Overview

Climate change is having, and will continue to have, an enormously varied set of impacts on the world’s oceans. Overall, we can expect several key changes on the oceans (from IPCC 2013) which include:

1. A further 2.6 – 4.8 °C warming by 2100

2. A further decrease in pH by 0.4 units by 2100

3. Decreases in dissolved oxygen, and more ‘dead spots’ of very low oxygen

4. Changes in salinity depending on location (salinity can increase with higher temperature, but can also decrease owing to other oceanographic factors like shifts in currents)

Research is showing implications of these changes for wildlife and ecosystems, but this work is particularly challenging for highly mobile marine animals, such as sharks. Most sharks’ body temperature follows that of the environment – unlike mammals (and some partially endothermic sharks), they are ectothermic and cannot generate their own body heat. Sharks, like other animals, have an ideal range for temperature, above or below which they are not able to perform basic functions optimally. We can measure shark responses to temperature ranges in controlled lab setting very precisely. For larger marine animals, such as large coastal sharks, which cannot be maintained in the lab, studying climate change impacts presents several logistical challenges. However, new techniques provide ways of approximating such relationships in the field. Here at SRC, we are conducting a series of research projects to begin exploring some of the impacts climate variability is having on sharks. Some of the primary projects we are conducting include:

1. Developing and using new types of satellite tags to explore optimal environmental conditions for shark activity in the wild

2. Measuring biomarkers of stress and capacity for aerobic and anaerobic activity from blood and muscle samples collected from sharks in the wild. These markers can help us look for changes in stress response and oxygen transport associated with catch-and-release fishing, with shifts in environmental conditions such as temperature and oxygen levels. Comparing our results across species can also shed light on whether certain species are predisposed to be more resilient to climate variability, either by making physiological adjustments to cope with a changing environment or being physiologically suited to a fluctuating ocean environment.

3. Exploring shark hunting behaviors in response to long-term climate variability. Recently, we analyzed a 15-year record of white shark predations on cape fur seals in False Bay, South Africa, in relation to climate variables. Past research has found water temperature to influence feeding behavior of fish. However, in a natural system, many other factors can drive feeding behavior, so temperature-driven patterns are not so simple to detect or even investigate. At Seal Island, water temperature was a significant predictor of daily and monthly variability in predation rates of white sharks on seals. However, year to year variability in predation rates appeared linked to other environmental factors such as wind, water visibility, and the occurrence of El Niño and La Niña events, rather than water temperature.

Study Highlight

Ocean warming alters the distributional range, migratory timing, and spatial protections of an apex predator, the tiger shark (Galeocerdo cuvier).

In a new collaborative, our team used multiple approaches to evaluate the effects of ocean warming on tiger shark movements in the Western North Atlantic. We found that over the past ~40 years, shark distributions have expanded northward, paralleling rising temperatures. Moreover, satellite tracking of sharks over the past decade has revealed their annual migrations have extended farther poleward and arrival times to northern areas have also occurred earlier in the year during extremely warm periods, which has subsequently decreased their spatial overlap with time/area closures. Potential consequences of these climate-driven alterations include increasing shark vulnerability to fishing, disruption of predator-prey interactions and changes in encounter rates with human water-users.

Figure: A year-long migration of a female tiger shark beginning in the Bahamas, travelling as far north as the state of Massachusetts. Point colors show water temperature sensed by the shark-borne satellite tag.(Figure via Rachel Skubel)

SRC In Focus

Understanding the relationship between sharks and water temperature is critical for predicting changes in their habitat.
We are investigating the capacity of tiger and great hammerhead sharks to withstand increased water temperatures.

Scientific Publication:

Hammerschlag N, McDonnell LH, Rider MJ, Street GM, Hazen EL, Natanson LJ, McCandless CT, Boudreau MR, Gallagher A J, Pinsky ML, Kirtman B (2022). Ocean warming alters the distributional range, migratory timing, and spatial protections of an apex predator, the tiger shark (Galeocerdo cuvier). Global Change Biology, 00, 1–16.https://doi.org/10.1111/gcb.16045

Gutowsky LF, Rider M, Roemer RP, Gallagher AJ, Heithaus MR, Cooke SJ, Hammerschlag N. (2021) Large sharks exhibit varying behavioral responses to major hurricanes. Estuarine, Coastal and Shelf Sciencehttps://doi.org/10.1016/j.ecss.2021.107373

Skubel RA, Kirtman BP, Fallows C, Hammerschlag N (2018) Patterns of long-term climate variability and predation rates by a marine apex predator, the white shark Carcharodon carcharias. Marine Ecology Progress Series 587:129-139.