Lemon sharks benefit from Marine Protected Area in Turks & Caicos

You may be forgiven for thinking that the creation of a marine protected area (MPA) would obviously lead to a greater abundance and diversity of marine life within the MPA as oppose to outside it's boundaries. However whilst creating marine reserves does typically lead to a greater density and size of organisms within the reserve boundaries, it is not to be assumed that this will be the case and until the particular reserve has been assessed it's success may largely be unknown.

In 1992, Bell Sound Nature Reserve (BSNR) in the Turks and Caicos Islands was established with a view to protect juvenile bonefish which are targeted in the Turks and Caicos Islands. A team of shark researchers led by Aaron Henderson from the Center for Marine Resource Studies in South Caicos have investigated whether this MPA is also having an effect on populations of the lemon shark (Negaprion brevirostris).

Lemon sharks are classified as Near Threatened in the IUCN Red List as they are caught in both commercial and recreational fisheries; as yet no management plans have been put in place to protect these sharks.

The researchers observed higher numbers of lemon sharks within BSNR than in the waters outside the reserve. Lemon sharks do exhibit a preference for shallower water and so the increased quantity of sharks within BSNR could be owing to habitat selection rather than protection from fishing, however he researchers surmised that the protection from predation offered by the MPA was attractive to the sharks and could cause them to want to remain in the reserve as oppose to moving outside.

Whilst the reasons for the higher number of sharks inside the MPA as oppose to outside is not yet entirely clear, the conclusions drawn were that BSNR is important to the local juvenile lemon shark population.

Shark research - Sharks vs magnets 2: visually deprived lemon sharks show heightened awareness of electric stimuli

Following on from their previous research (see The Shark Post 13th Jan), researchers at University of Massachusetts have investigated the reactions of visually impaired lemon sharks to magnets.

The team had already ascertained that C8 barium-ferrite (BaFe12O19) permanent magnets successfully repelled bull sharks, but were unsure as to the success magnets would have on repelling sharks which are more reliant on their visual system. The aims of this study were to ascertain whether magnets would successfully repel visually impaired juvenile lemon sharks (Negaprion brevirostris).

The researchers hypothesised that restricting the vision of lemon sharks would lead to a greater reliance on short range senses such as electro reception - an effect known as context dependent switching. In the wild the visual field of a marine animal could be restricted by bad visibility caused by environmental conditions such as turbidity. In this instance,

The sharks were visually impaired using a short term, simple surgery technique to suture closed the nictitating membrane of the eye. Once the experimental phase was completed, the sutures were removed, restoring the vision of the sharks. All sharks showed successful recovery post-experimentation.

The experimental area was separated into different compartments, both with and without magnets present. The sharks were divided into groups with differing levels of visual impairment. By assessing the behaviour of the different shark types to the magnets, the researchers were able to assess what impact visual impairment had on context dependent switching of senses.

Visually impaired sharks did indeed enter areas with magnets less frequently than sharks with visual ability. These results suggest that magnetic repellents would be more successful when sharks are visually impaired, and this could translate to the visual impairment experienced in turbid waters. Magnets could be an appropriate method of deterring all species of sharks from entering turbid regions, and not just those which are less reliant on their visual system to begin with.  

Connell, C., Guttridge, T., Gruber, S., Brooks, J., Finger, J. and He, P. (2014) Behavioral modification of visually deprived lemon sharks (Negaprion brevirostris) towards magnetic fields. Journal of Experimental Marine Biology and Ecology 453:131-137