Recent Research on Homing and Straying of Hatchery Pink Salmon in Hokkaido, Japan

Transcription

1 Recent Research on Homing and Straying of Hatchery Pink Salmon in Hokkaido, Japan State of the Salmon Workshop 7-9 Feb. 2013, Portland Mitsuru TORAO Salmon and Freshwater Fisheries Research Institute, Hokkaido Research Organization

2 Today s Contents Researches on Homing and Straying of Hatchery Pink Salmon in Nemuro Strait, Eastern Hokkaido 1. Homing rate and return rate of marked hatchery pink salmon in 2008 and 2009 released from the Tohoro river 2. Homing rate of the marked in 2010 released from three different rivers 3. Wild Pink Salmon Population reproducing independently of hatchery pink salmon in a tributary

3 Homing rate of Hatchery Pink Salmon in 2008 and 2009 Otolith-marked fry were released in the Tohoro River Release timing: March to April in 2007 and 2008 Marking: eyed eggs immersed in ALC (alizarin complexone) solution Mean release size: g Number of released: 4.4 million (2007) and 4.8 million (2008). All the released had ALC marking. Release site; Tohoro Hatchery (60 km from river mouth)

4 Sampling for Recovering Marked Adult Fish September in 2008 and 2009 Weirs in 13 rivers for stock enhancement programs mark ratio number of captured =Numbers of marked ascended were estimated

5 Recovery of Marked Adult Pink Salmon in 2008 Rivers No. sampled No.marked recovered Mark ratio (%) Total no. captured Estimated no.marked Sashirui R , Rausu R. & Shunkari-kotan R , Motosakimui R. (2.00) Kunbetsu R , Ichani R. (3.00) 2, Shibetsu R , Tohoro R. 1,626 1, ,819 5,570 Nishibetsu R. 1, , Shunbetsu R., Tokotan R., Furen R. & Bettouga R , Total 5,790 1,129 58,834 6,706 Percent of homing; 83.1% (percent of straying 16.9%)

6 Recovery of Marked Adult Pink Salmon in 2009 Rivers No. sampled No.marked recovered Mark ratio (%) Total no. captured Estimated no.marked Sashirui R ,476 0 Rausu R. & Shunkari-kotan R , Kunbetsu R , Ichani R , Shibetsu R ,499 0 Tohoro R , Shunbetsu R.& Tokotan R , Nishibetsu R , Furen R. & Bettouga R , Total 4, , Percent of homing; 38.4% (percent of straying 61.6%)

7 Estimated number of marked Straying Rate Perhaps Differs Between Even and Odd Year Classes in Pink Salmon y = ln(x) R² = Distance from Tohoro River mouth 2009 (km) Distance from natal river (km) Relation between the distances from release river to the number of strays in recovery rivers. The number of strays decreased so as to be far from the release river. Marked were relatively evenly scattered among the rivers sampled.

8 Otolith-marked Fry Were Released from The Three Deferent Rivers Stream type or release site influence the straying intensity of pink salmon? ALC Otolith-marking Release timing: March to April in 2010 Mean release size: g Release site; distance from river mouth Nishibetsu Hatchery; 45 km Bettouga Hatchery; 26 km Shunkari-kotan Hatchery; 0.6 km Number of released SH; 1.1million NH; 1.5million BH; 1.2million

9 Recovery of Marked Pink Salmon in 2011, NH Rivers No. sampled No.marked recovered Mark ratio (%) Total no. captured Estimated no.marked Sashirui R ,556 0 Rausu R , Shunkari-kotan R ,418 0 Kunbetsu R ,241 0 Ichani R ,699 8 Shibetsu R , Tohoro R. & Tokotan R ,394 4 Nishibetsu R. 1, , Furen R Bettouga R Total 5, , Percent of homing; 63.6% (percent of straying 36.4%)

10 Recovery of Marked Pink Salmon in 2011, BH Rivers No. sampled No.marked recovered Mark ratio (%) Total no. captured Estimated no.marked Sashirui R ,556 0 Rausu R ,690 0 Shunkari-kotan R ,418 0 Kunbetsu R ,241 0 Ichani R ,699 0 Shibetsu R ,072 0 Tohoro R. & Tokotan R ,394 0 Nishibetsu R. 1, , Furen R Bettouga R Total 5, , Percent of homing; 46.1% (percent of straying 53.9%)

