South African fur seals.
By Lloyd Edwards

Tuesday, 13th December 2022

With the advent of Ship to Ship fuel transfers in Algoa Bay since 2016, there have been many more vessels lying at anchor. Seals are quick to capitalise on this and they are often observed resting on the bulbous bow of ships awaiting bunkers.

South African fur seals are part of the “pinnipeds” family, which comes from the Latin meaning of “fin-footed”. They have a thick coat of short brown under-fur covered in long outer guard hairs. Sea lions only have one coat. Unfortunately for fur seals, it was this under-fur that makes their pelts suitable for the manufacture of sealskin clothing and led to millions being slaughtered. The pups from seven to ten months always constituted the bulk of the harvest, their thin skulls being shattered by a blow from a heavy club.

There are two main families, the eared seals (which include ours) and the true seals. Of all the pinnipeds worldwide, ours have the longest history of interaction with humans. Skeletal remains have been found in shell middens in caves that have been excavated along the Southern cape coast and date back 160 00 years.

The colony of 6000 at Blacks Rocks in the Bird Island group, is the eastern extremity of their breeding range, although they will forage further eastwards along our coast. They extend for 3000km westwards and have been observed 650km north of the Angola border, although the most northern colony is at Cape Frio in Namibia. The colonies at Kleinsee (almost 500 000) near Port Nolloth and Atlas Bay in Namibia are the largest mainland seal colonies in the world.

Seals are extremely efficient predators and have evolved numerous adaptions to extend their time beneath the waves. They have developed strong laryngeal muscles which prevent water entering the body, while catching prey at depth. Their nostrils are closed when relaxed, so as pressure increases with depth, they become even more watertight. As unlikely as it seems, they exhale before diving and the rib cage flattens to get rid of any remaining air. The bronchi and trachea also reduce to half, retaining only a small amount of air. Like cetaceans they do not take enough air down with them to get decompression sickness that is associated with breathing compressed air at depth.

The greatest adaption to enable these deep and extended dive times, is the modification to their blood system. Firstly, they have a proportionately higher volume of blood to their body size, which is super rich in haemoglobin. They also have a very high concentration of myoglobin in their muscles, which gives the meat a dark red colour. This allows them to store five times as much Oxygen in their bodies as humans. Throughout the dive, the flow of blood to the brain remains constant. The constriction of arteries however, limits the flow of blood to extremities so that there is a 90% reduction in flow to skin, muscles, intestines and flippers. The heart beats far less, at the rate of four to six times a minute, which further restricts flow to the extremities. Although they can dive to 200m and stay down for eight minutes, most dives are less than 50m and for a shorter duration. Initially, they dive straight to the bottom and come up slowly. They feed mainly at night doing progressively shorter dives, while probably taking advantage of the fact that squid (20% of their diet) move closer to the surface at this time. In our area they eat 75% fish made up of anchovy, sardine, maasbanker and hake.

A fur seal wrestles with a blue ray, breaking it up into small pieces. Taken with a Nikon D810 full frame, ISO 360, 200mm zoom, f7.1 and 1/2500th second.

These three old males were snapped napping in the sun next to a bulk carrier. They keep their appendages in the air in order to warm up. A bit like having a solar panel!

I couldn't resist this photo. It is almost like the seal is saying "full steam ahead Captain"!

A mixed group, some large males, smaller females and some juveniles.

Seal pups on their home on Black Rocks near Bird Island. Notice that the seal on the right has a fishing rope around it's neck. Unless Dr. Greg Hofmeyer and his team get to this animal it will surely die a slow and painful death. If you have not yet signed our petition about rope less fishing please go to our website and do so.