Verkkokoekalastus kalakantojen arviointimenetelmänä : pyynnin keston ja vuorokaudenajan vaikutus

Empirical Estimation of Accumulation-Induced Change in Gill Net Catchability: Mind the Observation Errors

We analyzed cumulative catches for 24 h gill net exposures divided into 4*6 h, 2*12 h and 1*24 h soak time treatments to estimate the reduction in its catchability due to accumulation of fish. The effects of loss of catch during net lifting, disturbance effect and fouling were eliminated as far as possible to reveal the true effect of accumulation. First we applied simple nonparametric and parametric tests in comparison of treatments. As expected, considerable reduction in catchability took place along with the increase in soak time, indicated by significantly lower total 24 h catches from longer soaks in comparison with shorter ones. The reduction was more pronounced for roach than for per…