Date: Tue, 10 Jun 1997 17:06:33 -0700
From: MARMAM Editors marmamed@UVic.CA>
Subject: med. monk seal die-off Update (fwd)
Forwarded message: From: manelg@porthos.bio.ub.es
The die-off continues afflicting the Cap Blanc colony of Mediterranean monk seals, although the mortality rate appears to have somewhat decreased during the last week. At the beginning of the process about 4-6 new corpses were found each day, but the rate has currently stabilized at about 1-2 per day.
The magnitude of the mortality is still to be evaluated but it is known for sure that it has produced a significant impact on the colony. So far, 81 seal corpses have been found washed ashore and, by comparing the counts of seals currently present in the main caves where the seals haul-out with similar counts conducted during the month of May of 1994, 1995 and 1996, it has been estimated that between 130 and 150 seals may have died. If these numbers are confirmed, this would mean that more than 50% of the population, estimated at 270 individuals in 1996, has perished during the event.
Four orphaned pups were rescued by the Spanish LIFE-CE research team and handed to the National Parc of the Banc d'Arguin (PNBA). The pups are currently being rehabilitated at the National Center of Oceanographic and Fisheries Investigations (CNROP) of Nouadhibou with the assistance of the Seal Rescue Center of Pieterburen. Following the Action Plan agreed between the PNBA and the CNROP, when the rehabilitation of these pups is completed the PNBA will be in charge of their acclimation and reintroduction in the wild.
On 31st May an Emergency Committee of Experts, chaired by Dr. Peter Reijnders, met at the Schiphol (Amsterdam) airport. The committee was composed of the members of the Steering Committee of the Spanish LIFE-CE Project on Mediterranean Monk Seals plus specialists in pinniped biology, virology, biotoxins and oceanography. The main aim of the meeting was to assess available information on the event and to draw the guidelines for a contingency plan to be put into action in the case that the die- off continues and threatens the survival of the colony.
The results of the investigation conducted indicated two potential causative agents of the die-off.
1) In the tissues of one seal, two independent researchers found signs that it had been exposed to a virus. However, the identity of such virus remains to be confirmed. Analyses of blood samples from three live seals did not show any alteration in hematological parameters, suggesting that a generalized infectious process is not affecting the population.
2) The analyses of tissues from 5 seals by bioassay and high performance liquid chromatography (HPLC) by two independent researchers indicated that seals had been exposed to a paralytic shellfish poisoning saxitoxin (PSP) of the type produced by dynoflagellates. Also, both laboratories conducted analyses of sea water samples collected in 3 different days in the proximities of the colony, and in both cases toxic dynoflagelates were detected, particularly Alexandrium spp, a species known to produce PSP toxins. On the other hand, bioassays conducted by a third laboratory was unable to establish the presence of the PSP toxin in seal samples although extracts also produced the death of the mice used in the test.
Research on the identity of the causative agent of the die-off continues. The two potential agents so far identified (saxitoxins transmitted via food and virus) may have acted combined. However, the observed symptoms in moribund animals and the lesions observed in the necropsies match those to be expected in an animal affected by PSP toxins. On the other hand, the observed mortality pattern, with the die-off mainly affecting adult seals, does not suggest an infectious process and, conversely, can be reasonably explained by differences in the diet and feeding areas known to exist between young and adult seals. It is remarkable, for example, that the four rescued orphaned pups are in excellent health condition whereas their mothers died in the event. In previous viral epizootics occurred in marine mammals, the mortality of pups and young was massive, contrary to the present situation in which young individuals appear to elude the lethal agent.
However, the existence of a virus in the colony must be studied in order to prevent potential infections in a population undoubtedly weakened by the present process. The Experts Committee recommended precautionary vaccination of individuals from the colony against morbillivirus. Such vaccination is not considered urgent, although it is planned to start as soon as the behaviour of the individuals of the colony, at present strongly disturbed, returns to normality.
Likewise, with the aim of evaluating the trend of the toxin levels in the region, the Experts Committee recommended the analysis of PSP toxins in fish species that constitute the diet of seals. In a parallel way, a constant vigilance of the colony will be maintained in order to detect the appearance of newly dead seals and the evolution of the survivors. If the population numbers continue to decrease it is not discarded a direct intervention to rescue the seals still alive.
Alex Aguilar, Department of Animal Biology,Faculty of Biology, University of Barcelona, E-08071 Barcelona, SPAIN