MARINE MAMMAL COMMISSION — Annual Report for 1992 
been fully identified and that completing the survey 
program, as proposed, will meet the minimum data 
needs. 
The second proposal is to continue an assessment 
of harbor porpoises in Washington and Oregon. The 
objectives of this study are to (1) calculate a “best” 
and “minimum” population estimate, (2) determine 
stock structure, and (3) determine relative distribution 
and abundance by season, water depth, and geograph- 
ic location, especially along the northwestern coast of 
Washington in areas where porpoises are incidentally 
taken in the salmon set gillnet fishery. The Commis- 
sion noted in its 3 December 1992 letter that the 
proposal seems likely to meet the stated objectives, 
but that further studies may be necessary to obtain 
both a “best” and “minimum” population estimate if 
there is a substantial between-year variation in either 
distribution or abundance. The Commission recom- 
mended that if it had not already done so, the Service 
compare the sighting and incidental catch data to 
determine whether incidental take might be avoided or 
reduced by altering fishing seasons, areas, gear types, 
or practices. The Commission also recommended that 
if the Service had not already done so, it convene a 
workshop to compare, evaluate, and standardize the 
methods being used to assess and monitor harbor 
porpoise abundance in the northeastern United States, 
Alaska, Washington, Oregon, and California. 
The Marine Mammal Commission remains con- 
cerned about the status of harbor porpoises in U.S. 
waters and elsewhere and in 1993 the Commission 
will continue to review actions taken and provide 
advice to the National Marine Fisheries Service. 
Bottlenose Dolphin 
(Tursiops truncatus) 
The bottlenose dolphin occurs throughout the 
temperate and tropical oceans of the world, frequently 
in nearshore waters. It is the most common cetacean 
species in the coastal waters of the southeastern 
United States, and the species most frequently main- 
tained in captivity for public display and scientific 
research. Capture of bottlenose dolphins for these 
purposes began in the early 1900s in the United 
States. Considerable although unknown numbers of 
76 
animals were taken prior to the enactment of the 
Marine Mammal Protection Act in 1972. A permit 
procedure for taking marine mammals was implement- 
ed under the Act, and since 1972 permits have been 
issued for collection of more than 500 bottlenose 
dolphins from U.S. waters. 
As discussed in previous annual reports, the 
discreteness and status of local and regional bottlenose 
dolphin populations in U.S. waters are uncertain. It 
is unlikely, however, that capture and removal alone 
have caused significant declines in the affected popula- 
tions. Unusual mortality events involving bottlenose 
dolphins appear to be a recurring phenomenon. 
Large-scale mortality of bottlenose dolphins occurred 
along the U.S. Atlantic coast in 1987-1988, along the 
coast of the Gulf of Mexico in 1990, and again off the 
coast of Texas in 1992. These events may have 
caused significant declines in these populations and 
are discussed in Chapter VI. 
Also, unknown but potentially significant numbers 
of bottlenose dolphins are killed incidentally in 
fisheries for menhaden, shark, shrimp, swordfish, and 
other species in the coastal waters of the southeastern 
United States and the Gulf of Mexico. In some areas, 
bottlenose dolphins and their habitat also may be 
affected by marine and coastal pollution, oil and gas 
development, dredging and dredge spoil disposal, and 
other activities. 
The independent and collective effects of unusual 
mortality events and various human activities have not 
been determined. It is possible that one or more local 
bottlenose dolphin populations have been depleted and 
that their recovery is being prevented or impeded by 
continued taking. It also is possible that essential 
habitat has been or is being damaged or destroyed by 
pollution, dredging, and other activities. 
Mid-Atlantic Coastal Migratory Population 
Between June 1987 and May 1988, more than 740 
bottlenose dolphins washed up along the Atlantic coast 
between New Jersey and Florida. Although the 
results are not conclusive, post-mortem examinations 
suggest that the proximate cause of the die-off was 
brevetoxin, a neurotoxin produced by the dinoflagel- 
late Gymnodinium breve, which also causes red tide. 
