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Trap fisheries targeting invertebrates are economically important but many of the target species lack stock assessments. One reason for this is the difficulty of estimating density. One important means by which density can be estimated uses the catch rates of baited traps that are spaced at different distances. With declining spacing, the sphere of attraction will increasingly overlap, leading to reductions in catches, allowing for the estimation of the density that is catchable by traps on the seabed. Here we review the analytical methods adopted across a range of studies and find that no consensus on robust methods exists. We propose an analytical method that assumes the trapping area is circular and that the chance of catching an individual declines linearly with distance from the trap. We apply this method to estimate the density and the trapping radius of crabs and gastropods from real and simulated datasets. The method estimated a trapping radius of between 4 and 86 m, and densities that are up to 2.5 times less and 13 times greater than estimates provided in the original sources, illustrating the sensitivity to methodology. In conclusion, we provide and test a standardized method to estimate the density of benthic invertebrates. [ABSTRACT FROM AUTHOR]

Calculating age and growth rate for the commercially important whelk, Buccinum undatum in the aid of fishery management has historically been undertaken using growth rings on the organic operculum. This is difficult due to their poor readability and confusion between two different sets of growth lines present. Recent work presented the calcium carbonate statolith as an alternative for age determination of B. undatum. Here we compare the use of statoliths and opercula, comparing their readability and creating growth curves for three distinct populations across the United Kingdom. Using these data, we also test the most appropriate growth equation to model this species. Lastly, we use oxygen isotope analysis of the shells to assign accurate ages to several individuals from each site. These data were used to test the accuracy of statolith and operculum ages. Statoliths, whilst more time consuming to process have improved clarity and accuracy compared with the opercula. This improved readability has highlighted that a Gompertz growth function should be used for populations of this species, when in past studies, von Bertalanffy is often used. Statoliths are a viable improvement to opercula when assessing B. undatum in the context of fishery monitoring and management. [ABSTRACT FROM AUTHOR]

There is little common rationale for the 45 to 75 mm total shell length (TSL) minimum landing sizes (MLS) for Buccinum undatum among countries in the Northeast Atlantic. Size at maturity and length frequency of B. undatum populations vary over small spatial scales; however, the driving mechanism for this is unknown. Size at maturity research for B. undatum dates back to the late 1980s; since then, there has been little consensus on laboratory methods or in which season to undertake the research. Here, we assess small-scale spatial variation in size at maturity over a year to identify the seasons that increase error in visual maturity estimates. We compare and contrast results from methods used in the literature to estimate maturity for B. undatum. Monthly, B. undatum samples were obtained from Welsh fishers between May 2013 and May 2014 from eight sites at four locations (n = 5080). All whelks were sexed, weighed, and measured, and up to 60 whelks from each location were assessed for maturity (n = 1659). Mature whelks were found in all months, with a peak in reproductive activity through summer and early autumn, followed by the onset of spawning in November. Size at maturity varied between sexes and sites, and ranged from 51 to 76 mm TSL. Whelks caught in shallow waters (0-10 m) matured at a smaller size than those from deeper waters (up to 60 m). Length frequency varied at each site suggesting that a single increase in MLS would impact fishers disproportionately. No methodology trialled was found without inherent errors when used in isolation, though a combination of methods proved ideal. The seasonal variation in maturity estimates suggested that assigning maturity is increasingly difficult outside annual reproductive periods and that prespawning is the ideal time to undertake visual gonad assessments for whelks. [ABSTRACT FROM AUTHOR]

The fine structure and function of the excretory system and associated veins of the muricid Nucella lapillus have been studied and compared with those of the buccinid Buccinum undatum. It is argued that in both species the nephridial gland vein is a functional unit with the auricle as it is in Littorina, and that its sinuses provide a compensation sac for blood displaced from the mantle skirt on retraction of the snail into the mantle cavity. This may be typical of marine caenogastropods. The epithelium lining the tubules of the gland recaptures organic solutes from the urine at the start of the systemic circulation, and phagocytes in its sinuses (the blood gland) abstract macromolecules and toxins from the blood. The development of two different types of folds on the dorsal wall of the kidney in neogastropods and other carnivorous neotaenioglossans is correlated with adaptations of the foregut to diet and with feeding mechanisms in which a retractile proboscis is accommodated in the cephalic haemocoel. It does not necessarily reflect phylogenetic relationship. On the basis of the observations reported here it is concluded that the dorsal afferent renal vein and secondary folds of the kidney act primarily as a compensation sac for blood displaced from the cephalopedal haemocoel during retraction of the proboscis, or when the snail withdraws into its shell. Aggregates of haemocyanin form in these blood spaces at such times. The relationship between the two sets of folds, which interdigitate in pycnonephridians or are largely separate in meronephridians, is related to shell shape, proboscis type and foregut structure in different families. Loss of the anal gland in the buccinoideans is correlated with changes in the efferent renal veins, a reduction in the size of the rectal sinus and the reduction or loss of the gland of Leiblein. Extracellular bacteria occur in the anal gland of the muricid Ocenebra erinacea similar to those previously reported in Nucella, suggesting that their presence may be typically associated with the gland in the Ocenebrinae and possibly other muricids. [ABSTRACT FROM PUBLISHER]

The feeding rate and behaviour of whelks (Buccinum undatum) offered cockles (Cerastoderma edule) in laboratory experiments were examined. When presented with cockles in a range of sizes (10–40 mm), 14 B. undatum (34.6–88.3 mm), held individually in aquaria, consumed a wide size range of cockles. Small whelks (60 mm) ate a greater number of larger cockles (>30 mm) and a wider size range of cockles (12–40 mm) than smaller whelks. The majority (90%) of the shells of the predated cockles were undamaged and the few (B. undatum feeding on C. edule showed a method of attack that has not previously been reported and involved the use of the whelks foot to asphyxiate the cockle or to pull the shell valves apart. No filmed evidence was found for the previously reported shell ‘wedging’ technique for prising open the closed shell valves of C. edule, although 10% of the shells of consumed cockles in feeding experiments had damaged shell margins. [ABSTRACT FROM AUTHOR]