الملخص الإنجليزي
Lethrinus nebulosus is one of the most common demersal species in Omani local
fish markets. In the Sea of Oman, no studies have addressed the biological aspects and
population dynamics of L. nebulosus, while there are records of this species being
overexploited in the Arabian Sea. Consequently, study of L. nebulosus population
dynamics is necessary to determine the status of this fishery in the Sea of Oman. The aims
of this study were to: (1) determine age, growth, recruitment, and mortality, (2) identify
the maturity stages and spawning season, and (3) determine the exploitation rate.
Biological parameters and population status of the spangled emperor (Family Lethrinidae,
Lethrinus nebulosus) in the Sea of Oman (Dibba, Musandam) were determined by
collecting monthly fish samples from local fish markets during 2016. A combination of
biological, length-frequency, age and reproductive data was used to investigate the
current status of L. nebulosus in the Sea of Oman (Musandam) and inform management
recommendations.
Fork length (FL) ranged from 14 - 61.5 cm, with an average size of 43 cm (± 0.51
S.E.) for males, and 41 cm (± 0.43 S.E.) for females. Growth parameters comparisons
showed there were no significant difference (p > 0.05) in growth between sexes. The vonBertalanffy Growth function (VBGF) parameters were an asymptotic maximum size (L∞)
of 56.76 cm, growth coefficient (k) of 0.38 year-1
, and average size at age zero (t0) of -
0.39, with a maximum age of 23 years old. The growth coefficient of 0.38 suggests that
this species is a slow-growing species, and is comparable to previous regional studies.
The sex ratio (males:females) was 1:1.75, indicating a slight female bias, as previously
observed in other studies of this species. The gonado-somatic index (GSI) highlighted a
spawning season of this species from February to April in Dibba, Musandam during 2016.
The mean length (L50) at which 50% of the population attained sexual maturity was 44
cm. The average size-at-first-capture was 42 cm which is smaller than the average sizeIV
at-first-maturity, suggesting that management policies (e.g., minimum size limits) are
needed to increase the length-at-first-capture to be higher than the average length of
sexual maturity (L50), and ensure a sustainable fishery of this species. Estimates of the
total mortality rate (Z) attained from length frequency data by catch-curve analysis, was
0.89 year-1
. The natural mortality rate (M) of 0.64 year−1
implies that the current fishing
mortality rate (F) was 0.26 year−1
, which is lower than recommended reference points F0.1
(0.30 year−1
) and Fmax (0.35 year−1
). The relative spawner-biomass-per-recruit was
estimated to be 34% of unexploited levels at the current fishing mortality rate.
In conclusion, these findings suggest that the spangled emperor stock in
Musandam, Sea of Oman, is currently not overexploited, but that the stock could be
experiencing recruitment overfishing. Consequently, management policies, such as
minimum size limits, spawning season catch bans, marine protected areas, and using highselectivity fishing gear are needed imminently to ensure the future sustainability of this
fishery under increasing pressures in the future.
المعرف
Al-Bulushiyah, Khulood Khalfan Obaid (2019). Population dynamics of the spangled emperor (Lethrinus nebulosus (Forsskal, 1775)) in Musandam, Sea of Oman (Master thesis, Sultan Qaboos University, Muscat, Oman).
