Growth changes in bighand thornyhead Sebastolobus�macrochir off the Pacific coast of northern Honshu, Japan

Abstract

The biomass of bighand thornyhead Sebastolobus macrochir was increased by the high recruitment success of the 1999-2002 year classes off the Pacific coast of northern Honshu, Japan. In this study, the growth of bighand thornyhead was examined over a 9-year period from 1996 to 2004 in this area. The growth of the 1999 year class and the 2000-2002 year classes was reduced at 3 and 2 years old, respectively, while the 1999-2002 year classes were smaller than the 1993-1998 year classes. In 2-, 3-and 4-year-old fish, the relationship between abundance and mean standard length was expressed by negative linear regressions, while fish became smaller when abundance of the year class was larger. Mean bottom temperatures were stable at depths of 350-900 m; variations in water temperature were small in the main distribution area of bighand thornyhead. We discuss the factors affecting the growth of bighand thornyhead via changes in the demersal fish community and feeding habits.

Spatiotemporal variations in nutritional status and feeding habits of immature female bighand thornyhead Sebastolobus macrochir off the Pacific coast of northern Honshu, Japan

“…In the present study, analyses of GLM indicated that the condition of immature bighand thornyhead deteriorated with an increase in depth, and small fish had lower K, HSI, and SCI than larger specimens. The latter result supports our hypothesis (small bighand thornyhead are potentially in poorer condition in the Tohoku area) derived from the previous studies [3][4][5]. It is probable that deeper waters are less favorable and offer a low quality habitat for immature bighand thornyhead because fish condition can be used as an indicator of habitat quality [13] and small fish are subordinate to large fish (dominant individuals).…”

“…Nutritional status is a particularly important factor for fish condition and for population success because it affects growth, reproduction, and survival. Hattori et al [3][4][5] reported that density-dependent distributional changes occurred in bighand thornyhead during the 2000s (with small fish occurring in deeper waters due to the increase in density of large fish), and that the growth of 2-and 3-yearold fish was reduced by the increase in fish biomass during the 2000s. In the present study, analyses of GLM indicated that the condition of immature bighand thornyhead deteriorated with an increase in depth, and small fish had lower K, HSI, and SCI than larger specimens.…”

“…The nutritional value of crustaceans is two-to fourfold higher than ophiuroids or polychaetes, and fish is considered the best quality food item for bighand thornyhead [9]. Firefly squid [18] and benthic shrimps [4] are also an important food item for bighand thornyhead in the Tohoku area. The study of the feeding habits also indicate that deeper waters are a low quality habitat for immature bighand thornyhead.…”

“…In the Tohoku area, off the Pacific coast of northern Honshu, Japan, most bighand thornyhead live at depth zones ranging from 500 to 800 m [1]. Hattori et al [3,4] reported that the biomass of this species during the 2000s showed an increase, with high recruitment success in the 1999-2002 year classes, and that the mean growth rate was reduced by the increase in fish biomass during the 2000s. Moreover, in a previous paper, Hattori et al [5] suggested that the main distribution depths of small fish [B10 cm standard length (SL)] increased (to 600-700 from 500-600 m) with an increase in density of large fish (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) cm SL) at depths of 500-600 m.…”

Long-term monitoring of bottom environments of the continental slope off Otsuchi Bay, northeastern Japan

“…The bathyal site is within the O 2 -depleted zone of the North Pacific (DO < 45 μM; found at water depths from 700 to 1300 m; Ogura 1970;Fontanier et al 2014). Although there is little fishery activity at the bathyal depth, some important fishery resources such as Sebastolobus macrochir is distributed at that depth (e.g., Hattori et al 2007;Sakaguchi-Orui et al 2014), and knowledge of benthic habitats is essential information for understanding the ecology of such fish. It is also important to observe environmental parameters at this depth to understand how intermediate waters change seasonally at the seafloor, because these variations have not been well understood.…”