Biological Parameters of Lethrinus nebulosus in the Arabian Gulf on the Saudi Arabian Coasts

In the present study about 277 specimens of Lethrinus nebulosus were used to determine some biological parameters which are needed in stock assessment in the region of Arabian Gulf on the Saudi Arabian coasts. The period of spawning was estimated using maturity indexes to April, Mai and June. This species is gonochoric, nevertheless some cases of hermaphrodism are noted. The length relationships were determined showing a correlation between total length and standard length, and between total length and fork length. The weight- length relationship is allometric minorante. The model of Von Bertalanffy was estimated for the studied species and it is as follows: Lt = 600 *(1-exp (-0.135*(t+1.69)) for both sexes, Lt = 600 (1-exp (-0.166*(t+0.746)) for females and Lt = 555 *(1-exp (-0.153*(t+1.62)) for males.

Spawning aggregations of fish in Cabo Delgado, Northern Mozambique: An interview-based survey of artisanal fishers

Seasonal aggregations at specific sites are common among some fish species. Experienced fishermen know where and when these aggregations happen, often targeting these spawning sites to increase their catch. This strategy can further contribute to endangering the survival of these species, especially for those already threatened by other forms of pressure. This study contributes knowledge to the spawning aggregation of fish in the north of Mozambique following survey work conducted around Cabo Delgado Province in six coastal villages in 2016, 2017 and 2018. The objectives of the study were 1) to identify the species and sites of spawning aggregation and 2) to determine the timing of spawning aggregations. Data collection consisted of interviews targeting the most experienced fishermen to obtain information on these subjects. The results indicate that out of 124 fishermen interviewed, 59% had knowledge of spawning aggregations. The information collected from fisher interviews revealed that there are at least six spawning locations and at least eight species aggregate to spawn (Leptoscarus vaigensis, Lethrinus harak, Lethrinus nebulosus, Lethrinus obsoletus, Lethrinus olivaceus, Plectorhinchus gaterinus, Plectorhinchus schotaf, Siganus sutor). Only Siganus sutor was reported to spawn in at least one of the fishing areas used by every village. The timing of spawning aggregations most reported by fishermen was during the Kusi (South) monsoon period.

Genetic analysis reveals harvested Lethrinus nebulosus in the Southwest Indian Ocean comprise two cryptic species

This study initially aimed to investigate the genetic population/stock structuring of Lethrinus nebulosus in the Southwest Indian Ocean (SWIO) to inform management practices in light of emerging evidence of overharvesting of this species throughout its distribution. Adult samples were genotyped for 14 nuclear microsatellites and by sequencing fragments of the mtDNA control region and COI gene. A salient feature of the data was the congruent cyto-nuclear partitioning of samples into two high divergent, reciprocally monophyletic groups. This indicates that despite no a priori evidence, hitherto described L. nebulosus in the SWIO comprises two cryptic species that co-occur among southern samples. This intermingling indicates that, at least in southern samples, both species are being indiscriminately harvested, which may severely compromise sustainability. Limited microsatellite differentiation was detected within both species, though there was some evidence of isolation in the Mauritian population. In contrast, mtDNA revealed a pattern consistent with chaotic genetic patchiness, likely promoted by stochastic recruitment, which may necessitate a spatial bet-hedging approach to management to satisfy fishery management and conservation goals.

Environmental and individual effects on the behaviour and spawning movements of Lethrinus nebulosus on a coral reef

Spatial management of fish populations can potentially be optimised by incorporating responses to environmental variables, such as diel, tidal, lunar and seasonal factors, but individual variability in habitat use and behaviour may complicate such efforts. Acoustic tagging and tracking of 84 Lethrinus nebulosus in the Ningaloo Marine Park indicated that sizes of individual habitat utilisation kernels were similar across diel and tidal cycles, but varied greatly among individuals. Clearly differentiated diel and tidal habitat use patterns were evident in significant proportions of individuals, particularly in relation to tidal phase. For the majority of residents, home-range sizes were reasonably stable over periods of 2–4 years, but in some cases core areas did shift over time. At seasonal time scales, peaks of seasonal activity and home range area were recorded during spawning season (October–December). Long-distance return migrations to spawning locations were observed that were among the longest observed for any reef fish (over 130km). Suspected spawning-related movements were recorded almost exclusively in fish >500-mm fork length, and were semilunar, following quarter moons in October–December. Significant individual-level variability in movement and habitat use patterns, evident across multiple temporal scales, has important implications for the management of L. nebulosus populations.