Yield- and biomass-per-recruit analysis for rotational fisheries, with an application to the Atlantic sea scallop (Placopecten magellanicus)

A general model for yield-per-recruit analysis of rotational (periodic) fisheries is developed and applied to the sea scallop (Placopecten magellanicus) fishery of the northwest Atlantic. Rotational fishing slightly increases both yield- and biomass-per-recruit for sea scallops at FMAX. These quantities decline less quickly when fishing mortality is increased beyond FMAX than when fishing is at a constant rate. The improvement in biomass-per-recruit appears to be nearly independent of the selectivity pattern but increased size-at-entry can reduce or eliminate the yield-per-recruit advantage of rotation. Area closures and rotational fishing can cause difficulties with the use of standard spatially averaged fishing mortality metrics and reference points. The concept of temporally averaged fishing mortality is introduced as one that is more appropriate for sedentary resources when fishing mortality varies in time and space.

Wadge Bank trawl fishery studies. Pt. 2. The effect of trawling on the catch per hour from 1945 to 1960

The object of this series of papers has been given in Part 1 (see Additional informations for details) which deals with the first known commercial fishery on the Wadge Bank from 1928 to 1935. There is no recorded trawling on the Bank between 1936 and 1944. This paper deals with the changes in the total catch (i.e. all species combined) per hour of trawling in relation to the changes in fishing intensity from 1945, when the present trawling activities started, to 1960. The effect of trawling on individual categories or varieties will be presented later.

Growth, mortality and yield-per-recruit of Copadichromis likomae (Cichlidae) in Lake Niassa, Mozambique

Analysis of the length-frequency data on Copadichromis likomae (Cichlidae) from Lake Niassa, Mozambique, suggests an asymptotic length of SL∞=14 cm associated with a K value of 0.93 yearˉ¹. Total and natural mortalities were estimated as 3.2 yearˉ¹ and 1.9 yearˉ¹, respectively. Yield-per-recruit analysis suggests that E=0.36 in this fishery.

Estimating the population density of prawns by the use of catch per effort data from prawn trawlers at Chilaw

The penaeid prawns of Sri Lanka from estuaries and sea are an important commercial fishery resource. This resource has been exploited over the last century or more by local fishermen using indigenous fishing gear from locally sail-driven or oar-driven fishing crafts. In more recent times, the Fisheries Research Division of the Department of Fisheries undertook surveys of the seas and lagoons of Sri Lanka with a view to ascertain whether any unexploited resources of prawns existed. These publications deal with the species composition, biology, distribution and abundance in the lagoons and inshore waters of Sri Lanka.