Resource degradation: a subtle effect of bottom fishing

Populations of hermit crabs are critically limitedby the availability of suitable gastropod shells thatthey utilise to reduce their risk of predation and environmentalstress. Common whelks are the main sourceof shells for large hermit crabs in the northern Atlanticbut are vulnerable to direct and indirect effects of fishingactivity. This study examined the potential consequencesof degrading shell resources for common hermit crabs.Laboratory trials demonstrated that hermit crabs avoidlow-quality damaged shells throughout their life history.This laboratory preference was corroborated by directfield observations of shells preferentially occupied byhermit crabs, compared with shells available for occupation.In the field, 8 times as many empty shells hadholes compared to shells occupied by hermit crabs. Inthe North Sea, the abundance and biomass of livewhelks and hermit crabs collected at sites where they cooccurredwere significantly related. However, whelksoccurred at far fewer sites overall and were morepatchily distributed at high abundance than hermitcrabs, which were more widespread. At a subset of sites,whelks of the same body-mass range occurred in theIrish and North Sea. However, at these sites, hermitcrabs sampled from the North Sea had a significantlylower biomass. This suggests that the shells available foroccupation at the North Sea sites would not supportcrabs of a body mass comparable to that found in theIrish Sea. Using published data, we calculated that insome of the intensively fished areas of the North Sea,24% of the available shell resource will be damaged eachyear. The reduction in shell quality in the North Sea mayimpose a physical constraint on the upper size limitcurrently attainable by hermit crabs and hence may haveimplications for population viability

Development and Implementation of Marine Contaminent Threshold Values.

This report compiles available Threshold Values (TVs) for marine chemical contaminants at EU, regional and beyond EU level, provides relevant information and discussion points for TV derivation and implementation, and outlines the main hindrances and potential approaches to fill the gaps. This document is a product of the MSFD Expert Network on Contaminants and is intended as a background guidance document to support developments to improve consistency in marine contaminant assessments. The report highlights the reality of the lack of knowledge about reference values (whether they are background, threshold or Environmental Quality Standard values) for many contaminants in the marine environment. Although regulations and frameworks are in place, and new ones are being implemented, the assessment of Good Environmental Status will remain difficult without high quality environmental and toxicological data. The variety of applied TVs is hindering a comparable assessment of problematic substances and the necessary reduction/phase-out measures. Considering the huge work needed to develop TVs and the high number of potential contaminants, current approaches need to be reviewed. Furthermore, the concerns on the environmental significance of TVs when they are not based on sufficient data and relevant assessment factors, and the difficulty to generalise TVs for all matrix/species monitored, call for discussions on resource-efficient TV development and potential alternative ways forward