Minimum Landing Size Research Articles

Assessment of minimum landing sizes of the edible crab, Cancer pagurus L., on the east coast of England

In 1986, the minimum landing size (MLS) of edible crab ( Cancer pagurus L.) was increased on the south coast of England and Wales from 115 mm carapace width (CW) to varying sizes of up to 160 mm CW depending on district. The MLS remained at 115 mm on the east coast of England. Fisheries in this area are likely to come under increasing pressure as they provide alternative early season supplies to the European continental market. For this reason, a reassessment of crab MLS from Norfolk to the Scottish border of Northumberland has been undertaken using length cohort analysis. Increasing the MLS would result in increases in both yield-per-recruit ( Y/R) and particularly biomass-per-recruit ( B/R) in all of the three main fisheries. Fishing mortality was highest in Norfolk where the mean size of crabs landed is low. Large increases in Y/R and B/R, preceded by considerable short-term losses, were predicted therefore for Norfolk, but emigration of mature females, the physical nature of the substrate, and possible density-dependent effects may limit the benefits. Two additional factors suggest that the overall gains and losses may be underestimates. Firstly, the introduction to the model of a stock-recruitment relationship predicts that much larger gains in long-term yield and stock biomass may accrue from an increase in MLS. Secondly, fishermen in Yorkshire obtain a lower price for crabs between 115 and 127 mm CW than for those over 127 mm, and when these prices are included in the model, the initial losses in revenue following an increase in MLS are less and the expected long-term gains are greater than the Y/R prediction. This assessment highlights the need for further studies on growth, maturity, fecundity and recruitment of Cancer pagurus.

Fish impingement at estuarine power stations and its significance to commercial fishing

The abstraction of cooling water at power stations sited on tidal waters inevitably leads to mortalities of some fish which are drawn in with the cooling water supply and become impinged on the intake screens. These fish are predominantly 0‐ or I‐group juveniles which, owing to their small size, are unable to resist intake currents.Commercial fishermen often object to the fact that juvenile fish are killed in this way. Their concern stems from the fact that, in order to protect stocks, commercial fishing is restricted to fish which are above a statutory minimum landing size, whereas the majority of fish killed by impingement are below this size.This paper considers the significance of impingement mortalities at estuarine sites in Britain for six commercially important species: cod, Gadus morhua, whiting, Merlangius merlangus, plaice, Pleuronectes platessa, dab, Limanda limanda, sole, Solea solea and herring, Clupea harengus. Life tables are used to establish expected survival trajectories for each species and to compute reproductive potential. Each fish killed on intake screens is then considered in terms of the fraction of the reproductive potential of a single adult at maturity, and is ascribed an ‘adult equivalent’ value. Total catches of mixed juveniles and adults are then presented as ‘adult equivalent’ values. The results are then compared with commercial landings data and it is shown that catches by power stations are trivial in comparison with commercial landings.