The noise of the hunt: Effects of noise on predator-prey relationships in a marine ecosystem

The effects of anthropogenic noise on interactions between predators and their prey are still little understood. This thesis aims to fill pressing knowledge gaps on this topic by studying how anthropogenic noise affected various stages in the prey-hunting of predators and the predator-avoidance of prey. For predators, I investigated whether an¬thropogenic noise could influence habitat choice (chapters 2 and 3), foraging efficiency (chapter 3) and communication between foraging group members (chapter 4). For prey, I studied how anthropogenic noise affected prey behaviour outside of predation con¬texts (chapter 5) and if current and previous vessel noise exposure affected anti-predator behaviour when a simulated predator attacked (chapter 6). The multi-disciplinary studies of this thesis combine to unravel more insight into the influence of noise on predator-prey relationships in the marine environment. Further investigations should focus on revealing the mechanistic underpinning of noise effects on behaviour of both predator and prey. Only then will we be able to reduce the impact of noise on marine ecosystems.Animal science

Spatial behavior, swimming speed and surfacing rate of two captive harbor porpoises in ambient sound control conditions

Foraging is made up of three steps: first, to search and encounter a suitable foraging patch; next prey has to be found, and finally the prey has to be caught and eaten. Behavioral responses to anthropogenic noise may lead to a disruption of vital activities within this process, such as area avoidance, or reduced abilities to locate or catch prey. Gaining insight into these behavioral effects starts with a thorough understanding of within- and between-individual variation in the baseline behavior of experimental conditions. In this study, we analyzed control trials for two captive harbor porpoises that were tested for spatial behavior in a set-up for experimental sound exposure. Data from trials without any experimental sound exposure were used to investigate relationships between the response variable - time spent away from the preferred area - and two other behavioral metrics: swimming speed and surfacing rate. The results show that these metrics can be used as independent measures, the first being correlated to the response variable, the second uncorrelated. Combining the two makes a better and more complete judgment. Performing an adequate exploration of the variation in behavior during control trials is important, as it will aid scientists in revealing and interpreting effects of disturbance in sound exposure trials.Animal science

An echosounder view on the potential effects of impulsive noise pollution on pelagic fish around windfarms in the North Sea

Anthropogenic noise in the oceans is disturbing marine life. Among other groups, pelagic fish are likely to be affected by sound from human activities, but so far have received relatively little attention. Offshore wind farms have become numerous and will become even more abundant in the next decades. Wind farms can be interesting to pelagic fish due to food abundance or fisheries restrictions. At the same time, construction of wind farms involves high levels of anthropogenic noise, likely disturbing and/or deterring pelagic fish. Here, we investigated whether bottom-moored echosounders are a suitable tool for studying the effects of impulsive - intermittent, high-intensity - anthropogenic noise on pelagic fish around wind farms and we explored the possible nature of their responses. Three different wind farms along the Dutch and Belgian coast were examined, one with exposure to the passing by of an experimental seismic survey with a full-scale airgun array, one with pile driving activity in an adjacent wind farm construction site and one control site without exposure. Two bottom-moored echosounders were placed in each wind farm and recorded fish presence and behaviour before, during and after the exposures. The echosounders were successful in detecting variation in the number of fish schools and their behaviour. During the seismic survey exposure there were significantly fewer, but more cohesive, schools than before, whereas during pile driving fish swam shallower with more cohesive schools. However, the types and magnitudes of response patterns were also observed at the control site with no impulsive sound exposure. We therefore stress the need for thorough replication beyond single case studies, before we can conclude that impulsive sounds, from either seismic surveys or pile driving, are a disturbing factor for pelagic fish in otherwise attractive habitat around wind farms.Animal science

The noise of the hunt: Effects of noise on predator-prey relationships in a marine ecosystem

The effects of anthropogenic noise on interactions between predators and their prey are still little understood. This thesis aims to fill pressing knowledge gaps on this topic by studying how anthropogenic noise affected various stages in the prey-hunting of predators and the predator-avoidance of prey. For predators, I investigated whether an¬thropogenic noise could influence habitat choice (chapters 2 and 3), foraging efficiency (chapter 3) and communication between foraging group members (chapter 4). For prey, I studied how anthropogenic noise affected prey behaviour outside of predation con¬texts (chapter 5) and if current and previous vessel noise exposure affected anti-predator behaviour when a simulated predator attacked (chapter 6). The multi-disciplinary studies of this thesis combine to unravel more insight into the influence of noise on predator-prey relationships in the marine environment. Further investigations should focus on revealing the mechanistic underpinning of noise effects on behaviour of both predator and prey. Only then will we be able to reduce the impact of noise on marine ecosystems.</table

Heuristics for setting reorder levels in periodic review inventory systems with an aggregate service constraint

