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Bay of Ambaro (Madagascar) - Key Species

Shrimp

Shrimp

Ponyfish

Ponyfish

Red snapper

King mackerel

Indian mackerel

Shark

Shark

Shrimp (Fenneropenaeus indicus)

Commercially known as white shrimp, this species is the most abundant of shrimp species in the Bay of Ambaro, contributing up to 95%. Spatial distribution depends mostly on salinity and biological stage: spawning occurs at sea, the post larvae migrate to estuaries and enter mangrove channels with low salinity. At sub adult stage, the shrimp moves to the intertidal area and seawards, and heavy rainfall resulting in high river flow flush them away from the intertidal area. This behaviour results in the development of a sequential fishery, sub adults being caught by various traditional / artisanal gears whilst adults are trawled further from the coast. The species aggregates at the end of rainy season and disperses during the dry season. Most of the catch is taken during the day when the shrimp are most active. The adult stock on trawling grounds has drastically decreased in size over the last five years; as no clear correlation with environmental conditions has been found, it is assumed that the situation results from over-exploitation of juveniles and sub adults.

Shrimp (Metapenaeus monoceros)

This species known as speckled shrimp is second to the white shrimp in terms of abundance. It is caught during both the day and at night. Speckled shrimp has the same life cycle as F. indicatus: spawning at sea, larvae and juveniles in estuaries and mangroves. Catch data over the past few years show that the species is overfished.

Ponyfish (Gazza minuta)

Ponyfish are known locally as lily or salelo. This species is found on muddy seabeds in coastal shallow water, constituting a major bycatch species of the shrimp fishery. Juveniles under 8 cm are encountered in estuaries. Formerly discarded at sea or recommended as animal feeding, the species is now retained and marketed for human consumption.

Ponyfish (Leiognathus equulus)

This species is one of the biggest lily species of the area. Formerly discarded in the trawl shrimp fishery, it is now marketed locally.

Red snapper (Lutjanus bohar)

Red snappers are locally called tsivaravara. This species schools in reef habitat and thus may contribute to a major part of the catch. Red snapper is highly appreciated on Nosy-Be markets after the king mackerel and big carangid species.

King mackerel (Scomberomorus commerson)

Locally called angoho, this species is the most appreciated one (fresh, smoked, dried) in local markets. This pelagic species is not particularly targeted but incidentally caught with lines set out during pirogue or boat movements (going to fishing grounds or back to villages). King mackerel is encountered in coastal waters as well as on the continental shelf.

Indian mackerel (Rastrelliger kanagurta)

Indian mackerel are locally known as mahaloky. Nets may catch a whole school of Indian mackerel on the continental shelf. They commonly reach a length of 24 cm TL, first maturity occurring at 19,6 cm TL. The species is oceanodromous and feeds on phytoplankton (diatoms) and small zooplankton (cladocerans, ostracods, larval polychaetes, etc.).
Adults occur in coastal bays, harbors and deep lagoons, usually in some turbid plankton-rich waters. Small groups have been seen eating eggs of Cheilio inermis straight after spawning. Adult individuals feed on macroplankton such as larval shrimps and fish. Eggs and larvae are pelagic. Catch is generally marketed fresh, frozen, canned, dried-salted, or smoked.

Shark (Sphyrna lewini)

The scalloped hammerhead shark, a cosmopolitan and semi oceanic species, is found in tropical seas, sub-tropical and warm temperate waters. This species is probably the most abundant among the hammerhead sharks that inhabit the continental shelves and slopes. Juveniles prefer shallow coastal waters such as bays and estuaries, which they use as nurseries. Hammerheads are viviparous. Size at birth varies 31 cm to 55 cm.  The number of oocysts in the ovary varies from 40 to 50 per female but only 12 to 38 embryos per female grow before birth.  Parturition always takes place in shallow coastal waters. Newborns and juveniles suffer very high predation by other Carcharhiniforms, even by adults of the same species, likely one of the sources of the high natural mortality of the species. The scalloped hammerhead shark feeds mainly on meso-pelagic fish and cephalopods. Also, there are other invertebrates and rays. Juveniles prefer mainly benthic fish such as Scaridae and demersal Gobiidae, and shellfish.

The fins are higher in commercial value than those of other sharks. The species is highly vulnerable to trawls, purse seines, gillnets, long lines and surface as well as traditional small-scale fisheries.  Traditional fishermen target newborns and juveniles. The significant decrease in the average size and weight of scalloped hammerhead shards in the catch (declining from 139 cm and 48.25kg in 2005, to 116 cm and 19kg in 2006) seems to confirm overexploitation.  S. Lewini is on IUCN Red list, in category Threatened (LR /nt).

Shark (Loxodon macrorhinus)

Loxodon macrorhinus is found in the Indo West Pacific from South Africa, Madagascar, Seychelles, Red Sea, India, Sri Lanka, Indonesia, China, Taiwan, Japan, Philippines and Australia. Sagrin (slit eye) shark is very common in tropical coastal waters and continental slopes of oceanic islands, found at depths from 7 m to 80 m. The species prefers the sea bottom but can return to the. Sagrin shark is viviparous with a true placental sac containing 2-4 embryos. It feeds mainly on small teleost fish, shrimp and cuttlefish. The maximum recorded size is 91 cm. The size at sexual maturity of females is estimated to be from 79 cm to 91 cm and males from 66 cm to 85 cm. Size at birth ranges from 40 cm to 43 cm.

This small shark is caught mainly by small-scale fishermen in tropical areas, often by artisanal and industrial fisheries, using bottom gill nets and surface long lines. The species constitutes a very important bycatch in traditional fishing for shrimp in the Bay of Ambaro. This suggests that the shark prefers the warmer waters in this part of the island.