Minimum Catch Size Research Articles

Differences in the exploited oyster (Crassostrea virginica (Gmelin, 1791)) populations from different coastal lagoons of the Gulf of Mexico.

1 - Oyster fishery is one of the most important coastal fisheries of Mexico. Production from the Gulf of Mexico coast makes up 93.4% of national production; during 2000-2002 it reached over 49,000 mT, with value of 9.2 to 15.5 million USD. Production is based on enhanced beds management. It is an activity of social importance, as many coastal communities find their income and work opportunities in it. In the state of Tabasco there are 1,371 oyster fishers in 14 cooperative societies, and 3,000 shuckers. There is an extensive bed management activity with seeding of collected spat and shell laying. Although a minimum legal size of 80 mm is required, it is not observed. 2 - We identified the growth equation parameters for size structure data for five beds from three lagoons. Maximum height varied between 118 and 140 mm with means between 58 and 63 mm. The von Bertalanffy growth equation parameters were L$∈fty$ between 124 and 154 mm, with K between 0.71 and 1.21. In most cases a significant influence of seasonality was detected, mostly during winter, but at some localities it was during summer. Total mortality Z varies from 1.64 to 2.39. As no data on natural mortality M were available we applied 25, 50 and 75% of Z to M, which allowed us to model the behaviour of the populations under different rates of fishing mortality F and the impact of different M in yields. 3 - We conclude that the populations are over exploited in size and this is affecting yields. Besides, the populations are at risk of collapse if natural mortality increases awing to any environmental impact. It is recommended to increase mean size to 90 mm which means a minimum catch size of over 70 mm, as required by the official norm, this would increase yields in weight 100% and there would be a significant number of organisms to buffer any increase on natural mortality.

Maturation in the male giant crab, Pseudocarcinus gigas, and the potential for sperm limitation in the Tasmanian fishery

The onset of sexual maturity of male giant crabs (Pseudocarcinus gigas) from Tasmania, Australia was assessed to determine the extent of protection of mature males provided by the minimum legal catch size of 150 mm carapace length (CL). Maturity was assessed by morphometric analysis of chela development, change in vaso-somatic index (VSI) with size and production of spermatophores. Males develop through three morphological groups based on development of the molariform chela relative to CL, termed `small-chela', `intermediate-chela', and 'large-chela'. The onset of morphological change to intermediate-chela occurs at approximately 120 mm CL at both sample sites (eastern and western Tasmania). Males with small-chela morphology were able to produce spermatophores and the mid vas deferens of all animals greater than 90 mm CL contained numerous well-formed spermatophores. Vaso-somatic index increases with CL, particularly for small-chela animals. Tank trials demonstrated that female giant crabs carry broods in successive years without moulting and stored sperm remains viable for at least four years under these conditions. Observation of functional maturity of males is required to fully assess the potential for sperm limitation in the fishery. Nonetheless, factors that appear to reduce the risk of sperm limitation include: both females and males are harvested; females do not moult every year thereby raising the operational sex ratio; and females can store sperm for extended periods.

GROWTH AND MINIMUM SUITABLE CATCH SIZE OF SPINY LOBSTERS, PANULIRUS PENICILLATUS (OLIVIER, 1791) AND PANULIRUS LONGIPES BISPINOSUS BORRADAILE, 1899 (DECAPODA, PALINURIDAE) IN THE SOUTHERN LAGOON OF NEW CALEDONIA

Panulirus penicillatus and Panulirus longipes bispinosus are the main species of spiny lobsters caught by commercial fishermen in the New Caledonian lagoon. The growth of the males and females of these two species is described by a Von Bertalanffy curve based on observing growth in captivity and in the field, and according to the statistical analysis of cephalothoracic length-frequency histograms obtained from commercial catches. A minimum suitable catch size has been calculated from the study of the males of P. penicillatus, which have the most rapid growth. For practical reasons, due to the artisanal frame of this fishery, this limit size (Cephalothorax Lengthlim = 7.5 cm) is recommended for both species and both sexes.

Differences in the length-age relationship of the snail Astraea undosa (Wood, 1828) between two localities of Tortugas Bay, Baja California Sur, Mexico

The differences in basal diameter (DB), age and DB-age of the snail Astraea undosa in two zones of Tortugas Bay (Mexico) were studied from November 1996 to November 1997. Age was determined by counting the opercular growth marks. The age groups were annual. The interval size was of 49 to 118 mm DB in snails of 2 to 12 years of age. Monthly frequency distributions of the DB and of age between zones were significantly different, except for the age distributions of November 1996, and June and November 1997. The legal minimum catch size (90 mm DB) is reached in one zone at 5 years and in the other at 9 years, on average, indicating a different growth pattern between zones. The differences in DB-age between zones were significant at 4 years of age. To promote a rapid growth of the snails from the slowgrowth zone, we suggest moving individuals of ≥63 mm DB to better growth zones.

Population structure, reproductive potential and increasing exploitation of the freshwater turtle Erymnochelys madagascariensis

A population of Erymnochelys madagascariensis was studied in a lake forming part of a tributary of the Betsiboka River in lowland Western Madagascar. Morphometric data, distribution by size, sex and maturity and reproductive parameters are reported. Female turtles first produce eggs when they reach 25 to 30 cm carapace length but do not attain full reproductive potential until they are at least 32 cm in length. Up to three clutches are laid each year, with large females producing up to 60 eggs in one year. Erymnochelys is exploited for food by the increasing human population of Madagascar. The minimum catch size is less than the size at sexual maturity; this is likely to lead to serious over-exploitation.