Yoshinari Endo

Krill fisheries: Development, management and ecosystem implications

Abstract There are currently at least six commercial fisheries harvesting six different species of euphausiid, or krill: Antarctic krill (Euphausia superba), fished in the Antarctic; North Pacific krill (Euphausia pacifica), fished off Japan and off western Canada; Euphausia nana, fished off the coast of Japan; Thysanoessa inermis, fished off the coast of Japan and off eastern Canada; and Thysanoessa raschii and Meganyctiphanes norvegica which have been experimentally harvested off eastern Canada. The current world catch of all species of krill is over 150 000 tonnes per annum but few fisheries are being exploited to their maximum theoretical potential. The size of the world krill harvest is currently limited by lack of demand, although some fisheries are being deliberately managed at low levels because of ecological concerns. We have outlined the history of these krill fisheries to determine where there are common trends and issues which will affect their future development. Krill products are currently mostly used for the aquaculture and sport fishing market but considerable effort has also been put into developing products for human consumption, particularly from Antarctic krill. The future development of krill fisheries is examined in the light of information on trends in krill products which include pharmaceutical and industrial uses in addition to nutritional products. Because of the central ecological role of krill in many marine ecosystems, the subject of krill harvesting is a sensitive issue and krill fisheries require careful management. This requirement has spawned an innovative international management regime in the Antarctic — the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) — which has developed procedures for managing the harvest of Antarctic krill that may be applicable to other fisheries. The common problems of managing krill fisheries are outlined particularly those relating to the role of krill in many coastal ecosystems, and as prey for many other species which are commercially fished.

Biological characteristics of euphausiids preyed upon by Adélie penguins in relation to sea-ice conditions in Lützow-Holm Bay, Antarctica

Abstract. We examined the biological characteristics of euphausiids found in the stomachs of Adélie penguins in relation to sea-ice conditions in Lützow-Holm Bay over three seasons. Euphausiids, especially Euphausia superba, proved to be a staple food for Adélie penguins irrespective of the ice condition. Body length and maturity-stage compositions of euphausiids were different among seasons, probably reflecting sea-ice condition in summer. The mean body length decreased and maturity regressed during each season in E. superba, which was partly attributable to the selective feeding on large, mature female krill by Adélie penguins. The 1995/1996 year class of E. superba, which was spawned when the sea ice was most developed, was strong and conspicuous in the 1996/1997 and 1997/1998 seasons. This vigor indicates that sea ice provided females with good spawning conditions and larvae with good growth and survival rates.

Seasonal changes of planktonic polychaete larvae and chlorophyll a concentration in Onagawa Bay, northeastern Japan

Abstract Seasonal changes of abundance and composition of planktonic polychaete larvae were investigated monthly from January 2007 to December 2009 in Onagawa Bay, northeastern Japan. Larvae belonging to 18 families were identified: Spionidae, Serpulidae, Nephtyidae, Magelonidae, Phyllodocidae, Polynoidae, Syllidae, Capitellidae, Nereididae, Terebellidae, Arenicolidae, Chaetopteridae, Oweniidae, Pectinariidae, Glyceridae, Dorvilleidae, Sabellidae, and Lumbrineridae. The density of polychaete larvae varied from 18 to 6901 ind m−3. Spionid larvae occurred throughout the year, being the dominant family throughout the year, comprising 88.7% of the total, with those belonging to genus Polydora dominant during winter to spring and Pseudopolydora during summer to autumn. Larvae belonging to the Serpulidae, Magelonidae, Nephtyidae, Phyllodocidae, and Polynoidae tended to be frequent in summer and autumn. The close timing between phytoplankton blooms and the production of planktonic polychaete larvae is discussed, and it is noted that most planktonic polychaete larvae tended to synchronize with summer phytoplankton increases and autumn blooms in the near-surface water, but not with spring blooms. One possible explanation is the diversity of food during summer to autumn in Onagawa Bay. Only larvae belonging to the genus Polydora were synchronized with spring phytoplankton blooms, perhaps reflecting their northern biogeographic origin.

