Program

Nearly all the chum salmon, Oncorhynchus keta, returning to Japan are assumed to originate from hatcheries. However, recent studies have reported that naturally spawning chum salmon are observed in many rivers in Hokkaido. Management of naturally spawning fish is necessary to conserve healthy stocks of this species; however, few studies exist on naturally spawning fish and very few of these are quantitative. In the present study, we quantitatively assessed the number of fish with natural-spawning origins and hatchery-origins in an enhanced river (Uebetsu River) and in non-enhanced rivers (Sakimui River and Kotanuka River) 5 km and 12 km from Uebetsu River in the northern region of Nemuro, Hokkaido. At the Uebetsu hatchery, all hatchery-reared chum salmon juveniles (2,084,000) of the 2010-year class were otolith-marked with alizarin complexone (ALC) and released in the Uebetsu River in the spring of 2011. Between mid- September and late December during the period 2013–2015, when the marked fish returned at age 3, 4, and 5, we counted the number of chum salmon and collected scales and otolith from carcasses via a foot survey in 10-day intervals in the three rivers. The escapements were estimated by the area-under-the-curve (AUC) method. The average escapements (ranges in parenthesis) were estimated as 3,470 (2,882–4,064) individuals in Uebetsu River, 532 (230–751) in Sakimui River and 355 (276–423) in Kotanuka River. In the 2010-year class, 1,285 individuals were estimated to be hatchery-origin fish and 1,474 were estimated to be of natural-spawning origin in Uebetsu River. Moreover, marked fish were also found in the non-enhanced Sakimui and Kotanuka Rivers, indicating that hatchery-reared fish released in the Uebetsu River entered and spawned in these rivers as well. Our study suggests that hatchery-origin fish contribute to maintaining naturally spawning chum salmon populations in Hokkaido.

The production of healthy fry is required to stem the sudden decline, since 2010, in the return rates of chum salmon, Oncorhynchus keta, in northeastern Japan. Both ground and river water are used for hatchery production; however, significant mortalities have been observed when high turbidity river water flows into the rearing tanks. Our study revealed that, in Iwate Prefecture, turbidity of Ugegawa River water which is used for hatchery production was high after rainfall in spring. The highest turbidities were nearly 350 mg/L in 2014 and 2015. Mean diameter of the particles was 42 µm and ignition loss was 23% in 2014. The increasing trend in turbidity corresponded with the precipitation.
Therefore, temporal changes in the turbidity of the river water were recorded and the effects of particles in the water on the survival of salmon fry were examined in a laboratory experiment. When the turbidity concentration was set at 20,000 mg/L, and the glass bead particle size at 45.2, 75, 94.3 and 156 μm, the survival rate after 72 hours, was 86, 50, 44, and 23 %, respectively. That is the survival rate after 72 hours was lower as the particle size increased. Many glass beads adhered to the gills in the dead fry.
From these results, it was considered that suspended particles with a high concentration and large particle size contained in rearing water in early spring caused death in relation to adhering to the gills of fry. To enhance survival, it is necessary to make rearing tanks deeper or to slow the flow rate of the river water to remove suspended particles when the river water is turbid.

Reproductive biology of Brook trout, Neolissochilus stracheyi (Day, 1871), were sampled in the Northern of Thailand during October 2010 - September 2011 from fisherman, using gillnet of various mesh sizes. For the study of relationships between total length and body weight, spawning seasons, sex ratio and fecundity. At least 66 fish samples were used every month. The result showed that the total 821 Brook trout had 7.4-61(23.32±5.91 cm). There were 353 males that had fish samples there were 8.5-45.1 cm of TL (22.36±5.91cm) and 468 females that had 7.4±61 cm of TL (24.04±7.09 cm). The relationships equation between total length and weight was W = 0.008TL^3.064 (r² = 0.940) for total fish, W=0.007TL^3.107 (r² = 0.946) for females and W=0.010TL^3.003 (r² = 0.930) for males. The relative condition factor (K) of male and female was 1.090±0.067 and 1.116±0.102 respectively. The max of GSI was in June for male and female. The spawning season was found all year round with 3 peaks: January, June and August. Estimated fecundity of mature ovaries ranged from 220 to 3,500 eggs. The estimated average fecundity was 1404.55 ±651.51 eggs. The relationships between fecundity and total length revealed F= 121.1TL-2100 and relationships between fecundity and weight revealed F= 4.535 + 128.78. The results from studies can be further applied for the economic culture, conservation and management of the Brook trout in Northern, Thailand.

