15.09.2020 – Food for thought

We had a wonderful tour on the flat ocean this morning and managed to enjoy sightings with some curious Atlantic spotted dolphins (Stenella frontalis) and a small group of Bottlenose dolphins (Tursiops truncatus). As we left the waters of Madalena do Mar, a hotspot for Bottlenose dolphin sightings our captain, Daniel, spotted a dead Atlantic mackerel (Scomber scombrus) drifting at the surface. The mackerel may have met its end in several ways; maybe it had been violently attacked by a predator or was caught as live bait and lost from a fishing boat. Whatever the cause, mackerels serve as an important source of food for several predators, including humans and are an extremely essential part of ocean ecosystems.

Mackerel represent energy rich prey for an enormous variety of marine predators including sharks, tuna, marlins, seabirds and, of course, cetaceans. Due to overfishing, several spawning populations have experienced a decrease of over 86% since the 1980s, a critical depletion that has biologists worried about the related implications for the food web. Climate change presents another challenge in understanding the sustenance of mackerel populations in specific areas subject to drastic environmental changes, since it may cause significant alterations in zooplankton populations, the favourite prey of mackerel and other schooling fish.

The most dangerous part of our detrimental attitude towards the natural environment is that the consequences are extremely difficult to predict. Our traditional image of food webs is a triangle with the primary producers at its base and the top consumers at its tip. In reality natural food webs, particularly marine food webs, are complex networks where slight shifts in some areas may translate into largely decisive effects on populations somewhere else.

It’s bad enough that we continue to exploit our oceans at an alarming rate despite the obvious consequences but, really and truly, the currently obscured results of our actions are much scarier to imagine and could serve as food for thought…or a motivation to change. 

By Paula Thake

Sightings of the day

Stenella

10:00 Atlantic spotted dolphins, Bottlenose dolphins