Microzooplankton standing crop in the western subtropical pacific off the Bonin Islands in winter, 1980

Quantitative data on the vertical distribution and biomass of microzooplankton are presented for the western subtropical Pacific west of the Bonin Islands in winter. Microzooplankton other than foraminifera and radiolarians showed similar vertical distribution to chlorophylla. Among microzooplankters, naked ciliates, tintinnids and copepod nauplii were dominant components both in number and volume. Naked ciliates were the most dominant, comprising 82.2 % and 47.7 % of the total microzooplankton by number and volume, respectively. Copepod nauplii, occupying less than 10 % by number, accounted for 35.7 % of the volume of all microzooplankton. Tintinnids contributed less to the microzooplankton standing crop, 12.6 % of the total by number and 17.3 % by volume. Calculated microzooplankton wet weight varied from 0.84 to 1.80 g m−2 and corresponded to 9.9–18.1 % of net zooplankton weight. The relative abundance of microzooplankton to net zooplankton in this study is comparable to that previously reported in the tropical and subtropical Pacific Ocean, but a little higher than in oceanic subarctic areas.

Swimming behavior of the spoon worm Urechis unicinctus (Annelida, Echiura).

Large numbers of swimming and stranding Urechis unicinctus were observed at night during low tide in Sasuhama, Miyagi Prefecture, northeastern Japan, during the periods from January to February in 2012 and 2013. Worms did not drift passively but swam actively, therefore hinting at a certain purpose for such behavior. As trochophore larvae of U. unicinctus were observed to occur simultaneously in the plankton, we infer the possibility that this is an event of reproductive swarming. Anatomical observations of both swimming and stranding U. unicinctus showed that none of the specimens had gametes, which may suggest that these were completely spent after spawning. Urechis unicinctus seemed to begin swimming after dusk and the observed swimming behavior occurred during the evening ebb tide throughout the night low tide during winter time. Stranding U. unicinctus have long been known in Japan and have been attributed to sea storms. The present study shows for the first time the possibility that U. unicinctus swims in order to reproduce at night and that this swimming behavior is closely linked to the stranding of U. unicinctus individuals.

Growth Characteristics of Ephelota gigantea: a Pest to Seaweed Culture along the Northeastern Coast of Japan

Suctorians of the genus Ephelota are stalked ciliates and ectocommensals of marine invertebrates and plants. Ephelota gigantea has long been known as a major nuisance to the cultured seaweed industries in the coastal area of northeastern Japan. However, little is known about its life history, so in situ growth experiments were performed in the vicinity of wakame (Undaria pinnatifida) long-line culture in Iwate Prefecture, and the development of swarmers was investigated in the laboratory. The stalk elongated first, followed by enlargement of body length and body width, with body width increasing linearly with time. Over 5-6 days, E. gigantea increased 4-5-fold by external budding. Such an experiment was carried out for the first time for E. gigantea and possibly for any Ephelota species. The information obtained is important not only in understanding the life history of this species but also for understanding the interactions with host organisms.

Morphological, developmental, and ecological characteristics of the suctorian ciliate Ephelota gigantea (Ciliophora, Phyllopharyngea, Ephelotidae) found on cultured wakame seaweed in Northeastern Japan

Wakame seaweed is an important aquatic resource in Iwate Prefecture. However, a suctorian Ephelota gigantea sometimes causes great damage to wakame culture. Since little is known about the biological characteristics of E. gigantea, its detailed morphology and temporal change of biological characteristics during the 2010 culture season were investigated. Scanning electron microscope observations showed that E. gigantea had different striation patterns on the stalk; there was a swell made of cement by which the stalk was attached to wakame firmly; and the buds had cilia arranged in concentric circles about a ring in the center of the ventral side. A suctorian parasite was found to infect E. gigantea, and the infection seemed to have decreased drastically the attached density of E. gigantea on wakame. Cell size of parasite-infected E. gigantea individuals was larger than that of uninfected individuals, probably because larger E. gigantea has larger surface area for attachment of the parasite. Cyst formation or conjugating individuals were not observed.