Reproductive Biology and Fishery-Related Characteristics of the Malabar Grouper (Epinephelus malabaricus) Caught in the Coastal Waters of Mafia Island, Tanzania

Abstract

The reproductive biology and fishery-related characteristics of the Malabar grouper (Epinephelus malabaricus) (Bloch and Schneider, 1801) specimens were investigated. The size of females ranged from 25 to 113 cm total length ( ), with 50% sexually mature at 79 cm , and the males (97 cm to 114 cm ) were larger than the females. Due to the sex ratios and size distribution of the sample, it appeared that the groupers change sex between 97 and 113 cm . However, the gonadal histology data lacked specimens in the transitional stage. The spawning peak occurred in November, as defined by the presence of ripe females, and the spawning season lasted from September to February. The size of the fish correlated positively with the water depth at capture, which is also related to oxygen levels in deep water being more favourable for larger fish. Larger specimens (>100 cm ) were targeted by fishers between December and February, when the northeast monsoon coincides with calmer weather and the spawning season. Fishers were interviewed, and observations were made on fishing gear, vessels, and grounds. There was no indication that smallscale fishers targeted spawning aggregations; therefore, fisheries independent research is recommended in order to verify the time, location, and behaviour of the spawning of Malabar groupers for management and conservation purposes.

Complementarity of fishers' traditional ecological knowledge and conventional science: Contributions to the management of groupers (Epinephelinae) fisheries around Mafia Island, Tanzania

“…These include parasites (Thompson and Munro, 1978) and death by unknown causes. Similar observations by fishers about deaths of groupers are reported by Gerhardinger et al (2006) on Epinephelus itajara in southern Brazil. Although fishers viewed death of groupers as a common event, the phenomenon is yet not documented by conventional science in the western Indian Ocean.…”

“…Furthermore, TEK on catching groupers corresponds to catch data, thereby placing more confidence on the absence of seasonality in catching groupers. The observed seasonal differences in landings of Epinephelus malabaricus reported by Gaspare and Bryceson (2013) may be due to variations in fishing effort caused by changes in sea conditions which limit access to fishing grounds. Thus, the evidence suggests that TEK could reliably be used by scientists and managers to document fish species of economic importance at the local scale.…”

“…Low level of knowledge from the same geographical area (Robinson et al, 2007;Gaspare and Bryceson, 2013) highlights the need for more research on the spawning season.…”

“…The responses revealed a fragmented understanding of grouper spawning, indicating that local knowledge of grouper reproductive behavior is poor. A study by Gaspare and Bryceson (2013) found that E. malabaricus spawn from September to January. Similarly, Nzioka (1979) studied spawning seasons of East African reef fishes and found that the spawning seasons are from October to January.…”

Temporal and spatial trends in size, biomass and abundance of groupers (Epinephelinae) in Mafia Island Marine Park: fishers’ perceptions and underwater visual census surveys

“…Consistent with UVC data, Kiegeani fishers reported that the size structure of groupers presently caught is dominated by small fish. This congruence reflects the spatial overlap between habitats for small groupers as indicated by UVC data, and fishing grounds currently accessed by fishers (Gaspare & Bryceson 2013; L. Gaspare, I. Bryceson & K. Kulindwa 2015).…”