We Warn Pregnant Women To Eat Less Fish But What About Marine Mammals?

Down to our basic biology, humans are mammals.

Just like the whales, dolphins, pinnipeds, and polar bears that live in our world’s oceans.

And since we’re all mammals, we actually have quite a lot in common:

  • We’re warm-blooded
  • We nurture our young with milk
  • We are intelligent animals, capable of advanced social behavior
  • We invest high levels of parental care in our young

We really aren’t all that different, right?

Sometimes we’ll even associate human emotions and feelings with marine mammals, believing that they might have a consciousness similar to our own.

Warning: Avoid Fish When Pregnant!

When humans decide the timing is right to settle down and start a family, one of the first things any doctor will warn is for the mother to limit her consumption of FISH.

Eating less fish is important because doctors know fish can contain high levels of pollutants like methyl-mercury and PCBs (PolyChlorinated Biphenyls) which can build up in a growing fetus, and ultimately harm the unborn baby.

These pollutants entered the environment as a by-product of industrial activity before being banned globally in the 1970’s. Unfortunately, they persist in our world for a very long time.

This is nothing but a slight inconvenience for most pregnant woman, who can supplement their nutritional needs with something else from the local supermarket.

But for marine mammals, there is no other choice. It’s all seafood every single day.

What are the dangers then for pregnant marine mammals? The doctor might warn against eating fish, but they live in the ocean!

Pollution Bioaccumulates Up The Food Chain

Methyl-mercury and other marine pollutants like PCBs aren’t deadly in small amounts, but the problem lies in the fact that they build up in the body over time and disrupt the reproductive system.

Plankton are the first to encounter these pollutants. Small fish then consume many of these plankton, and in turn, bigger fish consume those smaller fish. This continues all the way up to the top predators in the food web, which are often marine mammals, large fish, and sharks (elasmobranchs). The pollutants build up into greater concentrations as you move up the food web, and so it is often the top predators that become the most polluted.

Too high of a concentration, and these pollutants can become lethal to any animal.

Unfortunately, there are non-lethal dangers as well.

For example, Non-lethal effects of PCBs include the disruption of reproductive and immune systems. In short, exposure to PCBs is associated with miscarriages and low fertility for breeding mammals. This happens because the PCB’s disrupt an animal’s hormones (natural signaling molecules that are used to control important biological processes).

What’s Happening to The Sea Life?

Because marine mammals feed their young milk, the juvenile animals are especially vulnerable to their mother transferring over her accumulated pollutants.

When an adult female has her calf, she can offload up to 90% of her body’s burden of PCBsthrough the high-fat milk. These high concentrations of PCBs can lead to the premature death of juvenile marine mammals.

Some females are never even able to conceive a baby due to the PCB concentration in their bodies. Miscarriages and reproductive failures can wreak havoc on these populations because females simply become unable to reproduce successfully.

Marine Mammals face plenty of threats in our modern world, such as overfishing, by-catch, and noise pollution, so persistent pollutants that reduce their ability to raise healthy young really can hit a population hard.

Another important factor affecting the reproductive success of marine mammals is food availability.

In the case of resident killer whales versus transient killer whales off the coast of British Columbia, the transient populations who consume seals, sharks, and other larger species, actually are faring better than their residential killer whale neighbors (who stay in one location all year).

The problem with the resident killer whales is that their food source, Chinook Salmon, has been scarce and the animals are starving. When these animals don’t have enough excess fat from their food source, the mothers will metabolize their polluted fat tissues to help feed their baby.The transient killer whales are equally polluted (if not more so) but they are able to consume enough that their polluted fat tissue doesn’t need to be metabolized and transferred to the baby.

Some pregnant marine mammals are being threatened by more than just pollution. Some actually can’t even find enough food to support themselves, let alone their unborn child.

Food For Thought

So what’s going to happen to Killer Whales and other marine mammals?!

Well, unfortunately it will take many more years for these industrial pollutants to phase out of the marine environment. So, to help we can try to make life easier for these animals by reducing their other compounding threats (overfishing, marine debris, by-catch)

We can reduce our impact on these incredible marine mammals by taking effort to avoid noise pollution while boating in their habitat. We can also help to influence salmon populations that these animals rely on through our purchase decisions. By supporting sustainably caught salmon (or avoiding eating salmon altogether), we can work to ensure that these animals have enough food to support the next generation.

No mother should have to go through the trouble that marine mammals face in today’s world.

Photo: Jakub Kapusnak/Unsplash

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