Inventory managers are responsible for the trade-off between inventory holding costs and customer service. In this paper we consider a periodic review multi-item inventory system with exogenous lot-sizes and backordering. The objective is to minimize the total inventory holding costs subject to the constraint that the aggregate fill rate should be at least equal to a target level. The aggregate fill rate is a weighted average of the fill rates of all items in the assortment. We consider three ways of defining this aggregate fill rate: using generic weights, weights based on the average demand (volume) or weights based on the average (monetary) turnover. We show that the definition of the aggregate service can have huge effects on the performance of the system. So, inventory managers should be very careful on which definition to apply. We also derive four heuristics to determine the reorder levels for all items. One heuristic is very generic and can be applied to many problems including multi- item multi-echelon inventory systems and systems with a constrained aggregate ready rate. Since multiple assumptions made to derive the heuristics are common assumptions made in the literature, we first test the accuracy of these approximations using simulation. Next, we evaluate the heuristics based on data from a large international reseller. The heuristic based on the most accurate approximation performs best, is close to optimal and very efficient. Savings compared to no service level differentiation are large (up to 28.7%) and depend on the definition of the aggregate service

Interacting effects of short-term and long-term noise exposure on antipredator behaviour in sand gobies

In today's marine habitats, anthropogenic noise is widespread in space and time, affecting aquatic animalcommunities. Short-term exposure to noise is known to affect vital behaviours, such as the ability toevade predators. However, long-term noise pollution may lead to differences in short-term responsesbetween naïve and experienced animals. We investigated the interaction between short-term and longterm sound exposure on the antipredator response of free-ranging sand gobies, Pomatoschistus minutus.We tested the effects of short-term boat noise playback on the response to a simulated predator strike inareas across a range of low to high long-term noise disturbance levels. Exposure to boat noise did notaffect the startle response, time frozen or response latency of gobies to a predator stimulus. However,individuals exposed to short-term boat noise playback were absent from the experimental area forshorter periods after the predator strike than gobies exposed to the silent control. Moreover, gobies inlong-term noisy habitats also stopped avoiding the area after the predator strike under silent controlconditions. These changes point to a decreased magnitude in antipredator response, as a function ofinteracting short- and longer-term levels of disturbance. Thus, prey species alter their antipredatorbehaviour in ways that can potentially lead to higher mortality for individual prey. This could ultimatelyhave implications at the level of the food web.Animal science

Friend or foe: Risso’s dolphins eavesdrop on conspecific sounds to induce or avoid intra-specific interaction

The detection and use of emitters’ signals by unintended receivers, i.e., eavesdropping, represents an important and often low-cost way for animals to gather information from their environment. Acoustic eavesdropping can be a key driver in mediating intra- and interspecific interactions (e.g., cooperation, predator–prey systems), specifically in species such as cetaceans that use sound as a primary sensory modality. While most cetacean species produce context-specific sounds, little is known about the use of those sounds by potential conspecific eavesdroppers. We experimentallytested the hypothesis that a social cetacean, Risso’s dolphin ( Grampus griseus), is able to gather biologically relevant information by eavesdropping on conspecific sounds. We conducted playback experiments on free-ranging dolphins using three context-specific sounds stimuli and monitored their horizontal movement using visual or airborne focal follow observations. We broadcasted natural sequences of conspecific foraging sounds potentially providing an attractive dinner bell signal (n = 7), male social sounds simulating a risk of forthcoming agonistic interaction (n = 7) and female-calf social sounds representing no particularly threatening context (n = 7). We developed a quantitative movement response score and tested whether animals changed their direction of horizontal movement towards or away from the playback source. Dolphins approached the foraging and the social female-calf sounds whereas they avoided the social male sounds. Hence, by acoustically eavesdropping on conspecifics, dolphins can discriminate between social and behavioural contexts and anticipate potential threatening or beneficial situations. Eavesdropping and the ensuing classification of ‘friend or foe’ can thus shape intra-specific social interactions in cetaceans.</p

Diving apart together: call propagation in diving long-finned pilot whales

Group-living animals must communicate to stay in contact. In long- finned pilot whales, there is a trade-off between the benefits of foraging individually at depth and the formation of tight social groups at the surface. Using theoretical modelling and empirical data of tagged pairs within a group, we examined the potential of pilot whale social calls to reach dispersed group members during foraging periods. Both theoretical predictions and empirical data of tag pairs showed a potential for communication between diving and non-diving group members over separation distances up to 385 m (empirical) and 1800 m (theoretical). These distancesmatch orexceed pilot whale dive depths recorded across populations. Call characteristics and environmental characteristics were analysed to investigate determinants of call detectability. Longer calls with a higher sound pressure level (SPL) that were received in a quieter environment were more often detected than their shorter, lower SPL counterparts within a noisierenvironment. Ina noisierenvironment, calls were louderand had a lower peak frequency, indicating mechanisms for coping with varying conditions. However, the vulnerability of pilot whales to anthropogenic noise is still ofconcern as the ability to cope with increasing background noise may be limited. Our study shows that combining propagation modelling and actual tag recordings provides new insights into the communicative potential for social calls in orientation and reunion with group members for deep-diving pilot whales.Animal science