Landings of European lobster (Homarus gammarus) and edible crab (Cancer pagurus) from 1615 to 2009, Helgoland, North Sea

From 2000 to 2005 about 5400 one-year-old hatchery-reared lobsters (Homarus gammarus) were tagged and released at the rocky island of Helgoland, North Sea. To date, 1-8% of the different release cohorts were recaptured in the field and 8-19% of these lobsters were recaptured from the semi-open area of the outer harbour. The recaptured lobsters indicated good development and growth conditions. The smallest berried females caught were 83 mm carapace length and 4 years old. The proportion of cultured lobsters to all measured lobsters captured around the island was 3-8% in the years 2007-2009. The population size of two cohorts was assessed using the Lincoln-Peterson method and the estimated survival rate averaged 30% and 40%. Minimum landing size of cultured lobsters was reached after 4-7 years. Cultured lobsters showed strong fidelity to their release sites, and thus remained around the island of Helgoland. A basis has been laid to enhance this endangered lobster population by means of a large scale restocking programme.

Epibiosis between the sand crab Emerita analoga and the mussel Semimytilus algosus

Coastal zones of the Humboldt Current Upwelling System (HCUS) are composed both of rocky and sandy beaches inhabited by macrozoobenthic communities. These show oscillating changes in the dominance of species; the abundance of the sand crab Emerita analoga is linked to phases of the El Niño Southern Oscillation (ENSO). The biogenic surfaces of these crabs serve as substrate for opportunistic colonizers. This study is the first record of an epibiosis between E. analoga and the rock mussel Semimytilus algosus, detected at a southern Peruvian sandy beach. Mussels fouled a wide size-range of adult E. analoga (7.3%) but they themselves belonged to small-size classes. The largest S. algosus was 17.4 mm in length. Highest permanence of epibionts was found on larger sand crabs (maximum between 24 and 27 mm). Significantly more mussels were found on the ventral surface (39.4%) compared to 10 other surface areas of the sand crab. Possible benefits and disadvantages of the observed epibiosis for both the basibiont and the epibiont are discussed.