Prey use and nutritional differences between reproductive states and age classes in Atlantic spotted dolphins (Stenella frontalis) in the Bahamas

Abstract

Nutritional quality of prey is a significant driver of predator foraging patterns. In mammals, nutritional needs are known to change across ontogeny and reproductive state; however, little is known about nutrition in marine mammals. For this study, we used observational data of diurnal foraging events, collected annually from 1992 to 2009, to investigate nutrition and prey use in Atlantic spotted dolphins (Stenella frontalis) on Little Bahama Bank, Bahamas, between reproductive states (lactating, pregnant, nonreproductively active [NRA]. We also investigated the impact of age class association (various calf age groups [ages 1-6], older "noncalf" juveniles, and adults) on foraging group nutrition and prey use. To obtain representative nutrient values, we measured calories, lipids, proteins, and moisture in common prey. Using nutritional values and observational data, we investigated the influence of nutritional value on prey use. Results indicated that specific nutrients were targeted by different reproductive states and age class groups. Nutritional intake of all nutrients was higher for lactating females than pregnant females, but lower than NRA females. Investigation of age group associations revealed that nutritional intake of all four nutrients was higher for noncalf than calf-associated groups. This study represents one of the first investigations of intraspecific prey use and nutritional differences in cetaceans.Key words: calories, moisture, lipid, protein, pregnant, lactating, nonreproductively active, calf, diet, cetacean, forage.In order to meet basic metabolic demands, a predator must capture prey in an optimal way that results in the net gain of energy and other nutrients. The nutritional quality of prey, rather than quantity alone, is a major driver of predator foraging strategy (Brody 1945, Close et al. 1985, Bernard and Hohn 1989, Spitz et al. 2012. More "nutritious" prey may be selected for by all predators, especially large bodied, highly active and free-ranging animals. Prey quality can be defined by three major nutrient components: moisture, protein, and lipids (major determinants of energy value) (Worthy 2001), each of which may influence foraging strategy (Mayntz et al. 1Corresponding author (e-mail: cmali156@gmail.com). 14712009). Alverson (1992) described a shift in diet towards lower quality, more abundant prey (junk-food hypothesis) to help explain the dramatic population decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska caused in part by decades of intensive fishing pressure. Others have suggested that prey quality can be critical to reproductive success, growth, and overall population dynamics of many top marine predators (e.g., Donnelly 2003, € Osterblom et al. 2008). Marine mammals are top predators in many marine ecosystems and exhibit a wide range of foraging strategies that vary in degree of specialization. Cetaceans, and other small marine mammals, are often described as generalist predators with little or no prey preference. This predatory label, h...

Sex-specific macronutrient foraging strategies in a highly successful marine predator: the Australasian gannet

“…Drastic shifts in climate-related regimes are believed to be responsible for the decrease in availability of high-quality prey species (in terms of energy and lipid contents) and an increase in lowquality foods, which has negatively influenced marine predator populations around the world (Österblom et al 2008). Operating in such a complex environment, marine predators require particularly sophisticated foraging strategies that enable them to balance self-and offspring-feeding, and also in many circumstances simultaneously consider the nutritional constraints of their partners (Weimerskirch et al 1994;Machovsky-Capuska et al 2014a;Malinowski and Herzing 2015). Seabird chicks are under constant age-related fluctuations in lipid, protein, water and energy density until they reach functional maturity and are able to feed for themselves (Navarro 1992).…”

Dolphin Prey Availability and Calorific Value in an Estuarine and Coastal Environment

“…Since the abundance of dolphins is lower during winters (Smith et al, 2013;Sprogis et al, 2016a), it was hypothesized that prey quantity would be also be lower, but that prey quality would be relatively higher to support the mothers and calves that remain in local waters throughout the winter (Smith et al, 2016), as the energetic cost of lactation and growth is high (Malinowski and Herzing, 2015). As hypothesized, the highest energy contents of fish were generally found in the winter: the highest KJ in traps and gillnets were found in the winter season; while the energy content in the seine net was similar in summer and winter.…”

“…While prey density has long been associated with prey profitability for a predator, prey quality has been quantified in foraging models only in recent years (Spitz et al, 2010b) and has been seen to be a significant factor in determining cetacean foraging patterns (Malinowski and Herzing, 2015). The quality of prey can be measured by nutrient composition and digestibility, which is often measured by energy density or kilo joules per gram (KJ/g) (Spitz et al, 2010a(Spitz et al, , 2012.…”

“…Despite the documented wide variety of prey consumed globally, local populations and individual dolphins have been observed to use specialized foraging tactics that exploit targeted prey in specific habitats (Barros and Odell, 1990;Sargeant et al, 2005;McCabe et al, 2010;Allen et al, 2011). Other dolphin species, such as the Atlantic spotted dolphin (Stenella frontalis), have been found to consume different prey species of differing nutritional value based on age class and reproductive state, highlighting the selectivity of their diet (Malinowski and Herzing, 2015).…”

The nutritional nexus: Linking niche, habitat variability and prey composition in a generalist marine predator

“…A growing body of evidence suggests that vertebrate predators consume prey that varies in their nutritional and energetic compositions (Lenky, Eisert, Oftedal, & Metcalf, ; Machovsky‐Capuska, Coogan, Simpson, & Raubenheimer, ; Machovsky‐Capuska, Priddel et al., ; Malinowski & Herzing, ; Mayntz et al., ). Here, we demonstrated that there is an appreciable variation in the proportional wet mass contribution of P, L, W and PL ratio in the prey species consumed by gannets, which is consistent with previous findings on gannet prey species (Machovsky‐Capuska, Senior, Benn et al., ; Tait et al., ).…”