Oceanographic drivers of marine mammal and seabird habitat-use across shelf-seas: A guide to key features and recommendations for future research and conservation management

Abstract

Mid-latitude (~30-60 o) seasonally stratifying shelf-seas support a high abundance and diversity of marine predators such as marine mammals and seabirds. However, anthropogenic activities and climate change impacts are driving changes in the distributions and population dynamics of these animals, with negative consequences for ecosystem functioning. Across mid-latitude shelf-seas, marine mammals and seabirds are known to forage at a number of oceanographic habitats that structure the spatio-temporal distributions of prey. Knowledge of these and the bio-physical mechanisms driving such associations are needed to improve marine management and policy. Here, we provide a concise and easily accessible guide for both researchers and managers of marine systems on the predominant oceanographic habitats that are favoured for foraging by marine mammals and seabirds across mid-latitude shelf seas. We (1) identify and describe key discrete physical features present across the continental shelf, working inshore from the shelf-edge to the shore line, (2) provide an overview of findings relating to associations between these habitats and marine mammals and

Environmental heterogeneity amplifies behavioural response to a temporal cycle

“…Resource distribution in the marine environment is both spatially and temporally variable (Pinaud et al 2005, Weimerskirch et al 2005, and so marine ecosystems are a model system to study changes in habitat selection with temporal cycles and environmental heterogeneity. In coastal seas, the tidal cycle has an important influence on ecosystem dynamics (Embling et al 2012, Cox et al 2018. The tidal coupling hypothesis (Zamon 2003) suggests that interactions between tidal currents and variation in bathymetry (the depths of the sea floor) create predictable changes in resource availability.…”

“…There is also evidence that seabird numbers fluctuate with the tide further offshore (Zamon 2003, Embling et al 2012, Cox et al 2013, although the nature of these relationships varies between locations (Zamon 2003, Embling et al 2012, Cox et al 2013. Such geographic differences in behavioural responses to the tidal cycle may arise because of locationspecific interactions between bathymetry and tidal currents (Scott et al 2013, Waggitt et al 2016, Cox et al 2018). The surrounding environment may also play a key role in shaping behavioural responses, and therefore warrants further study (Benjamins et al 2015).…”

Ecological costs of climate change on marine predator–prey population distributions by 2050

“…The variables used are as follows: bottom temperature (BT) (°C), maximum chlorophyll-a (CHL) (mgC/m 3 ), net primary production (NPP) (gC m 2 year −1 ), potential energy anomaly (PEA, which is the energy required to mix the water column completely) (J/m 3 ), and depth-averaged current speed (SP) (m/s). These variables are important habitat variables as they capture the range of features: fronts, other areas of high production, and mixing characteristics of shallow seas including density differences due to regions of freshwater influence (Cox et al, 2018). These variables were chosen as they cover the main physical and biological parameters that can affect pelagic habitats and primary production (Holt, Butenschon, Wakelin, Artioli, & Allen, 2012;Holt, Hughes, et al, 2012;Holt & Proctor, 2008;Holt et al, 2016) under both climate change and, the next biggest change to our shallow seas, very large extraction of energy from offshore renewable developments (Boon et al, 2018;De Dominics et al, 2018;van der Molen et al, 2014).…”

“…BT is similar to PEA, in fact the two variables are highly correlated (r > .6) such that both will never be run in the same model. CHL represents much more fine-scale areas of higher localized production due to internal waves at shelf edges, banks, and troughs (Cox et al, 2018). Therefore, BT was also used to cover any physiological responses, especially from prey and mammals where temperature may play a more important role than stratification.…”

“…We need to understand more explicitly the spatial functioning of our marine systems and especially critical marine habitats: those limited areas that are more likely to be the foraging habitats of mobile species such as seabirds and mammals (Cox, Embling, Hosegood, Votier, & Ingram, 2018;Sharples, Scott, & Inall, 2013). This level of understanding is necessary if we are to use marine protected areas (MPAs), marine spatial planning, and changes in spatial management of fisheries effectively (Gaines, White, Carr, & Palumbi, 2010;Gissi, Fraschetti, & Micheli, 2019;Green et al, 2014).…”