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Anthropogenic Impacts on the Sensory Capabilities of the Lemon Shark

Overview

Across marine biota, elasmobranchs are unique in their hearing capabilities. Field studies have shown hearing to play an important role in lemon shark behaviour and the lemon shark, Negparion brevirostris, is one of the most sound-sensitive species within this taxonomic group (Nelson 1967). Thus, while studies of impacts of noise in the marine environment have substantially increased over the past 20 years, we cannot assume that elasmobranchs will respond in the same way as much-studied teleosts to a “noisy world” (Williams et al. 2015).

In contrast to hearing, vision in lemon sharks has been well studied since the late 1950s. Lemon sharks can be conditioned to visual targets to collect food rewards and rely heavily on vision in prey detection (Cohen 1990). Despite a multitude pioneering studies in the late 20th century, impacts of anthropogenic disturbance on key visual behaviours are as yet unexplored. Addressing this knowledge gap will provide a better understanding of the visual niche and the role humans might play in altering lemon shark perception of their environment.

Broadly speaking, effects of anthropogenic stressors can be broken into four categories: communication and masking, spatial movement and distributions, foraging and predator–prey interactions and direct fitness consequences (Slabbekoorn et al. 2010; Davies et al. 2014). While it is unlikely that anthropogenic noise and light will cause pathological damage to sensory organs in sharks, there is evidence in teleosts that these stressors can induce elevated stress, mask biologically relevant signals, compromise predator–prey interactions and reduce foraging success (Slabbekoorn et al. 2010).

 

With recent increases in anthropogenic disturbance in some locations around Bimini, particularly associated with hotel developments, this project will compare behaviour of lemon sharks across a spectrum of disturbed and pristine environments, optimising the value of working with a well-studied and highly monitored population. These findings will be used to assess the effectiveness of current protection efforts and inform conservation management.

Research questions

Aim: To distinguish the role of hearing and vision in behaviour and space use in lemon sharks, and explore how these are influenced by anthropogenic disturbance, using the monitored population in Bimini, Bahamas. To use these findings to assess the effectiveness of current protection efforts and advise how the local ecosystem could be best managed for lemon shark conservation.

 

Specific hypotheses/questions to be investigated:

  1. What are the roles of hearing and vision in foraging and homing behaviour of juvenile lemon sharks?

  2. What is the impact of anthropogenic noise and light on foraging and homing behaviour?

  3. What is the sensory landscape in Bimini and how does anthropogenic disturbance influence shark behaviour across it?

  4. How can these findings be applied to improve ecosystem management?

Conservation importance

 

As global interest in elasmobranchs and their conservation increases, the need for information to inform conservation policy and management is high. This is particularly pertinent regarding the effects of human derived noise and light, as both are increasing and further encroaching upon the marine realm.

 

In 2010, estimates suggested 22.2% of global coastline is exposed to artificial light pollution, and with developing technologies this is predicted to continue increasing (Davies et al. 2014). Similarly, a 2010 review of the effects of noise on the marine environment identified the lack of field studies concerning long-term noise exposure on marine biota as the key issue in our ability to address the problem of marine noise pollution (Slabbekoorn et al. 2010).

 

Having a detailed baseline across a species’ life history facilitates the best possible protection, and as lemon sharks are one of the best understood elasmobranch species the potential for effective management is considerable.

Principle Investigator:

Clemency White — Bimini Biological Field Station Foundation

Clemency White 
Principal Investigator

At lab since: Volunteer/Intern - April to June 2017;
MSc Project Student - June to September 2018;
Principal Investigator - October 2018 to present

From: Basingstoke, UK

Education/Background: BSc Zoology - University of Bristol, 2016; 
MSc Marine Environmental Management - University of York, 2018

I volunteered at the lab from April to June 2017, and I was so fascinated by the current research that I returned to complete a project of my own for my MSc thesis. For this project, I used a modelling technique to compile tracking data collected from lemon sharks since the lab began tracking projects in the early 1990s. I used this method to create a detailed baseline of lemon shark habitat use around the Bimini islands across life stages, inferring ontogenetic shift and the impact of anthropogenic development.

My PhD project focuses on my interest in elasmobranch spatial and sensory ecology and considers the role of different sensory modalities in orientation and navigation. I will also consider how navigation is affected by anthropogenic disturbances and how we can mitigate this, in order to inform sound conservation management that can be replicated in other systems.