Mankind strongly depends on the marine environment for ecosystem goods and services. But at the same time, human use also alters the ocean through direct and indirect impacts (Halpern et al., 2008). Resources are extracted (e.g. sand extraction, oil extraction, fisheries activities); artificial constructions are built (e.g. oil and gas platforms, offshore wind farms, aquaculture facilities) (Jørgensen, 2012; Reubens et al., 2014; Zintzen, 2007); large amounts of pollutants are deposited (O'Driscoll et al., 2013), and noise adds a further, relatively poorly explored, disturbance to the marine environment (Popper et al., 2003). 

All these human interventions have an impact on the marine environment and may influence the natural habitat and/or the ecosystem functioning. Fish species are vulnerable to these alterations, and information on how and to what extent these influence behaviour and health status is often lacking (Reubens, 2013). To match human activities in the marine environment with the protection of ecosystem goods and services and to reach economic and ecologic sustainability, thorough understanding of the different kinds of human impacts on fish ecology and health is needed.

In this PhD research we will use acoustic telemetry to focus on two case studies of human activities: pile driving and discarding.

This technique allows to study individual behaviour and physiology of fish in the wild for a long period of time at a low cost (Heupel et al., 2008; Heupel et al., 2006; Reubens et al., 2013). 
 

Pile driving

All across the North Sea and in many other coastal seas worldwide, offshore wind farms are being constructed and the numerous wind turbines induce changes in the marine environment. One of the activities with a very high impact on the local environment during construction is pile driving (i.e. the hammering of the wind turbine foundation into the seabed). This activity generates low-frequency impulsive underwater noise (Haelters et al., 2013). The noise travels large distances (in all directions) from the noise source and sound pressure levels of up to 200 dB re 1Pa at a distance of 750m have been measured or estimated (Madsen et al., 2006; Norro et al., 2012). Such noise levels may have severe consequences for living organisms in the surrounding waters, ranging from masking, behavioural disturbance, physiological stress, to injury and death (Haelters et al., 2013; Popper et al., 2003; Wahlberg and Westerberg, 2005). As hundreds to thousands of wind turbines will be constructed in the near future in the North Sea and in marine waters worldwide, this ‘noise pollution’ is considered a serious threat to marine organisms. In this PhD study the effect of pile driving on the movement behaviour and health status of Atlantic cod (Gadus morhua) will be investigated. Atlantic cod is a species with a high commercial value, but population densities have reached historically low levels in the past decades (ICES, 2013). 

 

Discarding

Discarding, i.e. returning unwanted catches to the sea, because the fishes are too small or have no commercial value, is a common practice in the fisheries industry worldwide. However, the new Common Fisheries Policy (CFP), introduces landing obligations to waive this wasteful practice. It is a driver toward higher selectivity and will provide more reliable catch data (Salomon and Holm-Müller, 2013; Sarda et al., 2013). Exemptions are however made for fish species that have a high chance of survival, in accordance to the best available scientific advice, after returning them to the sea (Salomon et al., 2014). As survival depends on the fishing gear and fishing practice used and only limited scientific advice is available, this possibility to grant exemptions creates large uncertainties.

In this PhD project we will investigate the health status and survival chances of rays and skates (Rajidae) after having been caught. Moreover, the behaviour of these fish species after having been discarded will be studied in close detail.

 

Methodology

Two different approaches will be used to investigate the effects of the above-mentioned human activities on fish: in-situ experiments and sampling. The in-situ experiments are performed to assess behavioural responses and health status before and after an impact (see below). In addition, sampling is done to measure health issues related to an impact.

Where possible a Before-After-Control-Impact (BACI) design will be used. This BACI design is a method to trace environmental effects from substantial manmade changes to the environment. It assesses the state of the environment before and after an impact at both a reference site and the impact site (Vandendriessche et al., 2013). 

 

The case study on pile driving will be performed in offshore wind farms in the Belgian part of the North Sea. The in-situ experiment will combine acoustic telemetry (to investigate movement behaviour) with a set-up of fish cages (to investigate health status). A BACI design will be used. The acoustic telemetry research will be performed from shortly before to a couple of months after pile driving to be able to investigate both short term and longer-term behavioural reactions. The set-up with cages will compare the health status of fishes before and shortly after pile driving. The necropsy-based health assessment index (HAI) score will be calculated by attributing numerical values to gross lesions in fins, spleen, gut, swim bladder, kidney, skin, liver, eyes and gills and summing these (Heath et al., 2003). Additionally, the histological alterations for these organs will be quantified in terms of reaction patterns (Wepener et al., 2011) and colligated into a microscopical index (MI). Special attention will be paid to bleedings and damage to the swim bladder (Popper and Hastings, 2009). Fish with high HAI and MI scores will be considered to be in poorer health than those with low HAI and MI scores.

Additional sampling (handline fishery) on a frequent basis will allow to gather backup information on movements and HAI.

 

The case study on discards will be performed in the Algarve (Portugal). An in-situ experiment, using acoustic telemetry, will provide information on survival and behaviour after discarding (both short and longer-term). The health status of rays and skates caught by local fisheries will be scored. Both external (on board) and internal (laboratory) investigations for lesions will be performed. Information on survival will be correlated to health status. 

 

 

This PhD study will provide insights in behavioural and physiological responses of fish to human impacts and will help to formulate advice and guidelines to better match human activities in the marine environment with the protection of ecosystem goods and services, and to reach a better compatibility of economic and ecological values in a healthy environment. The result of this study will contribute to develop regulations and measures to mitigate the effects of human impacts. 

Results will be published in A1 peer-reviewed articles. 

Both participation at international conferences/meetings and dissemination to the broad public (science communication) will be strongly encouraged.