Sea-entry conditions of juvenile chum salmon Oncorhynchus keta that improve post-sea-entry survival: a case study of the
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ORIGINAL ARTICLE Biology
Sea‑entry conditions of juvenile chum salmon Oncorhynchus keta that improve post‑sea‑entry survival: a case study of the 2012 brood‑year stock released from the Kushiro River, eastern Hokkaido, Japan Kentaro Honda1 · Kotaro Shirai2 · Shinji Komatsu3,4 · Toshihiko Saito1 Received: 9 March 2020 / Accepted: 29 June 2020 / Published online: 18 August 2020 © Japanese Society of Fisheries Science 2020
Abstract We examined the sea-entry conditions (i.e., timing and body size) of juvenile chum salmon that improve their survival during their coastal residency. On 25 June 2013, we sampled 365 juvenile chum salmon [57.5–98.6 mm fork length (FL)] off Konbumori, eastern Hokkaido, ⁓ 20 km east of the Kushiro River mouth, which originated from a hatchery in the Kushiro River. Sea-entry conditions of these Konbumori juveniles back-calculated using otolith daily increment analysis were compared with data from 373 juveniles released from the same hatchery that were captured at the mouth of Kushiro River (i.e., just before sea entry) from April to July 2013. Most of the Konbumori fish were estimated to have entered the sea from 25 May to 5 June, when coastal surface temperatures constantly exceeded 5 °C, which is considered favorable for juveniles. The estimated FLs at sea entry of the Konbumori fish were larger than FLs of fish sampled at the river mouth during a comparable period, which suggests that size-selective mortality existed. Back-calculated post-sea-entry growth rates of fish with larger FL at sea entry, particularly those with FL > 65 mm, tended to be high enough for survival among the Konbumori fish. Assuming growth-dependent mortality, this case study suggests that the release of larger-sized juveniles under favorable coastal temperature conditions improves their survival. Keywords Coastal condition · Daily growth increments · Early marine life · Hatchery fish · Pacific salmon · Sea entry · Size-selective mortality Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12562-020-01442-0) contains supplementary material, which is available to authorized users. * Kentaro Honda [email protected] 1
Hokkaido National Fisheries Research Institute, Japan Fisheries Research and Education Agency, 2‑2 Nakanoshima, Toyohira‑ku, Sapporo, Hokkaido 062‑0922, Japan
2
Atmosphere and Ocean Research Institute, The University of Tokyo, 5‑1‑5, Kashiwanoha, Kashiwa, Chiba 277‑8564, Japan
3
Hokkaido National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Kita 6‑sen, Higashi 4, Setsuri, Tsurui, Akan, Hokkaido 085‑1200, Japan
4
Present Address: Tohoku National Fisheries Research Institute, Japan Fisheries Research and Education Agency, 4‑9‑1, Sakiyama, Miyako, Iwate 027‑0097, Japan
Introduction Pacific salmon Oncorhynchus spp. are important fishery resources in the North Pacific. Species of this genus typically undergo massive mortality during their early life stages (Beamish 2018), and chum salmon Oncorhynchus keta are no
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