The effect of stocking size on the first winter survival of whitefish, Coregonus lavaretus (L.), in the Gulf of Bothnia, Baltic Sea

Abstract

The anadromous whitefish, Coregonus lavaretus (L.), is the most numerous fish species stocked in the Gulf of Bothnia, Baltic Sea. One‐summer‐old‐whitefish fingerlings are mostly 8–10 cm long when released annually in September–October, whereas the wild whitefish are 10–12 cm at that time. About 6 million, one‐summer‐old, spray‐marked, whitefish were released in the northern and central parts of the Gulf in 1995–1998. To study the effect of the stocking length on the survival of the marked fish, the length of the recaptured whitefish as 1‐year‐olds was back‐calculated. Altogether 1106 whitefish recaptured in the Gulf of Bothnia were analysed. The back‐calculated length was slightly greater than the stocking length but not as large as the length of the wild fish. In the central part of the Gulf of Bothnia, where the mean stocking length was more than 10 cm, the back‐calculated length was 10.5–11.1 cm. In the northern part of the Gulf the mean stocking length varied between 8.8 and 10.0 cm annually, and the corresponding back‐calculated mean lengths were 9.3–9.7 cm. It also seemed that bigger fingerlings started their feeding migration earlier or they migrated faster than the smaller ones to the southern parts of the Gulf of Bothnia.

Survival and Growth of Lake Whitefish from Two Stocking Strategies in Lake Simcoe, Ontario

“…Salojärvi (1991) found that stocking larger fingerlings of European whitefish did not necessarily increase survival rates. The mean size of the fish from five stocking events in this European study ranged from 76 to 115 mm and from 3.0 to 9.3 g. In contrast, Jokikokko et al (2002) suggested that larger fall fingerlings of the same European whitefish species stocked in the Baltic Sea had greater survival rates than smaller ones. The mean size of cohorts stocked in that study ranged from 88 to 106 mm, which is within the range of sizes stocked in the Salojärvi experiment but smaller than the fingerlings stocked into Lake Simcoe.…”

“…The size difference between fingerling fish at age 1, after their first winter in the lake, and yearling fish remains unknown. However, we expect that growth of fingerling fish would have slowed considerably during their first winter in the lake (Jokikokko et al 2002), resulting in a smaller size than the yearling fish maintained in the hatchery. Any difference in size that may have existed between fish of these two stocking strategies was undetectable by age 6.…”

“…Stocking has been used as an important tool in the management of whitefish around the world. It has been used in attempts to rehabilitate whitefish stocks (McMurtry et al 1997), as compensation for habitat alteration (Salonen et al 1998;Jokikokko et al 2002), to introduce the species to lakes (Lehtonen and Niemelä 1998;Wolos et al 1998), and to support recreational (Gerdeaux et al 1998;Amtstaetter 2002) and commercial fisheries (Tuunainen 1982). In North America, lake whitefish have predominantly been stocked as fry (Lasenby et al 2001).…”

Different growth trends of whitefish ( Coregonus lavaretus ) forms in the northern Baltic Sea

“…Whitefish stocks have undergone large‐scale changes since the 1950s (Urho, ). Due to the decline in natural stocks and intense hatchery releases of young fish (Jokikokko & Huhmarniemi, ; Jokikokko, Leskelä, & Huhmarniemi, ), the stock composition of the whitefish sea catch has changed over time. Nowadays, most of the captured whitefish are anadromous: 60%–70% of the catch in the northern GoB and nearly 100% in the southern GoB consists of anadromous whitefish (Raitaniemi & Manninen, ).…”