Combined stressors place ocean predators in jeopardy

Nearly a third of all elasmobranch species—sharks, rays, and skates—face extinction. Without proper management and conservation efforts climate change is likely to make things worse for them, now and into the future.

In our recent review, we discuss a suite of direct and indirect stressors on elasmobranch reproduction, growth, and development, as these key life phases are crucial to maintain and rebuild populations.

Direct stressors include fisheries interactions, poor coastal management, and runoff/pollution. Indirect stressors include climate change impacts—mainly ocean warming and acidification.

Broadly, we found that all of these stressors have varying negative effects on reproduction and development.

Sharks, rays and skates are slow growing, have a late age of maturity, and produce very few offspring in comparison to bony fishes. It’s these factors that make the elasmobranch species extremely susceptible to population declines, as they cannot reproduce quickly.

Currently, targeted fisheries and by-catch interactions—individuals that are caught accidentally when targeting another species—are the main threat to elasmobranchs globally.

Capture often results in incidental abortion, and post-release stress can disrupt reproduction long after the capture event has concluded. Poor coastal management can decrease areas that were once suitable nursery habitats and crucial for early development in both live-bearing and egg-laying elasmobranchs. Heavy metals and pesticides from runoff transfer to the offspring during development; though the specific effects of these chemicals on survival are still unknown.

Fig 1. Sharks, rays and skates are subject to a number of combined human impacts

Climate change will indirectly effect elasmobranch reproduction and development via increasing ocean temperatures and acidity. These changes can affect physiological processes and behaviours necessary for essential tasks such as foraging, movement, growth—ultimately, survival.

However, climate change stressors are not occurring in isolation, and more research is needed to assess combined stressors. For example, what happens when coastal nursery habitats are jeopardised and face increased water temperatures?

Although we often imagine elasmobranchs as large, free-roaming, tough ocean predators, approximately 40 percent of elasmobranch species spend most of their time on the bottom of the ocean and produce relatively small offspring that hatch from eggs.

In our review, we also performed a case study to examine the relationship between temperature and incubation time of 28 different egg-laying elasmobranch species. The data we collected are useful in predicting habitat suitability and elasmobranch development over the coming century.

Our review not only provides a comprehensive synthesis of the few examples we do have for these stressors, but it also highlights the many areas of research that are crucial moving forward to conserve and protect elasmobranchs—particularly in relation to climate change.

PAPER

Wheeler C, Gervais C, Johnson M, Vance S, Rui R, Mandelman J, Rummer J. (2020). ‘Anthropogenic stressors influence reproduction and development in elasmobranch fishes’. Reviews in Fish Biology and Fisheries. DOI: 10.1007/s11160-020-09604-0.