Spatio-temporal distribution and biomass of Benthosema pterotum (Pisces: Myctophidae) in the shelf region of the East China Sea

Abstract

We examined the spatio-temporal distribution and biomass of Benthosema pterotum, a dominant mesopelagic-boundary myctophid in the shelf region of the East China Sea, based on data from seasonal bottom-trawl surveys. They are a major prey item for commercially important demersal fishes in this area. A total of 980 000 individuals with a wet weight of 554 kg were collected from 694 bottom-trawl net samples. Dense distributions (>10 5 ind. km -2) of B. pterotum were observed mainly in the area south of Cheju Island in all seasons, where a persistent cyclonic eddy occurs. The distribution pattern indicated the presence of an independent population completing their life cycle in the area south of Cheju Island. Daytime habitat depth of B. pterotum (mainly 40 to 90 m depth) was a markedly shallower depth than previous reports for adult fishes for the family Myctophidae. The mechanism of population maintenance of this mesopelagic species in such a shallow area was hypothesized to be related to the presence of highly turbid waters in the benthopelagic layer, which produces dim light conditions during the daytime. The biomass of B. pterotum in the area south of Cheju Island was estimated to range from 3900 to 38 400 t.KEY WORDS: Population maintenance · Mesopelagic-boundary myctophid · Benthosema pterotum · Biomass · Highly turbid waters · Continental shelf region · Mesopelagic species Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 407: [227][228][229][230][231][232][233][234][235][236][237][238][239][240][241] 2010 The biomass of myctophids was shown to influence the population dynamics of demersal fishes in the continental slope off northern Japan (Yamamura & Inada 2001).Benthosema pterotum is a typical mesopelagicboundary myctophid, widely distributed in the subtropical-tropical waters of the Indo-West Pacific, especially over or near the continental shelves (Gjøsaeter 1984, Valinassab et al. 2007, Yamada et al. 2007). They are small-sized, with a maximum body size of ca. 55 mm standard length (SL), and have a life cycle of 1 yr (Gjøsaeter 1984, Dalpadado 1988). An extremely large biomass of B. pterotum (ca. 100 million t) was estimated in the Arabian Sea, and attempts were made to evaluate its potential as a fisheries resource (Gjøsaeter 1984, Valinassab et al. 2007). This species is one of the most abundant myctophids in the East China Sea (ECS), one of the largest marginal seas of the western Pacific, including important fishing grounds for various pelagic and demersal fishes (Seikai National Fisheries Research Institute 2001, Yamada et al. 2007).In the ECS, Benthosema pterotum occur in the epipelagic layer during the larval stage (Ozawa 1986, C. Sassa unpubl. data). Transformation to the juvenile stage begins at ca. 12 to 13 mm SL, after which they start diel vertical migrations (Gjøsaeter 1984, Ozawa 1986. The juveniles and adults occur in the epipelagic layer at night, and descend to the benthopelagic layer of the continental shelf (< 200 m depth) dur...

Internal wave-mediated shading causes frequent vertical migrations in fishes

“…The best documented example is DVM, such as the DVM of hake and horse mackerel in the Benguela Current (Axelsen et al 2004, Pillar & Barange 1995, but temporal fish migrations have also been observed for light variations related to variable cloudiness (Baliño & Aksnes 1993, Staby & Aksnes 2011. Similarly, spatial variations in the fish depth dis tribution have been associated with cooccurring variations in shading caused by chlorophyll (Kaart vedt et al 1996) and related to turbidity from re suspended sediments (Sassa et al 2010). We reject the alternative explanation that the fish movements that are in opposite phase with the wave were caused by physical displacement by a near-bottom Type II wave in the opposite phase (Shroyer et al 2010).…”

Comparative reproductive biology of three dominant myctophids of the genus Diaphus on the slope region of the East China Sea

“…A broad continental shelf (<200 m depth) occurs in the western part accounting for approximately 80% of the area of the ECS, contrasting with the deep Okinawa Trough (a maximum depth of 2,716 m) in the eastern part where the oligotrophic Kuroshio flows northeastward (Niino and Emery, 1961;Yamada et al, 2007). Oceanic myctophids occur abundantly in the Kuroshio waters, while pseudoceanic myctophids, adapting to certain habitats of continental slopes, slopes of islands, and seamounts (Hulley and Lutjeharms, 1989;Reid et al, 1991;Gartner et al, 1997), occur dominantly on the ECS shelf and slope (Ozawa and Tsukahara, 1971;Wang and Chen, 2001;Sassa et al, 2004Sassa et al, , 2010Sassa and Konishi, 2015).…”

Distribution, hatch-date, growth, and mortality of larval Benthosema pterotum (Pisces: Myctophidae) in the shelf region of the East China Sea

“…the area south-west of Cheju Island (Figure 1), where the biomass is estimated in the order of several thousands to several tens of thousands of metric tons . In the ECS they occur in the epipelagic layer at night, and migrate down to the benthopelagic layer during the daytime to form dense aggregations (Yamada et al, 2007;Sassa et al, 2010). In the ECS they occur in the epipelagic layer at night, and migrate down to the benthopelagic layer during the daytime to form dense aggregations (Yamada et al, 2007;Sassa et al, 2010).…”

“…In the ECS they occur in the epipelagic layer at night, and migrate down to the benthopelagic layer during the daytime to form dense aggregations (Yamada et al, 2007;Sassa et al, 2010). Morphology, distribution, feeding and reproduction of B. pterotum in the ECS have been studied (Ozawa & Peñaflor, 1990;Ishihara et al, 1995;Ishihara & Kubota, 1997;Sassa et al, 2010Sassa et al, , 2014a, but study of the early life history, which is essential for understanding the population dynamics of this species, has been limited in the ECS. Therefore, this species is a key species in the ECS, acting as an important link between secondary producers and upper trophic levels.…”