habitat_narrative
Marine
Argyrops spinifer inhabits a wide range of bottoms in depths to 400 m (Heemstra and Heemstra 2004), usually occurring between five and 100 m (Sommer et al. 1996). The maximum size for this species is 75 cm (S. Alam, Ministry of Environment, pers. comm. 2013) but is more common to 30 cm TL (Sommer et al. 1996). The maximum age for A. spinifer is to 25 years with oldest fish being females (Al-Mamry et al. 2009). Young fish occur in very shallow waters of sheltered bays (Sommer et al. 1996) while larger individuals occur in deeper water. It feeds on benthic invertebrates, mainly molluscs (Fischer et al. 1990, Salini et al. 1994).The spawning season for A. spinifer in the Arabian Sea was observed to occur from September to January, immediately after the monsoon period, with a peak in spawning around October-November. In the southern Persian Gulf, spawning occurs from January to April (Grandcourt et al. 2004). McIlwain et al. (2006) suggested that there are two spawning seasons for A. spinifer in the Arabian Sea: a small peak in July during the monsoon season and a main spawning season between November and March. There is some evidence of large aggregations during autumn in the Gulf of Aden (Druzhinin 1975).
The sizes at first maturity in Oman were 28.6 cm and 26.4 cm FL for A. spinifer females and males, respectively (McIlwain et al. 2006); these values were similar to results from the southern Persian Gulf, at 26.9 and 26.7 cm (Grandcourt et al. 2004). Al-Mamry et al. (2009) report mean sizes at sexual maturity (L50) at 36.5 cm TL for males and 37.2 cm TL for females, respectively. The estimated mean ages at sexual maturity (A50) are 5.0 and 5.6 years for male and female fish respectively in Oman, but was 2.4 years for both males and females in the southern Persian Gulf (Grandcourt et al. 2004).
A comparison of the spawning period with that at which peaks in recruitment occur suggests that A. spinifer recruit to the trap fishery at ages between fuve and 11 months. There were high levels of juvenile retention because fish were fully recruited before the mean size at which sexual maturity occurred (Grandcourt et al. 2004).
Parameter values of the von Bertalanffy growth function fitted to size at age data (males and females combined) were: k = 0.224 year−1, L∞ = 52.4 cm (LF), to = −0.44 years. Argyrops spinifer is fully exploited below the mean size at which females attained sexual maturity (26.9 cm LF). The overall sex ratio is significantly female biased although the bias was removed above the size at sexual maturation, potentially as a result of protogynous (female to male) sex change, although this has not been confirmed (Grandcourt et al. 2004). The von Bertalanffy growth parameters available for the Gulf of Aden and Arabian Sea indicate that A. spinifer in these regions have similar growth rates (i.e. k = 0.14–0.21 year-1) and attain a similar maximum size (Arabian Sea, L\ = 64.6 cm LT; Gulf of Aden, L\ = 63.5 cm LT)(Edwards et al. 1985). The von Bertalanffy growth parameters available for the southern Persian Gulf provide contrasting results, with El-Sayed et al. (1998) reporting coefficients of k = 0.09 year-1 and L\ = 81.0 cm LT in the early 1990s and Grandcourt et al. (2004) reporting coefficients of k = 0.22 year-1 and L\ = 58.2 cm LT in 2000–2003. However, it is not known to what degree these differences in growth patterns are due to regional differences in biological productivity, stock-dependent genetic differences in growth performance, the selectivity in fishing gear used in each study and, in the case of the southern Persian Gulf, any temporal changes in fishing pressure (Grandcourt et al. 2004, Al-Mamry 2006).
