LIMA, Peru – Peru's Sea Institute said in its final report Tuesday on the mass die-off earlier this year of nearly 900 dolphins and porpoises that the cause remains unknown.
It cast doubt on oil-exploration undersea seismic testing as the reason. The report also ruled out viral and bacterial infections, human intervention, pesticides or heavy metals. It speculated that biotoxins, algae blooms, or an unknown emerging disease could be to blame in the deaths, which it said were first noticed on Feb. 7 and lasted through mid-April.
It also said testing ruled out morbillivirus, a type of distemper that some government officials had suggested as a likely cause long before kits arrived from the United States to test for it.
The institute, known by its Spanish initials IMARPE, said experts found no evidence any of the deaths were a result of seismic soundings in undersea oil exploration in the area of the deaths. But it said it did notice damage to some plankton where the soundings were done.
The Peruvian environmental group Orca, which sounded the first public alert about the mass deaths, insists the seismic work, involving shooting compressed air at the sea floor, was the likely cause.
IMARPE said in its 79-page report that it found no signs of internal hemorrhages or brain lesions that would be compatible with damage from seismic testing.
Orca contests those findings.
It said in a report of its own Tuesday that it had independently confirmed hemorrhages and middle-ear infections as well as the presence of air bubbles in internal organs and severe lung damage.
Several leading Peruvian scientists complained that IMARPE was late in gathering samples, hurting chances of determining the cause of death as the tissue tested was so badly decomposed.
IMARPE based its findings on autopsies of just two dead dolphins, which were collected in mid-April.
Orca said it gathered the first of the samples it tested on Feb. 12.
The seismic testing was conducted between Feb. 7 and April 8 by Houston-based BPZ Energy.
The IMARPE report said the testing occurred between 50 and 80 miles (80 and 130 kilometers) offshore and that the equipment used was calibrated in those waters between Jan. 31 and Feb. 7.