Catch efficiency of dredge netting for sea cucumber, Apostichopus armata, in northern Hokkaido

We estimated the catch efficiency of dredge netting for sea cucumber, Apostichopus armata, by using fishery records and GPS data for fishing boats from coastal areas of northern Hokkaido. We calculated the catch efficiency by subtracting the abundance in weight recorded on the final capture day from the abundance in weight recorded on the first capture day, and dividing the remainder by the total catch within a grid. We showed that, for high catch rates, the range of estimated catch efficiency was narrow. We superimposed the distribution map of catch efficiency onto bathymetry data, and used regression tree analysis to evaluate catch efficiencies of <1. We revealed that the estimates of catch efficiency ranged from 0.09 to 0.53 (mean 0.29), because of the complexity of the sea bottom. Our results confirm the validity of estimating the catch efficiency of dredge netting, by considering the effect of bathymetry.
 

The effects of different methods of preservation and fixation in formalin and ethanol upon body size of juvenile chum salmon

The effects of preservation (freezing & thawing, chilling, and chilling plus freezing & thawing) and fixation in formalin and ethanol upon body size (length and weight) of three different fish size groups of juvenile chum salmon Oncorhynchus keta were investigated. Body size decreased in most fish of all size groups after preservation, although body size increased in some fish after chilling. Body size after fixation decreased in most fish compared to those after preservation. Decreases in body size fixed after freezing & thawing and chilling plus freezing & thawing were larger than those fixed after chilling and death. Changes in body size with preservation and fixation were different among the three size groups.
 

Characteristics of body size of chum salmon returning to Okhotsk rivers in Hokkaido

Fork length, body weight, and age of chum salmon Oncorhynchus keta returning to 7 rivers in the Okhotsk Sea region were measured, 2010-2012. Mean fork lengths of chum salmon were larger in the western region than those in the central or the eastern regions. Also, in many rivers, fork lengths were different among run timings; larger for fish captured in earlier timing (August and September) and smaller for fish captured in the later timing (November and December). When fork lengths of chum salmon of the same ages (age-4 and age-5) captured in October were compared, the difference of fork lengths among rivers was smaller, but was significant. In 2012, body sizes of chum salmon returning to Hokkaido were small, and the differences of fork lengths among rivers were not significant for all ages and sexes. When body sizes of chum salmon returning to rivers were compared, age and run timing should be taken into account.
 

Distribution and biochemical conditions of shishamo smelt Spirinchus lanceolatus larvae and juvenile in coastal waters off Mukawa River mouth

The spatial distribution and biochemical conditions of shishamo smelt Spirinchus lanceolatus larvae and juvenile were examined to elucidate the early life history of this species in the coastal waters. Shishamo smelt were collected with sledge nets in the coastal waters off Mukawa River mouth from May to July in 2004-2006. Shishamo larvae were collected from mid-May or mid-June, the highest densities in each year were observed in a range from 12 to 14 °C in water temperature. The total length of shishamo smelt collected was in a range of 9.3-42.4 mm. During the years of our study, the size distributions were unimodal. Although the RNA/DNA ratio showed a high value of 4-12 in 15-20 mmTL, it decreased rapidly to 25 mmTL. And then the ratio reached a constant level in 2-6 around 30 mmTL. The triglyceride/phospholipid ratio was in a range of 0.14-0.85, and was linearly related to total length. The biochemical state is assumed to fluctuate with the body size class of shihamo larvae and juveniles, and was not necessarily constant within the same year class.
 

Current status of naturally-spawning masu salmon (Oncorhynchus masou) populations in Shiribeshi region, Hokkaido, northern Japan (Note)

Evaluation of spawning habitat for chum and masu salmon in Tokachi River basin (Note)

Seasonal variation of various components of Saccharina cichorioides Miyabe（Note）