In Lake Towada, Japan, the kokanee salmon, Oncorhynchus nerka was registered with a trademark brand for additional values in recent years. However, it has been argued that the values can be degraded due to damage caused by gill nets currently used. To explore alternative better fishing way, it is important to study details of distribution and behavior of the kokanee salmon. Objectives of this study is to reveal horizontal swimming speed and migration path of the kokanee in Lake Towada by acoustic telemetry to enhance understanding of their basic ecology. Total of 19 kokanees were tagged with ultrasonic pingers (V9-2H, Vemco, Canada). An acoustic gate (Stations 1-6) was deployed using six receivers (VR2W and VR2TX, Vemco, Canada) at the west side of the Lake Towada. Another receiver (St. 7) was deployed in front of a hatchery where the salmons migrate for spawning. The pingers emit ID signals every 90 seconds on average and the estimated monitoring range was 400 m based on a range test. Positions of the tagged fish were determined by hyperbolic localization in order to calculate swimming speeds of the fish. Seasonal change in migration paths and residence times of each fish were also analyzed. The acoustic telemetry was conducted for 110 days from June 10th, 2016. Average total length of the kokanee was 0.26 m. Median of swimming speed was 0.69 m/s (n=294). Continuous residence times around the receivers were 0.0167-84.3 hours (Median: 0.425 hour). In July, the residence time peaked in all receivers except St.7 and decreased in August. In September, the residence times around 3 receivers near the west coast were 79, 167, 134, which were more than those in August. This study has shown that migration paths of the kokanees in Lake Towada in September, or spawning season, was near the west coast.

An important issue in the management of stream salmonid fisheries in Japan is the extent to which catch and release (C&R) regulations can be used to sustain a quality recreational fishery without the need for supplemental stocking. We examined this issue in the Itoshiro River where a catch and release (C&R) regulation for salmonids, particularly white-spotted charr, Salvelinus leucomaenis, was adopted in 2000, and stocking was discontinued in 2002. We compared fish populations under three treatments: sites that were C&R fishing only, sites where harvest was allowed under general fishing regulations, and sites that were closed to fishing all year. Fish were not stocked in the C&R and closed-fishing sites but were stocked in the general regulation sites every year where anglers could keep fish >15 cm with no daily creel limit. We electrofished and estimated the charr populations across all three treatments and found a total of 464 individuals of charr from 27 sites during 2014-2016. A significantly greater fish density was found in C&R sites (an average of 533 g fish per 100 m^2) compared to the sites with the general fishing regulation (203 g per 100 m^2). No significant difference was found between the C&R sites and the sites closed to fishing (an average of 226 g fish per 100 m^2). Moreover, fish >15 cm in total length comprised nearly 50% of the population in the C&R and 40% in the closed-fishing sites but only 15% in the general regulation sites. These results suggest that a C&R regulation can be used to maintain a quality recreational fishery without the need to stock hatchery charr.

Increasing evidences indicate that cephalopods have been thriving with declined commercial fish species in China Seas in spite of over-exploitation. It might be the joint effects of climate change and intensive fishing pressure that change the structure and function of coastal ecosystem. Cephalopods clearly take advantage of the “loophole” and turn out to occupy a broad niche. Here, we evaluate the abundance pattern and ecological role of cephalopods in the Chinese coastal area, taking Haizhou Bay as a typical example using integrative approaches. Fishery-independent surveys during 2011-2016 identified only eight cephalopod species but with substantial biomass compared to fish groups throughout the year. Although seasonal species composition in cephalopods varied largely year to year, Octopus ocellatus tends to be dominant species in winter and spring, while Loligo japonica shows high abundance in summer and autumn. Therefore, we focus on these two dominant cephalopod species with distinct seasonal patterns to examine their interaction with local ecosystem. O.ocellatus is characterized as a local, large-size benthic predator, while L. japonica is small-size, widely-distributed and important pelagic prey for many fish species. GAM analysis showed that surface and bottom water temperature are strongly correlated with abundance of L. japonica and O. ocellatus respectively. Additionally, a food-web model indicated that O. ocellatus turns out to be top predator with a high trophic level of 4.27, while L. japonica is in the core position of food web. It suggests that octopus have a significant top-down impact on other elements in the ecosystem, and bottom-up flow from loligo squid to predators is also crucial. Compared to previous study in 2001, our results indicate that ecosystem structure of Haizhou Bay has largely changed. In conclusion, ecological roles of cephalopod in over-exploited coastal ecosystem are gradually prominent in the context of changing environmental and ecological conditions.