Survival of vendace (Coregonus albula) escaping from a trawl cod end

Abstract

Many young (0 group) vendace (Coregonus albula) are thought to die after passing through trawl cod ends during commercial vendace fishery in Finnish lakes. Survival of 2- to 4-month-old vendace (5–10 cm) after escaping from a 24-mm square mesh trawl cod end was therefore studied in Lake Puulavesi, Finland, during July–August 1993. Escapees were collected in a hooped netting cage that was released from the cod end after the tow, closed, and left at the depth of capture for 3–7 days. The data consist of 59 cagings. On average, 50% of the escaped vendace died, although mortality varied considerably. Most mortality occurred during the first day after escaping. Hauls conducted in the late evening and at night were accompanied by the highest mortality (60–80%). Mortality was 30–40% in the afternoon and early evening hauls. Generally, higher mortality was observed in August than in July. Comparisons with caged fish caught by a purse seine suggested that the experimental procedure did not substantially contribute to the observed total mortality of escapees. Scale loss and exhaustion experienced by vendace during trawl capture may have caused the rapid death of escapees through loss of osmoregulatory control.