chondrichthyan | ConservationBytes.com

A long life can be a disadvantage

12 06 2025

Deep-sea sharks include some of the longest-lived vertebrates known. The record holder is the Greenland shark, with a recently estimated maximum age of nearly 400 years. Their slow life cycle makes them vulnerable to fisheries.

Humans rarely live longer than 100 years. But many other animals and plants can live for several centuries or even millennia, particularly in the ocean.

In the Arctic, there are whales that have survived since the time of Napoleon’s Empire; in the Atlantic, there are molluscs that were contemporary with Christopher Columbus’ voyages; and in Antarctica, there are sponges born before the Holocene when humans were still an insignificant species of hunter-gatherers (see video on lifespan variation in wildlife).

Long-lived species grow slowly and reproduce at later ages (1, 2). As a result, these animals require a long time to form abundant populations and to recover from fishing-related mortality.

Among cartilaginous fish (chimaeras, rays, sharks, and skates), the risk of extinction due to overfishing is twice as high for deep-sea species compared to coastal species, because the former have longer and slower life cycles (3).

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Tags: bycatch, chondrichthyan, elasmobranch, fishing, long-lived species, longevity, Overfishing, sharks
Categories : Arctic, biodiversity, conservation, decline, exploitation, extinction, fish, fisheries, food, IUCN, management, marine, predator, research, shark

Predicting sustainable shark harvests when stock assessments are lacking

26 03 2018

I love it when a good collaboration bears fruit, and our latest paper is a good demonstration of that principle.

It all started a few years ago with an ARC Linkage Project grant we received to examine how the whaler shark fishing industry in Australia might manage its stocks better.

As I’m sure many are aware, sharks around the world aren’t doing terribly well (surprise, surprise — yet another taxon suffering at the hands of humankind). And while some populations (‘stocks’, in the dissociative parlance of the fishing industry) are doing better than others, and some countries have a better track record in managing these stocks than others, the overall outlook is grim.

One of the main reasons sharks tend to fair worse than bony fishes (teleosts) for the same fishing effort is their ‘slow’ life histories. It doesn’t take an advanced quantitative ecology degree to understand that growing slowly, breeding late, and producing few offspring is a good indication that a species can’t handle too much killing before populations start to dwindle. As is the case for most large shark species, I tend to think of them in a life-history sense as similar to large terrestrial mammals.

Now, you’d figure that a taxon with intrinsic susceptibility to fishing would have heaps of good data with which managers could monitor catches and quotas so that declines could be avoided. However, the reality is generally the inverse, with many populations having poor information regarding vital rates (e.g., survival, fertility), age structure, density feedback characteristics, and even simple estimates of abundance. Without such key information, management tends to be ad hoc and often not very effective. Read the rest of this entry »

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Tags: bronze whaler sharks, bronze whalers, bronzies, Carchcarinus brachyurus, chondrichthyan, commercial fishing, copper shark, demographic model, fishing, global sensitivity analysis, Latin hypercube, sustainable fisheries
Categories : Australia, conservation, environmental policy, exploitation, fish, fisheries, genetics, harvest, management, marine, ocean, population dynamics, population viability analysis, shark

Empty seas coming to a shore near you

12 07 2012

Last week I had the pleasure of entertaining some old friends and colleagues for a writing workshop in Adelaide (don’t worry – they all came from southern Australia locations, so no massive carbon footprints for overseas travel). I’m happy to report it was a productive (and epicurean) week, but that’s not really the point of today’s post.

One of those participants was long-time colleague, Dr. Rik Buckworth. Rik and I first met in Darwin back in the early 2000s when he was lead fisheries scientist for Northern Territory Fisheries; this collaboration and friendship blossomed into an ARC Linkage Project (with Dr. Mark Meekan of AIMS) on shark fisheries (see some of the scientific outputs from that here, here, here and here). Rik has since moved to CSIRO in Brisbane, but keeps a hand in NT fisheries’ affairs. Incidentally, Rik trained under one of the most well-known fisheries modellers in the world – Carl Walters – when he did his PhD at the University of British Columbia back in the early 1990s.

During our workshop, Rik pointed out a paper he had co-authored back in 2009 in Reviews in Fish Biology and Fisheries that had completely escaped my attention – it’s a frightening and apocalyptic view of the Australasian marine tropics that seems to confirm our predictions about northern Australia’s marine future. Just take a look at the following two figures from their paper (Elasmobranchs in southern Indonesian fisheries: the fisheries, the status of the stocks and management options): Read the rest of this entry »