Notes on the fishes of the Severnaya Zemlya archipelago and the spawning area of polar cod Boreogadus saida (Gadidae)

Data on the fishes of the high-latitude Severnaya Zemlya archipelago (the North Land) is presented. The archipelago is located in the Arctic on the border between the Kara Sea and the Laptev Sea. The ichthyofauna of the archipelago has not been studied; therefore, even small collections are of interest. Fish samples were obtained during the expedition “Open Ocean: Arctic Archipelagos – 2019: Severnaya Zemlya”. In addition, the samples from this area in the collections of the Zoological Institute (ZIN) were studied, which have been received from polar expeditions to the Kara and Laptev seas during the entire era of polar research. The most significant fact is the discovery of mass accumulation of polar cod Boreogadus saida (Lepechin, 1774) larvae in Mikoyan Bay (Bolshevik Island), which gives evidence of important spawning grounds near Severnaya Zemlya. Indirect evidence of this can be found in the publications of polar explorers who overwintered on Severnaya Zemlya in the 1930s–1950s and have reported that the polar cod approaches the shores for spawning in August, in huge schools. The waters of Severnaya Zemlya represent the spawning area of polar cod in the central part of the Eurasian shelf, which is not mentioned in current literature. In addition to polar cod, a few more species are registered in samples from the coastal waters of the archipelago (depths to 38 m), rough hookear sculpin Artediellus scaber Knipowitsch, 1907, twohorn sculpin Icelus bicornis (Reinhardt, 1840) (family Cottidae), Liparis tunicatus Reinhardt, 1836, black-bellied snailfish L. cf. fabricii (Liparidae), Knipowich eelpout Gymnelus knipowitschi Chernova, 1999 (Zoarcidae) and three-spined stickleback Gasterosteus aculeatus (Linnaeus, 1758) (Gasterosteidae). In the deepwater straits, snailfish Careproctus sp. (174–234 m) and pale eelpout Lycodes pallidus Collett, 1879 (105–348 m) were found. The Arctic charr Salvelinus alpinus (Linnaeus, 1758) (Salmonidae) inhabits some lakes of the archipelago. This is the first finding of a three-spined stickleback in the east of the Kara Sea.

Distribution and size variability of Japanese eel leptocephali in their Pacific Ocean spawning area using carbon and nitrogen stable isotope ratio analyses

The diets of larval (leptocephali) anguillid and marine eels are poorly understood, despite studies on their gut contents or stable isotope ratios suggesting marine snow particles represent a food source. Concerns for Japanese eel Anguilla japonica stock conservation necessitate an improved knowledge of their larval ecology to better understand the causes of their recent decline in numbers and fluctuating recruitment into East Asia. To understand the distribution of and variation in size of leptocephali in relation to their feeding, we examine carbon and nitrogen stable isotope ratios of larvae from seven research cruises (2002–2013) in the North Equatorial Current spawning area. Preleptocephali (2–3 days old, ~5 mm total length) isotope ratios reflect maternal ratios, but feeding-stage leptocephali (8–56 mm) tend to have higher ∂15N values with decrease of latitude typically in areas south of a salinity front. Neither ∂15N nor ∂13C ratios are clearly related to longitude or larval size < 30 mm, but ∂13C values of larvae > 40 mm are lower further downstream in the North Equatorial Current and Subtropical Countercurrent. Differences in ∂13C values might be a function of varying spatial baselines in the two currents apart from the spawning area. Although among-year larval isotope ratio differences may reflect temporal baseline variation related to the location of the salinity front, more research with much wider range observations in the spawning season is required because ingested marine snow particles might differ with larval growth and location.

New clues on the Atlantic eels spawning behavior and area: the Mid-Atlantic Ridge hypothesis

The Sargasso Sea has long been considered as the only spawning area for Atlantic eels, despite the absence of direct observations. The present study raises a novel scenario, deviating from Schmidt’s dogma, begins with a review of historical and recent observations that were combined to build up a global theory on spawning ecology and migration behavior of Atlantic eels. From this, it is argued that a favorable spawning area could be located eastward of Sargasso Sea at the intersection between the Mid-Atlantic Ridge and the oceanic fronts. Ocean circulation models combined with 3D particle-tracking method confirmed that spawning at this specific area would result in larval distribution fitting the field observation. This study explores the hypothesis that leptocephali are able to swim and orientate to reach their specific growth areas. It proposes a novel framework about spawning ecology, based on orientation, navigation and meeting cues of silver eels to the spawning area. Together this framework may serve as a stepping-stone for solving the long-lasting mystery of eel reproduction which first came out 2,400 years ago and promotes the understanding of oceanic migration and reproduction of marine organisms.

Protection Efforts of Lutjanus bohar (The Two-Spot Red Snapper) Spawning Area in Hoga Island Waters, Kaledupa-Wakatobi National Park

A spawning area of Lutjanus bohar, a marine fish of high economic value, is one of the eight important resources of Wakatobi and also a critical habitat in the waters of Hoga Island. For protecting the area, Wakatobi National Park has stated the area as a tourism zone (no-take zone). This research was conducted to evaluate progress toward spawning-area protection by examine number of individuals, length size of fish, and trespassing cases that occurred in the spawning area. Research was carried out in 2018-2019. Number of individuals and size of fish were collected by referring to the monitoring guidelines for the Spawning Aggregation Site (SPAGs), and observations with an Underwater Visual Census. Trespassing case data were collected by interview key persons. Descriptive analysis was used to describe progress toward spawning-area protection. The results indicate that the protection effort of spawning area has a positive impact in increasing number of individuals and length of Lutjanus bohar. However, number of trespassing cases in the waters of Hoga Island still shows an increase. Fishing activities are the most trespassing cases occurred in the spawning area. This approach should be implemented to evaluate the progress towards protection efforts, besides increasing the number of patrols and socialization with fishermen to increase their awareness.

Tracking the marine migration routes of South Pacific silver eels

It is still a mystery how catadromous eels find their way through the seemingly featureless open ocean to their spawning areas. Three catadromous Pacific eels (2 Anguilla marmorata, 1 A. megastoma) from the Archipelago of Vanuatu were tagged with pop-up satellite archival transmitters, and their migration tracks towards their presumed spawning area approximately 870 km northeast of the point of release were reconstructed in order to evaluate their movements in relation to oceanographic conditions. We used the timing of diel vertical migrations to derive the eels’ positions. The 2 A. marmorata exhibited steep-angled turns resulting in a zig-zag migration path along the east-west axis, while the A. megastoma took a relatively straight course towards the presumed spawning area. They migrated with a speed over ground of 21-23 km d-1. In this region, the eastward flow of the South Equatorial Counter Current (SECC, ~5°-10°S) separates the westward flowing South Equatorial Current (SEC; ~0°-5°S and 10°-18°S) into 2 branches. During shallower nighttime migration depths around 150 m, eels crossed a variable flow field through the southern branch of the westward SEC with westward propagating mesoscale eddies and the eastward SECC, but stayed south of the stronger northern branch of the SEC, possibly increasing retention time of larvae within this area. The eels headed towards a tongue of high-salinity Subtropical Underwater (STUW). The eels did not move beyond a salinity front of 35.9-36.0 at a depth of 100-200 m, which may have provided cues for orientation towards the spawning area.