Posted 29 September 2012 - 12:03 AM
A few challenges with Nessie being a grey seal, or any aquatic mammal, is they do need to surface regularly to breath, and as many commenters know or suggest, this would likely give Nessie away fairly easy.
Second, historically, the sightings occur most often during the summer months of July and August, which is what you may expect with an ectothermic creature like a salamander. Seals could be active in the loch virtually any time of the year, and as grey seals live on the coast of Scotland and England, and I believe they do not migrate, the reason for them to appear in the loch would have to be seasonal to match the sightings. If not, the sightings would likely occur more evenly throughout the year. Perhaps this is due to movement of the fish population, but given the surrounding sea probably has much more sealife to feed on then the loch, the reason to enter it would have to be something other then food. Losing their way is a possibility, but seems unlikely to account all the sightings to lost seals.
A giant salamander is scientifically plausible, the Chinese Giant Salamander can reach 6.6ft (2m) in length and weigh 145lbs (65kg). The analysis of the Grey Photo suggests a specimen four times in length, which is not that unbelievably impossible, as that family of salamanders is almost exclusively aquatic, a large size and weight is not a hinderance. Also the family of salamanders can respire through their skin, called cutaneous gas exchange, so long as the water is sufficiently oxygenated. This means they can remain submerged as long as they can draw oxygen through their skin. Loch Ness, below its thermocline (~100 ft, or 33m), the water is highly oxygenated. Most often they still possess gills and lungs, and can gulp air to get extra oxygen when needed, either their activity as suggested in the analysis, or lower oxygen in the water. Colder water contains more dissolved gases then warmer, oxygen included. Loch Ness does contain plenty fish, clams, crayfish, and insects, all of which are eaten by these salamanders. Additionally all these food sources peak during the July and August months.
We see things only as we are constructed to see them, and can gain no idea of their absolute nature.
With five feeble senses we pretend to comprehend the boundlessly complex cosmos. - H.P. Lovecraft, "From Beyond" Published 1934