No abstract

The reproductive biology of Epinephelus coioides was determined from the examination of 1455 individuals collected between July 2005 and June 2007 in the southern Arabian Gulf. Histological preparations of gonads indicated that males were either derived from a juvenile phase or the transition of postspawning females, confirming a diandric protogynous sexual pattern. The spawning season was well defined, occurring once a year during April and early May. Peaks in spawning occurred after the full and new moons and was completed within a single lunar cycle. The presence of mature males over the entire size and age range and the absence of inactive mature females during the spawning season suggested that the population was not constrained by sperm limitation. While specimens undergoing sexual transition were only observed in size and age ranges of 335-685 mm total length (L(T)) and 5-6 years, patterns in the proportion of males in size and age classes suggested that sex change occurred at a relatively constant rate after female maturation up to the maximum size (1002 mm L(T)) and age (11 years). Relationships between reproductive output and capacity with size and age indicated that conventional regulations that equate the mean size at first capture to sexual maturation are unsuitable for the management of E. coioides. The maximum age, small size and young age at sexual maturation (L(min)= 320 mm L(T), 2 years, for females and 242 mm L(T), 1 year, for males) conflict with the general pattern for large epinepheline groupers and may be a direct result of the intensive demersal fishery in the southern Arabian Gulf.

The selectivity characteristics of 4 juvenile fish escape panel designs and their utility for the regulation of a multi-species demersal trap fishery were evaluated using a suite of objective socio-economic and biological criteria. The panel designs consisted of a control (type A) which had a hexagonal mesh size which was the same as that of the body of the trap (3.5 cm), a rectangular mesh (type B) which was representative of the current regulation (5.0 × 7.6 cm) and 2 escape panels with square meshes of 7.5 × 7.5 cm (type C) and 10.0 × 10.0 cm (type D). The results demonstrated that there was only a limited reduction in the proportion of juvenile fish and by-catch retained for the existing juvenile escape panel design (type B). Furthermore, as the selectivity characteristics for the key species (Epinephelus coioides and Diagramma pictum) were similar to the control type, the predicted increases in yields, revenues and spawning stock biomass were small by comparison. The escape panel with the largest mesh size (type D) retained the least un-utilized and discarded by-catch. Whilst simulations predicted the highest spawner biomass per recruit, long term yields and revenues for the key species, its use was associated with a dramatic short-term decline in revenues which were 23.3% of the value of the control type. Traps fitted with the type C which had a square mesh of 7.5 × 7.5 cm had the lowest juvenile retention and the highest overall score for all the assessment criteria combined. The study provides an empirical basis for gear regulations for the demersal trap fishery of the Emirate of Abu Dhabi and the wider Arabian Gulf region.

The off-shore demersal trap fishery in the southern Arabian Gulf has been managed by gear regulations and effort constraints which were aimed at rebuilding depleted stocks. In order to evaluate the success of these regulations, a variety of selectivity and other fishery metrics were compared for the key species (<i>Diagramma pictum, Epinephelus coioides</i> and <i>Lethrinus nebulosus</i>) before and after their introduction. With the exception of a minor increase in the mean age at first capture from 1.3 yrs to 1.9 yrs for <i>E. coioides</i>, there were no significant changes in the values or trends in juvenile retention, mean size or the mean sizes and ages at first capture. The comparison of selectivity ogives with data derived independently through an experimental fishing program indicated that the failure of juvenile escape panels to modify the selectivity characteristics of the fishery could not be attributed to a lack of compliance. Furthermore, there were no significant changes in fishing mortality rates, harvest rates, catch, effort, yield per recruit and relative spawner biomass per recruit following the introduction of the management regulations. Age structures were highly truncated and the management measures had failed to increase the relative proportion of older age classes. Stock status indicators suggested that all species were heavily over-exploited with evidence of both growth and recruitment over-fishing. Given the failure of existing regulations to modify gear selectivity, reduce effort and rebuild stocks, the results of the study suggest that management authorities should consider alternative measures including a moratorium on the use of traps in the off-shore demersal fishery of Abu Dhabi