Annual changes in the proportions of wild and hatchery Atlantic salmon (Salmo salar) caught in the Baltic Sea

Abstract

DNA-level information from an eight-loci microsatellite baseline database of 32 Atlantic salmon (Salmo salar) stocks was used with a Bayesian estimation method to assess the stock and stock group proportions of Finnish salmon catches in the Baltic Sea area. The proportions of seven stock groups, important to fisheries management, were assessed in catch samples taken between 2000 and 2005. In the Gulf of Bothnia area, the proportion of wild fish in catches showed an increasing trend in all areas until 2003, mainly because of the decrease in total catches caused by the relatively greater mortality of hatchery-reared fish compared with wild fish. In 2004, the total number of wild fish caught had also increased, indicating an increase in the abundance of wild stocks. In catches from the Åland Sea, the proportion of wild fish increased from 44% in 2000 to 70% in 2004, while the catch during the same period increased from 4628 to 7329 fish. In the Gulf of Finland, the local Neva salmon stock, which is released by Estonia, Finland, and Russia, made the largest contribution. In the western part of the Gulf of Finland, fish originating in the Baltic Main Basin also made a substantial contribution to catches. The threatened eastern Estonian and Russian wild stocks were recorded only in the western part of the Gulf of Finland, where the proportion of wild fish increased from 9% in 2003 to 19% in 2004.

Spawning-Age Differences and their Temporal Trends in Wild and Sea-Ranched Atlantic Salmon Stocks, from Stock Mixture Data

“…The data were pooled over ten years for each stock to analyze the mean spawning age distribution. Thus, annual variation in the spawning migration is not assumed to affect [34]. A comparison of the present situation with the situation 70-80 years ago was possible by making use of data on Luleälven and Kalixälven salmon stocks published by Alm [40].…”

“…In addition to the eight microsatellite loci used in Koljonen (2006) [34], a further nine loci were analyzed to increase the total number to 17, so that variation was determined at the following 17 microsatellite loci: (1) SSa14 [48], (2) SSa171 [49], (3) Ssa197 [49], (4) SSa202 [49], (5) SSa289 [48], (6) SSa407 [50], (7) SSa85 [48], (8) 8SSaD157 [51], (9) SSosl417 [52], (10) SSosl438 [52], (11) SSosl85 [52], (12) SSsp1605 [53], (13) SSsp2201 [53], (14) SSsp2210 [53], (15) SSsp2216 [53], (16) SSsp3016 [53] and (17) SSspG7 [53]. In addition to catch data, the same freshwater age distribution and DNA microsatellite data for 17 loci were available for all potentially contributing stocks, or baseline stocks [47].…”

“…Genetic information on 33 Atlantic salmon stocks around the Baltic Sea was available as baseline stock data for the catch analysis [34]. Of these, 20 were stocks of rivers draining into the Bothnian Bay and having stocks that could occur in the analyzed catches.…”

“…The last 1000 MCMC iterations of each 5000-iteration chain were combined and used to describe the posterior probability distributions of the proportions of each baseline stock, and correspondingly to estimate the probability of each individual fish belonging to any of the baseline stocks. Additional details of the baseline stocks and estimation method are provided in Koljonen [34], Koljonen et al [58], and [37].…”

“…The estimated natural production of salmon smolts is below the potential level in many Baltic Sea rivers [34], and many salmon stocks have been lost because of the dredging and damming of rivers for hydropower production since the 1940s. Salmon stocks originating from the currently closed rivers have been maintained by rearing offspring from both hatchery broodstocks and sea-ranched parents [16].…”