Food habits of threadfin hakeling Laemonema longipes along the Pacific coast of northern Japan

Abstract

Food habits of threadfin hakeling Laemonema longipes, the dominant demersal fish in the upper continental slope of the western sub-Arctic North Pacific, were described based upon >1400 specimens collected off north-eastern Honshu Island and south-eastern Hokkaido Island, Japan. Threadfin hakeling depended exclusively on pelagic organisms including copepods Neocalanus cristatus, Euphausia pacifica, shrimps Sergestes similis, firefly squid Watasenia scintillans and myctophids Diaphus theta. Threadfin hakeling showed a clear size-dependent dietary variation, with mesozooplankton and shrimps being important for small- and medium-sized fish (≤400 mm standard length (SL)), and myctophids being important for large-sized fish (>400 mm SL). Since all of these prey undertake diurnal vertical migration, it was concluded that threadfin hakeling take an important role in capturing energy and materials transported from the epipelagic zone to the bathypelagic layer over the upper continental slope. Dietary variation among different areas, seasons and depths were also examined. Of these, areal difference was rather obscure reflecting common prey field in the Tohoku and Doto areas under the prevalence of the North Pacific Intermediate Water, whereas clear seasonal difference was found in the Doto area; the 0-group of walleye pollock Theragra chalcogramma was ingested only in the late summer and early autumn in this area.

Influences of Ocean Currents on the Diets of Demersal Fish Communities in the Western North Pacific Revealed by Their Muscle Carbon and Nitrogen Isotopic Compositions

“…Laemonema longipes and P. japonicus also showed variable δ 15 N Phe values, supporting the speculation cited above that they had migrated from south of Sanriku where phytoplankton δ 15 N values vary up to 5 (Matsubayashi et al, 2020). The TP values of L. longipes were approximately 0.5 units higher than those of P. japonicus, possibly because L. longipes prefers to feed on squids and mesopelagic fish, whereas P. japonicus feeds on amphipods, small shrimps, and large zooplankton, such as Euphausia japonica and Neocalanus cristatus (Yamamura and Nobetsu, 2012). G. macrocephalus also showed a higher TP than other gadiform species, probably because it consumes a variety of food items, including squids, octopi, krills, crabs, and other fish, such as the juveniles of G. chalcogrammus, as well as practicing intraspecies cannibalism (Hashimoto, 1974;Fujita et al, 1995).…”

“…However, our data show that their TPs and 14 C Bulk values are extremely different. The lower 14 C Bulk values of L. longipes are consistent with its preference for deep water (Yamamura and Nobetsu, 2012) (catch-record depth: 318-656 m; Supplementary Table 1), where the Oyashio Current conveys 14 C-depleted food sources. By contrast, P. japonicus prefers shallower water (Kitagawa and Nagahora, 1983) (catch-record depth: 20-561 m; Supplementary Table 1).…”

Interannual variation in diets of walleye pollock in the Doto area, in relation to climate variation

“…Food depletion is likely in years of poor prey production in the EBS because the wide continental shelf (> 500 km) (Stabeno et al 1999) prevents the advective supply of prey from the outer shelf (Napp et al 2000, Ciannelli et al 2002, whereas a relatively narrow (< 30 km) continental shelf makes it easy for offshore prey to be advected into the coastal area (Tatebe et al 2010). Juvenile pollock in the Doto area are capable of accessing the outer-shelf production, although more predation risk is expected in deeper waters (Yamamura & Nobetsu 2012). Thus, pollock in the Doto area have flexible feeding habits to cope with environmental variability by utilizing a wide range of prey items and habitats.…”

“…In addition to being a target of one of the world's largest fisheries (FAO 2009), pollock plays an important role as a forage fish and as an intermediate predator in marine ecosystems due to its widespread distribution and high abundance. Besides being an important prey for demersal fishes and marine mammals (Springer 1992, Tamura et al 1998, Yamamura & Nobetsu 2012, its feeding impact has the potential to deplete local prey abundances (Ciannelli et al 2004, Wilson et al 2009). Numerous studies have examined the food habits of pollock throughout its range, describing geographical, ontogenetic and seasonal variations in diet (Dwyer et al 1987, Gorbatenko & Dolganova 1989, Yamamura et al 2002, Wilson et al 2011.…”