MARINE MAMMAL COMMISSION — Annual Report for 1995 



recent abundance estimates derived from boat and 

 aircraft surveys done between 1986 and 1993 range 

 from 224 to 885 individuals. These are among the 

 first quantitative estimates of vaquita population size, 

 and they confirm that the species is very rare. Also, 

 the researchers making the estimates indicated that the 

 population could be declining at a rate of about 20 

 percent annually. 



Data obtained in recent years further emphasizes 

 the gravity of the situation. Age and reproductive 

 data from a sample of 56 vaquitas obtained between 

 1985 and 1993 suggest that the life history of the 

 vaquita appears to be similar to that of depleted 

 harbor porpoise populations found elsewhere. How- 

 ever, the potential rate of increase may be lower for 

 the vaquita than for its congeners because the vaquita 

 does not calve annually. The sample consisted mainly 

 of young and old individuals, suggesting that there 

 may be few adults of prime reproductive age. The 

 analysis also revealed the presence of unusual ovarian 

 pathologies in many of the females. In addition, some 

 scientists believe that habitat alteration in the northern 

 Gulf of California may represent a significant threat 

 to the species. On the other hand, contaminants such 

 as chlorinated hydrocarbons and polychlorinated 

 biphenyls were found in low levels in the vaquita 

 relative to small cetaceans in other parts of the world, 

 and contaminants do not appear to pose an immediate 

 threat to the species. 



Incidental Mortality in Fisheries 



The greatest threat to the vaquita is entanglement 

 in gillnets. The species is known to have been caught 

 incidentally in the fishery for totoaba since the mid- 

 1940s. The fish stock itself was severely overexploit- 

 ed and in 1975 the Mexican Government banned the 

 fishery to allow it to recover. Despite the closure, the 

 fishery has continued at low levels, both illegally and 

 as a legal experimental fishery. In 1979 the totoaba 

 was listed as endangered under the U.S. Endangered 

 Species Act to help stop the illegal sale of the fish in 

 the United States. 



Historic levels of vaquita incidental take are not 

 known, and only recently have attempts been made to 

 quantify fishery-related mortality. Between February 

 1985 and June 1991 the deaths of 121 vaquitas were 



documented in gillnet operations for totoaba, shark, 

 ray, sierra (a mackerel-like fish) and in shrimp trawls. 

 At least five vaquitas are known to have died in 

 fishing operations in 1992. More recently, fishing 

 activities involving mesh sizes less than 25 centimeters 

 were monitored in one of the upper Gulfs primary 

 fishing ports between January 1993 and March 1994. 

 Fourteen vaquita deaths were documented in gillnets 

 with mesh sizes between 7 and 15 centimeters, and 

 one vaquita died in a shrimp trawl. 



In an effort to limit vaquita incidental mortality in 

 gillnets, the Mexican Secretary for Fisheries issued a 

 regulation in February 1992 reiterating the ban on the 

 totoaba fishery and prohibiting the use of large-mesh 

 gillnets in the northern Gulf of California. 



The mortality monitoring effort does not include all 

 fishing communities and fishermen do not report all 

 incidental takes; therefore the actual mortality is 

 probably higher than reported and may be higher than 

 previously believed. Given the small population size 

 and the low potential rate of increase, it is unlikely 

 that the population can sustain the current rate of 

 fishery-related mortality. 



International Efforts to Protect Vaquitas 



At its 1991 meeting the International Whaling 

 Commission's Scientific Committee recommended that 

 actions be taken to fully enforce the closure of the 

 totoaba fishery and halt illegal shipments of totoaba 

 into the United States. It also recommended prepara- 

 tion of a management plan for the vaquita that in- 

 cludes an evaluation of incidental take of vaquita in 

 fisheries and a program to monitor the species' status. 



At its 1994 meeting the IWC's Scientific Com- 

 mittee concluded that the present levels of incidental 

 catch could result in extinction of the species. The 

 Committee recommended that fishing activity and 

 incidental mortality be monitored throughout the 

 species' range and that surveys be conducted to 

 improve abundance estimates. The Committee ac- 

 knowledged the recent joint research efforts by 

 Mexican and U.S. Government agencies and com- 

 mended efforts by the Mexican Government to protect 

 the vaquita. In response to the Scientific Committee's 

 findings, in 1994 the IWC adopted a resolution 



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