This study reports the spatial and depth distributions, occurrence and prevalence, infestation rate and intensity of the pea crab Pinnotheres pisum colonising five commercial bivalve species (Chamelea gallina, Donax semistriatus, Donax trunculus, Donax vittatus, and Spisula solida) along the south and southwest coasts of Portugal. In addition, the study also analysed the colonisation pattern, morphometric measurements and relative growth of P. pisum inhabiting those bivalve species. Overall, 33,370 bivalves were analysed, collected in 371 sampling stations at depths ranging from 3 to 25 m. A total of 102 bivalves hosted 106 P. pisum, corresponding to an infestation rate of 0.31%. Besides 13 juveniles, were recorded 60 males and 33 females of P. pisum, corresponding to a male-biased sex ratio (1M: 0.6F). Pea crabs carapace width ranged from 1.3 to 13.5 mm and males were smaller than females (hard females were also smaller than ovigerous soft females). In general, larger and heavier bivalves hosted larger and heavier P. pisum. Pea crabs morphometric relationships presented negative allometries, reflecting slower growth rates in carapace length and total weight compared to carapace width throughout the species ontogeny. Overall, this study provides valuable insights into diverse descriptors of bivalves' colonisation by P. pisum, comparing the main results and trends with analogous information available throughout the species distributional range. Although the current fairly low infestation by P. pisum does not constitute a health concern for these bivalve species, its evolution under a climate change scenario should be periodically monitored in the mid- and long-term.

The striped venus clam Chamelea gallina (SVE), plays an important role as an infaunal filter-feeder in the ecosystem, besides an important economic role in the Black Sea coasts of Turkey. It is caught using hydraulic dredge boats, then processed, and the final product (frozen meat) is exported to EU countries. SVE fishing requires a special licence and regulations. Also, SVE beds were closed to fisheries for the recovery of stocks for 2 years. In the study, SVE beds were investigated during the closed season over two years to assess stock density. Additionally, the number of macrobenthic species that share the same habitat as the SVE was determined. The sampling area was divided into five sub-areas and four strata by depth and then stratified random sampling was applied to collect data. In 2011, SVE stock sizes in the sub-areas were 11,723.58 ± 5167.262 tons (Cide), 35,082.94 ± 27,510.95 tons (İnebolu), 10,077.05 ± 4970.68 tons (Türkeli), 3304.36 ± 3215.1 tons (Ayancık) and 1431.3 ± 1703.5 tons (Sarıkum). In 2012, these estimated stocks were 13,820.41 ± 6977.86 tons, 34,841.94 ± 14,623.71 tons, 8148.27 ± 5006.74 tons, 3420.72 ± 3093.67 tons and 2023.74 ± 2832.63 tons, respectively. However, the estimated SVE total biomass did not change significantly during the period when the fields were closed (P > 0.05). The results indicate that length-weight relationship parameters varied of b from 2.9011–2.9072 in two years. Shell damage during fishing, environmental factors, food competition and consumption by the main predator all have a significant impact on stock densities, and changes occurring in these conditions should be considered in fisheries management.

Mechanized dredging impact on discards was assessed along the northern Alboran Sea (W Mediterranean Sea). Data from 101 dredging operations were analysed for contrasting spatial and seasonal variability of damage, with the use of a three-level damage scale. 4.5% of discarded individuals displayed intermediate damage, whereas 11.3% displayed severe damage. Echinoderms displayed the highest level of damage (~75% of total collected individuals) and Echinocardium cf. mediterraneum was the most susceptible discarded species (85% with severe damage), followed by bivalves (7.3%) and crustaceans (3.3%). The target Chamelea gallina showed a low proportion of damaged individuals, probably due to their thick protective shell, which promotes the survival of discarded undersized target individuals. Spatial differences in damage level on discards were linked to some gear characteristics, to the higher amount of gravels and to longer tow durations, whereas damage was generally higher in cold months and partly related to higher quantities of hard shelled molluscs, in both cases increasing the abrasion and damage to retained organisms. Data suggest that dredges with a lower number of narrower iron teeth and towed for a shorter time could decrease the damage rate in discards of this fishery. A spatial management plan based on the type of grounds would be useful in order to improve efficiency of these fisheries and minimize their impact to soft bottoms with different commercial catches and biological communities.

Age and growth of the clam Chamelea gallina from dredged, non-dredged and closed areas of the Turkish Black Sea coast were estimated. Von Bertalanffy growth curves were fitted for each sampling site; asymptotic length (L∞) values ranged between 25.995 and 28.883 mm and the growth coefficient (K) from 0.164 to 0.217 per year. Results indicate growth rates were significantly reduced in the far eastern commercial populations compared with those in western populations. According to our results presented here it can be concluded that C. gallina at closed area does not grow as fast as non-dredged stock and this is because of the shortness of closure season. Nevertheless we suggest that fallowing is the major precaution for the recovery of C. gallina stocks in the Black Sea.