Assessment of the population of Ostrea edulis in Sweden: A marginal population of significance?

Abstract

The European flat oyster Ostrea edulis is an economically and ecologically important species subjected to extensive protection and restoration efforts, due to sharp population declines in Europe. In Sweden, O. edulis occurs at the northern fringe of its range. Knowledge of the distribution and abundance of the species is limited, and the size of the population has never been estimated. Oyster fishery sustainability has never been assessed. Using a random sampling approach and towed video, we collected data on oyster occurrence at 435 sites to estimate abundance and distribution of O. edulis in the Swedish Skagerrak region. Furthermore, the size of the population was assessed and the current management and legislation strategy of the species was analyzed. Living O. edulis was found in 27% of all sampled sites above 6 m, and the size of the population was estimated to 36.6 ± 16.3 million individuals (total population ± SE). The distribution was patchy, and approximately 60% of the population was found in oyster bed densities (≥5 oysters/m2), which corresponds to around 1% of the sampled sites. The nondestructive sampling method and representative design provided useful estimates of population size and error, which indicate that the marginal population of O. edulis in Sweden constitutes a significant part of the remaining European population. We argue that the relatively good status of the Swedish population can be explained by (a) private ownership of fishing rights, (b) a small‐scale fishery that exploits <0.5% of the estimated population annually, conducted using nondestructive methods, and (c) parasite‐free waters, potentially due to effective prevention of spread of infection. Open Research Badges This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The data is available at https://osf.io/jgpxw/?view_only=d070b45802a4426da028efffde3d0f76.

Identifying high‐density areas of oysters using species distribution modeling: Lessons for conservation of the native Ostrea edulis and management of the invasive Magallana (Crassostrea) gigas in Sweden

“…This coastal area is characterized by small tidal range (±0.2 m), fluctuating salinities (commonly 20-30 psu in surface water), naturally fragmented habitats, and a wide range of wave exposure conditions. Data on oyster abundance from two studies performed in 2013 and 2014 were used, one study covering the whole stretch of the coast mentioned above and one concentrated to the KNP (Lindegarth et al, 2014;Thorngren et al, 2019). Both studies used identical field protocols based on towed video transects and subsequent image analyses of oyster density and habitat characteristics (see Thorngren et al, 2017 for detailed description of methods).…”

Forty questions of importance to the policy and practice of native oyster reef restoration in Europe

“…Understanding and communicating the benefits can also open up new funding sources (Goldman & Tallis, 2009) There are three particular restoration settings which in particular require greater research to overcome barriers to oyster restoration: co-management of oyster fisheries, coordinating confidence in demand for spat and restoration in marine protected areas. Private ownership of existing fisheries has had a role to play in preserving some native oyster populations, as illustrated in Ireland, where privately owned fishing rights prevented overexploitation (Eagling, Ashton, & Eagle, 2015), and Sweden, where most of the O. edulis habitats have been privately owned for at least three centuries and oysters cannot be collected without permission from the landowner (Thorngren, Bergström, Holthuis, & Lindegarth, 2019). The potential for the fishery to positively interact with oyster restoration aims should not be underestimated, with fishers representing a fount of local ecological knowledge and in some cases safeguarding remaining populations (OSPAR Commission, 2009).…”

The late Holocene demise of a sublittoral oyster bed in the North Sea

“…Ostrea edulis beds are characterized by a high structural complexity and provide shelter and settling ground for a range of associated species, thus increasing local biodiversity [ 5 – 7 ]. Oysters further hold both cultural and commercial value, and provide a range of ecosystem services positively affecting the overall quality of marine and brackish environments [ 3 , 8 , 9 ]. Unfortunately, oyster populations have declined throughout Europe in recent historical times, which is attributed to the massive extraction and disturbance by targeted and non-targeted fisheries from the beginning of the industrial period [ 10 – 13 ].…”