Entanglement

So far, my blog has mentioned the impacts that humans are having on a number of Antarctic species such as krill and Gentoo and Adélie penguins. Today's post will look at yet another animal whose habitat is in Antarctica, the fur seal. Croxall et al. (1990) conducted research investigating how fur seals are becoming entangled by various man-made products that are roaming the oceans near Antarctica. Figure 1 shows what I mean by entanglement. It is when the fur seal gets caught up in man-made materials that are non-biodegradable, such as polypropylene or nylon string and fishing nets. Fur seals become entangled by putting their heading into the loops of material in the ocean while swimming. 

Figure 1. Entangled Antarctic fur seal

Antarctic fur seals are commonly found in the South Georgia and the South Sandwich Islands (see figure 2) and this is where Croxall et al. focus their study. The authors reported observations of fur seals that had man-made objects around the seals’ necks (referred to as neck collars) for 142 days at Bird Island (as shown in figure 2) from 1988 to 1989.

Figure 2: South Georgia and the South Sandwich Islands. Adapted from Cool Antarctica (2001) and Wikitravel (2011)

This study helped identify the extent of entanglement in South Georgia. Here is a summary of the main findings of the research:

• At least 0.1% of the total Bird Island population had a neck collar during the study period, of which 59% was due to packaging bands made from polypropylene straps, 16% was due to nylon strings and 13% was due to fishing nets.
• Males accounted for 71% of entanglements and young accounted for 88% of entanglements.
• 135 males and 55 females were observed to be entangled.
• 19% of the collars were loose enough to remove.

The table below, table 1, also shows the results.

Table 1. Observed Antarctic fur seals with entanglements at Bird Island and the type of collar. Source: Croxall et al. (1990)

There are some inadequacies in this research however. The authors claim that '15 were most probably of animals seen more than once or whose collars were subsequently removed’ (p. 223) so they did not count these in the results. Hence the total number of fur seal included in their results (i.e. the minimum number observed) is 208, not 223 (see table 1). I find this problematic because how can the authors be certain that a fur seal was observed more than once? The authors don’t mention that they were tagged or tracked in any way and due to the homogenous characteristics if fur seals, perhaps there is measurement error in the observations.  

Also, there are complications in measuring the exact proportion of the total population that is affected because the whole population is not observed. Many young don’t appear ashore and they could have neck collars. A further consideration is what about the fur seals that are entangled in the sea and don’t make it back to the island? Antarctic fur seals can go weeks in the oceans (National Geographic, 2014) so these seals are not observed. Hence, this sample is too small to infer the full extent of the total fur seal population affected by man-made debris.

Despite this, this research has shown that humans are involved in the entanglement of fur seals. Man-made debris is floating around in the waters surrounding Antarctica, causing danger to the Antarctic fur seal (see figure 1). Despite no permanent residents in Antarctica and despite its isolation from the rest of the world, man-made plastics, strings and ropes are still present in this environment. 

Where is it coming from?

The debris, i.e. nylon ropes, packaging plastic bands and rubber rings, comes mostly from fishing activities (Ivar do Sul et al. 2011). Other studies have found entangled seals in Signy Island, which is part of South Orkney Islands (Dunn and Waluda, 2008), and Marion Island, which is in the Southern Ocean (Hofmeyr et al. 2002). Both these studies concluded that entanglement is linked with fishing activities. The fishing industry is motivated by profit making which stems from the western capitalist society. The use of these materials is an efficient way to maximise catch and minimise costs, but fishing companies are less concerned about the effects of disposing ropes and nets into the sea.

Effects

Finally, what are the effects of entanglement? Although it might seem obvious, there are indirect impacts that surprised me. Below is a summary of the impacts of entanglement on fur seals (Hofmeyr et al., 2002 unless stated otherwise):

• Individual suffering
• Restriction of movement
• Drowning
• Strangulation
• Infection (even if the plastic collar is removed, the open wound can cause infection)
• Inability to protect itself from predators
• Starvation due to reduced ability to catch prey
• Female fur seals spend longer at sea than seals that are not entangled. This means they leave their pups unprotected for longer, making them more likely to die (Croxall et al. 1990)

Sum up

The idea that Antarctica would be excluded from human impact forever is deluded. Despite its isolation from the rest of the world, it seems that human impact is reaching a truly global scale. Antarctic oceans are being polluted by plastics and other man-made debris which is affecting Antarctic fur seals. What I want to demonstrate from this post is that man-made debris is inescapable wherever you go and Antarctic wildlife is bearing the brunt.

My next topic is scientific research. Are sites of scientific research doing more harm than good? One of the major concerns about research centres in Antarctica is waste disposal, so this topic follows on well from this post. The scores for negative human impacts verses positive/ natural impacts on Antarctica are 5-3.

Thanks for reading!