001 Midwater trawl with mouth diameter about 40 m was used for nekton collection Trawl tows were condacted by step-by by-step methods in the upper 200 m layer Standart Jedy net with mouth diameter 37 cm was used for plankton collection Plankton was devided into 3 fractions: small, middle and large-sized

6 Materials and methods Oceanographic studies were carried out in the upper 500 m layer We used TS-analysis method for water masses determination As a result, for types of water masses were marked out Depth, m Temperature, C Temperature, C WSA WSA FSA FSA FST FST NST Salinity, psu 75 NST Salinity, psu WSA FSA FST NST

7 Surface water masses disrtibution Urup Island WSA FST FSA NST

8 Phytoplankton Phytoplankton was found only in the Transformed Subarctic (TSA) and Transformed Subtropical (TST) waters. Coscinodiscus, Chaetoceros and Thalassiosira were abundant generas.

9 Biomass of small-sized sized zooplankton (small copepods were dominate species: Oithona similis, Pseudocalanus newmani, Oncaea borealis, Scollecithricella minor, Microsetella rosea, Metridia pacifica, Paracalanus parvus, Mesocalanus tenuicornis, Oncaea conifera) Biomass, mg/m SA TSA TST ST

10 Biomass of middle-sized zooplankton (copepods (copepods Metridia pacifica dominated, larvae of euphausiids,, small sagittas and pteropods also were found) Biomass, mg/m SA TSA TST ST

11 Biomass of large-sized zooplankton (saggitas,, copepods, euphausiids, hyperiids and salpas dominated) Biomass, mg/m SA TSA TST ST

12 Nekton composition 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% SA TSA TST ST Squids Fishes

13 Nekton density Density, tons per sq. km SA TSA TST ST Squids Fishes

14 Dominated species and groups 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% SA TSA TST ST Other planktivorous Other predator squids Other predator fishes Tunas and swordfish Neon flying squid Fireball squid Myctophids Anchovy

15 Small pelagic planktivouros are dominating in the all water masses Japanese anchovy (length less than 15 cm) Myctophids (length less than 15 cm) Fireball squid (mantle length less than 7 cm)

16 Predators density 2,5 Density, tons per sq. km 2 1,5 1 0,5 0 SA TSA TST ST

17 There are different trends for predators and small pelagics Predators Density, tons per sq. km 2,5 2 1,5 1 0,5 0 SA TSA TST ST S mall planktiv o urus Density, tons per sq. km SA TSA TST ST

18 Observations There are different trends of biomass changes for the plankton and nekton communities. Most productive area is transition zone between Western Subarctic gyre and Northern Subtropical one. Commercial fishery would be more effective in the subtropical waters. There is evident lack of predators in the Subarctic and Transformed Subarctic waters.

19 Is the high abundant small pelagics the deadlock in the Subarctic waters ecosystem? More abundant species Japanese anchovy will return on the shelf of Japanese Islands. There is a way to substance and energy transportation from oceanic to inshore region

20 Is the high abundant small pelagics the deadlock in the Subarctic waters ecosystem? Small mesopelagic fishes and squids can play the significant role as a pray for Pacific salmons. The salmoms feeding range concurs with nortern part of Transition zone in the winter time and small pelagics is ones of the main food components especially for coho and chinook salmons

21 Is the high abundant small pelagics the deadlock in the Subarctic waters ecosystem? Transition zone is the main spawning region of boreal myctophids.. Last ones may to penetrate into Bering and Okhotsk Seas due to Subarctic Gyre circulation and, as result, they increase nekton biomass in the deep-sea regions of marginal seas.

22 Results Our data suggest that plankton and nekton biomasses distribution was not typical in November, Is there mistake or reguliraty?

23 Our subsequent studies shown that there was tradional plankton and nekton abundance pattern in the summer, Phytoplankton, large-sized zooplankton and nekton density were decreased from north to south whereas small-sized sized zooplankton and ichthyoplankton abundance was increased southward.

24 Phytoplankton distribution in the July,

25 Small-sized zooplankton distribution in the July,

26 Large-sized zooplankton distribution in the July,

27 Conclusions There is tendence of increasing of plankton and nekton density in northward direction. However, main ecological groups trends are different. Seasonal aspects heavy affect to productivity of different waters. Biomass of epipelagic community of western Transition zone changes according to horizontal and vertical migrations of zooplankton and nekton.

28 Conclusions Stationary view on the dynamic of plankton and nekton community are not best approach. We must to store knowledge about communities status in all season for understanding how Western Transition zone ecosystem functionates.

29 THANK YOU FOR YOUR KIND ATTENTION