Temporal variation in abundance, return rate and life histories of previously spawned Atlantic salmon in a large subarctic river

Abstract

The 30 year time series analyses revealed large temporal variation in the return rates and a recent increase in abundance of previous spawning Atlantic salmon Salmo salar in the River Teno, northern Scandinavia. The mean proportion of repeat spawners was 7 and 4% in the total Atlantic salmon catch and 9 and 22% in multi‐sea‐winter (MSW) catch component for females and males, respectively. Previous spawners constituted on the average 7% of the catch in mass but up to 20%(31 t) and 30%(19 t) in 2003 and in 2004, respectively. In 1975–2000, the proportion of previous spawners varied between 1 and 6%(3–12% of MSW Atlantic salmon), whereas in 2001–2004, they accounted for 8–21%(16–35% of MSW Atlantic salmon) of the total Atlantic salmon catch. The number of previous spawners in the catch correlated significantly with the preceding numbers of respective 1–3 sea‐winter (SW) maiden Atlantic salmon 2 years earlier. The recent increase in the numbers of 1S1 and 2S1 (1 or 2 years at sea followed by first spawning and 1 year reconditioning period at sea) alternate spawning Atlantic salmon was a consequence of higher numbers of maiden 1SW and 2SW Atlantic salmon in the catches and increased sea temperatures. Similarly, the return rate of 1SW Atlantic salmon to second spawning has improved in recent years. Most previous spawners ascended and were captured early in the fishing season. The smolt and sea‐age combinations of repeat spawners comprised 68 age groups contributing with the annual mean of 15 age groups to the great diversity of the River Teno Atlantic salmon population complex.

Impact of catch-and-release practices on behavior and mortality of Atlantic salmon (Salmo salar L.) kelts

“…Conserving kelts in the river before outmigration might be of importance even in rivers with low proportions of repeat spawning, as the contribution of repeat spawners might be significant not only due to their numbers but also due to their mass as Niemelä et al (2006) suggested in their time-series from River Tana. In addition, the majority of the returning repeat spawners are females (Niemelä et al 2006, own unpublished data), which further increase their significance, as the females are usually the limiting factor to production.…”

“…Kelts can potentially return as repeat spawners, and even though typically less than 11% return to breed again (Belding, 1934;Fleming, 1998), in some populations the return rate is high, and in some instances increasing (Dempson et al, 2004;Jonsson and Jonsson, 2004;Niemelä et al, 2006). Furthermore, the kelts that do return as repeat spawners might contribute more to the overall population fitness than their sheer numbers would indicate due to their increased size.…”

“…Furthermore, the kelts that do return as repeat spawners might contribute more to the overall population fitness than their sheer numbers would indicate due to their increased size. For example, scale analysis data from 1975 to 2004 from the sub-arctic river Tana showed that the proportion of repeat spawners constituted on average 5% of total catches, but could amount up to 20-30% of catches in mass in certain years (Niemelä et al, 2006). Thus, repeat spawners might act as an important safety-valve for production in years with reduced runs of first time spawners (Niemelä et al, 2006).…”

Persistence of a southern Atlantic salmon population: diversity of natal origins from otolith elemental and Sr isotopic signatures

“…Populations located in southern European rivers are expected to be particularly affected by global warming (Valiente et al 2010). Poor salmon production associated with changes in life histories (for example, return rates) were all related to unfavorable climatic conditions, such as increasing seawater and freshwater temperatures (Jonsson and Jonsson 2004;Niemela et al 2006). Homing was shown to be less strict in southern regions because of opportunistic returns driven by unfavorable environmental conditions (Moran et al 2005b).…”

Iteroparity in Columbia River summer-run steelhead (Oncorhynchus mykiss): implications for conservation

“…Both strategies maintain genetic diversity and reduce demographic risks by increasing the number of unique adult pairings across years (Crespi and Teo 2002;Niemelä et al 2006). Iteroparous individuals may also be more productive than semelparous conspecifics because of higher cumulative fecundity and lifetime fitness (Fleming and Reynolds 2004).…”