11 Recovery of Marked Pink Salmon in 2011, SH Rivers No. sampled No.marked recovered Mark ratio (%) Total no. captured Estimated no.marked Sashirui R ,556 0 Rausu R , Shunkari-kotan R , Kunbetsu R ,241 0 Ichani R ,699 8 Shibetsu R , Tohoro R. & Tokotan R ,394 0 Nishibetsu R. 1, ,860 6 Furen R Bettouga R Total 5, , Percent of homing; 26.8% (percent of straying 73.2%)

12 Percent of Homing from The Three Hatcheries Homing rate (%) Release Site Distance from river mouth (km) Farther the release site of hatchery pink fry from river mouth is, the less staying pink salmon adults. Release site may have influenced the intensity of strays NH BH SH Estimated no. of returned to the natal river Percent of homing Estimated no. of returned to the non- natal river Percent of straying Nishibetsu H % % Bettouga H % % Shunkari-kotan H % %

13 However, as the weir to capture the adult were installed mostly near the mouth of river, some of pink salmon entering the weir may be proving or exploring rather than straying.

14 Wild Pink Salmon Population in Sakura River, tributary to Tohoro River Otoliths of the pink salmon carcasses were collected in spawning site of the Tohoro River and Sakura River, a tributary of the Tohoro R. in 2008 and Area surveyed for adult pink salmon in Tohoro River and Sakura River (a tributary) during September - October 2008 and July - October The juvenile pink salmon was released from the Tohoro Hatchery in 2007 and 2008, respectively.

15 Recovery of otolith marked from carcasses In 2008, otoliths were collected from 80 in the Tohoro River, 47 of which were ALC-marked (58.8%). On the other hand, in the Sakura River, otoliths were collected from 175, nine of which were ALC-marked (5.1%) % of marked was found in the Tohoro River in 2008 In 2009, the number of adult pink salmon returned was much smaller than that in 2008 both the Tohoro and Sakura Rivers. Tohoro River has no marked. A total of 23 carcasses found in the Sakura River in 2009, of which seven were marked (30.4%). Changes in the number of ALC marked and nomarked adult pink salmon carcasses collected in Tohoro River and Sakura River during

16 The unmarked were smaller in size than the marked 2008 Female: marked45-51cmfl, no-marked; 37-46cmFL Male: marked; 48-57cmFL Unmarked;37-47cmFL Comparisons of the mean fork length between ALC marked and no-marked pink salmon carcasses in Tohoro and Sakura rivers during Red triangles show ALC marked in Tohoro River. Red circles show ALC marked in Sakura River. Green triangles show no-marked in Tohoro River. Green circles show no-marked in Sakura River both females and males, the average fork length of the returned was 10 cm longer than in 2008 there was a size difference between of different year

17 It is suggested that the marked mainly escapement the Tohoro River and the no-marked mainly ran the Sakura River for spawning although there was straying each other. The Sakura River population had life-history traits differing from those of the marked (i.e., body size and reproduction timing). It is possible that such populations have been reproducing independently from the stock enhancement programs.

18 Summary Strays of pink salmon were assessed in the eastern Hokkaido. Percent of homing was quite different between 2 years in 2008 and 2009 in Tohoro River (83.1 % and 38.4 %, respectively) The farther the release site of hatchery pink fry from river mouth is the less staying pink salmon adults. Capture sites are near the river mouths : It might not be their final destination. Strays of pink salmon were assessed in spawning site in small tributary 83.9 % of marked was found in natal site in the Tohoro River in 2008 Wild population naturally reproduce in the tributary ( may be independent from the hatchery ).

19 Acknowledgements I thanks all of the people who assisted with these studies The Nemuro Salmon Enhancement Programs Association Members of the Salmon and Freshwater Fisheries Research Institute (Mitsuhiro Nagata, Toshio Izawa, Miki Kobayashi, Katsumi Takeuchi, Yutaka Murakami, Yoshitaka Sasaki, Mahito Miyamoto, Kiyoshi Kasugai, Hayato Saneyoshi, Yasuyuki Miyakoshi )