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Species that have a high likelihood of surviving the discarding process have become great concern since the European Union reformed the Common Fisheries Policy and enacted a landing obligation prohibiting the discarding any individuals of species under quota. Among species presenting an elevated survival potential, plaice (Pleuronectes platessa) is one of the most discarded in the coastal otter trawl fishery in the English Channel. The objective of this study is to provide the most reliable estimates of plaice survival after release in commercial conditions, and to identify the factors that influence survival rates. A captivity experiment was conducted in January-February in the English fishery to assess the survival of discarded plaice as a function of a semi-quantitative index of fish vitality, which has been demonstrated to be a good proxy of fish survival in comparable fishing and environmental conditions. This study examined the potential of this index to estimate discard survival in three trials from the English and French fisheries and at three different seasons. The vitality index was then used to analyse the influence of several factors (fishing practices, environmental conditions and fish biological characteristics) on the discard survival. The survival rates for plaice were accurately estimated at 62.8% in January-February, 66.6% in November and 45.2% in July. While these rates remained substantial whatever the fishing, environmental or fish biological conditions, the time fish spent on the deck, the bottom and air temperatures, the tow depth and the fish length had a significant influence on plaice survival. In practice, plaice survival could be enhanced by releasing the fish early during catch sorting and avoiding exposure to extreme air temperatures.

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Although unimolecular reactions of gas-phase ions are important and are commonly observed, it is difficult to gain much mechanistic insight into how highly activated ions decompose.1•2 We wish to report a detailed mechanistic study utilizing infrared multiphoton (IRMP) photochemistry3 in an ion cyclotron resonance (ICR) spectrometer.4 The mechanism of the IRMP-induced loss of methane from teri-butoxide ion to yield acetone enolate ion was probed by competitive kinetic isotope effects. The observation of unusually large secondary isotope effects (up to 6.9) and a small primary effect (1.6-2.0) is indicative of a stepwise mechanism involving bond cleavage as the first step and a subsequent hydrogen-transfer reaction from an intermediate ionmolecule complex.5