(CRITICALLY ENDANGERED)Totoaba

The totoaba or totuava (Totoaba macdonaldi) is a marine fish of the drum family (Sciaenidae) that is indigenous to the northern half of the Sea of Cortez in Mexico. Formerly abundant and subject to an intensive fishery, the totoaba has become rare, and is listed on CITES[1], the IUCN Red List of Threatened Species, and the Endangered Species Act (ESA).

The totoaba can grow up to two metres in length and 100 kg in weight. Their diet consists of finned fish and crustaceans. While individuals may live up to fifteen years, sexual maturity is usually not reached until the fish are six or seven years old. As totoaba spawn only once a year, population growth is slow, with a minimum population doubling time of four-and-a-half to fifteen years.The totoaba spawn in the Colorado River delta, which also serves as a nursery for the young fish. The diversion of water from the Colorado River within the United States leaves little or no fresh water to reach the delta, greatly altering the environment in the delta, and the salinity of the upper Sea of Cortez. The flow of fresh water to the mouth of the Colorado since the completion of the Hoover and Glen Canyon dams has been only about 4% of the average flow during the period from 1910 to 1920. This is considered to be a major cause of the depletion of the totoaba population.

The totoaba population is found in two distinct groups. Larval and juvenile stages occupy the Colorado delta, while the adult breeding population lives for most of the year in deeper water towards the middle of the Sea of Cortez. The adult population migrates to the Colorado delta in April and May to spawn. One-year old totoaba are metabolically most efficient in brackish water of about 20 ppt (parts per thousand) salinity, a level that occurred naturally in the delta before the diversion of water from the river that occurred in the middle of the 20th century. with the loss of the fresh water flow from the river, salinity in the delta is usually 35 ppt or higher.

Commercial fishing for totoaba began in the 1920s. The catch reached 2,000 metric tons in 1943, but had fallen to only 50 tons in 1975, when Mexico protected the totoaba and banned the fishery. Anectodal evidence suggests that totoaba were very abundant prior to the start of the commercial fishery, but there is no hard evidence of natural population size. Recent studies indicate that the totoaba population has stabilized at a low level, perhaps a bit bigger than when the commercial fishery was banned in 1975. Totoaba are still caught, as by-catch in fishing for other finned fish and for shrimp, and in illegal fishing for totoaba directly. Some totoaba are illegally exported to the United States, often misidentified as white seabass.

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