Climate change impacts on shark species across the Globe.

Climate change or more specifically a rise in global sea temperatures will see many shark species shifting their distributions towards the poles, according to a technical report of the project; Pollution and Climate Impacts. As a result of climate disruption, biodiversity, including marine, freshwater and terrestrial extinction rates are predicted to increase (Fischlin et al .,2007). Sharks, which are Chondrichthyes or cartilaginous fish are long lived, slow growing species that are late to mature and have low reproduction and mortality rates (Field et al ., 2009). As such sharks are extremely vulnerable to over-exploitation.

Increased fishing pressure, from targeted fisheries and by-catch, and illegal finning has resulted in several shark species becoming vulnerable, endangered or critically endangered on the IUCN Red List. Climate change is an additional stresses that threatens shark populations around the globe.

Global distribution of distribution of IUCN Red-listed threatened chondrichthyan species (Field et al. 2009; page 312) (see also www.iucnredlist.org ; www.fishbase.org) .

Climate change has direct and indirect effects on fish communities structure and distribution. Significant effects on marine fishes as a result of rise in sea temperatures, ocean acidification, sea level, and storm frequency/extreme weather events due to climate change can cause changes in movement, catch and growth, northward and deep water shift of species), fishing (increase in fishing costs due to change in fishing locations), corals (coral bleaching), pteropods, and krills (loss of shells), molluscs (reduced calcification, abundance, survival), echinoderms (reduced growth and development), marine mammals (reproduction of cetaceans, shifts in species ranges) (Jennings & Brander 2010; Kibria et al., 2017).

The shift in the many species distributions towards the poles in response to rising sea temperatures will challenge a once solid principal in ecology, that species diversity increases towards the equator. In contrast, for marine species, particularly mammal and bird species richness generally peaks in colder, temperate waters. Also unlike endothermic mammals, ectothermic sharks and fish peak in tropical or subtropical seas. This is linked to the differences in thermoregulatory capabilities between the taxa (Grady et al ., 2019).

Water temperature differences drive variations in metabolism and diversity in marine endotherms and ectotherms. (Grady et al ., 2019)

The depletion of shark population, can and will cause irreversible alterations to marine ecosystems. As top predators, sharks are keystone species and their loss can contribute to trophic cascades, thus, risks the entire health of an ecosystem. For example, tiger sharks ( Galeocerdo cuvier ) presence has been linked to the quality of seagrass beds through extorting a top down pressure on their prey, dugongs ( Dugong dugon ) and green sea turtles ( Chelonia mydas ), which forage in these beds. Without tiger sharks tocontrol their prey’s foraging, an important habitat will be lost.

Elasmobranch species in Irish waters which may be more vulnerable to climate impacts include species with coastal and shelf ecology such as, mackerel sharks; Lamnidae e.g. the porbeagle shark ( Lamna nasus),