The identification of individuals with hatchery and natural origin in a mixed sample of Amur River chum salmon by Otolith microchemistry

We estimated the proportion of hatchery and natural fall spawning chum salmon returning to the Amur River using chemical markers specific to hatchery-origin fry.We used otolith microchemistry technique to identify fish with artificial origin among returning spawners.First,we found that juveniles of artificial origin had higher values of the Sr:Ca molar ratio of the otoliths’edge zone compared with juveniles of natural origin,what can be related to the use of rearing feed produced from raw materials of marine origin rich in strontium.Then we observed that most of the spawners from Anyuisky Hatchery and from the Amur River mouth at the start of the spawning migration has also the higher value of Sr:Ca molar ratio of the juvenile zone of otoliths.Also,adults with higher values of the Sr:Ca molar ratio are characterized by a skewed right in the peak of the age distribution.Both,the age structure and phenological shift in the time of spawning migration of individuals with higher value of the used chemical marker corresponds to results of studies on hatchery-produced chum salmon completed at different parts on Northern Pacific.The results of this study will be used in the management of Amur fall chum salmon fisheries,and also demonstrates the necessity of the development of specific measures for increasing the survival of juvenile anadromous salmonids released at large rivers and exposed to prolonged freshwater migration to the ocean.As a further application of the methodology,we plan to identify the markers specific to each of the hatcheries and main spawning tributaries belonging to Amur River catchments.This will be an important step in the evaluation of the contribution of different stocks in mixed fisheries and also in the estimation of the effect of hatchery releases on naturally spawning stocks of Amur fall chum.Following to,our results may indicate the applicability of this approach for the determination of artificial-origin fish in a mixed sample of the Amur fall chum salmon.

Unravelling habitat use of Coilia nasus from the Rokkaku River and Chikugo River estuaries of Japan by otolith strontium and calcium

The migratory history of the engraulid fish Coilia nasus in the Rokkaku and Chikugo River estuaries of the Ariake Sea, Japan was assessed using otolith strontium（Sr） X-ray intensity maps and strontium：calcium（Sr：Ca） ratio life history transects by an electron probe microanalyzer（EPMA）. The results showed that seven of the ten specimens from the Rokkaku River Estuary（LJC） and all 15 specimens collected in the Chikugo River Estuary（ZHC） had low Sr：Ca ratios（≤3） at the central otolith area, indicating their riverine origin and initial freshwater residence. After the first regime shift adjacent to natal regions, the Sr level mapping displayed a wide variety of color patterns, and the Sr：Ca ratios obtained by the line transect analysis could be divided into one to six significantly different phases indicative of gradual life history transition. The other three specimens from the Rokkaku River Estuary had high Sr：Ca ratios（3–6.7） at the central otolith area but showed alternating changes between low and high values outside the natal region, suggesting that estuarine-origin individuals occurred in the Rokkaku River Estuary. The two-dimensional maps of the Sr level and average of the otolith Sr：Ca ratios along the life-history transects could be used as effective tools for reconstruction of past habitat use of the tapertail anchovy in estuaries of the Ariake Sea, Japan.

Early life migration and population discrimination of the small yellow croaker Larimichthys polyactis from the Yellow Sea: inferences from otolith Sr/Ca ratios

The small yellow croaker Larimichthys polyactis is a benthic marine fish species of high ecological and commercial importance and is widely distributed in the northwestern Pacifi c Ocean,especially in the Chinese coastal waters of the Bohai,Yellow,and East China Seas.As a highly migratory species,the whole life migration of L.polyactis has been intensively studied.However,knowledge about its early life migration is scarce,and population divisions are inconsistent,limiting the ability of fishery scientists and administrators to evaluate the design and potential benefits of thorough conservation and resource-management strategies.In the present study,otolith Sr/Ca was analyzed to investigate the early migratory patterns and discriminate the populations of L.polyactis in the Yellow Sea,including two spawning groups and one overwintering group.The variation in Sr/Ca ratios of ontogenetic growth zones,including the nucleus(N),larval(L),metamorphosis(M),juvenile(J),and edge(E)zones,was measured by electron probe microanalysis.The variation in Sr/Ca ratios in early developmental growth zones was generally characterized by an evident downward trend from the N to J zone,which suggests that the early migratory pattern of L.polyactis might be from inshore to nearshore water.Canonical discriminant analysis,based on the otolith Sr/Ca ratios of the N,L,M,and J zones,allowed the successful discrimination of the two populations,namely,the northern and southern Yellow Sea groups,whose diff erences were mainly reflected in the L and J zones.Compared with previous studies,the traditional geographic boundaries(34°N)separating these two populations might be moving northward.The application of otolith Sr/Ca ratios based on ontogenetic stage could improve our understanding of the migration and population discrimination of L.polyactis from the Yellow Sea.