Trophic cascades is the balanced filtering down of energy along the gradient of the food pyramid.
Trophic Cascades.
The concept of trophic cascades is a relatively recent biological concept which describes the progression of nutrients and energy (calorific) through the food chain.
There are numerous examples of trophic cascades of which the return of wolves to Yellowstone National Park is an iconic example (watch ‘How wolves changes rivers’).
Ocean View on Balance.
In the ocean the barometer of a healthy and sustainable marine environment is the presence of a robust population of sharks of all sizes.
Almost counter intuitive is the fact that the more prolific the population of sharks, the greater the population of both reef and pelagic fish.
Sadly, with both over fishing and the horrendous shark fin fishery, shark populations have plummeted globally. In areas, such as Mozambique, shark populations have decreased by 90% in the past decade.
In terms of shark reproduction, most of the larger species of sharks are live bearers with females, depending on species, giving birth to between 2 and 20 pups after a gestation of 9 to 12 months (again species specific).
Part of shark fishing requires a posed photo.
With fish stocks plummeting, recreational fishermen have started targeting sharks for ‘sport’ fishing, often ignorant of the life cycle of the targeted species.
A Bronze Whaler Shark lives to approximately 30 years. Females reach sexual maturity at 20 years (2m) and give birth to 20 pups after a 12 month gestation.
Sports Fishing for Sharks.
Today I watched a group of 8 sports fishermen targeting sharks. There were high fives all round and posing for trophy photos before the sharks were returned to the ocean.
This Hammerhead received bunt force trauma and abrasions to it’s eyes during handling to remove the fishing hook.
In an hour six sharks, 2 Hammerheads and 4 Bronze Whalers, were caught and released. Fortunately all survived, though a small Hammerhead nearly didn’t needing 3 minutes before it was able to swim away. During the removal of the hook, posing for photos and dragging to be released, the Hammerhead received numerous scratches and both it’s eyes received bunt force trauma and abrasions.
Newly acquired status
It was obvious watching the group that catching a shark conferred a status symbol to the catcher amongst his peers. Yet there was no tag and release, no care taken to reduce stress and injury to the sharks. In short, no contribution to understanding the ecological role of sharks to the integrity of the marine environment.
Frankly, in terms of status symbol, a quick social media search will populate your screen with numerous images of free divers swimming gently and safely with the likes of Great White, Tiger and Hammerhead sharks, which IS a big deal. Far more impressive than any fishing accomplishments. And way more exciting.
While there is little doubt that targeting sharks for sports fishing will not stop, hopefully the fisherman will start respecting the importance of sharks in the ecosystem and improve their handling of them out of the water when removing hooks, and through tag and release, contribute to the understanding of these apex predators.
The video below is of a young Bronze Whaler swimming away after it was released.
#trophiccascades #sharks
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