Whole otolith elemental analysis reveals feeding migration patterns causing growth rate differences in anadromous whitefish from the Baltic Sea

Abstract

Impact of feeding migration pattern on growth rate of whitefish (Coregonus lavaretus L.) from River Kemijoki was investigated. River Kemijoki is located in the northernmost Gulf of Bothnia (Baltic Sea). Whitefish ascending the river to spawn show major growth rate variations. To study whether these variations are related to different feeding areas (migratory connectivity), whole otoliths from fast‐growing (FASTG) whitefish (n = 9, age 4 years, average weight 790 g) and slowly growing (SLOWLYG) whitefish (n = 9, age 8 years, average weight 600 g) were analysed for elemental (Ba, Sr, Mg, Zn, Mn, Ca) concentrations by inductively coupled plasma‐optical emission spectrometry. Results showed that the FASTG whitefish had much lower otolith Ba concentration (~45%, p ≤ .01) than SLOWLYG whitefish, revealing that FASTG whitefish have spent more time in water of higher salinity/lower latitude, that is at feeding grounds in the southern Gulf of Bothnia. Otoliths of the FASTG whitefish had also higher Mg (~25%, p ≤ .001) and Zn (~20%, p ≤ .05) concentrations, but lower Ca (~5%, p ≤ .01) concentrations, than the otoliths from SLOWLYG whitefish. These results further reveal that FASTG and SLOWLYG whitefish have been spatially separated. In conclusion, bulk otolith elemental analysis revealed spatial separation and migration differences in river‐spawning whitefish subpopulations in the Gulf of Bothnia, which apparently lead to differences in fish growth rate. Our results increase the understanding of river‐spawning whitefish biology and its population structure and dynamics and may contribute to a sustainable management of river‐spawning whitefish stocks.

Short feeding migration associated with a lower mean size of whitefish in the River Tornionjoki, northern Baltic Sea

“…In the present study, there was also a significant difference in otolith Mg concentrations between LARGE and SMALL groups (Table 2). This further strengthens the idea of a separation in space during foraging of the groups, as Mg is regarded to be a habitat-and site-specific indicator in whitefish otoliths in the Gulf of Bothnia (Hägerstrand, Heimbrand et al, 2017). The dip-netted whitefish that were categorised in the SMALL group were nearly all males, and this was in agreement with the results of Lind and Kaukoranta (1974), further linking a short migration to a small size.…”

“…Such results suggest that the LARGE fish had migrated to the southern Gulf of Bothnia, where the salinity is higher than in the north. Similar differences in migration distances were found when the fast-and slow-growing mature whitefish were studied in the River Kemijoki, a large river flowing into the Bothnian Bay very close to the River Tornionjoki (Hägerstrand, Heimbrand et al, 2017). The results support earlier studies (Lehtonen & Himberg, 1992;Roff, 1991) indicating that longer migrations increase the probability of finding better ter ones were also slightly younger, verifying the suggestion of Lehtonen (1981) that not all young whitefish migrate to the southern foraging areas.…”

“…Typically, fish that hatch in the rivers flowing into the northern part of the Gulf of Bothnia migrate to feeding grounds in the Bothnian Sea and around Åland Island in the Archipelago Sea in the south (Lehtonen, ; Leskelä, Jokikokko & Huhmarniemi, ; Lind & Kaukoranta, ; Wikgren, ). However, not all whitefish migrate so far to the south, as a proportion of the population remains close to the natal rivers (Hägerstrand, Heimbrand et al., ; Lehtonen, ; Lehtonen & Jokikokko, ). Mature fish return to their natal rivers to spawn for the first time at an age of 4–6 years (e.g., Leskelä et al., ).…”

“…Barium (Ba) is known to be a freshwater indicator, and its concentration typically decreases as a function of increasing salinity (Campana, ; Gillanders, ; Hägerstrand, Heimbrand et al., ; Tabouret et al., ). In the brackish waters of the Gulf of Bothnia (Baltic Sea), where the salinity difference between the south and north is small (≤7‰), the Ba content of whitefish otoliths also significantly decreases with the residence time in water of higher salinity (Hägerstrand, Heimbrand et al., ; Hägerstrand, Himberg et al., ). Therefore, otolith Ba contents should be significantly higher in whitefish residing and foraging in the north compared with those residing and foraging in the south of the Gulf of Bothnia.…”

“…To test this hypothesis, otoliths from small and large whitefish caught with dip nets in the River Tornionjoki were removed for elemental analysis to examine their feeding migration in the sea area. Barium (Ba) is known to be a freshwater indicator, and its concentration typically decreases as a function of increasing salinity (Campana, 1999;Gillanders, 2005;Hägerstrand, Heimbrand et al, 2017;Tabouret et al, 2010). In the brackish waters of the Gulf of Bothnia (Baltic Sea), where the salinity difference between the south and north is small (≤7‰), the Ba content of whitefish otoliths also significantly decreases with the residence time in water of higher salinity (Hägerstrand, Heimbrand et al, 2017;Hägerstrand, Himberg et al, 2017).…”