Summary1. Animals facing partial habitat loss can try to survive in the remaining habitat or emigrate. Effects on survival and movements should be studied simultaneously since survival rates may be underestimated if emigrants are not considered, and since emigrants may experience reduced survival. 2. We analysed movements and survival of adult wintering oystercatcher Haematopus ostralegus in response to the 1986-1987 partial closure of the Oosterschelde in the Dutch Delta. This reduced by one-third the tidal area of this major European wintering area for waders. 3. We developed a novel variant of a multistate capture-recapture model allowing simultaneous estimation of survival and movement between sites using a mixture of data (live recaptures and dead recoveries). We used a two-step process, first estimating movements between sites followed by site-specific survival rates. 4. Most birds were faithful to their ringing site. Winter survival was negatively affected by winter severity and was lowest among birds changing wintering site (i.e. moving outside of the Oosterschelde). 5. During mild winters, survival rates were very high, and similar to before the closure in both changed and unchanged sectors of the Oosterschelde. However, the combined effect of habitat loss with severe winters decreased the survival of birds from changed sectors and induced emigration. 6. The coastal engineering project coincided with three severe winters and high food stock, making assessment of its effects difficult. However, the habitat loss seems to have had less impact on adult survival and movements than did winter severity. 7. Synthesis and applications . Human-induced habitat change may result in population decline through costly emigration or reduced survival or reproduction of individuals that stay. Long-term monitoring of marked individuals helps to understand how populations respond to environmental change, but site-specific survival and movement rates should be integrated in the same model in order to maximize the information yield. Our modelling approach facilitates this because it allows the inclusion of recoveries from outside the study area.

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The edible cockle (Cerastoderma edule L .) is a dominant suspension feeder in the Oosterschelde, a 351 km 2 tidal bay in the SW Netherlands . To establish its role in the benthic foodweb, and to assess the impact of human activities, data on density, age composition, biomass and growth were collected from several tidal flats in the Oosterschelde between 1980 and 1990 .To estimate the overall biomass development of the cockle, a simple model was used, in which three growing seasons are defined for the cockle population . A standard individual growth curve was constructed . A negative exponential mortality function was assumed to estimate the number of recruits . By combining the estimated number of recruits, the estimated specific mortality rate and the standard individual growth curve, numbers and biomass of each age group in the Oosterschelde population were estimated. Average biomass (including shell organics) per m 2 of tidal flat in August varied from 140 g AFDW in 1980 to 21 g AFDW in 1989, implying a total cockle stock on all tidal flats of 19170 to 2350 tonnes AFDW (72 x 10 3 to 9 x 103 tonnes flesh), respectively.A comparison of results from field surveys and the reconstructed stock estimations showed large deviations . However, an uncertainty analysis performed on the model showed that most field data fitted within the minimum and maximum biomass calculated .Total biomass is largely dependent on the strength of certain year classes . In this respect, the year classes 1979, 1982, and 1985 were good . Effects of the construction of the storm-surge barrier and the compartmentalisation dams could not be demonstrated .The year-to-year variation in cockle stocks, assessed in the way described in this paper should be regarded as relative, because a systematic survey of the intertidal flats was not performed every year, but population dynamics from selected stations were used instead .

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